1 /* $OpenBSD: kex.c,v 1.72 2006/07/22 20:48:23 stevesk Exp $ */
3 * Copyright (c) 2000, 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.
28 #include <openssl/crypto.h>
47 #define KEX_COOKIE_LEN 16
49 #if OPENSSL_VERSION_NUMBER >= 0x00907000L
50 # if defined(HAVE_EVP_SHA256)
51 # define evp_ssh_sha256 EVP_sha256
53 extern const EVP_MD *evp_ssh_sha256(void);
58 static void kex_kexinit_finish(Kex *);
59 static void kex_choose_conf(Kex *);
61 /* put algorithm proposal into buffer */
63 kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX])
69 * add a dummy cookie, the cookie will be overwritten by
70 * kex_send_kexinit(), each time a kexinit is set
72 for (i = 0; i < KEX_COOKIE_LEN; i++)
73 buffer_put_char(b, 0);
74 for (i = 0; i < PROPOSAL_MAX; i++)
75 buffer_put_cstring(b, proposal[i]);
76 buffer_put_char(b, 0); /* first_kex_packet_follows */
77 buffer_put_int(b, 0); /* uint32 reserved */
80 /* parse buffer and return algorithm proposal */
82 kex_buf2prop(Buffer *raw, int *first_kex_follows)
88 proposal = xcalloc(PROPOSAL_MAX, sizeof(char *));
91 buffer_append(&b, buffer_ptr(raw), buffer_len(raw));
93 for (i = 0; i < KEX_COOKIE_LEN; i++)
95 /* extract kex init proposal strings */
96 for (i = 0; i < PROPOSAL_MAX; i++) {
97 proposal[i] = buffer_get_string(&b,NULL);
98 debug2("kex_parse_kexinit: %s", proposal[i]);
100 /* first kex follows / reserved */
101 i = buffer_get_char(&b);
102 if (first_kex_follows != NULL)
103 *first_kex_follows = i;
104 debug2("kex_parse_kexinit: first_kex_follows %d ", i);
105 i = buffer_get_int(&b);
106 debug2("kex_parse_kexinit: reserved %d ", i);
112 kex_prop_free(char **proposal)
116 for (i = 0; i < PROPOSAL_MAX; i++)
122 kex_protocol_error(int type, u_int32_t seq, void *ctxt)
124 error("Hm, kex protocol error: type %d seq %u", type, seq);
128 kex_reset_dispatch(void)
130 dispatch_range(SSH2_MSG_TRANSPORT_MIN,
131 SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error);
132 dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit);
138 kex_reset_dispatch();
140 packet_start(SSH2_MSG_NEWKEYS);
142 /* packet_write_wait(); */
143 debug("SSH2_MSG_NEWKEYS sent");
145 debug("expecting SSH2_MSG_NEWKEYS");
146 packet_read_expect(SSH2_MSG_NEWKEYS);
148 debug("SSH2_MSG_NEWKEYS received");
151 buffer_clear(&kex->peer);
152 /* buffer_clear(&kex->my); */
153 kex->flags &= ~KEX_INIT_SENT;
159 kex_send_kexinit(Kex *kex)
166 error("kex_send_kexinit: no kex, cannot rekey");
169 if (kex->flags & KEX_INIT_SENT) {
170 debug("KEX_INIT_SENT");
175 /* generate a random cookie */
176 if (buffer_len(&kex->my) < KEX_COOKIE_LEN)
177 fatal("kex_send_kexinit: kex proposal too short");
178 cookie = buffer_ptr(&kex->my);
179 for (i = 0; i < KEX_COOKIE_LEN; i++) {
185 packet_start(SSH2_MSG_KEXINIT);
186 packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my));
188 debug("SSH2_MSG_KEXINIT sent");
189 kex->flags |= KEX_INIT_SENT;
193 kex_input_kexinit(int type, u_int32_t seq, void *ctxt)
197 Kex *kex = (Kex *)ctxt;
199 debug("SSH2_MSG_KEXINIT received");
201 fatal("kex_input_kexinit: no kex, cannot rekey");
203 ptr = packet_get_raw(&dlen);
204 buffer_append(&kex->peer, ptr, dlen);
207 for (i = 0; i < KEX_COOKIE_LEN; i++)
209 for (i = 0; i < PROPOSAL_MAX; i++)
210 xfree(packet_get_string(NULL));
211 (void) packet_get_char();
212 (void) packet_get_int();
215 kex_kexinit_finish(kex);
219 kex_setup(char *proposal[PROPOSAL_MAX])
223 kex = xcalloc(1, sizeof(*kex));
224 buffer_init(&kex->peer);
225 buffer_init(&kex->my);
226 kex_prop2buf(&kex->my, proposal);
229 kex_send_kexinit(kex); /* we start */
230 kex_reset_dispatch();
236 kex_kexinit_finish(Kex *kex)
238 if (!(kex->flags & KEX_INIT_SENT))
239 kex_send_kexinit(kex);
241 kex_choose_conf(kex);
