1 /* $OpenBSD: kex.c,v 1.80 2008/09/06 12:24:13 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>
52 #define KEX_COOKIE_LEN 16
54 #if OPENSSL_VERSION_NUMBER >= 0x00907000L
55 # if defined(HAVE_EVP_SHA256)
56 # define evp_ssh_sha256 EVP_sha256
58 extern const EVP_MD *evp_ssh_sha256(void);
63 static void kex_kexinit_finish(Kex *);
64 static void kex_choose_conf(Kex *);
66 /* put algorithm proposal into buffer */
68 kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX])
74 * add a dummy cookie, the cookie will be overwritten by
75 * kex_send_kexinit(), each time a kexinit is set
77 for (i = 0; i < KEX_COOKIE_LEN; i++)
78 buffer_put_char(b, 0);
79 for (i = 0; i < PROPOSAL_MAX; i++)
80 buffer_put_cstring(b, proposal[i]);
81 buffer_put_char(b, 0); /* first_kex_packet_follows */
82 buffer_put_int(b, 0); /* uint32 reserved */
85 /* parse buffer and return algorithm proposal */
87 kex_buf2prop(Buffer *raw, int *first_kex_follows)
93 proposal = xcalloc(PROPOSAL_MAX, sizeof(char *));
96 buffer_append(&b, buffer_ptr(raw), buffer_len(raw));
98 for (i = 0; i < KEX_COOKIE_LEN; i++)
100 /* extract kex init proposal strings */
101 for (i = 0; i < PROPOSAL_MAX; i++) {
102 proposal[i] = buffer_get_string(&b,NULL);
103 debug2("kex_parse_kexinit: %s", proposal[i]);
105 /* first kex follows / reserved */
106 i = buffer_get_char(&b);
107 if (first_kex_follows != NULL)
108 *first_kex_follows = i;
109 debug2("kex_parse_kexinit: first_kex_follows %d ", i);
110 i = buffer_get_int(&b);
111 debug2("kex_parse_kexinit: reserved %u ", i);
117 kex_prop_free(char **proposal)
121 for (i = 0; i < PROPOSAL_MAX; i++)
128 kex_protocol_error(int type, u_int32_t seq, void *ctxt)
130 error("Hm, kex protocol error: type %d seq %u", type, seq);
134 kex_reset_dispatch(void)
136 dispatch_range(SSH2_MSG_TRANSPORT_MIN,
137 SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error);
138 dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit);
144 kex_reset_dispatch();
146 packet_start(SSH2_MSG_NEWKEYS);
148 /* packet_write_wait(); */
149 debug("SSH2_MSG_NEWKEYS sent");
151 debug("expecting SSH2_MSG_NEWKEYS");
152 packet_read_expect(SSH2_MSG_NEWKEYS);
154 debug("SSH2_MSG_NEWKEYS received");
157 buffer_clear(&kex->peer);
158 /* buffer_clear(&kex->my); */
159 kex->flags &= ~KEX_INIT_SENT;
165 kex_send_kexinit(Kex *kex)
172 error("kex_send_kexinit: no kex, cannot rekey");
175 if (kex->flags & KEX_INIT_SENT) {
176 debug("KEX_INIT_SENT");
181 /* generate a random cookie */
182 if (buffer_len(&kex->my) < KEX_COOKIE_LEN)
183 fatal("kex_send_kexinit: kex proposal too short");
184 cookie = buffer_ptr(&kex->my);
185 for (i = 0; i < KEX_COOKIE_LEN; i++) {
191 packet_start(SSH2_MSG_KEXINIT);
192 packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my));
194 debug("SSH2_MSG_KEXINIT sent");
195 kex->flags |= KEX_INIT_SENT;
200 kex_input_kexinit(int type, u_int32_t seq, void *ctxt)
204 Kex *kex = (Kex *)ctxt;
206 debug("SSH2_MSG_KEXINIT received");
208 fatal("kex_input_kexinit: no kex, cannot rekey");
210 ptr = packet_get_raw(&dlen);
211 buffer_append(&kex->peer, ptr, dlen);
214 for (i = 0; i < KEX_COOKIE_LEN; i++)
216 for (i = 0; i < PROPOSAL_MAX; i++)
217 xfree(packet_get_string(NULL));
218 (void) packet_get_char();
219 (void) packet_get_int();
222 kex_kexinit_finish(kex);
226 kex_setup(char *proposal[PROPOSAL_MAX])
230 kex = xcalloc(1, sizeof(*kex));
231 buffer_init(&kex->peer);
232 buffer_init(&kex->my);
233 kex_prop2buf(&kex->my, proposal);
236 kex_send_kexinit(kex); /* we start */
237 kex_reset_dispatch();
243 kex_kexinit_finish(Kex *kex)
245 if (!(kex->flags & KEX_INIT_SENT))
246 kex_send_kexinit(kex);
248 kex_choose_conf(kex);
250 if (kex->kex_type >= 0 && kex->kex_type < KEX_MAX &&
