1 /* $OpenBSD: kex.c,v 1.74 2006/07/26 13:57:17 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 <sys/param.h>
30 #include <openssl/crypto.h>
50 #define KEX_COOKIE_LEN 16
52 #if OPENSSL_VERSION_NUMBER >= 0x00907000L
53 # if defined(HAVE_EVP_SHA256)
54 # define evp_ssh_sha256 EVP_sha256
56 extern const EVP_MD *evp_ssh_sha256(void);
61 static void kex_kexinit_finish(Kex *);
62 static void kex_choose_conf(Kex *);
64 /* put algorithm proposal into buffer */
66 kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX])
72 * add a dummy cookie, the cookie will be overwritten by
73 * kex_send_kexinit(), each time a kexinit is set
75 for (i = 0; i < KEX_COOKIE_LEN; i++)
76 buffer_put_char(b, 0);
77 for (i = 0; i < PROPOSAL_MAX; i++)
78 buffer_put_cstring(b, proposal[i]);
79 buffer_put_char(b, 0); /* first_kex_packet_follows */
80 buffer_put_int(b, 0); /* uint32 reserved */
83 /* parse buffer and return algorithm proposal */
85 kex_buf2prop(Buffer *raw, int *first_kex_follows)
91 proposal = xcalloc(PROPOSAL_MAX, sizeof(char *));
94 buffer_append(&b, buffer_ptr(raw), buffer_len(raw));
96 for (i = 0; i < KEX_COOKIE_LEN; i++)
98 /* extract kex init proposal strings */
99 for (i = 0; i < PROPOSAL_MAX; i++) {
100 proposal[i] = buffer_get_string(&b,NULL);
101 debug2("kex_parse_kexinit: %s", proposal[i]);
103 /* first kex follows / reserved */
104 i = buffer_get_char(&b);
105 if (first_kex_follows != NULL)
106 *first_kex_follows = i;
107 debug2("kex_parse_kexinit: first_kex_follows %d ", i);
108 i = buffer_get_int(&b);
109 debug2("kex_parse_kexinit: reserved %d ", i);
115 kex_prop_free(char **proposal)
119 for (i = 0; i < PROPOSAL_MAX; i++)
125 kex_protocol_error(int type, u_int32_t seq, void *ctxt)
127 error("Hm, kex protocol error: type %d seq %u", type, seq);
131 kex_reset_dispatch(void)
133 dispatch_range(SSH2_MSG_TRANSPORT_MIN,
134 SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error);
135 dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit);
141 kex_reset_dispatch();
143 packet_start(SSH2_MSG_NEWKEYS);
145 /* packet_write_wait(); */
146 debug("SSH2_MSG_NEWKEYS sent");
148 debug("expecting SSH2_MSG_NEWKEYS");
149 packet_read_expect(SSH2_MSG_NEWKEYS);
151 debug("SSH2_MSG_NEWKEYS received");
154 buffer_clear(&kex->peer);
155 /* buffer_clear(&kex->my); */
156 kex->flags &= ~KEX_INIT_SENT;
162 kex_send_kexinit(Kex *kex)
169 error("kex_send_kexinit: no kex, cannot rekey");
172 if (kex->flags & KEX_INIT_SENT) {
173 debug("KEX_INIT_SENT");
178 /* generate a random cookie */
179 if (buffer_len(&kex->my) < KEX_COOKIE_LEN)
180 fatal("kex_send_kexinit: kex proposal too short");
181 cookie = buffer_ptr(&kex->my);
182 for (i = 0; i < KEX_COOKIE_LEN; i++) {
188 packet_start(SSH2_MSG_KEXINIT);
189 packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my));
191 debug("SSH2_MSG_KEXINIT sent");
192 kex->flags |= KEX_INIT_SENT;
196 kex_input_kexinit(int type, u_int32_t seq, void *ctxt)
200 Kex *kex = (Kex *)ctxt;
202 debug("SSH2_MSG_KEXINIT received");
204 fatal("kex_input_kexinit: no kex, cannot rekey");
206 ptr = packet_get_raw(&dlen);
207 buffer_append(&kex->peer, ptr, dlen);
210 for (i = 0; i < KEX_COOKIE_LEN; i++)
212 for (i = 0; i < PROPOSAL_MAX; i++)
213 xfree(packet_get_string(NULL));
214 (void) packet_get_char();
215 (void) packet_get_int();
218 kex_kexinit_finish(kex);
222 kex_setup(char *proposal[PROPOSAL_MAX])
226 kex = xcalloc(1, sizeof(*kex));
227 buffer_init(&kex->peer);
228 buffer_init(&kex->my);
229 kex_prop2buf(&kex->my, proposal);
232 kex_send_kexinit(kex); /* we start */
233 kex_reset_dispatch();
239 kex_kexinit_finish(Kex *kex)
241 if (!(kex->flags & KEX_INIT_SENT))
242 kex_send_kexinit(kex);
244 kex_choose_conf(kex);