243 if (kex->kex_type >= 0 && kex->kex_type < KEX_MAX &&
244 kex->kex[kex->kex_type] != NULL) {
245 (kex->kex[kex->kex_type])(kex);
247 fatal("Unsupported key exchange %d", kex->kex_type);
252 choose_enc(Enc *enc, char *client, char *server)
254 char *name = match_list(client, server, NULL);
256 fatal("no matching cipher found: client %s server %s", client, server);
257 if ((enc->cipher = cipher_by_name(name)) == NULL)
258 fatal("matching cipher is not supported: %s", name);
263 enc->key_len = cipher_keylen(enc->cipher);
264 enc->block_size = cipher_blocksize(enc->cipher);
268 choose_mac(Mac *mac, char *client, char *server)
270 char *name = match_list(client, server, NULL);
272 fatal("no matching mac found: client %s server %s", client, server);
273 if (mac_init(mac, name) < 0)
274 fatal("unsupported mac %s", name);
275 /* truncate the key */
276 if (datafellows & SSH_BUG_HMAC)
284 choose_comp(Comp *comp, char *client, char *server)
286 char *name = match_list(client, server, NULL);
288 fatal("no matching comp found: client %s server %s", client, server);
289 if (strcmp(name, "zlib@openssh.com") == 0) {
290 comp->type = COMP_DELAYED;
291 } else if (strcmp(name, "zlib") == 0) {
292 comp->type = COMP_ZLIB;
293 } else if (strcmp(name, "none") == 0) {
294 comp->type = COMP_NONE;
296 fatal("unsupported comp %s", name);
302 choose_kex(Kex *k, char *client, char *server)
304 k->name = match_list(client, server, NULL);
307 if (strcmp(k->name, KEX_DH1) == 0) {
308 k->kex_type = KEX_DH_GRP1_SHA1;
309 k->evp_md = EVP_sha1();
310 } else if (strcmp(k->name, KEX_DH14) == 0) {
311 k->kex_type = KEX_DH_GRP14_SHA1;
312 k->evp_md = EVP_sha1();
313 } else if (strcmp(k->name, KEX_DHGEX_SHA1) == 0) {
314 k->kex_type = KEX_DH_GEX_SHA1;
315 k->evp_md = EVP_sha1();
316 #if OPENSSL_VERSION_NUMBER >= 0x00907000L
317 } else if (strcmp(k->name, KEX_DHGEX_SHA256) == 0) {
318 k->kex_type = KEX_DH_GEX_SHA256;
319 k->evp_md = evp_ssh_sha256();
322 fatal("bad kex alg %s", k->name);
326 choose_hostkeyalg(Kex *k, char *client, char *server)
328 char *hostkeyalg = match_list(client, server, NULL);
329 if (hostkeyalg == NULL)
330 fatal("no hostkey alg");
331 k->hostkey_type = key_type_from_name(hostkeyalg);
332 if (k->hostkey_type == KEY_UNSPEC)
333 fatal("bad hostkey alg '%s'", hostkeyalg);
338 proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX])
340 static int check[] = {
341 PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1
346 for (idx = &check[0]; *idx != -1; idx++) {
347 if ((p = strchr(my[*idx], ',')) != NULL)
349 if ((p = strchr(peer[*idx], ',')) != NULL)
351 if (strcmp(my[*idx], peer[*idx]) != 0) {
352 debug2("proposal mismatch: my %s peer %s",
353 my[*idx], peer[*idx]);
357 debug2("proposals match");
362 kex_choose_conf(Kex *kex)
366 char **cprop, **sprop;
367 int nenc, nmac, ncomp;
368 u_int mode, ctos, need;
369 int first_kex_follows, type;
371 my = kex_buf2prop(&kex->my, NULL);
372 peer = kex_buf2prop(&kex->peer, &first_kex_follows);
382 /* Algorithm Negotiation */
383 for (mode = 0; mode < MODE_MAX; mode++) {
384 newkeys = xcalloc(1, sizeof(*newkeys));
385 kex->newkeys[mode] = newkeys;
386 ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN);
387 nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC;
388 nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC;
389 ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC;
390 choose_enc (&newkeys->enc, cprop[nenc], sprop[nenc]);
391 choose_mac (&newkeys->mac, cprop[nmac], sprop[nmac]);
392 choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]);
393 debug("kex: %s %s %s %s",
394 ctos ? "client->server" : "server->client",
399 choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]);
