Switch SSH-1 channel message handlers to use ssh_channel_msg().

[PuTTY.git] / ssh.c

/*
 * SSH backend.
 */

#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
#include <assert.h>
#include <limits.h>
#include <signal.h>

#include "putty.h"
#include "tree234.h"
#include "storage.h"
#include "ssh.h"
#ifndef NO_GSSAPI
#include "sshgssc.h"
#include "sshgss.h"
#endif

#ifndef FALSE
#define FALSE 0
#endif
#ifndef TRUE
#define TRUE 1
#endif

/*
 * Packet type contexts, so that ssh2_pkt_type can correctly decode
 * the ambiguous type numbers back into the correct type strings.
 */
typedef enum {
    SSH2_PKTCTX_NOKEX,
    SSH2_PKTCTX_DHGROUP,
    SSH2_PKTCTX_DHGEX,
    SSH2_PKTCTX_ECDHKEX,
    SSH2_PKTCTX_RSAKEX
} Pkt_KCtx;
typedef enum {
    SSH2_PKTCTX_NOAUTH,
    SSH2_PKTCTX_PUBLICKEY,
    SSH2_PKTCTX_PASSWORD,
    SSH2_PKTCTX_GSSAPI,
    SSH2_PKTCTX_KBDINTER
} Pkt_ACtx;

static const char *const ssh2_disconnect_reasons[] = {
    NULL,
    "host not allowed to connect",
    "protocol error",
    "key exchange failed",
    "host authentication failed",
    "MAC error",
    "compression error",
    "service not available",
    "protocol version not supported",
    "host key not verifiable",
    "connection lost",
    "by application",
    "too many connections",
    "auth cancelled by user",
    "no more auth methods available",
    "illegal user name",
};

/*
 * Various remote-bug flags.
 */
#define BUG_CHOKES_ON_SSH1_IGNORE                 1
#define BUG_SSH2_HMAC                             2
#define BUG_NEEDS_SSH1_PLAIN_PASSWORD             4
#define BUG_CHOKES_ON_RSA                         8
#define BUG_SSH2_RSA_PADDING                     16
#define BUG_SSH2_DERIVEKEY                       32
#define BUG_SSH2_REKEY                           64
#define BUG_SSH2_PK_SESSIONID                   128
#define BUG_SSH2_MAXPKT                         256
#define BUG_CHOKES_ON_SSH2_IGNORE               512
#define BUG_CHOKES_ON_WINADJ                   1024
#define BUG_SENDS_LATE_REQUEST_REPLY           2048
#define BUG_SSH2_OLDGEX                        4096

#define DH_MIN_SIZE 1024
#define DH_MAX_SIZE 8192

/*
 * Codes for terminal modes.
 * Most of these are the same in SSH-1 and SSH-2.
 * This list is derived from RFC 4254 and
 * SSH-1 RFC-1.2.31.
 */
static const struct ssh_ttymode {
    const char* const mode;
    int opcode;
    enum { TTY_OP_CHAR, TTY_OP_BOOL } type;
} ssh_ttymodes[] = {
    /* "V" prefix discarded for special characters relative to SSH specs */
    { "INTR",         1, TTY_OP_CHAR },
    { "QUIT",         2, TTY_OP_CHAR },
    { "ERASE",        3, TTY_OP_CHAR },
    { "KILL",         4, TTY_OP_CHAR },
    { "EOF",          5, TTY_OP_CHAR },
    { "EOL",          6, TTY_OP_CHAR },
    { "EOL2",         7, TTY_OP_CHAR },
    { "START",        8, TTY_OP_CHAR },
    { "STOP",         9, TTY_OP_CHAR },
    { "SUSP",        10, TTY_OP_CHAR },
    { "DSUSP",       11, TTY_OP_CHAR },
    { "REPRINT",     12, TTY_OP_CHAR },
    { "WERASE",      13, TTY_OP_CHAR },
    { "LNEXT",       14, TTY_OP_CHAR },
    { "FLUSH",       15, TTY_OP_CHAR },
    { "SWTCH",       16, TTY_OP_CHAR },
    { "STATUS",      17, TTY_OP_CHAR },
    { "DISCARD",     18, TTY_OP_CHAR },
    { "IGNPAR",      30, TTY_OP_BOOL },
    { "PARMRK",      31, TTY_OP_BOOL },
    { "INPCK",       32, TTY_OP_BOOL },
    { "ISTRIP",      33, TTY_OP_BOOL },
    { "INLCR",       34, TTY_OP_BOOL },
    { "IGNCR",       35, TTY_OP_BOOL },
    { "ICRNL",       36, TTY_OP_BOOL },
    { "IUCLC",       37, TTY_OP_BOOL },
    { "IXON",        38, TTY_OP_BOOL },
    { "IXANY",       39, TTY_OP_BOOL },
    { "IXOFF",       40, TTY_OP_BOOL },
    { "IMAXBEL",     41, TTY_OP_BOOL },
    { "IUTF8",       42, TTY_OP_BOOL },
    { "ISIG",        50, TTY_OP_BOOL },
    { "ICANON",      51, TTY_OP_BOOL },
    { "XCASE",       52, TTY_OP_BOOL },
    { "ECHO",        53, TTY_OP_BOOL },
    { "ECHOE",       54, TTY_OP_BOOL },
    { "ECHOK",       55, TTY_OP_BOOL },
    { "ECHONL",      56, TTY_OP_BOOL },
    { "NOFLSH",      57, TTY_OP_BOOL },
    { "TOSTOP",      58, TTY_OP_BOOL },
    { "IEXTEN",      59, TTY_OP_BOOL },
    { "ECHOCTL",     60, TTY_OP_BOOL },
    { "ECHOKE",      61, TTY_OP_BOOL },
    { "PENDIN",      62, TTY_OP_BOOL }, /* XXX is this a real mode? */
    { "OPOST",       70, TTY_OP_BOOL },
    { "OLCUC",       71, TTY_OP_BOOL },
    { "ONLCR",       72, TTY_OP_BOOL },
    { "OCRNL",       73, TTY_OP_BOOL },
    { "ONOCR",       74, TTY_OP_BOOL },
    { "ONLRET",      75, TTY_OP_BOOL },
    { "CS7",         90, TTY_OP_BOOL },
    { "CS8",         91, TTY_OP_BOOL },
    { "PARENB",      92, TTY_OP_BOOL },
    { "PARODD",      93, TTY_OP_BOOL }
};

/* Miscellaneous other tty-related constants. */
#define SSH_TTY_OP_END            0
/* The opcodes for ISPEED/OSPEED differ between SSH-1 and SSH-2. */
#define SSH1_TTY_OP_ISPEED      192
#define SSH1_TTY_OP_OSPEED      193
#define SSH2_TTY_OP_ISPEED      128
#define SSH2_TTY_OP_OSPEED      129

/* Helper functions for parsing tty-related config. */
static unsigned int ssh_tty_parse_specchar(char *s)
{
    unsigned int ret;
    if (*s) {
        char *next = NULL;
        ret = ctrlparse(s, &next);
        if (!next) ret = s[0];
    } else {
        ret = 255; /* special value meaning "don't set" */
    }
    return ret;
}
static unsigned int ssh_tty_parse_boolean(char *s)
{
    if (stricmp(s, "yes") == 0 ||
        stricmp(s, "on") == 0 ||
        stricmp(s, "true") == 0 ||
        stricmp(s, "+") == 0)
        return 1; /* true */
    else if (stricmp(s, "no") == 0 ||
             stricmp(s, "off") == 0 ||
             stricmp(s, "false") == 0 ||
             stricmp(s, "-") == 0)
        return 0; /* false */
    else
        return (atoi(s) != 0);
}

#define translate(x) if (type == x) return #x
#define translatek(x,ctx) if (type == x && (pkt_kctx == ctx)) return #x
#define translatea(x,ctx) if (type == x && (pkt_actx == ctx)) return #x
static const char *ssh1_pkt_type(int type)
{
    translate(SSH1_MSG_DISCONNECT);
    translate(SSH1_SMSG_PUBLIC_KEY);
    translate(SSH1_CMSG_SESSION_KEY);
    translate(SSH1_CMSG_USER);
    translate(SSH1_CMSG_AUTH_RSA);
    translate(SSH1_SMSG_AUTH_RSA_CHALLENGE);
    translate(SSH1_CMSG_AUTH_RSA_RESPONSE);
    translate(SSH1_CMSG_AUTH_PASSWORD);
    translate(SSH1_CMSG_REQUEST_PTY);
    translate(SSH1_CMSG_WINDOW_SIZE);
    translate(SSH1_CMSG_EXEC_SHELL);
    translate(SSH1_CMSG_EXEC_CMD);
    translate(SSH1_SMSG_SUCCESS);
    translate(SSH1_SMSG_FAILURE);
    translate(SSH1_CMSG_STDIN_DATA);
    translate(SSH1_SMSG_STDOUT_DATA);
    translate(SSH1_SMSG_STDERR_DATA);
    translate(SSH1_CMSG_EOF);
    translate(SSH1_SMSG_EXIT_STATUS);
    translate(SSH1_MSG_CHANNEL_OPEN_CONFIRMATION);
    translate(SSH1_MSG_CHANNEL_OPEN_FAILURE);
    translate(SSH1_MSG_CHANNEL_DATA);
    translate(SSH1_MSG_CHANNEL_CLOSE);
    translate(SSH1_MSG_CHANNEL_CLOSE_CONFIRMATION);
    translate(SSH1_SMSG_X11_OPEN);
    translate(SSH1_CMSG_PORT_FORWARD_REQUEST);
    translate(SSH1_MSG_PORT_OPEN);
    translate(SSH1_CMSG_AGENT_REQUEST_FORWARDING);
    translate(SSH1_SMSG_AGENT_OPEN);
    translate(SSH1_MSG_IGNORE);
    translate(SSH1_CMSG_EXIT_CONFIRMATION);
    translate(SSH1_CMSG_X11_REQUEST_FORWARDING);
    translate(SSH1_CMSG_AUTH_RHOSTS_RSA);
    translate(SSH1_MSG_DEBUG);
    translate(SSH1_CMSG_REQUEST_COMPRESSION);
    translate(SSH1_CMSG_AUTH_TIS);
    translate(SSH1_SMSG_AUTH_TIS_CHALLENGE);
    translate(SSH1_CMSG_AUTH_TIS_RESPONSE);
    translate(SSH1_CMSG_AUTH_CCARD);
    translate(SSH1_SMSG_AUTH_CCARD_CHALLENGE);
    translate(SSH1_CMSG_AUTH_CCARD_RESPONSE);
    return "unknown";
}
static const char *ssh2_pkt_type(Pkt_KCtx pkt_kctx, Pkt_ACtx pkt_actx,
                                 int type)
{
    translatea(SSH2_MSG_USERAUTH_GSSAPI_RESPONSE,SSH2_PKTCTX_GSSAPI);
    translatea(SSH2_MSG_USERAUTH_GSSAPI_TOKEN,SSH2_PKTCTX_GSSAPI);
    translatea(SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE,SSH2_PKTCTX_GSSAPI);
    translatea(SSH2_MSG_USERAUTH_GSSAPI_ERROR,SSH2_PKTCTX_GSSAPI);
    translatea(SSH2_MSG_USERAUTH_GSSAPI_ERRTOK,SSH2_PKTCTX_GSSAPI);
    translatea(SSH2_MSG_USERAUTH_GSSAPI_MIC, SSH2_PKTCTX_GSSAPI);
    translate(SSH2_MSG_DISCONNECT);
    translate(SSH2_MSG_IGNORE);
    translate(SSH2_MSG_UNIMPLEMENTED);
    translate(SSH2_MSG_DEBUG);
    translate(SSH2_MSG_SERVICE_REQUEST);
    translate(SSH2_MSG_SERVICE_ACCEPT);
    translate(SSH2_MSG_KEXINIT);
    translate(SSH2_MSG_NEWKEYS);
    translatek(SSH2_MSG_KEXDH_INIT, SSH2_PKTCTX_DHGROUP);
    translatek(SSH2_MSG_KEXDH_REPLY, SSH2_PKTCTX_DHGROUP);
    translatek(SSH2_MSG_KEX_DH_GEX_REQUEST_OLD, SSH2_PKTCTX_DHGEX);
    translatek(SSH2_MSG_KEX_DH_GEX_REQUEST, SSH2_PKTCTX_DHGEX);
    translatek(SSH2_MSG_KEX_DH_GEX_GROUP, SSH2_PKTCTX_DHGEX);
    translatek(SSH2_MSG_KEX_DH_GEX_INIT, SSH2_PKTCTX_DHGEX);
    translatek(SSH2_MSG_KEX_DH_GEX_REPLY, SSH2_PKTCTX_DHGEX);
    translatek(SSH2_MSG_KEXRSA_PUBKEY, SSH2_PKTCTX_RSAKEX);
    translatek(SSH2_MSG_KEXRSA_SECRET, SSH2_PKTCTX_RSAKEX);
    translatek(SSH2_MSG_KEXRSA_DONE, SSH2_PKTCTX_RSAKEX);
    translatek(SSH2_MSG_KEX_ECDH_INIT, SSH2_PKTCTX_ECDHKEX);
    translatek(SSH2_MSG_KEX_ECDH_REPLY, SSH2_PKTCTX_ECDHKEX);
    translate(SSH2_MSG_USERAUTH_REQUEST);
    translate(SSH2_MSG_USERAUTH_FAILURE);
    translate(SSH2_MSG_USERAUTH_SUCCESS);
    translate(SSH2_MSG_USERAUTH_BANNER);
    translatea(SSH2_MSG_USERAUTH_PK_OK, SSH2_PKTCTX_PUBLICKEY);
    translatea(SSH2_MSG_USERAUTH_PASSWD_CHANGEREQ, SSH2_PKTCTX_PASSWORD);
    translatea(SSH2_MSG_USERAUTH_INFO_REQUEST, SSH2_PKTCTX_KBDINTER);
    translatea(SSH2_MSG_USERAUTH_INFO_RESPONSE, SSH2_PKTCTX_KBDINTER);
    translate(SSH2_MSG_GLOBAL_REQUEST);
    translate(SSH2_MSG_REQUEST_SUCCESS);
    translate(SSH2_MSG_REQUEST_FAILURE);
    translate(SSH2_MSG_CHANNEL_OPEN);
    translate(SSH2_MSG_CHANNEL_OPEN_CONFIRMATION);
    translate(SSH2_MSG_CHANNEL_OPEN_FAILURE);
    translate(SSH2_MSG_CHANNEL_WINDOW_ADJUST);
    translate(SSH2_MSG_CHANNEL_DATA);
    translate(SSH2_MSG_CHANNEL_EXTENDED_DATA);
    translate(SSH2_MSG_CHANNEL_EOF);
    translate(SSH2_MSG_CHANNEL_CLOSE);
    translate(SSH2_MSG_CHANNEL_REQUEST);
    translate(SSH2_MSG_CHANNEL_SUCCESS);
    translate(SSH2_MSG_CHANNEL_FAILURE);
    return "unknown";
}
#undef translate
#undef translatec

/* Enumeration values for fields in SSH-1 packets */
enum {
    PKT_END, PKT_INT, PKT_CHAR, PKT_DATA, PKT_STR, PKT_BIGNUM,
};

/*
 * Coroutine mechanics for the sillier bits of the code. If these
 * macros look impenetrable to you, you might find it helpful to
 * read
 * 
 *   http://www.chiark.greenend.org.uk/~sgtatham/coroutines.html
 * 
 * which explains the theory behind these macros.
 * 
 * In particular, if you are getting `case expression not constant'
 * errors when building with MS Visual Studio, this is because MS's
 * Edit and Continue debugging feature causes their compiler to
 * violate ANSI C. To disable Edit and Continue debugging:
 * 
 *  - right-click ssh.c in the FileView
 *  - click Settings
 *  - select the C/C++ tab and the General category
 *  - under `Debug info:', select anything _other_ than `Program
 *    Database for Edit and Continue'.
 */
#define crBegin(v)      { int *crLine = &v; switch(v) { case 0:;
#define crBeginState    crBegin(s->crLine)
#define crStateP(t, v)                          \
    struct t *s;                                \
    if (!(v)) { s = (v) = snew(struct t); s->crLine = 0; }      \
    s = (v);
#define crState(t)      crStateP(t, ssh->t)
#define crFinish(z)     } *crLine = 0; return (z); }
#define crFinishV       } *crLine = 0; return; }
#define crFinishFree(z) } sfree(s); return (z); }
#define crFinishFreeV   } sfree(s); return; }
#define crReturn(z)     \
        do {\
            *crLine =__LINE__; return (z); case __LINE__:;\
        } while (0)
#define crReturnV       \
        do {\
            *crLine=__LINE__; return; case __LINE__:;\
        } while (0)
#define crStop(z)       do{ *crLine = 0; return (z); }while(0)
#define crStopV         do{ *crLine = 0; return; }while(0)
#define crWaitUntil(c)  do { crReturn(0); } while (!(c))
#define crWaitUntilV(c) do { crReturnV; } while (!(c))

struct Packet;

static struct Packet *ssh1_pkt_init(int pkt_type);
static struct Packet *ssh2_pkt_init(int pkt_type);
static void ssh_pkt_ensure(struct Packet *, int length);
static void ssh_pkt_adddata(struct Packet *, const void *data, int len);
static void ssh_pkt_addbyte(struct Packet *, unsigned char value);
static void ssh2_pkt_addbool(struct Packet *, unsigned char value);
static void ssh_pkt_adduint32(struct Packet *, unsigned long value);
static void ssh_pkt_addstring_start(struct Packet *);
static void ssh_pkt_addstring_str(struct Packet *, const char *data);
static void ssh_pkt_addstring_data(struct Packet *, const char *data, int len);
static void ssh_pkt_addstring(struct Packet *, const char *data);
static unsigned char *ssh2_mpint_fmt(Bignum b, int *len);
static void ssh1_pkt_addmp(struct Packet *, Bignum b);
static void ssh2_pkt_addmp(struct Packet *, Bignum b);
static int ssh2_pkt_construct(Ssh, struct Packet *);
static void ssh2_pkt_send(Ssh, struct Packet *);
static void ssh2_pkt_send_noqueue(Ssh, struct Packet *);
static int do_ssh1_login(Ssh ssh, const unsigned char *in, int inlen,
                         struct Packet *pktin);
static void do_ssh2_authconn(Ssh ssh, const unsigned char *in, int inlen,
                             struct Packet *pktin);
static void ssh_channel_init(struct ssh_channel *c);
static struct ssh_channel *ssh_channel_msg(Ssh ssh, struct Packet *pktin);
static void ssh2_channel_check_close(struct ssh_channel *c);
static void ssh_channel_destroy(struct ssh_channel *c);
static void ssh_channel_unthrottle(struct ssh_channel *c, int bufsize);
static void ssh2_msg_something_unimplemented(Ssh ssh, struct Packet *pktin);

/*
 * Buffer management constants. There are several of these for
 * various different purposes:
 * 
 *  - SSH1_BUFFER_LIMIT is the amount of backlog that must build up
 *    on a local data stream before we throttle the whole SSH
 *    connection (in SSH-1 only). Throttling the whole connection is
 *    pretty drastic so we set this high in the hope it won't
 *    happen very often.
 * 
 *  - SSH_MAX_BACKLOG is the amount of backlog that must build up
 *    on the SSH connection itself before we defensively throttle
 *    _all_ local data streams. This is pretty drastic too (though
 *    thankfully unlikely in SSH-2 since the window mechanism should
 *    ensure that the server never has any need to throttle its end
 *    of the connection), so we set this high as well.
 * 
 *  - OUR_V2_WINSIZE is the default window size we present on SSH-2
 *    channels.
 *
 *  - OUR_V2_BIGWIN is the window size we advertise for the only
 *    channel in a simple connection.  It must be <= INT_MAX.
 *
 *  - OUR_V2_MAXPKT is the official "maximum packet size" we send
 *    to the remote side. This actually has nothing to do with the
 *    size of the _packet_, but is instead a limit on the amount
 *    of data we're willing to receive in a single SSH2 channel
 *    data message.
 *
 *  - OUR_V2_PACKETLIMIT is actually the maximum size of SSH
 *    _packet_ we're prepared to cope with.  It must be a multiple
 *    of the cipher block size, and must be at least 35000.
 */

#define SSH1_BUFFER_LIMIT 32768
#define SSH_MAX_BACKLOG 32768
#define OUR_V2_WINSIZE 16384
#define OUR_V2_BIGWIN 0x7fffffff
#define OUR_V2_MAXPKT 0x4000UL
#define OUR_V2_PACKETLIMIT 0x9000UL

struct ssh_signkey_with_user_pref_id {
    const struct ssh_signkey *alg;
    int id;
};
const static struct ssh_signkey_with_user_pref_id hostkey_algs[] = {
    { &ssh_ecdsa_ed25519, HK_ED25519 },
    { &ssh_ecdsa_nistp256, HK_ECDSA },
    { &ssh_ecdsa_nistp384, HK_ECDSA },
    { &ssh_ecdsa_nistp521, HK_ECDSA },
    { &ssh_dss, HK_DSA },
    { &ssh_rsa, HK_RSA },
};

const static struct ssh_mac *const macs[] = {
    &ssh_hmac_sha256, &ssh_hmac_sha1, &ssh_hmac_sha1_96, &ssh_hmac_md5
};
const static struct ssh_mac *const buggymacs[] = {
    &ssh_hmac_sha1_buggy, &ssh_hmac_sha1_96_buggy, &ssh_hmac_md5
};

static void *ssh_comp_none_init(void)
{
    return NULL;
}
static void ssh_comp_none_cleanup(void *handle)
{
}
static int ssh_comp_none_block(void *handle, unsigned char *block, int len,
                               unsigned char **outblock, int *outlen)
{
    return 0;
}
static int ssh_comp_none_disable(void *handle)
{
    return 0;
}
const static struct ssh_compress ssh_comp_none = {
    "none", NULL,
    ssh_comp_none_init, ssh_comp_none_cleanup, ssh_comp_none_block,
    ssh_comp_none_init, ssh_comp_none_cleanup, ssh_comp_none_block,
    ssh_comp_none_disable, NULL
};
extern const struct ssh_compress ssh_zlib;
const static struct ssh_compress *const compressions[] = {
    &ssh_zlib, &ssh_comp_none
};

enum {                                 /* channel types */
    CHAN_MAINSESSION,
    CHAN_X11,
    CHAN_AGENT,
    CHAN_SOCKDATA,
    CHAN_SOCKDATA_DORMANT,             /* one the remote hasn't confirmed */
    /*
     * CHAN_SHARING indicates a channel which is tracked here on
     * behalf of a connection-sharing downstream. We do almost nothing
     * with these channels ourselves: all messages relating to them
     * get thrown straight to sshshare.c and passed on almost
     * unmodified to downstream.
     */
    CHAN_SHARING,
    /*
     * CHAN_ZOMBIE is used to indicate a channel for which we've
     * already destroyed the local data source: for instance, if a
     * forwarded port experiences a socket error on the local side, we
     * immediately destroy its local socket and turn the SSH channel
     * into CHAN_ZOMBIE.
     */
    CHAN_ZOMBIE
};

typedef void (*handler_fn_t)(Ssh ssh, struct Packet *pktin);
typedef void (*chandler_fn_t)(Ssh ssh, struct Packet *pktin, void *ctx);
typedef void (*cchandler_fn_t)(struct ssh_channel *, struct Packet *, void *);

/*
 * Each channel has a queue of outstanding CHANNEL_REQUESTS and their
 * handlers.
 */
struct outstanding_channel_request {
    cchandler_fn_t handler;
    void *ctx;
    struct outstanding_channel_request *next;
};

/*
 * 2-3-4 tree storing channels.
 */
struct ssh_channel {
    Ssh ssh;                           /* pointer back to main context */
    unsigned remoteid, localid;
    int type;
    /* True if we opened this channel but server hasn't confirmed. */
    int halfopen;
    /*
     * In SSH-1, this value contains four bits:
     * 
     *   1   We have sent SSH1_MSG_CHANNEL_CLOSE.
     *   2   We have sent SSH1_MSG_CHANNEL_CLOSE_CONFIRMATION.
     *   4   We have received SSH1_MSG_CHANNEL_CLOSE.
     *   8   We have received SSH1_MSG_CHANNEL_CLOSE_CONFIRMATION.
     * 
     * A channel is completely finished with when all four bits are set.
     *
     * In SSH-2, the four bits mean:
     *
     *   1   We have sent SSH2_MSG_CHANNEL_EOF.
     *   2   We have sent SSH2_MSG_CHANNEL_CLOSE.
     *   4   We have received SSH2_MSG_CHANNEL_EOF.
     *   8   We have received SSH2_MSG_CHANNEL_CLOSE.
     *
     * A channel is completely finished with when we have both sent
     * and received CLOSE.
     *
     * The symbolic constants below use the SSH-2 terminology, which
     * is a bit confusing in SSH-1, but we have to use _something_.
     */
#define CLOSES_SENT_EOF    1
#define CLOSES_SENT_CLOSE  2
#define CLOSES_RCVD_EOF    4
#define CLOSES_RCVD_CLOSE  8
    int closes;

    /*
     * This flag indicates that an EOF is pending on the outgoing side
     * of the channel: that is, wherever we're getting the data for
     * this channel has sent us some data followed by EOF. We can't
     * actually send the EOF until we've finished sending the data, so
     * we set this flag instead to remind us to do so once our buffer
     * is clear.
     */
    int pending_eof;

    /*
     * True if this channel is causing the underlying connection to be
     * throttled.
     */
    int throttling_conn;
    union {
        struct ssh2_data_channel {
            bufchain outbuffer;
            unsigned remwindow, remmaxpkt;
            /* locwindow is signed so we can cope with excess data. */
            int locwindow, locmaxwin;
            /*
             * remlocwin is the amount of local window that we think
             * the remote end had available to it after it sent the
             * last data packet or window adjust ack.
             */
            int remlocwin;
            /*
             * These store the list of channel requests that haven't
             * been acked.
             */
            struct outstanding_channel_request *chanreq_head, *chanreq_tail;
            enum { THROTTLED, UNTHROTTLING, UNTHROTTLED } throttle_state;
        } v2;
    } v;
    union {
        struct ssh_agent_channel {
            unsigned char *message;
            unsigned char msglen[4];
            unsigned lensofar, totallen;
            int outstanding_requests;
        } a;
        struct ssh_x11_channel {
            struct X11Connection *xconn;
            int initial;
        } x11;
        struct ssh_pfd_channel {
            struct PortForwarding *pf;
        } pfd;
        struct ssh_sharing_channel {
            void *ctx;
        } sharing;
    } u;
};

/*
 * 2-3-4 tree storing remote->local port forwardings. SSH-1 and SSH-2
 * use this structure in different ways, reflecting SSH-2's
 * altogether saner approach to port forwarding.
 * 
 * In SSH-1, you arrange a remote forwarding by sending the server
 * the remote port number, and the local destination host:port.
 * When a connection comes in, the server sends you back that
 * host:port pair, and you connect to it. This is a ready-made
 * security hole if you're not on the ball: a malicious server
 * could send you back _any_ host:port pair, so if you trustingly
 * connect to the address it gives you then you've just opened the
 * entire inside of your corporate network just by connecting
 * through it to a dodgy SSH server. Hence, we must store a list of
 * host:port pairs we _are_ trying to forward to, and reject a
 * connection request from the server if it's not in the list.
 * 
 * In SSH-2, each side of the connection minds its own business and
 * doesn't send unnecessary information to the other. You arrange a
 * remote forwarding by sending the server just the remote port
 * number. When a connection comes in, the server tells you which
 * of its ports was connected to; and _you_ have to remember what
 * local host:port pair went with that port number.
 * 
 * Hence, in SSH-1 this structure is indexed by destination
 * host:port pair, whereas in SSH-2 it is indexed by source port.
 */
struct ssh_portfwd; /* forward declaration */

struct ssh_rportfwd {
    unsigned sport, dport;
    char *shost, *dhost;
    char *sportdesc;
    void *share_ctx;
    struct ssh_portfwd *pfrec;
};

static void free_rportfwd(struct ssh_rportfwd *pf)
{
    if (pf) {
        sfree(pf->sportdesc);
        sfree(pf->shost);
        sfree(pf->dhost);
        sfree(pf);
    }
}

/*
 * Separately to the rportfwd tree (which is for looking up port
 * open requests from the server), a tree of _these_ structures is
 * used to keep track of all the currently open port forwardings,
 * so that we can reconfigure in mid-session if the user requests
 * it.
 */
struct ssh_portfwd {
    enum { DESTROY, KEEP, CREATE } status;
    int type;
    unsigned sport, dport;
    char *saddr, *daddr;
    char *sserv, *dserv;
    struct ssh_rportfwd *remote;
    int addressfamily;
    struct PortListener *local;
};
#define free_portfwd(pf) ( \
    ((pf) ? (sfree((pf)->saddr), sfree((pf)->daddr), \
             sfree((pf)->sserv), sfree((pf)->dserv)) : (void)0 ), sfree(pf) )

struct Packet {
    long length;            /* length of packet: see below */
    long forcepad;          /* SSH-2: force padding to at least this length */
    int type;               /* only used for incoming packets */
    unsigned long sequence; /* SSH-2 incoming sequence number */
    unsigned char *data;    /* allocated storage */
    unsigned char *body;    /* offset of payload within `data' */
    long savedpos;          /* dual-purpose saved packet position: see below */
    long maxlen;            /* amount of storage allocated for `data' */
    long encrypted_len;     /* for SSH-2 total-size counting */

    /*
     * A note on the 'length' and 'savedpos' fields above.
     *
     * Incoming packets are set up so that pkt->length is measured
     * relative to pkt->body, which itself points to a few bytes after
     * pkt->data (skipping some uninteresting header fields including
     * the packet type code). The ssh_pkt_get* functions all expect
     * this setup, and they also use pkt->savedpos to indicate how far
     * through the packet being decoded they've got - and that, too,
     * is an offset from pkt->body rather than pkt->data.
     *
     * During construction of an outgoing packet, however, pkt->length
     * is measured relative to the base pointer pkt->data, and
     * pkt->body is not really used for anything until the packet is
     * ready for sending. In this mode, pkt->savedpos is reused as a
     * temporary variable by the addstring functions, which write out
     * a string length field and then keep going back and updating it
     * as more data is appended to the subsequent string data field;
     * pkt->savedpos stores the offset (again relative to pkt->data)
     * of the start of the string data field.
     */

    /* Extra metadata used in SSH packet logging mode, allowing us to
     * log in the packet header line that the packet came from a
     * connection-sharing downstream and what if anything unusual was
     * done to it. The additional_log_text field is expected to be a
     * static string - it will not be freed. */
    unsigned downstream_id;
    const char *additional_log_text;
};

static void ssh1_protocol(Ssh ssh, const void *vin, int inlen,
                          struct Packet *pktin);
static void ssh2_protocol(Ssh ssh, const void *vin, int inlen,
                          struct Packet *pktin);
static void ssh2_bare_connection_protocol(Ssh ssh, const void *vin, int inlen,
                                          struct Packet *pktin);
static void ssh1_protocol_setup(Ssh ssh);
static void ssh2_protocol_setup(Ssh ssh);
static void ssh2_bare_connection_protocol_setup(Ssh ssh);
static void ssh_size(void *handle, int width, int height);
static void ssh_special(void *handle, Telnet_Special);
static int ssh2_try_send(struct ssh_channel *c);
static int ssh_send_channel_data(struct ssh_channel *c,
                                 const char *buf, int len);
static void ssh_throttle_all(Ssh ssh, int enable, int bufsize);
static void ssh2_set_window(struct ssh_channel *c, int newwin);
static int ssh_sendbuffer(void *handle);
static int ssh_do_close(Ssh ssh, int notify_exit);
static unsigned long ssh_pkt_getuint32(struct Packet *pkt);
static int ssh2_pkt_getbool(struct Packet *pkt);
static void ssh_pkt_getstring(struct Packet *pkt, char **p, int *length);
static void ssh2_timer(void *ctx, unsigned long now);
static void do_ssh2_transport(Ssh ssh, const void *vin, int inlen,
                              struct Packet *pktin);
static void ssh2_msg_unexpected(Ssh ssh, struct Packet *pktin);

struct rdpkt1_state_tag {
    long len, pad, biglen, to_read;
    unsigned long realcrc, gotcrc;
    unsigned char *p;
    int i;
    int chunk;
    struct Packet *pktin;
};

struct rdpkt2_state_tag {
    long len, pad, payload, packetlen, maclen;
    int i;
    int cipherblk;
    unsigned long incoming_sequence;
    struct Packet *pktin;
};

struct rdpkt2_bare_state_tag {
    char length[4];
    long packetlen;
    int i;
    unsigned long incoming_sequence;
    struct Packet *pktin;
};

struct queued_handler;
struct queued_handler {
    int msg1, msg2;
    chandler_fn_t handler;
    void *ctx;
    struct queued_handler *next;
};

struct ssh_tag {
    const struct plug_function_table *fn;
    /* the above field _must_ be first in the structure */

    char *v_c, *v_s;
    void *exhash;

    Socket s;

    void *ldisc;
    void *logctx;

    unsigned char session_key[32];
    int v1_compressing;
    int v1_remote_protoflags;
    int v1_local_protoflags;
    int agentfwd_enabled;
    int X11_fwd_enabled;
    int remote_bugs;
    const struct ssh_cipher *cipher;
    void *v1_cipher_ctx;
    void *crcda_ctx;
    const struct ssh2_cipher *cscipher, *sccipher;
    void *cs_cipher_ctx, *sc_cipher_ctx;
    const struct ssh_mac *csmac, *scmac;
    int csmac_etm, scmac_etm;
    void *cs_mac_ctx, *sc_mac_ctx;
    const struct ssh_compress *cscomp, *sccomp;
    void *cs_comp_ctx, *sc_comp_ctx;
    const struct ssh_kex *kex;
    const struct ssh_signkey *hostkey;
    char *hostkey_str; /* string representation, for easy checking in rekeys */
    unsigned char v2_session_id[SSH2_KEX_MAX_HASH_LEN];
    int v2_session_id_len;
    void *kex_ctx;

    int bare_connection;
    int attempting_connshare;
    void *connshare;

    char *savedhost;
    int savedport;
    int send_ok;
    int echoing, editing;

    int session_started;
    void *frontend;

    int ospeed, ispeed;                /* temporaries */
    int term_width, term_height;

    tree234 *channels;                 /* indexed by local id */
    struct ssh_channel *mainchan;      /* primary session channel */
    int ncmode;                        /* is primary channel direct-tcpip? */
    int exitcode;
    int close_expected;
    int clean_exit;

    tree234 *rportfwds, *portfwds;

    enum {
        SSH_STATE_PREPACKET,
        SSH_STATE_BEFORE_SIZE,
        SSH_STATE_INTERMED,
        SSH_STATE_SESSION,
        SSH_STATE_CLOSED
    } state;

    int size_needed, eof_needed;
    int sent_console_eof;
    int got_pty;           /* affects EOF behaviour on main channel */

    struct Packet **queue;
    int queuelen, queuesize;
    int queueing;
    unsigned char *deferred_send_data;
    int deferred_len, deferred_size;

    /*
     * Gross hack: pscp will try to start SFTP but fall back to
     * scp1 if that fails. This variable is the means by which
     * scp.c can reach into the SSH code and find out which one it
     * got.
     */
    int fallback_cmd;

    bufchain banner;    /* accumulates banners during do_ssh2_authconn */

    Pkt_KCtx pkt_kctx;
    Pkt_ACtx pkt_actx;

    struct X11Display *x11disp;
    struct X11FakeAuth *x11auth;
    tree234 *x11authtree;

    int version;
    int conn_throttle_count;
    int overall_bufsize;
    int throttled_all;
    int v1_stdout_throttling;
    unsigned long v2_outgoing_sequence;

    int ssh1_rdpkt_crstate;
    int ssh2_rdpkt_crstate;
    int ssh2_bare_rdpkt_crstate;
    int ssh_gotdata_crstate;
    int do_ssh1_connection_crstate;

    void *do_ssh_init_state;
    void *do_ssh1_login_state;
    void *do_ssh2_transport_state;
    void *do_ssh2_authconn_state;
    void *do_ssh_connection_init_state;

    struct rdpkt1_state_tag rdpkt1_state;
    struct rdpkt2_state_tag rdpkt2_state;
    struct rdpkt2_bare_state_tag rdpkt2_bare_state;

    /* SSH-1 and SSH-2 use this for different things, but both use it */
    int protocol_initial_phase_done;

    void (*protocol) (Ssh ssh, const void *vin, int inlen,
                      struct Packet *pkt);
    struct Packet *(*s_rdpkt) (Ssh ssh, const unsigned char **data,
                               int *datalen);
    int (*do_ssh_init)(Ssh ssh, unsigned char c);

    /*
     * We maintain our own copy of a Conf structure here. That way,
     * when we're passed a new one for reconfiguration, we can check
     * the differences and potentially reconfigure port forwardings
     * etc in mid-session.
     */
    Conf *conf;

    /*
     * Values cached out of conf so as to avoid the tree234 lookup
     * cost every time they're used.
     */
    int logomitdata;

    /*
     * Dynamically allocated username string created during SSH
     * login. Stored in here rather than in the coroutine state so
     * that it'll be reliably freed if we shut down the SSH session
     * at some unexpected moment.
     */
    char *username;

    /*
     * Used to transfer data back from async callbacks.
     */
    void *agent_response;
    int agent_response_len;
    int user_response;

    /*
     * The SSH connection can be set as `frozen', meaning we are
     * not currently accepting incoming data from the network. This
     * is slightly more serious than setting the _socket_ as
     * frozen, because we may already have had data passed to us
     * from the network which we need to delay processing until
     * after the freeze is lifted, so we also need a bufchain to
     * store that data.
     */
    int frozen;
    bufchain queued_incoming_data;

    /*
     * Dispatch table for packet types that we may have to deal
     * with at any time.
     */
    handler_fn_t packet_dispatch[256];

    /*
     * Queues of one-off handler functions for success/failure
     * indications from a request.
     */
    struct queued_handler *qhead, *qtail;
    handler_fn_t q_saved_handler1, q_saved_handler2;

    /*
     * This module deals with sending keepalives.
     */
    Pinger pinger;

    /*
     * Track incoming and outgoing data sizes and time, for
     * size-based rekeys.
     */
    unsigned long incoming_data_size, outgoing_data_size, deferred_data_size;
    unsigned long max_data_size;
    int kex_in_progress;
    unsigned long next_rekey, last_rekey;
    const char *deferred_rekey_reason;

    /*
     * Fully qualified host name, which we need if doing GSSAPI.
     */
    char *fullhostname;

#ifndef NO_GSSAPI
    /*
     * GSSAPI libraries for this session.
     */
    struct ssh_gss_liblist *gsslibs;
#endif

    /*
     * The last list returned from get_specials.
     */
    struct telnet_special *specials;

    /*
     * List of host key algorithms for which we _don't_ have a stored
     * host key. These are indices into the main hostkey_algs[] array
     */
    int uncert_hostkeys[lenof(hostkey_algs)];
    int n_uncert_hostkeys;

    /*
     * Flag indicating that the current rekey is intended to finish
     * with a newly cross-certified host key.
     */
    int cross_certifying;
};

static const char *ssh_pkt_type(Ssh ssh, int type)
{
    if (ssh->version == 1)
        return ssh1_pkt_type(type);
    else
        return ssh2_pkt_type(ssh->pkt_kctx, ssh->pkt_actx, type);
}

#define logevent(s) logevent(ssh->frontend, s)

/* logevent, only printf-formatted. */
static void logeventf(Ssh ssh, const char *fmt, ...)
{
    va_list ap;
    char *buf;

    va_start(ap, fmt);
    buf = dupvprintf(fmt, ap);
    va_end(ap);
    logevent(buf);
    sfree(buf);
}

static void bomb_out(Ssh ssh, char *text)
{
    ssh_do_close(ssh, FALSE);
    logevent(text);
    connection_fatal(ssh->frontend, "%s", text);
    sfree(text);
}

#define bombout(msg) bomb_out(ssh, dupprintf msg)

/* Helper function for common bits of parsing ttymodes. */
static void parse_ttymodes(Ssh ssh,
                           void (*do_mode)(void *data,
                                           const struct ssh_ttymode *mode,
                                           char *val),
                           void *data)
{
    int i;
    const struct ssh_ttymode *mode;
    char *val;
    char default_val[2];

    strcpy(default_val, "A");

    for (i = 0; i < lenof(ssh_ttymodes); i++) {
        mode = ssh_ttymodes + i;
        val = conf_get_str_str_opt(ssh->conf, CONF_ttymodes, mode->mode);
        if (!val)
            val = default_val;

        /*
         * val[0] is either 'V', indicating that an explicit value
         * follows it, or 'A' indicating that we should pass the
         * value through from the local environment via get_ttymode.
         */
        if (val[0] == 'A') {
            val = get_ttymode(ssh->frontend, mode->mode);
            if (val) {
                do_mode(data, mode, val);
                sfree(val);
            }
        } else
            do_mode(data, mode, val + 1);              /* skip the 'V' */
    }
}

static int ssh_channelcmp(void *av, void *bv)
{
    struct ssh_channel *a = (struct ssh_channel *) av;
    struct ssh_channel *b = (struct ssh_channel *) bv;
    if (a->localid < b->localid)
        return -1;
    if (a->localid > b->localid)
        return +1;
    return 0;
}
static int ssh_channelfind(void *av, void *bv)
{
    unsigned *a = (unsigned *) av;
    struct ssh_channel *b = (struct ssh_channel *) bv;
    if (*a < b->localid)
        return -1;
    if (*a > b->localid)
        return +1;
    return 0;
}

static int ssh_rportcmp_ssh1(void *av, void *bv)
{
    struct ssh_rportfwd *a = (struct ssh_rportfwd *) av;
    struct ssh_rportfwd *b = (struct ssh_rportfwd *) bv;
    int i;
    if ( (i = strcmp(a->dhost, b->dhost)) != 0)
        return i < 0 ? -1 : +1;
    if (a->dport > b->dport)
        return +1;
    if (a->dport < b->dport)
        return -1;
    return 0;
}

static int ssh_rportcmp_ssh2(void *av, void *bv)
{
    struct ssh_rportfwd *a = (struct ssh_rportfwd *) av;
    struct ssh_rportfwd *b = (struct ssh_rportfwd *) bv;
    int i;
    if ( (i = strcmp(a->shost, b->shost)) != 0)
        return i < 0 ? -1 : +1;
    if (a->sport > b->sport)
        return +1;
    if (a->sport < b->sport)
        return -1;
    return 0;
}

/*
 * Special form of strcmp which can cope with NULL inputs. NULL is
 * defined to sort before even the empty string.
 */
static int nullstrcmp(const char *a, const char *b)
{
    if (a == NULL && b == NULL)
        return 0;
    if (a == NULL)
        return -1;
    if (b == NULL)
        return +1;
    return strcmp(a, b);
}

static int ssh_portcmp(void *av, void *bv)
{
    struct ssh_portfwd *a = (struct ssh_portfwd *) av;
    struct ssh_portfwd *b = (struct ssh_portfwd *) bv;
    int i;
    if (a->type > b->type)
        return +1;
    if (a->type < b->type)
        return -1;
    if (a->addressfamily > b->addressfamily)
        return +1;
    if (a->addressfamily < b->addressfamily)
        return -1;
    if ( (i = nullstrcmp(a->saddr, b->saddr)) != 0)
        return i < 0 ? -1 : +1;
    if (a->sport > b->sport)
        return +1;
    if (a->sport < b->sport)
        return -1;
    if (a->type != 'D') {
        if ( (i = nullstrcmp(a->daddr, b->daddr)) != 0)
            return i < 0 ? -1 : +1;
        if (a->dport > b->dport)
            return +1;
        if (a->dport < b->dport)
            return -1;
    }
    return 0;
}

static int alloc_channel_id(Ssh ssh)
{
    const unsigned CHANNEL_NUMBER_OFFSET = 256;
    unsigned low, high, mid;
    int tsize;
    struct ssh_channel *c;

    /*
     * First-fit allocation of channel numbers: always pick the
     * lowest unused one. To do this, binary-search using the
     * counted B-tree to find the largest channel ID which is in a
     * contiguous sequence from the beginning. (Precisely
     * everything in that sequence must have ID equal to its tree
     * index plus CHANNEL_NUMBER_OFFSET.)
     */
    tsize = count234(ssh->channels);

    low = -1;
    high = tsize;
    while (high - low > 1) {
        mid = (high + low) / 2;
        c = index234(ssh->channels, mid);
        if (c->localid == mid + CHANNEL_NUMBER_OFFSET)
            low = mid;                 /* this one is fine */
        else
            high = mid;                /* this one is past it */
    }
    /*
     * Now low points to either -1, or the tree index of the
     * largest ID in the initial sequence.
     */
    {
        unsigned i = low + 1 + CHANNEL_NUMBER_OFFSET;
        assert(NULL == find234(ssh->channels, &i, ssh_channelfind));
    }
    return low + 1 + CHANNEL_NUMBER_OFFSET;
}

static void c_write_stderr(int trusted, const char *buf, int len)
{
    int i;
    for (i = 0; i < len; i++)
        if (buf[i] != '\r' && (trusted || buf[i] == '\n' || (buf[i] & 0x60)))
            fputc(buf[i], stderr);
}

static void c_write(Ssh ssh, const char *buf, int len)
{
    if (flags & FLAG_STDERR)
        c_write_stderr(1, buf, len);
    else
        from_backend(ssh->frontend, 1, buf, len);
}

static void c_write_untrusted(Ssh ssh, const char *buf, int len)
{
    if (flags & FLAG_STDERR)
        c_write_stderr(0, buf, len);
    else
        from_backend_untrusted(ssh->frontend, buf, len);
}

static void c_write_str(Ssh ssh, const char *buf)
{
    c_write(ssh, buf, strlen(buf));
}

static void ssh_free_packet(struct Packet *pkt)
{
    sfree(pkt->data);
    sfree(pkt);
}
static struct Packet *ssh_new_packet(void)
{
    struct Packet *pkt = snew(struct Packet);

    pkt->body = pkt->data = NULL;
    pkt->maxlen = 0;

    return pkt;
}

static void ssh1_log_incoming_packet(Ssh ssh, struct Packet *pkt)
{
    int nblanks = 0;
    struct logblank_t blanks[4];
    char *str;
    int slen;

    pkt->savedpos = 0;

    if (ssh->logomitdata &&
        (pkt->type == SSH1_SMSG_STDOUT_DATA ||
         pkt->type == SSH1_SMSG_STDERR_DATA ||
         pkt->type == SSH1_MSG_CHANNEL_DATA)) {
        /* "Session data" packets - omit the data string. */
        if (pkt->type == SSH1_MSG_CHANNEL_DATA)
            ssh_pkt_getuint32(pkt);    /* skip channel id */
        blanks[nblanks].offset = pkt->savedpos + 4;
        blanks[nblanks].type = PKTLOG_OMIT;
        ssh_pkt_getstring(pkt, &str, &slen);
        if (str) {
            blanks[nblanks].len = slen;
            nblanks++;
        }
    }
    log_packet(ssh->logctx, PKT_INCOMING, pkt->type,
               ssh1_pkt_type(pkt->type),
               pkt->body, pkt->length, nblanks, blanks, NULL,
               0, NULL);
}

static void ssh1_log_outgoing_packet(Ssh ssh, struct Packet *pkt)
{
    int nblanks = 0;
    struct logblank_t blanks[4];
    char *str;
    int slen;

    /*
     * For outgoing packets, pkt->length represents the length of the
     * whole packet starting at pkt->data (including some header), and
     * pkt->body refers to the point within that where the log-worthy
     * payload begins. However, incoming packets expect pkt->length to
     * represent only the payload length (that is, it's measured from
     * pkt->body not from pkt->data). Temporarily adjust our outgoing
     * packet to conform to the incoming-packet semantics, so that we
     * can analyse it with the ssh_pkt_get functions.
     */
    pkt->length -= (pkt->body - pkt->data);
    pkt->savedpos = 0;

    if (ssh->logomitdata &&
        (pkt->type == SSH1_CMSG_STDIN_DATA ||
         pkt->type == SSH1_MSG_CHANNEL_DATA)) {
        /* "Session data" packets - omit the data string. */
        if (pkt->type == SSH1_MSG_CHANNEL_DATA)
            ssh_pkt_getuint32(pkt);    /* skip channel id */
        blanks[nblanks].offset = pkt->savedpos + 4;
        blanks[nblanks].type = PKTLOG_OMIT;
        ssh_pkt_getstring(pkt, &str, &slen);
        if (str) {
            blanks[nblanks].len = slen;
            nblanks++;
        }
    }

    if ((pkt->type == SSH1_CMSG_AUTH_PASSWORD ||
         pkt->type == SSH1_CMSG_AUTH_TIS_RESPONSE ||
         pkt->type == SSH1_CMSG_AUTH_CCARD_RESPONSE) &&
        conf_get_int(ssh->conf, CONF_logomitpass)) {
        /* If this is a password or similar packet, blank the password(s). */
        blanks[nblanks].offset = 0;
        blanks[nblanks].len = pkt->length;
        blanks[nblanks].type = PKTLOG_BLANK;
        nblanks++;
    } else if (pkt->type == SSH1_CMSG_X11_REQUEST_FORWARDING &&
               conf_get_int(ssh->conf, CONF_logomitpass)) {
        /*
         * If this is an X forwarding request packet, blank the fake
         * auth data.
         *
         * Note that while we blank the X authentication data here, we
         * don't take any special action to blank the start of an X11
         * channel, so using MIT-MAGIC-COOKIE-1 and actually opening
         * an X connection without having session blanking enabled is
         * likely to leak your cookie into the log.
         */
        pkt->savedpos = 0;
        ssh_pkt_getstring(pkt, &str, &slen);
        blanks[nblanks].offset = pkt->savedpos;
        blanks[nblanks].type = PKTLOG_BLANK;
        ssh_pkt_getstring(pkt, &str, &slen);
        if (str) {
            blanks[nblanks].len = pkt->savedpos - blanks[nblanks].offset;
            nblanks++;
        }
    }

    log_packet(ssh->logctx, PKT_OUTGOING, pkt->data[12],
               ssh1_pkt_type(pkt->data[12]),
               pkt->body, pkt->length,
               nblanks, blanks, NULL, 0, NULL);

    /*
     * Undo the above adjustment of pkt->length, to put the packet
     * back in the state we found it.
     */
    pkt->length += (pkt->body - pkt->data);
}

/*
 * Collect incoming data in the incoming packet buffer.
 * Decipher and verify the packet when it is completely read.
 * Drop SSH1_MSG_DEBUG and SSH1_MSG_IGNORE packets.
 * Update the *data and *datalen variables.
 * Return a Packet structure when a packet is completed.
 */
static struct Packet *ssh1_rdpkt(Ssh ssh, const unsigned char **data,
                                 int *datalen)
{
    struct rdpkt1_state_tag *st = &ssh->rdpkt1_state;

    crBegin(ssh->ssh1_rdpkt_crstate);

    st->pktin = ssh_new_packet();

    st->pktin->type = 0;
    st->pktin->length = 0;

    for (st->i = st->len = 0; st->i < 4; st->i++) {
        while ((*datalen) == 0)
            crReturn(NULL);
        st->len = (st->len << 8) + **data;
        (*data)++, (*datalen)--;
    }

    st->pad = 8 - (st->len % 8);
    st->biglen = st->len + st->pad;
    st->pktin->length = st->len - 5;

    if (st->biglen < 0) {
        bombout(("Extremely large packet length from server suggests"
                 " data stream corruption"));
        ssh_free_packet(st->pktin);
        crStop(NULL);
    }

    st->pktin->maxlen = st->biglen;
    st->pktin->data = snewn(st->biglen + APIEXTRA, unsigned char);

    st->to_read = st->biglen;
    st->p = st->pktin->data;
    while (st->to_read > 0) {
        st->chunk = st->to_read;
        while ((*datalen) == 0)
            crReturn(NULL);
        if (st->chunk > (*datalen))
            st->chunk = (*datalen);
        memcpy(st->p, *data, st->chunk);
        *data += st->chunk;
        *datalen -= st->chunk;
        st->p += st->chunk;
        st->to_read -= st->chunk;
    }

    if (ssh->cipher && detect_attack(ssh->crcda_ctx, st->pktin->data,
                                     st->biglen, NULL)) {
        bombout(("Network attack (CRC compensation) detected!"));
        ssh_free_packet(st->pktin);
        crStop(NULL);
    }

    if (ssh->cipher)
        ssh->cipher->decrypt(ssh->v1_cipher_ctx, st->pktin->data, st->biglen);

    st->realcrc = crc32_compute(st->pktin->data, st->biglen - 4);
    st->gotcrc = GET_32BIT(st->pktin->data + st->biglen - 4);
    if (st->gotcrc != st->realcrc) {
        bombout(("Incorrect CRC received on packet"));
        ssh_free_packet(st->pktin);
        crStop(NULL);
    }

    st->pktin->body = st->pktin->data + st->pad + 1;

    if (ssh->v1_compressing) {
        unsigned char *decompblk;
        int decomplen;
        if (!zlib_decompress_block(ssh->sc_comp_ctx,
                                   st->pktin->body - 1, st->pktin->length + 1,
                                   &decompblk, &decomplen)) {
            bombout(("Zlib decompression encountered invalid data"));
            ssh_free_packet(st->pktin);
            crStop(NULL);
        }

        if (st->pktin->maxlen < st->pad + decomplen) {
            st->pktin->maxlen = st->pad + decomplen;
            st->pktin->data = sresize(st->pktin->data,
                                      st->pktin->maxlen + APIEXTRA,
                                      unsigned char);
            st->pktin->body = st->pktin->data + st->pad + 1;
        }

        memcpy(st->pktin->body - 1, decompblk, decomplen);
        sfree(decompblk);
        st->pktin->length = decomplen - 1;
    }

    st->pktin->type = st->pktin->body[-1];

