2 * Copyright (c) 2000, 2001 Markus Friedl. All rights reserved.
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions
7 * 1. Redistributions of source code must retain the above copyright
8 * notice, this list of conditions and the following disclaimer.
9 * 2. Redistributions in binary form must reproduce the above copyright
10 * notice, this list of conditions and the following disclaimer in the
11 * documentation and/or other materials provided with the distribution.
13 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
14 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
15 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
16 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
17 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
18 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
19 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
20 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
21 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
22 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
26 RCSID("$OpenBSD: kex.c,v 1.66 2006/03/07 09:07:40 djm Exp $");
28 #include <openssl/crypto.h>
45 #define KEX_COOKIE_LEN 16
47 #ifdef HAVE_EVP_SHA256
48 # define evp_ssh_sha256 EVP_sha256
49 #else /* HAVE_EVP_SHA256 */
50 extern const EVP_MD *evp_ssh_sha256(void);
51 #endif /* HAVE_EVP_SHA256 */
54 static void kex_kexinit_finish(Kex *);
55 static void kex_choose_conf(Kex *);
57 /* put algorithm proposal into buffer */
59 kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX])
65 * add a dummy cookie, the cookie will be overwritten by
66 * kex_send_kexinit(), each time a kexinit is set
68 for (i = 0; i < KEX_COOKIE_LEN; i++)
69 buffer_put_char(b, 0);
70 for (i = 0; i < PROPOSAL_MAX; i++)
71 buffer_put_cstring(b, proposal[i]);
72 buffer_put_char(b, 0); /* first_kex_packet_follows */
73 buffer_put_int(b, 0); /* uint32 reserved */
76 /* parse buffer and return algorithm proposal */
78 kex_buf2prop(Buffer *raw, int *first_kex_follows)
84 proposal = xmalloc(PROPOSAL_MAX * sizeof(char *));
87 buffer_append(&b, buffer_ptr(raw), buffer_len(raw));
89 for (i = 0; i < KEX_COOKIE_LEN; i++)
91 /* extract kex init proposal strings */
92 for (i = 0; i < PROPOSAL_MAX; i++) {
93 proposal[i] = buffer_get_string(&b,NULL);
94 debug2("kex_parse_kexinit: %s", proposal[i]);
96 /* first kex follows / reserved */
97 i = buffer_get_char(&b);
98 if (first_kex_follows != NULL)
99 *first_kex_follows = i;
100 debug2("kex_parse_kexinit: first_kex_follows %d ", i);
101 i = buffer_get_int(&b);
102 debug2("kex_parse_kexinit: reserved %d ", i);
108 kex_prop_free(char **proposal)
112 for (i = 0; i < PROPOSAL_MAX; i++)
118 kex_protocol_error(int type, u_int32_t seq, void *ctxt)
120 error("Hm, kex protocol error: type %d seq %u", type, seq);
124 kex_reset_dispatch(void)
126 dispatch_range(SSH2_MSG_TRANSPORT_MIN,
127 SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error);
128 dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit);
134 kex_reset_dispatch();
136 packet_start(SSH2_MSG_NEWKEYS);
138 /* packet_write_wait(); */
139 debug("SSH2_MSG_NEWKEYS sent");
141 debug("expecting SSH2_MSG_NEWKEYS");
142 packet_read_expect(SSH2_MSG_NEWKEYS);
144 debug("SSH2_MSG_NEWKEYS received");
147 buffer_clear(&kex->peer);
148 /* buffer_clear(&kex->my); */
149 kex->flags &= ~KEX_INIT_SENT;
155 kex_send_kexinit(Kex *kex)
162 error("kex_send_kexinit: no kex, cannot rekey");
165 if (kex->flags & KEX_INIT_SENT) {
166 debug("KEX_INIT_SENT");
171 /* generate a random cookie */
172 if (buffer_len(&kex->my) < KEX_COOKIE_LEN)
173 fatal("kex_send_kexinit: kex proposal too short");
174 cookie = buffer_ptr(&kex->my);
175 for (i = 0; i < KEX_COOKIE_LEN; i++) {
181 packet_start(SSH2_MSG_KEXINIT);
182 packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my));
184 debug("SSH2_MSG_KEXINIT sent");
185 kex->flags |= KEX_INIT_SENT;
189 kex_input_kexinit(int type, u_int32_t seq, void *ctxt)
193 Kex *kex = (Kex *)ctxt;
195 debug("SSH2_MSG_KEXINIT received");
197 fatal("kex_input_kexinit: no kex, cannot rekey");
