1 /* $OpenBSD: kex.c,v 1.86 2010/09/22 05:01:29 djm 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>
36 #include <openssl/crypto.h>
53 #if OPENSSL_VERSION_NUMBER >= 0x00907000L
54 # if defined(HAVE_EVP_SHA256)
55 # define evp_ssh_sha256 EVP_sha256
57 extern const EVP_MD *evp_ssh_sha256(void);
62 static void kex_kexinit_finish(Kex *);
63 static void kex_choose_conf(Kex *);
65 /* Validate KEX method name list */
67 kex_names_valid(const char *names)
71 if (names == NULL || strcmp(names, "") == 0)
73 s = cp = xstrdup(names);
74 for ((p = strsep(&cp, ",")); p && *p != '\0';
75 (p = strsep(&cp, ","))) {
76 if (strcmp(p, KEX_DHGEX_SHA256) != 0 &&
77 strcmp(p, KEX_DHGEX_SHA1) != 0 &&
78 strcmp(p, KEX_DH14) != 0 &&
79 strcmp(p, KEX_DH1) != 0 &&
80 (strncmp(p, KEX_ECDH_SHA2_STEM,
81 sizeof(KEX_ECDH_SHA2_STEM) - 1) != 0 ||
82 kex_ecdh_name_to_nid(p) == -1)) {
83 error("Unsupported KEX algorithm \"%.100s\"", p);
88 debug3("kex names ok: [%s]", names);
93 /* put algorithm proposal into buffer */
95 kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX])
101 * add a dummy cookie, the cookie will be overwritten by
102 * kex_send_kexinit(), each time a kexinit is set
104 for (i = 0; i < KEX_COOKIE_LEN; i++)
105 buffer_put_char(b, 0);
106 for (i = 0; i < PROPOSAL_MAX; i++)
107 buffer_put_cstring(b, proposal[i]);
108 buffer_put_char(b, 0); /* first_kex_packet_follows */
109 buffer_put_int(b, 0); /* uint32 reserved */
112 /* parse buffer and return algorithm proposal */
114 kex_buf2prop(Buffer *raw, int *first_kex_follows)
120 proposal = xcalloc(PROPOSAL_MAX, sizeof(char *));
123 buffer_append(&b, buffer_ptr(raw), buffer_len(raw));
125 for (i = 0; i < KEX_COOKIE_LEN; i++)
127 /* extract kex init proposal strings */
128 for (i = 0; i < PROPOSAL_MAX; i++) {
129 proposal[i] = buffer_get_cstring(&b,NULL);
130 debug2("kex_parse_kexinit: %s", proposal[i]);
132 /* first kex follows / reserved */
133 i = buffer_get_char(&b);
134 if (first_kex_follows != NULL)
135 *first_kex_follows = i;
136 debug2("kex_parse_kexinit: first_kex_follows %d ", i);
137 i = buffer_get_int(&b);
138 debug2("kex_parse_kexinit: reserved %u ", i);
144 kex_prop_free(char **proposal)
148 for (i = 0; i < PROPOSAL_MAX; i++)
155 kex_protocol_error(int type, u_int32_t seq, void *ctxt)
157 error("Hm, kex protocol error: type %d seq %u", type, seq);
161 kex_reset_dispatch(void)
163 dispatch_range(SSH2_MSG_TRANSPORT_MIN,
164 SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error);
165 dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit);
171 kex_reset_dispatch();
173 packet_start(SSH2_MSG_NEWKEYS);
175 /* packet_write_wait(); */
176 debug("SSH2_MSG_NEWKEYS sent");
178 debug("expecting SSH2_MSG_NEWKEYS");
179 packet_read_expect(SSH2_MSG_NEWKEYS);
181 debug("SSH2_MSG_NEWKEYS received");
184 buffer_clear(&kex->peer);
185 /* buffer_clear(&kex->my); */
186 kex->flags &= ~KEX_INIT_SENT;
192 kex_send_kexinit(Kex *kex)
199 error("kex_send_kexinit: no kex, cannot rekey");
202 if (kex->flags & KEX_INIT_SENT) {