    /*
     * Now pktin->body and pktin->length identify the semantic content
     * of the packet, excluding the initial type byte.
     */

    if (ssh->logctx)
        ssh1_log_incoming_packet(ssh, st->pktin);

    st->pktin->savedpos = 0;

    crFinish(st->pktin);
}

static void ssh2_log_incoming_packet(Ssh ssh, struct Packet *pkt)
{
    int nblanks = 0;
    struct logblank_t blanks[4];
    char *str;
    int slen;

    pkt->savedpos = 0;

    if (ssh->logomitdata &&
        (pkt->type == SSH2_MSG_CHANNEL_DATA ||
         pkt->type == SSH2_MSG_CHANNEL_EXTENDED_DATA)) {
        /* "Session data" packets - omit the data string. */
        ssh_pkt_getuint32(pkt);    /* skip channel id */
        if (pkt->type == SSH2_MSG_CHANNEL_EXTENDED_DATA)
            ssh_pkt_getuint32(pkt);    /* skip extended data type */
        blanks[nblanks].offset = pkt->savedpos + 4;
        blanks[nblanks].type = PKTLOG_OMIT;
        ssh_pkt_getstring(pkt, &str, &slen);
        if (str) {
            blanks[nblanks].len = slen;
            nblanks++;
        }
    }

    log_packet(ssh->logctx, PKT_INCOMING, pkt->type,
               ssh2_pkt_type(ssh->pkt_kctx, ssh->pkt_actx, pkt->type),
               pkt->body, pkt->length, nblanks, blanks, &pkt->sequence,
               0, NULL);
}

static void ssh2_log_outgoing_packet(Ssh ssh, struct Packet *pkt)
{
    int nblanks = 0;
    struct logblank_t blanks[4];
    char *str;
    int slen;

    /*
     * For outgoing packets, pkt->length represents the length of the
     * whole packet starting at pkt->data (including some header), and
     * pkt->body refers to the point within that where the log-worthy
     * payload begins. However, incoming packets expect pkt->length to
     * represent only the payload length (that is, it's measured from
     * pkt->body not from pkt->data). Temporarily adjust our outgoing
     * packet to conform to the incoming-packet semantics, so that we
     * can analyse it with the ssh_pkt_get functions.
     */
    pkt->length -= (pkt->body - pkt->data);
    pkt->savedpos = 0;

    if (ssh->logomitdata &&
        (pkt->type == SSH2_MSG_CHANNEL_DATA ||
         pkt->type == SSH2_MSG_CHANNEL_EXTENDED_DATA)) {
        /* "Session data" packets - omit the data string. */
        ssh_pkt_getuint32(pkt);    /* skip channel id */
        if (pkt->type == SSH2_MSG_CHANNEL_EXTENDED_DATA)
            ssh_pkt_getuint32(pkt);    /* skip extended data type */
        blanks[nblanks].offset = pkt->savedpos + 4;
        blanks[nblanks].type = PKTLOG_OMIT;
        ssh_pkt_getstring(pkt, &str, &slen);
        if (str) {
            blanks[nblanks].len = slen;
            nblanks++;
        }
    }

    if (pkt->type == SSH2_MSG_USERAUTH_REQUEST &&
        conf_get_int(ssh->conf, CONF_logomitpass)) {
        /* If this is a password packet, blank the password(s). */
        pkt->savedpos = 0;
        ssh_pkt_getstring(pkt, &str, &slen);
        ssh_pkt_getstring(pkt, &str, &slen);
        ssh_pkt_getstring(pkt, &str, &slen);
        if (slen == 8 && !memcmp(str, "password", 8)) {
            ssh2_pkt_getbool(pkt);
            /* Blank the password field. */
            blanks[nblanks].offset = pkt->savedpos;
            blanks[nblanks].type = PKTLOG_BLANK;
            ssh_pkt_getstring(pkt, &str, &slen);
            if (str) {
                blanks[nblanks].len = pkt->savedpos - blanks[nblanks].offset;
                nblanks++;
                /* If there's another password field beyond it (change of
                 * password), blank that too. */
                ssh_pkt_getstring(pkt, &str, &slen);
                if (str)
                    blanks[nblanks-1].len =
                        pkt->savedpos - blanks[nblanks].offset;
            }
        }
    } else if (ssh->pkt_actx == SSH2_PKTCTX_KBDINTER &&
               pkt->type == SSH2_MSG_USERAUTH_INFO_RESPONSE &&
               conf_get_int(ssh->conf, CONF_logomitpass)) {
        /* If this is a keyboard-interactive response packet, blank
         * the responses. */
        pkt->savedpos = 0;
        ssh_pkt_getuint32(pkt);
        blanks[nblanks].offset = pkt->savedpos;
        blanks[nblanks].type = PKTLOG_BLANK;
        while (1) {
            ssh_pkt_getstring(pkt, &str, &slen);
            if (!str)
                break;
        }
        blanks[nblanks].len = pkt->savedpos - blanks[nblanks].offset;
        nblanks++;
    } else if (pkt->type == SSH2_MSG_CHANNEL_REQUEST &&
               conf_get_int(ssh->conf, CONF_logomitpass)) {
        /*
         * If this is an X forwarding request packet, blank the fake
         * auth data.
         *
         * Note that while we blank the X authentication data here, we
         * don't take any special action to blank the start of an X11
         * channel, so using MIT-MAGIC-COOKIE-1 and actually opening
         * an X connection without having session blanking enabled is
         * likely to leak your cookie into the log.
         */
        pkt->savedpos = 0;
        ssh_pkt_getuint32(pkt);
        ssh_pkt_getstring(pkt, &str, &slen);
        if (slen == 7 && !memcmp(str, "x11-req", 0)) {
            ssh2_pkt_getbool(pkt);
            ssh2_pkt_getbool(pkt);
            ssh_pkt_getstring(pkt, &str, &slen);
            blanks[nblanks].offset = pkt->savedpos;
            blanks[nblanks].type = PKTLOG_BLANK;
            ssh_pkt_getstring(pkt, &str, &slen);
            if (str) {
                blanks[nblanks].len = pkt->savedpos - blanks[nblanks].offset;
                nblanks++;
            }
        }
    }

    log_packet(ssh->logctx, PKT_OUTGOING, pkt->data[5],
               ssh2_pkt_type(ssh->pkt_kctx, ssh->pkt_actx, pkt->data[5]),
               pkt->body, pkt->length, nblanks, blanks,
               &ssh->v2_outgoing_sequence,
               pkt->downstream_id, pkt->additional_log_text);

    /*
     * Undo the above adjustment of pkt->length, to put the packet
     * back in the state we found it.
     */
    pkt->length += (pkt->body - pkt->data);
}

static struct Packet *ssh2_rdpkt(Ssh ssh, const unsigned char **data,
                                 int *datalen)
{
    struct rdpkt2_state_tag *st = &ssh->rdpkt2_state;

    crBegin(ssh->ssh2_rdpkt_crstate);

    st->pktin = ssh_new_packet();

    st->pktin->type = 0;
    st->pktin->length = 0;
    if (ssh->sccipher)
        st->cipherblk = ssh->sccipher->blksize;
    else
        st->cipherblk = 8;
    if (st->cipherblk < 8)
        st->cipherblk = 8;
    st->maclen = ssh->scmac ? ssh->scmac->len : 0;

    if (ssh->sccipher && (ssh->sccipher->flags & SSH_CIPHER_IS_CBC) &&
        ssh->scmac && !ssh->scmac_etm) {
        /*
         * When dealing with a CBC-mode cipher, we want to avoid the
         * possibility of an attacker's tweaking the ciphertext stream
         * so as to cause us to feed the same block to the block
         * cipher more than once and thus leak information
         * (VU#958563).  The way we do this is not to take any
         * decisions on the basis of anything we've decrypted until
         * we've verified it with a MAC.  That includes the packet
         * length, so we just read data and check the MAC repeatedly,
         * and when the MAC passes, see if the length we've got is
         * plausible.
         *
         * This defence is unnecessary in OpenSSH ETM mode, because
         * the whole point of ETM mode is that the attacker can't
         * tweak the ciphertext stream at all without the MAC
         * detecting it before we decrypt anything.
         */

        /* May as well allocate the whole lot now. */
        st->pktin->data = snewn(OUR_V2_PACKETLIMIT + st->maclen + APIEXTRA,
                                unsigned char);

        /* Read an amount corresponding to the MAC. */
        for (st->i = 0; st->i < st->maclen; st->i++) {
            while ((*datalen) == 0)
                crReturn(NULL);
            st->pktin->data[st->i] = *(*data)++;
            (*datalen)--;
        }

        st->packetlen = 0;
        {
            unsigned char seq[4];
            ssh->scmac->start(ssh->sc_mac_ctx);
            PUT_32BIT(seq, st->incoming_sequence);
            ssh->scmac->bytes(ssh->sc_mac_ctx, seq, 4);
        }

        for (;;) { /* Once around this loop per cipher block. */
            /* Read another cipher-block's worth, and tack it onto the end. */
            for (st->i = 0; st->i < st->cipherblk; st->i++) {
                while ((*datalen) == 0)
                    crReturn(NULL);
                st->pktin->data[st->packetlen+st->maclen+st->i] = *(*data)++;
                (*datalen)--;
            }
            /* Decrypt one more block (a little further back in the stream). */
            ssh->sccipher->decrypt(ssh->sc_cipher_ctx,
                                   st->pktin->data + st->packetlen,
                                   st->cipherblk);
            /* Feed that block to the MAC. */
            ssh->scmac->bytes(ssh->sc_mac_ctx,
                              st->pktin->data + st->packetlen, st->cipherblk);
            st->packetlen += st->cipherblk;
            /* See if that gives us a valid packet. */
            if (ssh->scmac->verresult(ssh->sc_mac_ctx,
                                      st->pktin->data + st->packetlen) &&
                ((st->len = toint(GET_32BIT(st->pktin->data))) ==
                 st->packetlen-4))
                    break;
            if (st->packetlen >= OUR_V2_PACKETLIMIT) {
                bombout(("No valid incoming packet found"));
                ssh_free_packet(st->pktin);
                crStop(NULL);
            }       
        }
        st->pktin->maxlen = st->packetlen + st->maclen;
        st->pktin->data = sresize(st->pktin->data,
                                  st->pktin->maxlen + APIEXTRA,
                                  unsigned char);
    } else if (ssh->scmac && ssh->scmac_etm) {
        st->pktin->data = snewn(4 + APIEXTRA, unsigned char);

        /*
         * OpenSSH encrypt-then-MAC mode: the packet length is
         * unencrypted, unless the cipher supports length encryption.
         */
        for (st->i = st->len = 0; st->i < 4; st->i++) {
            while ((*datalen) == 0)
                crReturn(NULL);
            st->pktin->data[st->i] = *(*data)++;
            (*datalen)--;
        }
        /* Cipher supports length decryption, so do it */
        if (ssh->sccipher && (ssh->sccipher->flags & SSH_CIPHER_SEPARATE_LENGTH)) {
            /* Keep the packet the same though, so the MAC passes */
            unsigned char len[4];
            memcpy(len, st->pktin->data, 4);
            ssh->sccipher->decrypt_length(ssh->sc_cipher_ctx, len, 4, st->incoming_sequence);
            st->len = toint(GET_32BIT(len));
        } else {
            st->len = toint(GET_32BIT(st->pktin->data));
        }

        /*
         * _Completely_ silly lengths should be stomped on before they
         * do us any more damage.
         */
        if (st->len < 0 || st->len > OUR_V2_PACKETLIMIT ||
            st->len % st->cipherblk != 0) {
            bombout(("Incoming packet length field was garbled"));
            ssh_free_packet(st->pktin);
            crStop(NULL);
        }

        /*
         * So now we can work out the total packet length.
         */
        st->packetlen = st->len + 4;

        /*
         * Allocate memory for the rest of the packet.
         */
        st->pktin->maxlen = st->packetlen + st->maclen;
        st->pktin->data = sresize(st->pktin->data,
                                  st->pktin->maxlen + APIEXTRA,
                                  unsigned char);

        /*
         * Read the remainder of the packet.
         */
        for (st->i = 4; st->i < st->packetlen + st->maclen; st->i++) {
            while ((*datalen) == 0)
                crReturn(NULL);
            st->pktin->data[st->i] = *(*data)++;
            (*datalen)--;
        }

        /*
         * Check the MAC.
         */
        if (ssh->scmac
            && !ssh->scmac->verify(ssh->sc_mac_ctx, st->pktin->data,
                                   st->len + 4, st->incoming_sequence)) {
            bombout(("Incorrect MAC received on packet"));
            ssh_free_packet(st->pktin);
            crStop(NULL);
        }

        /* Decrypt everything between the length field and the MAC. */
        if (ssh->sccipher)
            ssh->sccipher->decrypt(ssh->sc_cipher_ctx,
                                   st->pktin->data + 4,
                                   st->packetlen - 4);
    } else {
        st->pktin->data = snewn(st->cipherblk + APIEXTRA, unsigned char);

        /*
         * Acquire and decrypt the first block of the packet. This will
         * contain the length and padding details.
         */
        for (st->i = st->len = 0; st->i < st->cipherblk; st->i++) {
            while ((*datalen) == 0)
                crReturn(NULL);
            st->pktin->data[st->i] = *(*data)++;
            (*datalen)--;
        }

        if (ssh->sccipher)
            ssh->sccipher->decrypt(ssh->sc_cipher_ctx,
                                   st->pktin->data, st->cipherblk);

        /*
         * Now get the length figure.
         */
        st->len = toint(GET_32BIT(st->pktin->data));

        /*
         * _Completely_ silly lengths should be stomped on before they
         * do us any more damage.
         */
        if (st->len < 0 || st->len > OUR_V2_PACKETLIMIT ||
            (st->len + 4) % st->cipherblk != 0) {
            bombout(("Incoming packet was garbled on decryption"));
            ssh_free_packet(st->pktin);
            crStop(NULL);
        }

        /*
         * So now we can work out the total packet length.
         */
        st->packetlen = st->len + 4;

        /*
         * Allocate memory for the rest of the packet.
         */
        st->pktin->maxlen = st->packetlen + st->maclen;
        st->pktin->data = sresize(st->pktin->data,
                                  st->pktin->maxlen + APIEXTRA,
                                  unsigned char);

        /*
         * Read and decrypt the remainder of the packet.
         */
        for (st->i = st->cipherblk; st->i < st->packetlen + st->maclen;
             st->i++) {
            while ((*datalen) == 0)
                crReturn(NULL);
            st->pktin->data[st->i] = *(*data)++;
            (*datalen)--;
        }
        /* Decrypt everything _except_ the MAC. */
        if (ssh->sccipher)
            ssh->sccipher->decrypt(ssh->sc_cipher_ctx,
                                   st->pktin->data + st->cipherblk,
                                   st->packetlen - st->cipherblk);

        /*
         * Check the MAC.
         */
        if (ssh->scmac
            && !ssh->scmac->verify(ssh->sc_mac_ctx, st->pktin->data,
                                   st->len + 4, st->incoming_sequence)) {
            bombout(("Incorrect MAC received on packet"));
            ssh_free_packet(st->pktin);
            crStop(NULL);
        }
    }
    /* Get and sanity-check the amount of random padding. */
    st->pad = st->pktin->data[4];
    if (st->pad < 4 || st->len - st->pad < 1) {
        bombout(("Invalid padding length on received packet"));
        ssh_free_packet(st->pktin);
        crStop(NULL);
    }
    /*
     * This enables us to deduce the payload length.
     */
    st->payload = st->len - st->pad - 1;

    st->pktin->length = st->payload + 5;
    st->pktin->encrypted_len = st->packetlen;

    st->pktin->sequence = st->incoming_sequence++;

    st->pktin->length = st->packetlen - st->pad;
    assert(st->pktin->length >= 0);

    /*
     * Decompress packet payload.
     */
    {
        unsigned char *newpayload;
        int newlen;
        if (ssh->sccomp &&
            ssh->sccomp->decompress(ssh->sc_comp_ctx,
                                    st->pktin->data + 5, st->pktin->length - 5,
                                    &newpayload, &newlen)) {
            if (st->pktin->maxlen < newlen + 5) {
                st->pktin->maxlen = newlen + 5;
                st->pktin->data = sresize(st->pktin->data,
                                          st->pktin->maxlen + APIEXTRA,
                                          unsigned char);
            }
            st->pktin->length = 5 + newlen;
            memcpy(st->pktin->data + 5, newpayload, newlen);
            sfree(newpayload);
        }
    }

    /*
     * RFC 4253 doesn't explicitly say that completely empty packets
     * with no type byte are forbidden, so treat them as deserving
     * an SSH_MSG_UNIMPLEMENTED.
     */
    if (st->pktin->length <= 5) { /* == 5 we hope, but robustness */
        ssh2_msg_something_unimplemented(ssh, st->pktin);
        crStop(NULL);
    }
    /*
     * pktin->body and pktin->length should identify the semantic
     * content of the packet, excluding the initial type byte.
     */
    st->pktin->type = st->pktin->data[5];
    st->pktin->body = st->pktin->data + 6;
    st->pktin->length -= 6;
    assert(st->pktin->length >= 0);    /* one last double-check */

    if (ssh->logctx)
        ssh2_log_incoming_packet(ssh, st->pktin);

    st->pktin->savedpos = 0;

    crFinish(st->pktin);
}

static struct Packet *ssh2_bare_connection_rdpkt(Ssh ssh,
                                                 const unsigned char **data,
                                                 int *datalen)
{
    struct rdpkt2_bare_state_tag *st = &ssh->rdpkt2_bare_state;

    crBegin(ssh->ssh2_bare_rdpkt_crstate);

    /*
     * Read the packet length field.
     */
    for (st->i = 0; st->i < 4; st->i++) {
        while ((*datalen) == 0)
            crReturn(NULL);
        st->length[st->i] = *(*data)++;
        (*datalen)--;
    }

    st->packetlen = toint(GET_32BIT_MSB_FIRST(st->length));
    if (st->packetlen <= 0 || st->packetlen >= OUR_V2_PACKETLIMIT) {
        bombout(("Invalid packet length received"));
        crStop(NULL);
    }

    st->pktin = ssh_new_packet();
    st->pktin->data = snewn(st->packetlen, unsigned char);

    st->pktin->encrypted_len = st->packetlen;

    st->pktin->sequence = st->incoming_sequence++;

    /*
     * Read the remainder of the packet.
     */
    for (st->i = 0; st->i < st->packetlen; st->i++) {
        while ((*datalen) == 0)
            crReturn(NULL);
        st->pktin->data[st->i] = *(*data)++;
        (*datalen)--;
    }

    /*
     * pktin->body and pktin->length should identify the semantic
     * content of the packet, excluding the initial type byte.
     */
    st->pktin->type = st->pktin->data[0];
    st->pktin->body = st->pktin->data + 1;
    st->pktin->length = st->packetlen - 1;

    /*
     * Log incoming packet, possibly omitting sensitive fields.
     */
    if (ssh->logctx)
        ssh2_log_incoming_packet(ssh, st->pktin);

    st->pktin->savedpos = 0;

    crFinish(st->pktin);
}

static int s_wrpkt_prepare(Ssh ssh, struct Packet *pkt, int *offset_p)
{
    int pad, biglen, i, pktoffs;
    unsigned long crc;
#ifdef __SC__
    /*
     * XXX various versions of SC (including 8.8.4) screw up the
     * register allocation in this function and use the same register
     * (D6) for len and as a temporary, with predictable results.  The
     * following sledgehammer prevents this.
     */
    volatile
#endif
    int len;

    if (ssh->logctx)
        ssh1_log_outgoing_packet(ssh, pkt);

    if (ssh->v1_compressing) {
        unsigned char *compblk;
        int complen;
        zlib_compress_block(ssh->cs_comp_ctx,
                            pkt->data + 12, pkt->length - 12,
                            &compblk, &complen);
        ssh_pkt_ensure(pkt, complen + 2);   /* just in case it's got bigger */
        memcpy(pkt->data + 12, compblk, complen);
        sfree(compblk);
        pkt->length = complen + 12;
    }

    ssh_pkt_ensure(pkt, pkt->length + 4); /* space for CRC */
    pkt->length += 4;
    len = pkt->length - 4 - 8;  /* len(type+data+CRC) */
    pad = 8 - (len % 8);
    pktoffs = 8 - pad;
    biglen = len + pad;         /* len(padding+type+data+CRC) */

    for (i = pktoffs; i < 4+8; i++)
        pkt->data[i] = random_byte();
    crc = crc32_compute(pkt->data + pktoffs + 4, biglen - 4); /* all ex len */
    PUT_32BIT(pkt->data + pktoffs + 4 + biglen - 4, crc);
    PUT_32BIT(pkt->data + pktoffs, len);

    if (ssh->cipher)
        ssh->cipher->encrypt(ssh->v1_cipher_ctx,
                             pkt->data + pktoffs + 4, biglen);

    if (offset_p) *offset_p = pktoffs;
    return biglen + 4;          /* len(length+padding+type+data+CRC) */
}

static int s_write(Ssh ssh, void *data, int len)
{
    if (ssh->logctx)
        log_packet(ssh->logctx, PKT_OUTGOING, -1, NULL, data, len,
                   0, NULL, NULL, 0, NULL);
    if (!ssh->s)
        return 0;
    return sk_write(ssh->s, (char *)data, len);
}

static void s_wrpkt(Ssh ssh, struct Packet *pkt)
{
    int len, backlog, offset;
    len = s_wrpkt_prepare(ssh, pkt, &offset);
    backlog = s_write(ssh, pkt->data + offset, len);
    if (backlog > SSH_MAX_BACKLOG)
        ssh_throttle_all(ssh, 1, backlog);
    ssh_free_packet(pkt);
}

static void s_wrpkt_defer(Ssh ssh, struct Packet *pkt)
{
    int len, offset;
    len = s_wrpkt_prepare(ssh, pkt, &offset);
    if (ssh->deferred_len + len > ssh->deferred_size) {
        ssh->deferred_size = ssh->deferred_len + len + 128;
        ssh->deferred_send_data = sresize(ssh->deferred_send_data,
                                          ssh->deferred_size,
                                          unsigned char);
    }
    memcpy(ssh->deferred_send_data + ssh->deferred_len,
           pkt->data + offset, len);
    ssh->deferred_len += len;
    ssh_free_packet(pkt);
}

/*
 * Construct a SSH-1 packet with the specified contents.
 * (This all-at-once interface used to be the only one, but now SSH-1
 * packets can also be constructed incrementally.)
 */
static struct Packet *construct_packet(Ssh ssh, int pkttype, va_list ap)
{
    int argtype;
    Bignum bn;
    struct Packet *pkt;

    pkt = ssh1_pkt_init(pkttype);

    while ((argtype = va_arg(ap, int)) != PKT_END) {
        unsigned char *argp, argchar;
        char *sargp;
        unsigned long argint;
        int arglen;
        switch (argtype) {
          /* Actual fields in the packet */
          case PKT_INT:
            argint = va_arg(ap, int);
            ssh_pkt_adduint32(pkt, argint);
            break;
          case PKT_CHAR:
            argchar = (unsigned char) va_arg(ap, int);
            ssh_pkt_addbyte(pkt, argchar);
            break;
          case PKT_DATA:
            argp = va_arg(ap, unsigned char *);
            arglen = va_arg(ap, int);
            ssh_pkt_adddata(pkt, argp, arglen);
            break;
          case PKT_STR:
            sargp = va_arg(ap, char *);
            ssh_pkt_addstring(pkt, sargp);
            break;
          case PKT_BIGNUM:
            bn = va_arg(ap, Bignum);
            ssh1_pkt_addmp(pkt, bn);
            break;
        }
    }

    return pkt;
}

static void send_packet(Ssh ssh, int pkttype, ...)
{
    struct Packet *pkt;
    va_list ap;
    va_start(ap, pkttype);
    pkt = construct_packet(ssh, pkttype, ap);
    va_end(ap);
    s_wrpkt(ssh, pkt);
}

static void defer_packet(Ssh ssh, int pkttype, ...)
{
    struct Packet *pkt;
    va_list ap;
    va_start(ap, pkttype);
    pkt = construct_packet(ssh, pkttype, ap);
    va_end(ap);
    s_wrpkt_defer(ssh, pkt);
}

static int ssh_versioncmp(const char *a, const char *b)
{
    char *ae, *be;
    unsigned long av, bv;

    av = strtoul(a, &ae, 10);
    bv = strtoul(b, &be, 10);
    if (av != bv)
        return (av < bv ? -1 : +1);
    if (*ae == '.')
        ae++;
    if (*be == '.')
        be++;
    av = strtoul(ae, &ae, 10);
    bv = strtoul(be, &be, 10);
    if (av != bv)
        return (av < bv ? -1 : +1);
    return 0;
}

/*
 * Utility routines for putting an SSH-protocol `string' and
 * `uint32' into a hash state.
 */
static void hash_string(const struct ssh_hash *h, void *s, void *str, int len)
{
    unsigned char lenblk[4];
    PUT_32BIT(lenblk, len);
    h->bytes(s, lenblk, 4);
    h->bytes(s, str, len);
}

static void hash_uint32(const struct ssh_hash *h, void *s, unsigned i)
{
    unsigned char intblk[4];
    PUT_32BIT(intblk, i);
    h->bytes(s, intblk, 4);
}

/*
 * Packet construction functions. Mostly shared between SSH-1 and SSH-2.
 */
static void ssh_pkt_ensure(struct Packet *pkt, int length)
{
    if (pkt->maxlen < length) {
        unsigned char *body = pkt->body;
        int offset = body ? body - pkt->data : 0;
        pkt->maxlen = length + 256;
        pkt->data = sresize(pkt->data, pkt->maxlen + APIEXTRA, unsigned char);
        if (body) pkt->body = pkt->data + offset;
    }
}
static void ssh_pkt_adddata(struct Packet *pkt, const void *data, int len)
{
    pkt->length += len;
    ssh_pkt_ensure(pkt, pkt->length);
    memcpy(pkt->data + pkt->length - len, data, len);
}
static void ssh_pkt_addbyte(struct Packet *pkt, unsigned char byte)
{
    ssh_pkt_adddata(pkt, &byte, 1);
}
static void ssh2_pkt_addbool(struct Packet *pkt, unsigned char value)
{
    ssh_pkt_adddata(pkt, &value, 1);
}
static void ssh_pkt_adduint32(struct Packet *pkt, unsigned long value)
{
    unsigned char x[4];
    PUT_32BIT(x, value);
    ssh_pkt_adddata(pkt, x, 4);
}
static void ssh_pkt_addstring_start(struct Packet *pkt)
{
    ssh_pkt_adduint32(pkt, 0);
    pkt->savedpos = pkt->length;
}
static void ssh_pkt_addstring_data(struct Packet *pkt, const char *data,
                                   int len)
{
    ssh_pkt_adddata(pkt, data, len);
    PUT_32BIT(pkt->data + pkt->savedpos - 4, pkt->length - pkt->savedpos);
}
static void ssh_pkt_addstring_str(struct Packet *pkt, const char *data)
{
  ssh_pkt_addstring_data(pkt, data, strlen(data));
}
static void ssh_pkt_addstring(struct Packet *pkt, const char *data)
{
    ssh_pkt_addstring_start(pkt);
    ssh_pkt_addstring_str(pkt, data);
}
static void ssh1_pkt_addmp(struct Packet *pkt, Bignum b)
{
    int len = ssh1_bignum_length(b);
    unsigned char *data = snewn(len, unsigned char);
    (void) ssh1_write_bignum(data, b);
    ssh_pkt_adddata(pkt, data, len);
    sfree(data);
}
static unsigned char *ssh2_mpint_fmt(Bignum b, int *len)
{
    unsigned char *p;
    int i, n = (bignum_bitcount(b) + 7) / 8;
    p = snewn(n + 1, unsigned char);
    p[0] = 0;
    for (i = 1; i <= n; i++)
        p[i] = bignum_byte(b, n - i);
    i = 0;
    while (i <= n && p[i] == 0 && (p[i + 1] & 0x80) == 0)
        i++;
    memmove(p, p + i, n + 1 - i);
    *len = n + 1 - i;
    return p;
}
static void ssh2_pkt_addmp(struct Packet *pkt, Bignum b)
{
    unsigned char *p;
    int len;
    p = ssh2_mpint_fmt(b, &len);
    ssh_pkt_addstring_start(pkt);
    ssh_pkt_addstring_data(pkt, (char *)p, len);
    sfree(p);
}

static struct Packet *ssh1_pkt_init(int pkt_type)
{
    struct Packet *pkt = ssh_new_packet();
    pkt->length = 4 + 8;            /* space for length + max padding */
    ssh_pkt_addbyte(pkt, pkt_type);
    pkt->body = pkt->data + pkt->length;
    pkt->type = pkt_type;
    pkt->downstream_id = 0;
    pkt->additional_log_text = NULL;
    return pkt;
}

/* For legacy code (SSH-1 and -2 packet construction used to be separate) */
#define ssh2_pkt_ensure(pkt, length) ssh_pkt_ensure(pkt, length)
#define ssh2_pkt_adddata(pkt, data, len) ssh_pkt_adddata(pkt, data, len)
#define ssh2_pkt_addbyte(pkt, byte) ssh_pkt_addbyte(pkt, byte)
#define ssh2_pkt_adduint32(pkt, value) ssh_pkt_adduint32(pkt, value)
#define ssh2_pkt_addstring_start(pkt) ssh_pkt_addstring_start(pkt)
#define ssh2_pkt_addstring_str(pkt, data) ssh_pkt_addstring_str(pkt, data)
#define ssh2_pkt_addstring_data(pkt, data, len) ssh_pkt_addstring_data(pkt, data, len)
#define ssh2_pkt_addstring(pkt, data) ssh_pkt_addstring(pkt, data)

static struct Packet *ssh2_pkt_init(int pkt_type)
{
    struct Packet *pkt = ssh_new_packet();
    pkt->length = 5; /* space for packet length + padding length */
    pkt->forcepad = 0;
    pkt->type = pkt_type;
    ssh_pkt_addbyte(pkt, (unsigned char) pkt_type);
    pkt->body = pkt->data + pkt->length; /* after packet type */
    pkt->downstream_id = 0;
    pkt->additional_log_text = NULL;
    return pkt;
}

/*
 * Construct an SSH-2 final-form packet: compress it, encrypt it,
 * put the MAC on it. Final packet, ready to be sent, is stored in
 * pkt->data. Total length is returned.
 */
static int ssh2_pkt_construct(Ssh ssh, struct Packet *pkt)
{
    int cipherblk, maclen, padding, unencrypted_prefix, i;

    if (ssh->logctx)
        ssh2_log_outgoing_packet(ssh, pkt);

    if (ssh->bare_connection) {
        /*
         * Trivial packet construction for the bare connection
         * protocol.
         */
        PUT_32BIT(pkt->data + 1, pkt->length - 5);
        pkt->body = pkt->data + 1;
        ssh->v2_outgoing_sequence++;   /* only for diagnostics, really */
        return pkt->length - 1;
    }

    /*
     * Compress packet payload.
     */
    {
        unsigned char *newpayload;
        int newlen;
        if (ssh->cscomp &&
            ssh->cscomp->compress(ssh->cs_comp_ctx, pkt->data + 5,
                                  pkt->length - 5,
                                  &newpayload, &newlen)) {
            pkt->length = 5;
            ssh2_pkt_adddata(pkt, newpayload, newlen);
            sfree(newpayload);
        }
    }

    /*
     * Add padding. At least four bytes, and must also bring total
     * length (minus MAC) up to a multiple of the block size.
     * If pkt->forcepad is set, make sure the packet is at least that size
     * after padding.
     */
    cipherblk = ssh->cscipher ? ssh->cscipher->blksize : 8;  /* block size */
    cipherblk = cipherblk < 8 ? 8 : cipherblk;  /* or 8 if blksize < 8 */
    padding = 4;
    unencrypted_prefix = (ssh->csmac && ssh->csmac_etm) ? 4 : 0;
    if (pkt->length + padding < pkt->forcepad)
        padding = pkt->forcepad - pkt->length;
    padding +=
        (cipherblk - (pkt->length - unencrypted_prefix + padding) % cipherblk)
        % cipherblk;
    assert(padding <= 255);
    maclen = ssh->csmac ? ssh->csmac->len : 0;
    ssh2_pkt_ensure(pkt, pkt->length + padding + maclen);
    pkt->data[4] = padding;
    for (i = 0; i < padding; i++)
        pkt->data[pkt->length + i] = random_byte();
    PUT_32BIT(pkt->data, pkt->length + padding - 4);

    /* Encrypt length if the scheme requires it */
    if (ssh->cscipher && (ssh->cscipher->flags & SSH_CIPHER_SEPARATE_LENGTH)) {
        ssh->cscipher->encrypt_length(ssh->cs_cipher_ctx, pkt->data, 4,
                                      ssh->v2_outgoing_sequence);
    }

    if (ssh->csmac && ssh->csmac_etm) {
        /*
         * OpenSSH-defined encrypt-then-MAC protocol.
         */
        if (ssh->cscipher)
            ssh->cscipher->encrypt(ssh->cs_cipher_ctx,
                                   pkt->data + 4, pkt->length + padding - 4);
        ssh->csmac->generate(ssh->cs_mac_ctx, pkt->data,
                             pkt->length + padding,
                             ssh->v2_outgoing_sequence);
    } else {
        /*
         * SSH-2 standard protocol.
         */
        if (ssh->csmac)
            ssh->csmac->generate(ssh->cs_mac_ctx, pkt->data,
                                 pkt->length + padding,
                                 ssh->v2_outgoing_sequence);
        if (ssh->cscipher)
            ssh->cscipher->encrypt(ssh->cs_cipher_ctx,
                                   pkt->data, pkt->length + padding);
    }

    ssh->v2_outgoing_sequence++;       /* whether or not we MACed */
    pkt->encrypted_len = pkt->length + padding;

    /* Ready-to-send packet starts at pkt->data. We return length. */
    pkt->body = pkt->data;
    return pkt->length + padding + maclen;
}

/*
 * Routines called from the main SSH code to send packets. There
 * are quite a few of these, because we have two separate
 * mechanisms for delaying the sending of packets:
 * 
 *  - In order to send an IGNORE message and a password message in
 *    a single fixed-length blob, we require the ability to
 *    concatenate the encrypted forms of those two packets _into_ a
 *    single blob and then pass it to our <network.h> transport
 *    layer in one go. Hence, there's a deferment mechanism which
 *    works after packet encryption.
 * 
 *  - In order to avoid sending any connection-layer messages
 *    during repeat key exchange, we have to queue up any such
 *    outgoing messages _before_ they are encrypted (and in
 *    particular before they're allocated sequence numbers), and
 *    then send them once we've finished.
 * 
 * I call these mechanisms `defer' and `queue' respectively, so as
 * to distinguish them reasonably easily.
 * 
 * The functions send_noqueue() and defer_noqueue() free the packet
 * structure they are passed. Every outgoing packet goes through
 * precisely one of these functions in its life; packets passed to
 * ssh2_pkt_send() or ssh2_pkt_defer() either go straight to one of
 * these or get queued, and then when the queue is later emptied
 * the packets are all passed to defer_noqueue().
 *
 * When using a CBC-mode cipher, it's necessary to ensure that an
 * attacker can't provide data to be encrypted using an IV that they
 * know.  We ensure this by prefixing each packet that might contain
 * user data with an SSH_MSG_IGNORE.  This is done using the deferral
 * mechanism, so in this case send_noqueue() ends up redirecting to
 * defer_noqueue().  If you don't like this inefficiency, don't use
 * CBC.
 */

static void ssh2_pkt_defer_noqueue(Ssh, struct Packet *, int);
static void ssh_pkt_defersend(Ssh);

/*
 * Send an SSH-2 packet immediately, without queuing or deferring.
 */
static void ssh2_pkt_send_noqueue(Ssh ssh, struct Packet *pkt)
{
    int len;
    int backlog;
    if (ssh->cscipher != NULL && (ssh->cscipher->flags & SSH_CIPHER_IS_CBC)) {
        /* We need to send two packets, so use the deferral mechanism. */
        ssh2_pkt_defer_noqueue(ssh, pkt, FALSE);
        ssh_pkt_defersend(ssh);
        return;
    }
    len = ssh2_pkt_construct(ssh, pkt);
    backlog = s_write(ssh, pkt->body, len);
    if (backlog > SSH_MAX_BACKLOG)
        ssh_throttle_all(ssh, 1, backlog);

    ssh->outgoing_data_size += pkt->encrypted_len;
    if (!ssh->kex_in_progress &&
        !ssh->bare_connection &&
        ssh->max_data_size != 0 &&
        ssh->outgoing_data_size > ssh->max_data_size)
        do_ssh2_transport(ssh, "too much data sent", -1, NULL);

    ssh_free_packet(pkt);
}

/*
 * Defer an SSH-2 packet.
 */
static void ssh2_pkt_defer_noqueue(Ssh ssh, struct Packet *pkt, int noignore)
{
    int len;
    if (ssh->cscipher != NULL && (ssh->cscipher->flags & SSH_CIPHER_IS_CBC) &&
        ssh->deferred_len == 0 && !noignore &&
        !(ssh->remote_bugs & BUG_CHOKES_ON_SSH2_IGNORE)) {
        /*
         * Interpose an SSH_MSG_IGNORE to ensure that user data don't
         * get encrypted with a known IV.
         */
        struct Packet *ipkt = ssh2_pkt_init(SSH2_MSG_IGNORE);
        ssh2_pkt_addstring_start(ipkt);
        ssh2_pkt_defer_noqueue(ssh, ipkt, TRUE);
    }
    len = ssh2_pkt_construct(ssh, pkt);
    if (ssh->deferred_len + len > ssh->deferred_size) {
        ssh->deferred_size = ssh->deferred_len + len + 128;
        ssh->deferred_send_data = sresize(ssh->deferred_send_data,
                                          ssh->deferred_size,
                                          unsigned char);
    }
    memcpy(ssh->deferred_send_data + ssh->deferred_len, pkt->body, len);
    ssh->deferred_len += len;
    ssh->deferred_data_size += pkt->encrypted_len;
    ssh_free_packet(pkt);
}

/*
 * Queue an SSH-2 packet.
 */
static void ssh2_pkt_queue(Ssh ssh, struct Packet *pkt)
{
    assert(ssh->queueing);

    if (ssh->queuelen >= ssh->queuesize) {
        ssh->queuesize = ssh->queuelen + 32;
        ssh->queue = sresize(ssh->queue, ssh->queuesize, struct Packet *);
    }

    ssh->queue[ssh->queuelen++] = pkt;
}

/*
 * Either queue or send a packet, depending on whether queueing is
 * set.
 */
static void ssh2_pkt_send(Ssh ssh, struct Packet *pkt)
{
    if (ssh->queueing)
        ssh2_pkt_queue(ssh, pkt);
    else
        ssh2_pkt_send_noqueue(ssh, pkt);
}

/*
 * Either queue or defer a packet, depending on whether queueing is
 * set.
 */
static void ssh2_pkt_defer(Ssh ssh, struct Packet *pkt)
{
    if (ssh->queueing)
        ssh2_pkt_queue(ssh, pkt);
    else
        ssh2_pkt_defer_noqueue(ssh, pkt, FALSE);
}

/*
 * Send the whole deferred data block constructed by
 * ssh2_pkt_defer() or SSH-1's defer_packet().
 * 
 * The expected use of the defer mechanism is that you call
 * ssh2_pkt_defer() a few times, then call ssh_pkt_defersend(). If
 * not currently queueing, this simply sets up deferred_send_data
 * and then sends it. If we _are_ currently queueing, the calls to
 * ssh2_pkt_defer() put the deferred packets on to the queue
 * instead, and therefore ssh_pkt_defersend() has no deferred data
 * to send. Hence, there's no need to make it conditional on
 * ssh->queueing.
 */
static void ssh_pkt_defersend(Ssh ssh)
{
    int backlog;
    backlog = s_write(ssh, ssh->deferred_send_data, ssh->deferred_len);
    ssh->deferred_len = ssh->deferred_size = 0;
    sfree(ssh->deferred_send_data);
    ssh->deferred_send_data = NULL;
    if (backlog > SSH_MAX_BACKLOG)
        ssh_throttle_all(ssh, 1, backlog);

    if (ssh->version == 2) {
        ssh->outgoing_data_size += ssh->deferred_data_size;
        ssh->deferred_data_size = 0;
        if (!ssh->kex_in_progress &&
            !ssh->bare_connection &&
            ssh->max_data_size != 0 &&
            ssh->outgoing_data_size > ssh->max_data_size)
            do_ssh2_transport(ssh, "too much data sent", -1, NULL);
    }
}

/*
 * Send a packet whose length needs to be disguised (typically
 * passwords or keyboard-interactive responses).
 */
static void ssh2_pkt_send_with_padding(Ssh ssh, struct Packet *pkt,
                                       int padsize)
{
#if 0
    if (0) {
        /*
         * The simplest way to do this is to adjust the
         * variable-length padding field in the outgoing packet.
         * 
         * Currently compiled out, because some Cisco SSH servers
         * don't like excessively padded packets (bah, why's it
         * always Cisco?)
         */
        pkt->forcepad = padsize;
        ssh2_pkt_send(ssh, pkt);
    } else
#endif
    {
        /*
         * If we can't do that, however, an alternative approach is
         * to use the pkt_defer mechanism to bundle the packet
         * tightly together with an SSH_MSG_IGNORE such that their
         * combined length is a constant. So first we construct the
         * final form of this packet and defer its sending.
         */
        ssh2_pkt_defer(ssh, pkt);

        /*
         * Now construct an SSH_MSG_IGNORE which includes a string
         * that's an exact multiple of the cipher block size. (If
         * the cipher is NULL so that the block size is
         * unavailable, we don't do this trick at all, because we
         * gain nothing by it.)
         */
        if (ssh->cscipher &&
            !(ssh->remote_bugs & BUG_CHOKES_ON_SSH2_IGNORE)) {
            int stringlen, i;

            stringlen = (256 - ssh->deferred_len);
            stringlen += ssh->cscipher->blksize - 1;
            stringlen -= (stringlen % ssh->cscipher->blksize);
            if (ssh->cscomp) {
                /*
                 * Temporarily disable actual compression, so we
                 * can guarantee to get this string exactly the
                 * length we want it. The compression-disabling
                 * routine should return an integer indicating how
                 * many bytes we should adjust our string length
                 * by.
                 */
                stringlen -=
                    ssh->cscomp->disable_compression(ssh->cs_comp_ctx);
            }
            pkt = ssh2_pkt_init(SSH2_MSG_IGNORE);
            ssh2_pkt_addstring_start(pkt);
            for (i = 0; i < stringlen; i++) {
                char c = (char) random_byte();
                ssh2_pkt_addstring_data(pkt, &c, 1);
            }
            ssh2_pkt_defer(ssh, pkt);
        }
        ssh_pkt_defersend(ssh);
    }
}

/*
 * Send all queued SSH-2 packets. We send them by means of
 * ssh2_pkt_defer_noqueue(), in case they included a pair of
 * packets that needed to be lumped together.
 */
static void ssh2_pkt_queuesend(Ssh ssh)
{
    int i;

    assert(!ssh->queueing);

    for (i = 0; i < ssh->queuelen; i++)
        ssh2_pkt_defer_noqueue(ssh, ssh->queue[i], FALSE);
    ssh->queuelen = 0;

    ssh_pkt_defersend(ssh);
}

#if 0
void bndebug(char *string, Bignum b)
{
    unsigned char *p;
    int i, len;
    p = ssh2_mpint_fmt(b, &len);
    debug(("%s", string));
    for (i = 0; i < len; i++)
        debug((" %02x", p[i]));
    debug(("\n"));
    sfree(p);
}
#endif

static void hash_mpint(const struct ssh_hash *h, void *s, Bignum b)
{
    unsigned char *p;
    int len;
    p = ssh2_mpint_fmt(b, &len);
    hash_string(h, s, p, len);
    sfree(p);
}

/*
 * Packet decode functions for both SSH-1 and SSH-2.
 */
static unsigned long ssh_pkt_getuint32(struct Packet *pkt)
{
    unsigned long value;
    if (pkt->length - pkt->savedpos < 4)
        return 0;                      /* arrgh, no way to decline (FIXME?) */
    value = GET_32BIT(pkt->body + pkt->savedpos);
    pkt->savedpos += 4;
    return value;
}
static int ssh2_pkt_getbool(struct Packet *pkt)
{
    unsigned long value;
    if (pkt->length - pkt->savedpos < 1)
        return 0;                      /* arrgh, no way to decline (FIXME?) */
    value = pkt->body[pkt->savedpos] != 0;
    pkt->savedpos++;
    return value;
}
static void ssh_pkt_getstring(struct Packet *pkt, char **p, int *length)
{
    int len;
    *p = NULL;
    *length = 0;
    if (pkt->length - pkt->savedpos < 4)
        return;
    len = toint(GET_32BIT(pkt->body + pkt->savedpos));
    if (len < 0)
        return;
    *length = len;
    pkt->savedpos += 4;
    if (pkt->length - pkt->savedpos < *length)
        return;
    *p = (char *)(pkt->body + pkt->savedpos);
    pkt->savedpos += *length;
}
static void *ssh_pkt_getdata(struct Packet *pkt, int length)
{
    if (pkt->length - pkt->savedpos < length)
        return NULL;
    pkt->savedpos += length;
    return pkt->body + (pkt->savedpos - length);
}
static int ssh1_pkt_getrsakey(struct Packet *pkt, struct RSAKey *key,
                              const unsigned char **keystr)
{
    int j;

    j = makekey(pkt->body + pkt->savedpos,
                pkt->length - pkt->savedpos,
                key, keystr, 0);

    if (j < 0)
        return FALSE;
    
    pkt->savedpos += j;
    assert(pkt->savedpos < pkt->length);

    return TRUE;
}
static Bignum ssh1_pkt_getmp(struct Packet *pkt)
{
    int j;
    Bignum b;

    j = ssh1_read_bignum(pkt->body + pkt->savedpos,
                         pkt->length - pkt->savedpos, &b);

    if (j < 0)
        return NULL;

    pkt->savedpos += j;
    return b;
}
static Bignum ssh2_pkt_getmp(struct Packet *pkt)
{
    char *p;
    int length;
    Bignum b;

    ssh_pkt_getstring(pkt, &p, &length);
    if (!p)
        return NULL;
    if (p[0] & 0x80)
        return NULL;
    b = bignum_from_bytes((unsigned char *)p, length);
    return b;
}

/*
 * Helper function to add an SSH-2 signature blob to a packet.
 * Expects to be shown the public key blob as well as the signature
 * blob. Normally works just like ssh2_pkt_addstring, but will
 * fiddle with the signature packet if necessary for
 * BUG_SSH2_RSA_PADDING.
 */
static void ssh2_add_sigblob(Ssh ssh, struct Packet *pkt,
                             void *pkblob_v, int pkblob_len,
                             void *sigblob_v, int sigblob_len)
{
    unsigned char *pkblob = (unsigned char *)pkblob_v;
    unsigned char *sigblob = (unsigned char *)sigblob_v;

    /* dmemdump(pkblob, pkblob_len); */
    /* dmemdump(sigblob, sigblob_len); */

    /*
     * See if this is in fact an ssh-rsa signature and a buggy
     * server; otherwise we can just do this the easy way.
     */
    if ((ssh->remote_bugs & BUG_SSH2_RSA_PADDING) && pkblob_len > 4+7+4 &&
        (GET_32BIT(pkblob) == 7 && !memcmp(pkblob+4, "ssh-rsa", 7))) {
        int pos, len, siglen;

        /*
         * Find the byte length of the modulus.
         */

        pos = 4+7;                     /* skip over "ssh-rsa" */
        len = toint(GET_32BIT(pkblob+pos)); /* get length of exponent */
        if (len < 0 || len > pkblob_len - pos - 4)
            goto give_up;
        pos += 4 + len;                /* skip over exponent */
        if (pkblob_len - pos < 4)
            goto give_up;
        len = toint(GET_32BIT(pkblob+pos)); /* find length of modulus */
        if (len < 0 || len > pkblob_len - pos - 4)
            goto give_up;
        pos += 4;                      /* find modulus itself */
        while (len > 0 && pkblob[pos] == 0)
            len--, pos++;
        /* debug(("modulus length is %d\n", len)); */

        /*
         * Now find the signature integer.
         */
        pos = 4+7;                     /* skip over "ssh-rsa" */
        if (sigblob_len < pos+4)
            goto give_up;
        siglen = toint(GET_32BIT(sigblob+pos));
        if (siglen != sigblob_len - pos - 4)
            goto give_up;
        /* debug(("signature length is %d\n", siglen)); */

        if (len != siglen) {
            unsigned char newlen[4];
            ssh2_pkt_addstring_start(pkt);
            ssh2_pkt_addstring_data(pkt, (char *)sigblob, pos);
            /* dmemdump(sigblob, pos); */
            pos += 4;                  /* point to start of actual sig */
            PUT_32BIT(newlen, len);
            ssh2_pkt_addstring_data(pkt, (char *)newlen, 4);
            /* dmemdump(newlen, 4); */
            newlen[0] = 0;
            while (len-- > siglen) {
                ssh2_pkt_addstring_data(pkt, (char *)newlen, 1);
                /* dmemdump(newlen, 1); */
            }
            ssh2_pkt_addstring_data(pkt, (char *)(sigblob+pos), siglen);
            /* dmemdump(sigblob+pos, siglen); */
            return;
        }

        /* Otherwise fall through and do it the easy way. We also come
         * here as a fallback if we discover above that the key blob
         * is misformatted in some way. */
      give_up:;
    }

    ssh2_pkt_addstring_start(pkt);
    ssh2_pkt_addstring_data(pkt, (char *)sigblob, sigblob_len);
}

/*
 * Examine the remote side's version string and compare it against
 * a list of known buggy implementations.
 */
static void ssh_detect_bugs(Ssh ssh, char *vstring)
{
    char *imp;                         /* pointer to implementation part */
    imp = vstring;
    imp += strcspn(imp, "-");
    if (*imp) imp++;
    imp += strcspn(imp, "-");
    if (*imp) imp++;

    ssh->remote_bugs = 0;

    /*
     * General notes on server version strings:
     *  - Not all servers reporting "Cisco-1.25" have all the bugs listed
     *    here -- in particular, we've heard of one that's perfectly happy
     *    with SSH1_MSG_IGNOREs -- but this string never seems to change,
     *    so we can't distinguish them.
     */
    if (conf_get_int(ssh->conf, CONF_sshbug_ignore1) == FORCE_ON ||
        (conf_get_int(ssh->conf, CONF_sshbug_ignore1) == AUTO &&
         (!strcmp(imp, "1.2.18") || !strcmp(imp, "1.2.19") ||
          !strcmp(imp, "1.2.20") || !strcmp(imp, "1.2.21") ||
          !strcmp(imp, "1.2.22") || !strcmp(imp, "Cisco-1.25") ||
          !strcmp(imp, "OSU_1.4alpha3") || !strcmp(imp, "OSU_1.5alpha4")))) {
        /*
         * These versions don't support SSH1_MSG_IGNORE, so we have
         * to use a different defence against password length
         * sniffing.
         */
        ssh->remote_bugs |= BUG_CHOKES_ON_SSH1_IGNORE;
        logevent("We believe remote version has SSH-1 ignore bug");
    }

    if (conf_get_int(ssh->conf, CONF_sshbug_plainpw1) == FORCE_ON ||
        (conf_get_int(ssh->conf, CONF_sshbug_plainpw1) == AUTO &&
         (!strcmp(imp, "Cisco-1.25") || !strcmp(imp, "OSU_1.4alpha3")))) {
        /*
         * These versions need a plain password sent; they can't
         * handle having a null and a random length of data after
         * the password.
         */
        ssh->remote_bugs |= BUG_NEEDS_SSH1_PLAIN_PASSWORD;
        logevent("We believe remote version needs a plain SSH-1 password");
    }

    if (conf_get_int(ssh->conf, CONF_sshbug_rsa1) == FORCE_ON ||
        (conf_get_int(ssh->conf, CONF_sshbug_rsa1) == AUTO &&
         (!strcmp(imp, "Cisco-1.25")))) {
        /*
         * These versions apparently have no clue whatever about
         * RSA authentication and will panic and die if they see
         * an AUTH_RSA message.
         */
        ssh->remote_bugs |= BUG_CHOKES_ON_RSA;
        logevent("We believe remote version can't handle SSH-1 RSA authentication");
    }

    if (conf_get_int(ssh->conf, CONF_sshbug_hmac2) == FORCE_ON ||
        (conf_get_int(ssh->conf, CONF_sshbug_hmac2) == AUTO &&
         !wc_match("* VShell", imp) &&
         (wc_match("2.1.0*", imp) || wc_match("2.0.*", imp) ||
          wc_match("2.2.0*", imp) || wc_match("2.3.0*", imp) ||
          wc_match("2.1 *", imp)))) {
        /*
         * These versions have the HMAC bug.
         */
        ssh->remote_bugs |= BUG_SSH2_HMAC;
        logevent("We believe remote version has SSH-2 HMAC bug");
    }

    if (conf_get_int(ssh->conf, CONF_sshbug_derivekey2) == FORCE_ON ||
        (conf_get_int(ssh->conf, CONF_sshbug_derivekey2) == AUTO &&
         !wc_match("* VShell", imp) &&
         (wc_match("2.0.0*", imp) || wc_match("2.0.10*", imp) ))) {
        /*
         * These versions have the key-derivation bug (failing to
         * include the literal shared secret in the hashes that
         * generate the keys).
         */
        ssh->remote_bugs |= BUG_SSH2_DERIVEKEY;
        logevent("We believe remote version has SSH-2 key-derivation bug");
    }

    if (conf_get_int(ssh->conf, CONF_sshbug_rsapad2) == FORCE_ON ||
        (conf_get_int(ssh->conf, CONF_sshbug_rsapad2) == AUTO &&
         (wc_match("OpenSSH_2.[5-9]*", imp) ||
          wc_match("OpenSSH_3.[0-2]*", imp) ||
          wc_match("mod_sftp/0.[0-8]*", imp) ||
          wc_match("mod_sftp/0.9.[0-8]", imp)))) {
        /*
         * These versions have the SSH-2 RSA padding bug.
         */
        ssh->remote_bugs |= BUG_SSH2_RSA_PADDING;
        logevent("We believe remote version has SSH-2 RSA padding bug");
    }

    if (conf_get_int(ssh->conf, CONF_sshbug_pksessid2) == FORCE_ON ||
        (conf_get_int(ssh->conf, CONF_sshbug_pksessid2) == AUTO &&
         wc_match("OpenSSH_2.[0-2]*", imp))) {
        /*
         * These versions have the SSH-2 session-ID bug in
         * public-key authentication.
         */
        ssh->remote_bugs |= BUG_SSH2_PK_SESSIONID;
        logevent("We believe remote version has SSH-2 public-key-session-ID bug");
    }

    if (conf_get_int(ssh->conf, CONF_sshbug_rekey2) == FORCE_ON ||
        (conf_get_int(ssh->conf, CONF_sshbug_rekey2) == AUTO &&
         (wc_match("DigiSSH_2.0", imp) ||
          wc_match("OpenSSH_2.[0-4]*", imp) ||
          wc_match("OpenSSH_2.5.[0-3]*", imp) ||
          wc_match("Sun_SSH_1.0", imp) ||
          wc_match("Sun_SSH_1.0.1", imp) ||
          /* All versions <= 1.2.6 (they changed their format in 1.2.7) */
          wc_match("WeOnlyDo-*", imp)))) {
        /*
         * These versions have the SSH-2 rekey bug.
         */
        ssh->remote_bugs |= BUG_SSH2_REKEY;
        logevent("We believe remote version has SSH-2 rekey bug");
    }

    if (conf_get_int(ssh->conf, CONF_sshbug_maxpkt2) == FORCE_ON ||
        (conf_get_int(ssh->conf, CONF_sshbug_maxpkt2) == AUTO &&
         (wc_match("1.36_sshlib GlobalSCAPE", imp) ||
          wc_match("1.36 sshlib: GlobalScape", imp)))) {
        /*
         * This version ignores our makpkt and needs to be throttled.
         */
        ssh->remote_bugs |= BUG_SSH2_MAXPKT;
        logevent("We believe remote version ignores SSH-2 maximum packet size");
    }

    if (conf_get_int(ssh->conf, CONF_sshbug_ignore2) == FORCE_ON) {
        /*
         * Servers that don't support SSH2_MSG_IGNORE. Currently,
         * none detected automatically.
         */
        ssh->remote_bugs |= BUG_CHOKES_ON_SSH2_IGNORE;
        logevent("We believe remote version has SSH-2 ignore bug");
    }

    if (conf_get_int(ssh->conf, CONF_sshbug_oldgex2) == FORCE_ON ||
        (conf_get_int(ssh->conf, CONF_sshbug_oldgex2) == AUTO &&
         (wc_match("OpenSSH_2.[235]*", imp)))) {
        /*
         * These versions only support the original (pre-RFC4419)
         * SSH-2 GEX request, and disconnect with a protocol error if
         * we use the newer version.
         */
        ssh->remote_bugs |= BUG_SSH2_OLDGEX;
        logevent("We believe remote version has outdated SSH-2 GEX");
    }

    if (conf_get_int(ssh->conf, CONF_sshbug_winadj) == FORCE_ON) {
        /*
         * Servers that don't support our winadj request for one
         * reason or another. Currently, none detected automatically.
         */
        ssh->remote_bugs |= BUG_CHOKES_ON_WINADJ;
        logevent("We believe remote version has winadj bug");
    }

    if (conf_get_int(ssh->conf, CONF_sshbug_chanreq) == FORCE_ON ||
        (conf_get_int(ssh->conf, CONF_sshbug_chanreq) == AUTO &&
         (wc_match("OpenSSH_[2-5].*", imp) ||
          wc_match("OpenSSH_6.[0-6]*", imp) ||
          wc_match("dropbear_0.[2-4][0-9]*", imp) ||
          wc_match("dropbear_0.5[01]*", imp)))) {
        /*
         * These versions have the SSH-2 channel request bug.
         * OpenSSH 6.7 and above do not:
         * https://bugzilla.mindrot.org/show_bug.cgi?id=1818
         * dropbear_0.52 and above do not:
         * https://secure.ucc.asn.au/hg/dropbear/rev/cd02449b709c
         */
        ssh->remote_bugs |= BUG_SENDS_LATE_REQUEST_REPLY;
        logevent("We believe remote version has SSH-2 channel request bug");
    }
}

