]> asedeno.scripts.mit.edu Git - PuTTY.git/blobdiff - ssh.c
Giant const-correctness patch of doom!
[PuTTY.git] / ssh.c
diff --git a/ssh.c b/ssh.c
index cd672979b6f554afcd1cc0c5325b57c79db47cd4..616b87d3220f124f8bf6bdc0fdf705dc21bd06ae 100644 (file)
--- a/ssh.c
+++ b/ssh.c
 #define TRUE 1
 #endif
 
-#define SSH1_MSG_DISCONNECT                       1    /* 0x1 */
-#define SSH1_SMSG_PUBLIC_KEY                      2    /* 0x2 */
-#define SSH1_CMSG_SESSION_KEY                     3    /* 0x3 */
-#define SSH1_CMSG_USER                            4    /* 0x4 */
-#define SSH1_CMSG_AUTH_RSA                        6    /* 0x6 */
-#define SSH1_SMSG_AUTH_RSA_CHALLENGE              7    /* 0x7 */
-#define SSH1_CMSG_AUTH_RSA_RESPONSE               8    /* 0x8 */
-#define SSH1_CMSG_AUTH_PASSWORD                   9    /* 0x9 */
-#define SSH1_CMSG_REQUEST_PTY                     10   /* 0xa */
-#define SSH1_CMSG_WINDOW_SIZE                     11   /* 0xb */
-#define SSH1_CMSG_EXEC_SHELL                      12   /* 0xc */
-#define SSH1_CMSG_EXEC_CMD                        13   /* 0xd */
-#define SSH1_SMSG_SUCCESS                         14   /* 0xe */
-#define SSH1_SMSG_FAILURE                         15   /* 0xf */
-#define SSH1_CMSG_STDIN_DATA                      16   /* 0x10 */
-#define SSH1_SMSG_STDOUT_DATA                     17   /* 0x11 */
-#define SSH1_SMSG_STDERR_DATA                     18   /* 0x12 */
-#define SSH1_CMSG_EOF                             19   /* 0x13 */
-#define SSH1_SMSG_EXIT_STATUS                     20   /* 0x14 */
-#define SSH1_MSG_CHANNEL_OPEN_CONFIRMATION        21   /* 0x15 */
-#define SSH1_MSG_CHANNEL_OPEN_FAILURE             22   /* 0x16 */
-#define SSH1_MSG_CHANNEL_DATA                     23   /* 0x17 */
-#define SSH1_MSG_CHANNEL_CLOSE                    24   /* 0x18 */
-#define SSH1_MSG_CHANNEL_CLOSE_CONFIRMATION       25   /* 0x19 */
-#define SSH1_SMSG_X11_OPEN                        27   /* 0x1b */
-#define SSH1_CMSG_PORT_FORWARD_REQUEST            28   /* 0x1c */
-#define SSH1_MSG_PORT_OPEN                        29   /* 0x1d */
-#define SSH1_CMSG_AGENT_REQUEST_FORWARDING        30   /* 0x1e */
-#define SSH1_SMSG_AGENT_OPEN                      31   /* 0x1f */
-#define SSH1_MSG_IGNORE                           32   /* 0x20 */
-#define SSH1_CMSG_EXIT_CONFIRMATION               33   /* 0x21 */
-#define SSH1_CMSG_X11_REQUEST_FORWARDING          34   /* 0x22 */
-#define SSH1_CMSG_AUTH_RHOSTS_RSA                 35   /* 0x23 */
-#define SSH1_MSG_DEBUG                            36   /* 0x24 */
-#define SSH1_CMSG_REQUEST_COMPRESSION             37   /* 0x25 */
-#define SSH1_CMSG_AUTH_TIS                        39   /* 0x27 */
-#define SSH1_SMSG_AUTH_TIS_CHALLENGE              40   /* 0x28 */
-#define SSH1_CMSG_AUTH_TIS_RESPONSE               41   /* 0x29 */
-#define SSH1_CMSG_AUTH_CCARD                      70   /* 0x46 */
-#define SSH1_SMSG_AUTH_CCARD_CHALLENGE            71   /* 0x47 */
-#define SSH1_CMSG_AUTH_CCARD_RESPONSE             72   /* 0x48 */
-
-#define SSH1_AUTH_RHOSTS                          1    /* 0x1 */
-#define SSH1_AUTH_RSA                             2    /* 0x2 */
-#define SSH1_AUTH_PASSWORD                        3    /* 0x3 */
-#define SSH1_AUTH_RHOSTS_RSA                      4    /* 0x4 */
-#define SSH1_AUTH_TIS                             5    /* 0x5 */
-#define SSH1_AUTH_CCARD                           16   /* 0x10 */
-
-#define SSH1_PROTOFLAG_SCREEN_NUMBER              1    /* 0x1 */
-/* Mask for protoflags we will echo back to server if seen */
-#define SSH1_PROTOFLAGS_SUPPORTED                 0    /* 0x1 */
-
-#define SSH2_MSG_DISCONNECT                       1    /* 0x1 */
-#define SSH2_MSG_IGNORE                           2    /* 0x2 */
-#define SSH2_MSG_UNIMPLEMENTED                    3    /* 0x3 */
-#define SSH2_MSG_DEBUG                            4    /* 0x4 */
-#define SSH2_MSG_SERVICE_REQUEST                  5    /* 0x5 */
-#define SSH2_MSG_SERVICE_ACCEPT                   6    /* 0x6 */
-#define SSH2_MSG_KEXINIT                          20   /* 0x14 */
-#define SSH2_MSG_NEWKEYS                          21   /* 0x15 */
-#define SSH2_MSG_KEXDH_INIT                       30   /* 0x1e */
-#define SSH2_MSG_KEXDH_REPLY                      31   /* 0x1f */
-#define SSH2_MSG_KEX_DH_GEX_REQUEST               30   /* 0x1e */
-#define SSH2_MSG_KEX_DH_GEX_GROUP                 31   /* 0x1f */
-#define SSH2_MSG_KEX_DH_GEX_INIT                  32   /* 0x20 */
-#define SSH2_MSG_KEX_DH_GEX_REPLY                 33   /* 0x21 */
-#define SSH2_MSG_KEXRSA_PUBKEY                    30    /* 0x1e */
-#define SSH2_MSG_KEXRSA_SECRET                    31    /* 0x1f */
-#define SSH2_MSG_KEXRSA_DONE                      32    /* 0x20 */
-#define SSH2_MSG_USERAUTH_REQUEST                 50   /* 0x32 */
-#define SSH2_MSG_USERAUTH_FAILURE                 51   /* 0x33 */
-#define SSH2_MSG_USERAUTH_SUCCESS                 52   /* 0x34 */
-#define SSH2_MSG_USERAUTH_BANNER                  53   /* 0x35 */
-#define SSH2_MSG_USERAUTH_PK_OK                   60   /* 0x3c */
-#define SSH2_MSG_USERAUTH_PASSWD_CHANGEREQ        60   /* 0x3c */
-#define SSH2_MSG_USERAUTH_INFO_REQUEST            60   /* 0x3c */
-#define SSH2_MSG_USERAUTH_INFO_RESPONSE           61   /* 0x3d */
-#define SSH2_MSG_GLOBAL_REQUEST                   80   /* 0x50 */
-#define SSH2_MSG_REQUEST_SUCCESS                  81   /* 0x51 */
-#define SSH2_MSG_REQUEST_FAILURE                  82   /* 0x52 */
-#define SSH2_MSG_CHANNEL_OPEN                     90   /* 0x5a */
-#define SSH2_MSG_CHANNEL_OPEN_CONFIRMATION        91   /* 0x5b */
-#define SSH2_MSG_CHANNEL_OPEN_FAILURE             92   /* 0x5c */
-#define SSH2_MSG_CHANNEL_WINDOW_ADJUST            93   /* 0x5d */
-#define SSH2_MSG_CHANNEL_DATA                     94   /* 0x5e */
-#define SSH2_MSG_CHANNEL_EXTENDED_DATA            95   /* 0x5f */
-#define SSH2_MSG_CHANNEL_EOF                      96   /* 0x60 */
-#define SSH2_MSG_CHANNEL_CLOSE                    97   /* 0x61 */
-#define SSH2_MSG_CHANNEL_REQUEST                  98   /* 0x62 */
-#define SSH2_MSG_CHANNEL_SUCCESS                  99   /* 0x63 */
-#define SSH2_MSG_CHANNEL_FAILURE                  100  /* 0x64 */
-#define SSH2_MSG_USERAUTH_GSSAPI_RESPONSE               60
-#define SSH2_MSG_USERAUTH_GSSAPI_TOKEN                  61
-#define SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE      63
-#define SSH2_MSG_USERAUTH_GSSAPI_ERROR                  64
-#define SSH2_MSG_USERAUTH_GSSAPI_ERRTOK                 65
-#define SSH2_MSG_USERAUTH_GSSAPI_MIC                    66
-
 /*
  * Packet type contexts, so that ssh2_pkt_type can correctly decode
  * the ambiguous type numbers back into the correct type strings.
@@ -131,6 +32,7 @@ typedef enum {
     SSH2_PKTCTX_NOKEX,
     SSH2_PKTCTX_DHGROUP,
     SSH2_PKTCTX_DHGEX,
+    SSH2_PKTCTX_ECDHKEX,
     SSH2_PKTCTX_RSAKEX
 } Pkt_KCtx;
 typedef enum {
@@ -141,22 +43,6 @@ typedef enum {
     SSH2_PKTCTX_KBDINTER
 } Pkt_ACtx;
 
-#define SSH2_DISCONNECT_HOST_NOT_ALLOWED_TO_CONNECT 1  /* 0x1 */
-#define SSH2_DISCONNECT_PROTOCOL_ERROR            2    /* 0x2 */
-#define SSH2_DISCONNECT_KEY_EXCHANGE_FAILED       3    /* 0x3 */
-#define SSH2_DISCONNECT_HOST_AUTHENTICATION_FAILED 4   /* 0x4 */
-#define SSH2_DISCONNECT_MAC_ERROR                 5    /* 0x5 */
-#define SSH2_DISCONNECT_COMPRESSION_ERROR         6    /* 0x6 */
-#define SSH2_DISCONNECT_SERVICE_NOT_AVAILABLE     7    /* 0x7 */
-#define SSH2_DISCONNECT_PROTOCOL_VERSION_NOT_SUPPORTED 8       /* 0x8 */
-#define SSH2_DISCONNECT_HOST_KEY_NOT_VERIFIABLE   9    /* 0x9 */
-#define SSH2_DISCONNECT_CONNECTION_LOST           10   /* 0xa */
-#define SSH2_DISCONNECT_BY_APPLICATION            11   /* 0xb */
-#define SSH2_DISCONNECT_TOO_MANY_CONNECTIONS      12   /* 0xc */
-#define SSH2_DISCONNECT_AUTH_CANCELLED_BY_USER    13   /* 0xd */
-#define SSH2_DISCONNECT_NO_MORE_AUTH_METHODS_AVAILABLE 14      /* 0xe */
-#define SSH2_DISCONNECT_ILLEGAL_USER_NAME         15   /* 0xf */
-
 static const char *const ssh2_disconnect_reasons[] = {
     NULL,
     "host not allowed to connect",
@@ -176,13 +62,6 @@ static const char *const ssh2_disconnect_reasons[] = {
     "illegal user name",
 };
 
-#define SSH2_OPEN_ADMINISTRATIVELY_PROHIBITED     1    /* 0x1 */
-#define SSH2_OPEN_CONNECT_FAILED                  2    /* 0x2 */
-#define SSH2_OPEN_UNKNOWN_CHANNEL_TYPE            3    /* 0x3 */
-#define SSH2_OPEN_RESOURCE_SHORTAGE               4    /* 0x4 */
-
-#define SSH2_EXTENDED_DATA_STDERR                 1    /* 0x1 */
-
 /*
  * Various remote-bug flags.
  */
@@ -197,6 +76,11 @@ static const char *const ssh2_disconnect_reasons[] = {
 #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.
@@ -305,7 +189,7 @@ static unsigned int ssh_tty_parse_boolean(char *s)
 #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 char *ssh1_pkt_type(int type)
+static const char *ssh1_pkt_type(int type)
 {
     translate(SSH1_MSG_DISCONNECT);
     translate(SSH1_SMSG_PUBLIC_KEY);
@@ -350,7 +234,8 @@ static char *ssh1_pkt_type(int type)
     translate(SSH1_CMSG_AUTH_CCARD_RESPONSE);
     return "unknown";
 }
-static char *ssh2_pkt_type(Pkt_KCtx pkt_kctx, Pkt_ACtx pkt_actx, int type)
+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);
@@ -368,6 +253,7 @@ static char *ssh2_pkt_type(Pkt_KCtx pkt_kctx, Pkt_ACtx pkt_actx, int type)
     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);
@@ -375,6 +261,8 @@ static char *ssh2_pkt_type(Pkt_KCtx pkt_kctx, Pkt_ACtx pkt_actx, int type)
     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);
@@ -405,9 +293,6 @@ static char *ssh2_pkt_type(Pkt_KCtx pkt_kctx, Pkt_ACtx pkt_actx, int type)
 /* Enumeration values for fields in SSH-1 packets */
 enum {
     PKT_END, PKT_INT, PKT_CHAR, PKT_DATA, PKT_STR, PKT_BIGNUM,
-    /* These values are for communicating relevant semantics of
-     * fields to the packet logging code. */
-    PKTT_OTHER, PKTT_PASSWORD, PKTT_DATA
 };
 
 /*
@@ -454,7 +339,6 @@ enum {
 #define crWaitUntil(c) do { crReturn(0); } while (!(c))
 #define crWaitUntilV(c)        do { crReturnV; } while (!(c))
 
-typedef struct ssh_tag *Ssh;
 struct Packet;
 
 static struct Packet *ssh1_pkt_init(int pkt_type);
@@ -474,9 +358,9 @@ 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, unsigned char *in, int inlen,
+static int do_ssh1_login(Ssh ssh, const unsigned char *in, int inlen,
                         struct Packet *pktin);
-static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
+static void do_ssh2_authconn(Ssh ssh, const unsigned char *in, int inlen,
                             struct Packet *pktin);
 static void ssh2_channel_check_close(struct ssh_channel *c);
 static void ssh_channel_destroy(struct ssh_channel *c);
@@ -522,7 +406,11 @@ static void ssh_channel_destroy(struct ssh_channel *c);
 #define OUR_V2_MAXPKT 0x4000UL
 #define OUR_V2_PACKETLIMIT 0x9000UL
 
