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 #if OPENSSL_VERSION_NUMBER < 0x00907000L
48 # define evp_ssh_sha256() NULL
49 #elif defined(HAVE_EVP_SHA256)
50 # define evp_ssh_sha256 EVP_sha256
52 extern const EVP_MD *evp_ssh_sha256(void);
56 static void kex_kexinit_finish(Kex *);
57 static void kex_choose_conf(Kex *);
59 /* put algorithm proposal into buffer */
61 kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX])
67 * add a dummy cookie, the cookie will be overwritten by
68 * kex_send_kexinit(), each time a kexinit is set
70 for (i = 0; i < KEX_COOKIE_LEN; i++)
71 buffer_put_char(b, 0);
72 for (i = 0; i < PROPOSAL_MAX; i++)
73 buffer_put_cstring(b, proposal[i]);
74 buffer_put_char(b, 0); /* first_kex_packet_follows */
75 buffer_put_int(b, 0); /* uint32 reserved */
78 /* parse buffer and return algorithm proposal */
80 kex_buf2prop(Buffer *raw, int *first_kex_follows)
86 proposal = xmalloc(PROPOSAL_MAX * sizeof(char *));
89 buffer_append(&b, buffer_ptr(raw), buffer_len(raw));
91 for (i = 0; i < KEX_COOKIE_LEN; i++)
93 /* extract kex init proposal strings */
94 for (i = 0; i < PROPOSAL_MAX; i++) {
95 proposal[i] = buffer_get_string(&b,NULL);
96 debug2("kex_parse_kexinit: %s", proposal[i]);
98 /* first kex follows / reserved */
99 i = buffer_get_char(&b);
100 if (first_kex_follows != NULL)
101 *first_kex_follows = i;
102 debug2("kex_parse_kexinit: first_kex_follows %d ", i);
103 i = buffer_get_int(&b);
104 debug2("kex_parse_kexinit: reserved %d ", i);
110 kex_prop_free(char **proposal)
114 for (i = 0; i < PROPOSAL_MAX; i++)
120 kex_protocol_error(int type, u_int32_t seq, void *ctxt)
122 error("Hm, kex protocol error: type %d seq %u", type, seq);
126 kex_reset_dispatch(void)
128 dispatch_range(SSH2_MSG_TRANSPORT_MIN,
129 SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error);
130 dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit);
136 kex_reset_dispatch();
138 packet_start(SSH2_MSG_NEWKEYS);
140 /* packet_write_wait(); */
141 debug("SSH2_MSG_NEWKEYS sent");
143 debug("expecting SSH2_MSG_NEWKEYS");
144 packet_read_expect(SSH2_MSG_NEWKEYS);
146 debug("SSH2_MSG_NEWKEYS received");
149 buffer_clear(&kex->peer);
150 /* buffer_clear(&kex->my); */
151 kex->flags &= ~KEX_INIT_SENT;
157 kex_send_kexinit(Kex *kex)
164 error("kex_send_kexinit: no kex, cannot rekey");
167 if (kex->flags & KEX_INIT_SENT) {
168 debug("KEX_INIT_SENT");
173 /* generate a random cookie */
174 if (buffer_len(&kex->my) < KEX_COOKIE_LEN)
175 fatal("kex_send_kexinit: kex proposal too short");
176 cookie = buffer_ptr(&kex->my);
177 for (i = 0; i < KEX_COOKIE_LEN; i++) {
183 packet_start(SSH2_MSG_KEXINIT);
184 packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my));
186 debug("SSH2_MSG_KEXINIT sent");
187 kex->flags |= KEX_INIT_SENT;
191 kex_input_kexinit(int type, u_int32_t seq, void *ctxt)
195 Kex *kex = (Kex *)ctxt;
197 debug("SSH2_MSG_KEXINIT received");
199 fatal("kex_input_kexinit: no kex, cannot rekey");
201 ptr = packet_get_raw(&dlen);
202 buffer_append(&kex->peer, ptr, dlen);
205 for (i = 0; i < KEX_COOKIE_LEN; i++)
207 for (i = 0; i < PROPOSAL_MAX; i++)
208 xfree(packet_get_string(NULL));
209 (void) packet_get_char();
210 (void) packet_get_int();
213 kex_kexinit_finish(kex);
217 kex_setup(char *proposal[PROPOSAL_MAX])
221 kex = xmalloc(sizeof(*kex));
222 memset(kex, 0, sizeof(*kex));
223 buffer_init(&kex->peer);
224 buffer_init(&kex->my);
225 kex_prop2buf(&kex->my, proposal);
228 kex_send_kexinit(kex); /* we start */
229 kex_reset_dispatch();
235 kex_kexinit_finish(Kex *kex)
237 if (!(kex->flags & KEX_INIT_SENT))
238 kex_send_kexinit(kex);
240 kex_choose_conf(kex);
242 if (kex->kex_type >= 0 && kex->kex_type < KEX_MAX &&
