2 * Copyright (c) 2000 Niels Provos. All rights reserved.
3 * Copyright (c) 2001 Markus Friedl. All rights reserved.
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in the
12 * documentation and/or other materials provided with the distribution.
14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
15 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
16 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
17 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
18 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
19 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
20 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
21 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
22 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
23 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
27 RCSID("$OpenBSD: kexgex.c,v 1.9 2001/09/17 19:27:15 stevesk Exp $");
29 #include <openssl/bn.h>
44 char *client_version_string,
45 char *server_version_string,
46 char *ckexinit, int ckexinitlen,
47 char *skexinit, int skexinitlen,
48 u_char *serverhostkeyblob, int sbloblen,
49 int min, int wantbits, int max, BIGNUM *prime, BIGNUM *gen,
50 BIGNUM *client_dh_pub,
51 BIGNUM *server_dh_pub,
52 BIGNUM *shared_secret)
55 static u_char digest[EVP_MAX_MD_SIZE];
56 EVP_MD *evp_md = EVP_sha1();
60 buffer_put_cstring(&b, client_version_string);
61 buffer_put_cstring(&b, server_version_string);
63 /* kexinit messages: fake header: len+SSH2_MSG_KEXINIT */
64 buffer_put_int(&b, ckexinitlen+1);
65 buffer_put_char(&b, SSH2_MSG_KEXINIT);
66 buffer_append(&b, ckexinit, ckexinitlen);
67 buffer_put_int(&b, skexinitlen+1);
68 buffer_put_char(&b, SSH2_MSG_KEXINIT);
69 buffer_append(&b, skexinit, skexinitlen);
71 buffer_put_string(&b, serverhostkeyblob, sbloblen);
72 if (min == -1 || max == -1)
73 buffer_put_int(&b, wantbits);
75 buffer_put_int(&b, min);
76 buffer_put_int(&b, wantbits);
77 buffer_put_int(&b, max);
79 buffer_put_bignum2(&b, prime);
80 buffer_put_bignum2(&b, gen);
81 buffer_put_bignum2(&b, client_dh_pub);
82 buffer_put_bignum2(&b, server_dh_pub);
83 buffer_put_bignum2(&b, shared_secret);
88 EVP_DigestInit(&md, evp_md);
89 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
90 EVP_DigestFinal(&md, digest, NULL);
95 dump_digest("hash", digest, evp_md->md_size);
103 kexgex_client(Kex *kex)
105 BIGNUM *dh_server_pub = NULL, *shared_secret = NULL;
106 BIGNUM *p = NULL, *g = NULL;
107 Key *server_host_key;
108 u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
109 u_int klen, kout, slen, sbloblen;
110 int dlen, plen, min, max, nbits;
113 nbits = dh_estimate(kex->we_need * 8);
115 if (datafellows & SSH_OLD_DHGEX) {
116 debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD sent");
118 /* Old GEX request */
119 packet_start(SSH2_MSG_KEX_DH_GEX_REQUEST_OLD);
120 packet_put_int(nbits);
124 debug("SSH2_MSG_KEX_DH_GEX_REQUEST sent");
126 /* New GEX request */
129 packet_start(SSH2_MSG_KEX_DH_GEX_REQUEST);
131 packet_put_int(nbits);
135 fprintf(stderr, "\nmin = %d, nbits = %d, max = %d\n",
140 debug("expecting SSH2_MSG_KEX_DH_GEX_GROUP");