199 ptr = packet_get_raw(&dlen);
200 buffer_append(&kex->peer, ptr, dlen);
203 for (i = 0; i < KEX_COOKIE_LEN; i++)
205 for (i = 0; i < PROPOSAL_MAX; i++)
206 xfree(packet_get_string(NULL));
207 (void) packet_get_char();
208 (void) packet_get_int();
211 kex_kexinit_finish(kex);
215 kex_setup(char *proposal[PROPOSAL_MAX])
219 kex = xmalloc(sizeof(*kex));
220 memset(kex, 0, sizeof(*kex));
221 buffer_init(&kex->peer);
222 buffer_init(&kex->my);
223 kex_prop2buf(&kex->my, proposal);
226 kex_send_kexinit(kex); /* we start */
227 kex_reset_dispatch();
233 kex_kexinit_finish(Kex *kex)
235 if (!(kex->flags & KEX_INIT_SENT))
236 kex_send_kexinit(kex);
238 kex_choose_conf(kex);
240 if (kex->kex_type >= 0 && kex->kex_type < KEX_MAX &&
241 kex->kex[kex->kex_type] != NULL) {
242 (kex->kex[kex->kex_type])(kex);
244 fatal("Unsupported key exchange %d", kex->kex_type);
249 choose_enc(Enc *enc, char *client, char *server)
251 char *name = match_list(client, server, NULL);
253 fatal("no matching cipher found: client %s server %s", client, server);
254 if ((enc->cipher = cipher_by_name(name)) == NULL)
255 fatal("matching cipher is not supported: %s", name);
260 enc->key_len = cipher_keylen(enc->cipher);
261 enc->block_size = cipher_blocksize(enc->cipher);
264 choose_mac(Mac *mac, char *client, char *server)
266 char *name = match_list(client, server, NULL);
268 fatal("no matching mac found: client %s server %s", client, server);
269 if (mac_init(mac, name) < 0)
270 fatal("unsupported mac %s", name);
271 /* truncate the key */
272 if (datafellows & SSH_BUG_HMAC)
279 choose_comp(Comp *comp, char *client, char *server)
281 char *name = match_list(client, server, NULL);
283 fatal("no matching comp found: client %s server %s", client, server);
284 if (strcmp(name, "zlib@openssh.com") == 0) {
285 comp->type = COMP_DELAYED;
286 } else if (strcmp(name, "zlib") == 0) {
287 comp->type = COMP_ZLIB;
288 } else if (strcmp(name, "none") == 0) {
289 comp->type = COMP_NONE;
291 fatal("unsupported comp %s", name);
296 choose_kex(Kex *k, char *client, char *server)
298 k->name = match_list(client, server, NULL);
301 if (strcmp(k->name, KEX_DH1) == 0) {
302 k->kex_type = KEX_DH_GRP1_SHA1;
303 k->evp_md = EVP_sha1();
304 } else if (strcmp(k->name, KEX_DH14) == 0) {
305 k->kex_type = KEX_DH_GRP14_SHA1;
306 k->evp_md = EVP_sha1();
307 } else if (strcmp(k->name, KEX_DHGEX_SHA1) == 0) {
308 k->kex_type = KEX_DH_GEX_SHA1;
309 k->evp_md = EVP_sha1();
310 } else if (strcmp(k->name, KEX_DHGEX_SHA256) == 0) {
311 k->kex_type = KEX_DH_GEX_SHA256;
312 k->evp_md = evp_ssh_sha256();
314 fatal("bad kex alg %s", k->name);
318 choose_hostkeyalg(Kex *k, char *client, char *server)
320 char *hostkeyalg = match_list(client, server, NULL);
321 if (hostkeyalg == NULL)
322 fatal("no hostkey alg");
323 k->hostkey_type = key_type_from_name(hostkeyalg);
324 if (k->hostkey_type == KEY_UNSPEC)
325 fatal("bad hostkey alg '%s'", hostkeyalg);
330 proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX])
332 static int check[] = {
333 PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1
338 for (idx = &check[0]; *idx != -1; idx++) {
339 if ((p = strchr(my[*idx], ',')) != NULL)
341 if ((p = strchr(peer[*idx], ',')) != NULL)
343 if (strcmp(my[*idx], peer[*idx]) != 0) {
344 debug2("proposal mismatch: my %s peer %s",
345 my[*idx], peer[*idx]);
349 debug2("proposals match");
354 kex_choose_conf(Kex *kex)
358 char **cprop, **sprop;
359 int nenc, nmac, ncomp;
360 u_int mode, ctos, need;
361 int first_kex_follows, type;
363 my = kex_buf2prop(&kex->my, NULL);
364 peer = kex_buf2prop(&kex->peer, &first_kex_follows);
374 /* Algorithm Negotiation */
375 for (mode = 0; mode < MODE_MAX; mode++) {
376 newkeys = xmalloc(sizeof(*newkeys));
377 memset(newkeys, 0, sizeof(*newkeys));
378 kex->newkeys[mode] = newkeys;
379 ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN);
380 nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC;
381 nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC;
382 ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC;