243 kex->kex[kex->kex_type] != NULL) {
244 (kex->kex[kex->kex_type])(kex);
246 fatal("Unsupported key exchange %d", kex->kex_type);
251 choose_enc(Enc *enc, char *client, char *server)
253 char *name = match_list(client, server, NULL);
255 fatal("no matching cipher found: client %s server %s", client, server);
256 if ((enc->cipher = cipher_by_name(name)) == NULL)
257 fatal("matching cipher is not supported: %s", name);
262 enc->key_len = cipher_keylen(enc->cipher);
263 enc->block_size = cipher_blocksize(enc->cipher);
266 choose_mac(Mac *mac, char *client, char *server)
268 char *name = match_list(client, server, NULL);
270 fatal("no matching mac found: client %s server %s", client, server);
271 if (mac_init(mac, name) < 0)
272 fatal("unsupported mac %s", name);
273 /* truncate the key */
274 if (datafellows & SSH_BUG_HMAC)
281 choose_comp(Comp *comp, char *client, char *server)
283 char *name = match_list(client, server, NULL);
285 fatal("no matching comp found: client %s server %s", client, server);
286 if (strcmp(name, "zlib@openssh.com") == 0) {
287 comp->type = COMP_DELAYED;
288 } else if (strcmp(name, "zlib") == 0) {
289 comp->type = COMP_ZLIB;
290 } else if (strcmp(name, "none") == 0) {
291 comp->type = COMP_NONE;
293 fatal("unsupported comp %s", name);
298 choose_kex(Kex *k, char *client, char *server)
300 k->name = match_list(client, server, NULL);
303 if (strcmp(k->name, KEX_DH1) == 0) {
304 k->kex_type = KEX_DH_GRP1_SHA1;
305 k->evp_md = EVP_sha1();
306 } else if (strcmp(k->name, KEX_DH14) == 0) {
307 k->kex_type = KEX_DH_GRP14_SHA1;
308 k->evp_md = EVP_sha1();
309 } else if (strcmp(k->name, KEX_DHGEX_SHA1) == 0) {
310 k->kex_type = KEX_DH_GEX_SHA1;
311 k->evp_md = EVP_sha1();
312 } else if (strcmp(k->name, KEX_DHGEX_SHA256) == 0) {
313 k->kex_type = KEX_DH_GEX_SHA256;
314 k->evp_md = evp_ssh_sha256();
316 fatal("bad kex alg %s", k->name);
320 choose_hostkeyalg(Kex *k, char *client, char *server)
322 char *hostkeyalg = match_list(client, server, NULL);
323 if (hostkeyalg == NULL)
324 fatal("no hostkey alg");
325 k->hostkey_type = key_type_from_name(hostkeyalg);
326 if (k->hostkey_type == KEY_UNSPEC)
327 fatal("bad hostkey alg '%s'", hostkeyalg);
332 proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX])
334 static int check[] = {
335 PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1
340 for (idx = &check[0]; *idx != -1; idx++) {
341 if ((p = strchr(my[*idx], ',')) != NULL)
343 if ((p = strchr(peer[*idx], ',')) != NULL)
345 if (strcmp(my[*idx], peer[*idx]) != 0) {
346 debug2("proposal mismatch: my %s peer %s",
347 my[*idx], peer[*idx]);
351 debug2("proposals match");
356 kex_choose_conf(Kex *kex)
360 char **cprop, **sprop;
361 int nenc, nmac, ncomp;
362 u_int mode, ctos, need;
363 int first_kex_follows, type;
365 my = kex_buf2prop(&kex->my, NULL);
366 peer = kex_buf2prop(&kex->peer, &first_kex_follows);
376 /* Algorithm Negotiation */
377 for (mode = 0; mode < MODE_MAX; mode++) {
378 newkeys = xmalloc(sizeof(*newkeys));
379 memset(newkeys, 0, sizeof(*newkeys));
380 kex->newkeys[mode] = newkeys;
381 ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN);
382 nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC;
383 nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC;
384 ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC;
385 choose_enc (&newkeys->enc, cprop[nenc], sprop[nenc]);
386 choose_mac (&newkeys->mac, cprop[nmac], sprop[nmac]);
387 choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]);
388 debug("kex: %s %s %s %s",
389 ctos ? "client->server" : "server->client",
394 choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]);