251 kex->kex[kex->kex_type] != NULL) {
252 (kex->kex[kex->kex_type])(kex);
254 fatal("Unsupported key exchange %d", kex->kex_type);
259 choose_enc(Enc *enc, char *client, char *server)
261 char *name = match_list(client, server, NULL);
263 fatal("no matching cipher found: client %s server %s",
265 if ((enc->cipher = cipher_by_name(name)) == NULL)
266 fatal("matching cipher is not supported: %s", name);
271 enc->key_len = cipher_keylen(enc->cipher);
272 enc->block_size = cipher_blocksize(enc->cipher);
276 choose_mac(Mac *mac, char *client, char *server)
278 char *name = match_list(client, server, NULL);
280 fatal("no matching mac found: client %s server %s",
282 if (mac_setup(mac, name) < 0)
283 fatal("unsupported mac %s", name);
284 /* truncate the key */
285 if (datafellows & SSH_BUG_HMAC)
293 choose_comp(Comp *comp, char *client, char *server)
295 char *name = match_list(client, server, NULL);
297 fatal("no matching comp found: client %s server %s", client, server);
298 if (strcmp(name, "zlib@openssh.com") == 0) {
299 comp->type = COMP_DELAYED;
300 } else if (strcmp(name, "zlib") == 0) {
301 comp->type = COMP_ZLIB;
302 } else if (strcmp(name, "none") == 0) {
303 comp->type = COMP_NONE;
305 fatal("unsupported comp %s", name);
311 choose_kex(Kex *k, char *client, char *server)
313 k->name = match_list(client, server, NULL);
315 fatal("Unable to negotiate a key exchange method");
316 if (strcmp(k->name, KEX_DH1) == 0) {
317 k->kex_type = KEX_DH_GRP1_SHA1;
318 k->evp_md = EVP_sha1();
319 } else if (strcmp(k->name, KEX_DH14) == 0) {
320 k->kex_type = KEX_DH_GRP14_SHA1;
321 k->evp_md = EVP_sha1();
322 } else if (strcmp(k->name, KEX_DHGEX_SHA1) == 0) {
323 k->kex_type = KEX_DH_GEX_SHA1;
324 k->evp_md = EVP_sha1();
325 #if OPENSSL_VERSION_NUMBER >= 0x00907000L
326 } else if (strcmp(k->name, KEX_DHGEX_SHA256) == 0) {
327 k->kex_type = KEX_DH_GEX_SHA256;
328 k->evp_md = evp_ssh_sha256();
331 fatal("bad kex alg %s", k->name);
335 choose_hostkeyalg(Kex *k, char *client, char *server)
337 char *hostkeyalg = match_list(client, server, NULL);
338 if (hostkeyalg == NULL)
339 fatal("no hostkey alg");
340 k->hostkey_type = key_type_from_name(hostkeyalg);
341 if (k->hostkey_type == KEY_UNSPEC)
342 fatal("bad hostkey alg '%s'", hostkeyalg);
347 proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX])
349 static int check[] = {
350 PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1
355 for (idx = &check[0]; *idx != -1; idx++) {
356 if ((p = strchr(my[*idx], ',')) != NULL)
358 if ((p = strchr(peer[*idx], ',')) != NULL)
360 if (strcmp(my[*idx], peer[*idx]) != 0) {
361 debug2("proposal mismatch: my %s peer %s",
362 my[*idx], peer[*idx]);
366 debug2("proposals match");
371 kex_choose_conf(Kex *kex)
375 char **cprop, **sprop;
376 int nenc, nmac, ncomp;
377 u_int mode, ctos, need;
378 int first_kex_follows, type;
380 my = kex_buf2prop(&kex->my, NULL);
381 peer = kex_buf2prop(&kex->peer, &first_kex_follows);
391 /* Algorithm Negotiation */
392 for (mode = 0; mode < MODE_MAX; mode++) {
393 newkeys = xcalloc(1, sizeof(*newkeys));
394 kex->newkeys[mode] = newkeys;
395 ctos = (!kex->server && mode == MODE_OUT) ||
396 (kex->server && mode == MODE_IN);
397 nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC;
398 nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC;
399 ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC;
400 choose_enc (&newkeys->enc, cprop[nenc], sprop[nenc]);
401 choose_mac (&newkeys->mac, cprop[nmac], sprop[nmac]);
402 choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]);
403 debug("kex: %s %s %s %s",
404 ctos ? "client->server" : "server->client",
409 choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]);
