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;
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
* length, so we just read data and check the MAC repeatedly,
* and when the MAC passes, see if the length we've got is
* plausible.
+ *
+ * This defence is unnecessary in OpenSSH ETM mode, because
+ * the whole point of ETM mode is that the attacker can't
+ * tweak the ciphertext stream at all without the MAC
+ * detecting it before we decrypt anything.
*/
/* May as well allocate the whole lot now. */
st->pktin->data = 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);
*/
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)
ssh2_log_outgoing_packet(ssh, 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);
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. */
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;
/* 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++)
+ for (i = 0; i < s->nmacs; i++) {
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
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"));
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"));
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)
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);
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)
}
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);
projects / PuTTY.git / blobdiff