383 choose_enc (&newkeys->enc, cprop[nenc], sprop[nenc]);
384 choose_mac (&newkeys->mac, cprop[nmac], sprop[nmac]);
385 choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]);
386 debug("kex: %s %s %s %s",
387 ctos ? "client->server" : "server->client",
392 choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]);
393 choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
394 sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]);
396 for (mode = 0; mode < MODE_MAX; mode++) {
397 newkeys = kex->newkeys[mode];
398 if (need < newkeys->enc.key_len)
399 need = newkeys->enc.key_len;
400 if (need < newkeys->enc.block_size)
401 need = newkeys->enc.block_size;
402 if (need < newkeys->mac.key_len)
403 need = newkeys->mac.key_len;
405 /* XXX need runden? */
408 /* ignore the next message if the proposals do not match */
409 if (first_kex_follows && !proposals_match(my, peer) &&
410 !(datafellows & SSH_BUG_FIRSTKEX)) {
411 type = packet_read();
412 debug2("skipping next packet (type %u)", type);
420 derive_key(Kex *kex, int id, u_int need, u_char *hash, u_int hashlen,
421 BIGNUM *shared_secret)
430 if ((mdsz = EVP_MD_size(kex->evp_md)) <= 0)
431 fatal("bad kex md size %d", mdsz);
432 digest = xmalloc(roundup(need, mdsz));
435 buffer_put_bignum2(&b, shared_secret);
437 /* K1 = HASH(K || H || "A" || session_id) */
438 EVP_DigestInit(&md, kex->evp_md);
439 if (!(datafellows & SSH_BUG_DERIVEKEY))
440 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
441 EVP_DigestUpdate(&md, hash, hashlen);
442 EVP_DigestUpdate(&md, &c, 1);
443 EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len);
444 EVP_DigestFinal(&md, digest, NULL);
448 * Kn = HASH(K || H || K1 || K2 || ... || Kn-1)
449 * Key = K1 || K2 || ... || Kn
451 for (have = mdsz; need > have; have += mdsz) {
452 EVP_DigestInit(&md, kex->evp_md);
453 if (!(datafellows & SSH_BUG_DERIVEKEY))
454 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
455 EVP_DigestUpdate(&md, hash, hashlen);
456 EVP_DigestUpdate(&md, digest, have);
457 EVP_DigestFinal(&md, digest + have, NULL);
461 fprintf(stderr, "key '%c'== ", c);
462 dump_digest("key", digest, need);
467 Newkeys *current_keys[MODE_MAX];
471 kex_derive_keys(Kex *kex, u_char *hash, u_int hashlen, BIGNUM *shared_secret)
476 for (i = 0; i < NKEYS; i++) {
477 keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, hashlen,
481 debug2("kex_derive_keys");
482 for (mode = 0; mode < MODE_MAX; mode++) {
483 current_keys[mode] = kex->newkeys[mode];
484 kex->newkeys[mode] = NULL;
485 ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN);
486 current_keys[mode]->enc.iv = keys[ctos ? 0 : 1];
487 current_keys[mode]->enc.key = keys[ctos ? 2 : 3];
488 current_keys[mode]->mac.key = keys[ctos ? 4 : 5];
493 kex_get_newkeys(int mode)
497 ret = current_keys[mode];
498 current_keys[mode] = NULL;
503 derive_ssh1_session_id(BIGNUM *host_modulus, BIGNUM *server_modulus,
504 u_int8_t cookie[8], u_int8_t id[16])
506 const EVP_MD *evp_md = EVP_md5();
508 u_int8_t nbuf[2048], obuf[EVP_MAX_MD_SIZE];
511 EVP_DigestInit(&md, evp_md);
513 len = BN_num_bytes(host_modulus);
514 if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
515 fatal("%s: bad host modulus (len %d)", __func__, len);
516 BN_bn2bin(host_modulus, nbuf);
517 EVP_DigestUpdate(&md, nbuf, len);
519 len = BN_num_bytes(server_modulus);
520 if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
521 fatal("%s: bad server modulus (len %d)", __func__, len);
522 BN_bn2bin(server_modulus, nbuf);
523 EVP_DigestUpdate(&md, nbuf, len);
525 EVP_DigestUpdate(&md, cookie, 8);
527 EVP_DigestFinal(&md, obuf, NULL);
528 memcpy(id, obuf, 16);
530 memset(nbuf, 0, sizeof(nbuf));
531 memset(obuf, 0, sizeof(obuf));
532 memset(&md, 0, sizeof(md));
535 #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH)
537 dump_digest(char *msg, u_char *digest, int len)
541 fprintf(stderr, "%s\n", msg);
542 for (i = 0; i< len; i++) {
543 fprintf(stderr, "%02x", digest[i]);
545 fprintf(stderr, "\n");
547 fprintf(stderr, " ");
549 fprintf(stderr, "\n");