-const static struct ssh_signkey *hostkey_algs[] = { &ssh_rsa, &ssh_dss };
+const static struct ssh_signkey *hostkey_algs[] = {
+    &ssh_ecdsa_ed25519,
+    &ssh_ecdsa_nistp256, &ssh_ecdsa_nistp384, &ssh_ecdsa_nistp521,
+    &ssh_rsa, &ssh_dss
+};
 
 const static struct ssh_mac *macs[] = {
     &ssh_hmac_sha256, &ssh_hmac_sha1, &ssh_hmac_sha1_96, &ssh_hmac_md5
@@ -564,6 +452,14 @@ enum {                                    /* channel types */
     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
@@ -669,11 +565,15 @@ struct ssh_channel {
             int outstanding_requests;
        } a;
        struct ssh_x11_channel {
-           Socket s;
+           struct X11Connection *xconn;
+            int initial;
        } x11;
        struct ssh_pfd_channel {
-           Socket s;
+            struct PortForwarding *pf;
        } pfd;
+       struct ssh_sharing_channel {
+           void *ctx;
+       } sharing;
     } u;
 };
 
@@ -708,12 +608,21 @@ struct ssh_portfwd; /* forward declaration */
 
 struct ssh_rportfwd {
     unsigned sport, dport;
-    char dhost[256];
+    char *shost, *dhost;
     char *sportdesc;
+    void *share_ctx;
     struct ssh_portfwd *pfrec;
 };
-#define free_rportfwd(pf) ( \
-    ((pf) ? (sfree((pf)->sportdesc)) : (void)0 ), sfree(pf) )
+
+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
@@ -730,41 +639,68 @@ struct ssh_portfwd {
     char *sserv, *dserv;
     struct ssh_rportfwd *remote;
     int addressfamily;
-    void *local;
+    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 `data' actually used */
+    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;         /* temporary index into `data' (for strings) */
+    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 */
 
     /*
-     * State associated with packet logging
+     * 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.
      */
-    int logmode;
-    int nblanks;
-    struct logblank_t *blanks;
+
+    /* 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, void *vin, int inlen,
+static void ssh1_protocol(Ssh ssh, const void *vin, int inlen,
                          struct Packet *pktin);
-static void ssh2_protocol(Ssh ssh, void *vin, int inlen,
+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 void ssh2_add_channel_data(struct ssh_channel *c, char *buf, int len);
+static void ssh2_add_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);
@@ -773,7 +709,7 @@ 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, void *vin, int inlen,
+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);
 
@@ -794,6 +730,14 @@ struct rdpkt2_state_tag {
     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;
@@ -827,6 +771,7 @@ struct ssh_tag {
     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;
@@ -837,6 +782,10 @@ struct ssh_tag {
     int v2_session_id_len;
     void *kex_ctx;
 
+    int bare_connection;
+    int attempting_connshare;
+    void *connshare;
+
     char *savedhost;
     int savedport;
     int send_ok;
@@ -888,6 +837,8 @@ struct ssh_tag {
     Pkt_ACtx pkt_actx;
 
     struct X11Display *x11disp;
+    struct X11FakeAuth *x11auth;
+    tree234 *x11authtree;
 
     int version;
     int conn_throttle_count;
@@ -898,6 +849,7 @@ struct ssh_tag {
 
     int ssh1_rdpkt_crstate;
     int ssh2_rdpkt_crstate;
+    int ssh2_bare_rdpkt_crstate;
     int ssh_gotdata_crstate;
     int do_ssh1_connection_crstate;
 
@@ -905,16 +857,20 @@ struct ssh_tag {
     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, void *vin, int inlen,
+    void (*protocol) (Ssh ssh, const void *vin, int inlen,
                      struct Packet *pkt);
-    struct Packet *(*s_rdpkt) (Ssh ssh, unsigned char **data, int *datalen);
+    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,
@@ -983,7 +939,7 @@ struct ssh_tag {
     unsigned long max_data_size;
     int kex_in_progress;
     unsigned long next_rekey, last_rekey;
-    char *deferred_rekey_reason;    /* points to STATIC string; don't free */
+    const char *deferred_rekey_reason;
 
     /*
      * Fully qualified host name, which we need if doing GSSAPI.
@@ -1023,25 +979,6 @@ static void bomb_out(Ssh ssh, char *text)
 
 #define bombout(msg) bomb_out(ssh, dupprintf msg)
 
-/* Functions to leave bits out of the SSH packet log file. */
-
-static void dont_log_password(Ssh ssh, struct Packet *pkt, int blanktype)
-{
-    if (conf_get_int(ssh->conf, CONF_logomitpass))
-       pkt->logmode = blanktype;
-}
-
-static void dont_log_data(Ssh ssh, struct Packet *pkt, int blanktype)
-{
-    if (ssh->logomitdata)
-       pkt->logmode = blanktype;
-}
-
-static void end_log_omission(Ssh ssh, struct Packet *pkt)
-{
-    pkt->logmode = PKTLOG_EMIT;
-}
-
 /* Helper function for common bits of parsing ttymodes. */
 static void parse_ttymodes(Ssh ssh,
                           void (*do_mode)(void *data, char *mode, char *val),
@@ -1107,7 +1044,9 @@ 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)
@@ -1238,13 +1177,119 @@ static struct Packet *ssh_new_packet(void)
 
     pkt->body = pkt->data = NULL;
     pkt->maxlen = 0;
-    pkt->logmode = PKTLOG_EMIT;
-    pkt->nblanks = 0;
-    pkt->blanks = NULL;
 
     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.
@@ -1252,7 +1297,8 @@ static struct Packet *ssh_new_packet(void)
  * Update the *data and *datalen variables.
  * Return a Packet structure when a packet is completed.
  */
-static struct Packet *ssh1_rdpkt(Ssh ssh, unsigned char **data, int *datalen)
+static struct Packet *ssh1_rdpkt(Ssh ssh, const unsigned char **data,
+                                 int *datalen)
 {
     struct rdpkt1_state_tag *st = &ssh->rdpkt1_state;
 
@@ -1318,7 +1364,6 @@ static struct Packet *ssh1_rdpkt(Ssh ssh, unsigned char **data, int *datalen)
     }
 
     st->pktin->body = st->pktin->data + st->pad + 1;
-    st->pktin->savedpos = 0;
 
     if (ssh->v1_compressing) {
        unsigned char *decompblk;
@@ -1347,38 +1392,169 @@ static struct Packet *ssh1_rdpkt(Ssh ssh, unsigned char **data, int *datalen)
     st->pktin->type = st->pktin->body[-1];
 
     /*
-     * Log incoming packet, possibly omitting sensitive fields.
+     * Now pktin->body and pktin->length identify the semantic content
+     * of the packet, excluding the initial type byte.
      */
-    if (ssh->logctx) {
-       int nblanks = 0;
-       struct logblank_t blank;
-       if (ssh->logomitdata) {
-           int do_blank = FALSE, blank_prefix = 0;
-           /* "Session data" packets - omit the data field */
-           if ((st->pktin->type == SSH1_SMSG_STDOUT_DATA) ||
-               (st->pktin->type == SSH1_SMSG_STDERR_DATA)) {
-               do_blank = TRUE; blank_prefix = 4;
-           } else if (st->pktin->type == SSH1_MSG_CHANNEL_DATA) {
-               do_blank = TRUE; blank_prefix = 8;
-           }
-           if (do_blank) {
-               blank.offset = blank_prefix;
-               blank.len = st->pktin->length;
-               blank.type = PKTLOG_OMIT;
-               nblanks = 1;
-           }
-       }
-       log_packet(ssh->logctx,
-                  PKT_INCOMING, st->pktin->type,
-                  ssh1_pkt_type(st->pktin->type),
-                  st->pktin->body, st->pktin->length,
-                  nblanks, &blank, NULL);
-    }
+
+    if (ssh->logctx)
+        ssh1_log_incoming_packet(ssh, st->pktin);
+
+    st->pktin->savedpos = 0;
 
     crFinish(st->pktin);
 }
 
-static struct Packet *ssh2_rdpkt(Ssh ssh, unsigned char **data, int *datalen)
+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;
 
@@ -1397,7 +1573,7 @@ static struct Packet *ssh2_rdpkt(Ssh ssh, unsigned char **data, int *datalen)
     st->maclen = ssh->scmac ? ssh->scmac->len : 0;
 
     if (ssh->sccipher && (ssh->sccipher->flags & SSH_CIPHER_IS_CBC) &&
-       ssh->scmac) {
+       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
@@ -1409,6 +1585,11 @@ static struct Packet *ssh2_rdpkt(Ssh ssh, unsigned char **data, int *datalen)
         * 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. */
@@ -1463,6 +1644,71 @@ static struct Packet *ssh2_rdpkt(Ssh ssh, unsigned char **data, int *datalen)
        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.
+         */
+       for (st->i = st->len = 0; st->i < 4; st->i++) {
+           while ((*datalen) == 0)
+               crReturn(NULL);
+           st->pktin->data[st->i] = *(*data)++;
+           (*datalen)--;
+       }
+       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);
 
@@ -1554,6 +1800,9 @@ static struct Packet *ssh2_rdpkt(Ssh ssh, unsigned char **data, int *datalen)
 
     st->pktin->sequence = st->incoming_sequence++;
 
+    st->pktin->length = st->packetlen - st->pad;
+    assert(st->pktin->length >= 0);
+
     /*
      * Decompress packet payload.
      */
@@ -1576,38 +1825,80 @@ static struct Packet *ssh2_rdpkt(Ssh ssh, unsigned char **data, int *datalen)
        }
     }
 
-    st->pktin->savedpos = 6;
-    st->pktin->body = st->pktin->data;
+    /*
+     * 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);
 
     /*
-     * Log incoming packet, possibly omitting sensitive fields.
+     * Read the packet length field.
      */
-    if (ssh->logctx) {
-       int nblanks = 0;
-       struct logblank_t blank;
-       if (ssh->logomitdata) {
-           int do_blank = FALSE, blank_prefix = 0;
-           /* "Session data" packets - omit the data field */
-           if (st->pktin->type == SSH2_MSG_CHANNEL_DATA) {
-               do_blank = TRUE; blank_prefix = 8;
-           } else if (st->pktin->type == SSH2_MSG_CHANNEL_EXTENDED_DATA) {
-               do_blank = TRUE; blank_prefix = 12;
-           }
-           if (do_blank) {
-               blank.offset = blank_prefix;
-               blank.len = (st->pktin->length-6) - blank_prefix;
-               blank.type = PKTLOG_OMIT;
-               nblanks = 1;
-           }
-       }
-       log_packet(ssh->logctx, PKT_INCOMING, st->pktin->type,
-                  ssh2_pkt_type(ssh->pkt_kctx, ssh->pkt_actx,
-                                st->pktin->type),
-                  st->pktin->data+6, st->pktin->length-6,
-                  nblanks, &blank, &st->pktin->sequence);
+    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);
 }
 
@@ -1627,12 +1918,7 @@ static int s_wrpkt_prepare(Ssh ssh, struct Packet *pkt, int *offset_p)
     int len;
 
     if (ssh->logctx)
-       log_packet(ssh->logctx, PKT_OUTGOING, pkt->data[12],
-                  ssh1_pkt_type(pkt->data[12]),
-                  pkt->body, pkt->length - (pkt->body - pkt->data),
-                  pkt->nblanks, pkt->blanks, NULL);
-    sfree(pkt->blanks); pkt->blanks = NULL;
-    pkt->nblanks = 0;
+        ssh1_log_outgoing_packet(ssh, pkt);
 
     if (ssh->v1_compressing) {
        unsigned char *compblk;
@@ -1671,7 +1957,9 @@ 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, NULL, 0, NULL);
+    if (!ssh->s)
+        return 0;
     return sk_write(ssh->s, (char *)data, len);
 }
 
@@ -1742,16 +2030,6 @@ static struct Packet *construct_packet(Ssh ssh, int pkttype, va_list ap)
            bn = va_arg(ap, Bignum);
            ssh1_pkt_addmp(pkt, bn);
            break;
-         /* Tokens for modifications to packet logging */
-         case PKTT_PASSWORD:
-           dont_log_password(ssh, pkt, PKTLOG_BLANK);
-           break;
-         case PKTT_DATA:
-           dont_log_data(ssh, pkt, PKTLOG_OMIT);
-           break;
-         case PKTT_OTHER:
-           end_log_omission(ssh, pkt);
-           break;
        }
     }
 
@@ -1778,7 +2056,7 @@ static void defer_packet(Ssh ssh, int pkttype, ...)
     s_wrpkt_defer(ssh, pkt);
 }
 
-static int ssh_versioncmp(char *a, char *b)
+static int ssh_versioncmp(const char *a, const char *b)
 {
     char *ae, *be;
     unsigned long av, bv;
@@ -1832,15 +2110,6 @@ static void ssh_pkt_ensure(struct Packet *pkt, int length)
 }
 static void ssh_pkt_adddata(struct Packet *pkt, const void *data, int len)
 {
-    if (pkt->logmode != PKTLOG_EMIT) {
-       pkt->nblanks++;
-       pkt->blanks = sresize(pkt->blanks, pkt->nblanks, struct logblank_t);
-       assert(pkt->body);
-       pkt->blanks[pkt->nblanks-1].offset = pkt->length -
-                                            (pkt->body - pkt->data);
-       pkt->blanks[pkt->nblanks-1].len = len;
-       pkt->blanks[pkt->nblanks-1].type = pkt->logmode;
-    }
     pkt->length += len;
     ssh_pkt_ensure(pkt, pkt->length);
     memcpy(pkt->data + pkt->length - len, data, len);
@@ -1864,17 +2133,16 @@ static void ssh_pkt_addstring_start(struct Packet *pkt)
     ssh_pkt_adduint32(pkt, 0);
     pkt->savedpos = pkt->length;
 }
-static void ssh_pkt_addstring_str(struct Packet *pkt, const char *data)
-{
-    ssh_pkt_adddata(pkt, data, strlen(data));
-    PUT_32BIT(pkt->data + pkt->savedpos - 4, pkt->length - pkt->savedpos);
-}
 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);
@@ -1919,6 +2187,9 @@ static struct Packet *ssh1_pkt_init(int pkt_type)
     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;
 }
 