141 packet_read_expect(&plen, SSH2_MSG_KEX_DH_GEX_GROUP);
143 if ((p = BN_new()) == NULL)
145 packet_get_bignum2(p, &dlen);
146 if ((g = BN_new()) == NULL)
148 packet_get_bignum2(g, &dlen);
151 if (BN_num_bits(p) < min || BN_num_bits(p) > max)
152 fatal("DH_GEX group out of range: %d !< %d !< %d",
153 min, BN_num_bits(p), max);
155 dh = dh_new_group(g, p);
156 dh_gen_key(dh, kex->we_need * 8);
159 DHparams_print_fp(stderr, dh);
160 fprintf(stderr, "pub= ");
161 BN_print_fp(stderr, dh->pub_key);
162 fprintf(stderr, "\n");
165 debug("SSH2_MSG_KEX_DH_GEX_INIT sent");
166 /* generate and send 'e', client DH public key */
167 packet_start(SSH2_MSG_KEX_DH_GEX_INIT);
168 packet_put_bignum2(dh->pub_key);
171 debug("expecting SSH2_MSG_KEX_DH_GEX_REPLY");
172 packet_read_expect(&plen, SSH2_MSG_KEX_DH_GEX_REPLY);
175 server_host_key_blob = packet_get_string(&sbloblen);
176 server_host_key = key_from_blob(server_host_key_blob, sbloblen);
177 if (server_host_key == NULL)
178 fatal("cannot decode server_host_key_blob");
180 if (kex->verify_host_key == NULL)
181 fatal("cannot verify server_host_key");
182 if (kex->verify_host_key(server_host_key) == -1)
183 fatal("server_host_key verification failed");
185 /* DH paramter f, server public DH key */
186 dh_server_pub = BN_new();
187 if (dh_server_pub == NULL)
188 fatal("dh_server_pub == NULL");
189 packet_get_bignum2(dh_server_pub, &dlen);
192 fprintf(stderr, "dh_server_pub= ");
193 BN_print_fp(stderr, dh_server_pub);
194 fprintf(stderr, "\n");
195 debug("bits %d", BN_num_bits(dh_server_pub));
199 signature = packet_get_string(&slen);
202 if (!dh_pub_is_valid(dh, dh_server_pub))
203 packet_disconnect("bad server public DH value");
206 kbuf = xmalloc(klen);
207 kout = DH_compute_key(kbuf, dh_server_pub, dh);
209 dump_digest("shared secret", kbuf, kout);
211 shared_secret = BN_new();
212 BN_bin2bn(kbuf, kout, shared_secret);
213 memset(kbuf, 0, klen);
216 if (datafellows & SSH_OLD_DHGEX)
219 /* calc and verify H */
221 kex->client_version_string,
222 kex->server_version_string,
223 buffer_ptr(&kex->my), buffer_len(&kex->my),
224 buffer_ptr(&kex->peer), buffer_len(&kex->peer),
225 server_host_key_blob, sbloblen,
232 /* have keys, free DH */
234 xfree(server_host_key_blob);
235 BN_free(dh_server_pub);
237 if (key_verify(server_host_key, signature, slen, hash, 20) != 1)
238 fatal("key_verify failed for server_host_key");
239 key_free(server_host_key);
242 /* save session id */
243 if (kex->session_id == NULL) {
244 kex->session_id_len = 20;
245 kex->session_id = xmalloc(kex->session_id_len);
246 memcpy(kex->session_id, hash, kex->session_id_len);
248 kex_derive_keys(kex, hash, shared_secret);
249 BN_clear_free(shared_secret);
257 kexgex_server(Kex *kex)
259 BIGNUM *shared_secret = NULL, *dh_client_pub = NULL;
260 Key *server_host_key;
262 u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
263 u_int sbloblen, klen, kout;
264 int min = -1, max = -1, nbits = -1, type, plen, dlen, slen;
266 if (kex->load_host_key == NULL)
267 fatal("Cannot load hostkey");
268 server_host_key = kex->load_host_key(kex->hostkey_type);
269 if (server_host_key == NULL)