400 choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
401 sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]);
403 for (mode = 0; mode < MODE_MAX; mode++) {
404 newkeys = kex->newkeys[mode];
405 if (need < newkeys->enc.key_len)
406 need = newkeys->enc.key_len;
407 if (need < newkeys->enc.block_size)
408 need = newkeys->enc.block_size;
409 if (need < newkeys->mac.key_len)
410 need = newkeys->mac.key_len;
412 /* XXX need runden? */
415 /* ignore the next message if the proposals do not match */
416 if (first_kex_follows && !proposals_match(my, peer) &&
417 !(datafellows & SSH_BUG_FIRSTKEX)) {
418 type = packet_read();
419 debug2("skipping next packet (type %u)", type);
427 derive_key(Kex *kex, int id, u_int need, u_char *hash, u_int hashlen,
428 BIGNUM *shared_secret)
437 if ((mdsz = EVP_MD_size(kex->evp_md)) <= 0)
438 fatal("bad kex md size %d", mdsz);
439 digest = xmalloc(roundup(need, mdsz));
442 buffer_put_bignum2(&b, shared_secret);
444 /* K1 = HASH(K || H || "A" || session_id) */
445 EVP_DigestInit(&md, kex->evp_md);
446 if (!(datafellows & SSH_BUG_DERIVEKEY))
447 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
448 EVP_DigestUpdate(&md, hash, hashlen);
449 EVP_DigestUpdate(&md, &c, 1);
450 EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len);
451 EVP_DigestFinal(&md, digest, NULL);
455 * Kn = HASH(K || H || K1 || K2 || ... || Kn-1)
456 * Key = K1 || K2 || ... || Kn
458 for (have = mdsz; need > have; have += mdsz) {
459 EVP_DigestInit(&md, kex->evp_md);
460 if (!(datafellows & SSH_BUG_DERIVEKEY))
461 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
462 EVP_DigestUpdate(&md, hash, hashlen);
463 EVP_DigestUpdate(&md, digest, have);
464 EVP_DigestFinal(&md, digest + have, NULL);
468 fprintf(stderr, "key '%c'== ", c);
469 dump_digest("key", digest, need);
474 Newkeys *current_keys[MODE_MAX];
478 kex_derive_keys(Kex *kex, u_char *hash, u_int hashlen, BIGNUM *shared_secret)
483 for (i = 0; i < NKEYS; i++) {
484 keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, hashlen,
488 debug2("kex_derive_keys");
489 for (mode = 0; mode < MODE_MAX; mode++) {
490 current_keys[mode] = kex->newkeys[mode];
491 kex->newkeys[mode] = NULL;
492 ctos = (!kex->server && mode == MODE_OUT) ||
493 (kex->server && mode == MODE_IN);
494 current_keys[mode]->enc.iv = keys[ctos ? 0 : 1];
495 current_keys[mode]->enc.key = keys[ctos ? 2 : 3];
496 current_keys[mode]->mac.key = keys[ctos ? 4 : 5];
501 kex_get_newkeys(int mode)
505 ret = current_keys[mode];
506 current_keys[mode] = NULL;
511 derive_ssh1_session_id(BIGNUM *host_modulus, BIGNUM *server_modulus,
512 u_int8_t cookie[8], u_int8_t id[16])
514 const EVP_MD *evp_md = EVP_md5();
516 u_int8_t nbuf[2048], obuf[EVP_MAX_MD_SIZE];
519 EVP_DigestInit(&md, evp_md);
521 len = BN_num_bytes(host_modulus);
522 if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
523 fatal("%s: bad host modulus (len %d)", __func__, len);
524 BN_bn2bin(host_modulus, nbuf);
525 EVP_DigestUpdate(&md, nbuf, len);
527 len = BN_num_bytes(server_modulus);
528 if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
529 fatal("%s: bad server modulus (len %d)", __func__, len);
530 BN_bn2bin(server_modulus, nbuf);
531 EVP_DigestUpdate(&md, nbuf, len);
533 EVP_DigestUpdate(&md, cookie, 8);
535 EVP_DigestFinal(&md, obuf, NULL);
536 memcpy(id, obuf, 16);
538 memset(nbuf, 0, sizeof(nbuf));
539 memset(obuf, 0, sizeof(obuf));
540 memset(&md, 0, sizeof(md));
543 #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH)
545 dump_digest(char *msg, u_char *digest, int len)
549 fprintf(stderr, "%s\n", msg);
550 for (i = 0; i< len; i++) {
551 fprintf(stderr, "%02x", digest[i]);
553 fprintf(stderr, "\n");
555 fprintf(stderr, " ");
557 fprintf(stderr, "\n");