@@ -1937,8 +2208,11 @@ 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;
 }
 
@@ -1949,15 +2223,21 @@ static struct Packet *ssh2_pkt_init(int pkt_type)
  */
 static int ssh2_pkt_construct(Ssh ssh, struct Packet *pkt)
 {
-    int cipherblk, maclen, padding, i;
+    int cipherblk, maclen, padding, unencrypted_prefix, i;
 
     if (ssh->logctx)
-       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 - (pkt->body - pkt->data),
-                  pkt->nblanks, pkt->blanks, &ssh->v2_outgoing_sequence);
-    sfree(pkt->blanks); pkt->blanks = NULL;
-    pkt->nblanks = 0;
+        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.
@@ -1984,10 +2264,12 @@ static int ssh2_pkt_construct(Ssh ssh, struct Packet *pkt)
     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 + padding) % cipherblk) % cipherblk;
+       (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);
@@ -1995,19 +2277,34 @@ static int ssh2_pkt_construct(Ssh ssh, struct Packet *pkt)
     for (i = 0; i < padding; i++)
        pkt->data[pkt->length + i] = random_byte();
     PUT_32BIT(pkt->data, pkt->length + padding - 4);
-    if (ssh->csmac)
-       ssh->csmac->generate(ssh->cs_mac_ctx, pkt->data,
-                            pkt->length + padding,
-                            ssh->v2_outgoing_sequence);
-    ssh->v2_outgoing_sequence++;       /* whether or not we MACed */
-
-    if (ssh->cscipher)
-       ssh->cscipher->encrypt(ssh->cs_cipher_ctx,
-                              pkt->data, pkt->length + padding);
+    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;
 }
 
@@ -2065,12 +2362,13 @@ static void ssh2_pkt_send_noqueue(Ssh ssh, struct Packet *pkt)
        return;
     }
     len = ssh2_pkt_construct(ssh, pkt);
-    backlog = s_write(ssh, pkt->data, len);
+    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);
@@ -2102,7 +2400,7 @@ static void ssh2_pkt_defer_noqueue(Ssh ssh, struct Packet *pkt, int noignore)
                                          ssh->deferred_size,
                                          unsigned char);
     }
-    memcpy(ssh->deferred_send_data + ssh->deferred_len, pkt->data, len);
+    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);
@@ -2172,6 +2470,7 @@ static void ssh_pkt_defersend(Ssh ssh)
 
     ssh->outgoing_data_size += ssh->deferred_data_size;
     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);
@@ -2334,7 +2633,7 @@ static void *ssh_pkt_getdata(struct Packet *pkt, int length)
     return pkt->body + (pkt->savedpos - length);
 }
 static int ssh1_pkt_getrsakey(struct Packet *pkt, struct RSAKey *key,
-                             unsigned char **keystr)
+                             const unsigned char **keystr)
 {
     int j;
 
@@ -2553,7 +2852,9 @@ static void ssh_detect_bugs(Ssh ssh, char *vstring)
     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("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.
         */
@@ -2608,6 +2909,18 @@ static void ssh_detect_bugs(Ssh ssh, char *vstring)
        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
@@ -2616,6 +2929,23 @@ static void ssh_detect_bugs(Ssh ssh, char *vstring)
        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");
+    }
 }
 
 /*
@@ -2624,11 +2954,7 @@ static void ssh_detect_bugs(Ssh ssh, char *vstring)
  */
 static void ssh_fix_verstring(char *str)
 {
-    /* Eat "SSH-<protoversion>-". */
-    assert(*str == 'S'); str++;
-    assert(*str == 'S'); str++;
-    assert(*str == 'H'); str++;
-    assert(*str == '-'); str++;
+    /* Eat "<protoversion>-". */
     while (*str && *str != '-') str++;
     assert(*str == '-'); str++;
 
@@ -2644,7 +2970,7 @@ static void ssh_fix_verstring(char *str)
 /*
  * Send an appropriate SSH version string.
  */
-static void ssh_send_verstring(Ssh ssh, char *svers)
+static void ssh_send_verstring(Ssh ssh, const char *protoname, char *svers)
 {
     char *verstring;
 
@@ -2652,18 +2978,19 @@ static void ssh_send_verstring(Ssh ssh, char *svers)
        /*
         * Construct a v2 version string.
         */
-       verstring = dupprintf("SSH-2.0-%s\015\012", sshver);
+       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);
+    ssh_fix_verstring(verstring + strlen(protoname));
 
     if (ssh->version == 2) {
        size_t len;
@@ -2684,6 +3011,8 @@ static void ssh_send_verstring(Ssh ssh, char *svers)
 
 static int do_ssh_init(Ssh ssh, unsigned char c)
 {
+    static const char protoname[] = "SSH-";
+
     struct do_ssh_init_state {
        int crLine;
        int vslen;
@@ -2697,15 +3026,13 @@ static int do_ssh_init(Ssh ssh, unsigned char c)
     
     crBeginState;
 
-    /* Search for a line beginning with the string "SSH-" in the input. */
+    /* Search for a line beginning with the protocol name prefix in
+     * the input. */
     for (;;) {
-       if (c != 'S') goto no;
-       crReturn(1);
-       if (c != 'S') goto no;
-       crReturn(1);
-       if (c != 'H') goto no;
-       crReturn(1);
-       if (c != '-') goto no;
+        for (s->i = 0; protoname[s->i]; s->i++) {
+            if ((char)c != protoname[s->i]) goto no;
+            crReturn(1);
+        }
        break;
       no:
        while (c != '\012')
@@ -2713,13 +3040,12 @@ static int do_ssh_init(Ssh ssh, unsigned char c)
        crReturn(1);
     }
 
-    s->vstrsize = 16;
+    s->vstrsize = sizeof(protoname) + 16;
     s->vstring = snewn(s->vstrsize, char);
-    strcpy(s->vstring, "SSH-");
-    s->vslen = 4;
+    strcpy(s->vstring, protoname);
+    s->vslen = strlen(protoname);
     s->i = 0;
     while (1) {
-       crReturn(1);                   /* get another char */
        if (s->vslen >= s->vstrsize - 1) {
            s->vstrsize += 16;
            s->vstring = sresize(s->vstring, s->vstrsize, char);
@@ -2733,6 +3059,7 @@ static int do_ssh_init(Ssh ssh, unsigned char c)
                s->version[s->i++] = c;
        } else if (c == '\012')
            break;
+       crReturn(1);                   /* get another char */
     }
 
     ssh->agentfwd_enabled = FALSE;
@@ -2753,11 +3080,13 @@ static int do_ssh_init(Ssh ssh, unsigned char c)
     s->proto2 = ssh_versioncmp(s->version, "1.99") >= 0;
 
     if (conf_get_int(ssh->conf, CONF_sshprot) == 0 && !s->proto1) {
-       bombout(("SSH protocol version 1 required by user but not provided by server"));
+       bombout(("SSH protocol version 1 required by configuration but "
+                "not provided by server"));
        crStop(0);
     }
     if (conf_get_int(ssh->conf, CONF_sshprot) == 3 && !s->proto2) {
-       bombout(("SSH protocol version 2 required by user but not provided by server"));
+       bombout(("SSH protocol version 2 required by configuration but "
+                "not provided by server"));
        crStop(0);
     }
 
@@ -2770,7 +3099,7 @@ static int do_ssh_init(Ssh ssh, unsigned char c)
 
     /* Send the version string, if we haven't already */
     if (conf_get_int(ssh->conf, CONF_sshprot) != 3)
-       ssh_send_verstring(ssh, s->version);
+       ssh_send_verstring(ssh, protoname, s->version);
 
     if (ssh->version == 2) {
        size_t len;
@@ -2808,8 +3137,119 @@ static int do_ssh_init(Ssh ssh, unsigned char c)
     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,
-                                     unsigned char **data, int *datalen)
+                                     const unsigned char **data, int *datalen)
 {
     struct Packet *pktin;
 
@@ -2821,7 +3261,7 @@ static void ssh_process_incoming_data(Ssh ssh,
 }
 
 static void ssh_queue_incoming_data(Ssh ssh,
-                                   unsigned char **data, int *datalen)
+                                   const unsigned char **data, int *datalen)
 {
     bufchain_add(&ssh->queued_incoming_data, *data, *datalen);
     *data += *datalen;
@@ -2831,7 +3271,7 @@ static void ssh_queue_incoming_data(Ssh ssh,
 static void ssh_process_queued_incoming_data(Ssh ssh)
 {
     void *vdata;
-    unsigned char *data;
+    const unsigned char *data;
     int len, origlen;
 
     while (!ssh->frozen && bufchain_size(&ssh->queued_incoming_data)) {
@@ -2854,12 +3294,12 @@ static void ssh_set_frozen(Ssh ssh, int frozen)
     ssh->frozen = frozen;
 }
 
-static void ssh_gotdata(Ssh ssh, unsigned char *data, int datalen)
+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, NULL, 0, NULL);
 
     crBegin(ssh->ssh_gotdata_crstate);
 
@@ -2873,7 +3313,7 @@ static void ssh_gotdata(Ssh ssh, unsigned char *data, int datalen)
        int ret;                       /* need not be kept across crReturn */
        if (datalen == 0)
            crReturnV;                 /* more data please */
-       ret = do_ssh_init(ssh, *data);
+       ret = ssh->do_ssh_init(ssh, *data);
        data++;
        datalen--;
        if (ret == 0)
@@ -2937,11 +3377,11 @@ static int ssh_do_close(Ssh ssh, int notify_exit)
        while (NULL != (c = index234(ssh->channels, 0))) {
            switch (c->type) {
              case CHAN_X11:
-               x11_close(c->u.x11.s);
+               x11_close(c->u.x11.xconn);
                break;
              case CHAN_SOCKDATA:
              case CHAN_SOCKDATA_DORMANT:
-               pfd_close(c->u.pfd.s);
+               pfd_close(c->u.pfd.pf);
                break;
            }
            del234(ssh->channels, c); /* moving next one to index 0 */
@@ -2959,7 +3399,7 @@ static int ssh_do_close(Ssh ssh, int notify_exit)
        while (NULL != (pf = index234(ssh->portfwds, 0))) {
            /* Dispose of any listening socket. */
            if (pf->local)
-               pfd_terminate(pf->local);
+               pfl_terminate(pf->local);
            del234(ssh->portfwds, pf); /* moving next one to index 0 */
            free_portfwd(pf);
        }
@@ -2967,24 +3407,82 @@ static int ssh_do_close(Ssh ssh, int notify_exit)
        ssh->portfwds = NULL;
     }
 
+    /*
+     * Also stop attempting to connection-share.
+     */
+    if (ssh->connshare) {
+        sharestate_free(ssh->connshare);
+        ssh->connshare = NULL;
+    }
+
     return ret;
 }
 
-static void ssh_log(Plug plug, int type, SockAddr addr, int port,
-                   const char *error_msg, int error_code)
+static void ssh_socket_log(Plug plug, int type, SockAddr addr, int port,
+                           const char *error_msg, int error_code)
 {
     Ssh ssh = (Ssh) plug;
     char addrbuf[256], *msg;
 
-    sk_getaddr(addr, addrbuf, lenof(addrbuf));
+    if (ssh->attempting_connshare) {
+        /*
+         * 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.
+         */
+    } else {
+        sk_getaddr(addr, addrbuf, lenof(addrbuf));
 
-    if (type == 0)
-       msg = dupprintf("Connecting to %s port %d", addrbuf, port);
-    else
-       msg = dupprintf("Failed to connect to %s: %s", addrbuf, error_msg);
+        if (type == 0) {
+            if (sk_addr_needs_port(addr)) {
+                msg = dupprintf("Connecting to %s port %d", addrbuf, port);
+            } else {
+                msg = dupprintf("Connecting to %s", addrbuf);
+            }
+        } else {
+            msg = dupprintf("Failed to connect to %s: %s", addrbuf, error_msg);
+        }
 
-    logevent(msg);
-    sfree(msg);
+        logevent(msg);
+        sfree(msg);
+    }
+}
+
+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,
@@ -3041,11 +3539,11 @@ static void ssh_sent(Plug plug, int bufsize)
  * Also places the canonical host name into `realhost'. It must be
  * freed by the caller.
  */
-static const char *connect_to_host(Ssh ssh, char *host, int port,
+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_log,
+       ssh_socket_log,
        ssh_closing,
        ssh_receive,
        ssh_sent,
@@ -3059,54 +3557,85 @@ static const char *connect_to_host(Ssh ssh, char *host, int port,
     
     loghost = conf_get_str(ssh->conf, CONF_loghost);
     if (*loghost) {
-       char *colon;
+       char *tmphost;
+        char *colon;
 
-       ssh->savedhost = dupstr(loghost);
+        tmphost = dupstr(loghost);
        ssh->savedport = 22;           /* default ssh port */
 
        /*
-        * A colon suffix on savedhost also lets us affect
-        * savedport.
-        * 
-        * (FIXME: do something about IPv6 address literals here.)
+        * 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 = strrchr(ssh->savedhost, ':');
-       if (colon) {
+       colon = host_strrchr(tmphost, ':');
+       if (colon && colon == host_strchr(tmphost, ':')) {
            *colon++ = '\0';
            if (*colon)
                ssh->savedport = atoi(colon);
        }
+
+        ssh->savedhost = host_strduptrim(tmphost);
+        sfree(tmphost);
     } else {
-       ssh->savedhost = dupstr(host);
+       ssh->savedhost = host_strduptrim(host);
        if (port < 0)
            port = 22;                 /* default ssh port */
        ssh->savedport = port;
     }
 
-    /*
-     * Try to find host.
-     */
-    addressfamily = conf_get_int(ssh->conf, CONF_addressfamily);
-    logeventf(ssh, "Looking up host \"%s\"%s", host,
-             (addressfamily == ADDRTYPE_IPV4 ? " (IPv4)" :
-              (addressfamily == ADDRTYPE_IPV6 ? " (IPv6)" : "")));
-    addr = name_lookup(host, port, realhost, ssh->conf, addressfamily);
-    if ((err = sk_addr_error(addr)) != NULL) {
-       sk_addr_free(addr);
-       return err;
-    }
-    ssh->fullhostname = dupstr(*realhost);   /* save in case of GSSAPI */
+    ssh->fn = &fn_table;               /* make 'ssh' usable as a Plug */
 