203 debug("KEX_INIT_SENT");
208 /* generate a random cookie */
209 if (buffer_len(&kex->my) < KEX_COOKIE_LEN)
210 fatal("kex_send_kexinit: kex proposal too short");
211 cookie = buffer_ptr(&kex->my);
212 for (i = 0; i < KEX_COOKIE_LEN; i++) {
218 packet_start(SSH2_MSG_KEXINIT);
219 packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my));
221 debug("SSH2_MSG_KEXINIT sent");
222 kex->flags |= KEX_INIT_SENT;
227 kex_input_kexinit(int type, u_int32_t seq, void *ctxt)
231 Kex *kex = (Kex *)ctxt;
233 debug("SSH2_MSG_KEXINIT received");
235 fatal("kex_input_kexinit: no kex, cannot rekey");
237 ptr = packet_get_raw(&dlen);
238 buffer_append(&kex->peer, ptr, dlen);
241 for (i = 0; i < KEX_COOKIE_LEN; i++)
243 for (i = 0; i < PROPOSAL_MAX; i++)
244 xfree(packet_get_string(NULL));
245 (void) packet_get_char();
246 (void) packet_get_int();
249 kex_kexinit_finish(kex);
253 kex_setup(char *proposal[PROPOSAL_MAX])
257 kex = xcalloc(1, sizeof(*kex));
258 buffer_init(&kex->peer);
259 buffer_init(&kex->my);
260 kex_prop2buf(&kex->my, proposal);
263 kex_send_kexinit(kex); /* we start */
264 kex_reset_dispatch();
270 kex_kexinit_finish(Kex *kex)
272 if (!(kex->flags & KEX_INIT_SENT))
273 kex_send_kexinit(kex);
275 kex_choose_conf(kex);
277 if (kex->kex_type >= 0 && kex->kex_type < KEX_MAX &&
278 kex->kex[kex->kex_type] != NULL) {
279 (kex->kex[kex->kex_type])(kex);
281 fatal("Unsupported key exchange %d", kex->kex_type);
286 choose_enc(Enc *enc, char *client, char *server)
288 char *name = match_list(client, server, NULL);
290 fatal("no matching cipher found: client %s server %s",
292 if ((enc->cipher = cipher_by_name(name)) == NULL)
293 fatal("matching cipher is not supported: %s", name);
298 enc->key_len = cipher_keylen(enc->cipher);
299 enc->block_size = cipher_blocksize(enc->cipher);
303 choose_mac(Mac *mac, char *client, char *server)
305 char *name = match_list(client, server, NULL);
307 fatal("no matching mac found: client %s server %s",
309 if (mac_setup(mac, name) < 0)
310 fatal("unsupported mac %s", name);
311 /* truncate the key */
312 if (datafellows & SSH_BUG_HMAC)
320 choose_comp(Comp *comp, char *client, char *server)
322 char *name = match_list(client, server, NULL);
324 fatal("no matching comp found: client %s server %s", client, server);
325 if (strcmp(name, "zlib@openssh.com") == 0) {
326 comp->type = COMP_DELAYED;
327 } else if (strcmp(name, "zlib") == 0) {
328 comp->type = COMP_ZLIB;
329 } else if (strcmp(name, "none") == 0) {
330 comp->type = COMP_NONE;
332 fatal("unsupported comp %s", name);
338 choose_kex(Kex *k, char *client, char *server)
340 k->name = match_list(client, server, NULL);
342 fatal("Unable to negotiate a key exchange method");
343 if (strcmp(k->name, KEX_DH1) == 0) {
344 k->kex_type = KEX_DH_GRP1_SHA1;
345 k->evp_md = EVP_sha1();
346 } else if (strcmp(k->name, KEX_DH14) == 0) {
347 k->kex_type = KEX_DH_GRP14_SHA1;
348 k->evp_md = EVP_sha1();
349 } else if (strcmp(k->name, KEX_DHGEX_SHA1) == 0) {
350 k->kex_type = KEX_DH_GEX_SHA1;