/*
 * The `software version' part of an SSH version string is required
 * to contain no spaces or minus signs.
 */
static void ssh_fix_verstring(char *str)
{
    /* Eat "<protoversion>-". */
    while (*str && *str != '-') str++;
    assert(*str == '-'); str++;

    /* Convert minus signs and spaces in the remaining string into
     * underscores. */
    while (*str) {
        if (*str == '-' || *str == ' ')
            *str = '_';
        str++;
    }
}

/*
 * Send an appropriate SSH version string.
 */
static void ssh_send_verstring(Ssh ssh, const char *protoname, char *svers)
{
    char *verstring;

    if (ssh->version == 2) {
        /*
         * Construct a v2 version string.
         */
        verstring = dupprintf("%s2.0-%s\015\012", protoname, sshver);
    } else {
        /*
         * Construct a v1 version string.
         */
        assert(!strcmp(protoname, "SSH-")); /* no v1 bare connection protocol */
        verstring = dupprintf("SSH-%s-%s\012",
                              (ssh_versioncmp(svers, "1.5") <= 0 ?
                               svers : "1.5"),
                              sshver);
    }

    ssh_fix_verstring(verstring + strlen(protoname));
#ifdef FUZZING
    /* FUZZING make PuTTY insecure, so make live use difficult. */
    verstring[0] = 'I';
#endif

    if (ssh->version == 2) {
        size_t len;
        /*
         * Record our version string.
         */
        len = strcspn(verstring, "\015\012");
        ssh->v_c = snewn(len + 1, char);
        memcpy(ssh->v_c, verstring, len);
        ssh->v_c[len] = 0;
    }

    logeventf(ssh, "We claim version: %.*s",
              strcspn(verstring, "\015\012"), verstring);
    s_write(ssh, verstring, strlen(verstring));
    sfree(verstring);
}

static int do_ssh_init(Ssh ssh, unsigned char c)
{
    static const char protoname[] = "SSH-";

    struct do_ssh_init_state {
        int crLine;
        int vslen;
        char version[10];
        char *vstring;
        int vstrsize;
        int i;
        int proto1, proto2;
    };
    crState(do_ssh_init_state);
    
    crBeginState;

    /* Search for a line beginning with the protocol name prefix in
     * the input. */
    for (;;) {
        for (s->i = 0; protoname[s->i]; s->i++) {
            if ((char)c != protoname[s->i]) goto no;
            crReturn(1);
        }
        break;
      no:
        while (c != '\012')
            crReturn(1);
        crReturn(1);
    }

    ssh->session_started = TRUE;

    s->vstrsize = sizeof(protoname) + 16;
    s->vstring = snewn(s->vstrsize, char);
    strcpy(s->vstring, protoname);
    s->vslen = strlen(protoname);
    s->i = 0;
    while (1) {
        if (s->vslen >= s->vstrsize - 1) {
            s->vstrsize += 16;
            s->vstring = sresize(s->vstring, s->vstrsize, char);
        }
        s->vstring[s->vslen++] = c;
        if (s->i >= 0) {
            if (c == '-') {
                s->version[s->i] = '\0';
                s->i = -1;
            } else if (s->i < sizeof(s->version) - 1)
                s->version[s->i++] = c;
        } else if (c == '\012')
            break;
        crReturn(1);                   /* get another char */
    }

    ssh->agentfwd_enabled = FALSE;
    ssh->rdpkt2_state.incoming_sequence = 0;

    s->vstring[s->vslen] = 0;
    s->vstring[strcspn(s->vstring, "\015\012")] = '\0';/* remove EOL chars */
    logeventf(ssh, "Server version: %s", s->vstring);
    ssh_detect_bugs(ssh, s->vstring);

    /*
     * Decide which SSH protocol version to support.
     */

    /* Anything strictly below "2.0" means protocol 1 is supported. */
    s->proto1 = ssh_versioncmp(s->version, "2.0") < 0;
    /* Anything greater or equal to "1.99" means protocol 2 is supported. */
    s->proto2 = ssh_versioncmp(s->version, "1.99") >= 0;

    if (conf_get_int(ssh->conf, CONF_sshprot) == 0) {
        if (!s->proto1) {
            bombout(("SSH protocol version 1 required by our configuration "
                     "but not provided by server"));
            crStop(0);
        }
    } else if (conf_get_int(ssh->conf, CONF_sshprot) == 3) {
        if (!s->proto2) {
            bombout(("SSH protocol version 2 required by our configuration "
                     "but server only provides (old, insecure) SSH-1"));
            crStop(0);
        }
    } else {
        /* No longer support values 1 or 2 for CONF_sshprot */
        assert(!"Unexpected value for CONF_sshprot");
    }

    if (s->proto2 && (conf_get_int(ssh->conf, CONF_sshprot) >= 2 || !s->proto1))
        ssh->version = 2;
    else
        ssh->version = 1;

    logeventf(ssh, "Using SSH protocol version %d", ssh->version);

    /* Send the version string, if we haven't already */
    if (conf_get_int(ssh->conf, CONF_sshprot) != 3)
        ssh_send_verstring(ssh, protoname, s->version);

    if (ssh->version == 2) {
        size_t len;
        /*
         * Record their version string.
         */
        len = strcspn(s->vstring, "\015\012");
        ssh->v_s = snewn(len + 1, char);
        memcpy(ssh->v_s, s->vstring, len);
        ssh->v_s[len] = 0;
            
        /*
         * Initialise SSH-2 protocol.
         */
        ssh->protocol = ssh2_protocol;
        ssh2_protocol_setup(ssh);
        ssh->s_rdpkt = ssh2_rdpkt;
    } else {
        /*
         * Initialise SSH-1 protocol.
         */
        ssh->protocol = ssh1_protocol;
        ssh1_protocol_setup(ssh);
        ssh->s_rdpkt = ssh1_rdpkt;
    }
    if (ssh->version == 2)
        do_ssh2_transport(ssh, NULL, -1, NULL);

    update_specials_menu(ssh->frontend);
    ssh->state = SSH_STATE_BEFORE_SIZE;
    ssh->pinger = pinger_new(ssh->conf, &ssh_backend, ssh);

    sfree(s->vstring);

    crFinish(0);
}

static int do_ssh_connection_init(Ssh ssh, unsigned char c)
{
    /*
     * Ordinary SSH begins with the banner "SSH-x.y-...". This is just
     * the ssh-connection part, extracted and given a trivial binary
     * packet protocol, so we replace 'SSH-' at the start with a new
     * name. In proper SSH style (though of course this part of the
     * proper SSH protocol _isn't_ subject to this kind of
     * DNS-domain-based extension), we define the new name in our
     * extension space.
     */
    static const char protoname[] =
        "SSHCONNECTION@putty.projects.tartarus.org-";

    struct do_ssh_connection_init_state {
        int crLine;
        int vslen;
        char version[10];
        char *vstring;
        int vstrsize;
        int i;
    };
    crState(do_ssh_connection_init_state);
    
    crBeginState;

    /* Search for a line beginning with the protocol name prefix in
     * the input. */
    for (;;) {
        for (s->i = 0; protoname[s->i]; s->i++) {
            if ((char)c != protoname[s->i]) goto no;
            crReturn(1);
        }
        break;
      no:
        while (c != '\012')
            crReturn(1);
        crReturn(1);
    }

    s->vstrsize = sizeof(protoname) + 16;
    s->vstring = snewn(s->vstrsize, char);
    strcpy(s->vstring, protoname);
    s->vslen = strlen(protoname);
    s->i = 0;
    while (1) {
        if (s->vslen >= s->vstrsize - 1) {
            s->vstrsize += 16;
            s->vstring = sresize(s->vstring, s->vstrsize, char);
        }
        s->vstring[s->vslen++] = c;
        if (s->i >= 0) {
            if (c == '-') {
                s->version[s->i] = '\0';
                s->i = -1;
            } else if (s->i < sizeof(s->version) - 1)
                s->version[s->i++] = c;
        } else if (c == '\012')
            break;
        crReturn(1);                   /* get another char */
    }

    ssh->agentfwd_enabled = FALSE;
    ssh->rdpkt2_bare_state.incoming_sequence = 0;

    s->vstring[s->vslen] = 0;
    s->vstring[strcspn(s->vstring, "\015\012")] = '\0';/* remove EOL chars */
    logeventf(ssh, "Server version: %s", s->vstring);
    ssh_detect_bugs(ssh, s->vstring);

    /*
     * Decide which SSH protocol version to support. This is easy in
     * bare ssh-connection mode: only 2.0 is legal.
     */
    if (ssh_versioncmp(s->version, "2.0") < 0) {
        bombout(("Server announces compatibility with SSH-1 in bare ssh-connection protocol"));
        crStop(0);
    }
    if (conf_get_int(ssh->conf, CONF_sshprot) == 0) {
        bombout(("Bare ssh-connection protocol cannot be run in SSH-1-only mode"));
        crStop(0);
    }

    ssh->version = 2;

    logeventf(ssh, "Using bare ssh-connection protocol");

    /* Send the version string, if we haven't already */
    ssh_send_verstring(ssh, protoname, s->version);

    /*
     * Initialise bare connection protocol.
     */
    ssh->protocol = ssh2_bare_connection_protocol;
    ssh2_bare_connection_protocol_setup(ssh);
    ssh->s_rdpkt = ssh2_bare_connection_rdpkt;

    update_specials_menu(ssh->frontend);
    ssh->state = SSH_STATE_BEFORE_SIZE;
    ssh->pinger = pinger_new(ssh->conf, &ssh_backend, ssh);

    /*
     * Get authconn (really just conn) under way.
     */
    do_ssh2_authconn(ssh, NULL, 0, NULL);

    sfree(s->vstring);

    crFinish(0);
}

static void ssh_process_incoming_data(Ssh ssh,
                                      const unsigned char **data, int *datalen)
{
    struct Packet *pktin;

    pktin = ssh->s_rdpkt(ssh, data, datalen);
    if (pktin) {
        ssh->protocol(ssh, NULL, 0, pktin);
        ssh_free_packet(pktin);
    }
}

static void ssh_queue_incoming_data(Ssh ssh,
                                    const unsigned char **data, int *datalen)
{
    bufchain_add(&ssh->queued_incoming_data, *data, *datalen);
    *data += *datalen;
    *datalen = 0;
}

static void ssh_process_queued_incoming_data(Ssh ssh)
{
    void *vdata;
    const unsigned char *data;
    int len, origlen;

    while (!ssh->frozen && bufchain_size(&ssh->queued_incoming_data)) {
        bufchain_prefix(&ssh->queued_incoming_data, &vdata, &len);
        data = vdata;
        origlen = len;

        while (!ssh->frozen && len > 0)
            ssh_process_incoming_data(ssh, &data, &len);

        if (origlen > len)
            bufchain_consume(&ssh->queued_incoming_data, origlen - len);
    }
}

static void ssh_set_frozen(Ssh ssh, int frozen)
{
    if (ssh->s)
        sk_set_frozen(ssh->s, frozen);
    ssh->frozen = frozen;
}

static void ssh_gotdata(Ssh ssh, const unsigned char *data, int datalen)
{
    /* Log raw data, if we're in that mode. */
    if (ssh->logctx)
        log_packet(ssh->logctx, PKT_INCOMING, -1, NULL, data, datalen,
                   0, NULL, NULL, 0, NULL);

    crBegin(ssh->ssh_gotdata_crstate);

    /*
     * To begin with, feed the characters one by one to the
     * protocol initialisation / selection function do_ssh_init().
     * When that returns 0, we're done with the initial greeting
     * exchange and can move on to packet discipline.
     */
    while (1) {
        int ret;                       /* need not be kept across crReturn */
        if (datalen == 0)
            crReturnV;                 /* more data please */
        ret = ssh->do_ssh_init(ssh, *data);
        data++;
        datalen--;
        if (ret == 0)
            break;
    }

    /*
     * We emerge from that loop when the initial negotiation is
     * over and we have selected an s_rdpkt function. Now pass
     * everything to s_rdpkt, and then pass the resulting packets
     * to the proper protocol handler.
     */

    while (1) {
        while (bufchain_size(&ssh->queued_incoming_data) > 0 || datalen > 0) {
            if (ssh->frozen) {
                ssh_queue_incoming_data(ssh, &data, &datalen);
                /* This uses up all data and cannot cause anything interesting
                 * to happen; indeed, for anything to happen at all, we must
                 * return, so break out. */
                break;
            } else if (bufchain_size(&ssh->queued_incoming_data) > 0) {
                /* This uses up some or all data, and may freeze the
                 * session. */
                ssh_process_queued_incoming_data(ssh);
            } else {
                /* This uses up some or all data, and may freeze the
                 * session. */
                ssh_process_incoming_data(ssh, &data, &datalen);
            }
            /* FIXME this is probably EBW. */
            if (ssh->state == SSH_STATE_CLOSED)
                return;
        }
        /* We're out of data. Go and get some more. */
        crReturnV;
    }
    crFinishV;
}

static int ssh_do_close(Ssh ssh, int notify_exit)
{
    int ret = 0;
    struct ssh_channel *c;

    ssh->state = SSH_STATE_CLOSED;
    expire_timer_context(ssh);
    if (ssh->s) {
        sk_close(ssh->s);
        ssh->s = NULL;
        if (notify_exit)
            notify_remote_exit(ssh->frontend);
        else
            ret = 1;
    }
    /*
     * Now we must shut down any port- and X-forwarded channels going
     * through this connection.
     */
    if (ssh->channels) {
        while (NULL != (c = index234(ssh->channels, 0))) {
            switch (c->type) {
              case CHAN_X11:
                x11_close(c->u.x11.xconn);
                break;
              case CHAN_SOCKDATA:
              case CHAN_SOCKDATA_DORMANT:
                pfd_close(c->u.pfd.pf);
                break;
            }
            del234(ssh->channels, c); /* moving next one to index 0 */
            if (ssh->version == 2)
                bufchain_clear(&c->v.v2.outbuffer);
            sfree(c);
        }
    }
    /*
     * Go through port-forwardings, and close any associated
     * listening sockets.
     */
    if (ssh->portfwds) {
        struct ssh_portfwd *pf;
        while (NULL != (pf = index234(ssh->portfwds, 0))) {
            /* Dispose of any listening socket. */
            if (pf->local)
                pfl_terminate(pf->local);
            del234(ssh->portfwds, pf); /* moving next one to index 0 */
            free_portfwd(pf);
        }
        freetree234(ssh->portfwds);
        ssh->portfwds = NULL;
    }

    /*
     * Also stop attempting to connection-share.
     */
    if (ssh->connshare) {
        sharestate_free(ssh->connshare);
        ssh->connshare = NULL;
    }

    return ret;
}

static void ssh_socket_log(Plug plug, int type, SockAddr addr, int port,
                           const char *error_msg, int error_code)
{
    Ssh ssh = (Ssh) plug;

    /*
     * While we're attempting connection sharing, don't loudly log
     * everything that happens. Real TCP connections need to be logged
     * when we _start_ trying to connect, because it might be ages
     * before they respond if something goes wrong; but connection
     * sharing is local and quick to respond, and it's sufficient to
     * simply wait and see whether it worked afterwards.
     */

    if (!ssh->attempting_connshare)
        backend_socket_log(ssh->frontend, type, addr, port,
                           error_msg, error_code, ssh->conf,
                           ssh->session_started);
}

void ssh_connshare_log(Ssh ssh, int event, const char *logtext,
                       const char *ds_err, const char *us_err)
{
    if (event == SHARE_NONE) {
        /* In this case, 'logtext' is an error message indicating a
         * reason why connection sharing couldn't be set up _at all_.
         * Failing that, ds_err and us_err indicate why we couldn't be
         * a downstream and an upstream respectively. */
        if (logtext) {
            logeventf(ssh, "Could not set up connection sharing: %s", logtext);
        } else {
            if (ds_err)
                logeventf(ssh, "Could not set up connection sharing"
                          " as downstream: %s", ds_err);
            if (us_err)
                logeventf(ssh, "Could not set up connection sharing"
                          " as upstream: %s", us_err);
        }
    } else if (event == SHARE_DOWNSTREAM) {
        /* In this case, 'logtext' is a local endpoint address */
        logeventf(ssh, "Using existing shared connection at %s", logtext);
        /* Also we should mention this in the console window to avoid
         * confusing users as to why this window doesn't behave the
         * usual way. */
        if ((flags & FLAG_VERBOSE) || (flags & FLAG_INTERACTIVE)) {
            c_write_str(ssh,"Reusing a shared connection to this server.\r\n");
        }
    } else if (event == SHARE_UPSTREAM) {
        /* In this case, 'logtext' is a local endpoint address too */
        logeventf(ssh, "Sharing this connection at %s", logtext);
    }
}

static int ssh_closing(Plug plug, const char *error_msg, int error_code,
                       int calling_back)
{
    Ssh ssh = (Ssh) plug;
    int need_notify = ssh_do_close(ssh, FALSE);

    if (!error_msg) {
        if (!ssh->close_expected)
            error_msg = "Server unexpectedly closed network connection";
        else
            error_msg = "Server closed network connection";
    }

    if (ssh->close_expected && ssh->clean_exit && ssh->exitcode < 0)
        ssh->exitcode = 0;

    if (need_notify)
        notify_remote_exit(ssh->frontend);

    if (error_msg)
        logevent(error_msg);
    if (!ssh->close_expected || !ssh->clean_exit)
        connection_fatal(ssh->frontend, "%s", error_msg);
    return 0;
}

static int ssh_receive(Plug plug, int urgent, char *data, int len)
{
    Ssh ssh = (Ssh) plug;
    ssh_gotdata(ssh, (unsigned char *)data, len);
    if (ssh->state == SSH_STATE_CLOSED) {
        ssh_do_close(ssh, TRUE);
        return 0;
    }
    return 1;
}

static void ssh_sent(Plug plug, int bufsize)
{
    Ssh ssh = (Ssh) plug;
    /*
     * If the send backlog on the SSH socket itself clears, we
     * should unthrottle the whole world if it was throttled.
     */
    if (bufsize < SSH_MAX_BACKLOG)
        ssh_throttle_all(ssh, 0, bufsize);
}

static void ssh_hostport_setup(const char *host, int port, Conf *conf,
                               char **savedhost, int *savedport,
                               char **loghost_ret)
{
    char *loghost = conf_get_str(conf, CONF_loghost);
    if (loghost_ret)
        *loghost_ret = loghost;

    if (*loghost) {
        char *tmphost;
        char *colon;

        tmphost = dupstr(loghost);
        *savedport = 22;               /* default ssh port */

        /*
         * A colon suffix on the hostname string also lets us affect
         * savedport. (Unless there are multiple colons, in which case
         * we assume this is an unbracketed IPv6 literal.)
         */
        colon = host_strrchr(tmphost, ':');
        if (colon && colon == host_strchr(tmphost, ':')) {
            *colon++ = '\0';
            if (*colon)
                *savedport = atoi(colon);
        }

        *savedhost = host_strduptrim(tmphost);
        sfree(tmphost);
    } else {
        *savedhost = host_strduptrim(host);
        if (port < 0)
            port = 22;                 /* default ssh port */
        *savedport = port;
    }
}

static int ssh_test_for_upstream(const char *host, int port, Conf *conf)
{
    char *savedhost;
    int savedport;
    int ret;

    random_ref(); /* platform may need this to determine share socket name */
    ssh_hostport_setup(host, port, conf, &savedhost, &savedport, NULL);
    ret = ssh_share_test_for_upstream(savedhost, savedport, conf);
    sfree(savedhost);
    random_unref();

    return ret;
}

/*
 * Connect to specified host and port.
 * Returns an error message, or NULL on success.
 * Also places the canonical host name into `realhost'. It must be
 * freed by the caller.
 */
static const char *connect_to_host(Ssh ssh, const char *host, int port,
                                   char **realhost, int nodelay, int keepalive)
{
    static const struct plug_function_table fn_table = {
        ssh_socket_log,
        ssh_closing,
        ssh_receive,
        ssh_sent,
        NULL
    };

    SockAddr addr;
    const char *err;
    char *loghost;
    int addressfamily, sshprot;

    ssh_hostport_setup(host, port, ssh->conf,
                       &ssh->savedhost, &ssh->savedport, &loghost);

    ssh->fn = &fn_table;               /* make 'ssh' usable as a Plug */

    /*
     * Try connection-sharing, in case that means we don't open a
     * socket after all. ssh_connection_sharing_init will connect to a
     * previously established upstream if it can, and failing that,
     * establish a listening socket for _us_ to be the upstream. In
     * the latter case it will return NULL just as if it had done
     * nothing, because here we only need to care if we're a
     * downstream and need to do our connection setup differently.
     */
    ssh->connshare = NULL;
    ssh->attempting_connshare = TRUE;  /* affects socket logging behaviour */
    ssh->s = ssh_connection_sharing_init(ssh->savedhost, ssh->savedport,
                                         ssh->conf, ssh, &ssh->connshare);
    ssh->attempting_connshare = FALSE;
    if (ssh->s != NULL) {
        /*
         * We are a downstream.
         */
        ssh->bare_connection = TRUE;
        ssh->do_ssh_init = do_ssh_connection_init;
        ssh->fullhostname = NULL;
        *realhost = dupstr(host);      /* best we can do */
    } else {
        /*
         * We're not a downstream, so open a normal socket.
         */
        ssh->do_ssh_init = do_ssh_init;

        /*
         * Try to find host.
         */
        addressfamily = conf_get_int(ssh->conf, CONF_addressfamily);
        addr = name_lookup(host, port, realhost, ssh->conf, addressfamily,
                           ssh->frontend, "SSH connection");
        if ((err = sk_addr_error(addr)) != NULL) {
            sk_addr_free(addr);
            return err;
        }
        ssh->fullhostname = dupstr(*realhost);   /* save in case of GSSAPI */

        ssh->s = new_connection(addr, *realhost, port,
                                0, 1, nodelay, keepalive,
                                (Plug) ssh, ssh->conf);
        if ((err = sk_socket_error(ssh->s)) != NULL) {
            ssh->s = NULL;
            notify_remote_exit(ssh->frontend);
            return err;
        }
    }

    /*
     * The SSH version number is always fixed (since we no longer support
     * fallback between versions), so set it now, and if it's SSH-2,
     * send the version string now too.
     */
    sshprot = conf_get_int(ssh->conf, CONF_sshprot);
    assert(sshprot == 0 || sshprot == 3);
    if (sshprot == 0)
        /* SSH-1 only */
        ssh->version = 1;
    if (sshprot == 3 && !ssh->bare_connection) {
        /* SSH-2 only */
        ssh->version = 2;
        ssh_send_verstring(ssh, "SSH-", NULL);
    }

    /*
     * loghost, if configured, overrides realhost.
     */
    if (*loghost) {
        sfree(*realhost);
        *realhost = dupstr(loghost);
    }

    return NULL;
}

/*
 * Throttle or unthrottle the SSH connection.
 */
static void ssh_throttle_conn(Ssh ssh, int adjust)
{
    int old_count = ssh->conn_throttle_count;
    ssh->conn_throttle_count += adjust;
    assert(ssh->conn_throttle_count >= 0);
    if (ssh->conn_throttle_count && !old_count) {
        ssh_set_frozen(ssh, 1);
    } else if (!ssh->conn_throttle_count && old_count) {
        ssh_set_frozen(ssh, 0);
    }
}

/*
 * Throttle or unthrottle _all_ local data streams (for when sends
 * on the SSH connection itself back up).
 */
static void ssh_throttle_all(Ssh ssh, int enable, int bufsize)
{
    int i;
    struct ssh_channel *c;

    if (enable == ssh->throttled_all)
        return;
    ssh->throttled_all = enable;
    ssh->overall_bufsize = bufsize;
    if (!ssh->channels)
        return;
    for (i = 0; NULL != (c = index234(ssh->channels, i)); i++) {
        switch (c->type) {
          case CHAN_MAINSESSION:
            /*
             * This is treated separately, outside the switch.
             */
            break;
          case CHAN_X11:
            x11_override_throttle(c->u.x11.xconn, enable);
            break;
          case CHAN_AGENT:
            /* Agent channels require no buffer management. */
            break;
          case CHAN_SOCKDATA:
            pfd_override_throttle(c->u.pfd.pf, enable);
            break;
        }
    }
}

static void ssh_agent_callback(void *sshv, void *reply, int replylen)
{
    Ssh ssh = (Ssh) sshv;

    ssh->agent_response = reply;
    ssh->agent_response_len = replylen;

    if (ssh->version == 1)
        do_ssh1_login(ssh, NULL, -1, NULL);
    else
        do_ssh2_authconn(ssh, NULL, -1, NULL);
}

static void ssh_dialog_callback(void *sshv, int ret)
{
    Ssh ssh = (Ssh) sshv;

    ssh->user_response = ret;

    if (ssh->version == 1)
        do_ssh1_login(ssh, NULL, -1, NULL);
    else
        do_ssh2_transport(ssh, NULL, -1, NULL);

    /*
     * This may have unfrozen the SSH connection, so do a
     * queued-data run.
     */
    ssh_process_queued_incoming_data(ssh);
}

static void ssh_agentf_callback(void *cv, void *reply, int replylen)
{
    struct ssh_channel *c = (struct ssh_channel *)cv;
    const void *sentreply = reply;

    c->u.a.outstanding_requests--;
    if (!sentreply) {
        /* Fake SSH_AGENT_FAILURE. */
        sentreply = "\0\0\0\1\5";
        replylen = 5;
    }
    ssh_send_channel_data(c, sentreply, replylen);
    if (reply)
        sfree(reply);
    /*
     * If we've already seen an incoming EOF but haven't sent an
     * outgoing one, this may be the moment to send it.
     */
    if (c->u.a.outstanding_requests == 0 && (c->closes & CLOSES_RCVD_EOF))
        sshfwd_write_eof(c);
}

/*
 * Client-initiated disconnection. Send a DISCONNECT if `wire_reason'
 * non-NULL, otherwise just close the connection. `client_reason' == NULL
 * => log `wire_reason'.
 */
static void ssh_disconnect(Ssh ssh, const char *client_reason,
                           const char *wire_reason,
                           int code, int clean_exit)
{
    char *error;
    if (!client_reason)
        client_reason = wire_reason;
    if (client_reason)
        error = dupprintf("Disconnected: %s", client_reason);
    else
        error = dupstr("Disconnected");
    if (wire_reason) {
        if (ssh->version == 1) {
            send_packet(ssh, SSH1_MSG_DISCONNECT, PKT_STR, wire_reason,
                        PKT_END);
        } else if (ssh->version == 2) {
            struct Packet *pktout = ssh2_pkt_init(SSH2_MSG_DISCONNECT);
            ssh2_pkt_adduint32(pktout, code);
            ssh2_pkt_addstring(pktout, wire_reason);
            ssh2_pkt_addstring(pktout, "en");   /* language tag */
            ssh2_pkt_send_noqueue(ssh, pktout);
        }
    }
    ssh->close_expected = TRUE;
    ssh->clean_exit = clean_exit;
    ssh_closing((Plug)ssh, error, 0, 0);
    sfree(error);
}

int verify_ssh_manual_host_key(Ssh ssh, const char *fingerprint,
                               const struct ssh_signkey *ssh2keytype,
                               void *ssh2keydata)
{
    if (!conf_get_str_nthstrkey(ssh->conf, CONF_ssh_manual_hostkeys, 0)) {
        return -1;                     /* no manual keys configured */
    }

    if (fingerprint) {
        /*
         * The fingerprint string we've been given will have things
         * like 'ssh-rsa 2048' at the front of it. Strip those off and
         * narrow down to just the colon-separated hex block at the
         * end of the string.
         */
        const char *p = strrchr(fingerprint, ' ');
        fingerprint = p ? p+1 : fingerprint;
        /* Quick sanity checks, including making sure it's in lowercase */
        assert(strlen(fingerprint) == 16*3 - 1);
        assert(fingerprint[2] == ':');
        assert(fingerprint[strspn(fingerprint, "0123456789abcdef:")] == 0);

        if (conf_get_str_str_opt(ssh->conf, CONF_ssh_manual_hostkeys,
                                 fingerprint))
            return 1;                  /* success */
    }

    if (ssh2keydata) {
        /*
         * Construct the base64-encoded public key blob and see if
         * that's listed.
         */
        unsigned char *binblob;
        char *base64blob;
        int binlen, atoms, i;
        binblob = ssh2keytype->public_blob(ssh2keydata, &binlen);
        atoms = (binlen + 2) / 3;
        base64blob = snewn(atoms * 4 + 1, char);
        for (i = 0; i < atoms; i++)
            base64_encode_atom(binblob + 3*i, binlen - 3*i, base64blob + 4*i);
        base64blob[atoms * 4] = '\0';
        sfree(binblob);
        if (conf_get_str_str_opt(ssh->conf, CONF_ssh_manual_hostkeys,
                                 base64blob)) {
            sfree(base64blob);
            return 1;                  /* success */
        }
        sfree(base64blob);
    }

    return 0;
}

/*
 * Handle the key exchange and user authentication phases.
 */
static int do_ssh1_login(Ssh ssh, const unsigned char *in, int inlen,
                         struct Packet *pktin)
{
    int i, j, ret;
    unsigned char cookie[8], *ptr;
    struct MD5Context md5c;
    struct do_ssh1_login_state {
        int crLine;
        int len;
        unsigned char *rsabuf;
        const unsigned char *keystr1, *keystr2;
        unsigned long supported_ciphers_mask, supported_auths_mask;
        int tried_publickey, tried_agent;
        int tis_auth_refused, ccard_auth_refused;
        unsigned char session_id[16];
        int cipher_type;
        void *publickey_blob;
        int publickey_bloblen;
        char *publickey_comment;
        int privatekey_available, privatekey_encrypted;
        prompts_t *cur_prompt;
        char c;
        int pwpkt_type;
        unsigned char request[5], *response, *p;
        int responselen;
        int keyi, nkeys;
        int authed;
        struct RSAKey key;
        Bignum challenge;
        char *commentp;
        int commentlen;
        int dlgret;
        Filename *keyfile;
        struct RSAKey servkey, hostkey;
    };
    crState(do_ssh1_login_state);

    crBeginState;

    if (!pktin)
        crWaitUntil(pktin);

    if (pktin->type != SSH1_SMSG_PUBLIC_KEY) {
        bombout(("Public key packet not received"));
        crStop(0);
    }

    logevent("Received public keys");

    ptr = ssh_pkt_getdata(pktin, 8);
    if (!ptr) {
        bombout(("SSH-1 public key packet stopped before random cookie"));
        crStop(0);
    }
    memcpy(cookie, ptr, 8);

    if (!ssh1_pkt_getrsakey(pktin, &s->servkey, &s->keystr1) ||
        !ssh1_pkt_getrsakey(pktin, &s->hostkey, &s->keystr2)) { 
        bombout(("Failed to read SSH-1 public keys from public key packet"));
        crStop(0);
    }

    /*
     * Log the host key fingerprint.
     */
    {
        char logmsg[80];
        logevent("Host key fingerprint is:");
        strcpy(logmsg, "      ");
        s->hostkey.comment = NULL;
        rsa_fingerprint(logmsg + strlen(logmsg),
                        sizeof(logmsg) - strlen(logmsg), &s->hostkey);
        logevent(logmsg);
    }

    ssh->v1_remote_protoflags = ssh_pkt_getuint32(pktin);
    s->supported_ciphers_mask = ssh_pkt_getuint32(pktin);
    s->supported_auths_mask = ssh_pkt_getuint32(pktin);
    if ((ssh->remote_bugs & BUG_CHOKES_ON_RSA))
        s->supported_auths_mask &= ~(1 << SSH1_AUTH_RSA);

    ssh->v1_local_protoflags =
        ssh->v1_remote_protoflags & SSH1_PROTOFLAGS_SUPPORTED;
    ssh->v1_local_protoflags |= SSH1_PROTOFLAG_SCREEN_NUMBER;

    MD5Init(&md5c);
    MD5Update(&md5c, s->keystr2, s->hostkey.bytes);
    MD5Update(&md5c, s->keystr1, s->servkey.bytes);
    MD5Update(&md5c, cookie, 8);
    MD5Final(s->session_id, &md5c);

    for (i = 0; i < 32; i++)
        ssh->session_key[i] = random_byte();

    /*
     * Verify that the `bits' and `bytes' parameters match.
     */
    if (s->hostkey.bits > s->hostkey.bytes * 8 ||
        s->servkey.bits > s->servkey.bytes * 8) {
        bombout(("SSH-1 public keys were badly formatted"));
        crStop(0);
    }

    s->len = (s->hostkey.bytes > s->servkey.bytes ?
              s->hostkey.bytes : s->servkey.bytes);

    s->rsabuf = snewn(s->len, unsigned char);

    /*
     * Verify the host key.
     */
    {
        /*
         * First format the key into a string.
         */
        int len = rsastr_len(&s->hostkey);
        char fingerprint[100];
        char *keystr = snewn(len, char);
        rsastr_fmt(keystr, &s->hostkey);
        rsa_fingerprint(fingerprint, sizeof(fingerprint), &s->hostkey);

        /* First check against manually configured host keys. */
        s->dlgret = verify_ssh_manual_host_key(ssh, fingerprint, NULL, NULL);
        if (s->dlgret == 0) {          /* did not match */
            bombout(("Host key did not appear in manually configured list"));
            sfree(keystr);
            crStop(0);
        } else if (s->dlgret < 0) { /* none configured; use standard handling */
            ssh_set_frozen(ssh, 1);
            s->dlgret = verify_ssh_host_key(ssh->frontend,
                                            ssh->savedhost, ssh->savedport,
                                            "rsa", keystr, fingerprint,
                                            ssh_dialog_callback, ssh);
            sfree(keystr);
#ifdef FUZZING
            s->dlgret = 1;
#endif
            if (s->dlgret < 0) {
                do {
                    crReturn(0);
                    if (pktin) {
                        bombout(("Unexpected data from server while waiting"
                                 " for user host key response"));
                        crStop(0);
                    }
                } while (pktin || inlen > 0);
                s->dlgret = ssh->user_response;
            }
            ssh_set_frozen(ssh, 0);

            if (s->dlgret == 0) {
                ssh_disconnect(ssh, "User aborted at host key verification",
                               NULL, 0, TRUE);
                crStop(0);
            }
        } else {
            sfree(keystr);
        }
    }

    for (i = 0; i < 32; i++) {
        s->rsabuf[i] = ssh->session_key[i];
        if (i < 16)
            s->rsabuf[i] ^= s->session_id[i];
    }

    if (s->hostkey.bytes > s->servkey.bytes) {
        ret = rsaencrypt(s->rsabuf, 32, &s->servkey);
        if (ret)
            ret = rsaencrypt(s->rsabuf, s->servkey.bytes, &s->hostkey);
    } else {
        ret = rsaencrypt(s->rsabuf, 32, &s->hostkey);
        if (ret)
            ret = rsaencrypt(s->rsabuf, s->hostkey.bytes, &s->servkey);
    }
    if (!ret) {
        bombout(("SSH-1 public key encryptions failed due to bad formatting"));
        crStop(0);      
    }

    logevent("Encrypted session key");

    {
        int cipher_chosen = 0, warn = 0;
        const char *cipher_string = NULL;
        int i;
        for (i = 0; !cipher_chosen && i < CIPHER_MAX; i++) {
            int next_cipher = conf_get_int_int(ssh->conf,
                                               CONF_ssh_cipherlist, i);
            if (next_cipher == CIPHER_WARN) {
                /* If/when we choose a cipher, warn about it */
                warn = 1;
            } else if (next_cipher == CIPHER_AES) {
                /* XXX Probably don't need to mention this. */
                logevent("AES not supported in SSH-1, skipping");
            } else {
                switch (next_cipher) {
                  case CIPHER_3DES:     s->cipher_type = SSH_CIPHER_3DES;
                                        cipher_string = "3DES"; break;
                  case CIPHER_BLOWFISH: s->cipher_type = SSH_CIPHER_BLOWFISH;
                                        cipher_string = "Blowfish"; break;
                  case CIPHER_DES:      s->cipher_type = SSH_CIPHER_DES;
                                        cipher_string = "single-DES"; break;
                }
                if (s->supported_ciphers_mask & (1 << s->cipher_type))
                    cipher_chosen = 1;
            }
        }
        if (!cipher_chosen) {
            if ((s->supported_ciphers_mask & (1 << SSH_CIPHER_3DES)) == 0)
                bombout(("Server violates SSH-1 protocol by not "
                         "supporting 3DES encryption"));
            else
                /* shouldn't happen */
                bombout(("No supported ciphers found"));
            crStop(0);
        }

        /* Warn about chosen cipher if necessary. */
        if (warn) {
            ssh_set_frozen(ssh, 1);
            s->dlgret = askalg(ssh->frontend, "cipher", cipher_string,
                               ssh_dialog_callback, ssh);
            if (s->dlgret < 0) {
                do {
                    crReturn(0);
                    if (pktin) {
                        bombout(("Unexpected data from server while waiting"
                                 " for user response"));
                        crStop(0);
                    }
                } while (pktin || inlen > 0);
                s->dlgret = ssh->user_response;
            }
            ssh_set_frozen(ssh, 0);
            if (s->dlgret == 0) {
                ssh_disconnect(ssh, "User aborted at cipher warning", NULL,
                               0, TRUE);
                crStop(0);
            }
        }
    }

    switch (s->cipher_type) {
      case SSH_CIPHER_3DES:
        logevent("Using 3DES encryption");
        break;
      case SSH_CIPHER_DES:
        logevent("Using single-DES encryption");
        break;
      case SSH_CIPHER_BLOWFISH:
        logevent("Using Blowfish encryption");
        break;
    }

    send_packet(ssh, SSH1_CMSG_SESSION_KEY,
                PKT_CHAR, s->cipher_type,
                PKT_DATA, cookie, 8,
                PKT_CHAR, (s->len * 8) >> 8, PKT_CHAR, (s->len * 8) & 0xFF,
                PKT_DATA, s->rsabuf, s->len,
                PKT_INT, ssh->v1_local_protoflags, PKT_END);

    logevent("Trying to enable encryption...");

    sfree(s->rsabuf);

    ssh->cipher = (s->cipher_type == SSH_CIPHER_BLOWFISH ? &ssh_blowfish_ssh1 :
                   s->cipher_type == SSH_CIPHER_DES ? &ssh_des :
                   &ssh_3des);
    ssh->v1_cipher_ctx = ssh->cipher->make_context();
    ssh->cipher->sesskey(ssh->v1_cipher_ctx, ssh->session_key);
    logeventf(ssh, "Initialised %s encryption", ssh->cipher->text_name);

    ssh->crcda_ctx = crcda_make_context();
    logevent("Installing CRC compensation attack detector");

    if (s->servkey.modulus) {
        sfree(s->servkey.modulus);
        s->servkey.modulus = NULL;
    }
    if (s->servkey.exponent) {
        sfree(s->servkey.exponent);
        s->servkey.exponent = NULL;
    }
    if (s->hostkey.modulus) {
        sfree(s->hostkey.modulus);
        s->hostkey.modulus = NULL;
    }
    if (s->hostkey.exponent) {
        sfree(s->hostkey.exponent);
        s->hostkey.exponent = NULL;
    }
    crWaitUntil(pktin);

    if (pktin->type != SSH1_SMSG_SUCCESS) {
        bombout(("Encryption not successfully enabled"));
        crStop(0);
    }

    logevent("Successfully started encryption");

    fflush(stdout); /* FIXME eh? */
    {
        if ((ssh->username = get_remote_username(ssh->conf)) == NULL) {
            int ret; /* need not be kept over crReturn */
            s->cur_prompt = new_prompts(ssh->frontend);
            s->cur_prompt->to_server = TRUE;
            s->cur_prompt->name = dupstr("SSH login name");
            add_prompt(s->cur_prompt, dupstr("login as: "), TRUE);
            ret = get_userpass_input(s->cur_prompt, NULL, 0);
            while (ret < 0) {
                ssh->send_ok = 1;
                crWaitUntil(!pktin);
                ret = get_userpass_input(s->cur_prompt, in, inlen);
                ssh->send_ok = 0;
            }
            if (!ret) {
                /*
                 * Failed to get a username. Terminate.
                 */
                free_prompts(s->cur_prompt);
                ssh_disconnect(ssh, "No username provided", NULL, 0, TRUE);
                crStop(0);
            }
            ssh->username = dupstr(s->cur_prompt->prompts[0]->result);
            free_prompts(s->cur_prompt);
        }

        send_packet(ssh, SSH1_CMSG_USER, PKT_STR, ssh->username, PKT_END);
        {
            char *userlog = dupprintf("Sent username \"%s\"", ssh->username);
            logevent(userlog);
            if (flags & FLAG_INTERACTIVE &&
                (!((flags & FLAG_STDERR) && (flags & FLAG_VERBOSE)))) {
                c_write_str(ssh, userlog);
                c_write_str(ssh, "\r\n");
            }
            sfree(userlog);
        }
    }

    crWaitUntil(pktin);

    if ((s->supported_auths_mask & (1 << SSH1_AUTH_RSA)) == 0) {
        /* We must not attempt PK auth. Pretend we've already tried it. */
        s->tried_publickey = s->tried_agent = 1;
    } else {
        s->tried_publickey = s->tried_agent = 0;
    }
    s->tis_auth_refused = s->ccard_auth_refused = 0;
    /*
     * Load the public half of any configured keyfile for later use.
     */
    s->keyfile = conf_get_filename(ssh->conf, CONF_keyfile);
    if (!filename_is_null(s->keyfile)) {
        int keytype;
        logeventf(ssh, "Reading key file \"%.150s\"",
                  filename_to_str(s->keyfile));
        keytype = key_type(s->keyfile);
        if (keytype == SSH_KEYTYPE_SSH1 ||
            keytype == SSH_KEYTYPE_SSH1_PUBLIC) {
            const char *error;
            if (rsakey_pubblob(s->keyfile,
                               &s->publickey_blob, &s->publickey_bloblen,
                               &s->publickey_comment, &error)) {
                s->privatekey_available = (keytype == SSH_KEYTYPE_SSH1);
                if (!s->privatekey_available)
                    logeventf(ssh, "Key file contains public key only");
                s->privatekey_encrypted = rsakey_encrypted(s->keyfile,
                                                           NULL);
            } else {
                char *msgbuf;
                logeventf(ssh, "Unable to load key (%s)", error);
                msgbuf = dupprintf("Unable to load key file "
                                   "\"%.150s\" (%s)\r\n",
                                   filename_to_str(s->keyfile),
                                   error);
                c_write_str(ssh, msgbuf);
                sfree(msgbuf);
                s->publickey_blob = NULL;
            }
        } else {
            char *msgbuf;
            logeventf(ssh, "Unable to use this key file (%s)",
                      key_type_to_str(keytype));
            msgbuf = dupprintf("Unable to use key file \"%.150s\""
                               " (%s)\r\n",
                               filename_to_str(s->keyfile),
                               key_type_to_str(keytype));
            c_write_str(ssh, msgbuf);
            sfree(msgbuf);
            s->publickey_blob = NULL;
        }
    } else
        s->publickey_blob = NULL;

    while (pktin->type == SSH1_SMSG_FAILURE) {
        s->pwpkt_type = SSH1_CMSG_AUTH_PASSWORD;

        if (conf_get_int(ssh->conf, CONF_tryagent) && agent_exists() && !s->tried_agent) {
            /*
             * Attempt RSA authentication using Pageant.
             */
            void *r;

            s->authed = FALSE;
            s->tried_agent = 1;
            logevent("Pageant is running. Requesting keys.");

            /* Request the keys held by the agent. */
            PUT_32BIT(s->request, 1);
            s->request[4] = SSH1_AGENTC_REQUEST_RSA_IDENTITIES;
            if (!agent_query(s->request, 5, &r, &s->responselen,
                             ssh_agent_callback, ssh)) {
                do {
                    crReturn(0);
                    if (pktin) {
                        bombout(("Unexpected data from server while waiting"
                                 " for agent response"));
                        crStop(0);
                    }
                } while (pktin || inlen > 0);
                r = ssh->agent_response;
                s->responselen = ssh->agent_response_len;
            }
            s->response = (unsigned char *) r;
            if (s->response && s->responselen >= 5 &&
                s->response[4] == SSH1_AGENT_RSA_IDENTITIES_ANSWER) {
                s->p = s->response + 5;
                s->nkeys = toint(GET_32BIT(s->p));
                if (s->nkeys < 0) {
                    logeventf(ssh, "Pageant reported negative key count %d",
                              s->nkeys);
                    s->nkeys = 0;
                }
                s->p += 4;
                logeventf(ssh, "Pageant has %d SSH-1 keys", s->nkeys);
                for (s->keyi = 0; s->keyi < s->nkeys; s->keyi++) {
                    unsigned char *pkblob = s->p;
                    s->p += 4;
                    {
                        int n, ok = FALSE;
                        do {           /* do while (0) to make breaking easy */
                            n = ssh1_read_bignum
                                (s->p, toint(s->responselen-(s->p-s->response)),
                                 &s->key.exponent);
                            if (n < 0)
                                break;
                            s->p += n;
                            n = ssh1_read_bignum
                                (s->p, toint(s->responselen-(s->p-s->response)),
                                 &s->key.modulus);
                            if (n < 0)
                                break;
                            s->p += n;
                            if (s->responselen - (s->p-s->response) < 4)
                                break;
                            s->commentlen = toint(GET_32BIT(s->p));
                            s->p += 4;
                            if (s->commentlen < 0 ||
                                toint(s->responselen - (s->p-s->response)) <
                                s->commentlen)
                                break;
                            s->commentp = (char *)s->p;
                            s->p += s->commentlen;
                            ok = TRUE;
                        } while (0);
                        if (!ok) {
                            logevent("Pageant key list packet was truncated");
                            break;
                        }
                    }
                    if (s->publickey_blob) {
                        if (!memcmp(pkblob, s->publickey_blob,
                                    s->publickey_bloblen)) {
                            logeventf(ssh, "Pageant key #%d matches "
                                      "configured key file", s->keyi);
                            s->tried_publickey = 1;
                        } else
                            /* Skip non-configured key */
                            continue;
                    }
                    logeventf(ssh, "Trying Pageant key #%d", s->keyi);
                    send_packet(ssh, SSH1_CMSG_AUTH_RSA,
                                PKT_BIGNUM, s->key.modulus, PKT_END);
                    crWaitUntil(pktin);
                    if (pktin->type != SSH1_SMSG_AUTH_RSA_CHALLENGE) {
                        logevent("Key refused");
                        continue;
                    }
                    logevent("Received RSA challenge");
                    if ((s->challenge = ssh1_pkt_getmp(pktin)) == NULL) {
                        bombout(("Server's RSA challenge was badly formatted"));
                        crStop(0);
                    }

                    {
                        char *agentreq, *q, *ret;
                        void *vret;
                        int len, retlen;
                        len = 1 + 4;   /* message type, bit count */
                        len += ssh1_bignum_length(s->key.exponent);
                        len += ssh1_bignum_length(s->key.modulus);
                        len += ssh1_bignum_length(s->challenge);
                        len += 16;     /* session id */
                        len += 4;      /* response format */
                        agentreq = snewn(4 + len, char);
                        PUT_32BIT(agentreq, len);
                        q = agentreq + 4;
                        *q++ = SSH1_AGENTC_RSA_CHALLENGE;
                        PUT_32BIT(q, bignum_bitcount(s->key.modulus));
                        q += 4;
                        q += ssh1_write_bignum(q, s->key.exponent);
                        q += ssh1_write_bignum(q, s->key.modulus);
                        q += ssh1_write_bignum(q, s->challenge);
                        memcpy(q, s->session_id, 16);
                        q += 16;
                        PUT_32BIT(q, 1);        /* response format */
                        if (!agent_query(agentreq, len + 4, &vret, &retlen,
                                         ssh_agent_callback, ssh)) {
                            sfree(agentreq);
                            do {
                                crReturn(0);
                                if (pktin) {
                                    bombout(("Unexpected data from server"
                                             " while waiting for agent"
                                             " response"));
                                    crStop(0);
                                }
                            } while (pktin || inlen > 0);
                            vret = ssh->agent_response;
                            retlen = ssh->agent_response_len;
                        } else
                            sfree(agentreq);
                        ret = vret;
                        if (ret) {
                            if (ret[4] == SSH1_AGENT_RSA_RESPONSE) {
                                logevent("Sending Pageant's response");
                                send_packet(ssh, SSH1_CMSG_AUTH_RSA_RESPONSE,
                                            PKT_DATA, ret + 5, 16,
                                            PKT_END);
                                sfree(ret);
                                crWaitUntil(pktin);
                                if (pktin->type == SSH1_SMSG_SUCCESS) {
                                    logevent
                                        ("Pageant's response accepted");
                                    if (flags & FLAG_VERBOSE) {
                                        c_write_str(ssh, "Authenticated using"
                                                    " RSA key \"");
                                        c_write(ssh, s->commentp,
                                                s->commentlen);
                                        c_write_str(ssh, "\" from agent\r\n");
                                    }
                                    s->authed = TRUE;
                                } else
                                    logevent
                                        ("Pageant's response not accepted");
                            } else {
                                logevent
                                    ("Pageant failed to answer challenge");
                                sfree(ret);
                            }
                        } else {
                            logevent("No reply received from Pageant");
                        }
                    }
                    freebn(s->key.exponent);
                    freebn(s->key.modulus);
                    freebn(s->challenge);
                    if (s->authed)
                        break;
                }
                sfree(s->response);
                if (s->publickey_blob && !s->tried_publickey)
                    logevent("Configured key file not in Pageant");
            } else {
                logevent("Failed to get reply from Pageant");
            }
            if (s->authed)
                break;
        }
        if (s->publickey_blob && s->privatekey_available &&
            !s->tried_publickey) {
            /*
             * Try public key authentication with the specified
             * key file.
             */
            int got_passphrase; /* need not be kept over crReturn */
            if (flags & FLAG_VERBOSE)
                c_write_str(ssh, "Trying public key authentication.\r\n");
            s->keyfile = conf_get_filename(ssh->conf, CONF_keyfile);
            logeventf(ssh, "Trying public key \"%s\"",
                      filename_to_str(s->keyfile));
            s->tried_publickey = 1;
            got_passphrase = FALSE;
            while (!got_passphrase) {
                /*
                 * Get a passphrase, if necessary.
                 */
                char *passphrase = NULL;    /* only written after crReturn */
                const char *error;
                if (!s->privatekey_encrypted) {
                    if (flags & FLAG_VERBOSE)
                        c_write_str(ssh, "No passphrase required.\r\n");
                    passphrase = NULL;
                } else {
                    int ret; /* need not be kept over crReturn */
                    s->cur_prompt = new_prompts(ssh->frontend);
                    s->cur_prompt->to_server = FALSE;
                    s->cur_prompt->name = dupstr("SSH key passphrase");
                    add_prompt(s->cur_prompt,
                               dupprintf("Passphrase for key \"%.100s\": ",
                                         s->publickey_comment), FALSE);
                    ret = get_userpass_input(s->cur_prompt, NULL, 0);
                    while (ret < 0) {
                        ssh->send_ok = 1;
                        crWaitUntil(!pktin);
                        ret = get_userpass_input(s->cur_prompt, in, inlen);
                        ssh->send_ok = 0;
                    }
                    if (!ret) {
                        /* Failed to get a passphrase. Terminate. */
                        free_prompts(s->cur_prompt);
                        ssh_disconnect(ssh, NULL, "Unable to authenticate",
                                       0, TRUE);
                        crStop(0);
                    }
                    passphrase = dupstr(s->cur_prompt->prompts[0]->result);
                    free_prompts(s->cur_prompt);
                }
                /*
                 * Try decrypting key with passphrase.
                 */
                s->keyfile = conf_get_filename(ssh->conf, CONF_keyfile);
                ret = loadrsakey(s->keyfile, &s->key, passphrase,
                                 &error);
                if (passphrase) {
                    smemclr(passphrase, strlen(passphrase));
                    sfree(passphrase);
                }
                if (ret == 1) {
                    /* Correct passphrase. */
                    got_passphrase = TRUE;
                } else if (ret == 0) {
                    c_write_str(ssh, "Couldn't load private key from ");
                    c_write_str(ssh, filename_to_str(s->keyfile));
                    c_write_str(ssh, " (");
                    c_write_str(ssh, error);
                    c_write_str(ssh, ").\r\n");
                    got_passphrase = FALSE;
                    break;             /* go and try something else */
                } else if (ret == -1) {
                    c_write_str(ssh, "Wrong passphrase.\r\n"); /* FIXME */
                    got_passphrase = FALSE;
                    /* and try again */
                } else {
                    assert(0 && "unexpected return from loadrsakey()");
                    got_passphrase = FALSE;   /* placate optimisers */
                }
            }

            if (got_passphrase) {

                /*
                 * Send a public key attempt.
                 */
                send_packet(ssh, SSH1_CMSG_AUTH_RSA,
                            PKT_BIGNUM, s->key.modulus, PKT_END);

                crWaitUntil(pktin);
                if (pktin->type == SSH1_SMSG_FAILURE) {
                    c_write_str(ssh, "Server refused our public key.\r\n");
                    continue;          /* go and try something else */
                }
                if (pktin->type != SSH1_SMSG_AUTH_RSA_CHALLENGE) {
                    bombout(("Bizarre response to offer of public key"));
                    crStop(0);
                }