270 fatal("Unsupported hostkey type %d", kex->hostkey_type);
272 type = packet_read(&plen);
274 case SSH2_MSG_KEX_DH_GEX_REQUEST:
275 debug("SSH2_MSG_KEX_DH_GEX_REQUEST received");
276 min = packet_get_int();
277 nbits = packet_get_int();
278 max = packet_get_int();
279 min = MAX(DH_GRP_MIN, min);
280 max = MIN(DH_GRP_MAX, max);
282 case SSH2_MSG_KEX_DH_GEX_REQUEST_OLD:
283 debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD received");
284 nbits = packet_get_int();
287 /* unused for old GEX */
290 fatal("protocol error during kex, no DH_GEX_REQUEST: %d", type);
294 if (max < min || nbits < min || max < nbits)
295 fatal("DH_GEX_REQUEST, bad parameters: %d !< %d !< %d",
298 dh = choose_dh(min, nbits, max);
300 packet_disconnect("Protocol error: no matching DH grp found");
302 debug("SSH2_MSG_KEX_DH_GEX_GROUP sent");
303 packet_start(SSH2_MSG_KEX_DH_GEX_GROUP);
304 packet_put_bignum2(dh->p);
305 packet_put_bignum2(dh->g);
311 /* Compute our exchange value in parallel with the client */
312 dh_gen_key(dh, kex->we_need * 8);
314 debug("expecting SSH2_MSG_KEX_DH_GEX_INIT");
315 packet_read_expect(&plen, SSH2_MSG_KEX_DH_GEX_INIT);
318 dh_client_pub = BN_new();
319 if (dh_client_pub == NULL)
320 fatal("dh_client_pub == NULL");
321 packet_get_bignum2(dh_client_pub, &dlen);
324 fprintf(stderr, "dh_client_pub= ");
325 BN_print_fp(stderr, dh_client_pub);
326 fprintf(stderr, "\n");
327 debug("bits %d", BN_num_bits(dh_client_pub));
331 DHparams_print_fp(stderr, dh);
332 fprintf(stderr, "pub= ");
333 BN_print_fp(stderr, dh->pub_key);
334 fprintf(stderr, "\n");
336 if (!dh_pub_is_valid(dh, dh_client_pub))
337 packet_disconnect("bad client public DH value");
340 kbuf = xmalloc(klen);
341 kout = DH_compute_key(kbuf, dh_client_pub, dh);
343 dump_digest("shared secret", kbuf, kout);
345 shared_secret = BN_new();
346 BN_bin2bn(kbuf, kout, shared_secret);
347 memset(kbuf, 0, klen);
350 key_to_blob(server_host_key, &server_host_key_blob, &sbloblen);
352 if (type == SSH2_MSG_KEX_DH_GEX_REQUEST_OLD)
355 /* calc H */ /* XXX depends on 'kex' */
357 kex->client_version_string,
358 kex->server_version_string,
359 buffer_ptr(&kex->peer), buffer_len(&kex->peer),
360 buffer_ptr(&kex->my), buffer_len(&kex->my),
361 server_host_key_blob, sbloblen,
368 BN_free(dh_client_pub);
370 /* save session id := H */
371 /* XXX hashlen depends on KEX */
372 if (kex->session_id == NULL) {
373 kex->session_id_len = 20;
374 kex->session_id = xmalloc(kex->session_id_len);
375 memcpy(kex->session_id, hash, kex->session_id_len);
379 /* XXX hashlen depends on KEX */
380 key_sign(server_host_key, &signature, &slen, hash, 20);
382 /* destroy_sensitive_data(); */
384 /* send server hostkey, DH pubkey 'f' and singed H */
385 debug("SSH2_MSG_KEX_DH_GEX_REPLY sent");
386 packet_start(SSH2_MSG_KEX_DH_GEX_REPLY);
387 packet_put_string(server_host_key_blob, sbloblen);
388 packet_put_bignum2(dh->pub_key); /* f */
389 packet_put_string(signature, slen);
392 xfree(server_host_key_blob);
393 /* have keys, free DH */
396 kex_derive_keys(kex, hash, shared_secret);
397 BN_clear_free(shared_secret);