246 if (kex->kex_type >= 0 && kex->kex_type < KEX_MAX &&
247 kex->kex[kex->kex_type] != NULL) {
248 (kex->kex[kex->kex_type])(kex);
250 fatal("Unsupported key exchange %d", kex->kex_type);
255 choose_enc(Enc *enc, char *client, char *server)
257 char *name = match_list(client, server, NULL);
259 fatal("no matching cipher found: client %s server %s", client, server);
260 if ((enc->cipher = cipher_by_name(name)) == NULL)
261 fatal("matching cipher is not supported: %s", name);
266 enc->key_len = cipher_keylen(enc->cipher);
267 enc->block_size = cipher_blocksize(enc->cipher);
271 choose_mac(Mac *mac, char *client, char *server)
273 char *name = match_list(client, server, NULL);
275 fatal("no matching mac found: client %s server %s", client, server);
276 if (mac_init(mac, name) < 0)
277 fatal("unsupported mac %s", name);
278 /* truncate the key */
279 if (datafellows & SSH_BUG_HMAC)
287 choose_comp(Comp *comp, char *client, char *server)
289 char *name = match_list(client, server, NULL);
291 fatal("no matching comp found: client %s server %s", client, server);
292 if (strcmp(name, "zlib@openssh.com") == 0) {
293 comp->type = COMP_DELAYED;
294 } else if (strcmp(name, "zlib") == 0) {
295 comp->type = COMP_ZLIB;
296 } else if (strcmp(name, "none") == 0) {
297 comp->type = COMP_NONE;
299 fatal("unsupported comp %s", name);
305 choose_kex(Kex *k, char *client, char *server)
307 k->name = match_list(client, server, NULL);
310 if (strcmp(k->name, KEX_DH1) == 0) {
311 k->kex_type = KEX_DH_GRP1_SHA1;
312 k->evp_md = EVP_sha1();
313 } else if (strcmp(k->name, KEX_DH14) == 0) {
314 k->kex_type = KEX_DH_GRP14_SHA1;
315 k->evp_md = EVP_sha1();
316 } else if (strcmp(k->name, KEX_DHGEX_SHA1) == 0) {
317 k->kex_type = KEX_DH_GEX_SHA1;
318 k->evp_md = EVP_sha1();
319 #if OPENSSL_VERSION_NUMBER >= 0x00907000L
320 } else if (strcmp(k->name, KEX_DHGEX_SHA256) == 0) {
321 k->kex_type = KEX_DH_GEX_SHA256;
322 k->evp_md = evp_ssh_sha256();
325 fatal("bad kex alg %s", k->name);
329 choose_hostkeyalg(Kex *k, char *client, char *server)
331 char *hostkeyalg = match_list(client, server, NULL);
332 if (hostkeyalg == NULL)
333 fatal("no hostkey alg");
334 k->hostkey_type = key_type_from_name(hostkeyalg);
335 if (k->hostkey_type == KEY_UNSPEC)
336 fatal("bad hostkey alg '%s'", hostkeyalg);
341 proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX])
343 static int check[] = {
344 PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1
349 for (idx = &check[0]; *idx != -1; idx++) {
350 if ((p = strchr(my[*idx], ',')) != NULL)
352 if ((p = strchr(peer[*idx], ',')) != NULL)
354 if (strcmp(my[*idx], peer[*idx]) != 0) {
355 debug2("proposal mismatch: my %s peer %s",
356 my[*idx], peer[*idx]);
360 debug2("proposals match");
365 kex_choose_conf(Kex *kex)
369 char **cprop, **sprop;
370 int nenc, nmac, ncomp;
371 u_int mode, ctos, need;
372 int first_kex_follows, type;
374 my = kex_buf2prop(&kex->my, NULL);
375 peer = kex_buf2prop(&kex->peer, &first_kex_follows);
385 /* Algorithm Negotiation */
386 for (mode = 0; mode < MODE_MAX; mode++) {
387 newkeys = xcalloc(1, sizeof(*newkeys));
388 kex->newkeys[mode] = newkeys;
389 ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN);
390 nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC;
391 nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC;
392 ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC;
393 choose_enc (&newkeys->enc, cprop[nenc], sprop[nenc]);
394 choose_mac (&newkeys->mac, cprop[nmac], sprop[nmac]);
395 choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]);
396 debug("kex: %s %s %s %s",
397 ctos ? "client->server" : "server->client",
402 choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]);