                {
                    int i;
                    unsigned char buffer[32];
                    Bignum challenge, response;

                    if ((challenge = ssh1_pkt_getmp(pktin)) == NULL) {
                        bombout(("Server's RSA challenge was badly formatted"));
                        crStop(0);
                    }
                    response = rsadecrypt(challenge, &s->key);
                    freebn(s->key.private_exponent);/* burn the evidence */

                    for (i = 0; i < 32; i++) {
                        buffer[i] = bignum_byte(response, 31 - i);
                    }

                    MD5Init(&md5c);
                    MD5Update(&md5c, buffer, 32);
                    MD5Update(&md5c, s->session_id, 16);
                    MD5Final(buffer, &md5c);

                    send_packet(ssh, SSH1_CMSG_AUTH_RSA_RESPONSE,
                                PKT_DATA, buffer, 16, PKT_END);

                    freebn(challenge);
                    freebn(response);
                }

                crWaitUntil(pktin);
                if (pktin->type == SSH1_SMSG_FAILURE) {
                    if (flags & FLAG_VERBOSE)
                        c_write_str(ssh, "Failed to authenticate with"
                                    " our public key.\r\n");
                    continue;          /* go and try something else */
                } else if (pktin->type != SSH1_SMSG_SUCCESS) {
                    bombout(("Bizarre response to RSA authentication response"));
                    crStop(0);
                }

                break;                 /* we're through! */
            }

        }

        /*
         * Otherwise, try various forms of password-like authentication.
         */
        s->cur_prompt = new_prompts(ssh->frontend);

        if (conf_get_int(ssh->conf, CONF_try_tis_auth) &&
            (s->supported_auths_mask & (1 << SSH1_AUTH_TIS)) &&
            !s->tis_auth_refused) {
            s->pwpkt_type = SSH1_CMSG_AUTH_TIS_RESPONSE;
            logevent("Requested TIS authentication");
            send_packet(ssh, SSH1_CMSG_AUTH_TIS, PKT_END);
            crWaitUntil(pktin);
            if (pktin->type != SSH1_SMSG_AUTH_TIS_CHALLENGE) {
                logevent("TIS authentication declined");
                if (flags & FLAG_INTERACTIVE)
                    c_write_str(ssh, "TIS authentication refused.\r\n");
                s->tis_auth_refused = 1;
                continue;
            } else {
                char *challenge;
                int challengelen;
                char *instr_suf, *prompt;

                ssh_pkt_getstring(pktin, &challenge, &challengelen);
                if (!challenge) {
                    bombout(("TIS challenge packet was badly formed"));
                    crStop(0);
                }
                logevent("Received TIS challenge");
                s->cur_prompt->to_server = TRUE;
                s->cur_prompt->name = dupstr("SSH TIS authentication");
                /* Prompt heuristic comes from OpenSSH */
                if (memchr(challenge, '\n', challengelen)) {
                    instr_suf = dupstr("");
                    prompt = dupprintf("%.*s", challengelen, challenge);
                } else {
                    instr_suf = dupprintf("%.*s", challengelen, challenge);
                    prompt = dupstr("Response: ");
                }
                s->cur_prompt->instruction =
                    dupprintf("Using TIS authentication.%s%s",
                              (*instr_suf) ? "\n" : "",
                              instr_suf);
                s->cur_prompt->instr_reqd = TRUE;
                add_prompt(s->cur_prompt, prompt, FALSE);
                sfree(instr_suf);
            }
        }
        if (conf_get_int(ssh->conf, CONF_try_tis_auth) &&
            (s->supported_auths_mask & (1 << SSH1_AUTH_CCARD)) &&
            !s->ccard_auth_refused) {
            s->pwpkt_type = SSH1_CMSG_AUTH_CCARD_RESPONSE;
            logevent("Requested CryptoCard authentication");
            send_packet(ssh, SSH1_CMSG_AUTH_CCARD, PKT_END);
            crWaitUntil(pktin);
            if (pktin->type != SSH1_SMSG_AUTH_CCARD_CHALLENGE) {
                logevent("CryptoCard authentication declined");
                c_write_str(ssh, "CryptoCard authentication refused.\r\n");
                s->ccard_auth_refused = 1;
                continue;
            } else {
                char *challenge;
                int challengelen;
                char *instr_suf, *prompt;

                ssh_pkt_getstring(pktin, &challenge, &challengelen);
                if (!challenge) {
                    bombout(("CryptoCard challenge packet was badly formed"));
                    crStop(0);
                }
                logevent("Received CryptoCard challenge");
                s->cur_prompt->to_server = TRUE;
                s->cur_prompt->name = dupstr("SSH CryptoCard authentication");
                s->cur_prompt->name_reqd = FALSE;
                /* Prompt heuristic comes from OpenSSH */
                if (memchr(challenge, '\n', challengelen)) {
                    instr_suf = dupstr("");
                    prompt = dupprintf("%.*s", challengelen, challenge);
                } else {
                    instr_suf = dupprintf("%.*s", challengelen, challenge);
                    prompt = dupstr("Response: ");
                }
                s->cur_prompt->instruction =
                    dupprintf("Using CryptoCard authentication.%s%s",
                              (*instr_suf) ? "\n" : "",
                              instr_suf);
                s->cur_prompt->instr_reqd = TRUE;
                add_prompt(s->cur_prompt, prompt, FALSE);
                sfree(instr_suf);
            }
        }
        if (s->pwpkt_type == SSH1_CMSG_AUTH_PASSWORD) {
            if ((s->supported_auths_mask & (1 << SSH1_AUTH_PASSWORD)) == 0) {
                bombout(("No supported authentication methods available"));
                crStop(0);
            }
            s->cur_prompt->to_server = TRUE;
            s->cur_prompt->name = dupstr("SSH password");
            add_prompt(s->cur_prompt, dupprintf("%s@%s's password: ",
                                                ssh->username, ssh->savedhost),
                       FALSE);
        }

        /*
         * Show password prompt, having first obtained it via a TIS
         * or CryptoCard exchange if we're doing TIS or CryptoCard
         * authentication.
         */
        {
            int ret; /* need not be kept over crReturn */
            ret = get_userpass_input(s->cur_prompt, NULL, 0);
            while (ret < 0) {
                ssh->send_ok = 1;
                crWaitUntil(!pktin);
                ret = get_userpass_input(s->cur_prompt, in, inlen);
                ssh->send_ok = 0;
            }
            if (!ret) {
                /*
                 * Failed to get a password (for example
                 * because one was supplied on the command line
                 * which has already failed to work). Terminate.
                 */
                free_prompts(s->cur_prompt);
                ssh_disconnect(ssh, NULL, "Unable to authenticate", 0, TRUE);
                crStop(0);
            }
        }

        if (s->pwpkt_type == SSH1_CMSG_AUTH_PASSWORD) {
            /*
             * Defence against traffic analysis: we send a
             * whole bunch of packets containing strings of
             * different lengths. One of these strings is the
             * password, in a SSH1_CMSG_AUTH_PASSWORD packet.
             * The others are all random data in
             * SSH1_MSG_IGNORE packets. This way a passive
             * listener can't tell which is the password, and
             * hence can't deduce the password length.
             * 
             * Anybody with a password length greater than 16
             * bytes is going to have enough entropy in their
             * password that a listener won't find it _that_
             * much help to know how long it is. So what we'll
             * do is:
             * 
             *  - if password length < 16, we send 15 packets
             *    containing string lengths 1 through 15
             * 
             *  - otherwise, we let N be the nearest multiple
             *    of 8 below the password length, and send 8
             *    packets containing string lengths N through
             *    N+7. This won't obscure the order of
             *    magnitude of the password length, but it will
             *    introduce a bit of extra uncertainty.
             * 
             * A few servers can't deal with SSH1_MSG_IGNORE, at
             * least in this context. For these servers, we need
             * an alternative defence. We make use of the fact
             * that the password is interpreted as a C string:
             * so we can append a NUL, then some random data.
             * 
             * A few servers can deal with neither SSH1_MSG_IGNORE
             * here _nor_ a padded password string.
             * For these servers we are left with no defences
             * against password length sniffing.
             */
            if (!(ssh->remote_bugs & BUG_CHOKES_ON_SSH1_IGNORE) &&
                !(ssh->remote_bugs & BUG_NEEDS_SSH1_PLAIN_PASSWORD)) {
                /*
                 * The server can deal with SSH1_MSG_IGNORE, so
                 * we can use the primary defence.
                 */
                int bottom, top, pwlen, i;
                char *randomstr;

                pwlen = strlen(s->cur_prompt->prompts[0]->result);
                if (pwlen < 16) {
                    bottom = 0;    /* zero length passwords are OK! :-) */
                    top = 15;
                } else {
                    bottom = pwlen & ~7;
                    top = bottom + 7;
                }

                assert(pwlen >= bottom && pwlen <= top);

                randomstr = snewn(top + 1, char);

                for (i = bottom; i <= top; i++) {
                    if (i == pwlen) {
                        defer_packet(ssh, s->pwpkt_type,
                                     PKT_STR,s->cur_prompt->prompts[0]->result,
                                     PKT_END);
                    } else {
                        for (j = 0; j < i; j++) {
                            do {
                                randomstr[j] = random_byte();
                            } while (randomstr[j] == '\0');
                        }
                        randomstr[i] = '\0';
                        defer_packet(ssh, SSH1_MSG_IGNORE,
                                     PKT_STR, randomstr, PKT_END);
                    }
                }
                logevent("Sending password with camouflage packets");
                ssh_pkt_defersend(ssh);
                sfree(randomstr);
            } 
            else if (!(ssh->remote_bugs & BUG_NEEDS_SSH1_PLAIN_PASSWORD)) {
                /*
                 * The server can't deal with SSH1_MSG_IGNORE
                 * but can deal with padded passwords, so we
                 * can use the secondary defence.
                 */
                char string[64];
                char *ss;
                int len;

                len = strlen(s->cur_prompt->prompts[0]->result);
                if (len < sizeof(string)) {
                    ss = string;
                    strcpy(string, s->cur_prompt->prompts[0]->result);
                    len++;             /* cover the zero byte */
                    while (len < sizeof(string)) {
                        string[len++] = (char) random_byte();
                    }
                } else {
                    ss = s->cur_prompt->prompts[0]->result;
                }
                logevent("Sending length-padded password");
                send_packet(ssh, s->pwpkt_type,
                            PKT_INT, len, PKT_DATA, ss, len,
                            PKT_END);
            } else {
                /*
                 * The server is believed unable to cope with
                 * any of our password camouflage methods.
                 */
                int len;
                len = strlen(s->cur_prompt->prompts[0]->result);
                logevent("Sending unpadded password");
                send_packet(ssh, s->pwpkt_type,
                            PKT_INT, len,
                            PKT_DATA, s->cur_prompt->prompts[0]->result, len,
                            PKT_END);
            }
        } else {
            send_packet(ssh, s->pwpkt_type,
                        PKT_STR, s->cur_prompt->prompts[0]->result,
                        PKT_END);
        }
        logevent("Sent password");
        free_prompts(s->cur_prompt);
        crWaitUntil(pktin);
        if (pktin->type == SSH1_SMSG_FAILURE) {
            if (flags & FLAG_VERBOSE)
                c_write_str(ssh, "Access denied\r\n");
            logevent("Authentication refused");
        } else if (pktin->type != SSH1_SMSG_SUCCESS) {
            bombout(("Strange packet received, type %d", pktin->type));
            crStop(0);
        }
    }

    /* Clear up */
    if (s->publickey_blob) {
        sfree(s->publickey_blob);
        sfree(s->publickey_comment);
    }

    logevent("Authentication successful");

    crFinish(1);
}

static void ssh_channel_try_eof(struct ssh_channel *c)
{
    Ssh ssh = c->ssh;
    assert(c->pending_eof);          /* precondition for calling us */
    if (c->halfopen)
        return;                 /* can't close: not even opened yet */
    if (ssh->version == 2 && bufchain_size(&c->v.v2.outbuffer) > 0)
        return;              /* can't send EOF: pending outgoing data */

    c->pending_eof = FALSE;            /* we're about to send it */
    if (ssh->version == 1) {
        send_packet(ssh, SSH1_MSG_CHANNEL_CLOSE, PKT_INT, c->remoteid,
                    PKT_END);
        c->closes |= CLOSES_SENT_EOF;
    } else {
        struct Packet *pktout;
        pktout = ssh2_pkt_init(SSH2_MSG_CHANNEL_EOF);
        ssh2_pkt_adduint32(pktout, c->remoteid);
        ssh2_pkt_send(ssh, pktout);
        c->closes |= CLOSES_SENT_EOF;
        ssh2_channel_check_close(c);
    }
}

Conf *sshfwd_get_conf(struct ssh_channel *c)
{
    Ssh ssh = c->ssh;
    return ssh->conf;
}

void sshfwd_write_eof(struct ssh_channel *c)
{
    Ssh ssh = c->ssh;

    if (ssh->state == SSH_STATE_CLOSED)
        return;

    if (c->closes & CLOSES_SENT_EOF)
        return;

    c->pending_eof = TRUE;
    ssh_channel_try_eof(c);
}

void sshfwd_unclean_close(struct ssh_channel *c, const char *err)
{
    Ssh ssh = c->ssh;

    if (ssh->state == SSH_STATE_CLOSED)
        return;

    switch (c->type) {
      case CHAN_X11:
        x11_close(c->u.x11.xconn);
        logeventf(ssh, "Forwarded X11 connection terminated due to local "
                  "error: %s", err);
        break;
      case CHAN_SOCKDATA:
      case CHAN_SOCKDATA_DORMANT:
        pfd_close(c->u.pfd.pf);
        logeventf(ssh, "Forwarded port closed due to local error: %s", err);
        break;
    }
    c->type = CHAN_ZOMBIE;
    c->pending_eof = FALSE;   /* this will confuse a zombie channel */

    ssh2_channel_check_close(c);
}

int sshfwd_write(struct ssh_channel *c, char *buf, int len)
{
    Ssh ssh = c->ssh;

    if (ssh->state == SSH_STATE_CLOSED)
        return 0;

    return ssh_send_channel_data(c, buf, len);
}

void sshfwd_unthrottle(struct ssh_channel *c, int bufsize)
{
    Ssh ssh = c->ssh;

    if (ssh->state == SSH_STATE_CLOSED)
        return;

    ssh_channel_unthrottle(c, bufsize);
}

static void ssh_queueing_handler(Ssh ssh, struct Packet *pktin)
{
    struct queued_handler *qh = ssh->qhead;

    assert(qh != NULL);

    assert(pktin->type == qh->msg1 || pktin->type == qh->msg2);

    if (qh->msg1 > 0) {
        assert(ssh->packet_dispatch[qh->msg1] == ssh_queueing_handler);
        ssh->packet_dispatch[qh->msg1] = ssh->q_saved_handler1;
    }
    if (qh->msg2 > 0) {
        assert(ssh->packet_dispatch[qh->msg2] == ssh_queueing_handler);
        ssh->packet_dispatch[qh->msg2] = ssh->q_saved_handler2;
    }

    if (qh->next) {
        ssh->qhead = qh->next;

        if (ssh->qhead->msg1 > 0) {
            ssh->q_saved_handler1 = ssh->packet_dispatch[ssh->qhead->msg1];
            ssh->packet_dispatch[ssh->qhead->msg1] = ssh_queueing_handler;
        }
        if (ssh->qhead->msg2 > 0) {
            ssh->q_saved_handler2 = ssh->packet_dispatch[ssh->qhead->msg2];
            ssh->packet_dispatch[ssh->qhead->msg2] = ssh_queueing_handler;
        }
    } else {
        ssh->qhead = ssh->qtail = NULL;
    }

    qh->handler(ssh, pktin, qh->ctx);

    sfree(qh);
}

static void ssh_queue_handler(Ssh ssh, int msg1, int msg2,
                              chandler_fn_t handler, void *ctx)
{
    struct queued_handler *qh;

    qh = snew(struct queued_handler);
    qh->msg1 = msg1;
    qh->msg2 = msg2;
    qh->handler = handler;
    qh->ctx = ctx;
    qh->next = NULL;

    if (ssh->qtail == NULL) {
        ssh->qhead = qh;

        if (qh->msg1 > 0) {
            ssh->q_saved_handler1 = ssh->packet_dispatch[ssh->qhead->msg1];
            ssh->packet_dispatch[qh->msg1] = ssh_queueing_handler;
        }
        if (qh->msg2 > 0) {
            ssh->q_saved_handler2 = ssh->packet_dispatch[ssh->qhead->msg2];
            ssh->packet_dispatch[qh->msg2] = ssh_queueing_handler;
        }
    } else {
        ssh->qtail->next = qh;
    }
    ssh->qtail = qh;
}

static void ssh_rportfwd_succfail(Ssh ssh, struct Packet *pktin, void *ctx)
{
    struct ssh_rportfwd *rpf, *pf = (struct ssh_rportfwd *)ctx;

    if (pktin->type == (ssh->version == 1 ? SSH1_SMSG_SUCCESS :
                        SSH2_MSG_REQUEST_SUCCESS)) {
        logeventf(ssh, "Remote port forwarding from %s enabled",
                  pf->sportdesc);
    } else {
        logeventf(ssh, "Remote port forwarding from %s refused",
                  pf->sportdesc);

        rpf = del234(ssh->rportfwds, pf);
        assert(rpf == pf);
        pf->pfrec->remote = NULL;
        free_rportfwd(pf);
    }
}

int ssh_alloc_sharing_rportfwd(Ssh ssh, const char *shost, int sport,
                               void *share_ctx)
{
    struct ssh_rportfwd *pf = snew(struct ssh_rportfwd);
    pf->dhost = NULL;
    pf->dport = 0;
    pf->share_ctx = share_ctx;
    pf->shost = dupstr(shost);
    pf->sport = sport;
    pf->sportdesc = NULL;
    if (!ssh->rportfwds) {
        assert(ssh->version == 2);
        ssh->rportfwds = newtree234(ssh_rportcmp_ssh2);
    }
    if (add234(ssh->rportfwds, pf) != pf) {
        sfree(pf->shost);
        sfree(pf);
        return FALSE;
    }
    return TRUE;
}

static void ssh_sharing_global_request_response(Ssh ssh, struct Packet *pktin,
                                                void *ctx)
{
    share_got_pkt_from_server(ctx, pktin->type,
                              pktin->body, pktin->length);
}

void ssh_sharing_queue_global_request(Ssh ssh, void *share_ctx)
{
    ssh_queue_handler(ssh, SSH2_MSG_REQUEST_SUCCESS, SSH2_MSG_REQUEST_FAILURE,
                      ssh_sharing_global_request_response, share_ctx);
}

static void ssh_setup_portfwd(Ssh ssh, Conf *conf)
{
    struct ssh_portfwd *epf;
    int i;
    char *key, *val;

    if (!ssh->portfwds) {
        ssh->portfwds = newtree234(ssh_portcmp);
    } else {
        /*
         * Go through the existing port forwardings and tag them
         * with status==DESTROY. Any that we want to keep will be
         * re-enabled (status==KEEP) as we go through the
         * configuration and find out which bits are the same as
         * they were before.
         */
        struct ssh_portfwd *epf;
        int i;
        for (i = 0; (epf = index234(ssh->portfwds, i)) != NULL; i++)
            epf->status = DESTROY;
    }

    for (val = conf_get_str_strs(conf, CONF_portfwd, NULL, &key);
         val != NULL;
         val = conf_get_str_strs(conf, CONF_portfwd, key, &key)) {
        char *kp, *kp2, *vp, *vp2;
        char address_family, type;
        int sport,dport,sserv,dserv;
        char *sports, *dports, *saddr, *host;

        kp = key;

        address_family = 'A';
        type = 'L';
        if (*kp == 'A' || *kp == '4' || *kp == '6')
            address_family = *kp++;
        if (*kp == 'L' || *kp == 'R')
            type = *kp++;

        if ((kp2 = host_strchr(kp, ':')) != NULL) {
            /*
             * There's a colon in the middle of the source port
             * string, which means that the part before it is
             * actually a source address.
             */
            char *saddr_tmp = dupprintf("%.*s", (int)(kp2 - kp), kp);
            saddr = host_strduptrim(saddr_tmp);
            sfree(saddr_tmp);
            sports = kp2+1;
        } else {
            saddr = NULL;
            sports = kp;
        }
        sport = atoi(sports);
        sserv = 0;
        if (sport == 0) {
            sserv = 1;
            sport = net_service_lookup(sports);
            if (!sport) {
                logeventf(ssh, "Service lookup failed for source"
                          " port \"%s\"", sports);
            }
        }

        if (type == 'L' && !strcmp(val, "D")) {
            /* dynamic forwarding */
            host = NULL;
            dports = NULL;
            dport = -1;
            dserv = 0;
            type = 'D';
        } else {
            /* ordinary forwarding */
            vp = val;
            vp2 = vp + host_strcspn(vp, ":");
            host = dupprintf("%.*s", (int)(vp2 - vp), vp);
            if (*vp2)
                vp2++;
            dports = vp2;
            dport = atoi(dports);
            dserv = 0;
            if (dport == 0) {
                dserv = 1;
                dport = net_service_lookup(dports);
                if (!dport) {
                    logeventf(ssh, "Service lookup failed for destination"
                              " port \"%s\"", dports);
                }
            }
        }

        if (sport && dport) {
            /* Set up a description of the source port. */
            struct ssh_portfwd *pfrec, *epfrec;

            pfrec = snew(struct ssh_portfwd);
            pfrec->type = type;
            pfrec->saddr = saddr;
            pfrec->sserv = sserv ? dupstr(sports) : NULL;
            pfrec->sport = sport;
            pfrec->daddr = host;
            pfrec->dserv = dserv ? dupstr(dports) : NULL;
            pfrec->dport = dport;
            pfrec->local = NULL;
            pfrec->remote = NULL;
            pfrec->addressfamily = (address_family == '4' ? ADDRTYPE_IPV4 :
                                    address_family == '6' ? ADDRTYPE_IPV6 :
                                    ADDRTYPE_UNSPEC);

            epfrec = add234(ssh->portfwds, pfrec);
            if (epfrec != pfrec) {
                if (epfrec->status == DESTROY) {
                    /*
                     * We already have a port forwarding up and running
                     * with precisely these parameters. Hence, no need
                     * to do anything; simply re-tag the existing one
                     * as KEEP.
                     */
                    epfrec->status = KEEP;
                }
                /*
                 * Anything else indicates that there was a duplicate
                 * in our input, which we'll silently ignore.
                 */
                free_portfwd(pfrec);
            } else {
                pfrec->status = CREATE;
            }
        } else {
            sfree(saddr);
            sfree(host);
        }
    }

    /*
     * Now go through and destroy any port forwardings which were
     * not re-enabled.
     */
    for (i = 0; (epf = index234(ssh->portfwds, i)) != NULL; i++)
        if (epf->status == DESTROY) {
            char *message;

            message = dupprintf("%s port forwarding from %s%s%d",
                                epf->type == 'L' ? "local" :
                                epf->type == 'R' ? "remote" : "dynamic",
                                epf->saddr ? epf->saddr : "",
                                epf->saddr ? ":" : "",
                                epf->sport);

            if (epf->type != 'D') {
                char *msg2 = dupprintf("%s to %s:%d", message,
                                       epf->daddr, epf->dport);
                sfree(message);
                message = msg2;
            }

            logeventf(ssh, "Cancelling %s", message);
            sfree(message);

            /* epf->remote or epf->local may be NULL if setting up a
             * forwarding failed. */
            if (epf->remote) {
                struct ssh_rportfwd *rpf = epf->remote;
                struct Packet *pktout;

                /*
                 * Cancel the port forwarding at the server
                 * end.
                 */
                if (ssh->version == 1) {
                    /*
                     * We cannot cancel listening ports on the
                     * server side in SSH-1! There's no message
                     * to support it. Instead, we simply remove
                     * the rportfwd record from the local end
                     * so that any connections the server tries
                     * to make on it are rejected.
                     */
                } else {
                    pktout = ssh2_pkt_init(SSH2_MSG_GLOBAL_REQUEST);
                    ssh2_pkt_addstring(pktout, "cancel-tcpip-forward");
                    ssh2_pkt_addbool(pktout, 0);/* _don't_ want reply */
                    if (epf->saddr) {
                        ssh2_pkt_addstring(pktout, epf->saddr);
                    } else if (conf_get_int(conf, CONF_rport_acceptall)) {
                        /* XXX: rport_acceptall may not represent
                         * what was used to open the original connection,
                         * since it's reconfigurable. */
                        ssh2_pkt_addstring(pktout, "");
                    } else {
                        ssh2_pkt_addstring(pktout, "localhost");
                    }
                    ssh2_pkt_adduint32(pktout, epf->sport);
                    ssh2_pkt_send(ssh, pktout);
                }

                del234(ssh->rportfwds, rpf);
                free_rportfwd(rpf);
            } else if (epf->local) {
                pfl_terminate(epf->local);
            }

            delpos234(ssh->portfwds, i);
            free_portfwd(epf);
            i--;                       /* so we don't skip one in the list */
        }

    /*
     * And finally, set up any new port forwardings (status==CREATE).
     */
    for (i = 0; (epf = index234(ssh->portfwds, i)) != NULL; i++)
        if (epf->status == CREATE) {
            char *sportdesc, *dportdesc;
            sportdesc = dupprintf("%s%s%s%s%d%s",
                                  epf->saddr ? epf->saddr : "",
                                  epf->saddr ? ":" : "",
                                  epf->sserv ? epf->sserv : "",
                                  epf->sserv ? "(" : "",
                                  epf->sport,
                                  epf->sserv ? ")" : "");
            if (epf->type == 'D') {
                dportdesc = NULL;
            } else {
                dportdesc = dupprintf("%s:%s%s%d%s",
                                      epf->daddr,
                                      epf->dserv ? epf->dserv : "",
                                      epf->dserv ? "(" : "",
                                      epf->dport,
                                      epf->dserv ? ")" : "");
            }

            if (epf->type == 'L') {
                char *err = pfl_listen(epf->daddr, epf->dport,
                                       epf->saddr, epf->sport,
                                       ssh, conf, &epf->local,
                                       epf->addressfamily);

                logeventf(ssh, "Local %sport %s forwarding to %s%s%s",
                          epf->addressfamily == ADDRTYPE_IPV4 ? "IPv4 " :
                          epf->addressfamily == ADDRTYPE_IPV6 ? "IPv6 " : "",
                          sportdesc, dportdesc,
                          err ? " failed: " : "", err ? err : "");
                if (err)
                    sfree(err);
            } else if (epf->type == 'D') {
                char *err = pfl_listen(NULL, -1, epf->saddr, epf->sport,
                                       ssh, conf, &epf->local,
                                       epf->addressfamily);

                logeventf(ssh, "Local %sport %s SOCKS dynamic forwarding%s%s",
                          epf->addressfamily == ADDRTYPE_IPV4 ? "IPv4 " :
                          epf->addressfamily == ADDRTYPE_IPV6 ? "IPv6 " : "",
                          sportdesc,
                          err ? " failed: " : "", err ? err : "");

                if (err)
                    sfree(err);
            } else {
                struct ssh_rportfwd *pf;

                /*
                 * Ensure the remote port forwardings tree exists.
                 */
                if (!ssh->rportfwds) {
                    if (ssh->version == 1)
                        ssh->rportfwds = newtree234(ssh_rportcmp_ssh1);
                    else
                        ssh->rportfwds = newtree234(ssh_rportcmp_ssh2);
                }

                pf = snew(struct ssh_rportfwd);
                pf->share_ctx = NULL;
                pf->dhost = dupstr(epf->daddr);
                pf->dport = epf->dport;
                if (epf->saddr) {
                    pf->shost = dupstr(epf->saddr);
                } else if (conf_get_int(conf, CONF_rport_acceptall)) {
                    pf->shost = dupstr("");
                } else {
                    pf->shost = dupstr("localhost");
                }
                pf->sport = epf->sport;
                if (add234(ssh->rportfwds, pf) != pf) {
                    logeventf(ssh, "Duplicate remote port forwarding to %s:%d",
                              epf->daddr, epf->dport);
                    sfree(pf);
                } else {
                    logeventf(ssh, "Requesting remote port %s"
                              " forward to %s", sportdesc, dportdesc);

                    pf->sportdesc = sportdesc;
                    sportdesc = NULL;
                    epf->remote = pf;
                    pf->pfrec = epf;

                    if (ssh->version == 1) {
                        send_packet(ssh, SSH1_CMSG_PORT_FORWARD_REQUEST,
                                    PKT_INT, epf->sport,
                                    PKT_STR, epf->daddr,
                                    PKT_INT, epf->dport,
                                    PKT_END);
                        ssh_queue_handler(ssh, SSH1_SMSG_SUCCESS,
                                          SSH1_SMSG_FAILURE,
                                          ssh_rportfwd_succfail, pf);
                    } else {
                        struct Packet *pktout;
                        pktout = ssh2_pkt_init(SSH2_MSG_GLOBAL_REQUEST);
                        ssh2_pkt_addstring(pktout, "tcpip-forward");
                        ssh2_pkt_addbool(pktout, 1);/* want reply */
                        ssh2_pkt_addstring(pktout, pf->shost);
                        ssh2_pkt_adduint32(pktout, pf->sport);
                        ssh2_pkt_send(ssh, pktout);

                        ssh_queue_handler(ssh, SSH2_MSG_REQUEST_SUCCESS,
                                          SSH2_MSG_REQUEST_FAILURE,
                                          ssh_rportfwd_succfail, pf);
                    }
                }
            }
            sfree(sportdesc);
            sfree(dportdesc);
        }
}

static void ssh1_smsg_stdout_stderr_data(Ssh ssh, struct Packet *pktin)
{
    char *string;
    int stringlen, bufsize;

    ssh_pkt_getstring(pktin, &string, &stringlen);
    if (string == NULL) {
        bombout(("Incoming terminal data packet was badly formed"));
        return;
    }

    bufsize = from_backend(ssh->frontend, pktin->type == SSH1_SMSG_STDERR_DATA,
                           string, stringlen);
    if (!ssh->v1_stdout_throttling && bufsize > SSH1_BUFFER_LIMIT) {
        ssh->v1_stdout_throttling = 1;
        ssh_throttle_conn(ssh, +1);
    }
}

static void ssh1_smsg_x11_open(Ssh ssh, struct Packet *pktin)
{
    /* Remote side is trying to open a channel to talk to our
     * X-Server. Give them back a local channel number. */
    struct ssh_channel *c;
    int remoteid = ssh_pkt_getuint32(pktin);

    logevent("Received X11 connect request");
    /* Refuse if X11 forwarding is disabled. */
    if (!ssh->X11_fwd_enabled) {
        send_packet(ssh, SSH1_MSG_CHANNEL_OPEN_FAILURE,
                    PKT_INT, remoteid, PKT_END);
        logevent("Rejected X11 connect request");
    } else {
        c = snew(struct ssh_channel);
        c->ssh = ssh;

        ssh_channel_init(c);
        c->u.x11.xconn = x11_init(ssh->x11authtree, c, NULL, -1);
        c->remoteid = remoteid;
        c->halfopen = FALSE;
        c->type = CHAN_X11;     /* identify channel type */
        send_packet(ssh, SSH1_MSG_CHANNEL_OPEN_CONFIRMATION,
                    PKT_INT, c->remoteid, PKT_INT,
                    c->localid, PKT_END);
        logevent("Opened X11 forward channel");
    }
}

static void ssh1_smsg_agent_open(Ssh ssh, struct Packet *pktin)
{
    /* Remote side is trying to open a channel to talk to our
     * agent. Give them back a local channel number. */
    struct ssh_channel *c;
    int remoteid = ssh_pkt_getuint32(pktin);

    /* Refuse if agent forwarding is disabled. */
    if (!ssh->agentfwd_enabled) {
        send_packet(ssh, SSH1_MSG_CHANNEL_OPEN_FAILURE,
                    PKT_INT, remoteid, PKT_END);
    } else {
        c = snew(struct ssh_channel);
        c->ssh = ssh;
        ssh_channel_init(c);
        c->remoteid = remoteid;
        c->halfopen = FALSE;
        c->type = CHAN_AGENT;   /* identify channel type */
        c->u.a.lensofar = 0;
        c->u.a.message = NULL;
        c->u.a.outstanding_requests = 0;
        send_packet(ssh, SSH1_MSG_CHANNEL_OPEN_CONFIRMATION,
                    PKT_INT, c->remoteid, PKT_INT, c->localid,
                    PKT_END);
    }
}

static void ssh1_msg_port_open(Ssh ssh, struct Packet *pktin)
{
    /* Remote side is trying to open a channel to talk to a
     * forwarded port. Give them back a local channel number. */
    struct ssh_rportfwd pf, *pfp;
    int remoteid;
    int hostsize, port;
    char *host;
    char *err;

    remoteid = ssh_pkt_getuint32(pktin);
    ssh_pkt_getstring(pktin, &host, &hostsize);
    port = ssh_pkt_getuint32(pktin);

    pf.dhost = dupprintf("%.*s", hostsize, NULLTOEMPTY(host));
    pf.dport = port;
    pfp = find234(ssh->rportfwds, &pf, NULL);

    if (pfp == NULL) {
        logeventf(ssh, "Rejected remote port open request for %s:%d",
                  pf.dhost, port);
        send_packet(ssh, SSH1_MSG_CHANNEL_OPEN_FAILURE,
                    PKT_INT, remoteid, PKT_END);
    } else {
        struct ssh_channel *c = snew(struct ssh_channel);
        c->ssh = ssh;

        logeventf(ssh, "Received remote port open request for %s:%d",
                  pf.dhost, port);
        err = pfd_connect(&c->u.pfd.pf, pf.dhost, port,
                          c, ssh->conf, pfp->pfrec->addressfamily);
        if (err != NULL) {
            logeventf(ssh, "Port open failed: %s", err);
            sfree(err);
            sfree(c);
            send_packet(ssh, SSH1_MSG_CHANNEL_OPEN_FAILURE,
                        PKT_INT, remoteid, PKT_END);
        } else {
            ssh_channel_init(c);
            c->remoteid = remoteid;
            c->halfopen = FALSE;
            c->type = CHAN_SOCKDATA;    /* identify channel type */
            send_packet(ssh, SSH1_MSG_CHANNEL_OPEN_CONFIRMATION,
                        PKT_INT, c->remoteid, PKT_INT,
                        c->localid, PKT_END);
            logevent("Forwarded port opened successfully");
        }
    }

    sfree(pf.dhost);
}

static void ssh1_msg_channel_open_confirmation(Ssh ssh, struct Packet *pktin)
{
    struct ssh_channel *c;

    c = ssh_channel_msg(ssh, pktin);
    if (c && c->type == CHAN_SOCKDATA_DORMANT) {
        c->remoteid = ssh_pkt_getuint32(pktin);
        c->halfopen = FALSE;
        c->type = CHAN_SOCKDATA;
        c->throttling_conn = 0;
        pfd_confirm(c->u.pfd.pf);
    }

    if (c && c->pending_eof) {
        /*
         * We have a pending close on this channel,
         * which we decided on before the server acked
         * the channel open. So now we know the
         * remoteid, we can close it again.
         */
        ssh_channel_try_eof(c);
    }
}

static void ssh1_msg_channel_open_failure(Ssh ssh, struct Packet *pktin)
{
    struct ssh_channel *c;

    c = ssh_channel_msg(ssh, pktin);
    if (c && c->type == CHAN_SOCKDATA_DORMANT) {
        logevent("Forwarded connection refused by server");
        pfd_close(c->u.pfd.pf);
        del234(ssh->channels, c);
        sfree(c);
    }
}

static void ssh1_msg_channel_close(Ssh ssh, struct Packet *pktin)
{
    /* Remote side closes a channel. */
    struct ssh_channel *c;

    c = ssh_channel_msg(ssh, pktin);
    if (c) {

        if (pktin->type == SSH1_MSG_CHANNEL_CLOSE &&
            !(c->closes & CLOSES_RCVD_EOF)) {
            /*
             * Received CHANNEL_CLOSE, which we translate into
             * outgoing EOF.
             */
            int send_close = FALSE;

            c->closes |= CLOSES_RCVD_EOF;

            switch (c->type) {
              case CHAN_X11:
                if (c->u.x11.xconn)
                    x11_send_eof(c->u.x11.xconn);
                else
                    send_close = TRUE;
                break;
              case CHAN_SOCKDATA:
                if (c->u.pfd.pf)
                    pfd_send_eof(c->u.pfd.pf);
                else
                    send_close = TRUE;
                break;
              case CHAN_AGENT:
                send_close = TRUE;
                break;
            }

            if (send_close && !(c->closes & CLOSES_SENT_EOF)) {
                send_packet(ssh, SSH1_MSG_CHANNEL_CLOSE, PKT_INT, c->remoteid,
                            PKT_END);
                c->closes |= CLOSES_SENT_EOF;
            }
        }

        if (pktin->type == SSH1_MSG_CHANNEL_CLOSE_CONFIRMATION &&
            !(c->closes & CLOSES_RCVD_CLOSE)) {

            if (!(c->closes & CLOSES_SENT_EOF)) {
                bombout(("Received CHANNEL_CLOSE_CONFIRMATION for channel %u"
                         " for which we never sent CHANNEL_CLOSE\n",
                         c->localid));
            }

            c->closes |= CLOSES_RCVD_CLOSE;
        }

        if (!((CLOSES_SENT_EOF | CLOSES_RCVD_EOF) & ~c->closes) &&
            !(c->closes & CLOSES_SENT_CLOSE)) {
            send_packet(ssh, SSH1_MSG_CHANNEL_CLOSE_CONFIRMATION,
                        PKT_INT, c->remoteid, PKT_END);
            c->closes |= CLOSES_SENT_CLOSE;
        }

        if (!((CLOSES_SENT_CLOSE | CLOSES_RCVD_CLOSE) & ~c->closes))
            ssh_channel_destroy(c);
    }
}

/*
 * Handle incoming data on an SSH-1 or SSH-2 agent-forwarding channel.
 */
static int ssh_agent_channel_data(struct ssh_channel *c, char *data,
                                  int length)
{
    while (length > 0) {
        if (c->u.a.lensofar < 4) {
            unsigned int l = min(4 - c->u.a.lensofar, (unsigned)length);
            memcpy(c->u.a.msglen + c->u.a.lensofar, data, l);
            data += l;
            length -= l;
            c->u.a.lensofar += l;
        }
        if (c->u.a.lensofar == 4) {
            c->u.a.totallen = 4 + GET_32BIT(c->u.a.msglen);
            c->u.a.message = snewn(c->u.a.totallen, unsigned char);
            memcpy(c->u.a.message, c->u.a.msglen, 4);
        }
        if (c->u.a.lensofar >= 4 && length > 0) {
            unsigned int l = min(c->u.a.totallen - c->u.a.lensofar,
                                 (unsigned)length);
            memcpy(c->u.a.message + c->u.a.lensofar, data, l);
            data += l;
            length -= l;
            c->u.a.lensofar += l;
        }
        if (c->u.a.lensofar == c->u.a.totallen) {
            void *reply;
            int replylen;
            c->u.a.outstanding_requests++;
            if (agent_query(c->u.a.message, c->u.a.totallen, &reply, &replylen,
                            ssh_agentf_callback, c))
                ssh_agentf_callback(c, reply, replylen);
            sfree(c->u.a.message);
            c->u.a.message = NULL;
            c->u.a.lensofar = 0;
        }
    }
    return 0;   /* agent channels never back up */
}

static int ssh_channel_data(struct ssh_channel *c, int is_stderr,
                            char *data,  int length)
{
    switch (c->type) {
      case CHAN_MAINSESSION:
        return from_backend(c->ssh->frontend, is_stderr, data, length);
      case CHAN_X11:
        return x11_send(c->u.x11.xconn, data, length);
      case CHAN_SOCKDATA:
        return pfd_send(c->u.pfd.pf, data, length);
      case CHAN_AGENT:
        return ssh_agent_channel_data(c, data, length);
    }
    return 0;
}

static void ssh1_msg_channel_data(Ssh ssh, struct Packet *pktin)
{
    /* Data sent down one of our channels. */
    char *p;
    int len;
    struct ssh_channel *c;

    c = ssh_channel_msg(ssh, pktin);
    ssh_pkt_getstring(pktin, &p, &len);

    if (c) {
        int bufsize = ssh_channel_data(c, FALSE, p, len);
        if (!c->throttling_conn && bufsize > SSH1_BUFFER_LIMIT) {
            c->throttling_conn = 1;
            ssh_throttle_conn(ssh, +1);
        }
    }
}

static void ssh1_smsg_exit_status(Ssh ssh, struct Packet *pktin)
{
    ssh->exitcode = ssh_pkt_getuint32(pktin);
    logeventf(ssh, "Server sent command exit status %d", ssh->exitcode);
    send_packet(ssh, SSH1_CMSG_EXIT_CONFIRMATION, PKT_END);
    /*
     * In case `helpful' firewalls or proxies tack
     * extra human-readable text on the end of the
     * session which we might mistake for another
     * encrypted packet, we close the session once
     * we've sent EXIT_CONFIRMATION.
     */
    ssh_disconnect(ssh, NULL, NULL, 0, TRUE);
}

/* Helper function to deal with sending tty modes for REQUEST_PTY */
static void ssh1_send_ttymode(void *data,
                              const struct ssh_ttymode *mode, char *val)
{
    struct Packet *pktout = (struct Packet *)data;
    unsigned int arg = 0;

    switch (mode->type) {
      case TTY_OP_CHAR:
        arg = ssh_tty_parse_specchar(val);
        break;
      case TTY_OP_BOOL:
        arg = ssh_tty_parse_boolean(val);
        break;
    }
    ssh2_pkt_addbyte(pktout, mode->opcode);
    ssh2_pkt_addbyte(pktout, arg);
}

int ssh_agent_forwarding_permitted(Ssh ssh)
{
    return conf_get_int(ssh->conf, CONF_agentfwd) && agent_exists();
}

static void do_ssh1_connection(Ssh ssh, const unsigned char *in, int inlen,
                               struct Packet *pktin)
{
    crBegin(ssh->do_ssh1_connection_crstate);

    ssh->packet_dispatch[SSH1_SMSG_STDOUT_DATA] = 
        ssh->packet_dispatch[SSH1_SMSG_STDERR_DATA] =
        ssh1_smsg_stdout_stderr_data;

    ssh->packet_dispatch[SSH1_MSG_CHANNEL_OPEN_CONFIRMATION] =
        ssh1_msg_channel_open_confirmation;
    ssh->packet_dispatch[SSH1_MSG_CHANNEL_OPEN_FAILURE] =
        ssh1_msg_channel_open_failure;
    ssh->packet_dispatch[SSH1_MSG_CHANNEL_CLOSE] =
        ssh->packet_dispatch[SSH1_MSG_CHANNEL_CLOSE_CONFIRMATION] =
        ssh1_msg_channel_close;
    ssh->packet_dispatch[SSH1_MSG_CHANNEL_DATA] = ssh1_msg_channel_data;
    ssh->packet_dispatch[SSH1_SMSG_EXIT_STATUS] = ssh1_smsg_exit_status;

    if (ssh_agent_forwarding_permitted(ssh)) {
        logevent("Requesting agent forwarding");
        send_packet(ssh, SSH1_CMSG_AGENT_REQUEST_FORWARDING, PKT_END);
        do {
            crReturnV;
        } while (!pktin);
        if (pktin->type != SSH1_SMSG_SUCCESS
            && pktin->type != SSH1_SMSG_FAILURE) {
            bombout(("Protocol confusion"));
            crStopV;
        } else if (pktin->type == SSH1_SMSG_FAILURE) {
            logevent("Agent forwarding refused");
        } else {
            logevent("Agent forwarding enabled");
            ssh->agentfwd_enabled = TRUE;
            ssh->packet_dispatch[SSH1_SMSG_AGENT_OPEN] = ssh1_smsg_agent_open;
        }
    }

    if (conf_get_int(ssh->conf, CONF_x11_forward)) {
        ssh->x11disp =
            x11_setup_display(conf_get_str(ssh->conf, CONF_x11_display),
                              ssh->conf);
        if (!ssh->x11disp) {
            /* FIXME: return an error message from x11_setup_display */
            logevent("X11 forwarding not enabled: unable to"
                     " initialise X display");
        } else {
            ssh->x11auth = x11_invent_fake_auth
                (ssh->x11authtree, conf_get_int(ssh->conf, CONF_x11_auth));
            ssh->x11auth->disp = ssh->x11disp;

            logevent("Requesting X11 forwarding");
            if (ssh->v1_local_protoflags & SSH1_PROTOFLAG_SCREEN_NUMBER) {
                send_packet(ssh, SSH1_CMSG_X11_REQUEST_FORWARDING,
                            PKT_STR, ssh->x11auth->protoname,
                            PKT_STR, ssh->x11auth->datastring,
                            PKT_INT, ssh->x11disp->screennum,
                            PKT_END);
            } else {
                send_packet(ssh, SSH1_CMSG_X11_REQUEST_FORWARDING,
                            PKT_STR, ssh->x11auth->protoname,
                            PKT_STR, ssh->x11auth->datastring,
                            PKT_END);
            }
            do {
                crReturnV;
            } while (!pktin);
            if (pktin->type != SSH1_SMSG_SUCCESS
                && pktin->type != SSH1_SMSG_FAILURE) {
                bombout(("Protocol confusion"));
                crStopV;
            } else if (pktin->type == SSH1_SMSG_FAILURE) {
                logevent("X11 forwarding refused");
            } else {
                logevent("X11 forwarding enabled");
                ssh->X11_fwd_enabled = TRUE;
                ssh->packet_dispatch[SSH1_SMSG_X11_OPEN] = ssh1_smsg_x11_open;
            }
        }
    }

    ssh_setup_portfwd(ssh, ssh->conf);
    ssh->packet_dispatch[SSH1_MSG_PORT_OPEN] = ssh1_msg_port_open;

    if (!conf_get_int(ssh->conf, CONF_nopty)) {
        struct Packet *pkt;
        /* Unpick the terminal-speed string. */
        /* XXX perhaps we should allow no speeds to be sent. */
        ssh->ospeed = 38400; ssh->ispeed = 38400; /* last-resort defaults */
        sscanf(conf_get_str(ssh->conf, CONF_termspeed), "%d,%d", &ssh->ospeed, &ssh->ispeed);
        /* Send the pty request. */
        pkt = ssh1_pkt_init(SSH1_CMSG_REQUEST_PTY);
        ssh_pkt_addstring(pkt, conf_get_str(ssh->conf, CONF_termtype));
        ssh_pkt_adduint32(pkt, ssh->term_height);
        ssh_pkt_adduint32(pkt, ssh->term_width);
        ssh_pkt_adduint32(pkt, 0); /* width in pixels */
        ssh_pkt_adduint32(pkt, 0); /* height in pixels */
        parse_ttymodes(ssh, ssh1_send_ttymode, (void *)pkt);
        ssh_pkt_addbyte(pkt, SSH1_TTY_OP_ISPEED);
        ssh_pkt_adduint32(pkt, ssh->ispeed);
        ssh_pkt_addbyte(pkt, SSH1_TTY_OP_OSPEED);
        ssh_pkt_adduint32(pkt, ssh->ospeed);
        ssh_pkt_addbyte(pkt, SSH_TTY_OP_END);
        s_wrpkt(ssh, pkt);
        ssh->state = SSH_STATE_INTERMED;
        do {
            crReturnV;
        } while (!pktin);
        if (pktin->type != SSH1_SMSG_SUCCESS
            && pktin->type != SSH1_SMSG_FAILURE) {
            bombout(("Protocol confusion"));
            crStopV;
        } else if (pktin->type == SSH1_SMSG_FAILURE) {
            c_write_str(ssh, "Server refused to allocate pty\r\n");
            ssh->editing = ssh->echoing = 1;
        } else {
            logeventf(ssh, "Allocated pty (ospeed %dbps, ispeed %dbps)",
                      ssh->ospeed, ssh->ispeed);
            ssh->got_pty = TRUE;
        }
    } else {
        ssh->editing = ssh->echoing = 1;
    }

    if (conf_get_int(ssh->conf, CONF_compression)) {
        send_packet(ssh, SSH1_CMSG_REQUEST_COMPRESSION, PKT_INT, 6, PKT_END);
        do {
            crReturnV;
        } while (!pktin);
        if (pktin->type != SSH1_SMSG_SUCCESS
            && pktin->type != SSH1_SMSG_FAILURE) {
            bombout(("Protocol confusion"));
            crStopV;
        } else if (pktin->type == SSH1_SMSG_FAILURE) {
            c_write_str(ssh, "Server refused to compress\r\n");
        }
        logevent("Started compression");
        ssh->v1_compressing = TRUE;
        ssh->cs_comp_ctx = zlib_compress_init();
        logevent("Initialised zlib (RFC1950) compression");
        ssh->sc_comp_ctx = zlib_decompress_init();
        logevent("Initialised zlib (RFC1950) decompression");
    }

    /*
     * Start the shell or command.
     * 
     * Special case: if the first-choice command is an SSH-2
     * subsystem (hence not usable here) and the second choice
     * exists, we fall straight back to that.
     */
    {
        char *cmd = conf_get_str(ssh->conf, CONF_remote_cmd);
        
        if (conf_get_int(ssh->conf, CONF_ssh_subsys) &&
            conf_get_str(ssh->conf, CONF_remote_cmd2)) {
            cmd = conf_get_str(ssh->conf, CONF_remote_cmd2);
            ssh->fallback_cmd = TRUE;
        }
        if (*cmd)
            send_packet(ssh, SSH1_CMSG_EXEC_CMD, PKT_STR, cmd, PKT_END);
        else
            send_packet(ssh, SSH1_CMSG_EXEC_SHELL, PKT_END);
        logevent("Started session");
    }

    ssh->state = SSH_STATE_SESSION;
    if (ssh->size_needed)
        ssh_size(ssh, ssh->term_width, ssh->term_height);
    if (ssh->eof_needed)
        ssh_special(ssh, TS_EOF);

    if (ssh->ldisc)
        ldisc_echoedit_update(ssh->ldisc);  /* cause ldisc to notice changes */
    ssh->send_ok = 1;
    ssh->channels = newtree234(ssh_channelcmp);
    while (1) {

        /*
         * By this point, most incoming packets are already being
         * handled by the dispatch table, and we need only pay
         * attention to the unusual ones.
         */

        crReturnV;
        if (pktin) {
            if (pktin->type == SSH1_SMSG_SUCCESS) {
                /* may be from EXEC_SHELL on some servers */
            } else if (pktin->type == SSH1_SMSG_FAILURE) {
                /* may be from EXEC_SHELL on some servers
                 * if no pty is available or in other odd cases. Ignore */
            } else {
                bombout(("Strange packet received: type %d", pktin->type));
                crStopV;
            }
        } else {
            while (inlen > 0) {
                int len = min(inlen, 512);
                send_packet(ssh, SSH1_CMSG_STDIN_DATA,
                            PKT_INT, len, PKT_DATA, in, len,
                            PKT_END);
                in += len;
                inlen -= len;
            }
        }
    }

    crFinishV;
}

/*
 * Handle the top-level SSH-2 protocol.
 */
static void ssh1_msg_debug(Ssh ssh, struct Packet *pktin)
{
    char *msg;
    int msglen;

    ssh_pkt_getstring(pktin, &msg, &msglen);
    logeventf(ssh, "Remote debug message: %.*s", msglen, NULLTOEMPTY(msg));
}

static void ssh1_msg_disconnect(Ssh ssh, struct Packet *pktin)
{
    /* log reason code in disconnect message */
    char *msg;
    int msglen;

    ssh_pkt_getstring(pktin, &msg, &msglen);
    bombout(("Server sent disconnect message:\n\"%.*s\"",
             msglen, NULLTOEMPTY(msg)));
}

static void ssh_msg_ignore(Ssh ssh, struct Packet *pktin)
{
    /* Do nothing, because we're ignoring it! Duhh. */
}

static void ssh1_protocol_setup(Ssh ssh)
{
    int i;