351 k->evp_md = EVP_sha1();
352 #if OPENSSL_VERSION_NUMBER >= 0x00907000L
353 } else if (strcmp(k->name, KEX_DHGEX_SHA256) == 0) {
354 k->kex_type = KEX_DH_GEX_SHA256;
355 k->evp_md = evp_ssh_sha256();
356 } else if (strncmp(k->name, KEX_ECDH_SHA2_STEM,
357 sizeof(KEX_ECDH_SHA2_STEM) - 1) == 0) {
358 k->kex_type = KEX_ECDH_SHA2;
359 k->evp_md = kex_ecdh_name_to_evpmd(k->name);
362 fatal("bad kex alg %s", k->name);
366 choose_hostkeyalg(Kex *k, char *client, char *server)
368 char *hostkeyalg = match_list(client, server, NULL);
369 if (hostkeyalg == NULL)
370 fatal("no hostkey alg");
371 k->hostkey_type = key_type_from_name(hostkeyalg);
372 if (k->hostkey_type == KEY_UNSPEC)
373 fatal("bad hostkey alg '%s'", hostkeyalg);
378 proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX])
380 static int check[] = {
381 PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1
386 for (idx = &check[0]; *idx != -1; idx++) {
387 if ((p = strchr(my[*idx], ',')) != NULL)
389 if ((p = strchr(peer[*idx], ',')) != NULL)
391 if (strcmp(my[*idx], peer[*idx]) != 0) {
392 debug2("proposal mismatch: my %s peer %s",
393 my[*idx], peer[*idx]);
397 debug2("proposals match");
402 kex_choose_conf(Kex *kex)
406 char **cprop, **sprop;
407 int nenc, nmac, ncomp;
408 u_int mode, ctos, need;
409 int first_kex_follows, type;
411 my = kex_buf2prop(&kex->my, NULL);
412 peer = kex_buf2prop(&kex->peer, &first_kex_follows);
422 /* Check whether server offers roaming */
425 roaming = match_list(KEX_RESUME, peer[PROPOSAL_KEX_ALGS], NULL);
432 /* Algorithm Negotiation */
433 for (mode = 0; mode < MODE_MAX; mode++) {
434 newkeys = xcalloc(1, sizeof(*newkeys));
435 kex->newkeys[mode] = newkeys;
436 ctos = (!kex->server && mode == MODE_OUT) ||
437 (kex->server && mode == MODE_IN);
438 nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC;
439 nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC;
440 ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC;
441 choose_enc (&newkeys->enc, cprop[nenc], sprop[nenc]);
442 choose_mac (&newkeys->mac, cprop[nmac], sprop[nmac]);
443 choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]);
444 debug("kex: %s %s %s %s",
445 ctos ? "client->server" : "server->client",
450 choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]);
451 choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
452 sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]);
454 for (mode = 0; mode < MODE_MAX; mode++) {
455 newkeys = kex->newkeys[mode];
456 if (need < newkeys->enc.key_len)
457 need = newkeys->enc.key_len;
458 if (need < newkeys->enc.block_size)
459 need = newkeys->enc.block_size;
460 if (need < newkeys->mac.key_len)
461 need = newkeys->mac.key_len;
463 /* XXX need runden? */
466 /* ignore the next message if the proposals do not match */
467 if (first_kex_follows && !proposals_match(my, peer) &&
468 !(datafellows & SSH_BUG_FIRSTKEX)) {
469 type = packet_read();
470 debug2("skipping next packet (type %u)", type);
478 derive_key(Kex *kex, int id, u_int need, u_char *hash, u_int hashlen,