410 choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
411 sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]);
413 for (mode = 0; mode < MODE_MAX; mode++) {
414 newkeys = kex->newkeys[mode];
415 if (need < newkeys->enc.key_len)
416 need = newkeys->enc.key_len;
417 if (need < newkeys->enc.block_size)
418 need = newkeys->enc.block_size;
419 if (need < newkeys->mac.key_len)
420 need = newkeys->mac.key_len;
422 /* XXX need runden? */
425 /* ignore the next message if the proposals do not match */
426 if (first_kex_follows && !proposals_match(my, peer) &&
427 !(datafellows & SSH_BUG_FIRSTKEX)) {
428 type = packet_read();
429 debug2("skipping next packet (type %u)", type);
437 derive_key(Kex *kex, int id, u_int need, u_char *hash, u_int hashlen,
438 BIGNUM *shared_secret)
447 if ((mdsz = EVP_MD_size(kex->evp_md)) <= 0)
448 fatal("bad kex md size %d", mdsz);
449 digest = xmalloc(roundup(need, mdsz));
452 buffer_put_bignum2(&b, shared_secret);
454 /* K1 = HASH(K || H || "A" || session_id) */
455 EVP_DigestInit(&md, kex->evp_md);
456 if (!(datafellows & SSH_BUG_DERIVEKEY))
457 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
458 EVP_DigestUpdate(&md, hash, hashlen);
459 EVP_DigestUpdate(&md, &c, 1);
460 EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len);
461 EVP_DigestFinal(&md, digest, NULL);
465 * Kn = HASH(K || H || K1 || K2 || ... || Kn-1)
466 * Key = K1 || K2 || ... || Kn
468 for (have = mdsz; need > have; have += mdsz) {
469 EVP_DigestInit(&md, kex->evp_md);
470 if (!(datafellows & SSH_BUG_DERIVEKEY))
471 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
472 EVP_DigestUpdate(&md, hash, hashlen);
473 EVP_DigestUpdate(&md, digest, have);
474 EVP_DigestFinal(&md, digest + have, NULL);
478 fprintf(stderr, "key '%c'== ", c);
479 dump_digest("key", digest, need);
484 Newkeys *current_keys[MODE_MAX];
488 kex_derive_keys(Kex *kex, u_char *hash, u_int hashlen, BIGNUM *shared_secret)
493 for (i = 0; i < NKEYS; i++) {
494 keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, hashlen,
498 debug2("kex_derive_keys");
499 for (mode = 0; mode < MODE_MAX; mode++) {
500 current_keys[mode] = kex->newkeys[mode];
501 kex->newkeys[mode] = NULL;
502 ctos = (!kex->server && mode == MODE_OUT) ||
503 (kex->server && mode == MODE_IN);
504 current_keys[mode]->enc.iv = keys[ctos ? 0 : 1];
505 current_keys[mode]->enc.key = keys[ctos ? 2 : 3];
506 current_keys[mode]->mac.key = keys[ctos ? 4 : 5];
511 kex_get_newkeys(int mode)
515 ret = current_keys[mode];
516 current_keys[mode] = NULL;
521 derive_ssh1_session_id(BIGNUM *host_modulus, BIGNUM *server_modulus,
522 u_int8_t cookie[8], u_int8_t id[16])
524 const EVP_MD *evp_md = EVP_md5();
526 u_int8_t nbuf[2048], obuf[EVP_MAX_MD_SIZE];
529 EVP_DigestInit(&md, evp_md);
531 len = BN_num_bytes(host_modulus);
532 if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
533 fatal("%s: bad host modulus (len %d)", __func__, len);
534 BN_bn2bin(host_modulus, nbuf);
535 EVP_DigestUpdate(&md, nbuf, len);
537 len = BN_num_bytes(server_modulus);
538 if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
539 fatal("%s: bad server modulus (len %d)", __func__, len);
540 BN_bn2bin(server_modulus, nbuf);
541 EVP_DigestUpdate(&md, nbuf, len);
543 EVP_DigestUpdate(&md, cookie, 8);
545 EVP_DigestFinal(&md, obuf, NULL);
546 memcpy(id, obuf, 16);
548 memset(nbuf, 0, sizeof(nbuf));
549 memset(obuf, 0, sizeof(obuf));
550 memset(&md, 0, sizeof(md));
553 #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH)
555 dump_digest(char *msg, u_char *digest, int len)
559 fprintf(stderr, "%s\n", msg);
560 for (i = 0; i < len; i++) {
561 fprintf(stderr, "%02x", digest[i]);
563 fprintf(stderr, "\n");
565 fprintf(stderr, " ");
567 fprintf(stderr, "\n");