    /*
     * Most messages are handled by the coroutines.
     */
    for (i = 0; i < 256; i++)
        ssh->packet_dispatch[i] = NULL;

    /*
     * These special message types we install handlers for.
     */
    ssh->packet_dispatch[SSH1_MSG_DISCONNECT] = ssh1_msg_disconnect;
    ssh->packet_dispatch[SSH1_MSG_IGNORE] = ssh_msg_ignore;
    ssh->packet_dispatch[SSH1_MSG_DEBUG] = ssh1_msg_debug;
}

static void ssh1_protocol(Ssh ssh, const void *vin, int inlen,
                          struct Packet *pktin)
{
    const unsigned char *in = (const unsigned char *)vin;
    if (ssh->state == SSH_STATE_CLOSED)
        return;

    if (pktin && ssh->packet_dispatch[pktin->type]) {
        ssh->packet_dispatch[pktin->type](ssh, pktin);
        return;
    }

    if (!ssh->protocol_initial_phase_done) {
        if (do_ssh1_login(ssh, in, inlen, pktin))
            ssh->protocol_initial_phase_done = TRUE;
        else
            return;
    }

    do_ssh1_connection(ssh, in, inlen, pktin);
}

/*
 * Utility routines for decoding comma-separated strings in KEXINIT.
 */
static int first_in_commasep_string(char const *needle, char const *haystack,
                                    int haylen)
{
    int needlen;
    if (!needle || !haystack)          /* protect against null pointers */
        return 0;
    needlen = strlen(needle);

    if (haylen >= needlen &&       /* haystack is long enough */
        !memcmp(needle, haystack, needlen) &&   /* initial match */
        (haylen == needlen || haystack[needlen] == ',')
        /* either , or EOS follows */
        )
        return 1;
    return 0;
}

static int in_commasep_string(char const *needle, char const *haystack,
                              int haylen)
{
    char *p;

    if (!needle || !haystack)          /* protect against null pointers */
        return 0;
    /*
     * Is it at the start of the string?
     */
    if (first_in_commasep_string(needle, haystack, haylen))
        return 1;
    /*
     * If not, search for the next comma and resume after that.
     * If no comma found, terminate.
     */
    p = memchr(haystack, ',', haylen);
    if (!p) return 0;
    /* + 1 to skip over comma */
    return in_commasep_string(needle, p + 1, haylen - (p + 1 - haystack));
}

/*
 * Add a value to the comma-separated string at the end of the packet.
 */
static void ssh2_pkt_addstring_commasep(struct Packet *pkt, const char *data)
{
    if (pkt->length - pkt->savedpos > 0)
        ssh_pkt_addstring_str(pkt, ",");
    ssh_pkt_addstring_str(pkt, data);
}


/*
 * SSH-2 key derivation (RFC 4253 section 7.2).
 */
static unsigned char *ssh2_mkkey(Ssh ssh, Bignum K, unsigned char *H,
                                 char chr, int keylen)
{
    const struct ssh_hash *h = ssh->kex->hash;
    int keylen_padded;
    unsigned char *key;
    void *s, *s2;

    if (keylen == 0)
        return NULL;

    /* Round up to the next multiple of hash length. */
    keylen_padded = ((keylen + h->hlen - 1) / h->hlen) * h->hlen;

    key = snewn(keylen_padded, unsigned char);

    /* First hlen bytes. */
    s = h->init();
    if (!(ssh->remote_bugs & BUG_SSH2_DERIVEKEY))
        hash_mpint(h, s, K);
    h->bytes(s, H, h->hlen);
    h->bytes(s, &chr, 1);
    h->bytes(s, ssh->v2_session_id, ssh->v2_session_id_len);
    h->final(s, key);

    /* Subsequent blocks of hlen bytes. */
    if (keylen_padded > h->hlen) {
        int offset;

        s = h->init();
        if (!(ssh->remote_bugs & BUG_SSH2_DERIVEKEY))
            hash_mpint(h, s, K);
        h->bytes(s, H, h->hlen);

        for (offset = h->hlen; offset < keylen_padded; offset += h->hlen) {
            h->bytes(s, key + offset - h->hlen, h->hlen);
            s2 = h->copy(s);
            h->final(s2, key + offset);
        }

        h->free(s);
    }

    /* Now clear any extra bytes of key material beyond the length
     * we're officially returning, because the caller won't know to
     * smemclr those. */
    if (keylen_padded > keylen)
        smemclr(key + keylen, keylen_padded - keylen);

    return key;
}

/*
 * Structure for constructing KEXINIT algorithm lists.
 */
#define MAXKEXLIST 16
struct kexinit_algorithm {
    const char *name;
    union {
        struct {
            const struct ssh_kex *kex;
            int warn;
        } kex;
        struct {
            const struct ssh_signkey *hostkey;
            int warn;
        } hk;
        struct {
            const struct ssh2_cipher *cipher;
            int warn;
        } cipher;
        struct {
            const struct ssh_mac *mac;
            int etm;
        } mac;
        const struct ssh_compress *comp;
    } u;
};

/*
 * Find a slot in a KEXINIT algorithm list to use for a new algorithm.
 * If the algorithm is already in the list, return a pointer to its
 * entry, otherwise return an entry from the end of the list.
 * This assumes that every time a particular name is passed in, it
 * comes from the same string constant.  If this isn't true, this
 * function may need to be rewritten to use strcmp() instead.
 */
static struct kexinit_algorithm *ssh2_kexinit_addalg(struct kexinit_algorithm
                                                     *list, const char *name)
{
    int i;

    for (i = 0; i < MAXKEXLIST; i++)
        if (list[i].name == NULL || list[i].name == name) {
            list[i].name = name;
            return &list[i];
        }
    assert(!"No space in KEXINIT list");
    return NULL;
}

/*
 * Handle the SSH-2 transport layer.
 */
static void do_ssh2_transport(Ssh ssh, const void *vin, int inlen,
                             struct Packet *pktin)
{
    const unsigned char *in = (const unsigned char *)vin;
    enum kexlist {
        KEXLIST_KEX, KEXLIST_HOSTKEY, KEXLIST_CSCIPHER, KEXLIST_SCCIPHER,
        KEXLIST_CSMAC, KEXLIST_SCMAC, KEXLIST_CSCOMP, KEXLIST_SCCOMP,
        NKEXLIST
    };
    const char * kexlist_descr[NKEXLIST] = {
        "key exchange algorithm", "host key algorithm",
        "client-to-server cipher", "server-to-client cipher",
        "client-to-server MAC", "server-to-client MAC",
        "client-to-server compression method",
        "server-to-client compression method" };
    struct do_ssh2_transport_state {
        int crLine;
        int nbits, pbits, warn_kex, warn_hk, warn_cscipher, warn_sccipher;
        Bignum p, g, e, f, K;
        void *our_kexinit;
        int our_kexinitlen;
        int kex_init_value, kex_reply_value;
        const struct ssh_mac *const *maclist;
        int nmacs;
        const struct ssh2_cipher *cscipher_tobe;
        const struct ssh2_cipher *sccipher_tobe;
        const struct ssh_mac *csmac_tobe;
        const struct ssh_mac *scmac_tobe;
        int csmac_etm_tobe, scmac_etm_tobe;
        const struct ssh_compress *cscomp_tobe;
        const struct ssh_compress *sccomp_tobe;
        char *hostkeydata, *sigdata, *rsakeydata, *keystr, *fingerprint;
        int hostkeylen, siglen, rsakeylen;
        void *hkey;                    /* actual host key */
        void *rsakey;                  /* for RSA kex */
        void *eckey;                   /* for ECDH kex */
        unsigned char exchange_hash[SSH2_KEX_MAX_HASH_LEN];
        int n_preferred_kex;
        const struct ssh_kexes *preferred_kex[KEX_MAX];
        int n_preferred_hk;
        int preferred_hk[HK_MAX];
        int n_preferred_ciphers;
        const struct ssh2_ciphers *preferred_ciphers[CIPHER_MAX];
        const struct ssh_compress *preferred_comp;
        int userauth_succeeded;     /* for delayed compression */
        int pending_compression;
        int got_session_id, activated_authconn;
        struct Packet *pktout;
        int dlgret;
        int guessok;
        int ignorepkt;
        struct kexinit_algorithm kexlists[NKEXLIST][MAXKEXLIST];
    };
    crState(do_ssh2_transport_state);

    assert(!ssh->bare_connection);
    assert(ssh->version == 2);

    crBeginState;

    s->cscipher_tobe = s->sccipher_tobe = NULL;
    s->csmac_tobe = s->scmac_tobe = NULL;
    s->cscomp_tobe = s->sccomp_tobe = NULL;

    s->got_session_id = s->activated_authconn = FALSE;
    s->userauth_succeeded = FALSE;
    s->pending_compression = FALSE;

    /*
     * Be prepared to work around the buggy MAC problem.
     */
    if (ssh->remote_bugs & BUG_SSH2_HMAC)
        s->maclist = buggymacs, s->nmacs = lenof(buggymacs);
    else
        s->maclist = macs, s->nmacs = lenof(macs);

  begin_key_exchange:
    ssh->pkt_kctx = SSH2_PKTCTX_NOKEX;
    {
        int i, j, k, warn;
        struct kexinit_algorithm *alg;

        /*
         * Set up the preferred key exchange. (NULL => warn below here)
         */
        s->n_preferred_kex = 0;
        for (i = 0; i < KEX_MAX; i++) {
            switch (conf_get_int_int(ssh->conf, CONF_ssh_kexlist, i)) {
              case KEX_DHGEX:
                s->preferred_kex[s->n_preferred_kex++] =
                    &ssh_diffiehellman_gex;
                break;
              case KEX_DHGROUP14:
                s->preferred_kex[s->n_preferred_kex++] =
                    &ssh_diffiehellman_group14;
                break;
              case KEX_DHGROUP1:
                s->preferred_kex[s->n_preferred_kex++] =
                    &ssh_diffiehellman_group1;
                break;
              case KEX_RSA:
                s->preferred_kex[s->n_preferred_kex++] =
                    &ssh_rsa_kex;
                break;
              case KEX_ECDH:
                s->preferred_kex[s->n_preferred_kex++] =
                    &ssh_ecdh_kex;
                break;
              case KEX_WARN:
                /* Flag for later. Don't bother if it's the last in
                 * the list. */
                if (i < KEX_MAX - 1) {
                    s->preferred_kex[s->n_preferred_kex++] = NULL;
                }
                break;
            }
        }

        /*
         * Set up the preferred host key types. These are just the ids
         * in the enum in putty.h, so 'warn below here' is indicated
         * by HK_WARN.
         */
        s->n_preferred_hk = 0;
        for (i = 0; i < HK_MAX; i++) {
            int id = conf_get_int_int(ssh->conf, CONF_ssh_hklist, i);
            /* As above, don't bother with HK_WARN if it's last in the
             * list */
            if (id != HK_WARN || i < HK_MAX - 1)
                s->preferred_hk[s->n_preferred_hk++] = id;
        }

        /*
         * Set up the preferred ciphers. (NULL => warn below here)
         */
        s->n_preferred_ciphers = 0;
        for (i = 0; i < CIPHER_MAX; i++) {
            switch (conf_get_int_int(ssh->conf, CONF_ssh_cipherlist, i)) {
              case CIPHER_BLOWFISH:
                s->preferred_ciphers[s->n_preferred_ciphers++] = &ssh2_blowfish;
                break;
              case CIPHER_DES:
                if (conf_get_int(ssh->conf, CONF_ssh2_des_cbc)) {
                    s->preferred_ciphers[s->n_preferred_ciphers++] = &ssh2_des;
                }
                break;
              case CIPHER_3DES:
                s->preferred_ciphers[s->n_preferred_ciphers++] = &ssh2_3des;
                break;
              case CIPHER_AES:
                s->preferred_ciphers[s->n_preferred_ciphers++] = &ssh2_aes;
                break;
              case CIPHER_ARCFOUR:
                s->preferred_ciphers[s->n_preferred_ciphers++] = &ssh2_arcfour;
                break;
              case CIPHER_CHACHA20:
                s->preferred_ciphers[s->n_preferred_ciphers++] = &ssh2_ccp;
                break;
              case CIPHER_WARN:
                /* Flag for later. Don't bother if it's the last in
                 * the list. */
                if (i < CIPHER_MAX - 1) {
                    s->preferred_ciphers[s->n_preferred_ciphers++] = NULL;
                }
                break;
            }
        }

        /*
         * Set up preferred compression.
         */
        if (conf_get_int(ssh->conf, CONF_compression))
            s->preferred_comp = &ssh_zlib;
        else
            s->preferred_comp = &ssh_comp_none;

        /*
         * Enable queueing of outgoing auth- or connection-layer
         * packets while we are in the middle of a key exchange.
         */
        ssh->queueing = TRUE;

        /*
         * Flag that KEX is in progress.
         */
        ssh->kex_in_progress = TRUE;

        for (i = 0; i < NKEXLIST; i++)
            for (j = 0; j < MAXKEXLIST; j++)
                s->kexlists[i][j].name = NULL;
        /* List key exchange algorithms. */
        warn = FALSE;
        for (i = 0; i < s->n_preferred_kex; i++) {
            const struct ssh_kexes *k = s->preferred_kex[i];
            if (!k) warn = TRUE;
            else for (j = 0; j < k->nkexes; j++) {
                alg = ssh2_kexinit_addalg(s->kexlists[KEXLIST_KEX],
                                          k->list[j]->name);
                alg->u.kex.kex = k->list[j];
                alg->u.kex.warn = warn;
            }
        }
        /* List server host key algorithms. */
        if (!s->got_session_id) {
            /*
             * In the first key exchange, we list all the algorithms
             * we're prepared to cope with, but prefer those algorithms
             * for which we have a host key for this host.
             *
             * If the host key algorithm is below the warning
             * threshold, we warn even if we did already have a key
             * for it, on the basis that if the user has just
             * reconfigured that host key type to be warned about,
             * they surely _do_ want to be alerted that a server
             * they're actually connecting to is using it.
             */
            warn = FALSE;
            for (i = 0; i < s->n_preferred_hk; i++) {
                if (s->preferred_hk[i] == HK_WARN)
                    warn = TRUE;
                for (j = 0; j < lenof(hostkey_algs); j++) {
                    if (hostkey_algs[j].id != s->preferred_hk[i])
                        continue;
                    if (have_ssh_host_key(ssh->savedhost, ssh->savedport,
                                          hostkey_algs[j].alg->keytype)) {
                        alg = ssh2_kexinit_addalg(s->kexlists[KEXLIST_HOSTKEY],
                                                  hostkey_algs[j].alg->name);
                        alg->u.hk.hostkey = hostkey_algs[j].alg;
                        alg->u.hk.warn = warn;
                    }
                }
            }
            warn = FALSE;
            for (i = 0; i < s->n_preferred_hk; i++) {
                if (s->preferred_hk[i] == HK_WARN)
                    warn = TRUE;
                for (j = 0; j < lenof(hostkey_algs); j++) {
                    if (hostkey_algs[j].id != s->preferred_hk[i])
                        continue;
                    alg = ssh2_kexinit_addalg(s->kexlists[KEXLIST_HOSTKEY],
                                              hostkey_algs[j].alg->name);
                    alg->u.hk.hostkey = hostkey_algs[j].alg;
                    alg->u.hk.warn = warn;
                }
            }
        } else {
            /*
             * In subsequent key exchanges, we list only the kex
             * algorithm that was selected in the first key exchange,
             * so that we keep getting the same host key and hence
             * don't have to interrupt the user's session to ask for
             * reverification.
             */
            assert(ssh->kex);
            alg = ssh2_kexinit_addalg(s->kexlists[KEXLIST_HOSTKEY],
                                      ssh->hostkey->name);
            alg->u.hk.hostkey = ssh->hostkey;
            alg->u.hk.warn = FALSE;
        }
        /* List encryption algorithms (client->server then server->client). */
        for (k = KEXLIST_CSCIPHER; k <= KEXLIST_SCCIPHER; k++) {
            warn = FALSE;
#ifdef FUZZING
            alg = ssh2_kexinit_addalg(s->kexlists[k], "none");
            alg->u.cipher.cipher = NULL;
            alg->u.cipher.warn = warn;
#endif /* FUZZING */
            for (i = 0; i < s->n_preferred_ciphers; i++) {
                const struct ssh2_ciphers *c = s->preferred_ciphers[i];
                if (!c) warn = TRUE;
                else for (j = 0; j < c->nciphers; j++) {
                    alg = ssh2_kexinit_addalg(s->kexlists[k],
                                              c->list[j]->name);
                    alg->u.cipher.cipher = c->list[j];
                    alg->u.cipher.warn = warn;
                }
            }
        }
        /* List MAC algorithms (client->server then server->client). */
        for (j = KEXLIST_CSMAC; j <= KEXLIST_SCMAC; j++) {
#ifdef FUZZING
            alg = ssh2_kexinit_addalg(s->kexlists[j], "none");
            alg->u.mac.mac = NULL;
            alg->u.mac.etm = FALSE;
#endif /* FUZZING */
            for (i = 0; i < s->nmacs; i++) {
                alg = ssh2_kexinit_addalg(s->kexlists[j], s->maclist[i]->name);
                alg->u.mac.mac = s->maclist[i];
                alg->u.mac.etm = FALSE;
            }
            for (i = 0; i < s->nmacs; i++)
                /* For each MAC, there may also be an ETM version,
                 * which we list second. */
                if (s->maclist[i]->etm_name) {
                    alg = ssh2_kexinit_addalg(s->kexlists[j],
                                              s->maclist[i]->etm_name);
                    alg->u.mac.mac = s->maclist[i];
                    alg->u.mac.etm = TRUE;
                }
        }
        /* List client->server compression algorithms,
         * then server->client compression algorithms. (We use the
         * same set twice.) */
        for (j = KEXLIST_CSCOMP; j <= KEXLIST_SCCOMP; j++) {
            assert(lenof(compressions) > 1);
            /* Prefer non-delayed versions */
            alg = ssh2_kexinit_addalg(s->kexlists[j], s->preferred_comp->name);
            alg->u.comp = s->preferred_comp;
            /* We don't even list delayed versions of algorithms until
             * they're allowed to be used, to avoid a race. See the end of
             * this function. */
            if (s->userauth_succeeded && s->preferred_comp->delayed_name) {
                alg = ssh2_kexinit_addalg(s->kexlists[j],
                                          s->preferred_comp->delayed_name);
                alg->u.comp = s->preferred_comp;
            }
            for (i = 0; i < lenof(compressions); i++) {
                const struct ssh_compress *c = compressions[i];
                alg = ssh2_kexinit_addalg(s->kexlists[j], c->name);
                alg->u.comp = c;
                if (s->userauth_succeeded && c->delayed_name) {
                    alg = ssh2_kexinit_addalg(s->kexlists[j], c->delayed_name);
                    alg->u.comp = c;
                }
            }
        }
        /*
         * Construct and send our key exchange packet.
         */
        s->pktout = ssh2_pkt_init(SSH2_MSG_KEXINIT);
        for (i = 0; i < 16; i++)
            ssh2_pkt_addbyte(s->pktout, (unsigned char) random_byte());
        for (i = 0; i < NKEXLIST; i++) {
            ssh2_pkt_addstring_start(s->pktout);
            for (j = 0; j < MAXKEXLIST; j++) {
                if (s->kexlists[i][j].name == NULL) break;
                ssh2_pkt_addstring_commasep(s->pktout, s->kexlists[i][j].name);
            }
        }
        /* List client->server languages. Empty list. */
        ssh2_pkt_addstring_start(s->pktout);
        /* List server->client languages. Empty list. */
        ssh2_pkt_addstring_start(s->pktout);
        /* First KEX packet does _not_ follow, because we're not that brave. */
        ssh2_pkt_addbool(s->pktout, FALSE);
        /* Reserved. */
        ssh2_pkt_adduint32(s->pktout, 0);
    }

    s->our_kexinitlen = s->pktout->length - 5;
    s->our_kexinit = snewn(s->our_kexinitlen, unsigned char);
    memcpy(s->our_kexinit, s->pktout->data + 5, s->our_kexinitlen); 

    ssh2_pkt_send_noqueue(ssh, s->pktout);

    if (!pktin)
        crWaitUntilV(pktin);

    /*
     * Now examine the other side's KEXINIT to see what we're up
     * to.
     */
    {
        char *str;
        int i, j, len;

        if (pktin->type != SSH2_MSG_KEXINIT) {
            bombout(("expected key exchange packet from server"));
            crStopV;
        }
        ssh->kex = NULL;
        ssh->hostkey = NULL;
        s->cscipher_tobe = NULL;
        s->sccipher_tobe = NULL;
        s->csmac_tobe = NULL;
        s->scmac_tobe = NULL;
        s->cscomp_tobe = NULL;
        s->sccomp_tobe = NULL;
        s->warn_kex = s->warn_hk = FALSE;
        s->warn_cscipher = s->warn_sccipher = FALSE;

        pktin->savedpos += 16;          /* skip garbage cookie */

        s->guessok = FALSE;
        for (i = 0; i < NKEXLIST; i++) {
            ssh_pkt_getstring(pktin, &str, &len);
            if (!str) {
                bombout(("KEXINIT packet was incomplete"));
                crStopV;
            }

            /* If we've already selected a cipher which requires a
             * particular MAC, then just select that, and don't even
             * bother looking through the server's KEXINIT string for
             * MACs. */
            if (i == KEXLIST_CSMAC && s->cscipher_tobe &&
                s->cscipher_tobe->required_mac) {
                s->csmac_tobe = s->cscipher_tobe->required_mac;
                s->csmac_etm_tobe = !!(s->csmac_tobe->etm_name);
                goto matched;
            }
            if (i == KEXLIST_SCMAC && s->sccipher_tobe &&
                s->sccipher_tobe->required_mac) {
                s->scmac_tobe = s->sccipher_tobe->required_mac;
                s->scmac_etm_tobe = !!(s->scmac_tobe->etm_name);
                goto matched;
            }

            for (j = 0; j < MAXKEXLIST; j++) {
                struct kexinit_algorithm *alg = &s->kexlists[i][j];
                if (alg->name == NULL) break;
                if (in_commasep_string(alg->name, str, len)) {
                    /* We've found a matching algorithm. */
                    if (i == KEXLIST_KEX || i == KEXLIST_HOSTKEY) {
                        /* Check if we might need to ignore first kex pkt */
                        if (j != 0 ||
                            !first_in_commasep_string(alg->name, str, len))
                            s->guessok = FALSE;
                    }
                    if (i == KEXLIST_KEX) {
                        ssh->kex = alg->u.kex.kex;
                        s->warn_kex = alg->u.kex.warn;
                    } else if (i == KEXLIST_HOSTKEY) {
                        ssh->hostkey = alg->u.hk.hostkey;
                        s->warn_hk = alg->u.hk.warn;
                    } else if (i == KEXLIST_CSCIPHER) {
                        s->cscipher_tobe = alg->u.cipher.cipher;
                        s->warn_cscipher = alg->u.cipher.warn;
                    } else if (i == KEXLIST_SCCIPHER) {
                        s->sccipher_tobe = alg->u.cipher.cipher;
                        s->warn_sccipher = alg->u.cipher.warn;
                    } else if (i == KEXLIST_CSMAC) {
                        s->csmac_tobe = alg->u.mac.mac;
                        s->csmac_etm_tobe = alg->u.mac.etm;
                    } else if (i == KEXLIST_SCMAC) {
                        s->scmac_tobe = alg->u.mac.mac;
                        s->scmac_etm_tobe = alg->u.mac.etm;
                    } else if (i == KEXLIST_CSCOMP) {
                        s->cscomp_tobe = alg->u.comp;
                    } else if (i == KEXLIST_SCCOMP) {
                        s->sccomp_tobe = alg->u.comp;
                    }
                    goto matched;
                }
                if ((i == KEXLIST_CSCOMP || i == KEXLIST_SCCOMP) &&
                    in_commasep_string(alg->u.comp->delayed_name, str, len))
                    s->pending_compression = TRUE;  /* try this later */
            }
            bombout(("Couldn't agree a %s (available: %.*s)",
                     kexlist_descr[i], len, str));
            crStopV;
          matched:;

            if (i == KEXLIST_HOSTKEY) {
                int j;

                /*
                 * In addition to deciding which host key we're
                 * actually going to use, we should make a list of the
                 * host keys offered by the server which we _don't_
                 * have cached. These will be offered as cross-
                 * certification options by ssh_get_specials.
                 *
                 * We also count the key we're currently using for KEX
                 * as one we've already got, because by the time this
                 * menu becomes visible, it will be.
                 */
                ssh->n_uncert_hostkeys = 0;

                for (j = 0; j < lenof(hostkey_algs); j++) {
                    if (hostkey_algs[j].alg != ssh->hostkey &&
                        in_commasep_string(hostkey_algs[j].alg->name,
                                           str, len) &&
                        !have_ssh_host_key(ssh->savedhost, ssh->savedport,
                                           hostkey_algs[j].alg->keytype)) {
                        ssh->uncert_hostkeys[ssh->n_uncert_hostkeys++] = j;
                    }
                }
            }
        }

        if (s->pending_compression) {
            logevent("Server supports delayed compression; "
                     "will try this later");
        }
        ssh_pkt_getstring(pktin, &str, &len);  /* client->server language */
        ssh_pkt_getstring(pktin, &str, &len);  /* server->client language */
        s->ignorepkt = ssh2_pkt_getbool(pktin) && !s->guessok;

        ssh->exhash = ssh->kex->hash->init();
        hash_string(ssh->kex->hash, ssh->exhash, ssh->v_c, strlen(ssh->v_c));
        hash_string(ssh->kex->hash, ssh->exhash, ssh->v_s, strlen(ssh->v_s));
        hash_string(ssh->kex->hash, ssh->exhash,
            s->our_kexinit, s->our_kexinitlen);
        sfree(s->our_kexinit);
        /* Include the type byte in the hash of server's KEXINIT */
        hash_string(ssh->kex->hash, ssh->exhash,
                    pktin->body - 1, pktin->length + 1);

        if (s->warn_kex) {
            ssh_set_frozen(ssh, 1);
            s->dlgret = askalg(ssh->frontend, "key-exchange algorithm",
                               ssh->kex->name,
                               ssh_dialog_callback, ssh);
            if (s->dlgret < 0) {
                do {
                    crReturnV;
                    if (pktin) {
                        bombout(("Unexpected data from server while"
                                 " waiting for user response"));
                        crStopV;
                    }
                } while (pktin || inlen > 0);
                s->dlgret = ssh->user_response;
            }
            ssh_set_frozen(ssh, 0);
            if (s->dlgret == 0) {
                ssh_disconnect(ssh, "User aborted at kex warning", NULL,
                               0, TRUE);
                crStopV;
            }
        }

        if (s->warn_hk) {
            int j, k;
            char *betteralgs;

            ssh_set_frozen(ssh, 1);

            /*
             * Change warning box wording depending on why we chose a
             * warning-level host key algorithm. If it's because
             * that's all we have *cached*, use the askhk mechanism,
             * and list the host keys we could usefully cross-certify.
             * Otherwise, use askalg for the standard wording.
             */
            betteralgs = NULL;
            for (j = 0; j < ssh->n_uncert_hostkeys; j++) {
                const struct ssh_signkey_with_user_pref_id *hktype =
                    &hostkey_algs[ssh->uncert_hostkeys[j]];
                int better = FALSE;
                for (k = 0; k < HK_MAX; k++) {
                    int id = conf_get_int_int(ssh->conf, CONF_ssh_hklist, k);
                    if (id == HK_WARN) {
                        break;
                    } else if (id == hktype->id) {
                        better = TRUE;
                        break;
                    }
                }
                if (better) {
                    if (betteralgs) {
                        char *old_ba = betteralgs;
                        betteralgs = dupcat(betteralgs, ",",
                                            hktype->alg->name,
                                            (const char *)NULL);
                        sfree(old_ba);
                    } else {
                        betteralgs = dupstr(hktype->alg->name);
                    }
                }
            }
            if (betteralgs) {
                s->dlgret = askhk(ssh->frontend, ssh->hostkey->name,
                                  betteralgs, ssh_dialog_callback, ssh);
                sfree(betteralgs);
            } else {
                s->dlgret = askalg(ssh->frontend, "host key type",
                                   ssh->hostkey->name,
                                   ssh_dialog_callback, ssh);
            }
            if (s->dlgret < 0) {
                do {
                    crReturnV;
                    if (pktin) {
                        bombout(("Unexpected data from server while"
                                 " waiting for user response"));
                        crStopV;
                    }
                } while (pktin || inlen > 0);
                s->dlgret = ssh->user_response;
            }
            ssh_set_frozen(ssh, 0);
            if (s->dlgret == 0) {
                ssh_disconnect(ssh, "User aborted at host key warning", NULL,
                               0, TRUE);
                crStopV;
            }
        }

        if (s->warn_cscipher) {
            ssh_set_frozen(ssh, 1);
            s->dlgret = askalg(ssh->frontend,
                               "client-to-server cipher",
                               s->cscipher_tobe->name,
                               ssh_dialog_callback, ssh);
            if (s->dlgret < 0) {
                do {
                    crReturnV;
                    if (pktin) {
                        bombout(("Unexpected data from server while"
                                 " waiting for user response"));
                        crStopV;
                    }
                } while (pktin || inlen > 0);
                s->dlgret = ssh->user_response;
            }
            ssh_set_frozen(ssh, 0);
            if (s->dlgret == 0) {
                ssh_disconnect(ssh, "User aborted at cipher warning", NULL,
                               0, TRUE);
                crStopV;
            }
        }

        if (s->warn_sccipher) {
            ssh_set_frozen(ssh, 1);
            s->dlgret = askalg(ssh->frontend,
                               "server-to-client cipher",
                               s->sccipher_tobe->name,
                               ssh_dialog_callback, ssh);
            if (s->dlgret < 0) {
                do {
                    crReturnV;
                    if (pktin) {
                        bombout(("Unexpected data from server while"
                                 " waiting for user response"));
                        crStopV;
                    }
                } while (pktin || inlen > 0);
                s->dlgret = ssh->user_response;
            }
            ssh_set_frozen(ssh, 0);
            if (s->dlgret == 0) {
                ssh_disconnect(ssh, "User aborted at cipher warning", NULL,
                               0, TRUE);
                crStopV;
            }
        }

        if (s->ignorepkt) /* first_kex_packet_follows */
            crWaitUntilV(pktin);                /* Ignore packet */
    }

    if (ssh->kex->main_type == KEXTYPE_DH) {
        /*
         * Work out the number of bits of key we will need from the
         * key exchange. We start with the maximum key length of
         * either cipher...
         */
        {
            int csbits, scbits;

            csbits = s->cscipher_tobe ? s->cscipher_tobe->real_keybits : 0;
            scbits = s->sccipher_tobe ? s->sccipher_tobe->real_keybits : 0;
            s->nbits = (csbits > scbits ? csbits : scbits);
        }
        /* The keys only have hlen-bit entropy, since they're based on
         * a hash. So cap the key size at hlen bits. */
        if (s->nbits > ssh->kex->hash->hlen * 8)
            s->nbits = ssh->kex->hash->hlen * 8;

        /*
         * If we're doing Diffie-Hellman group exchange, start by
         * requesting a group.
         */
        if (dh_is_gex(ssh->kex)) {
            logevent("Doing Diffie-Hellman group exchange");
            ssh->pkt_kctx = SSH2_PKTCTX_DHGEX;
            /*
             * Work out how big a DH group we will need to allow that
             * much data.
             */
            s->pbits = 512 << ((s->nbits - 1) / 64);
            if (s->pbits < DH_MIN_SIZE)
                s->pbits = DH_MIN_SIZE;
            if (s->pbits > DH_MAX_SIZE)
                s->pbits = DH_MAX_SIZE;
            if ((ssh->remote_bugs & BUG_SSH2_OLDGEX)) {
                s->pktout = ssh2_pkt_init(SSH2_MSG_KEX_DH_GEX_REQUEST_OLD);
                ssh2_pkt_adduint32(s->pktout, s->pbits);
            } else {
                s->pktout = ssh2_pkt_init(SSH2_MSG_KEX_DH_GEX_REQUEST);
                ssh2_pkt_adduint32(s->pktout, DH_MIN_SIZE);
                ssh2_pkt_adduint32(s->pktout, s->pbits);
                ssh2_pkt_adduint32(s->pktout, DH_MAX_SIZE);
            }
            ssh2_pkt_send_noqueue(ssh, s->pktout);

            crWaitUntilV(pktin);
            if (pktin->type != SSH2_MSG_KEX_DH_GEX_GROUP) {
                bombout(("expected key exchange group packet from server"));
                crStopV;
            }
            s->p = ssh2_pkt_getmp(pktin);
            s->g = ssh2_pkt_getmp(pktin);
            if (!s->p || !s->g) {
                bombout(("unable to read mp-ints from incoming group packet"));
                crStopV;
            }
            ssh->kex_ctx = dh_setup_gex(s->p, s->g);
            s->kex_init_value = SSH2_MSG_KEX_DH_GEX_INIT;
            s->kex_reply_value = SSH2_MSG_KEX_DH_GEX_REPLY;
        } else {
            ssh->pkt_kctx = SSH2_PKTCTX_DHGROUP;
            ssh->kex_ctx = dh_setup_group(ssh->kex);
            s->kex_init_value = SSH2_MSG_KEXDH_INIT;
            s->kex_reply_value = SSH2_MSG_KEXDH_REPLY;
            logeventf(ssh, "Using Diffie-Hellman with standard group \"%s\"",
                      ssh->kex->groupname);
        }

        logeventf(ssh, "Doing Diffie-Hellman key exchange with hash %s",
                  ssh->kex->hash->text_name);
        /*
         * Now generate and send e for Diffie-Hellman.
         */
        set_busy_status(ssh->frontend, BUSY_CPU); /* this can take a while */
        s->e = dh_create_e(ssh->kex_ctx, s->nbits * 2);
        s->pktout = ssh2_pkt_init(s->kex_init_value);
        ssh2_pkt_addmp(s->pktout, s->e);
        ssh2_pkt_send_noqueue(ssh, s->pktout);

        set_busy_status(ssh->frontend, BUSY_WAITING); /* wait for server */
        crWaitUntilV(pktin);
        if (pktin->type != s->kex_reply_value) {
            bombout(("expected key exchange reply packet from server"));
            crStopV;
        }
        set_busy_status(ssh->frontend, BUSY_CPU); /* cogitate */
        ssh_pkt_getstring(pktin, &s->hostkeydata, &s->hostkeylen);
        if (!s->hostkeydata) {
            bombout(("unable to parse key exchange reply packet"));
            crStopV;
        }
        s->hkey = ssh->hostkey->newkey(ssh->hostkey,
                                       s->hostkeydata, s->hostkeylen);
        s->f = ssh2_pkt_getmp(pktin);
        if (!s->f) {
            bombout(("unable to parse key exchange reply packet"));
            crStopV;
        }
        ssh_pkt_getstring(pktin, &s->sigdata, &s->siglen);
        if (!s->sigdata) {
            bombout(("unable to parse key exchange reply packet"));
            crStopV;
        }

        {
            const char *err = dh_validate_f(ssh->kex_ctx, s->f);
            if (err) {
                bombout(("key exchange reply failed validation: %s", err));
                crStopV;
            }
        }
        s->K = dh_find_K(ssh->kex_ctx, s->f);

        /* We assume everything from now on will be quick, and it might
         * involve user interaction. */
        set_busy_status(ssh->frontend, BUSY_NOT);

        hash_string(ssh->kex->hash, ssh->exhash, s->hostkeydata, s->hostkeylen);
        if (dh_is_gex(ssh->kex)) {
            if (!(ssh->remote_bugs & BUG_SSH2_OLDGEX))
                hash_uint32(ssh->kex->hash, ssh->exhash, DH_MIN_SIZE);
            hash_uint32(ssh->kex->hash, ssh->exhash, s->pbits);
            if (!(ssh->remote_bugs & BUG_SSH2_OLDGEX))
                hash_uint32(ssh->kex->hash, ssh->exhash, DH_MAX_SIZE);
            hash_mpint(ssh->kex->hash, ssh->exhash, s->p);
            hash_mpint(ssh->kex->hash, ssh->exhash, s->g);
        }
        hash_mpint(ssh->kex->hash, ssh->exhash, s->e);
        hash_mpint(ssh->kex->hash, ssh->exhash, s->f);

        dh_cleanup(ssh->kex_ctx);
        freebn(s->f);
        if (dh_is_gex(ssh->kex)) {
            freebn(s->g);
            freebn(s->p);
        }
    } else if (ssh->kex->main_type == KEXTYPE_ECDH) {

        logeventf(ssh, "Doing ECDH key exchange with curve %s and hash %s",
                  ssh_ecdhkex_curve_textname(ssh->kex),
                  ssh->kex->hash->text_name);
        ssh->pkt_kctx = SSH2_PKTCTX_ECDHKEX;

        s->eckey = ssh_ecdhkex_newkey(ssh->kex);
        if (!s->eckey) {
            bombout(("Unable to generate key for ECDH"));
            crStopV;
        }

        {
            char *publicPoint;
            int publicPointLength;
            publicPoint = ssh_ecdhkex_getpublic(s->eckey, &publicPointLength);
            if (!publicPoint) {
                ssh_ecdhkex_freekey(s->eckey);
                bombout(("Unable to encode public key for ECDH"));
                crStopV;
            }
            s->pktout = ssh2_pkt_init(SSH2_MSG_KEX_ECDH_INIT);
            ssh2_pkt_addstring_start(s->pktout);
            ssh2_pkt_addstring_data(s->pktout, publicPoint, publicPointLength);
            sfree(publicPoint);
        }

        ssh2_pkt_send_noqueue(ssh, s->pktout);

        crWaitUntilV(pktin);
        if (pktin->type != SSH2_MSG_KEX_ECDH_REPLY) {
            ssh_ecdhkex_freekey(s->eckey);
            bombout(("expected ECDH reply packet from server"));
            crStopV;
        }

        ssh_pkt_getstring(pktin, &s->hostkeydata, &s->hostkeylen);
        if (!s->hostkeydata) {
            bombout(("unable to parse ECDH reply packet"));
            crStopV;
        }
        hash_string(ssh->kex->hash, ssh->exhash, s->hostkeydata, s->hostkeylen);
        s->hkey = ssh->hostkey->newkey(ssh->hostkey,
                                       s->hostkeydata, s->hostkeylen);

        {
            char *publicPoint;
            int publicPointLength;
            publicPoint = ssh_ecdhkex_getpublic(s->eckey, &publicPointLength);
            if (!publicPoint) {
                ssh_ecdhkex_freekey(s->eckey);
                bombout(("Unable to encode public key for ECDH hash"));
                crStopV;
            }
            hash_string(ssh->kex->hash, ssh->exhash,
                        publicPoint, publicPointLength);
            sfree(publicPoint);
        }

        {
            char *keydata;
            int keylen;
            ssh_pkt_getstring(pktin, &keydata, &keylen);
            if (!keydata) {
                bombout(("unable to parse ECDH reply packet"));
                crStopV;
            }
            hash_string(ssh->kex->hash, ssh->exhash, keydata, keylen);
            s->K = ssh_ecdhkex_getkey(s->eckey, keydata, keylen);
            if (!s->K) {
                ssh_ecdhkex_freekey(s->eckey);
                bombout(("point received in ECDH was not valid"));
                crStopV;
            }
        }

        ssh_pkt_getstring(pktin, &s->sigdata, &s->siglen);
        if (!s->sigdata) {
            bombout(("unable to parse key exchange reply packet"));
            crStopV;
        }

        ssh_ecdhkex_freekey(s->eckey);
    } else {
        logeventf(ssh, "Doing RSA key exchange with hash %s",
                  ssh->kex->hash->text_name);
        ssh->pkt_kctx = SSH2_PKTCTX_RSAKEX;
        /*
         * RSA key exchange. First expect a KEXRSA_PUBKEY packet
         * from the server.
         */
        crWaitUntilV(pktin);
        if (pktin->type != SSH2_MSG_KEXRSA_PUBKEY) {
            bombout(("expected RSA public key packet from server"));
            crStopV;
        }

        ssh_pkt_getstring(pktin, &s->hostkeydata, &s->hostkeylen);
        if (!s->hostkeydata) {
            bombout(("unable to parse RSA public key packet"));
            crStopV;
        }
        hash_string(ssh->kex->hash, ssh->exhash,
                    s->hostkeydata, s->hostkeylen);
        s->hkey = ssh->hostkey->newkey(ssh->hostkey,
                                       s->hostkeydata, s->hostkeylen);

        {
            char *keydata;
            ssh_pkt_getstring(pktin, &keydata, &s->rsakeylen);
            if (!keydata) {
                bombout(("unable to parse RSA public key packet"));
                crStopV;
            }
            s->rsakeydata = snewn(s->rsakeylen, char);
            memcpy(s->rsakeydata, keydata, s->rsakeylen);
        }

        s->rsakey = ssh_rsakex_newkey(s->rsakeydata, s->rsakeylen);
        if (!s->rsakey) {
            sfree(s->rsakeydata);
            bombout(("unable to parse RSA public key from server"));
            crStopV;
        }

        hash_string(ssh->kex->hash, ssh->exhash, s->rsakeydata, s->rsakeylen);

        /*
         * Next, set up a shared secret K, of precisely KLEN -
         * 2*HLEN - 49 bits, where KLEN is the bit length of the
         * RSA key modulus and HLEN is the bit length of the hash
         * we're using.
         */
        {
            int klen = ssh_rsakex_klen(s->rsakey);
            int nbits = klen - (2*ssh->kex->hash->hlen*8 + 49);
            int i, byte = 0;
            unsigned char *kstr1, *kstr2, *outstr;
            int kstr1len, kstr2len, outstrlen;

            s->K = bn_power_2(nbits - 1);

            for (i = 0; i < nbits; i++) {
                if ((i & 7) == 0) {
                    byte = random_byte();
                }
                bignum_set_bit(s->K, i, (byte >> (i & 7)) & 1);
            }

            /*
             * Encode this as an mpint.
             */
            kstr1 = ssh2_mpint_fmt(s->K, &kstr1len);
            kstr2 = snewn(kstr2len = 4 + kstr1len, unsigned char);
            PUT_32BIT(kstr2, kstr1len);
            memcpy(kstr2 + 4, kstr1, kstr1len);

            /*
             * Encrypt it with the given RSA key.
             */
            outstrlen = (klen + 7) / 8;
            outstr = snewn(outstrlen, unsigned char);
            ssh_rsakex_encrypt(ssh->kex->hash, kstr2, kstr2len,
                               outstr, outstrlen, s->rsakey);

            /*
             * And send it off in a return packet.
             */
            s->pktout = ssh2_pkt_init(SSH2_MSG_KEXRSA_SECRET);
            ssh2_pkt_addstring_start(s->pktout);
            ssh2_pkt_addstring_data(s->pktout, (char *)outstr, outstrlen);
            ssh2_pkt_send_noqueue(ssh, s->pktout);

            hash_string(ssh->kex->hash, ssh->exhash, outstr, outstrlen);

            sfree(kstr2);
            sfree(kstr1);
            sfree(outstr);
        }

        ssh_rsakex_freekey(s->rsakey);

        crWaitUntilV(pktin);
        if (pktin->type != SSH2_MSG_KEXRSA_DONE) {
            sfree(s->rsakeydata);
            bombout(("expected signature packet from server"));
            crStopV;
        }

        ssh_pkt_getstring(pktin, &s->sigdata, &s->siglen);
        if (!s->sigdata) {
            bombout(("unable to parse signature packet"));
            crStopV;
        }

        sfree(s->rsakeydata);
    }

    hash_mpint(ssh->kex->hash, ssh->exhash, s->K);
    assert(ssh->kex->hash->hlen <= sizeof(s->exchange_hash));
    ssh->kex->hash->final(ssh->exhash, s->exchange_hash);

    ssh->kex_ctx = NULL;

#if 0
    debug(("Exchange hash is:\n"));
    dmemdump(s->exchange_hash, ssh->kex->hash->hlen);
#endif

    if (!s->hkey) {
        bombout(("Server's host key is invalid"));
        crStopV;
    }

    if (!ssh->hostkey->verifysig(s->hkey, s->sigdata, s->siglen,
                                 (char *)s->exchange_hash,
                                 ssh->kex->hash->hlen)) {
#ifndef FUZZING
        bombout(("Server's host key did not match the signature supplied"));
        crStopV;
#endif
    }

    s->keystr = ssh->hostkey->fmtkey(s->hkey);
    if (!s->got_session_id) {
        /*
         * Make a note of any other host key formats that are available.
         */
        {
            int i, j, nkeys = 0;
            char *list = NULL;
            for (i = 0; i < lenof(hostkey_algs); i++) {
                if (hostkey_algs[i].alg == ssh->hostkey)
                    continue;

                for (j = 0; j < ssh->n_uncert_hostkeys; j++)
                    if (ssh->uncert_hostkeys[j] == i)
                        break;

                if (j < ssh->n_uncert_hostkeys) {
                    char *newlist;
                    if (list)
                        newlist = dupprintf("%s/%s", list,
                                            hostkey_algs[i].alg->name);
                    else
                        newlist = dupprintf("%s", hostkey_algs[i].alg->name);
                    sfree(list);
                    list = newlist;
                    nkeys++;
                }
            }
            if (list) {
                logeventf(ssh,
                          "Server also has %s host key%s, but we "
                          "don't know %s", list,
                          nkeys > 1 ? "s" : "",
                          nkeys > 1 ? "any of them" : "it");
                sfree(list);
            }
        }

        /*
         * Authenticate remote host: verify host key. (We've already
         * checked the signature of the exchange hash.)
         */
        s->fingerprint = ssh2_fingerprint(ssh->hostkey, s->hkey);
        logevent("Host key fingerprint is:");
        logevent(s->fingerprint);
        /* First check against manually configured host keys. */
        s->dlgret = verify_ssh_manual_host_key(ssh, s->fingerprint,
                                               ssh->hostkey, s->hkey);
        if (s->dlgret == 0) {          /* did not match */
            bombout(("Host key did not appear in manually configured list"));
            crStopV;
        } else if (s->dlgret < 0) { /* none configured; use standard handling */
            ssh_set_frozen(ssh, 1);
            s->dlgret = verify_ssh_host_key(ssh->frontend,
                                            ssh->savedhost, ssh->savedport,
                                            ssh->hostkey->keytype, s->keystr,
                                            s->fingerprint,
                                            ssh_dialog_callback, ssh);
#ifdef FUZZING
            s->dlgret = 1;
#endif
            if (s->dlgret < 0) {
                do {
                    crReturnV;
                    if (pktin) {
                        bombout(("Unexpected data from server while waiting"
                                 " for user host key response"));
                        crStopV;
                    }
                } while (pktin || inlen > 0);
                s->dlgret = ssh->user_response;
            }
            ssh_set_frozen(ssh, 0);
            if (s->dlgret == 0) {
                ssh_disconnect(ssh, "Aborted at host key verification", NULL,
                               0, TRUE);
                crStopV;
            }
        }
        sfree(s->fingerprint);
        /*
         * Save this host key, to check against the one presented in
         * subsequent rekeys.
         */
        ssh->hostkey_str = s->keystr;
    } else if (ssh->cross_certifying) {
        s->fingerprint = ssh2_fingerprint(ssh->hostkey, s->hkey);
        logevent("Storing additional host key for this host:");
        logevent(s->fingerprint);
        store_host_key(ssh->savedhost, ssh->savedport,
                       ssh->hostkey->keytype, s->keystr);
        ssh->cross_certifying = FALSE;
        /*
         * Don't forget to store the new key as the one we'll be
         * re-checking in future normal rekeys.
         */
        ssh->hostkey_str = s->keystr;
    } else {
        /*
         * In a rekey, we never present an interactive host key
         * verification request to the user. Instead, we simply
         * enforce that the key we're seeing this time is identical to
         * the one we saw before.
         */
        if (strcmp(ssh->hostkey_str, s->keystr)) {
#ifndef FUZZING
            bombout(("Host key was different in repeat key exchange"));
            crStopV;
#endif
        }
        sfree(s->keystr);
    }
    ssh->hostkey->freekey(s->hkey);

    /*
     * The exchange hash from the very first key exchange is also
     * the session id, used in session key construction and
     * authentication.
     */
    if (!s->got_session_id) {
        assert(sizeof(s->exchange_hash) <= sizeof(ssh->v2_session_id));
        memcpy(ssh->v2_session_id, s->exchange_hash,
               sizeof(s->exchange_hash));
        ssh->v2_session_id_len = ssh->kex->hash->hlen;
        assert(ssh->v2_session_id_len <= sizeof(ssh->v2_session_id));
        s->got_session_id = TRUE;
    }

    /*
     * Send SSH2_MSG_NEWKEYS.
     */
    s->pktout = ssh2_pkt_init(SSH2_MSG_NEWKEYS);
    ssh2_pkt_send_noqueue(ssh, s->pktout);
    ssh->outgoing_data_size = 0;       /* start counting from here */

    /*
     * We've sent client NEWKEYS, so create and initialise
     * client-to-server session keys.
     */
    if (ssh->cs_cipher_ctx)
        ssh->cscipher->free_context(ssh->cs_cipher_ctx);
    ssh->cscipher = s->cscipher_tobe;
    if (ssh->cscipher) ssh->cs_cipher_ctx = ssh->cscipher->make_context();

    if (ssh->cs_mac_ctx)
        ssh->csmac->free_context(ssh->cs_mac_ctx);
    ssh->csmac = s->csmac_tobe;
    ssh->csmac_etm = s->csmac_etm_tobe;
    if (ssh->csmac)
        ssh->cs_mac_ctx = ssh->csmac->make_context(ssh->cs_cipher_ctx);

    if (ssh->cs_comp_ctx)
        ssh->cscomp->compress_cleanup(ssh->cs_comp_ctx);
    ssh->cscomp = s->cscomp_tobe;
    ssh->cs_comp_ctx = ssh->cscomp->compress_init();

    /*
     * Set IVs on client-to-server keys. Here we use the exchange
     * hash from the _first_ key exchange.
     */
    if (ssh->cscipher) {
        unsigned char *key;

        key = ssh2_mkkey(ssh, s->K, s->exchange_hash, 'C',
                         ssh->cscipher->padded_keybytes);
        ssh->cscipher->setkey(ssh->cs_cipher_ctx, key);
        smemclr(key, ssh->cscipher->padded_keybytes);
        sfree(key);

        key = ssh2_mkkey(ssh, s->K, s->exchange_hash, 'A',
                         ssh->cscipher->blksize);
        ssh->cscipher->setiv(ssh->cs_cipher_ctx, key);
        smemclr(key, ssh->cscipher->blksize);
        sfree(key);
    }
    if (ssh->csmac) {
        unsigned char *key;

        key = ssh2_mkkey(ssh, s->K, s->exchange_hash, 'E',
                         ssh->csmac->keylen);
        ssh->csmac->setkey(ssh->cs_mac_ctx, key);
        smemclr(key, ssh->csmac->keylen);
        sfree(key);
    }

    if (ssh->cscipher)
        logeventf(ssh, "Initialised %.200s client->server encryption",
                  ssh->cscipher->text_name);
    if (ssh->csmac)
        logeventf(ssh, "Initialised %.200s client->server MAC algorithm%s%s",
                  ssh->csmac->text_name,
                  ssh->csmac_etm ? " (in ETM mode)" : "",
                  ssh->cscipher->required_mac ? " (required by cipher)" : "");
    if (ssh->cscomp->text_name)
        logeventf(ssh, "Initialised %s compression",
                  ssh->cscomp->text_name);

    /*
     * Now our end of the key exchange is complete, we can send all
     * our queued higher-layer packets.
     */
    ssh->queueing = FALSE;
    ssh2_pkt_queuesend(ssh);

    /*
     * Expect SSH2_MSG_NEWKEYS from server.
     */
    crWaitUntilV(pktin);
    if (pktin->type != SSH2_MSG_NEWKEYS) {
        bombout(("expected new-keys packet from server"));
        crStopV;
    }
    ssh->incoming_data_size = 0;       /* start counting from here */

    /*
     * We've seen server NEWKEYS, so create and initialise
     * server-to-client session keys.
     */
    if (ssh->sc_cipher_ctx)
        ssh->sccipher->free_context(ssh->sc_cipher_ctx);
    if (s->sccipher_tobe) {
        ssh->sccipher = s->sccipher_tobe;
        ssh->sc_cipher_ctx = ssh->sccipher->make_context();
    }

    if (ssh->sc_mac_ctx)
        ssh->scmac->free_context(ssh->sc_mac_ctx);
    if (s->scmac_tobe) {
        ssh->scmac = s->scmac_tobe;
        ssh->scmac_etm = s->scmac_etm_tobe;
        ssh->sc_mac_ctx = ssh->scmac->make_context(ssh->sc_cipher_ctx);
    }

    if (ssh->sc_comp_ctx)
        ssh->sccomp->decompress_cleanup(ssh->sc_comp_ctx);
    ssh->sccomp = s->sccomp_tobe;
    ssh->sc_comp_ctx = ssh->sccomp->decompress_init();

    /*
     * Set IVs on server-to-client keys. Here we use the exchange
     * hash from the _first_ key exchange.
     */
    if (ssh->sccipher) {
        unsigned char *key;

        key = ssh2_mkkey(ssh, s->K, s->exchange_hash, 'D',
                         ssh->sccipher->padded_keybytes);
        ssh->sccipher->setkey(ssh->sc_cipher_ctx, key);
        smemclr(key, ssh->sccipher->padded_keybytes);
        sfree(key);

        key = ssh2_mkkey(ssh, s->K, s->exchange_hash, 'B',
                         ssh->sccipher->blksize);
        ssh->sccipher->setiv(ssh->sc_cipher_ctx, key);
        smemclr(key, ssh->sccipher->blksize);
        sfree(key);
    }
    if (ssh->scmac) {
        unsigned char *key;

        key = ssh2_mkkey(ssh, s->K, s->exchange_hash, 'F',
                         ssh->scmac->keylen);
        ssh->scmac->setkey(ssh->sc_mac_ctx, key);
        smemclr(key, ssh->scmac->keylen);
        sfree(key);
    }
    if (ssh->sccipher)
        logeventf(ssh, "Initialised %.200s server->client encryption",
                  ssh->sccipher->text_name);
    if (ssh->scmac)
        logeventf(ssh, "Initialised %.200s server->client MAC algorithm%s%s",
                  ssh->scmac->text_name,
                  ssh->scmac_etm ? " (in ETM mode)" : "",
                  ssh->sccipher->required_mac ? " (required by cipher)" : "");
    if (ssh->sccomp->text_name)
        logeventf(ssh, "Initialised %s decompression",
                  ssh->sccomp->text_name);