     /*
-     * Open socket.
+     * 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->fn = &fn_table;
-    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;
+    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);
+        logeventf(ssh, "Looking up host \"%s\"%s", host,
+                  (addressfamily == ADDRTYPE_IPV4 ? " (IPv4)" :
+                   (addressfamily == ADDRTYPE_IPV6 ? " (IPv6)" : "")));
+        addr = name_lookup(host, port, realhost, ssh->conf, addressfamily);
+        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;
+        }
     }
 
     /*
@@ -3116,9 +3645,9 @@ static const char *connect_to_host(Ssh ssh, char *host, int port,
     sshprot = conf_get_int(ssh->conf, CONF_sshprot);
     if (sshprot == 0)
        ssh->version = 1;
-    if (sshprot == 3) {
+    if (sshprot == 3 && !ssh->bare_connection) {
        ssh->version = 2;
-       ssh_send_verstring(ssh, NULL);
+       ssh_send_verstring(ssh, "SSH-", NULL);
     }
 
     /*
@@ -3170,13 +3699,13 @@ static void ssh_throttle_all(Ssh ssh, int enable, int bufsize)
             */
            break;
          case CHAN_X11:
-           x11_override_throttle(c->u.x11.s, enable);
+           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.s, enable);
+           pfd_override_throttle(c->u.pfd.pf, enable);
            break;
        }
     }
@@ -3217,7 +3746,7 @@ static void ssh_agentf_callback(void *cv, void *reply, int replylen)
 {
     struct ssh_channel *c = (struct ssh_channel *)cv;
     Ssh ssh = c->ssh;
-    void *sentreply = reply;
+    const void *sentreply = reply;
 
     c->u.a.outstanding_requests--;
     if (!sentreply) {
@@ -3232,9 +3761,7 @@ static void ssh_agentf_callback(void *cv, void *reply, int replylen)
        send_packet(ssh, SSH1_MSG_CHANNEL_DATA,
                    PKT_INT, c->remoteid,
                    PKT_INT, replylen,
-                   PKTT_DATA,
                    PKT_DATA, sentreply, replylen,
-                   PKTT_OTHER,
                    PKT_END);
     }
     if (reply)
@@ -3252,7 +3779,8 @@ static void ssh_agentf_callback(void *cv, void *reply, int replylen)
  * non-NULL, otherwise just close the connection. `client_reason' == NULL
  * => log `wire_reason'.
  */
-static void ssh_disconnect(Ssh ssh, char *client_reason, char *wire_reason,
+static void ssh_disconnect(Ssh ssh, const char *client_reason,
+                           const char *wire_reason,
                           int code, int clean_exit)
 {
     char *error;
@@ -3280,10 +3808,63 @@ static void ssh_disconnect(Ssh ssh, char *client_reason, char *wire_reason,
     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, unsigned char *in, int inlen,
+static int do_ssh1_login(Ssh ssh, const unsigned char *in, int inlen,
                         struct Packet *pktin)
 {
     int i, j, ret;
@@ -3292,7 +3873,8 @@ static int do_ssh1_login(Ssh ssh, unsigned char *in, int inlen,
     struct do_ssh1_login_state {
        int crLine;
        int len;
-       unsigned char *rsabuf, *keystr1, *keystr2;
+       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;
@@ -3301,7 +3883,7 @@ static int do_ssh1_login(Ssh ssh, unsigned char *in, int inlen,
        void *publickey_blob;
        int publickey_bloblen;
        char *publickey_comment;
-       int publickey_encrypted;
+       int privatekey_available, privatekey_encrypted;
        prompts_t *cur_prompt;
        char c;
        int pwpkt_type;
@@ -3403,29 +3985,39 @@ static int do_ssh1_login(Ssh ssh, unsigned char *in, int inlen,
        rsastr_fmt(keystr, &s->hostkey);
        rsa_fingerprint(fingerprint, sizeof(fingerprint), &s->hostkey);
 
-        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);
-        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);
+        /* 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);
+            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);
+            if (s->dlgret == 0) {
+                ssh_disconnect(ssh, "User aborted at host key verification",
+                               NULL, 0, TRUE);
+                crStop(0);
+            }
+        } else {
+            sfree(keystr);
         }
     }
 
@@ -3453,7 +4045,7 @@ static int do_ssh1_login(Ssh ssh, unsigned char *in, int inlen,
 
     {
        int cipher_chosen = 0, warn = 0;
-       char *cipher_string = NULL;
+       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,
@@ -3625,20 +4217,24 @@ static int do_ssh1_login(Ssh ssh, unsigned char *in, int inlen,
     s->keyfile = conf_get_filename(ssh->conf, CONF_keyfile);
     if (!filename_is_null(s->keyfile)) {
        int keytype;
-       logeventf(ssh, "Reading private key file \"%.150s\"",
+       logeventf(ssh, "Reading key file \"%.150s\"",
                  filename_to_str(s->keyfile));
        keytype = key_type(s->keyfile);
-       if (keytype == SSH_KEYTYPE_SSH1) {
+       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->publickey_encrypted = rsakey_encrypted(s->keyfile,
-                                                         NULL);
+                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 private key (%s)", error);
-               msgbuf = dupprintf("Unable to load private key file "
+               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);
@@ -3846,7 +4442,8 @@ static int do_ssh1_login(Ssh ssh, unsigned char *in, int inlen,
            if (s->authed)
                break;
        }
-       if (s->publickey_blob && !s->tried_publickey) {
+       if (s->publickey_blob && s->privatekey_available &&
+            !s->tried_publickey) {
            /*
             * Try public key authentication with the specified
             * key file.
@@ -3865,7 +4462,7 @@ static int do_ssh1_login(Ssh ssh, unsigned char *in, int inlen,
                 */
                char *passphrase = NULL;    /* only written after crReturn */
                const char *error;
-               if (!s->publickey_encrypted) {
+               if (!s->privatekey_encrypted) {
                    if (flags & FLAG_VERBOSE)
                        c_write_str(ssh, "No passphrase required.\r\n");
                    passphrase = NULL;
@@ -4179,9 +4776,8 @@ static int do_ssh1_login(Ssh ssh, unsigned char *in, int inlen,
                for (i = bottom; i <= top; i++) {
                    if (i == pwlen) {
                        defer_packet(ssh, s->pwpkt_type,
-                                    PKTT_PASSWORD, PKT_STR,
-                                    s->cur_prompt->prompts[0]->result,
-                                    PKTT_OTHER, PKT_END);
+                                     PKT_STR,s->cur_prompt->prompts[0]->result,
+                                    PKT_END);
                    } else {
                        for (j = 0; j < i; j++) {
                            do {
@@ -4219,9 +4815,9 @@ static int do_ssh1_login(Ssh ssh, unsigned char *in, int inlen,
                    ss = s->cur_prompt->prompts[0]->result;
                }
                logevent("Sending length-padded password");
-               send_packet(ssh, s->pwpkt_type, PKTT_PASSWORD,
+               send_packet(ssh, s->pwpkt_type,
                            PKT_INT, len, PKT_DATA, ss, len,
-                           PKTT_OTHER, PKT_END);
+                           PKT_END);
            } else {
                /*
                 * The server is believed unable to cope with
@@ -4231,14 +4827,14 @@ static int do_ssh1_login(Ssh ssh, unsigned char *in, int inlen,
                len = strlen(s->cur_prompt->prompts[0]->result);
                logevent("Sending unpadded password");
                send_packet(ssh, s->pwpkt_type,
-                           PKTT_PASSWORD, PKT_INT, len,
+                            PKT_INT, len,
                            PKT_DATA, s->cur_prompt->prompts[0]->result, len,
-                           PKTT_OTHER, PKT_END);
+                           PKT_END);
            }
        } else {
-           send_packet(ssh, s->pwpkt_type, PKTT_PASSWORD,
+           send_packet(ssh, s->pwpkt_type,
                        PKT_STR, s->cur_prompt->prompts[0]->result,
-                       PKTT_OTHER, PKT_END);
+                       PKT_END);
        }
        logevent("Sent password");
        free_prompts(s->cur_prompt);
@@ -4288,6 +4884,12 @@ static void ssh_channel_try_eof(struct ssh_channel *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;
@@ -4311,13 +4913,13 @@ void sshfwd_unclean_close(struct ssh_channel *c, const char *err)
 
     switch (c->type) {
       case CHAN_X11:
-        x11_close(c->u.x11.s);
+        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.s);
+        pfd_close(c->u.pfd.pf);
         logeventf(ssh, "Forwarded port closed due to local error: %s", err);
         break;
     }
@@ -4337,8 +4939,8 @@ int sshfwd_write(struct ssh_channel *c, char *buf, int len)
     if (ssh->version == 1) {
        send_packet(ssh, SSH1_MSG_CHANNEL_DATA,
                    PKT_INT, c->remoteid,
-                   PKT_INT, len, PKTT_DATA, PKT_DATA, buf, len,
-                   PKTT_OTHER, PKT_END);
+                   PKT_INT, len, PKT_DATA, buf, len,
+                   PKT_END);
        /*
         * In SSH-1 we can return 0 here - implying that forwarded
         * connections are never individually throttled - because
@@ -4458,6 +5060,41 @@ static void ssh_rportfwd_succfail(Ssh ssh, struct Packet *pktin, void *ctx)
     }
 }
 
+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;
@@ -4497,13 +5134,15 @@ static void ssh_setup_portfwd(Ssh ssh, Conf *conf)
        if (*kp == 'L' || *kp == 'R')
            type = *kp++;
 
-       if ((kp2 = strchr(kp, ':')) != NULL) {
+       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.
             */
-           saddr = dupprintf("%.*s", (int)(kp2 - kp), kp);
+           char *saddr_tmp = dupprintf("%.*s", (int)(kp2 - kp), kp);
+            saddr = host_strduptrim(saddr_tmp);
+            sfree(saddr_tmp);
            sports = kp2+1;
        } else {
            saddr = NULL;
@@ -4530,9 +5169,9 @@ static void ssh_setup_portfwd(Ssh ssh, Conf *conf)
         } else {
             /* ordinary forwarding */
            vp = val;
-           vp2 = vp + strcspn(vp, ":");
+           vp2 = vp + host_strcspn(vp, ":");
            host = dupprintf("%.*s", (int)(vp2 - vp), vp);
-           if (vp2)
+           if (*vp2)
                vp2++;
            dports = vp2;
            dport = atoi(dports);
@@ -4655,7 +5294,7 @@ static void ssh_setup_portfwd(Ssh ssh, Conf *conf)
                del234(ssh->rportfwds, rpf);
                free_rportfwd(rpf);
            } else if (epf->local) {
-               pfd_terminate(epf->local);
+               pfl_terminate(epf->local);
            }
 
            delpos234(ssh->portfwds, i);
@@ -4688,29 +5327,31 @@ static void ssh_setup_portfwd(Ssh ssh, Conf *conf)
            }
 
            if (epf->type == 'L') {
-               const char *err = pfd_addforward(epf->daddr, epf->dport,
-                                                epf->saddr, epf->sport,
-                                                ssh, conf,
-                                                &epf->local,
-                                                epf->addressfamily);
+                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') {
-               const char *err = pfd_addforward(NULL, -1,
-                                                epf->saddr, epf->sport,
-                                                ssh, conf,
-                                                &epf->local,
-                                                epf->addressfamily);
+               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;
 
@@ -4725,9 +5366,16 @@ static void ssh_setup_portfwd(Ssh ssh, Conf *conf)
                }
 
                pf = snew(struct ssh_rportfwd);
-               strncpy(pf->dhost, epf->daddr, lenof(pf->dhost)-1);
-               pf->dhost[lenof(pf->dhost)-1] = '\0';
+                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",
@@ -4756,14 +5404,8 @@ static void ssh_setup_portfwd(Ssh ssh, Conf *conf)
                        pktout = ssh2_pkt_init(SSH2_MSG_GLOBAL_REQUEST);
                        ssh2_pkt_addstring(pktout, "tcpip-forward");
                        ssh2_pkt_addbool(pktout, 1);/* want reply */
-                       if (epf->saddr) {
-                           ssh2_pkt_addstring(pktout, epf->saddr);
-                       } else if (conf_get_int(conf, CONF_rport_acceptall)) {
-                           ssh2_pkt_addstring(pktout, "");
-                       } else {
-                           ssh2_pkt_addstring(pktout, "localhost");
-                       }
-                       ssh2_pkt_adduint32(pktout, epf->sport);
+                       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,
@@ -4813,28 +5455,19 @@ static void ssh1_smsg_x11_open(Ssh ssh, struct Packet *pktin)
        c = snew(struct ssh_channel);
        c->ssh = ssh;
 
-       if (x11_init(&c->u.x11.s, ssh->x11disp, c,
-                    NULL, -1, ssh->conf) != NULL) {
-           logevent("Opening X11 forward connection failed");
-           sfree(c);
-           send_packet(ssh, SSH1_MSG_CHANNEL_OPEN_FAILURE,
-                       PKT_INT, remoteid, PKT_END);
-       } else {
-           logevent
-               ("Opening X11 forward connection succeeded");
-           c->remoteid = remoteid;
-           c->halfopen = FALSE;
-           c->localid = alloc_channel_id(ssh);
-           c->closes = 0;
-           c->pending_eof = FALSE;
-           c->throttling_conn = 0;
-           c->type = CHAN_X11; /* identify channel type */
-           add234(ssh->channels, c);
-           send_packet(ssh, SSH1_MSG_CHANNEL_OPEN_CONFIRMATION,
-                       PKT_INT, c->remoteid, PKT_INT,
-                       c->localid, PKT_END);
-           logevent("Opened X11 forward channel");
-       }
+       c->u.x11.xconn = x11_init(ssh->x11authtree, c, NULL, -1);
+        c->remoteid = remoteid;
+        c->halfopen = FALSE;
+        c->localid = alloc_channel_id(ssh);
+        c->closes = 0;
+        c->pending_eof = FALSE;
+        c->throttling_conn = 0;
+        c->type = CHAN_X11;    /* identify channel type */
+        add234(ssh->channels, c);
+        send_packet(ssh, SSH1_MSG_CHANNEL_OPEN_CONFIRMATION,
+                    PKT_INT, c->remoteid, PKT_INT,
+                    c->localid, PKT_END);
+        logevent("Opened X11 forward channel");
     }
 }
 