479 BIGNUM *shared_secret)
488 if ((mdsz = EVP_MD_size(kex->evp_md)) <= 0)
489 fatal("bad kex md size %d", mdsz);
490 digest = xmalloc(roundup(need, mdsz));
493 buffer_put_bignum2(&b, shared_secret);
495 /* K1 = HASH(K || H || "A" || session_id) */
496 EVP_DigestInit(&md, kex->evp_md);
497 if (!(datafellows & SSH_BUG_DERIVEKEY))
498 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
499 EVP_DigestUpdate(&md, hash, hashlen);
500 EVP_DigestUpdate(&md, &c, 1);
501 EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len);
502 EVP_DigestFinal(&md, digest, NULL);
506 * Kn = HASH(K || H || K1 || K2 || ... || Kn-1)
507 * Key = K1 || K2 || ... || Kn
509 for (have = mdsz; need > have; have += mdsz) {
510 EVP_DigestInit(&md, kex->evp_md);
511 if (!(datafellows & SSH_BUG_DERIVEKEY))
512 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
513 EVP_DigestUpdate(&md, hash, hashlen);
514 EVP_DigestUpdate(&md, digest, have);
515 EVP_DigestFinal(&md, digest + have, NULL);
519 fprintf(stderr, "key '%c'== ", c);
520 dump_digest("key", digest, need);
525 Newkeys *current_keys[MODE_MAX];
529 kex_derive_keys(Kex *kex, u_char *hash, u_int hashlen, BIGNUM *shared_secret)
534 for (i = 0; i < NKEYS; i++) {
535 keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, hashlen,
539 debug2("kex_derive_keys");
540 for (mode = 0; mode < MODE_MAX; mode++) {
541 current_keys[mode] = kex->newkeys[mode];
542 kex->newkeys[mode] = NULL;
543 ctos = (!kex->server && mode == MODE_OUT) ||
544 (kex->server && mode == MODE_IN);
545 current_keys[mode]->enc.iv = keys[ctos ? 0 : 1];
546 current_keys[mode]->enc.key = keys[ctos ? 2 : 3];
547 current_keys[mode]->mac.key = keys[ctos ? 4 : 5];
552 kex_get_newkeys(int mode)
556 ret = current_keys[mode];
557 current_keys[mode] = NULL;
562 derive_ssh1_session_id(BIGNUM *host_modulus, BIGNUM *server_modulus,
563 u_int8_t cookie[8], u_int8_t id[16])
565 const EVP_MD *evp_md = EVP_md5();
567 u_int8_t nbuf[2048], obuf[EVP_MAX_MD_SIZE];
570 EVP_DigestInit(&md, evp_md);
572 len = BN_num_bytes(host_modulus);
573 if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
574 fatal("%s: bad host modulus (len %d)", __func__, len);
575 BN_bn2bin(host_modulus, nbuf);
576 EVP_DigestUpdate(&md, nbuf, len);
578 len = BN_num_bytes(server_modulus);
579 if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
580 fatal("%s: bad server modulus (len %d)", __func__, len);
581 BN_bn2bin(server_modulus, nbuf);
582 EVP_DigestUpdate(&md, nbuf, len);
584 EVP_DigestUpdate(&md, cookie, 8);
586 EVP_DigestFinal(&md, obuf, NULL);
587 memcpy(id, obuf, 16);
589 memset(nbuf, 0, sizeof(nbuf));
590 memset(obuf, 0, sizeof(obuf));
591 memset(&md, 0, sizeof(md));
594 #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH) || defined(DEBUG_KEXECDH)
596 dump_digest(char *msg, u_char *digest, int len)
600 fprintf(stderr, "%s\n", msg);
601 for (i = 0; i < len; i++) {
602 fprintf(stderr, "%02x", digest[i]);
604 fprintf(stderr, "\n");
606 fprintf(stderr, " ");
608 fprintf(stderr, "\n");