    /*
     * Free shared secret.
     */
    freebn(s->K);

    /*
     * Update the specials menu to list the remaining uncertified host
     * keys.
     */
    update_specials_menu(ssh->frontend);

    /*
     * Key exchange is over. Loop straight back round if we have a
     * deferred rekey reason.
     */
    if (ssh->deferred_rekey_reason) {
        logevent(ssh->deferred_rekey_reason);
        pktin = NULL;
        ssh->deferred_rekey_reason = NULL;
        goto begin_key_exchange;
    }

    /*
     * Otherwise, schedule a timer for our next rekey.
     */
    ssh->kex_in_progress = FALSE;
    ssh->last_rekey = GETTICKCOUNT();
    if (conf_get_int(ssh->conf, CONF_ssh_rekey_time) != 0)
        ssh->next_rekey = schedule_timer(conf_get_int(ssh->conf, CONF_ssh_rekey_time)*60*TICKSPERSEC,
                                         ssh2_timer, ssh);

    /*
     * Now we're encrypting. Begin returning 1 to the protocol main
     * function so that other things can run on top of the
     * transport. If we ever see a KEXINIT, we must go back to the
     * start.
     * 
     * We _also_ go back to the start if we see pktin==NULL and
     * inlen negative, because this is a special signal meaning
     * `initiate client-driven rekey', and `in' contains a message
     * giving the reason for the rekey.
     *
     * inlen==-1 means always initiate a rekey;
     * inlen==-2 means that userauth has completed successfully and
     *   we should consider rekeying (for delayed compression).
     */
    while (!((pktin && pktin->type == SSH2_MSG_KEXINIT) ||
             (!pktin && inlen < 0))) {
        wait_for_rekey:
        if (!ssh->protocol_initial_phase_done) {
            ssh->protocol_initial_phase_done = TRUE;
            /*
             * Allow authconn to initialise itself.
             */
            do_ssh2_authconn(ssh, NULL, 0, NULL);
        }
        crReturnV;
    }
    if (pktin) {
        logevent("Server initiated key re-exchange");
    } else {
        if (inlen == -2) {
            /* 
             * authconn has seen a USERAUTH_SUCCEEDED. Time to enable
             * delayed compression, if it's available.
             *
             * draft-miller-secsh-compression-delayed-00 says that you
             * negotiate delayed compression in the first key exchange, and
             * both sides start compressing when the server has sent
             * USERAUTH_SUCCESS. This has a race condition -- the server
             * can't know when the client has seen it, and thus which incoming
             * packets it should treat as compressed.
             *
             * Instead, we do the initial key exchange without offering the
             * delayed methods, but note if the server offers them; when we
             * get here, if a delayed method was available that was higher
             * on our list than what we got, we initiate a rekey in which we
             * _do_ list the delayed methods (and hopefully get it as a
             * result). Subsequent rekeys will do the same.
             */
            assert(!s->userauth_succeeded); /* should only happen once */
            s->userauth_succeeded = TRUE;
            if (!s->pending_compression)
                /* Can't see any point rekeying. */
                goto wait_for_rekey;       /* this is utterly horrid */
            /* else fall through to rekey... */
            s->pending_compression = FALSE;
        }
        /*
         * Now we've decided to rekey.
         *
         * Special case: if the server bug is set that doesn't
         * allow rekeying, we give a different log message and
         * continue waiting. (If such a server _initiates_ a rekey,
         * we process it anyway!)
         */
        if ((ssh->remote_bugs & BUG_SSH2_REKEY)) {
            logeventf(ssh, "Server bug prevents key re-exchange (%s)",
                      (char *)in);
            /* Reset the counters, so that at least this message doesn't
             * hit the event log _too_ often. */
            ssh->outgoing_data_size = 0;
            ssh->incoming_data_size = 0;
            if (conf_get_int(ssh->conf, CONF_ssh_rekey_time) != 0) {
                ssh->next_rekey =
                    schedule_timer(conf_get_int(ssh->conf, CONF_ssh_rekey_time)*60*TICKSPERSEC,
                                   ssh2_timer, ssh);
            }
            goto wait_for_rekey;       /* this is still utterly horrid */
        } else {
            logeventf(ssh, "Initiating key re-exchange (%s)", (char *)in);
        }
    }
    goto begin_key_exchange;

    crFinishV;
}

/*
 * Send data on an SSH channel.  In SSH-2, this involves buffering it
 * first.
 */
static int ssh_send_channel_data(struct ssh_channel *c, const char *buf,
                                   int len)
{
    if (c->ssh->version == 2) {
        bufchain_add(&c->v.v2.outbuffer, buf, len);
        return ssh2_try_send(c);
    } else {
        send_packet(c->ssh, SSH1_MSG_CHANNEL_DATA,
                    PKT_INT, c->remoteid,
                    PKT_INT, len,
                    PKT_DATA, buf, len,
                    PKT_END);
        /*
         * In SSH-1 we can return 0 here - implying that channels are
         * never individually throttled - because the only
         * circumstance that can cause throttling will be the whole
         * SSH connection backing up, in which case _everything_ will
         * be throttled as a whole.
         */
        return 0;
    }
}

/*
 * Attempt to send data on an SSH-2 channel.
 */
static int ssh2_try_send(struct ssh_channel *c)
{
    Ssh ssh = c->ssh;
    struct Packet *pktout;
    int ret;

    while (c->v.v2.remwindow > 0 && bufchain_size(&c->v.v2.outbuffer) > 0) {
        int len;
        void *data;
        bufchain_prefix(&c->v.v2.outbuffer, &data, &len);
        if ((unsigned)len > c->v.v2.remwindow)
            len = c->v.v2.remwindow;
        if ((unsigned)len > c->v.v2.remmaxpkt)
            len = c->v.v2.remmaxpkt;
        pktout = ssh2_pkt_init(SSH2_MSG_CHANNEL_DATA);
        ssh2_pkt_adduint32(pktout, c->remoteid);
        ssh2_pkt_addstring_start(pktout);
        ssh2_pkt_addstring_data(pktout, data, len);
        ssh2_pkt_send(ssh, pktout);
        bufchain_consume(&c->v.v2.outbuffer, len);
        c->v.v2.remwindow -= len;
    }

    /*
     * After having sent as much data as we can, return the amount
     * still buffered.
     */
    ret = bufchain_size(&c->v.v2.outbuffer);

    /*
     * And if there's no data pending but we need to send an EOF, send
     * it.
     */
    if (!ret && c->pending_eof)
        ssh_channel_try_eof(c);

    return ret;
}

static void ssh2_try_send_and_unthrottle(Ssh ssh, struct ssh_channel *c)
{
    int bufsize;
    if (c->closes & CLOSES_SENT_EOF)
        return;                   /* don't send on channels we've EOFed */
    bufsize = ssh2_try_send(c);
    if (bufsize == 0) {
        switch (c->type) {
          case CHAN_MAINSESSION:
            /* stdin need not receive an unthrottle
             * notification since it will be polled */
            break;
          case CHAN_X11:
            x11_unthrottle(c->u.x11.xconn);
            break;
          case CHAN_AGENT:
            /* agent sockets are request/response and need no
             * buffer management */
            break;
          case CHAN_SOCKDATA:
            pfd_unthrottle(c->u.pfd.pf);
            break;
        }
    }
}

static int ssh_is_simple(Ssh ssh)
{
    /*
     * We use the 'simple' variant of the SSH protocol if we're asked
     * to, except not if we're also doing connection-sharing (either
     * tunnelling our packets over an upstream or expecting to be
     * tunnelled over ourselves), since then the assumption that we
     * have only one channel to worry about is not true after all.
     */
    return (conf_get_int(ssh->conf, CONF_ssh_simple) &&
            !ssh->bare_connection && !ssh->connshare);
}

/*
 * Set up most of a new ssh_channel.
 */
static void ssh_channel_init(struct ssh_channel *c)
{
    Ssh ssh = c->ssh;
    c->localid = alloc_channel_id(ssh);
    c->closes = 0;
    c->pending_eof = FALSE;
    c->throttling_conn = FALSE;
    if (ssh->version == 2) {
        c->v.v2.locwindow = c->v.v2.locmaxwin = c->v.v2.remlocwin =
            ssh_is_simple(ssh) ? OUR_V2_BIGWIN : OUR_V2_WINSIZE;
        c->v.v2.chanreq_head = NULL;
        c->v.v2.throttle_state = UNTHROTTLED;
        bufchain_init(&c->v.v2.outbuffer);
    }
    add234(ssh->channels, c);
}

/*
 * Construct the common parts of a CHANNEL_OPEN.
 */
static struct Packet *ssh2_chanopen_init(struct ssh_channel *c,
                                         const char *type)
{
    struct Packet *pktout;

    pktout = ssh2_pkt_init(SSH2_MSG_CHANNEL_OPEN);
    ssh2_pkt_addstring(pktout, type);
    ssh2_pkt_adduint32(pktout, c->localid);
    ssh2_pkt_adduint32(pktout, c->v.v2.locwindow);/* our window size */
    ssh2_pkt_adduint32(pktout, OUR_V2_MAXPKT);      /* our max pkt size */
    return pktout;
}

/*
 * CHANNEL_FAILURE doesn't come with any indication of what message
 * caused it, so we have to keep track of the outstanding
 * CHANNEL_REQUESTs ourselves.
 */
static void ssh2_queue_chanreq_handler(struct ssh_channel *c,
                                       cchandler_fn_t handler, void *ctx)
{
    struct outstanding_channel_request *ocr =
        snew(struct outstanding_channel_request);

    assert(!(c->closes & (CLOSES_SENT_CLOSE | CLOSES_RCVD_CLOSE)));
    ocr->handler = handler;
    ocr->ctx = ctx;
    ocr->next = NULL;
    if (!c->v.v2.chanreq_head)
        c->v.v2.chanreq_head = ocr;
    else
        c->v.v2.chanreq_tail->next = ocr;
    c->v.v2.chanreq_tail = ocr;
}

/*
 * Construct the common parts of a CHANNEL_REQUEST.  If handler is not
 * NULL then a reply will be requested and the handler will be called
 * when it arrives.  The returned packet is ready to have any
 * request-specific data added and be sent.  Note that if a handler is
 * provided, it's essential that the request actually be sent.
 *
 * The handler will usually be passed the response packet in pktin. If
 * pktin is NULL, this means that no reply will ever be forthcoming
 * (e.g. because the entire connection is being destroyed, or because
 * the server initiated channel closure before we saw the response)
 * and the handler should free any storage it's holding.
 */
static struct Packet *ssh2_chanreq_init(struct ssh_channel *c,
                                        const char *type,
                                        cchandler_fn_t handler, void *ctx)
{
    struct Packet *pktout;

    assert(!(c->closes & (CLOSES_SENT_CLOSE | CLOSES_RCVD_CLOSE)));
    pktout = ssh2_pkt_init(SSH2_MSG_CHANNEL_REQUEST);
    ssh2_pkt_adduint32(pktout, c->remoteid);
    ssh2_pkt_addstring(pktout, type);
    ssh2_pkt_addbool(pktout, handler != NULL);
    if (handler != NULL)
        ssh2_queue_chanreq_handler(c, handler, ctx);
    return pktout;
}

static void ssh_channel_unthrottle(struct ssh_channel *c, int bufsize)
{
    Ssh ssh = c->ssh;
    int buflimit;

    if (ssh->version == 1) {
        buflimit = SSH1_BUFFER_LIMIT;
    } else {
        if (ssh_is_simple(ssh))
            buflimit = 0;
        else
            buflimit = c->v.v2.locmaxwin;
        if (bufsize < buflimit)
            ssh2_set_window(c, buflimit - bufsize);
    }
    if (c->throttling_conn && bufsize <= buflimit) {
        c->throttling_conn = 0;
        ssh_throttle_conn(ssh, -1);
    }
}

/*
 * Potentially enlarge the window on an SSH-2 channel.
 */
static void ssh2_handle_winadj_response(struct ssh_channel *, struct Packet *,
                                        void *);
static void ssh2_set_window(struct ssh_channel *c, int newwin)
{
    Ssh ssh = c->ssh;

    /*
     * Never send WINDOW_ADJUST for a channel that the remote side has
     * already sent EOF on; there's no point, since it won't be
     * sending any more data anyway. Ditto if _we've_ already sent
     * CLOSE.
     */
    if (c->closes & (CLOSES_RCVD_EOF | CLOSES_SENT_CLOSE))
        return;

    /*
     * Also, never widen the window for an X11 channel when we're
     * still waiting to see its initial auth and may yet hand it off
     * to a downstream.
     */
    if (c->type == CHAN_X11 && c->u.x11.initial)
        return;

    /*
     * If the remote end has a habit of ignoring maxpkt, limit the
     * window so that it has no choice (assuming it doesn't ignore the
     * window as well).
     */
    if ((ssh->remote_bugs & BUG_SSH2_MAXPKT) && newwin > OUR_V2_MAXPKT)
        newwin = OUR_V2_MAXPKT;

    /*
     * Only send a WINDOW_ADJUST if there's significantly more window
     * available than the other end thinks there is.  This saves us
     * sending a WINDOW_ADJUST for every character in a shell session.
     *
     * "Significant" is arbitrarily defined as half the window size.
     */
    if (newwin / 2 >= c->v.v2.locwindow) {
        struct Packet *pktout;
        unsigned *up;

        /*
         * In order to keep track of how much window the client
         * actually has available, we'd like it to acknowledge each
         * WINDOW_ADJUST.  We can't do that directly, so we accompany
         * it with a CHANNEL_REQUEST that has to be acknowledged.
         *
         * This is only necessary if we're opening the window wide.
         * If we're not, then throughput is being constrained by
         * something other than the maximum window size anyway.
         */
        if (newwin == c->v.v2.locmaxwin &&
            !(ssh->remote_bugs & BUG_CHOKES_ON_WINADJ)) {
            up = snew(unsigned);
            *up = newwin - c->v.v2.locwindow;
            pktout = ssh2_chanreq_init(c, "winadj@putty.projects.tartarus.org",
                                       ssh2_handle_winadj_response, up);
            ssh2_pkt_send(ssh, pktout);

            if (c->v.v2.throttle_state != UNTHROTTLED)
                c->v.v2.throttle_state = UNTHROTTLING;
        } else {
            /* Pretend the WINDOW_ADJUST was acked immediately. */
            c->v.v2.remlocwin = newwin;
            c->v.v2.throttle_state = THROTTLED;
        }
        pktout = ssh2_pkt_init(SSH2_MSG_CHANNEL_WINDOW_ADJUST);
        ssh2_pkt_adduint32(pktout, c->remoteid);
        ssh2_pkt_adduint32(pktout, newwin - c->v.v2.locwindow);
        ssh2_pkt_send(ssh, pktout);
        c->v.v2.locwindow = newwin;
    }
}

/*
 * Find the channel associated with a message.  If there's no channel,
 * or it's not properly open, make a noise about it and return NULL.
 */
static struct ssh_channel *ssh_channel_msg(Ssh ssh, struct Packet *pktin)
{
    unsigned localid = ssh_pkt_getuint32(pktin);
    struct ssh_channel *c;
    int halfopen_ok;

    /* Is this message OK on a half-open connection? */
    if (ssh->version == 1)
        halfopen_ok = (pktin->type == SSH1_MSG_CHANNEL_OPEN_CONFIRMATION ||
                       pktin->type == SSH1_MSG_CHANNEL_OPEN_FAILURE);
    else
        halfopen_ok = (pktin->type == SSH2_MSG_CHANNEL_OPEN_CONFIRMATION ||
                       pktin->type == SSH2_MSG_CHANNEL_OPEN_FAILURE);
    c = find234(ssh->channels, &localid, ssh_channelfind);
    if (!c || (c->type != CHAN_SHARING && c->halfopen && !halfopen_ok)) {
        char *buf = dupprintf("Received %s for %s channel %u",
                              ssh_pkt_type(ssh, pktin->type),
                              c ? "half-open" : "nonexistent", localid);
        ssh_disconnect(ssh, NULL, buf, SSH2_DISCONNECT_PROTOCOL_ERROR, FALSE);
        sfree(buf);
        return NULL;
    }
    return c;
}

static void ssh2_handle_winadj_response(struct ssh_channel *c,
                                        struct Packet *pktin, void *ctx)
{
    unsigned *sizep = ctx;

    /*
     * Winadj responses should always be failures. However, at least
     * one server ("boks_sshd") is known to return SUCCESS for channel
     * requests it's never heard of, such as "winadj@putty". Raised
     * with foxt.com as bug 090916-090424, but for the sake of a quiet
     * life, we don't worry about what kind of response we got.
     */

    c->v.v2.remlocwin += *sizep;
    sfree(sizep);
    /*
     * winadj messages are only sent when the window is fully open, so
     * if we get an ack of one, we know any pending unthrottle is
     * complete.
     */
    if (c->v.v2.throttle_state == UNTHROTTLING)
        c->v.v2.throttle_state = UNTHROTTLED;
}

static void ssh2_msg_channel_response(Ssh ssh, struct Packet *pktin)
{
    struct ssh_channel *c = ssh_channel_msg(ssh, pktin);
    struct outstanding_channel_request *ocr;

    if (!c) return;
    if (c->type == CHAN_SHARING) {
        share_got_pkt_from_server(c->u.sharing.ctx, pktin->type,
                                  pktin->body, pktin->length);
        return;
    }
    ocr = c->v.v2.chanreq_head;
    if (!ocr) {
        ssh2_msg_unexpected(ssh, pktin);
        return;
    }
    ocr->handler(c, pktin, ocr->ctx);
    c->v.v2.chanreq_head = ocr->next;
    sfree(ocr);
    /*
     * We may now initiate channel-closing procedures, if that
     * CHANNEL_REQUEST was the last thing outstanding before we send
     * CHANNEL_CLOSE.
     */
    ssh2_channel_check_close(c);
}

static void ssh2_msg_channel_window_adjust(Ssh ssh, struct Packet *pktin)
{
    struct ssh_channel *c;
    c = ssh_channel_msg(ssh, pktin);
    if (!c)
        return;
    if (c->type == CHAN_SHARING) {
        share_got_pkt_from_server(c->u.sharing.ctx, pktin->type,
                                  pktin->body, pktin->length);
        return;
    }
    if (!(c->closes & CLOSES_SENT_EOF)) {
        c->v.v2.remwindow += ssh_pkt_getuint32(pktin);
        ssh2_try_send_and_unthrottle(ssh, c);
    }
}

static void ssh2_msg_channel_data(Ssh ssh, struct Packet *pktin)
{
    char *data;
    int length;
    struct ssh_channel *c;
    c = ssh_channel_msg(ssh, pktin);
    if (!c)
        return;
    if (c->type == CHAN_SHARING) {
        share_got_pkt_from_server(c->u.sharing.ctx, pktin->type,
                                  pktin->body, pktin->length);
        return;
    }
    if (pktin->type == SSH2_MSG_CHANNEL_EXTENDED_DATA &&
        ssh_pkt_getuint32(pktin) != SSH2_EXTENDED_DATA_STDERR)
        return;                        /* extended but not stderr */
    ssh_pkt_getstring(pktin, &data, &length);
    if (data) {
        int bufsize;
        c->v.v2.locwindow -= length;
        c->v.v2.remlocwin -= length;
        bufsize = ssh_channel_data(c, pktin->type ==
                                   SSH2_MSG_CHANNEL_EXTENDED_DATA,
                                   data, length);
        /*
         * If it looks like the remote end hit the end of its window,
         * and we didn't want it to do that, think about using a
         * larger window.
         */
        if (c->v.v2.remlocwin <= 0 && c->v.v2.throttle_state == UNTHROTTLED &&
            c->v.v2.locmaxwin < 0x40000000)
            c->v.v2.locmaxwin += OUR_V2_WINSIZE;
        /*
         * If we are not buffering too much data,
         * enlarge the window again at the remote side.
         * If we are buffering too much, we may still
         * need to adjust the window if the server's
         * sent excess data.
         */
        if (bufsize < c->v.v2.locmaxwin)
            ssh2_set_window(c, c->v.v2.locmaxwin - bufsize);
        /*
         * If we're either buffering way too much data, or if we're
         * buffering anything at all and we're in "simple" mode,
         * throttle the whole channel.
         */
        if ((bufsize > c->v.v2.locmaxwin || (ssh_is_simple(ssh) && bufsize>0))
            && !c->throttling_conn) {
            c->throttling_conn = 1;
            ssh_throttle_conn(ssh, +1);
        }
    }
}

static void ssh_check_termination(Ssh ssh)
{
    if (ssh->version == 2 &&
        !conf_get_int(ssh->conf, CONF_ssh_no_shell) &&
        (ssh->channels && count234(ssh->channels) == 0) &&
        !(ssh->connshare && share_ndownstreams(ssh->connshare) > 0)) {
        /*
         * We used to send SSH_MSG_DISCONNECT here, because I'd
         * believed that _every_ conforming SSH-2 connection had to
         * end with a disconnect being sent by at least one side;
         * apparently I was wrong and it's perfectly OK to
         * unceremoniously slam the connection shut when you're done,
         * and indeed OpenSSH feels this is more polite than sending a
         * DISCONNECT. So now we don't.
         */
        ssh_disconnect(ssh, "All channels closed", NULL, 0, TRUE);
    }
}

void ssh_sharing_downstream_connected(Ssh ssh, unsigned id,
                                      const char *peerinfo)
{
    if (peerinfo)
        logeventf(ssh, "Connection sharing downstream #%u connected from %s",
                  id, peerinfo);
    else
        logeventf(ssh, "Connection sharing downstream #%u connected", id);
}

void ssh_sharing_downstream_disconnected(Ssh ssh, unsigned id)
{
    logeventf(ssh, "Connection sharing downstream #%u disconnected", id);
    ssh_check_termination(ssh);
}

void ssh_sharing_logf(Ssh ssh, unsigned id, const char *logfmt, ...)
{
    va_list ap;
    char *buf;

    va_start(ap, logfmt);
    buf = dupvprintf(logfmt, ap);
    va_end(ap);
    if (id)
        logeventf(ssh, "Connection sharing downstream #%u: %s", id, buf);
    else
        logeventf(ssh, "Connection sharing: %s", buf);
    sfree(buf);
}

static void ssh_channel_destroy(struct ssh_channel *c)
{
    Ssh ssh = c->ssh;

    switch (c->type) {
      case CHAN_MAINSESSION:
        ssh->mainchan = NULL;
        update_specials_menu(ssh->frontend);
        break;
      case CHAN_X11:
        if (c->u.x11.xconn != NULL)
            x11_close(c->u.x11.xconn);
        logevent("Forwarded X11 connection terminated");
        break;
      case CHAN_AGENT:
        sfree(c->u.a.message);
        break;
      case CHAN_SOCKDATA:
        if (c->u.pfd.pf != NULL)
            pfd_close(c->u.pfd.pf);
        logevent("Forwarded port closed");
        break;
    }

    del234(ssh->channels, c);
    if (ssh->version == 2) {
        bufchain_clear(&c->v.v2.outbuffer);
        assert(c->v.v2.chanreq_head == NULL);
    }
    sfree(c);

    /*
     * If that was the last channel left open, we might need to
     * terminate.
     */
    ssh_check_termination(ssh);
}

static void ssh2_channel_check_close(struct ssh_channel *c)
{
    Ssh ssh = c->ssh;
    struct Packet *pktout;

    assert(ssh->version == 2);
    if (c->halfopen) {
        /*
         * If we've sent out our own CHANNEL_OPEN but not yet seen
         * either OPEN_CONFIRMATION or OPEN_FAILURE in response, then
         * it's too early to be sending close messages of any kind.
         */
        return;
    }

    if ((!((CLOSES_SENT_EOF | CLOSES_RCVD_EOF) & ~c->closes) ||
         c->type == CHAN_ZOMBIE) &&
        !c->v.v2.chanreq_head &&
        !(c->closes & CLOSES_SENT_CLOSE)) {
        /*
         * We have both sent and received EOF (or the channel is a
         * zombie), and we have no outstanding channel requests, which
         * means the channel is in final wind-up. But we haven't sent
         * CLOSE, so let's do so now.
         */
        pktout = ssh2_pkt_init(SSH2_MSG_CHANNEL_CLOSE);
        ssh2_pkt_adduint32(pktout, c->remoteid);
        ssh2_pkt_send(ssh, pktout);
        c->closes |= CLOSES_SENT_EOF | CLOSES_SENT_CLOSE;
    }

    if (!((CLOSES_SENT_CLOSE | CLOSES_RCVD_CLOSE) & ~c->closes)) {
        assert(c->v.v2.chanreq_head == NULL);
        /*
         * We have both sent and received CLOSE, which means we're
         * completely done with the channel.
         */
        ssh_channel_destroy(c);
    }
}

static void ssh2_channel_got_eof(struct ssh_channel *c)
{
    if (c->closes & CLOSES_RCVD_EOF)
        return;                        /* already seen EOF */
    c->closes |= CLOSES_RCVD_EOF;

    if (c->type == CHAN_X11) {
        x11_send_eof(c->u.x11.xconn);
    } else if (c->type == CHAN_AGENT) {
        if (c->u.a.outstanding_requests == 0) {
            /* Manufacture an outgoing EOF in response to the incoming one. */
            sshfwd_write_eof(c);
        }
    } else if (c->type == CHAN_SOCKDATA) {
        pfd_send_eof(c->u.pfd.pf);
    } else if (c->type == CHAN_MAINSESSION) {
        Ssh ssh = c->ssh;

        if (!ssh->sent_console_eof &&
            (from_backend_eof(ssh->frontend) || ssh->got_pty)) {
            /*
             * Either from_backend_eof told us that the front end
             * wants us to close the outgoing side of the connection
             * as soon as we see EOF from the far end, or else we've
             * unilaterally decided to do that because we've allocated
             * a remote pty and hence EOF isn't a particularly
             * meaningful concept.
             */
            sshfwd_write_eof(c);
        }
        ssh->sent_console_eof = TRUE;
    }

    ssh2_channel_check_close(c);
}

static void ssh2_msg_channel_eof(Ssh ssh, struct Packet *pktin)
{
    struct ssh_channel *c;

    c = ssh_channel_msg(ssh, pktin);
    if (!c)
        return;
    if (c->type == CHAN_SHARING) {
        share_got_pkt_from_server(c->u.sharing.ctx, pktin->type,
                                  pktin->body, pktin->length);
        return;
    }
    ssh2_channel_got_eof(c);
}

static void ssh2_msg_channel_close(Ssh ssh, struct Packet *pktin)
{
    struct ssh_channel *c;

    c = ssh_channel_msg(ssh, pktin);
    if (!c)
        return;
    if (c->type == CHAN_SHARING) {
        share_got_pkt_from_server(c->u.sharing.ctx, pktin->type,
                                  pktin->body, pktin->length);
        return;
    }

    /*
     * When we receive CLOSE on a channel, we assume it comes with an
     * implied EOF if we haven't seen EOF yet.
     */
    ssh2_channel_got_eof(c);

    if (!(ssh->remote_bugs & BUG_SENDS_LATE_REQUEST_REPLY)) {
        /*
         * It also means we stop expecting to see replies to any
         * outstanding channel requests, so clean those up too.
         * (ssh_chanreq_init will enforce by assertion that we don't
         * subsequently put anything back on this list.)
         */
        while (c->v.v2.chanreq_head) {
            struct outstanding_channel_request *ocr = c->v.v2.chanreq_head;
            ocr->handler(c, NULL, ocr->ctx);
            c->v.v2.chanreq_head = ocr->next;
            sfree(ocr);
        }
    }

    /*
     * And we also send an outgoing EOF, if we haven't already, on the
     * assumption that CLOSE is a pretty forceful announcement that
     * the remote side is doing away with the entire channel. (If it
     * had wanted to send us EOF and continue receiving data from us,
     * it would have just sent CHANNEL_EOF.)
     */
    if (!(c->closes & CLOSES_SENT_EOF)) {
        /*
         * Make sure we don't read any more from whatever our local
         * data source is for this channel.
         */
        switch (c->type) {
          case CHAN_MAINSESSION:
            ssh->send_ok = 0;     /* stop trying to read from stdin */
            break;
          case CHAN_X11:
            x11_override_throttle(c->u.x11.xconn, 1);
            break;
          case CHAN_SOCKDATA:
            pfd_override_throttle(c->u.pfd.pf, 1);
            break;
        }

        /*
         * Abandon any buffered data we still wanted to send to this
         * channel. Receiving a CHANNEL_CLOSE is an indication that
         * the server really wants to get on and _destroy_ this
         * channel, and it isn't going to send us any further
         * WINDOW_ADJUSTs to permit us to send pending stuff.
         */
        bufchain_clear(&c->v.v2.outbuffer);

        /*
         * Send outgoing EOF.
         */
        sshfwd_write_eof(c);
    }

    /*
     * Now process the actual close.
     */
    if (!(c->closes & CLOSES_RCVD_CLOSE)) {
        c->closes |= CLOSES_RCVD_CLOSE;
        ssh2_channel_check_close(c);
    }
}

static void ssh2_msg_channel_open_confirmation(Ssh ssh, struct Packet *pktin)
{
    struct ssh_channel *c;

    c = ssh_channel_msg(ssh, pktin);
    if (!c)
        return;
    if (c->type == CHAN_SHARING) {
        share_got_pkt_from_server(c->u.sharing.ctx, pktin->type,
                                  pktin->body, pktin->length);
        return;
    }
    assert(c->halfopen); /* ssh_channel_msg will have enforced this */
    c->remoteid = ssh_pkt_getuint32(pktin);
    c->halfopen = FALSE;
    c->v.v2.remwindow = ssh_pkt_getuint32(pktin);
    c->v.v2.remmaxpkt = ssh_pkt_getuint32(pktin);

    if (c->type == CHAN_SOCKDATA_DORMANT) {
        c->type = CHAN_SOCKDATA;
        if (c->u.pfd.pf)
            pfd_confirm(c->u.pfd.pf);
    } else if (c->type == CHAN_ZOMBIE) {
        /*
         * This case can occur if a local socket error occurred
         * between us sending out CHANNEL_OPEN and receiving
         * OPEN_CONFIRMATION. In this case, all we can do is
         * immediately initiate close proceedings now that we know the
         * server's id to put in the close message.
         */
        ssh2_channel_check_close(c);
    } else {
        /*
         * We never expect to receive OPEN_CONFIRMATION for any
         * *other* channel type (since only local-to-remote port
         * forwardings cause us to send CHANNEL_OPEN after the main
         * channel is live - all other auxiliary channel types are
         * initiated from the server end). It's safe to enforce this
         * by assertion rather than by ssh_disconnect, because the
         * real point is that we never constructed a half-open channel
         * structure in the first place with any type other than the
         * above.
         */
        assert(!"Funny channel type in ssh2_msg_channel_open_confirmation");
    }

    if (c->pending_eof)
        ssh_channel_try_eof(c);        /* in case we had a pending EOF */
}

static void ssh2_msg_channel_open_failure(Ssh ssh, struct Packet *pktin)
{
    static const char *const reasons[] = {
        "<unknown reason code>",
            "Administratively prohibited",
            "Connect failed",
            "Unknown channel type",
            "Resource shortage",
    };
    unsigned reason_code;
    char *reason_string;
    int reason_length;
    struct ssh_channel *c;

    c = ssh_channel_msg(ssh, pktin);
    if (!c)
        return;
    if (c->type == CHAN_SHARING) {
        share_got_pkt_from_server(c->u.sharing.ctx, pktin->type,
                                  pktin->body, pktin->length);
        return;
    }
    assert(c->halfopen); /* ssh_channel_msg will have enforced this */

    if (c->type == CHAN_SOCKDATA_DORMANT) {
        reason_code = ssh_pkt_getuint32(pktin);
        if (reason_code >= lenof(reasons))
            reason_code = 0; /* ensure reasons[reason_code] in range */
        ssh_pkt_getstring(pktin, &reason_string, &reason_length);
        logeventf(ssh, "Forwarded connection refused by server: %s [%.*s]",
                  reasons[reason_code], reason_length,
                  NULLTOEMPTY(reason_string));

        pfd_close(c->u.pfd.pf);
    } else if (c->type == CHAN_ZOMBIE) {
        /*
         * This case can occur if a local socket error occurred
         * between us sending out CHANNEL_OPEN and receiving
         * OPEN_FAILURE. In this case, we need do nothing except allow
         * the code below to throw the half-open channel away.
         */
    } else {
        /*
         * We never expect to receive OPEN_FAILURE for any *other*
         * channel type (since only local-to-remote port forwardings
         * cause us to send CHANNEL_OPEN after the main channel is
         * live - all other auxiliary channel types are initiated from
         * the server end). It's safe to enforce this by assertion
         * rather than by ssh_disconnect, because the real point is
         * that we never constructed a half-open channel structure in
         * the first place with any type other than the above.
         */
        assert(!"Funny channel type in ssh2_msg_channel_open_failure");
    }

    del234(ssh->channels, c);
    sfree(c);
}

static void ssh2_msg_channel_request(Ssh ssh, struct Packet *pktin)
{
    char *type;
    int typelen, want_reply;
    int reply = SSH2_MSG_CHANNEL_FAILURE; /* default */
    struct ssh_channel *c;
    struct Packet *pktout;

    c = ssh_channel_msg(ssh, pktin);
    if (!c)
        return;
    if (c->type == CHAN_SHARING) {
        share_got_pkt_from_server(c->u.sharing.ctx, pktin->type,
                                  pktin->body, pktin->length);
        return;
    }
    ssh_pkt_getstring(pktin, &type, &typelen);
    want_reply = ssh2_pkt_getbool(pktin);

    if (c->closes & CLOSES_SENT_CLOSE) {
        /*
         * We don't reply to channel requests after we've sent
         * CHANNEL_CLOSE for the channel, because our reply might
         * cross in the network with the other side's CHANNEL_CLOSE
         * and arrive after they have wound the channel up completely.
         */
        want_reply = FALSE;
    }

    /*
     * Having got the channel number, we now look at
     * the request type string to see if it's something
     * we recognise.
     */
    if (c == ssh->mainchan) {
        /*
         * We recognise "exit-status" and "exit-signal" on
         * the primary channel.
         */
        if (typelen == 11 &&
            !memcmp(type, "exit-status", 11)) {

            ssh->exitcode = ssh_pkt_getuint32(pktin);
            logeventf(ssh, "Server sent command exit status %d",
                      ssh->exitcode);
            reply = SSH2_MSG_CHANNEL_SUCCESS;

        } else if (typelen == 11 &&
                   !memcmp(type, "exit-signal", 11)) {

            int is_plausible = TRUE, is_int = FALSE;
            char *fmt_sig = NULL, *fmt_msg = NULL;
            char *msg;
            int msglen = 0, core = FALSE;
            /* ICK: older versions of OpenSSH (e.g. 3.4p1)
             * provide an `int' for the signal, despite its
             * having been a `string' in the drafts of RFC 4254 since at
             * least 2001. (Fixed in session.c 1.147.) Try to
             * infer which we can safely parse it as. */
            {
                unsigned char *p = pktin->body +
                    pktin->savedpos;
                long len = pktin->length - pktin->savedpos;
                unsigned long num = GET_32BIT(p); /* what is it? */
                /* If it's 0, it hardly matters; assume string */
                if (num == 0) {
                    is_int = FALSE;
                } else {
                    int maybe_int = FALSE, maybe_str = FALSE;
#define CHECK_HYPOTHESIS(offset, result)                                \
                    do                                                  \
                    {                                                   \
                        int q = toint(offset);                          \
                        if (q >= 0 && q+4 <= len) {                     \
                            q = toint(q + 4 + GET_32BIT(p+q));          \
                            if (q >= 0 && q+4 <= len &&                 \
                                ((q = toint(q + 4 + GET_32BIT(p+q))) != 0) && \
                                q == len)                               \
                                result = TRUE;                          \
                        }                                               \
                    } while(0)
                    CHECK_HYPOTHESIS(4+1, maybe_int);
                    CHECK_HYPOTHESIS(4+num+1, maybe_str);
#undef CHECK_HYPOTHESIS
                    if (maybe_int && !maybe_str)
                        is_int = TRUE;
                    else if (!maybe_int && maybe_str)
                        is_int = FALSE;
                    else
                        /* Crikey. Either or neither. Panic. */
                        is_plausible = FALSE;
                }
            }
            ssh->exitcode = 128;       /* means `unknown signal' */
            if (is_plausible) {
                if (is_int) {
                    /* Old non-standard OpenSSH. */
                    int signum = ssh_pkt_getuint32(pktin);
                    fmt_sig = dupprintf(" %d", signum);
                    ssh->exitcode = 128 + signum;
                } else {
                    /* As per RFC 4254. */
                    char *sig;
                    int siglen;
                    ssh_pkt_getstring(pktin, &sig, &siglen);
                    /* Signal name isn't supposed to be blank, but
                     * let's cope gracefully if it is. */
                    if (siglen) {
                        fmt_sig = dupprintf(" \"%.*s\"",
                                            siglen, sig);
                    }

                    /*
                     * Really hideous method of translating the
                     * signal description back into a locally
                     * meaningful number.
                     */

                    if (0)
                        ;
#define TRANSLATE_SIGNAL(s) \
    else if (siglen == lenof(#s)-1 && !memcmp(sig, #s, siglen)) \
        ssh->exitcode = 128 + SIG ## s
#ifdef SIGABRT
                    TRANSLATE_SIGNAL(ABRT);
#endif
#ifdef SIGALRM
                    TRANSLATE_SIGNAL(ALRM);
#endif
#ifdef SIGFPE
                    TRANSLATE_SIGNAL(FPE);
#endif
#ifdef SIGHUP
                    TRANSLATE_SIGNAL(HUP);
#endif
#ifdef SIGILL
                    TRANSLATE_SIGNAL(ILL);
#endif
#ifdef SIGINT
                    TRANSLATE_SIGNAL(INT);
#endif
#ifdef SIGKILL
                    TRANSLATE_SIGNAL(KILL);
#endif
#ifdef SIGPIPE
                    TRANSLATE_SIGNAL(PIPE);
#endif
#ifdef SIGQUIT
                    TRANSLATE_SIGNAL(QUIT);
#endif
#ifdef SIGSEGV
                    TRANSLATE_SIGNAL(SEGV);
#endif
#ifdef SIGTERM
                    TRANSLATE_SIGNAL(TERM);
#endif
#ifdef SIGUSR1
                    TRANSLATE_SIGNAL(USR1);
#endif
#ifdef SIGUSR2
                    TRANSLATE_SIGNAL(USR2);
#endif
#undef TRANSLATE_SIGNAL
                    else
                        ssh->exitcode = 128;
                }
                core = ssh2_pkt_getbool(pktin);
                ssh_pkt_getstring(pktin, &msg, &msglen);
                if (msglen) {
                    fmt_msg = dupprintf(" (\"%.*s\")", msglen, msg);
                }
                /* ignore lang tag */
            } /* else don't attempt to parse */
            logeventf(ssh, "Server exited on signal%s%s%s",
                      fmt_sig ? fmt_sig : "",
                      core ? " (core dumped)" : "",
                      fmt_msg ? fmt_msg : "");
            sfree(fmt_sig);
            sfree(fmt_msg);
            reply = SSH2_MSG_CHANNEL_SUCCESS;

        }
    } else {
        /*
         * This is a channel request we don't know
         * about, so we now either ignore the request
         * or respond with CHANNEL_FAILURE, depending
         * on want_reply.
         */
        reply = SSH2_MSG_CHANNEL_FAILURE;
    }
    if (want_reply) {
        pktout = ssh2_pkt_init(reply);
        ssh2_pkt_adduint32(pktout, c->remoteid);
        ssh2_pkt_send(ssh, pktout);
    }
}

static void ssh2_msg_global_request(Ssh ssh, struct Packet *pktin)
{
    char *type;
    int typelen, want_reply;
    struct Packet *pktout;

    ssh_pkt_getstring(pktin, &type, &typelen);
    want_reply = ssh2_pkt_getbool(pktin);

    /*
     * We currently don't support any global requests
     * at all, so we either ignore the request or
     * respond with REQUEST_FAILURE, depending on
     * want_reply.
     */
    if (want_reply) {
        pktout = ssh2_pkt_init(SSH2_MSG_REQUEST_FAILURE);
        ssh2_pkt_send(ssh, pktout);
    }
}

struct X11FakeAuth *ssh_sharing_add_x11_display(Ssh ssh, int authtype,
                                                void *share_cs,
                                                void *share_chan)
{
    struct X11FakeAuth *auth;

    /*
     * Make up a new set of fake X11 auth data, and add it to the tree
     * of currently valid ones with an indication of the sharing
     * context that it's relevant to.
     */
    auth = x11_invent_fake_auth(ssh->x11authtree, authtype);
    auth->share_cs = share_cs;
    auth->share_chan = share_chan;

    return auth;
}

void ssh_sharing_remove_x11_display(Ssh ssh, struct X11FakeAuth *auth)
{
    del234(ssh->x11authtree, auth);
    x11_free_fake_auth(auth);
}

static void ssh2_msg_channel_open(Ssh ssh, struct Packet *pktin)
{
    char *type;
    int typelen;
    char *peeraddr;
    int peeraddrlen;
    int peerport;
    const char *error = NULL;
    struct ssh_channel *c;
    unsigned remid, winsize, pktsize;
    unsigned our_winsize_override = 0;
    struct Packet *pktout;

    ssh_pkt_getstring(pktin, &type, &typelen);
    c = snew(struct ssh_channel);
    c->ssh = ssh;

    remid = ssh_pkt_getuint32(pktin);
    winsize = ssh_pkt_getuint32(pktin);
    pktsize = ssh_pkt_getuint32(pktin);

    if (typelen == 3 && !memcmp(type, "x11", 3)) {
        char *addrstr;

        ssh_pkt_getstring(pktin, &peeraddr, &peeraddrlen);
        addrstr = dupprintf("%.*s", peeraddrlen, NULLTOEMPTY(peeraddr));
        peerport = ssh_pkt_getuint32(pktin);

        logeventf(ssh, "Received X11 connect request from %s:%d",
                  addrstr, peerport);

        if (!ssh->X11_fwd_enabled && !ssh->connshare)
            error = "X11 forwarding is not enabled";
        else {
            c->u.x11.xconn = x11_init(ssh->x11authtree, c,
                                      addrstr, peerport);
            c->type = CHAN_X11;
            c->u.x11.initial = TRUE;

            /*
             * If we are a connection-sharing upstream, then we should
             * initially present a very small window, adequate to take
             * the X11 initial authorisation packet but not much more.
             * Downstream will then present us a larger window (by
             * fiat of the connection-sharing protocol) and we can
             * guarantee to send a positive-valued WINDOW_ADJUST.
             */
            if (ssh->connshare)
                our_winsize_override = 128;

            logevent("Opened X11 forward channel");
        }

        sfree(addrstr);
    } else if (typelen == 15 &&
               !memcmp(type, "forwarded-tcpip", 15)) {
        struct ssh_rportfwd pf, *realpf;
        char *shost;
        int shostlen;
        ssh_pkt_getstring(pktin, &shost, &shostlen);/* skip address */
        pf.shost = dupprintf("%.*s", shostlen, NULLTOEMPTY(shost));
        pf.sport = ssh_pkt_getuint32(pktin);
        ssh_pkt_getstring(pktin, &peeraddr, &peeraddrlen);
        peerport = ssh_pkt_getuint32(pktin);
        realpf = find234(ssh->rportfwds, &pf, NULL);
        logeventf(ssh, "Received remote port %s:%d open request "
                  "from %.*s:%d", pf.shost, pf.sport,
                  peeraddrlen, NULLTOEMPTY(peeraddr), peerport);
        sfree(pf.shost);

        if (realpf == NULL) {
            error = "Remote port is not recognised";
        } else {
            char *err;

            if (realpf->share_ctx) {
                /*
                 * This port forwarding is on behalf of a
                 * connection-sharing downstream, so abandon our own
                 * channel-open procedure and just pass the message on
                 * to sshshare.c.
                 */
                share_got_pkt_from_server(realpf->share_ctx, pktin->type,
                                          pktin->body, pktin->length);
                sfree(c);
                return;
            }

            err = pfd_connect(&c->u.pfd.pf, realpf->dhost, realpf->dport,
                              c, ssh->conf, realpf->pfrec->addressfamily);
            logeventf(ssh, "Attempting to forward remote port to "
                      "%s:%d", realpf->dhost, realpf->dport);
            if (err != NULL) {
                logeventf(ssh, "Port open failed: %s", err);
                sfree(err);
                error = "Port open failed";
            } else {
                logevent("Forwarded port opened successfully");
                c->type = CHAN_SOCKDATA;
            }
        }
    } else if (typelen == 22 &&
               !memcmp(type, "auth-agent@openssh.com", 22)) {
        if (!ssh->agentfwd_enabled)
            error = "Agent forwarding is not enabled";
        else {
            c->type = CHAN_AGENT;       /* identify channel type */
            c->u.a.lensofar = 0;
            c->u.a.message = NULL;
            c->u.a.outstanding_requests = 0;
        }
    } else {
        error = "Unsupported channel type requested";
    }

    c->remoteid = remid;
    c->halfopen = FALSE;
    if (error) {
        pktout = ssh2_pkt_init(SSH2_MSG_CHANNEL_OPEN_FAILURE);
        ssh2_pkt_adduint32(pktout, c->remoteid);
        ssh2_pkt_adduint32(pktout, SSH2_OPEN_CONNECT_FAILED);
        ssh2_pkt_addstring(pktout, error);
        ssh2_pkt_addstring(pktout, "en");       /* language tag */
        ssh2_pkt_send(ssh, pktout);
        logeventf(ssh, "Rejected channel open: %s", error);
        sfree(c);
    } else {
        ssh_channel_init(c);
        c->v.v2.remwindow = winsize;
        c->v.v2.remmaxpkt = pktsize;
        if (our_winsize_override) {
            c->v.v2.locwindow = c->v.v2.locmaxwin = c->v.v2.remlocwin =
                our_winsize_override;
        }
        pktout = ssh2_pkt_init(SSH2_MSG_CHANNEL_OPEN_CONFIRMATION);
        ssh2_pkt_adduint32(pktout, c->remoteid);
        ssh2_pkt_adduint32(pktout, c->localid);
        ssh2_pkt_adduint32(pktout, c->v.v2.locwindow);
        ssh2_pkt_adduint32(pktout, OUR_V2_MAXPKT);      /* our max pkt size */
        ssh2_pkt_send(ssh, pktout);
    }
}

void sshfwd_x11_sharing_handover(struct ssh_channel *c,
                                 void *share_cs, void *share_chan,
                                 const char *peer_addr, int peer_port,
                                 int endian, int protomajor, int protominor,
                                 const void *initial_data, int initial_len)
{
    /*
     * This function is called when we've just discovered that an X
     * forwarding channel on which we'd been handling the initial auth
     * ourselves turns out to be destined for a connection-sharing
     * downstream. So we turn the channel into a CHAN_SHARING, meaning
     * that we completely stop tracking windows and buffering data and
     * just pass more or less unmodified SSH messages back and forth.
     */
    c->type = CHAN_SHARING;
    c->u.sharing.ctx = share_cs;
    share_setup_x11_channel(share_cs, share_chan,
                            c->localid, c->remoteid, c->v.v2.remwindow,
                            c->v.v2.remmaxpkt, c->v.v2.locwindow,
                            peer_addr, peer_port, endian,
                            protomajor, protominor,
                            initial_data, initial_len);
}

void sshfwd_x11_is_local(struct ssh_channel *c)
{
    /*
     * This function is called when we've just discovered that an X
     * forwarding channel is _not_ destined for a connection-sharing
     * downstream but we're going to handle it ourselves. We stop
     * presenting a cautiously small window and go into ordinary data
     * exchange mode.
     */
    c->u.x11.initial = FALSE;
    ssh2_set_window(c, ssh_is_simple(c->ssh) ? OUR_V2_BIGWIN : OUR_V2_WINSIZE);
}

/*
 * Buffer banner messages for later display at some convenient point,
 * if we're going to display them.
 */
static void ssh2_msg_userauth_banner(Ssh ssh, struct Packet *pktin)
{
    /* Arbitrary limit to prevent unbounded inflation of buffer */
    if (conf_get_int(ssh->conf, CONF_ssh_show_banner) &&
        bufchain_size(&ssh->banner) <= 131072) {
        char *banner = NULL;
        int size = 0;
        ssh_pkt_getstring(pktin, &banner, &size);
        if (banner)
            bufchain_add(&ssh->banner, banner, size);
    }
}

/* Helper function to deal with sending tty modes for "pty-req" */
static void ssh2_send_ttymode(void *data,
                              const struct ssh_ttymode *mode, char *val)
{
    struct Packet *pktout = (struct Packet *)data;
    unsigned int arg = 0;

    switch (mode->type) {
      case TTY_OP_CHAR:
        arg = ssh_tty_parse_specchar(val);
        break;
      case TTY_OP_BOOL:
        arg = ssh_tty_parse_boolean(val);
        break;
    }
    ssh2_pkt_addbyte(pktout, mode->opcode);
    ssh2_pkt_adduint32(pktout, arg);
}

static void ssh2_setup_x11(struct ssh_channel *c, struct Packet *pktin,
                           void *ctx)
{
    struct ssh2_setup_x11_state {
        int crLine;
    };
    Ssh ssh = c->ssh;
    struct Packet *pktout;
    crStateP(ssh2_setup_x11_state, ctx);

    crBeginState;

    logevent("Requesting X11 forwarding");
    pktout = ssh2_chanreq_init(ssh->mainchan, "x11-req",
                               ssh2_setup_x11, s);
    ssh2_pkt_addbool(pktout, 0);               /* many connections */
    ssh2_pkt_addstring(pktout, ssh->x11auth->protoname);
    ssh2_pkt_addstring(pktout, ssh->x11auth->datastring);
    ssh2_pkt_adduint32(pktout, ssh->x11disp->screennum);
    ssh2_pkt_send(ssh, pktout);

    /* Wait to be called back with either a response packet, or NULL
     * meaning clean up and free our data */
    crReturnV;

    if (pktin) {
        if (pktin->type == SSH2_MSG_CHANNEL_SUCCESS) {
            logevent("X11 forwarding enabled");
            ssh->X11_fwd_enabled = TRUE;
        } else
            logevent("X11 forwarding refused");
    }

    crFinishFreeV;
}

static void ssh2_setup_agent(struct ssh_channel *c, struct Packet *pktin,
                                   void *ctx)
{
    struct ssh2_setup_agent_state {
        int crLine;
    };
    Ssh ssh = c->ssh;
    struct Packet *pktout;
    crStateP(ssh2_setup_agent_state, ctx);

    crBeginState;

    logevent("Requesting OpenSSH-style agent forwarding");
    pktout = ssh2_chanreq_init(ssh->mainchan, "auth-agent-req@openssh.com",
                               ssh2_setup_agent, s);
    ssh2_pkt_send(ssh, pktout);

    /* Wait to be called back with either a response packet, or NULL
     * meaning clean up and free our data */
    crReturnV;

    if (pktin) {
        if (pktin->type == SSH2_MSG_CHANNEL_SUCCESS) {
            logevent("Agent forwarding enabled");
            ssh->agentfwd_enabled = TRUE;
        } else
            logevent("Agent forwarding refused");
    }

    crFinishFreeV;
}

static void ssh2_setup_pty(struct ssh_channel *c, struct Packet *pktin,
                                 void *ctx)
{
    struct ssh2_setup_pty_state {
        int crLine;
    };
    Ssh ssh = c->ssh;
    struct Packet *pktout;
    crStateP(ssh2_setup_pty_state, ctx);

    crBeginState;

    /* Unpick the terminal-speed string. */
    /* XXX perhaps we should allow no speeds to be sent. */
    ssh->ospeed = 38400; ssh->ispeed = 38400; /* last-resort defaults */
    sscanf(conf_get_str(ssh->conf, CONF_termspeed), "%d,%d", &ssh->ospeed, &ssh->ispeed);
    /* Build the pty request. */
    pktout = ssh2_chanreq_init(ssh->mainchan, "pty-req",
                               ssh2_setup_pty, s);
    ssh2_pkt_addstring(pktout, conf_get_str(ssh->conf, CONF_termtype));
    ssh2_pkt_adduint32(pktout, ssh->term_width);
    ssh2_pkt_adduint32(pktout, ssh->term_height);
    ssh2_pkt_adduint32(pktout, 0);             /* pixel width */
    ssh2_pkt_adduint32(pktout, 0);             /* pixel height */
    ssh2_pkt_addstring_start(pktout);
    parse_ttymodes(ssh, ssh2_send_ttymode, (void *)pktout);
    ssh2_pkt_addbyte(pktout, SSH2_TTY_OP_ISPEED);
    ssh2_pkt_adduint32(pktout, ssh->ispeed);
    ssh2_pkt_addbyte(pktout, SSH2_TTY_OP_OSPEED);
    ssh2_pkt_adduint32(pktout, ssh->ospeed);
    ssh2_pkt_addstring_data(pktout, "\0", 1); /* TTY_OP_END */
    ssh2_pkt_send(ssh, pktout);
    ssh->state = SSH_STATE_INTERMED;

    /* Wait to be called back with either a response packet, or NULL
     * meaning clean up and free our data */
    crReturnV;

    if (pktin) {
        if (pktin->type == SSH2_MSG_CHANNEL_SUCCESS) {
            logeventf(ssh, "Allocated pty (ospeed %dbps, ispeed %dbps)",
                      ssh->ospeed, ssh->ispeed);
            ssh->got_pty = TRUE;
        } else {
            c_write_str(ssh, "Server refused to allocate pty\r\n");
            ssh->editing = ssh->echoing = 1;
        }
    }

    crFinishFreeV;
}

static void ssh2_setup_env(struct ssh_channel *c, struct Packet *pktin,
                           void *ctx)
{
    struct ssh2_setup_env_state {
        int crLine;
        int num_env, env_left, env_ok;
    };
    Ssh ssh = c->ssh;
    struct Packet *pktout;
    crStateP(ssh2_setup_env_state, ctx);

    crBeginState;