@@ -4877,16 +5510,13 @@ static void ssh1_msg_port_open(Ssh ssh, struct Packet *pktin)
     int remoteid;
     int hostsize, port;
     char *host;
-    const char *e;
+    char *err;
 
     remoteid = ssh_pkt_getuint32(pktin);
     ssh_pkt_getstring(pktin, &host, &hostsize);
     port = ssh_pkt_getuint32(pktin);
 
-    if (hostsize >= lenof(pf.dhost))
-       hostsize = lenof(pf.dhost)-1;
-    memcpy(pf.dhost, host, hostsize);
-    pf.dhost[hostsize] = '\0';
+    pf.dhost = dupprintf("%.*s", hostsize, host);
     pf.dport = port;
     pfp = find234(ssh->rportfwds, &pf, NULL);
 
@@ -4901,10 +5531,11 @@ static void ssh1_msg_port_open(Ssh ssh, struct Packet *pktin)
 
        logeventf(ssh, "Received remote port open request for %s:%d",
                  pf.dhost, port);
-       e = pfd_newconnect(&c->u.pfd.s, pf.dhost, port,
-                          c, ssh->conf, pfp->pfrec->addressfamily);
-       if (e != NULL) {
-           logeventf(ssh, "Port open failed: %s", e);
+       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);
@@ -4923,6 +5554,8 @@ static void ssh1_msg_port_open(Ssh ssh, struct Packet *pktin)
            logevent("Forwarded port opened successfully");
        }
     }
+
+    sfree(pf.dhost);
 }
 
 static void ssh1_msg_channel_open_confirmation(Ssh ssh, struct Packet *pktin)
@@ -4937,7 +5570,7 @@ static void ssh1_msg_channel_open_confirmation(Ssh ssh, struct Packet *pktin)
        c->halfopen = FALSE;
        c->type = CHAN_SOCKDATA;
        c->throttling_conn = 0;
-       pfd_confirm(c->u.pfd.s);
+       pfd_confirm(c->u.pfd.pf);
     }
 
     if (c && c->pending_eof) {
@@ -4959,7 +5592,7 @@ static void ssh1_msg_channel_open_failure(Ssh ssh, struct Packet *pktin)
     c = find234(ssh->channels, &remoteid, ssh_channelfind);
     if (c && c->type == CHAN_SOCKDATA_DORMANT) {
        logevent("Forwarded connection refused by server");
-       pfd_close(c->u.pfd.s);
+       pfd_close(c->u.pfd.pf);
        del234(ssh->channels, c);
        sfree(c);
     }
@@ -4985,14 +5618,14 @@ static void ssh1_msg_channel_close(Ssh ssh, struct Packet *pktin)
 
             switch (c->type) {
               case CHAN_X11:
-                if (c->u.x11.s)
-                    x11_send_eof(c->u.x11.s);
+                if (c->u.x11.xconn)
+                    x11_send_eof(c->u.x11.xconn);
                 else
                     send_close = TRUE;
                break;
               case CHAN_SOCKDATA:
-                if (c->u.pfd.s)
-                    pfd_send_eof(c->u.pfd.s);
+                if (c->u.pfd.pf)
+                    pfd_send_eof(c->u.pfd.pf);
                 else
                     send_close = TRUE;
                break;
@@ -5051,10 +5684,10 @@ static void ssh1_msg_channel_data(Ssh ssh, struct Packet *pktin)
        int bufsize = 0;
        switch (c->type) {
          case CHAN_X11:
-           bufsize = x11_send(c->u.x11.s, p, len);
+           bufsize = x11_send(c->u.x11.xconn, p, len);
            break;
          case CHAN_SOCKDATA:
-           bufsize = pfd_send(c->u.pfd.s, p, len);
+           bufsize = pfd_send(c->u.pfd.pf, p, len);
            break;
          case CHAN_AGENT:
            /* Data for an agent message. Buffer it. */
@@ -5142,8 +5775,12 @@ static void ssh1_send_ttymode(void *data, char *mode, char *val)
     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, unsigned char *in, int inlen,
+static void do_ssh1_connection(Ssh ssh, const unsigned char *in, int inlen,
                               struct Packet *pktin)
 {
     crBegin(ssh->do_ssh1_connection_crstate);
@@ -5162,7 +5799,7 @@ static void do_ssh1_connection(Ssh ssh, unsigned char *in, int inlen,
     ssh->packet_dispatch[SSH1_MSG_CHANNEL_DATA] = ssh1_msg_channel_data;
     ssh->packet_dispatch[SSH1_SMSG_EXIT_STATUS] = ssh1_smsg_exit_status;
 
-    if (conf_get_int(ssh->conf, CONF_agentfwd) && agent_exists()) {
+    if (ssh_agent_forwarding_permitted(ssh)) {
        logevent("Requesting agent forwarding");
        send_packet(ssh, SSH1_CMSG_AGENT_REQUEST_FORWARDING, PKT_END);
        do {
@@ -5181,47 +5818,47 @@ static void do_ssh1_connection(Ssh ssh, unsigned char *in, int inlen,
        }
     }
 
-    if (conf_get_int(ssh->conf, CONF_x11_forward) &&
-       (ssh->x11disp = x11_setup_display(conf_get_str(ssh->conf, CONF_x11_display),
-                                         conf_get_int(ssh->conf, CONF_x11_auth), ssh->conf))) {
-       logevent("Requesting X11 forwarding");
-       /*
-        * 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.
-        */
-       if (ssh->v1_local_protoflags & SSH1_PROTOFLAG_SCREEN_NUMBER) {
-           send_packet(ssh, SSH1_CMSG_X11_REQUEST_FORWARDING,
-                       PKT_STR, ssh->x11disp->remoteauthprotoname,
-                       PKTT_PASSWORD,
-                       PKT_STR, ssh->x11disp->remoteauthdatastring,
-                       PKTT_OTHER,
-                       PKT_INT, ssh->x11disp->screennum,
-                       PKT_END);
-       } else {
-           send_packet(ssh, SSH1_CMSG_X11_REQUEST_FORWARDING,
-                       PKT_STR, ssh->x11disp->remoteauthprotoname,
-                       PKTT_PASSWORD,
-                       PKT_STR, ssh->x11disp->remoteauthdatastring,
-                       PKTT_OTHER,
-                       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;
-       }
+    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);
@@ -5316,7 +5953,7 @@ static void do_ssh1_connection(Ssh ssh, unsigned char *in, int inlen,
        ssh_special(ssh, TS_EOF);
 
     if (ssh->ldisc)
-       ldisc_send(ssh->ldisc, NULL, 0, 0);/* cause ldisc to notice changes */
+       ldisc_echoedit_update(ssh->ldisc);  /* cause ldisc to notice changes */
     ssh->send_ok = 1;
     ssh->channels = newtree234(ssh_channelcmp);
     while (1) {
@@ -5342,8 +5979,8 @@ static void do_ssh1_connection(Ssh ssh, unsigned char *in, int inlen,
            while (inlen > 0) {
                int len = min(inlen, 512);
                send_packet(ssh, SSH1_CMSG_STDIN_DATA,
-                           PKT_INT, len,  PKTT_DATA, PKT_DATA, in, len,
-                           PKTT_OTHER, PKT_END);
+                           PKT_INT, len, PKT_DATA, in, len,
+                            PKT_END);
                in += len;
                inlen -= len;
            }
@@ -5398,10 +6035,10 @@ static void ssh1_protocol_setup(Ssh ssh)
     ssh->packet_dispatch[SSH1_MSG_DEBUG] = ssh1_msg_debug;
 }
 
-static void ssh1_protocol(Ssh ssh, void *vin, int inlen,
+static void ssh1_protocol(Ssh ssh, const void *vin, int inlen,
                          struct Packet *pktin)
 {
-    unsigned char *in=(unsigned char*)vin;
+    const unsigned char *in = (const unsigned char *)vin;
     if (ssh->state == SSH_STATE_CLOSED)
        return;
 
@@ -5423,7 +6060,8 @@ static void ssh1_protocol(Ssh ssh, void *vin, int inlen,
 /*
  * Utility routine for decoding comma-separated strings in KEXINIT.
  */
-static int in_commasep_string(char *needle, char *haystack, int haylen)
+static int in_commasep_string(char const *needle, char const *haystack,
+                             int haylen)
 {
     int needlen;
     if (!needle || !haystack)         /* protect against null pointers */
@@ -5454,7 +6092,8 @@ static int in_commasep_string(char *needle, char *haystack, int haylen)
 /*
  * Similar routine for checking whether we have the first string in a list.
  */
-static int first_in_commasep_string(char *needle, char *haystack, int haylen)
+static int first_in_commasep_string(char const *needle, char const *haystack,
+                                   int haylen)
 {
     int needlen;
     if (!needle || !haystack)         /* protect against null pointers */
@@ -5472,6 +6111,19 @@ static int first_in_commasep_string(char *needle, char *haystack, int haylen)
     return 0;
 }
 
+/*
+ * Add a value to the comma-separated string at the end of the packet.
+ * If the value is already in the string, don't bother adding it again.
+ */
+static void ssh2_pkt_addstring_commasep(struct Packet *pkt, const char *data)
+{
+    if (in_commasep_string(data, (char *)pkt->data + pkt->savedpos,
+                          pkt->length - pkt->savedpos)) return;
+    if (pkt->length - pkt->savedpos > 0)
+       ssh_pkt_addstring_str(pkt, ",");
+    ssh_pkt_addstring_str(pkt, data);
+}
+
 
 /*
  * SSH-2 key creation method.
@@ -5504,10 +6156,10 @@ static void ssh2_mkkey(Ssh ssh, Bignum K, unsigned char *H, char chr,
 /*
  * Handle the SSH-2 transport layer.
  */
-static void do_ssh2_transport(Ssh ssh, void *vin, int inlen,
+static void do_ssh2_transport(Ssh ssh, const void *vin, int inlen,
                             struct Packet *pktin)
 {
-    unsigned char *in = (unsigned char *)vin;
+    const unsigned char *in = (const unsigned char *)vin;
     struct do_ssh2_transport_state {
        int crLine;
        int nbits, pbits, warn_kex, warn_cscipher, warn_sccipher;
@@ -5521,12 +6173,14 @@ static void do_ssh2_transport(Ssh ssh, void *vin, int inlen,
        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];
@@ -5543,6 +6197,8 @@ static void do_ssh2_transport(Ssh ssh, void *vin, int inlen,
     };
     crState(do_ssh2_transport_state);
 
+    assert(!ssh->bare_connection);
+
     crBeginState;
 
     s->cscipher_tobe = s->sccipher_tobe = NULL;
@@ -5564,7 +6220,7 @@ static void do_ssh2_transport(Ssh ssh, void *vin, int inlen,
   begin_key_exchange:
     ssh->pkt_kctx = SSH2_PKTCTX_NOKEX;
     {
-       int i, j, k, commalist_started;
+       int i, j, k;
 
        /*
         * Set up the preferred key exchange. (NULL => warn below here)
@@ -5588,6 +6244,10 @@ static void do_ssh2_transport(Ssh ssh, void *vin, int inlen,
                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. */
@@ -5658,16 +6318,11 @@ static void do_ssh2_transport(Ssh ssh, void *vin, int inlen,
            ssh2_pkt_addbyte(s->pktout, (unsigned char) random_byte());
        /* List key exchange algorithms. */
        ssh2_pkt_addstring_start(s->pktout);
-       commalist_started = 0;
        for (i = 0; i < s->n_preferred_kex; i++) {
            const struct ssh_kexes *k = s->preferred_kex[i];
            if (!k) continue;          /* warning flag */
-           for (j = 0; j < k->nkexes; j++) {
-               if (commalist_started)
-                   ssh2_pkt_addstring_str(s->pktout, ",");
-               ssh2_pkt_addstring_str(s->pktout, k->list[j]->name);
-               commalist_started = 1;
-           }
+           for (j = 0; j < k->nkexes; j++)
+               ssh2_pkt_addstring_commasep(s->pktout, k->list[j]->name);
        }
        /* List server host key algorithms. */
         if (!s->got_session_id) {
@@ -5676,11 +6331,8 @@ static void do_ssh2_transport(Ssh ssh, void *vin, int inlen,
              * we're prepared to cope with.
              */
             ssh2_pkt_addstring_start(s->pktout);
-            for (i = 0; i < lenof(hostkey_algs); i++) {
-                ssh2_pkt_addstring_str(s->pktout, hostkey_algs[i]->name);
-                if (i < lenof(hostkey_algs) - 1)
-                    ssh2_pkt_addstring_str(s->pktout, ",");
-            }
+            for (i = 0; i < lenof(hostkey_algs); i++)
+                ssh2_pkt_addstring_commasep(s->pktout, hostkey_algs[i]->name);
         } else {
             /*
              * In subsequent key exchanges, we list only the kex
@@ -5695,26 +6347,25 @@ static void do_ssh2_transport(Ssh ssh, void *vin, int inlen,
        /* List encryption algorithms (client->server then server->client). */
        for (k = 0; k < 2; k++) {
            ssh2_pkt_addstring_start(s->pktout);
-           commalist_started = 0;
            for (i = 0; i < s->n_preferred_ciphers; i++) {
                const struct ssh2_ciphers *c = s->preferred_ciphers[i];
                if (!c) continue;              /* warning flag */
-               for (j = 0; j < c->nciphers; j++) {
-                   if (commalist_started)
-                       ssh2_pkt_addstring_str(s->pktout, ",");
-                   ssh2_pkt_addstring_str(s->pktout, c->list[j]->name);
-                   commalist_started = 1;
-               }
+               for (j = 0; j < c->nciphers; j++)
+                   ssh2_pkt_addstring_commasep(s->pktout, c->list[j]->name);
            }
        }
        /* List MAC algorithms (client->server then server->client). */
        for (j = 0; j < 2; j++) {
            ssh2_pkt_addstring_start(s->pktout);
            for (i = 0; i < s->nmacs; i++) {
-               ssh2_pkt_addstring_str(s->pktout, s->maclist[i]->name);
-               if (i < s->nmacs - 1)
-                   ssh2_pkt_addstring_str(s->pktout, ",");
-           }
+               ssh2_pkt_addstring_commasep(s->pktout, s->maclist[i]->name);
+            }
+           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)
+                    ssh2_pkt_addstring_commasep(s->pktout, s->maclist[i]->etm_name);
+            }
        }
        /* List client->server compression algorithms,
         * then server->client compression algorithms. (We use the
@@ -5723,25 +6374,18 @@ static void do_ssh2_transport(Ssh ssh, void *vin, int inlen,
            ssh2_pkt_addstring_start(s->pktout);
            assert(lenof(compressions) > 1);
            /* Prefer non-delayed versions */
-           ssh2_pkt_addstring_str(s->pktout, s->preferred_comp->name);
+           ssh2_pkt_addstring_commasep(s->pktout, s->preferred_comp->name);
            /* 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) {
-               ssh2_pkt_addstring_str(s->pktout, ",");
-               ssh2_pkt_addstring_str(s->pktout,
-                                      s->preferred_comp->delayed_name);
-           }
+           if (s->userauth_succeeded && s->preferred_comp->delayed_name)
+               ssh2_pkt_addstring_commasep(s->pktout,
+                                           s->preferred_comp->delayed_name);
            for (i = 0; i < lenof(compressions); i++) {
                const struct ssh_compress *c = compressions[i];
-               if (c != s->preferred_comp) {
-                   ssh2_pkt_addstring_str(s->pktout, ",");
-                   ssh2_pkt_addstring_str(s->pktout, c->name);
-                   if (s->userauth_succeeded && c->delayed_name) {
-                       ssh2_pkt_addstring_str(s->pktout, ",");
-                       ssh2_pkt_addstring_str(s->pktout, c->delayed_name);
-                   }
-               }
+               ssh2_pkt_addstring_commasep(s->pktout, c->name);
+               if (s->userauth_succeeded && c->delayed_name)
+                   ssh2_pkt_addstring_commasep(s->pktout, c->delayed_name);
            }
        }
        /* List client->server languages. Empty list. */
@@ -5768,7 +6412,8 @@ static void do_ssh2_transport(Ssh ssh, void *vin, int inlen,
      * to.
      */
     {
-       char *str, *preferred;
+       char *str;
+        const char *preferred;
        int i, j, len;
 
