#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_USERAUTH_REQUEST 50 /* 0x32 */
#define SSH2_MSG_USERAUTH_FAILURE 51 /* 0x33 */
#define SSH2_MSG_USERAUTH_SUCCESS 52 /* 0x34 */
const static struct ssh_cipher *ciphers[] = { &ssh_blowfish_ssh2, &ssh_3des_ssh2 };
extern const struct ssh_kex ssh_diffiehellman;
-const static struct ssh_kex *kex_algs[] = { &ssh_diffiehellman };
+extern const struct ssh_kex ssh_diffiehellman_gex;
+const static struct ssh_kex *kex_algs[] = {
+#ifdef DO_DIFFIE_HELLMAN_GEX
+ &ssh_diffiehellman_gex,
+#endif
+ &ssh_diffiehellman };
extern const struct ssh_signkey ssh_dss;
const static struct ssh_signkey *hostkey_algs[] = { &ssh_dss };
/*
- * Utility routine for putting an SSH-protocol `string' into a SHA
- * state.
+ * Utility routines for putting an SSH-protocol `string' and
+ * `uint32' into a SHA state.
*/
#include <stdio.h>
static void sha_string(SHA_State *s, void *str, int len) {
SHA_Bytes(s, str, len);
}
+static void sha_uint32(SHA_State *s, unsigned i) {
+ unsigned char intblk[4];
+ PUT_32BIT(intblk, i);
+ SHA_Bytes(s, intblk, 4);
+}
+
/*
* SSH2 packet construction functions.
*/
*/
static int do_ssh2_transport(unsigned char *in, int inlen, int ispkt)
{
- static int i, len;
+ static int i, len, nbits;
static char *str;
- static Bignum e, f, K;
+ static Bignum p, g, e, f, K;
+ static int kex_init_value, kex_reply_value;
static const struct ssh_mac **maclist;
static int nmacs;
static const struct ssh_cipher *cscipher_tobe = NULL;
}
/*
- * Currently we only support Diffie-Hellman and DSS, so let's
- * bomb out if those aren't selected.
+ * If we're doing Diffie-Hellman group exchange, start by
+ * requesting a group.
*/
- if (kex != &ssh_diffiehellman || hostkey != &ssh_dss) {
- bombout(("internal fault: chaos in SSH 2 transport layer"));
- crReturn(0);
+ if (kex == &ssh_diffiehellman_gex) {
+ int csbits, scbits;
+
+ logevent("Doing Diffie-Hellman group exchange");
+ /*
+ * Work out number of bits. We start with the maximum key
+ * length of either cipher...
+ */
+ csbits = cscipher_tobe->keylen;
+ scbits = sccipher_tobe->keylen;
+ nbits = (csbits > scbits ? csbits : scbits);
+ /* The keys only have 160-bit entropy, since they're based on
+ * a SHA-1 hash. So cap the key size at 160 bits. */
+ if (nbits > 160) nbits = 160;
+ /*
+ * ... and then work out how big a DH group we will need to
+ * allow that much data.
+ */
+ nbits = 512 << ((nbits-1) / 64);
+ ssh2_pkt_init(SSH2_MSG_KEX_DH_GEX_REQUEST);
+ ssh2_pkt_adduint32(nbits);
+ ssh2_pkt_send();
+
+ crWaitUntil(ispkt);
+ if (pktin.type != SSH2_MSG_KEX_DH_GEX_GROUP) {
+ bombout(("expected key exchange group packet from server"));
+ crReturn(0);
+ }
+ p = ssh2_pkt_getmp();
+ g = ssh2_pkt_getmp();
+ dh_setup_group(p, g);
+ kex_init_value = SSH2_MSG_KEX_DH_GEX_INIT;
+ kex_reply_value = SSH2_MSG_KEX_DH_GEX_REPLY;
+ } else {
+ dh_setup_group1();
+ kex_init_value = SSH2_MSG_KEXDH_INIT;
+ kex_reply_value = SSH2_MSG_KEXDH_REPLY;
}
+ logevent("Doing Diffie-Hellman key exchange");
/*
- * Now we begin the fun. Generate and send e for Diffie-Hellman.
+ * Now generate and send e for Diffie-Hellman.
*/
- dh_setup_group1();
-
e = dh_create_e();
- ssh2_pkt_init(SSH2_MSG_KEXDH_INIT);
+ ssh2_pkt_init(kex_init_value);
ssh2_pkt_addmp(e);
ssh2_pkt_send();
crWaitUntil(ispkt);
- if (pktin.type != SSH2_MSG_KEXDH_REPLY) {
- bombout(("expected key exchange packet from server"));
+ if (pktin.type != kex_reply_value) {
+ bombout(("expected key exchange reply packet from server"));
crReturn(0);
}
ssh2_pkt_getstring(&hostkeydata, &hostkeylen);
K = dh_find_K(f);
sha_string(&exhash, hostkeydata, hostkeylen);
+ if (kex == &ssh_diffiehellman_gex) {
+ sha_uint32(&exhash, nbits);
+ sha_mpint(&exhash, p);
+ sha_mpint(&exhash, g);
+ }
sha_mpint(&exhash, e);
sha_mpint(&exhash, f);
sha_mpint(&exhash, K);
fingerprint = hostkey->fingerprint(hkey);
verify_ssh_host_key(savedhost, savedport, hostkey->keytype,
keystr, fingerprint);
- if (first_kex) { /* don't bother logging this in rekeys */
+ if (first_kex) { /* don't bother logging this in rekeys */
logevent("Host key fingerprint is:");
logevent(fingerprint);
}