    /*
     * Send environment variables.
     * 
     * Simplest thing here is to send all the requests at once, and
     * then wait for a whole bunch of successes or failures.
     */
    s->num_env = 0;
    {
        char *key, *val;

        for (val = conf_get_str_strs(ssh->conf, CONF_environmt, NULL, &key);
             val != NULL;
             val = conf_get_str_strs(ssh->conf, CONF_environmt, key, &key)) {
            pktout = ssh2_chanreq_init(ssh->mainchan, "env", ssh2_setup_env, s);
            ssh2_pkt_addstring(pktout, key);
            ssh2_pkt_addstring(pktout, val);
            ssh2_pkt_send(ssh, pktout);

            s->num_env++;
        }
        if (s->num_env)
            logeventf(ssh, "Sent %d environment variables", s->num_env);
    }

    if (s->num_env) {
        s->env_ok = 0;
        s->env_left = s->num_env;

        while (s->env_left > 0) {
            /* Wait to be called back with either a response packet,
             * or NULL meaning clean up and free our data */
            crReturnV;
            if (!pktin) goto out;
            if (pktin->type == SSH2_MSG_CHANNEL_SUCCESS)
                s->env_ok++;
            s->env_left--;
        }

        if (s->env_ok == s->num_env) {
            logevent("All environment variables successfully set");
        } else if (s->env_ok == 0) {
            logevent("All environment variables refused");
            c_write_str(ssh, "Server refused to set environment variables\r\n");
        } else {
            logeventf(ssh, "%d environment variables refused",
                      s->num_env - s->env_ok);
            c_write_str(ssh, "Server refused to set all environment variables\r\n");
        }
    }
  out:;
    crFinishFreeV;
}

/*
 * Handle the SSH-2 userauth and connection layers.
 */
static void ssh2_msg_authconn(Ssh ssh, struct Packet *pktin)
{
    do_ssh2_authconn(ssh, NULL, 0, pktin);
}

static void ssh2_response_authconn(struct ssh_channel *c, struct Packet *pktin,
                                   void *ctx)
{
    if (pktin)
        do_ssh2_authconn(c->ssh, NULL, 0, pktin);
}

static void do_ssh2_authconn(Ssh ssh, const unsigned char *in, int inlen,
                             struct Packet *pktin)
{
    struct do_ssh2_authconn_state {
        int crLine;
        enum {
            AUTH_TYPE_NONE,
                AUTH_TYPE_PUBLICKEY,
                AUTH_TYPE_PUBLICKEY_OFFER_LOUD,
                AUTH_TYPE_PUBLICKEY_OFFER_QUIET,
                AUTH_TYPE_PASSWORD,
                AUTH_TYPE_GSSAPI,      /* always QUIET */
                AUTH_TYPE_KEYBOARD_INTERACTIVE,
                AUTH_TYPE_KEYBOARD_INTERACTIVE_QUIET
        } type;
        int done_service_req;
        int gotit, need_pw, can_pubkey, can_passwd, can_keyb_inter;
        int tried_pubkey_config, done_agent;
#ifndef NO_GSSAPI
        int can_gssapi;
        int tried_gssapi;
#endif
        int kbd_inter_refused;
        int we_are_in, userauth_success;
        prompts_t *cur_prompt;
        int num_prompts;
        char *username;
        char *password;
        int got_username;
        void *publickey_blob;
        int publickey_bloblen;
        int privatekey_available, privatekey_encrypted;
        char *publickey_algorithm;
        char *publickey_comment;
        unsigned char agent_request[5], *agent_response, *agentp;
        int agent_responselen;
        unsigned char *pkblob_in_agent;
        int keyi, nkeys;
        char *pkblob, *alg, *commentp;
        int pklen, alglen, commentlen;
        int siglen, retlen, len;
        char *q, *agentreq, *ret;
        struct Packet *pktout;
        Filename *keyfile;
#ifndef NO_GSSAPI
        struct ssh_gss_library *gsslib;
        Ssh_gss_ctx gss_ctx;
        Ssh_gss_buf gss_buf;
        Ssh_gss_buf gss_rcvtok, gss_sndtok;
        Ssh_gss_name gss_srv_name;
        Ssh_gss_stat gss_stat;
#endif
    };
    crState(do_ssh2_authconn_state);

    crBeginState;

    /* Register as a handler for all the messages this coroutine handles. */
    ssh->packet_dispatch[SSH2_MSG_SERVICE_ACCEPT] = ssh2_msg_authconn;
    ssh->packet_dispatch[SSH2_MSG_USERAUTH_REQUEST] = ssh2_msg_authconn;
    ssh->packet_dispatch[SSH2_MSG_USERAUTH_FAILURE] = ssh2_msg_authconn;
    ssh->packet_dispatch[SSH2_MSG_USERAUTH_SUCCESS] = ssh2_msg_authconn;
    ssh->packet_dispatch[SSH2_MSG_USERAUTH_BANNER] = ssh2_msg_authconn;
    ssh->packet_dispatch[SSH2_MSG_USERAUTH_PK_OK] = ssh2_msg_authconn;
    /* ssh->packet_dispatch[SSH2_MSG_USERAUTH_PASSWD_CHANGEREQ] = ssh2_msg_authconn; duplicate case value */
    /* ssh->packet_dispatch[SSH2_MSG_USERAUTH_INFO_REQUEST] = ssh2_msg_authconn; duplicate case value */
    ssh->packet_dispatch[SSH2_MSG_USERAUTH_INFO_RESPONSE] = ssh2_msg_authconn;
    ssh->packet_dispatch[SSH2_MSG_GLOBAL_REQUEST] = ssh2_msg_authconn;
    ssh->packet_dispatch[SSH2_MSG_REQUEST_SUCCESS] = ssh2_msg_authconn;
    ssh->packet_dispatch[SSH2_MSG_REQUEST_FAILURE] = ssh2_msg_authconn;
    ssh->packet_dispatch[SSH2_MSG_CHANNEL_OPEN] = ssh2_msg_authconn;
    ssh->packet_dispatch[SSH2_MSG_CHANNEL_OPEN_CONFIRMATION] = ssh2_msg_authconn;
    ssh->packet_dispatch[SSH2_MSG_CHANNEL_OPEN_FAILURE] = ssh2_msg_authconn;
    ssh->packet_dispatch[SSH2_MSG_CHANNEL_WINDOW_ADJUST] = ssh2_msg_authconn;
    ssh->packet_dispatch[SSH2_MSG_CHANNEL_DATA] = ssh2_msg_authconn;
    ssh->packet_dispatch[SSH2_MSG_CHANNEL_EXTENDED_DATA] = ssh2_msg_authconn;
    ssh->packet_dispatch[SSH2_MSG_CHANNEL_EOF] = ssh2_msg_authconn;
    ssh->packet_dispatch[SSH2_MSG_CHANNEL_CLOSE] = ssh2_msg_authconn;
    
    s->done_service_req = FALSE;
    s->we_are_in = s->userauth_success = FALSE;
    s->agent_response = NULL;
#ifndef NO_GSSAPI
    s->tried_gssapi = FALSE;
#endif

    if (!ssh->bare_connection) {
        if (!conf_get_int(ssh->conf, CONF_ssh_no_userauth)) {
            /*
             * Request userauth protocol, and await a response to it.
             */
            s->pktout = ssh2_pkt_init(SSH2_MSG_SERVICE_REQUEST);
            ssh2_pkt_addstring(s->pktout, "ssh-userauth");
            ssh2_pkt_send(ssh, s->pktout);
            crWaitUntilV(pktin);
            if (pktin->type == SSH2_MSG_SERVICE_ACCEPT)
                s->done_service_req = TRUE;
        }
        if (!s->done_service_req) {
            /*
             * Request connection protocol directly, without authentication.
             */
            s->pktout = ssh2_pkt_init(SSH2_MSG_SERVICE_REQUEST);
            ssh2_pkt_addstring(s->pktout, "ssh-connection");
            ssh2_pkt_send(ssh, s->pktout);
            crWaitUntilV(pktin);
            if (pktin->type == SSH2_MSG_SERVICE_ACCEPT) {
                s->we_are_in = TRUE; /* no auth required */
            } else {
                bombout(("Server refused service request"));
                crStopV;
            }
        }
    } else {
        s->we_are_in = TRUE;
    }

    /* Arrange to be able to deal with any BANNERs that come in.
     * (We do this now as packets may come in during the next bit.) */
    bufchain_init(&ssh->banner);
    ssh->packet_dispatch[SSH2_MSG_USERAUTH_BANNER] =
        ssh2_msg_userauth_banner;

    /*
     * Misc one-time setup for authentication.
     */
    s->publickey_blob = NULL;
    if (!s->we_are_in) {

        /*
         * Load the public half of any configured public key file
         * for later use.
         */
        s->keyfile = conf_get_filename(ssh->conf, CONF_keyfile);
        if (!filename_is_null(s->keyfile)) {
            int keytype;
            logeventf(ssh, "Reading key file \"%.150s\"",
                      filename_to_str(s->keyfile));
            keytype = key_type(s->keyfile);
            if (keytype == SSH_KEYTYPE_SSH2 ||
                keytype == SSH_KEYTYPE_SSH2_PUBLIC_RFC4716 ||
                keytype == SSH_KEYTYPE_SSH2_PUBLIC_OPENSSH) {
                const char *error;
                s->publickey_blob =
                    ssh2_userkey_loadpub(s->keyfile,
                                         &s->publickey_algorithm,
                                         &s->publickey_bloblen, 
                                         &s->publickey_comment, &error);
                if (s->publickey_blob) {
                    s->privatekey_available = (keytype == SSH_KEYTYPE_SSH2);
                    if (!s->privatekey_available)
                        logeventf(ssh, "Key file contains public key only");
                    s->privatekey_encrypted =
                        ssh2_userkey_encrypted(s->keyfile, NULL);
                } else {
                    char *msgbuf;
                    logeventf(ssh, "Unable to load key (%s)", 
                              error);
                    msgbuf = dupprintf("Unable to load key file "
                                       "\"%.150s\" (%s)\r\n",
                                       filename_to_str(s->keyfile),
                                       error);
                    c_write_str(ssh, msgbuf);
                    sfree(msgbuf);
                }
            } else {
                char *msgbuf;
                logeventf(ssh, "Unable to use this key file (%s)",
                          key_type_to_str(keytype));
                msgbuf = dupprintf("Unable to use key file \"%.150s\""
                                   " (%s)\r\n",
                                   filename_to_str(s->keyfile),
                                   key_type_to_str(keytype));
                c_write_str(ssh, msgbuf);
                sfree(msgbuf);
                s->publickey_blob = NULL;
            }
        }

        /*
         * Find out about any keys Pageant has (but if there's a
         * public key configured, filter out all others).
         */
        s->nkeys = 0;
        s->agent_response = NULL;
        s->pkblob_in_agent = NULL;
        if (conf_get_int(ssh->conf, CONF_tryagent) && agent_exists()) {

            void *r;

            logevent("Pageant is running. Requesting keys.");

            /* Request the keys held by the agent. */
            PUT_32BIT(s->agent_request, 1);
            s->agent_request[4] = SSH2_AGENTC_REQUEST_IDENTITIES;
            if (!agent_query(s->agent_request, 5, &r, &s->agent_responselen,
                             ssh_agent_callback, ssh)) {
                do {
                    crReturnV;
                    if (pktin) {
                        bombout(("Unexpected data from server while"
                                 " waiting for agent response"));
                        crStopV;
                    }
                } while (pktin || inlen > 0);
                r = ssh->agent_response;
                s->agent_responselen = ssh->agent_response_len;
            }
            s->agent_response = (unsigned char *) r;
            if (s->agent_response && s->agent_responselen >= 5 &&
                s->agent_response[4] == SSH2_AGENT_IDENTITIES_ANSWER) {
                int keyi;
                unsigned char *p;
                p = s->agent_response + 5;
                s->nkeys = toint(GET_32BIT(p));

                /*
                 * Vet the Pageant response to ensure that the key
                 * count and blob lengths make sense.
                 */
                if (s->nkeys < 0) {
                    logeventf(ssh, "Pageant response contained a negative"
                              " key count %d", s->nkeys);
                    s->nkeys = 0;
                    goto done_agent_query;
                } else {
                    unsigned char *q = p + 4;
                    int lenleft = s->agent_responselen - 5 - 4;

                    for (keyi = 0; keyi < s->nkeys; keyi++) {
                        int bloblen, commentlen;
                        if (lenleft < 4) {
                            logeventf(ssh, "Pageant response was truncated");
                            s->nkeys = 0;
                            goto done_agent_query;
                        }
                        bloblen = toint(GET_32BIT(q));
                        if (bloblen < 0 || bloblen > lenleft) {
                            logeventf(ssh, "Pageant response was truncated");
                            s->nkeys = 0;
                            goto done_agent_query;
                        }
                        lenleft -= 4 + bloblen;
                        q += 4 + bloblen;
                        commentlen = toint(GET_32BIT(q));
                        if (commentlen < 0 || commentlen > lenleft) {
                            logeventf(ssh, "Pageant response was truncated");
                            s->nkeys = 0;
                            goto done_agent_query;
                        }
                        lenleft -= 4 + commentlen;
                        q += 4 + commentlen;
                    }
                }

                p += 4;
                logeventf(ssh, "Pageant has %d SSH-2 keys", s->nkeys);
                if (s->publickey_blob) {
                    /* See if configured key is in agent. */
                    for (keyi = 0; keyi < s->nkeys; keyi++) {
                        s->pklen = toint(GET_32BIT(p));
                        if (s->pklen == s->publickey_bloblen &&
                            !memcmp(p+4, s->publickey_blob,
                                    s->publickey_bloblen)) {
                            logeventf(ssh, "Pageant key #%d matches "
                                      "configured key file", keyi);
                            s->keyi = keyi;
                            s->pkblob_in_agent = p;
                            break;
                        }
                        p += 4 + s->pklen;
                        p += toint(GET_32BIT(p)) + 4; /* comment */
                    }
                    if (!s->pkblob_in_agent) {
                        logevent("Configured key file not in Pageant");
                        s->nkeys = 0;
                    }
                }
            } else {
                logevent("Failed to get reply from Pageant");
            }
          done_agent_query:;
        }

    }

    /*
     * We repeat this whole loop, including the username prompt,
     * until we manage a successful authentication. If the user
     * types the wrong _password_, they can be sent back to the
     * beginning to try another username, if this is configured on.
     * (If they specify a username in the config, they are never
     * asked, even if they do give a wrong password.)
     * 
     * I think this best serves the needs of
     * 
     *  - the people who have no configuration, no keys, and just
     *    want to try repeated (username,password) pairs until they
     *    type both correctly
     * 
     *  - people who have keys and configuration but occasionally
     *    need to fall back to passwords
     * 
     *  - people with a key held in Pageant, who might not have
     *    logged in to a particular machine before; so they want to
     *    type a username, and then _either_ their key will be
     *    accepted, _or_ they will type a password. If they mistype
     *    the username they will want to be able to get back and
     *    retype it!
     */
    s->got_username = FALSE;
    while (!s->we_are_in) {
        /*
         * Get a username.
         */
        if (s->got_username && !conf_get_int(ssh->conf, CONF_change_username)) {
            /*
             * We got a username last time round this loop, and
             * with change_username turned off we don't try to get
             * it again.
             */
        } else if ((ssh->username = get_remote_username(ssh->conf)) == NULL) {
            int ret; /* need not be kept over crReturn */
            s->cur_prompt = new_prompts(ssh->frontend);
            s->cur_prompt->to_server = TRUE;
            s->cur_prompt->name = dupstr("SSH login name");
            add_prompt(s->cur_prompt, dupstr("login as: "), TRUE); 
            ret = get_userpass_input(s->cur_prompt, NULL, 0);
            while (ret < 0) {
                ssh->send_ok = 1;
                crWaitUntilV(!pktin);
                ret = get_userpass_input(s->cur_prompt, in, inlen);
                ssh->send_ok = 0;
            }
            if (!ret) {
                /*
                 * get_userpass_input() failed to get a username.
                 * Terminate.
                 */
                free_prompts(s->cur_prompt);
                ssh_disconnect(ssh, "No username provided", NULL, 0, TRUE);
                crStopV;
            }
            ssh->username = dupstr(s->cur_prompt->prompts[0]->result);
            free_prompts(s->cur_prompt);
        } else {
            char *stuff;
            if ((flags & FLAG_VERBOSE) || (flags & FLAG_INTERACTIVE)) {
                stuff = dupprintf("Using username \"%s\".\r\n", ssh->username);
                c_write_str(ssh, stuff);
                sfree(stuff);
            }
        }
        s->got_username = TRUE;

        /*
         * Send an authentication request using method "none": (a)
         * just in case it succeeds, and (b) so that we know what
         * authentication methods we can usefully try next.
         */
        ssh->pkt_actx = SSH2_PKTCTX_NOAUTH;

        s->pktout = ssh2_pkt_init(SSH2_MSG_USERAUTH_REQUEST);
        ssh2_pkt_addstring(s->pktout, ssh->username);
        ssh2_pkt_addstring(s->pktout, "ssh-connection");/* service requested */
        ssh2_pkt_addstring(s->pktout, "none");    /* method */
        ssh2_pkt_send(ssh, s->pktout);
        s->type = AUTH_TYPE_NONE;
        s->gotit = FALSE;
        s->we_are_in = FALSE;

        s->tried_pubkey_config = FALSE;
        s->kbd_inter_refused = FALSE;

        /* Reset agent request state. */
        s->done_agent = FALSE;
        if (s->agent_response) {
            if (s->pkblob_in_agent) {
                s->agentp = s->pkblob_in_agent;
            } else {
                s->agentp = s->agent_response + 5 + 4;
                s->keyi = 0;
            }
        }

        while (1) {
            char *methods = NULL;
            int methlen = 0;

            /*
             * Wait for the result of the last authentication request.
             */
            if (!s->gotit)
                crWaitUntilV(pktin);
            /*
             * Now is a convenient point to spew any banner material
             * that we've accumulated. (This should ensure that when
             * we exit the auth loop, we haven't any left to deal
             * with.)
             */
            {
                int size = bufchain_size(&ssh->banner);
                /*
                 * Don't show the banner if we're operating in
                 * non-verbose non-interactive mode. (It's probably
                 * a script, which means nobody will read the
                 * banner _anyway_, and moreover the printing of
                 * the banner will screw up processing on the
                 * output of (say) plink.)
                 */
                if (size && (flags & (FLAG_VERBOSE | FLAG_INTERACTIVE))) {
                    char *banner = snewn(size, char);
                    bufchain_fetch(&ssh->banner, banner, size);
                    c_write_untrusted(ssh, banner, size);
                    sfree(banner);
                }
                bufchain_clear(&ssh->banner);
            }
            if (pktin->type == SSH2_MSG_USERAUTH_SUCCESS) {
                logevent("Access granted");
                s->we_are_in = s->userauth_success = TRUE;
                break;
            }

            if (pktin->type != SSH2_MSG_USERAUTH_FAILURE && s->type != AUTH_TYPE_GSSAPI) {
                bombout(("Strange packet received during authentication: "
                         "type %d", pktin->type));
                crStopV;
            }

            s->gotit = FALSE;

            /*
             * OK, we're now sitting on a USERAUTH_FAILURE message, so
             * we can look at the string in it and know what we can
             * helpfully try next.
             */
            if (pktin->type == SSH2_MSG_USERAUTH_FAILURE) {
                ssh_pkt_getstring(pktin, &methods, &methlen);
                if (!ssh2_pkt_getbool(pktin)) {
                    /*
                     * We have received an unequivocal Access
                     * Denied. This can translate to a variety of
                     * messages, or no message at all.
                     *
                     * For forms of authentication which are attempted
                     * implicitly, by which I mean without printing
                     * anything in the window indicating that we're
                     * trying them, we should never print 'Access
                     * denied'.
                     *
                     * If we do print a message saying that we're
                     * attempting some kind of authentication, it's OK
                     * to print a followup message saying it failed -
                     * but the message may sometimes be more specific
                     * than simply 'Access denied'.
                     *
                     * Additionally, if we'd just tried password
                     * authentication, we should break out of this
                     * whole loop so as to go back to the username
                     * prompt (iff we're configured to allow
                     * username change attempts).
                     */
                    if (s->type == AUTH_TYPE_NONE) {
                        /* do nothing */
                    } else if (s->type == AUTH_TYPE_PUBLICKEY_OFFER_LOUD ||
                               s->type == AUTH_TYPE_PUBLICKEY_OFFER_QUIET) {
                        if (s->type == AUTH_TYPE_PUBLICKEY_OFFER_LOUD)
                            c_write_str(ssh, "Server refused our key\r\n");
                        logevent("Server refused our key");
                    } else if (s->type == AUTH_TYPE_PUBLICKEY) {
                        /* This _shouldn't_ happen except by a
                         * protocol bug causing client and server to
                         * disagree on what is a correct signature. */
                        c_write_str(ssh, "Server refused public-key signature"
                                    " despite accepting key!\r\n");
                        logevent("Server refused public-key signature"
                                 " despite accepting key!");
                    } else if (s->type==AUTH_TYPE_KEYBOARD_INTERACTIVE_QUIET) {
                        /* quiet, so no c_write */
                        logevent("Server refused keyboard-interactive authentication");
                    } else if (s->type==AUTH_TYPE_GSSAPI) {
                        /* always quiet, so no c_write */
                        /* also, the code down in the GSSAPI block has
                         * already logged this in the Event Log */
                    } else if (s->type == AUTH_TYPE_KEYBOARD_INTERACTIVE) {
                        logevent("Keyboard-interactive authentication failed");
                        c_write_str(ssh, "Access denied\r\n");
                    } else {
                        assert(s->type == AUTH_TYPE_PASSWORD);
                        logevent("Password authentication failed");
                        c_write_str(ssh, "Access denied\r\n");

                        if (conf_get_int(ssh->conf, CONF_change_username)) {
                            /* XXX perhaps we should allow
                             * keyboard-interactive to do this too? */
                            s->we_are_in = FALSE;
                            break;
                        }
                    }
                } else {
                    c_write_str(ssh, "Further authentication required\r\n");
                    logevent("Further authentication required");
                }

                s->can_pubkey =
                    in_commasep_string("publickey", methods, methlen);
                s->can_passwd =
                    in_commasep_string("password", methods, methlen);
                s->can_keyb_inter = conf_get_int(ssh->conf, CONF_try_ki_auth) &&
                    in_commasep_string("keyboard-interactive", methods, methlen);
#ifndef NO_GSSAPI
                if (conf_get_int(ssh->conf, CONF_try_gssapi_auth) &&
                    in_commasep_string("gssapi-with-mic", methods, methlen)) {
                    /* Try loading the GSS libraries and see if we
                     * have any. */
                    if (!ssh->gsslibs)
                        ssh->gsslibs = ssh_gss_setup(ssh->conf);
                    s->can_gssapi = (ssh->gsslibs->nlibraries > 0);
                } else {
                    /* No point in even bothering to try to load the
                     * GSS libraries, if the user configuration and
                     * server aren't both prepared to attempt GSSAPI
                     * auth in the first place. */
                    s->can_gssapi = FALSE;
                }
#endif
            }

            ssh->pkt_actx = SSH2_PKTCTX_NOAUTH;

            if (s->can_pubkey && !s->done_agent && s->nkeys) {

                /*
                 * Attempt public-key authentication using a key from Pageant.
                 */

                ssh->pkt_actx = SSH2_PKTCTX_PUBLICKEY;

                logeventf(ssh, "Trying Pageant key #%d", s->keyi);

                /* Unpack key from agent response */
                s->pklen = toint(GET_32BIT(s->agentp));
                s->agentp += 4;
                s->pkblob = (char *)s->agentp;
                s->agentp += s->pklen;
                s->alglen = toint(GET_32BIT(s->pkblob));
                s->alg = s->pkblob + 4;
                s->commentlen = toint(GET_32BIT(s->agentp));
                s->agentp += 4;
                s->commentp = (char *)s->agentp;
                s->agentp += s->commentlen;
                /* s->agentp now points at next key, if any */

                /* See if server will accept it */
                s->pktout = ssh2_pkt_init(SSH2_MSG_USERAUTH_REQUEST);
                ssh2_pkt_addstring(s->pktout, ssh->username);
                ssh2_pkt_addstring(s->pktout, "ssh-connection");
                                                    /* service requested */
                ssh2_pkt_addstring(s->pktout, "publickey");
                                                    /* method */
                ssh2_pkt_addbool(s->pktout, FALSE); /* no signature included */
                ssh2_pkt_addstring_start(s->pktout);
                ssh2_pkt_addstring_data(s->pktout, s->alg, s->alglen);
                ssh2_pkt_addstring_start(s->pktout);
                ssh2_pkt_addstring_data(s->pktout, s->pkblob, s->pklen);
                ssh2_pkt_send(ssh, s->pktout);
                s->type = AUTH_TYPE_PUBLICKEY_OFFER_QUIET;

                crWaitUntilV(pktin);
                if (pktin->type != SSH2_MSG_USERAUTH_PK_OK) {

                    /* Offer of key refused. */
                    s->gotit = TRUE;

                } else {
                    
                    void *vret;

                    if (flags & FLAG_VERBOSE) {
                        c_write_str(ssh, "Authenticating with "
                                    "public key \"");
                        c_write(ssh, s->commentp, s->commentlen);
                        c_write_str(ssh, "\" from agent\r\n");
                    }

                    /*
                     * Server is willing to accept the key.
                     * Construct a SIGN_REQUEST.
                     */
                    s->pktout = ssh2_pkt_init(SSH2_MSG_USERAUTH_REQUEST);
                    ssh2_pkt_addstring(s->pktout, ssh->username);
                    ssh2_pkt_addstring(s->pktout, "ssh-connection");
                                                        /* service requested */
                    ssh2_pkt_addstring(s->pktout, "publickey");
                                                        /* method */
                    ssh2_pkt_addbool(s->pktout, TRUE);  /* signature included */
                    ssh2_pkt_addstring_start(s->pktout);
                    ssh2_pkt_addstring_data(s->pktout, s->alg, s->alglen);
                    ssh2_pkt_addstring_start(s->pktout);
                    ssh2_pkt_addstring_data(s->pktout, s->pkblob, s->pklen);

                    /* Ask agent for signature. */
                    s->siglen = s->pktout->length - 5 + 4 +
                        ssh->v2_session_id_len;
                    if (ssh->remote_bugs & BUG_SSH2_PK_SESSIONID)
                        s->siglen -= 4;
                    s->len = 1;       /* message type */
                    s->len += 4 + s->pklen;     /* key blob */
                    s->len += 4 + s->siglen;    /* data to sign */
                    s->len += 4;      /* flags */
                    s->agentreq = snewn(4 + s->len, char);
                    PUT_32BIT(s->agentreq, s->len);
                    s->q = s->agentreq + 4;
                    *s->q++ = SSH2_AGENTC_SIGN_REQUEST;
                    PUT_32BIT(s->q, s->pklen);
                    s->q += 4;
                    memcpy(s->q, s->pkblob, s->pklen);
                    s->q += s->pklen;
                    PUT_32BIT(s->q, s->siglen);
                    s->q += 4;
                    /* Now the data to be signed... */
                    if (!(ssh->remote_bugs & BUG_SSH2_PK_SESSIONID)) {
                        PUT_32BIT(s->q, ssh->v2_session_id_len);
                        s->q += 4;
                    }
                    memcpy(s->q, ssh->v2_session_id,
                           ssh->v2_session_id_len);
                    s->q += ssh->v2_session_id_len;
                    memcpy(s->q, s->pktout->data + 5,
                           s->pktout->length - 5);
                    s->q += s->pktout->length - 5;
                    /* And finally the (zero) flags word. */
                    PUT_32BIT(s->q, 0);
                    if (!agent_query(s->agentreq, s->len + 4,
                                     &vret, &s->retlen,
                                     ssh_agent_callback, ssh)) {
                        do {
                            crReturnV;
                            if (pktin) {
                                bombout(("Unexpected data from server"
                                         " while waiting for agent"
                                         " response"));
                                crStopV;
                            }
                        } while (pktin || inlen > 0);
                        vret = ssh->agent_response;
                        s->retlen = ssh->agent_response_len;
                    }
                    s->ret = vret;
                    sfree(s->agentreq);
                    if (s->ret) {
                        if (s->retlen >= 9 &&
                            s->ret[4] == SSH2_AGENT_SIGN_RESPONSE &&
                            GET_32BIT(s->ret + 5) <= (unsigned)(s->retlen-9)) {
                            logevent("Sending Pageant's response");
                            ssh2_add_sigblob(ssh, s->pktout,
                                             s->pkblob, s->pklen,
                                             s->ret + 9,
                                             GET_32BIT(s->ret + 5));
                            ssh2_pkt_send(ssh, s->pktout);
                            s->type = AUTH_TYPE_PUBLICKEY;
                        } else {
                            /* FIXME: less drastic response */
                            bombout(("Pageant failed to answer challenge"));
                            crStopV;
                        }
                    }
                }

                /* Do we have any keys left to try? */
                if (s->pkblob_in_agent) {
                    s->done_agent = TRUE;
                    s->tried_pubkey_config = TRUE;
                } else {
                    s->keyi++;
                    if (s->keyi >= s->nkeys)
                        s->done_agent = TRUE;
                }

            } else if (s->can_pubkey && s->publickey_blob &&
                       s->privatekey_available && !s->tried_pubkey_config) {

                struct ssh2_userkey *key;   /* not live over crReturn */
                char *passphrase;           /* not live over crReturn */

                ssh->pkt_actx = SSH2_PKTCTX_PUBLICKEY;

                s->tried_pubkey_config = TRUE;

                /*
                 * Try the public key supplied in the configuration.
                 *
                 * First, offer the public blob to see if the server is
                 * willing to accept it.
                 */
                s->pktout = ssh2_pkt_init(SSH2_MSG_USERAUTH_REQUEST);
                ssh2_pkt_addstring(s->pktout, ssh->username);
                ssh2_pkt_addstring(s->pktout, "ssh-connection");
                                                /* service requested */
                ssh2_pkt_addstring(s->pktout, "publickey");     /* method */
                ssh2_pkt_addbool(s->pktout, FALSE);
                                                /* no signature included */
                ssh2_pkt_addstring(s->pktout, s->publickey_algorithm);
                ssh2_pkt_addstring_start(s->pktout);
                ssh2_pkt_addstring_data(s->pktout,
                                        (char *)s->publickey_blob,
                                        s->publickey_bloblen);
                ssh2_pkt_send(ssh, s->pktout);
                logevent("Offered public key");

                crWaitUntilV(pktin);
                if (pktin->type != SSH2_MSG_USERAUTH_PK_OK) {
                    /* Key refused. Give up. */
                    s->gotit = TRUE; /* reconsider message next loop */
                    s->type = AUTH_TYPE_PUBLICKEY_OFFER_LOUD;
                    continue; /* process this new message */
                }
                logevent("Offer of public key accepted");

                /*
                 * Actually attempt a serious authentication using
                 * the key.
                 */
                if (flags & FLAG_VERBOSE) {
                    c_write_str(ssh, "Authenticating with public key \"");
                    c_write_str(ssh, s->publickey_comment);
                    c_write_str(ssh, "\"\r\n");
                }
                key = NULL;
                while (!key) {
                    const char *error;  /* not live over crReturn */
                    if (s->privatekey_encrypted) {
                        /*
                         * Get a passphrase from the user.
                         */
                        int ret; /* need not be kept over crReturn */
                        s->cur_prompt = new_prompts(ssh->frontend);
                        s->cur_prompt->to_server = FALSE;
                        s->cur_prompt->name = dupstr("SSH key passphrase");
                        add_prompt(s->cur_prompt,
                                   dupprintf("Passphrase for key \"%.100s\": ",
                                             s->publickey_comment),
                                   FALSE);
                        ret = get_userpass_input(s->cur_prompt, NULL, 0);
                        while (ret < 0) {
                            ssh->send_ok = 1;
                            crWaitUntilV(!pktin);
                            ret = get_userpass_input(s->cur_prompt,
                                                     in, inlen);
                            ssh->send_ok = 0;
                        }
                        if (!ret) {
                            /* Failed to get a passphrase. Terminate. */
                            free_prompts(s->cur_prompt);
                            ssh_disconnect(ssh, NULL,
                                           "Unable to authenticate",
                                           SSH2_DISCONNECT_AUTH_CANCELLED_BY_USER,
                                           TRUE);
                            crStopV;
                        }
                        passphrase =
                            dupstr(s->cur_prompt->prompts[0]->result);
                        free_prompts(s->cur_prompt);
                    } else {
                        passphrase = NULL; /* no passphrase needed */
                    }

                    /*
                     * Try decrypting the key.
                     */
                    s->keyfile = conf_get_filename(ssh->conf, CONF_keyfile);
                    key = ssh2_load_userkey(s->keyfile, passphrase, &error);
                    if (passphrase) {
                        /* burn the evidence */
                        smemclr(passphrase, strlen(passphrase));
                        sfree(passphrase);
                    }
                    if (key == SSH2_WRONG_PASSPHRASE || key == NULL) {
                        if (passphrase &&
                            (key == SSH2_WRONG_PASSPHRASE)) {
                            c_write_str(ssh, "Wrong passphrase\r\n");
                            key = NULL;
                            /* and loop again */
                        } else {
                            c_write_str(ssh, "Unable to load private key (");
                            c_write_str(ssh, error);
                            c_write_str(ssh, ")\r\n");
                            key = NULL;
                            break; /* try something else */
                        }
                    }
                }

                if (key) {
                    unsigned char *pkblob, *sigblob, *sigdata;
                    int pkblob_len, sigblob_len, sigdata_len;
                    int p;

                    /*
                     * We have loaded the private key and the server
                     * has announced that it's willing to accept it.
                     * Hallelujah. Generate a signature and send it.
                     */
                    s->pktout = ssh2_pkt_init(SSH2_MSG_USERAUTH_REQUEST);
                    ssh2_pkt_addstring(s->pktout, ssh->username);
                    ssh2_pkt_addstring(s->pktout, "ssh-connection");
                                                    /* service requested */
                    ssh2_pkt_addstring(s->pktout, "publickey");
                                                    /* method */
                    ssh2_pkt_addbool(s->pktout, TRUE);
                                                    /* signature follows */
                    ssh2_pkt_addstring(s->pktout, key->alg->name);
                    pkblob = key->alg->public_blob(key->data,
                                                   &pkblob_len);
                    ssh2_pkt_addstring_start(s->pktout);
                    ssh2_pkt_addstring_data(s->pktout, (char *)pkblob,
                                            pkblob_len);

                    /*
                     * The data to be signed is:
                     *
                     *   string  session-id
                     *
                     * followed by everything so far placed in the
                     * outgoing packet.
                     */
                    sigdata_len = s->pktout->length - 5 + 4 +
                        ssh->v2_session_id_len;
                    if (ssh->remote_bugs & BUG_SSH2_PK_SESSIONID)
                        sigdata_len -= 4;
                    sigdata = snewn(sigdata_len, unsigned char);
                    p = 0;
                    if (!(ssh->remote_bugs & BUG_SSH2_PK_SESSIONID)) {
                        PUT_32BIT(sigdata+p, ssh->v2_session_id_len);
                        p += 4;
                    }
                    memcpy(sigdata+p, ssh->v2_session_id,
                           ssh->v2_session_id_len);
                    p += ssh->v2_session_id_len;
                    memcpy(sigdata+p, s->pktout->data + 5,
                           s->pktout->length - 5);
                    p += s->pktout->length - 5;
                    assert(p == sigdata_len);
                    sigblob = key->alg->sign(key->data, (char *)sigdata,
                                             sigdata_len, &sigblob_len);
                    ssh2_add_sigblob(ssh, s->pktout, pkblob, pkblob_len,
                                     sigblob, sigblob_len);
                    sfree(pkblob);
                    sfree(sigblob);
                    sfree(sigdata);

                    ssh2_pkt_send(ssh, s->pktout);
                    logevent("Sent public key signature");
                    s->type = AUTH_TYPE_PUBLICKEY;
                    key->alg->freekey(key->data);
                    sfree(key->comment);
                    sfree(key);
                }

#ifndef NO_GSSAPI
            } else if (s->can_gssapi && !s->tried_gssapi) {

                /* GSSAPI Authentication */

                int micoffset, len;
                char *data;
                Ssh_gss_buf mic;
                s->type = AUTH_TYPE_GSSAPI;
                s->tried_gssapi = TRUE;
                s->gotit = TRUE;
                ssh->pkt_actx = SSH2_PKTCTX_GSSAPI;

                /*
                 * Pick the highest GSS library on the preference
                 * list.
                 */
                {
                    int i, j;
                    s->gsslib = NULL;
                    for (i = 0; i < ngsslibs; i++) {
                        int want_id = conf_get_int_int(ssh->conf,
                                                       CONF_ssh_gsslist, i);
                        for (j = 0; j < ssh->gsslibs->nlibraries; j++)
                            if (ssh->gsslibs->libraries[j].id == want_id) {
                                s->gsslib = &ssh->gsslibs->libraries[j];
                                goto got_gsslib;   /* double break */
                            }
                    }
                    got_gsslib:
                    /*
                     * We always expect to have found something in
                     * the above loop: we only came here if there
                     * was at least one viable GSS library, and the
                     * preference list should always mention
                     * everything and only change the order.
                     */
                    assert(s->gsslib);
                }

                if (s->gsslib->gsslogmsg)
                    logevent(s->gsslib->gsslogmsg);

                /* Sending USERAUTH_REQUEST with "gssapi-with-mic" method */
                s->pktout = ssh2_pkt_init(SSH2_MSG_USERAUTH_REQUEST);
                ssh2_pkt_addstring(s->pktout, ssh->username);
                ssh2_pkt_addstring(s->pktout, "ssh-connection");
                ssh2_pkt_addstring(s->pktout, "gssapi-with-mic");
                logevent("Attempting GSSAPI authentication");

                /* add mechanism info */
                s->gsslib->indicate_mech(s->gsslib, &s->gss_buf);

                /* number of GSSAPI mechanisms */
                ssh2_pkt_adduint32(s->pktout,1);

                /* length of OID + 2 */
                ssh2_pkt_adduint32(s->pktout, s->gss_buf.length + 2);
                ssh2_pkt_addbyte(s->pktout, SSH2_GSS_OIDTYPE);

                /* length of OID */
                ssh2_pkt_addbyte(s->pktout, (unsigned char) s->gss_buf.length);

                ssh_pkt_adddata(s->pktout, s->gss_buf.value,
                                s->gss_buf.length);
                ssh2_pkt_send(ssh, s->pktout);
                crWaitUntilV(pktin);
                if (pktin->type != SSH2_MSG_USERAUTH_GSSAPI_RESPONSE) {
                    logevent("GSSAPI authentication request refused");
                    continue;
                }

                /* check returned packet ... */

                ssh_pkt_getstring(pktin, &data, &len);
                s->gss_rcvtok.value = data;
                s->gss_rcvtok.length = len;
                if (s->gss_rcvtok.length != s->gss_buf.length + 2 ||
                    ((char *)s->gss_rcvtok.value)[0] != SSH2_GSS_OIDTYPE ||
                    ((char *)s->gss_rcvtok.value)[1] != s->gss_buf.length ||
                    memcmp((char *)s->gss_rcvtok.value + 2,
                           s->gss_buf.value,s->gss_buf.length) ) {
                    logevent("GSSAPI authentication - wrong response from server");
                    continue;
                }

                /* now start running */
                s->gss_stat = s->gsslib->import_name(s->gsslib,
                                                     ssh->fullhostname,
                                                     &s->gss_srv_name);
                if (s->gss_stat != SSH_GSS_OK) {
                    if (s->gss_stat == SSH_GSS_BAD_HOST_NAME)
                        logevent("GSSAPI import name failed - Bad service name");
                    else
                        logevent("GSSAPI import name failed");
                    continue;
                }

                /* fetch TGT into GSS engine */
                s->gss_stat = s->gsslib->acquire_cred(s->gsslib, &s->gss_ctx);

                if (s->gss_stat != SSH_GSS_OK) {
                    logevent("GSSAPI authentication failed to get credentials");
                    s->gsslib->release_name(s->gsslib, &s->gss_srv_name);
                    continue;
                }

                /* initial tokens are empty */
                SSH_GSS_CLEAR_BUF(&s->gss_rcvtok);
                SSH_GSS_CLEAR_BUF(&s->gss_sndtok);

                /* now enter the loop */
                do {
                    s->gss_stat = s->gsslib->init_sec_context
                        (s->gsslib,
                         &s->gss_ctx,
                         s->gss_srv_name,
                         conf_get_int(ssh->conf, CONF_gssapifwd),
                         &s->gss_rcvtok,
                         &s->gss_sndtok);

                    if (s->gss_stat!=SSH_GSS_S_COMPLETE &&
                        s->gss_stat!=SSH_GSS_S_CONTINUE_NEEDED) {
                        logevent("GSSAPI authentication initialisation failed");

                        if (s->gsslib->display_status(s->gsslib, s->gss_ctx,
                                                      &s->gss_buf) == SSH_GSS_OK) {
                            logevent(s->gss_buf.value);
                            sfree(s->gss_buf.value);
                        }

                        break;
                    }
                    logevent("GSSAPI authentication initialised");

                    /* Client and server now exchange tokens until GSSAPI
                     * no longer says CONTINUE_NEEDED */

                    if (s->gss_sndtok.length != 0) {
                        s->pktout = ssh2_pkt_init(SSH2_MSG_USERAUTH_GSSAPI_TOKEN);
                        ssh_pkt_addstring_start(s->pktout);
                        ssh_pkt_addstring_data(s->pktout,s->gss_sndtok.value,s->gss_sndtok.length);
                        ssh2_pkt_send(ssh, s->pktout);
                        s->gsslib->free_tok(s->gsslib, &s->gss_sndtok);
                    }

                    if (s->gss_stat == SSH_GSS_S_CONTINUE_NEEDED) {
                        crWaitUntilV(pktin);
                        if (pktin->type != SSH2_MSG_USERAUTH_GSSAPI_TOKEN) {
                            logevent("GSSAPI authentication - bad server response");
                            s->gss_stat = SSH_GSS_FAILURE;
                            break;
                        }
                        ssh_pkt_getstring(pktin, &data, &len);
                        s->gss_rcvtok.value = data;
                        s->gss_rcvtok.length = len;
                    }
                } while (s-> gss_stat == SSH_GSS_S_CONTINUE_NEEDED);

                if (s->gss_stat != SSH_GSS_OK) {
                    s->gsslib->release_name(s->gsslib, &s->gss_srv_name);
                    s->gsslib->release_cred(s->gsslib, &s->gss_ctx);
                    continue;
                }
                logevent("GSSAPI authentication loop finished OK");

                /* Now send the MIC */

                s->pktout = ssh2_pkt_init(0);
                micoffset = s->pktout->length;
                ssh_pkt_addstring_start(s->pktout);
                ssh_pkt_addstring_data(s->pktout, (char *)ssh->v2_session_id, ssh->v2_session_id_len);
                ssh_pkt_addbyte(s->pktout, SSH2_MSG_USERAUTH_REQUEST);
                ssh_pkt_addstring(s->pktout, ssh->username);
                ssh_pkt_addstring(s->pktout, "ssh-connection");
                ssh_pkt_addstring(s->pktout, "gssapi-with-mic");

                s->gss_buf.value = (char *)s->pktout->data + micoffset;
                s->gss_buf.length = s->pktout->length - micoffset;

                s->gsslib->get_mic(s->gsslib, s->gss_ctx, &s->gss_buf, &mic);
                s->pktout = ssh2_pkt_init(SSH2_MSG_USERAUTH_GSSAPI_MIC);
                ssh_pkt_addstring_start(s->pktout);
                ssh_pkt_addstring_data(s->pktout, mic.value, mic.length);
                ssh2_pkt_send(ssh, s->pktout);
                s->gsslib->free_mic(s->gsslib, &mic);

                s->gotit = FALSE;

                s->gsslib->release_name(s->gsslib, &s->gss_srv_name);
                s->gsslib->release_cred(s->gsslib, &s->gss_ctx);
                continue;
#endif
            } else if (s->can_keyb_inter && !s->kbd_inter_refused) {

                /*
                 * Keyboard-interactive authentication.
                 */

                s->type = AUTH_TYPE_KEYBOARD_INTERACTIVE;

                ssh->pkt_actx = SSH2_PKTCTX_KBDINTER;

                s->pktout = ssh2_pkt_init(SSH2_MSG_USERAUTH_REQUEST);
                ssh2_pkt_addstring(s->pktout, ssh->username);
                ssh2_pkt_addstring(s->pktout, "ssh-connection");
                                                        /* service requested */
                ssh2_pkt_addstring(s->pktout, "keyboard-interactive");
                                                        /* method */
                ssh2_pkt_addstring(s->pktout, "");      /* lang */
                ssh2_pkt_addstring(s->pktout, "");      /* submethods */
                ssh2_pkt_send(ssh, s->pktout);
                
                logevent("Attempting keyboard-interactive authentication");

                crWaitUntilV(pktin);
                if (pktin->type != SSH2_MSG_USERAUTH_INFO_REQUEST) {
                    /* Server is not willing to do keyboard-interactive
                     * at all (or, bizarrely but legally, accepts the
                     * user without actually issuing any prompts).
                     * Give up on it entirely. */
                    s->gotit = TRUE;
                    s->type = AUTH_TYPE_KEYBOARD_INTERACTIVE_QUIET;
                    s->kbd_inter_refused = TRUE; /* don't try it again */
                    continue;
                }

                /*
                 * Loop while the server continues to send INFO_REQUESTs.
                 */
                while (pktin->type == SSH2_MSG_USERAUTH_INFO_REQUEST) {

                    char *name, *inst, *lang;
                    int name_len, inst_len, lang_len;
                    int i;

                    /*
                     * We've got a fresh USERAUTH_INFO_REQUEST.
                     * Get the preamble and start building a prompt.
                     */
                    ssh_pkt_getstring(pktin, &name, &name_len);
                    ssh_pkt_getstring(pktin, &inst, &inst_len);
                    ssh_pkt_getstring(pktin, &lang, &lang_len);
                    s->cur_prompt = new_prompts(ssh->frontend);
                    s->cur_prompt->to_server = TRUE;

                    /*
                     * Get any prompt(s) from the packet.
                     */
                    s->num_prompts = ssh_pkt_getuint32(pktin);
                    for (i = 0; i < s->num_prompts; i++) {
                        char *prompt;
                        int prompt_len;
                        int echo;
                        static char noprompt[] =
                            "<server failed to send prompt>: ";

                        ssh_pkt_getstring(pktin, &prompt, &prompt_len);
                        echo = ssh2_pkt_getbool(pktin);
                        if (!prompt_len) {
                            prompt = noprompt;
                            prompt_len = lenof(noprompt)-1;
                        }
                        add_prompt(s->cur_prompt,
                                   dupprintf("%.*s", prompt_len, prompt),
                                   echo);
                    }

                    if (name_len) {
                        /* FIXME: better prefix to distinguish from
                         * local prompts? */
                        s->cur_prompt->name =
                            dupprintf("SSH server: %.*s", name_len, name);
                        s->cur_prompt->name_reqd = TRUE;
                    } else {
                        s->cur_prompt->name =
                            dupstr("SSH server authentication");
                        s->cur_prompt->name_reqd = FALSE;
                    }
                    /* We add a prefix to try to make it clear that a prompt
                     * has come from the server.
                     * FIXME: ugly to print "Using..." in prompt _every_
                     * time round. Can this be done more subtly? */
                    /* Special case: for reasons best known to themselves,
                     * some servers send k-i requests with no prompts and
                     * nothing to display. Keep quiet in this case. */
                    if (s->num_prompts || name_len || inst_len) {
                        s->cur_prompt->instruction =
                            dupprintf("Using keyboard-interactive authentication.%s%.*s",
                                      inst_len ? "\n" : "", inst_len, inst);
                        s->cur_prompt->instr_reqd = TRUE;
                    } else {
                        s->cur_prompt->instr_reqd = FALSE;
                    }

                    /*
                     * Display any instructions, and get the user's
                     * response(s).
                     */
                    {
                        int ret; /* not live over crReturn */
                        ret = get_userpass_input(s->cur_prompt, NULL, 0);
                        while (ret < 0) {
                            ssh->send_ok = 1;
                            crWaitUntilV(!pktin);
                            ret = get_userpass_input(s->cur_prompt, in, inlen);
                            ssh->send_ok = 0;
                        }
                        if (!ret) {
                            /*
                             * Failed to get responses. Terminate.
                             */
                            free_prompts(s->cur_prompt);
                            ssh_disconnect(ssh, NULL, "Unable to authenticate",
                                           SSH2_DISCONNECT_AUTH_CANCELLED_BY_USER,
                                           TRUE);
                            crStopV;
                        }
                    }

                    /*
                     * Send the response(s) to the server.
                     */
                    s->pktout = ssh2_pkt_init(SSH2_MSG_USERAUTH_INFO_RESPONSE);
                    ssh2_pkt_adduint32(s->pktout, s->num_prompts);
                    for (i=0; i < s->num_prompts; i++) {
                        ssh2_pkt_addstring(s->pktout,
                                           s->cur_prompt->prompts[i]->result);
                    }
                    ssh2_pkt_send_with_padding(ssh, s->pktout, 256);

                    /*
                     * Free the prompts structure from this iteration.
                     * If there's another, a new one will be allocated
                     * when we return to the top of this while loop.
                     */
                    free_prompts(s->cur_prompt);

                    /*
                     * Get the next packet in case it's another
                     * INFO_REQUEST.
                     */
                    crWaitUntilV(pktin);

                }

                /*
                 * We should have SUCCESS or FAILURE now.
                 */
                s->gotit = TRUE;

            } else if (s->can_passwd) {

                /*
                 * Plain old password authentication.
                 */
                int ret; /* not live over crReturn */
                int changereq_first_time; /* not live over crReturn */

                ssh->pkt_actx = SSH2_PKTCTX_PASSWORD;

                s->cur_prompt = new_prompts(ssh->frontend);
                s->cur_prompt->to_server = TRUE;
                s->cur_prompt->name = dupstr("SSH password");
                add_prompt(s->cur_prompt, dupprintf("%s@%s's password: ",
                                                    ssh->username,
                                                    ssh->savedhost),
                           FALSE);

                ret = get_userpass_input(s->cur_prompt, NULL, 0);
                while (ret < 0) {
                    ssh->send_ok = 1;
                    crWaitUntilV(!pktin);
                    ret = get_userpass_input(s->cur_prompt, in, inlen);
                    ssh->send_ok = 0;
                }
                if (!ret) {
                    /*
                     * Failed to get responses. Terminate.
                     */
                    free_prompts(s->cur_prompt);
                    ssh_disconnect(ssh, NULL, "Unable to authenticate",
                                   SSH2_DISCONNECT_AUTH_CANCELLED_BY_USER,
                                   TRUE);
                    crStopV;
                }
                /*
                 * Squirrel away the password. (We may need it later if
                 * asked to change it.)
                 */
                s->password = dupstr(s->cur_prompt->prompts[0]->result);
                free_prompts(s->cur_prompt);

                /*
                 * Send the password packet.
                 *
                 * We pad out the password packet to 256 bytes to make
                 * it harder for an attacker to find the length of the
                 * user's password.
                 *
                 * Anyone using a password longer than 256 bytes
                 * probably doesn't have much to worry about from
                 * people who find out how long their password is!
                 */
                s->pktout = ssh2_pkt_init(SSH2_MSG_USERAUTH_REQUEST);
                ssh2_pkt_addstring(s->pktout, ssh->username);
                ssh2_pkt_addstring(s->pktout, "ssh-connection");
                                                        /* service requested */
                ssh2_pkt_addstring(s->pktout, "password");
                ssh2_pkt_addbool(s->pktout, FALSE);
                ssh2_pkt_addstring(s->pktout, s->password);
                ssh2_pkt_send_with_padding(ssh, s->pktout, 256);
                logevent("Sent password");
                s->type = AUTH_TYPE_PASSWORD;

                /*
                 * Wait for next packet, in case it's a password change
                 * request.
                 */
                crWaitUntilV(pktin);
                changereq_first_time = TRUE;

                while (pktin->type == SSH2_MSG_USERAUTH_PASSWD_CHANGEREQ) {

                    /* 
                     * We're being asked for a new password
                     * (perhaps not for the first time).
                     * Loop until the server accepts it.
                     */

                    int got_new = FALSE; /* not live over crReturn */
                    char *prompt;   /* not live over crReturn */
                    int prompt_len; /* not live over crReturn */
                    
                    {
                        const char *msg;
                        if (changereq_first_time)
                            msg = "Server requested password change";
                        else
                            msg = "Server rejected new password";
                        logevent(msg);
                        c_write_str(ssh, msg);
                        c_write_str(ssh, "\r\n");
                    }

                    ssh_pkt_getstring(pktin, &prompt, &prompt_len);

                    s->cur_prompt = new_prompts(ssh->frontend);
                    s->cur_prompt->to_server = TRUE;
                    s->cur_prompt->name = dupstr("New SSH password");
                    s->cur_prompt->instruction =
                        dupprintf("%.*s", prompt_len, NULLTOEMPTY(prompt));
                    s->cur_prompt->instr_reqd = TRUE;
                    /*
                     * There's no explicit requirement in the protocol
                     * for the "old" passwords in the original and
                     * password-change messages to be the same, and
                     * apparently some Cisco kit supports password change
                     * by the user entering a blank password originally
                     * and the real password subsequently, so,
                     * reluctantly, we prompt for the old password again.
                     *
                     * (On the other hand, some servers don't even bother
                     * to check this field.)
                     */
                    add_prompt(s->cur_prompt,
                               dupstr("Current password (blank for previously entered password): "),
                               FALSE);
                    add_prompt(s->cur_prompt, dupstr("Enter new password: "),
                               FALSE);
                    add_prompt(s->cur_prompt, dupstr("Confirm new password: "),
                               FALSE);

                    /*
                     * Loop until the user manages to enter the same
                     * password twice.
                     */
                    while (!got_new) {