        if (pktin->type != SSH2_MSG_KEXINIT) {
@@ -5787,6 +6432,10 @@ static void do_ssh2_transport(Ssh ssh, void *vin, int inlen,
 
        pktin->savedpos += 16;          /* skip garbage cookie */
        ssh_pkt_getstring(pktin, &str, &len);    /* key exchange algorithms */
+        if (!str) {
+            bombout(("KEXINIT packet was incomplete"));
+            crStopV;
+        }
 
        preferred = NULL;
        for (i = 0; i < s->n_preferred_kex; i++) {
@@ -5806,8 +6455,8 @@ static void do_ssh2_transport(Ssh ssh, void *vin, int inlen,
                break;
        }
        if (!ssh->kex) {
-           bombout(("Couldn't agree a key exchange algorithm (available: %s)",
-                    str ? str : "(null)"));
+            bombout(("Couldn't agree a key exchange algorithm"
+                     " (available: %.*s)", len, str));
            crStopV;
        }
        /*
@@ -5817,6 +6466,10 @@ static void do_ssh2_transport(Ssh ssh, void *vin, int inlen,
         */
        s->guessok = first_in_commasep_string(preferred, str, len);
        ssh_pkt_getstring(pktin, &str, &len);    /* host key algorithms */
+        if (!str) {
+            bombout(("KEXINIT packet was incomplete"));
+            crStopV;
+        }
        for (i = 0; i < lenof(hostkey_algs); i++) {
            if (in_commasep_string(hostkey_algs[i]->name, str, len)) {
                ssh->hostkey = hostkey_algs[i];
@@ -5824,14 +6477,18 @@ static void do_ssh2_transport(Ssh ssh, void *vin, int inlen,
            }
        }
        if (!ssh->hostkey) {
-           bombout(("Couldn't agree a host key algorithm (available: %s)",
-                    str ? str : "(null)"));
+            bombout(("Couldn't agree a host key algorithm"
+                     " (available: %.*s)", len, str));
            crStopV;
        }
 
        s->guessok = s->guessok &&
            first_in_commasep_string(hostkey_algs[0]->name, str, len);
        ssh_pkt_getstring(pktin, &str, &len);    /* client->server cipher */
+        if (!str) {
+            bombout(("KEXINIT packet was incomplete"));
+            crStopV;
+        }
        for (i = 0; i < s->n_preferred_ciphers; i++) {
            const struct ssh2_ciphers *c = s->preferred_ciphers[i];
            if (!c) {
@@ -5848,12 +6505,16 @@ static void do_ssh2_transport(Ssh ssh, void *vin, int inlen,
                break;
        }
        if (!s->cscipher_tobe) {
-           bombout(("Couldn't agree a client-to-server cipher (available: %s)",
-                    str ? str : "(null)"));
+            bombout(("Couldn't agree a client-to-server cipher"
+                     " (available: %.*s)", len, str));
            crStopV;
        }
 
        ssh_pkt_getstring(pktin, &str, &len);    /* server->client cipher */
+        if (!str) {
+            bombout(("KEXINIT packet was incomplete"));
+            crStopV;
+        }
        for (i = 0; i < s->n_preferred_ciphers; i++) {
            const struct ssh2_ciphers *c = s->preferred_ciphers[i];
            if (!c) {
@@ -5870,26 +6531,70 @@ static void do_ssh2_transport(Ssh ssh, void *vin, int inlen,
                break;
        }
        if (!s->sccipher_tobe) {
-           bombout(("Couldn't agree a server-to-client cipher (available: %s)",
-                    str ? str : "(null)"));
+            bombout(("Couldn't agree a server-to-client cipher"
+                     " (available: %.*s)", len, str));
            crStopV;
        }
 
        ssh_pkt_getstring(pktin, &str, &len);    /* client->server mac */
+        if (!str) {
+            bombout(("KEXINIT packet was incomplete"));
+            crStopV;
+        }
        for (i = 0; i < s->nmacs; i++) {
            if (in_commasep_string(s->maclist[i]->name, str, len)) {
                s->csmac_tobe = s->maclist[i];
-               break;
+               s->csmac_etm_tobe = FALSE;
+                break;
            }
        }
+        if (!s->csmac_tobe) {
+            for (i = 0; i < s->nmacs; i++) {
+                if (s->maclist[i]->etm_name &&
+                    in_commasep_string(s->maclist[i]->etm_name, str, len)) {
+                    s->csmac_tobe = s->maclist[i];
+                    s->csmac_etm_tobe = TRUE;
+                    break;
+                }
+            }
+        }
+        if (!s->csmac_tobe) {
+            bombout(("Couldn't agree a client-to-server MAC"
+                     " (available: %.*s)", len, str));
+           crStopV;
+        }
        ssh_pkt_getstring(pktin, &str, &len);    /* server->client mac */
+        if (!str) {
+            bombout(("KEXINIT packet was incomplete"));
+            crStopV;
+        }
        for (i = 0; i < s->nmacs; i++) {
            if (in_commasep_string(s->maclist[i]->name, str, len)) {
                s->scmac_tobe = s->maclist[i];
-               break;
+               s->scmac_etm_tobe = FALSE;
+                break;
            }
        }
+        if (!s->scmac_tobe) {
+            for (i = 0; i < s->nmacs; i++) {
+                if (s->maclist[i]->etm_name &&
+                    in_commasep_string(s->maclist[i]->etm_name, str, len)) {
+                    s->scmac_tobe = s->maclist[i];
+                    s->scmac_etm_tobe = TRUE;
+                    break;
+                }
+            }
+        }
+        if (!s->scmac_tobe) {
+            bombout(("Couldn't agree a server-to-client MAC"
+                     " (available: %.*s)", len, str));
+           crStopV;
+        }
        ssh_pkt_getstring(pktin, &str, &len);  /* client->server compression */
+        if (!str) {
+            bombout(("KEXINIT packet was incomplete"));
+            crStopV;
+        }
        for (i = 0; i < lenof(compressions) + 1; i++) {
            const struct ssh_compress *c =
                i == 0 ? s->preferred_comp : compressions[i - 1];
@@ -5906,6 +6611,10 @@ static void do_ssh2_transport(Ssh ssh, void *vin, int inlen,
            }
        }
        ssh_pkt_getstring(pktin, &str, &len);  /* server->client compression */
+        if (!str) {
+            bombout(("KEXINIT packet was incomplete"));
+            crStopV;
+        }
        for (i = 0; i < lenof(compressions) + 1; i++) {
            const struct ssh_compress *c =
                i == 0 ? s->preferred_comp : compressions[i - 1];
@@ -5935,9 +6644,9 @@ static void do_ssh2_transport(Ssh ssh, void *vin, int inlen,
        hash_string(ssh->kex->hash, ssh->exhash,
            s->our_kexinit, s->our_kexinitlen);
        sfree(s->our_kexinit);
-       if (pktin->length > 5)
-           hash_string(ssh->kex->hash, ssh->exhash,
-               pktin->data + 5, pktin->length - 5);
+        /* 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);
@@ -6039,7 +6748,7 @@ static void do_ssh2_transport(Ssh ssh, void *vin, int inlen,
          * If we're doing Diffie-Hellman group exchange, start by
          * requesting a group.
          */
-        if (!ssh->kex->pdata) {
+        if (dh_is_gex(ssh->kex)) {
             logevent("Doing Diffie-Hellman group exchange");
             ssh->pkt_kctx = SSH2_PKTCTX_DHGEX;
             /*
@@ -6047,8 +6756,19 @@ static void do_ssh2_transport(Ssh ssh, void *vin, int inlen,
              * much data.
              */
             s->pbits = 512 << ((s->nbits - 1) / 64);
-            s->pktout = ssh2_pkt_init(SSH2_MSG_KEX_DH_GEX_REQUEST);
-            ssh2_pkt_adduint32(s->pktout, s->pbits);
+            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);
@@ -6093,14 +6813,22 @@ static void do_ssh2_transport(Ssh ssh, void *vin, int inlen,
         }
         set_busy_status(ssh->frontend, BUSY_CPU); /* cogitate */
         ssh_pkt_getstring(pktin, &s->hostkeydata, &s->hostkeylen);
-        s->hkey = ssh->hostkey->newkey(s->hostkeydata, s->hostkeylen);
+        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);
-
+        ssh_pkt_getstring(pktin, &s->sigdata, &s->siglen);
+
+        {
+            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
@@ -6108,8 +6836,12 @@ static void do_ssh2_transport(Ssh ssh, void *vin, int inlen,
         set_busy_status(ssh->frontend, BUSY_NOT);
 
         hash_string(ssh->kex->hash, ssh->exhash, s->hostkeydata, s->hostkeylen);
-        if (!ssh->kex->pdata) {
+        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);
         }
@@ -6118,10 +6850,81 @@ static void do_ssh2_transport(Ssh ssh, void *vin, int inlen,
 
         dh_cleanup(ssh->kex_ctx);
         freebn(s->f);
-        if (!ssh->kex->pdata) {
+        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 hash %s",
+                  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);
+        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);
+            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);
+
+        ssh_ecdhkex_freekey(s->eckey);
     } else {
        logeventf(ssh, "Doing RSA key exchange with hash %s",
                  ssh->kex->hash->text_name);
@@ -6139,7 +6942,8 @@ static void do_ssh2_transport(Ssh ssh, void *vin, int inlen,
         ssh_pkt_getstring(pktin, &s->hostkeydata, &s->hostkeylen);
         hash_string(ssh->kex->hash, ssh->exhash,
                    s->hostkeydata, s->hostkeylen);
-       s->hkey = ssh->hostkey->newkey(s->hostkeydata, s->hostkeylen);
+       s->hkey = ssh->hostkey->newkey(ssh->hostkey,
+                                       s->hostkeydata, s->hostkeylen);
 
         {
             char *keydata;
@@ -6249,32 +7053,40 @@ static void do_ssh2_transport(Ssh ssh, void *vin, int inlen,
          * Authenticate remote host: verify host key. (We've already
          * checked the signature of the exchange hash.)
          */
-        s->fingerprint = ssh->hostkey->fingerprint(s->hkey);
-        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);
-        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, "User aborted at host key verification", NULL,
-                           0, TRUE);
-            crStopV;
-        }
+        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);
+            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
@@ -6329,6 +7141,7 @@ static void do_ssh2_transport(Ssh ssh, void *vin, int inlen,
     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;
     ssh->cs_mac_ctx = ssh->csmac->make_context();
 
     if (ssh->cs_comp_ctx)
@@ -6360,8 +7173,9 @@ static void do_ssh2_transport(Ssh ssh, void *vin, int inlen,
 
     logeventf(ssh, "Initialised %.200s client->server encryption",
              ssh->cscipher->text_name);
-    logeventf(ssh, "Initialised %.200s client->server MAC algorithm",
-             ssh->csmac->text_name);
+    logeventf(ssh, "Initialised %.200s client->server MAC algorithm%s",
+             ssh->csmac->text_name,
+              ssh->csmac_etm ? " (in ETM mode)" : "");
     if (ssh->cscomp->text_name)
        logeventf(ssh, "Initialised %s compression",
                  ssh->cscomp->text_name);
@@ -6395,6 +7209,7 @@ static void do_ssh2_transport(Ssh ssh, void *vin, int inlen,
     if (ssh->sc_mac_ctx)
        ssh->scmac->free_context(ssh->sc_mac_ctx);
     ssh->scmac = s->scmac_tobe;
+    ssh->scmac_etm = s->scmac_etm_tobe;
     ssh->sc_mac_ctx = ssh->scmac->make_context();
 
     if (ssh->sc_comp_ctx)
@@ -6425,8 +7240,9 @@ static void do_ssh2_transport(Ssh ssh, void *vin, int inlen,
     }
     logeventf(ssh, "Initialised %.200s server->client encryption",
              ssh->sccipher->text_name);
-    logeventf(ssh, "Initialised %.200s server->client MAC algorithm",
-             ssh->scmac->text_name);
+    logeventf(ssh, "Initialised %.200s server->client MAC algorithm%s",
+             ssh->scmac->text_name,
+              ssh->scmac_etm ? " (in ETM mode)" : "");
     if (ssh->sccomp->text_name)
        logeventf(ssh, "Initialised %s decompression",
                  ssh->sccomp->text_name);
@@ -6546,7 +7362,7 @@ static void do_ssh2_transport(Ssh ssh, void *vin, int inlen,
 /*
  * Add data to an SSH-2 channel output buffer.
  */
-static void ssh2_add_channel_data(struct ssh_channel *c, char *buf,
+static void ssh2_add_channel_data(struct ssh_channel *c, const char *buf,
                                  int len)
 {
     bufchain_add(&c->v.v2.outbuffer, buf, len);
@@ -6572,9 +7388,7 @@ static int ssh2_try_send(struct ssh_channel *c)
        pktout = ssh2_pkt_init(SSH2_MSG_CHANNEL_DATA);
        ssh2_pkt_adduint32(pktout, c->remoteid);
        ssh2_pkt_addstring_start(pktout);
-       dont_log_data(ssh, pktout, PKTLOG_OMIT);
        ssh2_pkt_addstring_data(pktout, data, len);
-       end_log_omission(ssh, pktout);
        ssh2_pkt_send(ssh, pktout);
        bufchain_consume(&c->v.v2.outbuffer, len);
        c->v.v2.remwindow -= len;
@@ -6609,19 +7423,32 @@ static void ssh2_try_send_and_unthrottle(Ssh ssh, struct ssh_channel *c)
             * notification since it will be polled */
            break;
          case CHAN_X11:
-           x11_unthrottle(c->u.x11.s);
+           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.s);
+           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 for SSH-2.
  */
@@ -6633,7 +7460,7 @@ static void ssh2_channel_init(struct ssh_channel *c)
     c->pending_eof = FALSE;
     c->throttling_conn = FALSE;
     c->v.v2.locwindow = c->v.v2.locmaxwin = c->v.v2.remlocwin =
-       conf_get_int(ssh->conf, CONF_ssh_simple) ? OUR_V2_BIGWIN : OUR_V2_WINSIZE;
+       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);
@@ -6642,7 +7469,8 @@ static void ssh2_channel_init(struct ssh_channel *c)
 /*
  * Construct the common parts of a CHANNEL_OPEN.
  */
-static struct Packet *ssh2_chanopen_init(struct ssh_channel *c, char *type)
+static struct Packet *ssh2_chanopen_init(struct ssh_channel *c,
+                                         const char *type)
 {
     struct Packet *pktout;
 