395 choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
396 sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]);
398 for (mode = 0; mode < MODE_MAX; mode++) {
399 newkeys = kex->newkeys[mode];
400 if (need < newkeys->enc.key_len)
401 need = newkeys->enc.key_len;
402 if (need < newkeys->enc.block_size)
403 need = newkeys->enc.block_size;
404 if (need < newkeys->mac.key_len)
405 need = newkeys->mac.key_len;
407 /* XXX need runden? */
410 /* ignore the next message if the proposals do not match */
411 if (first_kex_follows && !proposals_match(my, peer) &&
412 !(datafellows & SSH_BUG_FIRSTKEX)) {
413 type = packet_read();
414 debug2("skipping next packet (type %u)", type);
422 derive_key(Kex *kex, int id, u_int need, u_char *hash, u_int hashlen,
423 BIGNUM *shared_secret)
432 if ((mdsz = EVP_MD_size(kex->evp_md)) <= 0)
433 fatal("bad kex md size %d", mdsz);
434 digest = xmalloc(roundup(need, mdsz));
437 buffer_put_bignum2(&b, shared_secret);
439 /* K1 = HASH(K || H || "A" || session_id) */
440 EVP_DigestInit(&md, kex->evp_md);
441 if (!(datafellows & SSH_BUG_DERIVEKEY))
442 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
443 EVP_DigestUpdate(&md, hash, hashlen);
444 EVP_DigestUpdate(&md, &c, 1);
445 EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len);
446 EVP_DigestFinal(&md, digest, NULL);
450 * Kn = HASH(K || H || K1 || K2 || ... || Kn-1)
451 * Key = K1 || K2 || ... || Kn
453 for (have = mdsz; need > have; have += mdsz) {
454 EVP_DigestInit(&md, kex->evp_md);
455 if (!(datafellows & SSH_BUG_DERIVEKEY))
456 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
457 EVP_DigestUpdate(&md, hash, hashlen);
458 EVP_DigestUpdate(&md, digest, have);
459 EVP_DigestFinal(&md, digest + have, NULL);
463 fprintf(stderr, "key '%c'== ", c);
464 dump_digest("key", digest, need);
469 Newkeys *current_keys[MODE_MAX];
473 kex_derive_keys(Kex *kex, u_char *hash, u_int hashlen, BIGNUM *shared_secret)
478 for (i = 0; i < NKEYS; i++) {
479 keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, hashlen,
483 debug2("kex_derive_keys");
484 for (mode = 0; mode < MODE_MAX; mode++) {
485 current_keys[mode] = kex->newkeys[mode];
486 kex->newkeys[mode] = NULL;
487 ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN);
488 current_keys[mode]->enc.iv = keys[ctos ? 0 : 1];
489 current_keys[mode]->enc.key = keys[ctos ? 2 : 3];
490 current_keys[mode]->mac.key = keys[ctos ? 4 : 5];
495 kex_get_newkeys(int mode)
499 ret = current_keys[mode];
500 current_keys[mode] = NULL;
505 derive_ssh1_session_id(BIGNUM *host_modulus, BIGNUM *server_modulus,
506 u_int8_t cookie[8], u_int8_t id[16])
508 const EVP_MD *evp_md = EVP_md5();
510 u_int8_t nbuf[2048], obuf[EVP_MAX_MD_SIZE];
513 EVP_DigestInit(&md, evp_md);
515 len = BN_num_bytes(host_modulus);
516 if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
517 fatal("%s: bad host modulus (len %d)", __func__, len);
518 BN_bn2bin(host_modulus, nbuf);
519 EVP_DigestUpdate(&md, nbuf, len);
521 len = BN_num_bytes(server_modulus);
522 if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
523 fatal("%s: bad server modulus (len %d)", __func__, len);
524 BN_bn2bin(server_modulus, nbuf);
525 EVP_DigestUpdate(&md, nbuf, len);
527 EVP_DigestUpdate(&md, cookie, 8);
529 EVP_DigestFinal(&md, obuf, NULL);
530 memcpy(id, obuf, 16);
532 memset(nbuf, 0, sizeof(nbuf));
533 memset(obuf, 0, sizeof(obuf));
534 memset(&md, 0, sizeof(md));
537 #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH)
539 dump_digest(char *msg, u_char *digest, int len)
543 fprintf(stderr, "%s\n", msg);
544 for (i = 0; i< len; i++) {
545 fprintf(stderr, "%02x", digest[i]);
547 fprintf(stderr, "\n");
549 fprintf(stderr, " ");
551 fprintf(stderr, "\n");