                        ret = get_userpass_input(s->cur_prompt, NULL, 0);
                        while (ret < 0) {
                            ssh->send_ok = 1;
                            crWaitUntilV(!pktin);
                            ret = get_userpass_input(s->cur_prompt, in, inlen);
                            ssh->send_ok = 0;
                        }
                        if (!ret) {
                            /*
                             * Failed to get responses. Terminate.
                             */
                            /* burn the evidence */
                            free_prompts(s->cur_prompt);
                            smemclr(s->password, strlen(s->password));
                            sfree(s->password);
                            ssh_disconnect(ssh, NULL, "Unable to authenticate",
                                           SSH2_DISCONNECT_AUTH_CANCELLED_BY_USER,
                                           TRUE);
                            crStopV;
                        }

                        /*
                         * If the user specified a new original password
                         * (IYSWIM), overwrite any previously specified
                         * one.
                         * (A side effect is that the user doesn't have to
                         * re-enter it if they louse up the new password.)
                         */
                        if (s->cur_prompt->prompts[0]->result[0]) {
                            smemclr(s->password, strlen(s->password));
                                /* burn the evidence */
                            sfree(s->password);
                            s->password =
                                dupstr(s->cur_prompt->prompts[0]->result);
                        }

                        /*
                         * Check the two new passwords match.
                         */
                        got_new = (strcmp(s->cur_prompt->prompts[1]->result,
                                          s->cur_prompt->prompts[2]->result)
                                   == 0);
                        if (!got_new)
                            /* They don't. Silly user. */
                            c_write_str(ssh, "Passwords do not match\r\n");

                    }

                    /*
                     * Send the new password (along with the old one).
                     * (see above for padding rationale)
                     */
                    s->pktout = ssh2_pkt_init(SSH2_MSG_USERAUTH_REQUEST);
                    ssh2_pkt_addstring(s->pktout, ssh->username);
                    ssh2_pkt_addstring(s->pktout, "ssh-connection");
                                                        /* service requested */
                    ssh2_pkt_addstring(s->pktout, "password");
                    ssh2_pkt_addbool(s->pktout, TRUE);
                    ssh2_pkt_addstring(s->pktout, s->password);
                    ssh2_pkt_addstring(s->pktout,
                                       s->cur_prompt->prompts[1]->result);
                    free_prompts(s->cur_prompt);
                    ssh2_pkt_send_with_padding(ssh, s->pktout, 256);
                    logevent("Sent new password");
                    
                    /*
                     * Now see what the server has to say about it.
                     * (If it's CHANGEREQ again, it's not happy with the
                     * new password.)
                     */
                    crWaitUntilV(pktin);
                    changereq_first_time = FALSE;

                }

                /*
                 * We need to reexamine the current pktin at the top
                 * of the loop. Either:
                 *  - we weren't asked to change password at all, in
                 *    which case it's a SUCCESS or FAILURE with the
                 *    usual meaning
                 *  - we sent a new password, and the server was
                 *    either OK with it (SUCCESS or FAILURE w/partial
                 *    success) or unhappy with the _old_ password
                 *    (FAILURE w/o partial success)
                 * In any of these cases, we go back to the top of
                 * the loop and start again.
                 */
                s->gotit = TRUE;

                /*
                 * We don't need the old password any more, in any
                 * case. Burn the evidence.
                 */
                smemclr(s->password, strlen(s->password));
                sfree(s->password);

            } else {
                char *str = dupprintf("No supported authentication methods available"
                                      " (server sent: %.*s)",
                                      methlen, methods);

                ssh_disconnect(ssh, str,
                               "No supported authentication methods available",
                               SSH2_DISCONNECT_NO_MORE_AUTH_METHODS_AVAILABLE,
                               FALSE);
                sfree(str);

                crStopV;

            }

        }
    }
    ssh->packet_dispatch[SSH2_MSG_USERAUTH_BANNER] = NULL;

    /* Clear up various bits and pieces from authentication. */
    if (s->publickey_blob) {
        sfree(s->publickey_algorithm);
        sfree(s->publickey_blob);
        sfree(s->publickey_comment);
    }
    if (s->agent_response)
        sfree(s->agent_response);

    if (s->userauth_success && !ssh->bare_connection) {
        /*
         * We've just received USERAUTH_SUCCESS, and we haven't sent any
         * packets since. Signal the transport layer to consider enacting
         * delayed compression.
         *
         * (Relying on we_are_in is not sufficient, as
         * draft-miller-secsh-compression-delayed is quite clear that it
         * triggers on USERAUTH_SUCCESS specifically, and we_are_in can
         * become set for other reasons.)
         */
        do_ssh2_transport(ssh, "enabling delayed compression", -2, NULL);
    }

    ssh->channels = newtree234(ssh_channelcmp);

    /*
     * Set up handlers for some connection protocol messages, so we
     * don't have to handle them repeatedly in this coroutine.
     */
    ssh->packet_dispatch[SSH2_MSG_CHANNEL_WINDOW_ADJUST] =
        ssh2_msg_channel_window_adjust;
    ssh->packet_dispatch[SSH2_MSG_GLOBAL_REQUEST] =
        ssh2_msg_global_request;

    /*
     * Create the main session channel.
     */
    if (conf_get_int(ssh->conf, CONF_ssh_no_shell)) {
        ssh->mainchan = NULL;
    } else {
        ssh->mainchan = snew(struct ssh_channel);
        ssh->mainchan->ssh = ssh;
        ssh_channel_init(ssh->mainchan);

        if (*conf_get_str(ssh->conf, CONF_ssh_nc_host)) {
            /*
             * Just start a direct-tcpip channel and use it as the main
             * channel.
             */
            ssh_send_port_open(ssh->mainchan,
                               conf_get_str(ssh->conf, CONF_ssh_nc_host),
                               conf_get_int(ssh->conf, CONF_ssh_nc_port),
                               "main channel");
            ssh->ncmode = TRUE;
        } else {
            s->pktout = ssh2_chanopen_init(ssh->mainchan, "session");
            logevent("Opening session as main channel");
            ssh2_pkt_send(ssh, s->pktout);
            ssh->ncmode = FALSE;
        }
        crWaitUntilV(pktin);
        if (pktin->type != SSH2_MSG_CHANNEL_OPEN_CONFIRMATION) {
            bombout(("Server refused to open channel"));
            crStopV;
            /* FIXME: error data comes back in FAILURE packet */
        }
        if (ssh_pkt_getuint32(pktin) != ssh->mainchan->localid) {
            bombout(("Server's channel confirmation cited wrong channel"));
            crStopV;
        }
        ssh->mainchan->remoteid = ssh_pkt_getuint32(pktin);
        ssh->mainchan->halfopen = FALSE;
        ssh->mainchan->type = CHAN_MAINSESSION;
        ssh->mainchan->v.v2.remwindow = ssh_pkt_getuint32(pktin);
        ssh->mainchan->v.v2.remmaxpkt = ssh_pkt_getuint32(pktin);
        update_specials_menu(ssh->frontend);
        logevent("Opened main channel");
    }

    /*
     * Now we have a channel, make dispatch table entries for
     * general channel-based messages.
     */
    ssh->packet_dispatch[SSH2_MSG_CHANNEL_DATA] =
    ssh->packet_dispatch[SSH2_MSG_CHANNEL_EXTENDED_DATA] =
        ssh2_msg_channel_data;
    ssh->packet_dispatch[SSH2_MSG_CHANNEL_EOF] = ssh2_msg_channel_eof;
    ssh->packet_dispatch[SSH2_MSG_CHANNEL_CLOSE] = ssh2_msg_channel_close;
    ssh->packet_dispatch[SSH2_MSG_CHANNEL_OPEN_CONFIRMATION] =
        ssh2_msg_channel_open_confirmation;
    ssh->packet_dispatch[SSH2_MSG_CHANNEL_OPEN_FAILURE] =
        ssh2_msg_channel_open_failure;
    ssh->packet_dispatch[SSH2_MSG_CHANNEL_REQUEST] =
        ssh2_msg_channel_request;
    ssh->packet_dispatch[SSH2_MSG_CHANNEL_OPEN] =
        ssh2_msg_channel_open;
    ssh->packet_dispatch[SSH2_MSG_CHANNEL_SUCCESS] = ssh2_msg_channel_response;
    ssh->packet_dispatch[SSH2_MSG_CHANNEL_FAILURE] = ssh2_msg_channel_response;

    /*
     * Now the connection protocol is properly up and running, with
     * all those dispatch table entries, so it's safe to let
     * downstreams start trying to open extra channels through us.
     */
    if (ssh->connshare)
        share_activate(ssh->connshare, ssh->v_s);

    if (ssh->mainchan && ssh_is_simple(ssh)) {
        /*
         * This message indicates to the server that we promise
         * not to try to run any other channel in parallel with
         * this one, so it's safe for it to advertise a very large
         * window and leave the flow control to TCP.
         */
        s->pktout = ssh2_chanreq_init(ssh->mainchan,
                                      "simple@putty.projects.tartarus.org",
                                      NULL, NULL);
        ssh2_pkt_send(ssh, s->pktout);
    }

    /*
     * Enable port forwardings.
     */
    ssh_setup_portfwd(ssh, ssh->conf);

    if (ssh->mainchan && !ssh->ncmode) {
        /*
         * Send the CHANNEL_REQUESTS for the main session channel.
         * Each one is handled by its own little asynchronous
         * co-routine.
         */

        /* Potentially enable X11 forwarding. */
        if (conf_get_int(ssh->conf, CONF_x11_forward)) {
            ssh->x11disp =
                x11_setup_display(conf_get_str(ssh->conf, CONF_x11_display),
                                  ssh->conf);
            if (!ssh->x11disp) {
                /* FIXME: return an error message from x11_setup_display */
                logevent("X11 forwarding not enabled: unable to"
                         " initialise X display");
            } else {
                ssh->x11auth = x11_invent_fake_auth
                    (ssh->x11authtree, conf_get_int(ssh->conf, CONF_x11_auth));
                ssh->x11auth->disp = ssh->x11disp;

                ssh2_setup_x11(ssh->mainchan, NULL, NULL);
            }
        }

        /* Potentially enable agent forwarding. */
        if (ssh_agent_forwarding_permitted(ssh))
            ssh2_setup_agent(ssh->mainchan, NULL, NULL);

        /* Now allocate a pty for the session. */
        if (!conf_get_int(ssh->conf, CONF_nopty))
            ssh2_setup_pty(ssh->mainchan, NULL, NULL);

        /* Send environment variables. */
        ssh2_setup_env(ssh->mainchan, NULL, NULL);

        /*
         * Start a shell or a remote command. We may have to attempt
         * this twice if the config data has provided a second choice
         * of command.
         */
        while (1) {
            int subsys;
            char *cmd;

            if (ssh->fallback_cmd) {
                subsys = conf_get_int(ssh->conf, CONF_ssh_subsys2);
                cmd = conf_get_str(ssh->conf, CONF_remote_cmd2);
            } else {
                subsys = conf_get_int(ssh->conf, CONF_ssh_subsys);
                cmd = conf_get_str(ssh->conf, CONF_remote_cmd);
            }

            if (subsys) {
                s->pktout = ssh2_chanreq_init(ssh->mainchan, "subsystem",
                                              ssh2_response_authconn, NULL);
                ssh2_pkt_addstring(s->pktout, cmd);
            } else if (*cmd) {
                s->pktout = ssh2_chanreq_init(ssh->mainchan, "exec",
                                              ssh2_response_authconn, NULL);
                ssh2_pkt_addstring(s->pktout, cmd);
            } else {
                s->pktout = ssh2_chanreq_init(ssh->mainchan, "shell",
                                              ssh2_response_authconn, NULL);
            }
            ssh2_pkt_send(ssh, s->pktout);

            crWaitUntilV(pktin);

            if (pktin->type != SSH2_MSG_CHANNEL_SUCCESS) {
                if (pktin->type != SSH2_MSG_CHANNEL_FAILURE) {
                    bombout(("Unexpected response to shell/command request:"
                             " packet type %d", pktin->type));
                    crStopV;
                }
                /*
                 * We failed to start the command. If this is the
                 * fallback command, we really are finished; if it's
                 * not, and if the fallback command exists, try falling
                 * back to it before complaining.
                 */
                if (!ssh->fallback_cmd &&
                    *conf_get_str(ssh->conf, CONF_remote_cmd2)) {
                    logevent("Primary command failed; attempting fallback");
                    ssh->fallback_cmd = TRUE;
                    continue;
                }
                bombout(("Server refused to start a shell/command"));
                crStopV;
            } else {
                logevent("Started a shell/command");
            }
            break;
        }
    } else {
        ssh->editing = ssh->echoing = TRUE;
    }

    ssh->state = SSH_STATE_SESSION;
    if (ssh->size_needed)
        ssh_size(ssh, ssh->term_width, ssh->term_height);
    if (ssh->eof_needed)
        ssh_special(ssh, TS_EOF);

    /*
     * Transfer data!
     */
    if (ssh->ldisc)
        ldisc_echoedit_update(ssh->ldisc);  /* cause ldisc to notice changes */
    if (ssh->mainchan)
        ssh->send_ok = 1;
    while (1) {
        crReturnV;
        if (pktin) {

            /*
             * _All_ the connection-layer packets we expect to
             * receive are now handled by the dispatch table.
             * Anything that reaches here must be bogus.
             */

            bombout(("Strange packet received: type %d", pktin->type));
            crStopV;
        } else if (ssh->mainchan) {
            /*
             * We have spare data. Add it to the channel buffer.
             */
            ssh_send_channel_data(ssh->mainchan, (char *)in, inlen);
        }
    }

    crFinishV;
}

/*
 * Handlers for SSH-2 messages that might arrive at any moment.
 */
static void ssh2_msg_disconnect(Ssh ssh, struct Packet *pktin)
{
    /* log reason code in disconnect message */
    char *buf, *msg;
    int reason, msglen;

    reason = ssh_pkt_getuint32(pktin);
    ssh_pkt_getstring(pktin, &msg, &msglen);

    if (reason > 0 && reason < lenof(ssh2_disconnect_reasons)) {
        buf = dupprintf("Received disconnect message (%s)",
                        ssh2_disconnect_reasons[reason]);
    } else {
        buf = dupprintf("Received disconnect message (unknown"
                        " type %d)", reason);
    }
    logevent(buf);
    sfree(buf);
    buf = dupprintf("Disconnection message text: %.*s",
                    msglen, NULLTOEMPTY(msg));
    logevent(buf);
    bombout(("Server sent disconnect message\ntype %d (%s):\n\"%.*s\"",
             reason,
             (reason > 0 && reason < lenof(ssh2_disconnect_reasons)) ?
             ssh2_disconnect_reasons[reason] : "unknown",
             msglen, NULLTOEMPTY(msg)));
    sfree(buf);
}

static void ssh2_msg_debug(Ssh ssh, struct Packet *pktin)
{
    /* log the debug message */
    char *msg;
    int msglen;

    /* XXX maybe we should actually take notice of the return value */
    ssh2_pkt_getbool(pktin);
    ssh_pkt_getstring(pktin, &msg, &msglen);

    logeventf(ssh, "Remote debug message: %.*s", msglen, NULLTOEMPTY(msg));
}

static void ssh2_msg_transport(Ssh ssh, struct Packet *pktin)
{
    do_ssh2_transport(ssh, NULL, 0, pktin);
}

/*
 * Called if we receive a packet that isn't allowed by the protocol.
 * This only applies to packets whose meaning PuTTY understands.
 * Entirely unknown packets are handled below.
 */
static void ssh2_msg_unexpected(Ssh ssh, struct Packet *pktin)
{
    char *buf = dupprintf("Server protocol violation: unexpected %s packet",
                          ssh2_pkt_type(ssh->pkt_kctx, ssh->pkt_actx,
                                        pktin->type));
    ssh_disconnect(ssh, NULL, buf, SSH2_DISCONNECT_PROTOCOL_ERROR, FALSE);
    sfree(buf);
}

static void ssh2_msg_something_unimplemented(Ssh ssh, struct Packet *pktin)
{
    struct Packet *pktout;
    pktout = ssh2_pkt_init(SSH2_MSG_UNIMPLEMENTED);
    ssh2_pkt_adduint32(pktout, pktin->sequence);
    /*
     * UNIMPLEMENTED messages MUST appear in the same order as the
     * messages they respond to. Hence, never queue them.
     */
    ssh2_pkt_send_noqueue(ssh, pktout);
}

/*
 * Handle the top-level SSH-2 protocol.
 */
static void ssh2_protocol_setup(Ssh ssh)
{
    int i;

    /*
     * Most messages cause SSH2_MSG_UNIMPLEMENTED.
     */
    for (i = 0; i < 256; i++)
        ssh->packet_dispatch[i] = ssh2_msg_something_unimplemented;

    /*
     * Initially, we only accept transport messages (and a few generic
     * ones).  do_ssh2_authconn will add more when it starts.
     * Messages that are understood but not currently acceptable go to
     * ssh2_msg_unexpected.
     */
    ssh->packet_dispatch[SSH2_MSG_UNIMPLEMENTED] = ssh2_msg_unexpected;
    ssh->packet_dispatch[SSH2_MSG_SERVICE_REQUEST] = ssh2_msg_unexpected;
    ssh->packet_dispatch[SSH2_MSG_SERVICE_ACCEPT] = ssh2_msg_unexpected;
    ssh->packet_dispatch[SSH2_MSG_KEXINIT] = ssh2_msg_transport;
    ssh->packet_dispatch[SSH2_MSG_NEWKEYS] = ssh2_msg_transport;
    ssh->packet_dispatch[SSH2_MSG_KEXDH_INIT] = ssh2_msg_transport;
    ssh->packet_dispatch[SSH2_MSG_KEXDH_REPLY] = ssh2_msg_transport;
    /* ssh->packet_dispatch[SSH2_MSG_KEX_DH_GEX_REQUEST] = ssh2_msg_transport; duplicate case value */
    /* ssh->packet_dispatch[SSH2_MSG_KEX_DH_GEX_GROUP] = ssh2_msg_transport; duplicate case value */
    ssh->packet_dispatch[SSH2_MSG_KEX_DH_GEX_INIT] = ssh2_msg_transport;
    ssh->packet_dispatch[SSH2_MSG_KEX_DH_GEX_REPLY] = ssh2_msg_transport;
    ssh->packet_dispatch[SSH2_MSG_USERAUTH_REQUEST] = ssh2_msg_unexpected;
    ssh->packet_dispatch[SSH2_MSG_USERAUTH_FAILURE] = ssh2_msg_unexpected;
    ssh->packet_dispatch[SSH2_MSG_USERAUTH_SUCCESS] = ssh2_msg_unexpected;
    ssh->packet_dispatch[SSH2_MSG_USERAUTH_BANNER] = ssh2_msg_unexpected;
    ssh->packet_dispatch[SSH2_MSG_USERAUTH_PK_OK] = ssh2_msg_unexpected;
    /* ssh->packet_dispatch[SSH2_MSG_USERAUTH_PASSWD_CHANGEREQ] = ssh2_msg_unexpected; duplicate case value */
    /* ssh->packet_dispatch[SSH2_MSG_USERAUTH_INFO_REQUEST] = ssh2_msg_unexpected; duplicate case value */
    ssh->packet_dispatch[SSH2_MSG_USERAUTH_INFO_RESPONSE] = ssh2_msg_unexpected;
    ssh->packet_dispatch[SSH2_MSG_GLOBAL_REQUEST] = ssh2_msg_unexpected;
    ssh->packet_dispatch[SSH2_MSG_REQUEST_SUCCESS] = ssh2_msg_unexpected;
    ssh->packet_dispatch[SSH2_MSG_REQUEST_FAILURE] = ssh2_msg_unexpected;
    ssh->packet_dispatch[SSH2_MSG_CHANNEL_OPEN] = ssh2_msg_unexpected;
    ssh->packet_dispatch[SSH2_MSG_CHANNEL_OPEN_CONFIRMATION] = ssh2_msg_unexpected;
    ssh->packet_dispatch[SSH2_MSG_CHANNEL_OPEN_FAILURE] = ssh2_msg_unexpected;
    ssh->packet_dispatch[SSH2_MSG_CHANNEL_WINDOW_ADJUST] = ssh2_msg_unexpected;
    ssh->packet_dispatch[SSH2_MSG_CHANNEL_DATA] = ssh2_msg_unexpected;
    ssh->packet_dispatch[SSH2_MSG_CHANNEL_EXTENDED_DATA] = ssh2_msg_unexpected;
    ssh->packet_dispatch[SSH2_MSG_CHANNEL_EOF] = ssh2_msg_unexpected;
    ssh->packet_dispatch[SSH2_MSG_CHANNEL_CLOSE] = ssh2_msg_unexpected;
    ssh->packet_dispatch[SSH2_MSG_CHANNEL_REQUEST] = ssh2_msg_unexpected;
    ssh->packet_dispatch[SSH2_MSG_CHANNEL_SUCCESS] = ssh2_msg_unexpected;
    ssh->packet_dispatch[SSH2_MSG_CHANNEL_FAILURE] = ssh2_msg_unexpected;

    /*
     * These messages have a special handler from the start.
     */
    ssh->packet_dispatch[SSH2_MSG_DISCONNECT] = ssh2_msg_disconnect;
    ssh->packet_dispatch[SSH2_MSG_IGNORE] = ssh_msg_ignore; /* shared with SSH-1 */
    ssh->packet_dispatch[SSH2_MSG_DEBUG] = ssh2_msg_debug;
}

static void ssh2_bare_connection_protocol_setup(Ssh ssh)
{
    int i;

    /*
     * Most messages cause SSH2_MSG_UNIMPLEMENTED.
     */
    for (i = 0; i < 256; i++)
        ssh->packet_dispatch[i] = ssh2_msg_something_unimplemented;

    /*
     * Initially, we set all ssh-connection messages to 'unexpected';
     * do_ssh2_authconn will fill things in properly. We also handle a
     * couple of messages from the transport protocol which aren't
     * related to key exchange (UNIMPLEMENTED, IGNORE, DEBUG,
     * DISCONNECT).
     */
    ssh->packet_dispatch[SSH2_MSG_GLOBAL_REQUEST] = ssh2_msg_unexpected;
    ssh->packet_dispatch[SSH2_MSG_REQUEST_SUCCESS] = ssh2_msg_unexpected;
    ssh->packet_dispatch[SSH2_MSG_REQUEST_FAILURE] = ssh2_msg_unexpected;
    ssh->packet_dispatch[SSH2_MSG_CHANNEL_OPEN] = ssh2_msg_unexpected;
    ssh->packet_dispatch[SSH2_MSG_CHANNEL_OPEN_CONFIRMATION] = ssh2_msg_unexpected;
    ssh->packet_dispatch[SSH2_MSG_CHANNEL_OPEN_FAILURE] = ssh2_msg_unexpected;
    ssh->packet_dispatch[SSH2_MSG_CHANNEL_WINDOW_ADJUST] = ssh2_msg_unexpected;
    ssh->packet_dispatch[SSH2_MSG_CHANNEL_DATA] = ssh2_msg_unexpected;
    ssh->packet_dispatch[SSH2_MSG_CHANNEL_EXTENDED_DATA] = ssh2_msg_unexpected;
    ssh->packet_dispatch[SSH2_MSG_CHANNEL_EOF] = ssh2_msg_unexpected;
    ssh->packet_dispatch[SSH2_MSG_CHANNEL_CLOSE] = ssh2_msg_unexpected;
    ssh->packet_dispatch[SSH2_MSG_CHANNEL_REQUEST] = ssh2_msg_unexpected;
    ssh->packet_dispatch[SSH2_MSG_CHANNEL_SUCCESS] = ssh2_msg_unexpected;
    ssh->packet_dispatch[SSH2_MSG_CHANNEL_FAILURE] = ssh2_msg_unexpected;

    ssh->packet_dispatch[SSH2_MSG_UNIMPLEMENTED] = ssh2_msg_unexpected;

    /*
     * These messages have a special handler from the start.
     */
    ssh->packet_dispatch[SSH2_MSG_DISCONNECT] = ssh2_msg_disconnect;
    ssh->packet_dispatch[SSH2_MSG_IGNORE] = ssh_msg_ignore;
    ssh->packet_dispatch[SSH2_MSG_DEBUG] = ssh2_msg_debug;
}

static void ssh2_timer(void *ctx, unsigned long now)
{
    Ssh ssh = (Ssh)ctx;

    if (ssh->state == SSH_STATE_CLOSED)
        return;

    if (!ssh->kex_in_progress && !ssh->bare_connection &&
        conf_get_int(ssh->conf, CONF_ssh_rekey_time) != 0 &&
        now == ssh->next_rekey) {
        do_ssh2_transport(ssh, "timeout", -1, NULL);
    }
}

static void ssh2_protocol(Ssh ssh, const void *vin, int inlen,
                          struct Packet *pktin)
{
    const unsigned char *in = (const unsigned char *)vin;
    if (ssh->state == SSH_STATE_CLOSED)
        return;

    if (pktin) {
        ssh->incoming_data_size += pktin->encrypted_len;
        if (!ssh->kex_in_progress &&
            ssh->max_data_size != 0 &&
            ssh->incoming_data_size > ssh->max_data_size)
            do_ssh2_transport(ssh, "too much data received", -1, NULL);
    }

    if (pktin)
        ssh->packet_dispatch[pktin->type](ssh, pktin);
    else if (!ssh->protocol_initial_phase_done)
        do_ssh2_transport(ssh, in, inlen, pktin);
    else
        do_ssh2_authconn(ssh, in, inlen, pktin);
}

static void ssh2_bare_connection_protocol(Ssh ssh, const void *vin, int inlen,
                                          struct Packet *pktin)
{
    const unsigned char *in = (const unsigned char *)vin;
    if (ssh->state == SSH_STATE_CLOSED)
        return;

    if (pktin)
        ssh->packet_dispatch[pktin->type](ssh, pktin);
    else
        do_ssh2_authconn(ssh, in, inlen, pktin);
}

static void ssh_cache_conf_values(Ssh ssh)
{
    ssh->logomitdata = conf_get_int(ssh->conf, CONF_logomitdata);
}

/*
 * Called to set up the connection.
 *
 * Returns an error message, or NULL on success.
 */
static const char *ssh_init(void *frontend_handle, void **backend_handle,
                            Conf *conf,
                            const char *host, int port, char **realhost,
                            int nodelay, int keepalive)
{
    const char *p;
    Ssh ssh;

    ssh = snew(struct ssh_tag);
    ssh->conf = conf_copy(conf);
    ssh_cache_conf_values(ssh);
    ssh->version = 0;                  /* when not ready yet */
    ssh->s = NULL;
    ssh->cipher = NULL;
    ssh->v1_cipher_ctx = NULL;
    ssh->crcda_ctx = NULL;
    ssh->cscipher = NULL;
    ssh->cs_cipher_ctx = NULL;
    ssh->sccipher = NULL;
    ssh->sc_cipher_ctx = NULL;
    ssh->csmac = NULL;
    ssh->cs_mac_ctx = NULL;
    ssh->scmac = NULL;
    ssh->sc_mac_ctx = NULL;
    ssh->cscomp = NULL;
    ssh->cs_comp_ctx = NULL;
    ssh->sccomp = NULL;
    ssh->sc_comp_ctx = NULL;
    ssh->kex = NULL;
    ssh->kex_ctx = NULL;
    ssh->hostkey = NULL;
    ssh->hostkey_str = NULL;
    ssh->exitcode = -1;
    ssh->close_expected = FALSE;
    ssh->clean_exit = FALSE;
    ssh->state = SSH_STATE_PREPACKET;
    ssh->size_needed = FALSE;
    ssh->eof_needed = FALSE;
    ssh->ldisc = NULL;
    ssh->logctx = NULL;
    ssh->deferred_send_data = NULL;
    ssh->deferred_len = 0;
    ssh->deferred_size = 0;
    ssh->fallback_cmd = 0;
    ssh->pkt_kctx = SSH2_PKTCTX_NOKEX;
    ssh->pkt_actx = SSH2_PKTCTX_NOAUTH;
    ssh->x11disp = NULL;
    ssh->x11auth = NULL;
    ssh->x11authtree = newtree234(x11_authcmp);
    ssh->v1_compressing = FALSE;
    ssh->v2_outgoing_sequence = 0;
    ssh->ssh1_rdpkt_crstate = 0;
    ssh->ssh2_rdpkt_crstate = 0;
    ssh->ssh2_bare_rdpkt_crstate = 0;
    ssh->ssh_gotdata_crstate = 0;
    ssh->do_ssh1_connection_crstate = 0;
    ssh->do_ssh_init_state = NULL;
    ssh->do_ssh_connection_init_state = NULL;
    ssh->do_ssh1_login_state = NULL;
    ssh->do_ssh2_transport_state = NULL;
    ssh->do_ssh2_authconn_state = NULL;
    ssh->v_c = NULL;
    ssh->v_s = NULL;
    ssh->mainchan = NULL;
    ssh->throttled_all = 0;
    ssh->v1_stdout_throttling = 0;
    ssh->queue = NULL;
    ssh->queuelen = ssh->queuesize = 0;
    ssh->queueing = FALSE;
    ssh->qhead = ssh->qtail = NULL;
    ssh->deferred_rekey_reason = NULL;
    bufchain_init(&ssh->queued_incoming_data);
    ssh->frozen = FALSE;
    ssh->username = NULL;
    ssh->sent_console_eof = FALSE;
    ssh->got_pty = FALSE;
    ssh->bare_connection = FALSE;
    ssh->X11_fwd_enabled = FALSE;
    ssh->connshare = NULL;
    ssh->attempting_connshare = FALSE;
    ssh->session_started = FALSE;
    ssh->specials = NULL;
    ssh->n_uncert_hostkeys = 0;
    ssh->cross_certifying = FALSE;

    *backend_handle = ssh;

#ifdef MSCRYPTOAPI
    if (crypto_startup() == 0)
        return "Microsoft high encryption pack not installed!";
#endif

    ssh->frontend = frontend_handle;
    ssh->term_width = conf_get_int(ssh->conf, CONF_width);
    ssh->term_height = conf_get_int(ssh->conf, CONF_height);

    ssh->channels = NULL;
    ssh->rportfwds = NULL;
    ssh->portfwds = NULL;

    ssh->send_ok = 0;
    ssh->editing = 0;
    ssh->echoing = 0;
    ssh->conn_throttle_count = 0;
    ssh->overall_bufsize = 0;
    ssh->fallback_cmd = 0;

    ssh->protocol = NULL;

    ssh->protocol_initial_phase_done = FALSE;

    ssh->pinger = NULL;

    ssh->incoming_data_size = ssh->outgoing_data_size =
        ssh->deferred_data_size = 0L;
    ssh->max_data_size = parse_blocksize(conf_get_str(ssh->conf,
                                                      CONF_ssh_rekey_data));
    ssh->kex_in_progress = FALSE;

#ifndef NO_GSSAPI
    ssh->gsslibs = NULL;
#endif

    random_ref(); /* do this now - may be needed by sharing setup code */

    p = connect_to_host(ssh, host, port, realhost, nodelay, keepalive);
    if (p != NULL) {
        random_unref();
        return p;
    }

    return NULL;
}

static void ssh_free(void *handle)
{
    Ssh ssh = (Ssh) handle;
    struct ssh_channel *c;
    struct ssh_rportfwd *pf;
    struct X11FakeAuth *auth;

    if (ssh->v1_cipher_ctx)
        ssh->cipher->free_context(ssh->v1_cipher_ctx);
    if (ssh->cs_cipher_ctx)
        ssh->cscipher->free_context(ssh->cs_cipher_ctx);
    if (ssh->sc_cipher_ctx)
        ssh->sccipher->free_context(ssh->sc_cipher_ctx);
    if (ssh->cs_mac_ctx)
        ssh->csmac->free_context(ssh->cs_mac_ctx);
    if (ssh->sc_mac_ctx)
        ssh->scmac->free_context(ssh->sc_mac_ctx);
    if (ssh->cs_comp_ctx) {
        if (ssh->cscomp)
            ssh->cscomp->compress_cleanup(ssh->cs_comp_ctx);
        else
            zlib_compress_cleanup(ssh->cs_comp_ctx);
    }
    if (ssh->sc_comp_ctx) {
        if (ssh->sccomp)
            ssh->sccomp->decompress_cleanup(ssh->sc_comp_ctx);
        else
            zlib_decompress_cleanup(ssh->sc_comp_ctx);
    }
    if (ssh->kex_ctx)
        dh_cleanup(ssh->kex_ctx);
    sfree(ssh->savedhost);

    while (ssh->queuelen-- > 0)
        ssh_free_packet(ssh->queue[ssh->queuelen]);
    sfree(ssh->queue);

    while (ssh->qhead) {
        struct queued_handler *qh = ssh->qhead;
        ssh->qhead = qh->next;
        sfree(qh);
    }
    ssh->qhead = ssh->qtail = NULL;

    if (ssh->channels) {
        while ((c = delpos234(ssh->channels, 0)) != NULL) {
            switch (c->type) {
              case CHAN_X11:
                if (c->u.x11.xconn != NULL)
                    x11_close(c->u.x11.xconn);
                break;
              case CHAN_SOCKDATA:
              case CHAN_SOCKDATA_DORMANT:
                if (c->u.pfd.pf != NULL)
                    pfd_close(c->u.pfd.pf);
                break;
            }
            if (ssh->version == 2) {
                struct outstanding_channel_request *ocr, *nocr;
                ocr = c->v.v2.chanreq_head;
                while (ocr) {
                    ocr->handler(c, NULL, ocr->ctx);
                    nocr = ocr->next;
                    sfree(ocr);
                    ocr = nocr;
                }
                bufchain_clear(&c->v.v2.outbuffer);
            }
            sfree(c);
        }
        freetree234(ssh->channels);
        ssh->channels = NULL;
    }

    if (ssh->connshare)
        sharestate_free(ssh->connshare);

    if (ssh->rportfwds) {
        while ((pf = delpos234(ssh->rportfwds, 0)) != NULL)
            free_rportfwd(pf);
        freetree234(ssh->rportfwds);
        ssh->rportfwds = NULL;
    }
    sfree(ssh->deferred_send_data);
    if (ssh->x11disp)
        x11_free_display(ssh->x11disp);
    while ((auth = delpos234(ssh->x11authtree, 0)) != NULL)
        x11_free_fake_auth(auth);
    freetree234(ssh->x11authtree);
    sfree(ssh->do_ssh_init_state);
    sfree(ssh->do_ssh1_login_state);
    sfree(ssh->do_ssh2_transport_state);
    sfree(ssh->do_ssh2_authconn_state);
    sfree(ssh->v_c);
    sfree(ssh->v_s);
    sfree(ssh->fullhostname);
    sfree(ssh->hostkey_str);
    sfree(ssh->specials);
    if (ssh->crcda_ctx) {
        crcda_free_context(ssh->crcda_ctx);
        ssh->crcda_ctx = NULL;
    }
    if (ssh->s)
        ssh_do_close(ssh, TRUE);
    expire_timer_context(ssh);
    if (ssh->pinger)
        pinger_free(ssh->pinger);
    bufchain_clear(&ssh->queued_incoming_data);
    sfree(ssh->username);
    conf_free(ssh->conf);
#ifndef NO_GSSAPI
    if (ssh->gsslibs)
        ssh_gss_cleanup(ssh->gsslibs);
#endif
    sfree(ssh);

    random_unref();
}

/*
 * Reconfigure the SSH backend.
 */
static void ssh_reconfig(void *handle, Conf *conf)
{
    Ssh ssh = (Ssh) handle;
    const char *rekeying = NULL;
    int rekey_mandatory = FALSE;
    unsigned long old_max_data_size;
    int i, rekey_time;

    pinger_reconfig(ssh->pinger, ssh->conf, conf);
    if (ssh->portfwds)
        ssh_setup_portfwd(ssh, conf);

    rekey_time = conf_get_int(conf, CONF_ssh_rekey_time);
    if (conf_get_int(ssh->conf, CONF_ssh_rekey_time) != rekey_time &&
        rekey_time != 0) {
        unsigned long new_next = ssh->last_rekey + rekey_time*60*TICKSPERSEC;
        unsigned long now = GETTICKCOUNT();

        if (now - ssh->last_rekey > rekey_time*60*TICKSPERSEC) {
            rekeying = "timeout shortened";
        } else {
            ssh->next_rekey = schedule_timer(new_next - now, ssh2_timer, ssh);
        }
    }

    old_max_data_size = ssh->max_data_size;
    ssh->max_data_size = parse_blocksize(conf_get_str(ssh->conf,
                                                      CONF_ssh_rekey_data));
    if (old_max_data_size != ssh->max_data_size &&
        ssh->max_data_size != 0) {
        if (ssh->outgoing_data_size > ssh->max_data_size ||
            ssh->incoming_data_size > ssh->max_data_size)
            rekeying = "data limit lowered";
    }

    if (conf_get_int(ssh->conf, CONF_compression) !=
        conf_get_int(conf, CONF_compression)) {
        rekeying = "compression setting changed";
        rekey_mandatory = TRUE;
    }

    for (i = 0; i < CIPHER_MAX; i++)
        if (conf_get_int_int(ssh->conf, CONF_ssh_cipherlist, i) !=
            conf_get_int_int(conf, CONF_ssh_cipherlist, i)) {
        rekeying = "cipher settings changed";
        rekey_mandatory = TRUE;
    }
    if (conf_get_int(ssh->conf, CONF_ssh2_des_cbc) !=
        conf_get_int(conf, CONF_ssh2_des_cbc)) {
        rekeying = "cipher settings changed";
        rekey_mandatory = TRUE;
    }

    conf_free(ssh->conf);
    ssh->conf = conf_copy(conf);
    ssh_cache_conf_values(ssh);

    if (!ssh->bare_connection && rekeying) {
        if (!ssh->kex_in_progress) {
            do_ssh2_transport(ssh, rekeying, -1, NULL);
        } else if (rekey_mandatory) {
            ssh->deferred_rekey_reason = rekeying;
        }
    }
}

/*
 * Called to send data down the SSH connection.
 */
static int ssh_send(void *handle, const char *buf, int len)
{
    Ssh ssh = (Ssh) handle;

    if (ssh == NULL || ssh->s == NULL || ssh->protocol == NULL)
        return 0;

    ssh->protocol(ssh, (const unsigned char *)buf, len, 0);

    return ssh_sendbuffer(ssh);
}

/*
 * Called to query the current amount of buffered stdin data.
 */
static int ssh_sendbuffer(void *handle)
{
    Ssh ssh = (Ssh) handle;
    int override_value;

    if (ssh == NULL || ssh->s == NULL || ssh->protocol == NULL)
        return 0;

    /*
     * If the SSH socket itself has backed up, add the total backup
     * size on that to any individual buffer on the stdin channel.
     */
    override_value = 0;
    if (ssh->throttled_all)
        override_value = ssh->overall_bufsize;

    if (ssh->version == 1) {
        return override_value;
    } else if (ssh->version == 2) {
        if (!ssh->mainchan)
            return override_value;
        else
            return (override_value +
                    bufchain_size(&ssh->mainchan->v.v2.outbuffer));
    }

    return 0;
}

/*
 * Called to set the size of the window from SSH's POV.
 */
static void ssh_size(void *handle, int width, int height)
{
    Ssh ssh = (Ssh) handle;
    struct Packet *pktout;

    ssh->term_width = width;
    ssh->term_height = height;

    switch (ssh->state) {
      case SSH_STATE_BEFORE_SIZE:
      case SSH_STATE_PREPACKET:
      case SSH_STATE_CLOSED:
        break;                         /* do nothing */
      case SSH_STATE_INTERMED:
        ssh->size_needed = TRUE;       /* buffer for later */
        break;
      case SSH_STATE_SESSION:
        if (!conf_get_int(ssh->conf, CONF_nopty)) {
            if (ssh->version == 1) {
                send_packet(ssh, SSH1_CMSG_WINDOW_SIZE,
                            PKT_INT, ssh->term_height,
                            PKT_INT, ssh->term_width,
                            PKT_INT, 0, PKT_INT, 0, PKT_END);
            } else if (ssh->mainchan) {
                pktout = ssh2_chanreq_init(ssh->mainchan, "window-change",
                                           NULL, NULL);
                ssh2_pkt_adduint32(pktout, ssh->term_width);
                ssh2_pkt_adduint32(pktout, ssh->term_height);
                ssh2_pkt_adduint32(pktout, 0);
                ssh2_pkt_adduint32(pktout, 0);
                ssh2_pkt_send(ssh, pktout);
            }
        }
        break;
    }
}

/*
 * Return a list of the special codes that make sense in this
 * protocol.
 */
static const struct telnet_special *ssh_get_specials(void *handle)
{
    static const struct telnet_special ssh1_ignore_special[] = {
        {"IGNORE message", TS_NOP}
    };
    static const struct telnet_special ssh2_ignore_special[] = {
        {"IGNORE message", TS_NOP},
    };
    static const struct telnet_special ssh2_rekey_special[] = {
        {"Repeat key exchange", TS_REKEY},
    };
    static const struct telnet_special ssh2_session_specials[] = {
        {NULL, TS_SEP},
        {"Break", TS_BRK},
        /* These are the signal names defined by RFC 4254.
         * They include all the ISO C signals, but are a subset of the POSIX
         * required signals. */
        {"SIGINT (Interrupt)", TS_SIGINT},
        {"SIGTERM (Terminate)", TS_SIGTERM},
        {"SIGKILL (Kill)", TS_SIGKILL},
        {"SIGQUIT (Quit)", TS_SIGQUIT},
        {"SIGHUP (Hangup)", TS_SIGHUP},
        {"More signals", TS_SUBMENU},
          {"SIGABRT", TS_SIGABRT}, {"SIGALRM", TS_SIGALRM},
          {"SIGFPE",  TS_SIGFPE},  {"SIGILL",  TS_SIGILL},
          {"SIGPIPE", TS_SIGPIPE}, {"SIGSEGV", TS_SIGSEGV},
          {"SIGUSR1", TS_SIGUSR1}, {"SIGUSR2", TS_SIGUSR2},
        {NULL, TS_EXITMENU}
    };
    static const struct telnet_special specials_end[] = {
        {NULL, TS_EXITMENU}
    };

    struct telnet_special *specials = NULL;
    int nspecials = 0, specialsize = 0;

    Ssh ssh = (Ssh) handle;

    sfree(ssh->specials);

#define ADD_SPECIALS(name) do                                           \
    {                                                                   \
        int len = lenof(name);                                          \
        if (nspecials + len > specialsize) {                            \
            specialsize = (nspecials + len) * 5 / 4 + 32;               \
            specials = sresize(specials, specialsize, struct telnet_special); \
        }                                                               \
        memcpy(specials+nspecials, name, len*sizeof(struct telnet_special)); \
        nspecials += len;                                               \
    } while (0)

    if (ssh->version == 1) {
        /* Don't bother offering IGNORE if we've decided the remote
         * won't cope with it, since we wouldn't bother sending it if
         * asked anyway. */
        if (!(ssh->remote_bugs & BUG_CHOKES_ON_SSH1_IGNORE))
            ADD_SPECIALS(ssh1_ignore_special);
    } else if (ssh->version == 2) {
        if (!(ssh->remote_bugs & BUG_CHOKES_ON_SSH2_IGNORE))
            ADD_SPECIALS(ssh2_ignore_special);
        if (!(ssh->remote_bugs & BUG_SSH2_REKEY) && !ssh->bare_connection)
            ADD_SPECIALS(ssh2_rekey_special);
        if (ssh->mainchan)
            ADD_SPECIALS(ssh2_session_specials);

        if (ssh->n_uncert_hostkeys) {
            static const struct telnet_special uncert_start[] = {
                {NULL, TS_SEP},
                {"Cache new host key type", TS_SUBMENU},
            };
            static const struct telnet_special uncert_end[] = {
                {NULL, TS_EXITMENU},
            };
            int i;

            ADD_SPECIALS(uncert_start);
            for (i = 0; i < ssh->n_uncert_hostkeys; i++) {
                struct telnet_special uncert[1];
                const struct ssh_signkey *alg =
                    hostkey_algs[ssh->uncert_hostkeys[i]].alg;
                uncert[0].name = alg->name;
                uncert[0].code = TS_LOCALSTART + ssh->uncert_hostkeys[i];
                ADD_SPECIALS(uncert);
            }
            ADD_SPECIALS(uncert_end);
        }
    } /* else we're not ready yet */

    if (nspecials)
        ADD_SPECIALS(specials_end);

    ssh->specials = specials;

    if (nspecials) {
        return specials;
    } else {
        return NULL;
    }
#undef ADD_SPECIALS
}

/*
 * Send special codes. TS_EOF is useful for `plink', so you
 * can send an EOF and collect resulting output (e.g. `plink
 * hostname sort').
 */
static void ssh_special(void *handle, Telnet_Special code)
{
    Ssh ssh = (Ssh) handle;
    struct Packet *pktout;

    if (code == TS_EOF) {
        if (ssh->state != SSH_STATE_SESSION) {
            /*
             * Buffer the EOF in case we are pre-SESSION, so we can
             * send it as soon as we reach SESSION.
             */
            if (code == TS_EOF)
                ssh->eof_needed = TRUE;
            return;
        }
        if (ssh->version == 1) {
            send_packet(ssh, SSH1_CMSG_EOF, PKT_END);
        } else if (ssh->mainchan) {
            sshfwd_write_eof(ssh->mainchan);
            ssh->send_ok = 0;          /* now stop trying to read from stdin */
        }
        logevent("Sent EOF message");
    } else if (code == TS_PING || code == TS_NOP) {
        if (ssh->state == SSH_STATE_CLOSED
            || ssh->state == SSH_STATE_PREPACKET) return;
        if (ssh->version == 1) {
            if (!(ssh->remote_bugs & BUG_CHOKES_ON_SSH1_IGNORE))
                send_packet(ssh, SSH1_MSG_IGNORE, PKT_STR, "", PKT_END);
        } else {
            if (!(ssh->remote_bugs & BUG_CHOKES_ON_SSH2_IGNORE)) {
                pktout = ssh2_pkt_init(SSH2_MSG_IGNORE);
                ssh2_pkt_addstring_start(pktout);
                ssh2_pkt_send_noqueue(ssh, pktout);
            }
        }
    } else if (code == TS_REKEY) {
        if (!ssh->kex_in_progress && !ssh->bare_connection &&
            ssh->version == 2) {
            do_ssh2_transport(ssh, "at user request", -1, NULL);
        }
    } else if (code >= TS_LOCALSTART) {
        ssh->hostkey = hostkey_algs[code - TS_LOCALSTART].alg;
        ssh->cross_certifying = TRUE;
        if (!ssh->kex_in_progress && !ssh->bare_connection &&
            ssh->version == 2) {
            do_ssh2_transport(ssh, "cross-certifying new host key", -1, NULL);
        }
    } else if (code == TS_BRK) {
        if (ssh->state == SSH_STATE_CLOSED
            || ssh->state == SSH_STATE_PREPACKET) return;
        if (ssh->version == 1) {
            logevent("Unable to send BREAK signal in SSH-1");
        } else if (ssh->mainchan) {
            pktout = ssh2_chanreq_init(ssh->mainchan, "break", NULL, NULL);
            ssh2_pkt_adduint32(pktout, 0);   /* default break length */
            ssh2_pkt_send(ssh, pktout);
        }
    } else {
        /* Is is a POSIX signal? */
        const char *signame = NULL;
        if (code == TS_SIGABRT) signame = "ABRT";
        if (code == TS_SIGALRM) signame = "ALRM";
        if (code == TS_SIGFPE)  signame = "FPE";
        if (code == TS_SIGHUP)  signame = "HUP";
        if (code == TS_SIGILL)  signame = "ILL";
        if (code == TS_SIGINT)  signame = "INT";
        if (code == TS_SIGKILL) signame = "KILL";
        if (code == TS_SIGPIPE) signame = "PIPE";
        if (code == TS_SIGQUIT) signame = "QUIT";
        if (code == TS_SIGSEGV) signame = "SEGV";
        if (code == TS_SIGTERM) signame = "TERM";
        if (code == TS_SIGUSR1) signame = "USR1";
        if (code == TS_SIGUSR2) signame = "USR2";
        /* The SSH-2 protocol does in principle support arbitrary named
         * signals, including signame@domain, but we don't support those. */
        if (signame) {
            /* It's a signal. */
            if (ssh->version == 2 && ssh->mainchan) {
                pktout = ssh2_chanreq_init(ssh->mainchan, "signal", NULL, NULL);
                ssh2_pkt_addstring(pktout, signame);
                ssh2_pkt_send(ssh, pktout);
                logeventf(ssh, "Sent signal SIG%s", signame);
            }
        } else {
            /* Never heard of it. Do nothing */
        }
    }
}

void *new_sock_channel(void *handle, struct PortForwarding *pf)
{
    Ssh ssh = (Ssh) handle;
    struct ssh_channel *c;
    c = snew(struct ssh_channel);

    c->ssh = ssh;
    ssh_channel_init(c);
    c->halfopen = TRUE;
    c->type = CHAN_SOCKDATA_DORMANT;/* identify channel type */
    c->u.pfd.pf = pf;
    return c;
}

unsigned ssh_alloc_sharing_channel(Ssh ssh, void *sharing_ctx)
{
    struct ssh_channel *c;
    c = snew(struct ssh_channel);

    c->ssh = ssh;
    ssh_channel_init(c);
    c->type = CHAN_SHARING;
    c->u.sharing.ctx = sharing_ctx;
    return c->localid;
}

void ssh_delete_sharing_channel(Ssh ssh, unsigned localid)
{
    struct ssh_channel *c;

    c = find234(ssh->channels, &localid, ssh_channelfind);
    if (c)
        ssh_channel_destroy(c);
}

void ssh_send_packet_from_downstream(Ssh ssh, unsigned id, int type,
                                     const void *data, int datalen,
                                     const char *additional_log_text)
{
    struct Packet *pkt;

    pkt = ssh2_pkt_init(type);
    pkt->downstream_id = id;
    pkt->additional_log_text = additional_log_text;
    ssh2_pkt_adddata(pkt, data, datalen);
    ssh2_pkt_send(ssh, pkt);
}

/*
 * This is called when stdout/stderr (the entity to which
 * from_backend sends data) manages to clear some backlog.
 */
static void ssh_unthrottle(void *handle, int bufsize)
{
    Ssh ssh = (Ssh) handle;

    if (ssh->version == 1) {
        if (ssh->v1_stdout_throttling && bufsize < SSH1_BUFFER_LIMIT) {
            ssh->v1_stdout_throttling = 0;
            ssh_throttle_conn(ssh, -1);
        }
    } else {
        if (ssh->mainchan)
            ssh_channel_unthrottle(ssh->mainchan, bufsize);
    }

    /*
     * Now process any SSH connection data that was stashed in our
     * queue while we were frozen.
     */
    ssh_process_queued_incoming_data(ssh);
}

void ssh_send_port_open(void *channel, const char *hostname, int port,
                        const char *org)
{
    struct ssh_channel *c = (struct ssh_channel *)channel;
    Ssh ssh = c->ssh;
    struct Packet *pktout;

    logeventf(ssh, "Opening connection to %s:%d for %s", hostname, port, org);

    if (ssh->version == 1) {
        send_packet(ssh, SSH1_MSG_PORT_OPEN,
                    PKT_INT, c->localid,
                    PKT_STR, hostname,
                    PKT_INT, port,
                    /* PKT_STR, <org:orgport>, */
                    PKT_END);
    } else {
        pktout = ssh2_chanopen_init(c, "direct-tcpip");
        {
            char *trimmed_host = host_strduptrim(hostname);
            ssh2_pkt_addstring(pktout, trimmed_host);
            sfree(trimmed_host);
        }
        ssh2_pkt_adduint32(pktout, port);
        /*
         * We make up values for the originator data; partly it's
         * too much hassle to keep track, and partly I'm not
         * convinced the server should be told details like that
         * about my local network configuration.
         * The "originator IP address" is syntactically a numeric
         * IP address, and some servers (e.g., Tectia) get upset
         * if it doesn't match this syntax.
         */
        ssh2_pkt_addstring(pktout, "0.0.0.0");
        ssh2_pkt_adduint32(pktout, 0);
        ssh2_pkt_send(ssh, pktout);
    }
}

static int ssh_connected(void *handle)
{
    Ssh ssh = (Ssh) handle;
    return ssh->s != NULL;
}

static int ssh_sendok(void *handle)
{
    Ssh ssh = (Ssh) handle;
    return ssh->send_ok;
}

static int ssh_ldisc(void *handle, int option)
{
    Ssh ssh = (Ssh) handle;
    if (option == LD_ECHO)
        return ssh->echoing;
    if (option == LD_EDIT)
        return ssh->editing;
    return FALSE;
}

static void ssh_provide_ldisc(void *handle, void *ldisc)
{
    Ssh ssh = (Ssh) handle;
    ssh->ldisc = ldisc;
}

static void ssh_provide_logctx(void *handle, void *logctx)
{
    Ssh ssh = (Ssh) handle;
    ssh->logctx = logctx;
}

static int ssh_return_exitcode(void *handle)
{
    Ssh ssh = (Ssh) handle;
    if (ssh->s != NULL)
        return -1;
    else
        return (ssh->exitcode >= 0 ? ssh->exitcode : INT_MAX);
}

/*
 * cfg_info for SSH is the protocol running in this session.
 * (1 or 2 for the full SSH-1 or SSH-2 protocol; -1 for the bare
 * SSH-2 connection protocol, i.e. a downstream; 0 for not-decided-yet.)
 */
static int ssh_cfg_info(void *handle)
{
    Ssh ssh = (Ssh) handle;
    if (ssh->version == 0)
        return 0; /* don't know yet */
    else if (ssh->bare_connection)
        return -1;
    else
        return ssh->version;
}

/*
 * Gross hack: pscp will try to start SFTP but fall back to scp1 if
 * that fails. This variable is the means by which scp.c can reach
 * into the SSH code and find out which one it got.
 */
extern int ssh_fallback_cmd(void *handle)
{
    Ssh ssh = (Ssh) handle;
    return ssh->fallback_cmd;
}

Backend ssh_backend = {
    ssh_init,
    ssh_free,
    ssh_reconfig,
    ssh_send,
    ssh_sendbuffer,
    ssh_size,
    ssh_special,
    ssh_get_specials,
    ssh_connected,
    ssh_return_exitcode,
    ssh_sendok,
    ssh_ldisc,
    ssh_provide_ldisc,
    ssh_provide_logctx,
    ssh_unthrottle,
    ssh_cfg_info,
    ssh_test_for_upstream,
    "ssh",
    PROT_SSH,
    22
};