@@ -6683,12 +7511,14 @@ static void ssh2_queue_chanreq_handler(struct ssh_channel *c,
  * 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) and the
- * handler should free any storage it's holding.
+ * 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, char *type,
+static struct Packet *ssh2_chanreq_init(struct ssh_channel *c,
+                                        const char *type,
                                        cchandler_fn_t handler, void *ctx)
 {
     struct Packet *pktout;
@@ -6721,6 +7551,14 @@ static void ssh2_set_window(struct ssh_channel *c, int newwin)
     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
@@ -6784,7 +7622,8 @@ static struct ssh_channel *ssh2_channel_msg(Ssh ssh, struct Packet *pktin)
 
     c = find234(ssh->channels, &localid, ssh_channelfind);
     if (!c ||
-       (c->halfopen && pktin->type != SSH2_MSG_CHANNEL_OPEN_CONFIRMATION &&
+       (c->type != CHAN_SHARING && c->halfopen &&
+         pktin->type != SSH2_MSG_CHANNEL_OPEN_CONFIRMATION &&
         pktin->type != SSH2_MSG_CHANNEL_OPEN_FAILURE)) {
        char *buf = dupprintf("Received %s for %s channel %u",
                              ssh2_pkt_type(ssh->pkt_kctx, ssh->pkt_actx,
@@ -6827,6 +7666,11 @@ static void ssh2_msg_channel_response(Ssh ssh, struct Packet *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);
@@ -6849,6 +7693,11 @@ static void ssh2_msg_channel_window_adjust(Ssh ssh, struct Packet *pktin)
     c = ssh2_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);
@@ -6863,6 +7712,11 @@ static void ssh2_msg_channel_data(Ssh ssh, struct Packet *pktin)
     c = ssh2_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 */
@@ -6879,10 +7733,10 @@ static void ssh2_msg_channel_data(Ssh ssh, struct Packet *pktin)
                             data, length);
            break;
          case CHAN_X11:
-           bufsize = x11_send(c->u.x11.s, data, length);
+           bufsize = x11_send(c->u.x11.xconn, data, length);
            break;
          case CHAN_SOCKDATA:
-           bufsize = pfd_send(c->u.pfd.s, data, length);
+           bufsize = pfd_send(c->u.pfd.pf, data, length);
            break;
          case CHAN_AGENT:
            while (length > 0) {
@@ -6951,15 +7805,59 @@ static void ssh2_msg_channel_data(Ssh ssh, struct Packet *pktin)
         * buffering anything at all and we're in "simple" mode,
         * throttle the whole channel.
         */
-       if ((bufsize > c->v.v2.locmaxwin ||
-            (conf_get_int(ssh->conf, CONF_ssh_simple) && bufsize > 0)) &&
-           !c->throttling_conn) {
+       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) &&
+        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)
+{
+    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;
@@ -6970,16 +7868,16 @@ static void ssh_channel_destroy(struct ssh_channel *c)
         update_specials_menu(ssh->frontend);
         break;
       case CHAN_X11:
-        if (c->u.x11.s != NULL)
-            x11_close(c->u.x11.s);
+        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.s != NULL)
-            pfd_close(c->u.pfd.s);
+        if (c->u.pfd.pf != NULL)
+            pfd_close(c->u.pfd.pf);
         logevent("Forwarded port closed");
         break;
     }
@@ -6992,26 +7890,10 @@ static void ssh_channel_destroy(struct ssh_channel *c)
     sfree(c);
 
     /*
-     * See if that was the last channel left open.
-     * (This is only our termination condition if we're
-     * not running in -N mode.)
+     * If that was the last channel left open, we might need to
+     * terminate.
      */
-    if (ssh->version == 2 &&
-        !conf_get_int(ssh->conf, CONF_ssh_no_shell) &&
-        count234(ssh->channels) == 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);
-    }
+    ssh_check_termination(ssh);
 }
 
 static void ssh2_channel_check_close(struct ssh_channel *c)
@@ -7061,14 +7943,14 @@ static void ssh2_channel_got_eof(struct ssh_channel *c)
     c->closes |= CLOSES_RCVD_EOF;
 
     if (c->type == CHAN_X11) {
-       x11_send_eof(c->u.x11.s);
+       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.s);
+       pfd_send_eof(c->u.pfd.pf);
     } else if (c->type == CHAN_MAINSESSION) {
         Ssh ssh = c->ssh;
 
@@ -7097,6 +7979,11 @@ static void ssh2_msg_channel_eof(Ssh ssh, struct Packet *pktin)
     c = ssh2_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);
 }
 
@@ -7107,6 +7994,11 @@ static void ssh2_msg_channel_close(Ssh ssh, struct Packet *pktin)
     c = ssh2_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
@@ -7114,6 +8006,21 @@ static void ssh2_msg_channel_close(Ssh ssh, struct Packet *pktin)
      */
     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
@@ -7131,10 +8038,10 @@ static void ssh2_msg_channel_close(Ssh ssh, struct Packet *pktin)
             ssh->send_ok = 0;     /* stop trying to read from stdin */
             break;
           case CHAN_X11:
-           x11_override_throttle(c->u.x11.s, 1);
+           x11_override_throttle(c->u.x11.xconn, 1);
            break;
          case CHAN_SOCKDATA:
-           pfd_override_throttle(c->u.pfd.s, 1);
+           pfd_override_throttle(c->u.pfd.pf, 1);
            break;
         }
 
@@ -7169,6 +8076,11 @@ static void ssh2_msg_channel_open_confirmation(Ssh ssh, struct Packet *pktin)
     c = ssh2_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); /* ssh2_channel_msg will have enforced this */
     c->remoteid = ssh_pkt_getuint32(pktin);
     c->halfopen = FALSE;
@@ -7177,8 +8089,8 @@ static void ssh2_msg_channel_open_confirmation(Ssh ssh, struct Packet *pktin)
 
     if (c->type == CHAN_SOCKDATA_DORMANT) {
         c->type = CHAN_SOCKDATA;
-        if (c->u.pfd.s)
-            pfd_confirm(c->u.pfd.s);
+        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
@@ -7224,6 +8136,11 @@ static void ssh2_msg_channel_open_failure(Ssh ssh, struct Packet *pktin)
     c = ssh2_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); /* ssh2_channel_msg will have enforced this */
 
     if (c->type == CHAN_SOCKDATA_DORMANT) {
@@ -7234,7 +8151,7 @@ static void ssh2_msg_channel_open_failure(Ssh ssh, struct Packet *pktin)
         logeventf(ssh, "Forwarded connection refused by server: %s [%.*s]",
                   reasons[reason_code], reason_length, reason_string);
 
-        pfd_close(c->u.pfd.s);
+        pfd_close(c->u.pfd.pf);
     } else if (c->type == CHAN_ZOMBIE) {
         /*
          * This case can occur if a local socket error occurred
@@ -7271,9 +8188,24 @@ static void ssh2_msg_channel_request(Ssh ssh, struct Packet *pktin)
     c = ssh2_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
@@ -7296,7 +8228,7 @@ static void ssh2_msg_channel_request(Ssh ssh, struct Packet *pktin)
                   !memcmp(type, "exit-signal", 11)) {
 
            int is_plausible = TRUE, is_int = FALSE;
-           char *fmt_sig = "", *fmt_msg = "";
+            char *fmt_sig = NULL, *fmt_msg = NULL;
            char *msg;
            int msglen = 0, core = FALSE;
            /* ICK: older versions of OpenSSH (e.g. 3.4p1)
@@ -7419,10 +8351,11 @@ static void ssh2_msg_channel_request(Ssh ssh, struct Packet *pktin)
                /* ignore lang tag */
            } /* else don't attempt to parse */
            logeventf(ssh, "Server exited on signal%s%s%s",
-                     fmt_sig, core ? " (core dumped)" : "",
-                     fmt_msg);
-           if (*fmt_sig) sfree(fmt_sig);
-           if (*fmt_msg) sfree(fmt_msg);
+                     fmt_sig ? fmt_sig : "",
+                      core ? " (core dumped)" : "",
+                     fmt_msg ? fmt_msg : "");
+           sfree(fmt_sig);
+            sfree(fmt_msg);
            reply = SSH2_MSG_CHANNEL_SUCCESS;
 
        }
@@ -7463,6 +8396,30 @@ static void ssh2_msg_global_request(Ssh ssh, struct Packet *pktin)
     }
 }
 
+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;
@@ -7470,9 +8427,10 @@ static void ssh2_msg_channel_open(Ssh ssh, struct Packet *pktin)
     char *peeraddr;
     int peeraddrlen;
     int peerport;
-    char *error = NULL;
+    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);
@@ -7485,7 +8443,6 @@ static void ssh2_msg_channel_open(Ssh ssh, struct Packet *pktin)
 
     if (typelen == 3 && !memcmp(type, "x11", 3)) {
        char *addrstr;
-       const char *x11err;
 
        ssh_pkt_getstring(pktin, &peeraddr, &peeraddrlen);
        addrstr = snewn(peeraddrlen+1, char);
@@ -7496,42 +8453,69 @@ static void ssh2_msg_channel_open(Ssh ssh, struct Packet *pktin)
        logeventf(ssh, "Received X11 connect request from %s:%d",
                  addrstr, peerport);
 
-       if (!ssh->X11_fwd_enabled)
+       if (!ssh->X11_fwd_enabled && !ssh->connshare)
            error = "X11 forwarding is not enabled";
-       else if ((x11err = x11_init(&c->u.x11.s, ssh->x11disp, c,
-                                   addrstr, peerport, ssh->conf)) != NULL) {
-           logeventf(ssh, "Local X11 connection failed: %s", x11err);
-           error = "Unable to open an X11 connection";
-       } else {
-           logevent("Opening X11 forward connection succeeded");
+       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 *dummy;
-       int dummylen;
-       ssh_pkt_getstring(pktin, &dummy, &dummylen);/* skip address */
+       char *shost;
+       int shostlen;
+       ssh_pkt_getstring(pktin, &shost, &shostlen);/* skip address */
+        pf.shost = dupprintf("%.*s", shostlen, 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 %d open request "
-                 "from %s:%d", pf.sport, peeraddr, peerport);
+       logeventf(ssh, "Received remote port %s:%d open request "
+                 "from %s:%d", pf.shost, pf.sport, peeraddr, peerport);
+        sfree(pf.shost);
+
        if (realpf == NULL) {
            error = "Remote port is not recognised";
        } else {
-           const char *e = pfd_newconnect(&c->u.pfd.s,
-                                          realpf->dhost,
-                                          realpf->dport, c,
-                                          ssh->conf,
-                                          realpf->pfrec->addressfamily);
+            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 (e != NULL) {
-               logeventf(ssh, "Port open failed: %s", e);
+           if (err != NULL) {
+               logeventf(ssh, "Port open failed: %s", err);
+                sfree(err);
                error = "Port open failed";
            } else {
                logevent("Forwarded port opened successfully");
@@ -7567,6 +8551,10 @@ static void ssh2_msg_channel_open(Ssh ssh, struct Packet *pktin)
        ssh2_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;
+        }
        add234(ssh->channels, c);
        pktout = ssh2_pkt_init(SSH2_MSG_CHANNEL_OPEN_CONFIRMATION);
        ssh2_pkt_adduint32(pktout, c->remoteid);
@@ -7577,6 +8565,43 @@ static void ssh2_msg_channel_open(Ssh ssh, struct Packet *pktin)
     }
 }
 
+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.
@@ -7630,17 +8655,8 @@ static void ssh2_setup_x11(struct ssh_channel *c, struct Packet *pktin,
     pktout = ssh2_chanreq_init(ssh->mainchan, "x11-req",
                                ssh2_setup_x11, s);
     ssh2_pkt_addbool(pktout, 0);              /* many connections */
-    ssh2_pkt_addstring(pktout, ssh->x11disp->remoteauthprotoname);
-    /*
-     * 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.
-     */
-    dont_log_password(ssh, pktout, PKTLOG_BLANK);
-    ssh2_pkt_addstring(pktout, ssh->x11disp->remoteauthdatastring);
-    end_log_omission(ssh, pktout);
+    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);
 