403 choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
404 sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]);
406 for (mode = 0; mode < MODE_MAX; mode++) {
407 newkeys = kex->newkeys[mode];
408 if (need < newkeys->enc.key_len)
409 need = newkeys->enc.key_len;
410 if (need < newkeys->enc.block_size)
411 need = newkeys->enc.block_size;
412 if (need < newkeys->mac.key_len)
413 need = newkeys->mac.key_len;
415 /* XXX need runden? */
418 /* ignore the next message if the proposals do not match */
419 if (first_kex_follows && !proposals_match(my, peer) &&
420 !(datafellows & SSH_BUG_FIRSTKEX)) {
421 type = packet_read();
422 debug2("skipping next packet (type %u)", type);
430 derive_key(Kex *kex, int id, u_int need, u_char *hash, u_int hashlen,
431 BIGNUM *shared_secret)
440 if ((mdsz = EVP_MD_size(kex->evp_md)) <= 0)
441 fatal("bad kex md size %d", mdsz);
442 digest = xmalloc(roundup(need, mdsz));
445 buffer_put_bignum2(&b, shared_secret);
447 /* K1 = HASH(K || H || "A" || session_id) */
448 EVP_DigestInit(&md, kex->evp_md);
449 if (!(datafellows & SSH_BUG_DERIVEKEY))
450 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
451 EVP_DigestUpdate(&md, hash, hashlen);
452 EVP_DigestUpdate(&md, &c, 1);
453 EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len);
454 EVP_DigestFinal(&md, digest, NULL);
458 * Kn = HASH(K || H || K1 || K2 || ... || Kn-1)
459 * Key = K1 || K2 || ... || Kn
461 for (have = mdsz; need > have; have += mdsz) {
462 EVP_DigestInit(&md, kex->evp_md);
463 if (!(datafellows & SSH_BUG_DERIVEKEY))
464 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
465 EVP_DigestUpdate(&md, hash, hashlen);
466 EVP_DigestUpdate(&md, digest, have);
467 EVP_DigestFinal(&md, digest + have, NULL);
471 fprintf(stderr, "key '%c'== ", c);
472 dump_digest("key", digest, need);
477 Newkeys *current_keys[MODE_MAX];
481 kex_derive_keys(Kex *kex, u_char *hash, u_int hashlen, BIGNUM *shared_secret)
486 for (i = 0; i < NKEYS; i++) {
487 keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, hashlen,
491 debug2("kex_derive_keys");
492 for (mode = 0; mode < MODE_MAX; mode++) {
493 current_keys[mode] = kex->newkeys[mode];
494 kex->newkeys[mode] = NULL;
495 ctos = (!kex->server && mode == MODE_OUT) ||
496 (kex->server && mode == MODE_IN);
497 current_keys[mode]->enc.iv = keys[ctos ? 0 : 1];
498 current_keys[mode]->enc.key = keys[ctos ? 2 : 3];
499 current_keys[mode]->mac.key = keys[ctos ? 4 : 5];
504 kex_get_newkeys(int mode)
508 ret = current_keys[mode];
509 current_keys[mode] = NULL;
514 derive_ssh1_session_id(BIGNUM *host_modulus, BIGNUM *server_modulus,
515 u_int8_t cookie[8], u_int8_t id[16])
517 const EVP_MD *evp_md = EVP_md5();
519 u_int8_t nbuf[2048], obuf[EVP_MAX_MD_SIZE];
522 EVP_DigestInit(&md, evp_md);
524 len = BN_num_bytes(host_modulus);
525 if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
526 fatal("%s: bad host modulus (len %d)", __func__, len);
527 BN_bn2bin(host_modulus, nbuf);
528 EVP_DigestUpdate(&md, nbuf, len);
530 len = BN_num_bytes(server_modulus);
531 if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
532 fatal("%s: bad server modulus (len %d)", __func__, len);
533 BN_bn2bin(server_modulus, nbuf);
534 EVP_DigestUpdate(&md, nbuf, len);
536 EVP_DigestUpdate(&md, cookie, 8);
538 EVP_DigestFinal(&md, obuf, NULL);
539 memcpy(id, obuf, 16);
541 memset(nbuf, 0, sizeof(nbuf));
542 memset(obuf, 0, sizeof(obuf));
543 memset(&md, 0, sizeof(md));
546 #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH)
548 dump_digest(char *msg, u_char *digest, int len)
552 fprintf(stderr, "%s\n", msg);
553 for (i = 0; i< len; i++) {
554 fprintf(stderr, "%02x", digest[i]);
556 fprintf(stderr, "\n");
558 fprintf(stderr, " ");
560 fprintf(stderr, "\n");