@@ -7820,10 +8836,11 @@ static void ssh2_msg_authconn(Ssh ssh, struct Packet *pktin)
 static void ssh2_response_authconn(struct ssh_channel *c, struct Packet *pktin,
                                   void *ctx)
 {
-    do_ssh2_authconn(c->ssh, NULL, 0, pktin);
+    if (pktin)
+        do_ssh2_authconn(c->ssh, NULL, 0, pktin);
 }
 
-static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
+static void do_ssh2_authconn(Ssh ssh, const unsigned char *in, int inlen,
                             struct Packet *pktin)
 {
     struct do_ssh2_authconn_state {
@@ -7854,7 +8871,7 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
        int got_username;
        void *publickey_blob;
        int publickey_bloblen;
-       int publickey_encrypted;
+       int privatekey_available, privatekey_encrypted;
        char *publickey_algorithm;
        char *publickey_comment;
        unsigned char agent_request[5], *agent_response, *agentp;
@@ -7905,35 +8922,40 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
     
     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 (!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;
-       }
+    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.
@@ -7955,10 +8977,12 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
        s->keyfile = conf_get_filename(ssh->conf, CONF_keyfile);
        if (!filename_is_null(s->keyfile)) {
            int keytype;
-           logeventf(ssh, "Reading private key file \"%.150s\"",
+           logeventf(ssh, "Reading key file \"%.150s\"",
                      filename_to_str(s->keyfile));
            keytype = key_type(s->keyfile);
-           if (keytype == SSH_KEYTYPE_SSH2) {
+           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,
@@ -7966,13 +8990,16 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
                                         &s->publickey_bloblen, 
                                         &s->publickey_comment, &error);
                if (s->publickey_blob) {
-                   s->publickey_encrypted =
+                   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 private key (%s)", 
+                   logeventf(ssh, "Unable to load key (%s)", 
                              error);
-                   msgbuf = dupprintf("Unable to load private key file "
+                   msgbuf = dupprintf("Unable to load key file "
                                       "\"%.150s\" (%s)\r\n",
                                       filename_to_str(s->keyfile),
                                       error);
@@ -8486,7 +9513,7 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
                }
 
            } else if (s->can_pubkey && s->publickey_blob &&
-                      !s->tried_pubkey_config) {
+                      s->privatekey_available && !s->tried_pubkey_config) {
 
                struct ssh2_userkey *key;   /* not live over crReturn */
                char *passphrase;           /* not live over crReturn */
@@ -8537,7 +9564,7 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
                key = NULL;
                while (!key) {
                    const char *error;  /* not live over crReturn */
-                   if (s->publickey_encrypted) {
+                   if (s->privatekey_encrypted) {
                        /*
                         * Get a passphrase from the user.
                         */
@@ -8661,6 +9688,8 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
                     logevent("Sent public key signature");
                    s->type = AUTH_TYPE_PUBLICKEY;
                    key->alg->freekey(key->data);
+                    sfree(key->comment);
+                    sfree(key);
                }
 
 #ifndef NO_GSSAPI
@@ -8989,10 +10018,8 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
                    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++) {
-                       dont_log_password(ssh, s->pktout, PKTLOG_BLANK);
                        ssh2_pkt_addstring(s->pktout,
                                           s->cur_prompt->prompts[i]->result);
-                       end_log_omission(ssh, s->pktout);
                    }
                    ssh2_pkt_send_with_padding(ssh, s->pktout, 256);
 
@@ -9075,9 +10102,7 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
                                                        /* service requested */
                ssh2_pkt_addstring(s->pktout, "password");
                ssh2_pkt_addbool(s->pktout, FALSE);
-               dont_log_password(ssh, s->pktout, PKTLOG_BLANK);
                ssh2_pkt_addstring(s->pktout, s->password);
-               end_log_omission(ssh, s->pktout);
                ssh2_pkt_send_with_padding(ssh, s->pktout, 256);
                logevent("Sent password");
                s->type = AUTH_TYPE_PASSWORD;
@@ -9102,7 +10127,7 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
                    int prompt_len; /* not live over crReturn */
                    
                    {
-                       char *msg;
+                       const char *msg;
                        if (changereq_first_time)
                            msg = "Server requested password change";
                        else
@@ -9204,12 +10229,10 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
                                                        /* service requested */
                    ssh2_pkt_addstring(s->pktout, "password");
                    ssh2_pkt_addbool(s->pktout, TRUE);
-                   dont_log_password(ssh, s->pktout, PKTLOG_BLANK);
                    ssh2_pkt_addstring(s->pktout, s->password);
                    ssh2_pkt_addstring(s->pktout,
                                       s->cur_prompt->prompts[1]->result);
                    free_prompts(s->cur_prompt);
-                   end_log_omission(ssh, s->pktout);
                    ssh2_pkt_send_with_padding(ssh, s->pktout, 256);
                    logevent("Sent new password");
                    
@@ -9266,13 +10289,14 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
 
     /* 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) {
+    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
@@ -9286,10 +10310,6 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
        do_ssh2_transport(ssh, "enabling delayed compression", -2, NULL);
     }
 
-    /*
-     * Now the connection protocol has started, one way or another.
-     */
-
     ssh->channels = newtree234(ssh_channelcmp);
 
     /*
@@ -9367,8 +10387,15 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
     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 && conf_get_int(ssh->conf, CONF_ssh_simple)) {
+    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
@@ -9394,15 +10421,25 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
         */
 
        /* 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),
-                              conf_get_int(ssh->conf, CONF_x11_auth),
-                              ssh->conf)))
-           ssh2_setup_x11(ssh->mainchan, NULL, NULL);
+       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 (conf_get_int(ssh->conf, CONF_agentfwd) && agent_exists())
+       if (ssh_agent_forwarding_permitted(ssh))
            ssh2_setup_agent(ssh->mainchan, NULL, NULL);
 
        /* Now allocate a pty for the session. */
@@ -9484,7 +10521,7 @@ static void do_ssh2_authconn(Ssh ssh, unsigned char *in, int inlen,
      * Transfer data!
      */
     if (ssh->ldisc)
-       ldisc_send(ssh->ldisc, NULL, 0, 0);/* cause ldisc to notice changes */
+       ldisc_echoedit_update(ssh->ldisc);  /* cause ldisc to notice changes */
     if (ssh->mainchan)
        ssh->send_ok = 1;
     while (1) {
@@ -9658,6 +10695,48 @@ static void ssh2_protocol_setup(Ssh ssh)
     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;
@@ -9665,16 +10744,17 @@ static void ssh2_timer(void *ctx, unsigned long now)
     if (ssh->state == SSH_STATE_CLOSED)
        return;
 
-    if (!ssh->kex_in_progress && conf_get_int(ssh->conf, CONF_ssh_rekey_time) != 0 &&
+    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, void *vin, int inlen,
+static void ssh2_protocol(Ssh ssh, const void *vin, int inlen,
                          struct Packet *pktin)
 {
-    unsigned char *in = (unsigned char *)vin;
+    const unsigned char *in = (const unsigned char *)vin;
     if (ssh->state == SSH_STATE_CLOSED)
        return;
 
@@ -9694,6 +10774,19 @@ static void ssh2_protocol(Ssh ssh, void *vin, int inlen,
        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);
@@ -9705,7 +10798,8 @@ static void ssh_cache_conf_values(Ssh ssh)
  * Returns an error message, or NULL on success.
  */
 static const char *ssh_init(void *frontend_handle, void **backend_handle,
-                           Conf *conf, char *host, int port, char **realhost,
+                           Conf *conf,
+                            const char *host, int port, char **realhost,
                            int nodelay, int keepalive)
 {
     const char *p;
@@ -9750,13 +10844,17 @@ static const char *ssh_init(void *frontend_handle, void **backend_handle,
     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;
@@ -9775,6 +10873,10 @@ static const char *ssh_init(void *frontend_handle, void **backend_handle,
     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;
 
     *backend_handle = ssh;
 
@@ -9814,11 +10916,13 @@ static const char *ssh_init(void *frontend_handle, void **backend_handle,
     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)
+    if (p != NULL) {
+        random_unref();
        return p;
-
-    random_ref();
+    }
 
     return NULL;
 }
@@ -9828,6 +10932,7 @@ 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);
@@ -9870,13 +10975,13 @@ static void ssh_free(void *handle)
        while ((c = delpos234(ssh->channels, 0)) != NULL) {
            switch (c->type) {
              case CHAN_X11:
-               if (c->u.x11.s != NULL)
-                   x11_close(c->u.x11.s);
+               if (c->u.x11.xconn != NULL)
+                   x11_close(c->u.x11.xconn);
                break;
              case CHAN_SOCKDATA:
              case CHAN_SOCKDATA_DORMANT:
-               if (c->u.pfd.s != NULL)
-                   pfd_close(c->u.pfd.s);
+               if (c->u.pfd.pf != NULL)
+                   pfd_close(c->u.pfd.pf);
                break;
            }
            if (ssh->version == 2) {
@@ -9896,6 +11001,9 @@ static void ssh_free(void *handle)
        ssh->channels = NULL;
     }
 
+    if (ssh->connshare)
+        sharestate_free(ssh->connshare);
+
     if (ssh->rportfwds) {
        while ((pf = delpos234(ssh->rportfwds, 0)) != NULL)
            free_rportfwd(pf);
@@ -9905,6 +11013,9 @@ static void ssh_free(void *handle)
     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);
@@ -9940,7 +11051,8 @@ static void ssh_free(void *handle)
 static void ssh_reconfig(void *handle, Conf *conf)
 {
     Ssh ssh = (Ssh) handle;
-    char *rekeying = NULL, rekey_mandatory = FALSE;
+    const char *rekeying = NULL;
+    int rekey_mandatory = FALSE;
     unsigned long old_max_data_size;
     int i, rekey_time;
 
@@ -9993,7 +11105,7 @@ static void ssh_reconfig(void *handle, Conf *conf)
     ssh->conf = conf_copy(conf);
     ssh_cache_conf_values(ssh);
 
-    if (rekeying) {
+    if (!ssh->bare_connection && rekeying) {
        if (!ssh->kex_in_progress) {
            do_ssh2_transport(ssh, rekeying, -1, NULL);
        } else if (rekey_mandatory) {
@@ -10005,14 +11117,14 @@ static void ssh_reconfig(void *handle, Conf *conf)
 /*
  * Called to send data down the SSH connection.
  */
-static int ssh_send(void *handle, char *buf, int len)
+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, (unsigned char *)buf, len, 0);
+    ssh->protocol(ssh, (const unsigned char *)buf, len, 0);
 
     return ssh_sendbuffer(ssh);
 }
@@ -10148,7 +11260,7 @@ static const struct telnet_special *ssh_get_specials(void *handle)
     } 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))
+       if (!(ssh->remote_bugs & BUG_SSH2_REKEY) && !ssh->bare_connection)
            ADD_SPECIALS(ssh2_rekey_special);
        if (ssh->mainchan)
            ADD_SPECIALS(ssh2_session_specials);
@@ -10204,7 +11316,8 @@ static void ssh_special(void *handle, Telnet_Special code)
            }
        }
     } else if (code == TS_REKEY) {
-       if (!ssh->kex_in_progress && ssh->version == 2) {
+       if (!ssh->kex_in_progress && !ssh->bare_connection &&
+            ssh->version == 2) {
            do_ssh2_transport(ssh, "at user request", -1, NULL);
        }
     } else if (code == TS_BRK) {
@@ -10219,7 +11332,7 @@ static void ssh_special(void *handle, Telnet_Special code)
        }
     } else {
        /* Is is a POSIX signal? */
-       char *signame = NULL;
+       const char *signame = NULL;
        if (code == TS_SIGABRT) signame = "ABRT";
        if (code == TS_SIGALRM) signame = "ALRM";
        if (code == TS_SIGFPE)  signame = "FPE";
@@ -10249,7 +11362,7 @@ static void ssh_special(void *handle, Telnet_Special code)
     }
 }
 
-void *new_sock_channel(void *handle, Socket s)
+void *new_sock_channel(void *handle, struct PortForwarding *pf)
 {
     Ssh ssh = (Ssh) handle;
     struct ssh_channel *c;
@@ -10259,11 +11372,46 @@ void *new_sock_channel(void *handle, Socket s)
     ssh2_channel_init(c);
     c->halfopen = TRUE;
     c->type = CHAN_SOCKDATA_DORMANT;/* identify channel type */
-    c->u.pfd.s = s;
+    c->u.pfd.pf = pf;
     add234(ssh->channels, c);
     return c;
 }
 
+unsigned ssh_alloc_sharing_channel(Ssh ssh, void *sharing_ctx)
+{
+    struct ssh_channel *c;
+    c = snew(struct ssh_channel);
+
+    c->ssh = ssh;
+    ssh2_channel_init(c);
+    c->type = CHAN_SHARING;
+    c->u.sharing.ctx = sharing_ctx;
+    add234(ssh->channels, c);
+    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.
@@ -10283,7 +11431,7 @@ static void ssh_unthrottle(void *handle, int bufsize)
            ssh2_set_window(ssh->mainchan,
                            bufsize < ssh->mainchan->v.v2.locmaxwin ?
                            ssh->mainchan->v.v2.locmaxwin - bufsize : 0);
-           if (conf_get_int(ssh->conf, CONF_ssh_simple))
+           if (ssh_is_simple(ssh))
                buflimit = 0;
            else
                buflimit = ssh->mainchan->v.v2.locmaxwin;
@@ -10301,7 +11449,8 @@ static void ssh_unthrottle(void *handle, int bufsize)
     ssh_process_queued_incoming_data(ssh);
 }
 
-void ssh_send_port_open(void *channel, char *hostname, int port, char *org)
+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;
@@ -10318,7 +11467,11 @@ void ssh_send_port_open(void *channel, char *hostname, int port, char *org)
                    PKT_END);
     } else {
        pktout = ssh2_chanopen_init(c, "direct-tcpip");
-       ssh2_pkt_addstring(pktout, hostname);
+        {
+            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
@@ -10379,13 +11532,19 @@ static int ssh_return_exitcode(void *handle)
 }
 
 /*
- * cfg_info for SSH is the currently running version of the
- * protocol. (1 for 1; 2 for 2; 0 for not-decided-yet.)
+ * 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;
-    return ssh->version;
+    if (ssh->version == 0)
+       return 0; /* don't know yet */
+    else if (ssh->bare_connection)
+       return -1;
+    else
+       return ssh->version;
 }
 
 /*