1 /* $OpenBSD: kex.c,v 1.79 2007/06/05 06:52:37 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>
56 #define KEX_COOKIE_LEN 16
58 #if OPENSSL_VERSION_NUMBER >= 0x00907000L
59 # if defined(HAVE_EVP_SHA256)
60 # define evp_ssh_sha256 EVP_sha256
62 extern const EVP_MD *evp_ssh_sha256(void);
67 static void kex_kexinit_finish(Kex *);
68 static void kex_choose_conf(Kex *);
70 /* put algorithm proposal into buffer */
72 kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX])
78 * add a dummy cookie, the cookie will be overwritten by
79 * kex_send_kexinit(), each time a kexinit is set
81 for (i = 0; i < KEX_COOKIE_LEN; i++)
82 buffer_put_char(b, 0);
83 for (i = 0; i < PROPOSAL_MAX; i++)
84 buffer_put_cstring(b, proposal[i]);
85 buffer_put_char(b, 0); /* first_kex_packet_follows */
86 buffer_put_int(b, 0); /* uint32 reserved */
89 /* parse buffer and return algorithm proposal */
91 kex_buf2prop(Buffer *raw, int *first_kex_follows)
97 proposal = xcalloc(PROPOSAL_MAX, sizeof(char *));
100 buffer_append(&b, buffer_ptr(raw), buffer_len(raw));
102 for (i = 0; i < KEX_COOKIE_LEN; i++)
104 /* extract kex init proposal strings */
105 for (i = 0; i < PROPOSAL_MAX; i++) {
106 proposal[i] = buffer_get_string(&b,NULL);
107 debug2("kex_parse_kexinit: %s", proposal[i]);
109 /* first kex follows / reserved */
110 i = buffer_get_char(&b);
111 if (first_kex_follows != NULL)
112 *first_kex_follows = i;
113 debug2("kex_parse_kexinit: first_kex_follows %d ", i);
114 i = buffer_get_int(&b);
115 debug2("kex_parse_kexinit: reserved %u ", i);
121 kex_prop_free(char **proposal)
125 for (i = 0; i < PROPOSAL_MAX; i++)
132 kex_protocol_error(int type, u_int32_t seq, void *ctxt)
134 error("Hm, kex protocol error: type %d seq %u", type, seq);
138 kex_reset_dispatch(void)
140 dispatch_range(SSH2_MSG_TRANSPORT_MIN,
141 SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error);
142 dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit);
148 kex_reset_dispatch();
150 packet_start(SSH2_MSG_NEWKEYS);
152 /* packet_write_wait(); */
153 debug("SSH2_MSG_NEWKEYS sent");
155 debug("expecting SSH2_MSG_NEWKEYS");
156 packet_read_expect(SSH2_MSG_NEWKEYS);
158 debug("SSH2_MSG_NEWKEYS received");
161 buffer_clear(&kex->peer);
162 /* buffer_clear(&kex->my); */
163 kex->flags &= ~KEX_INIT_SENT;
169 kex_send_kexinit(Kex *kex)
176 error("kex_send_kexinit: no kex, cannot rekey");
179 if (kex->flags & KEX_INIT_SENT) {
180 debug("KEX_INIT_SENT");
185 /* generate a random cookie */
186 if (buffer_len(&kex->my) < KEX_COOKIE_LEN)
187 fatal("kex_send_kexinit: kex proposal too short");
188 cookie = buffer_ptr(&kex->my);
189 for (i = 0; i < KEX_COOKIE_LEN; i++) {
195 packet_start(SSH2_MSG_KEXINIT);
196 packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my));
198 debug("SSH2_MSG_KEXINIT sent");
199 kex->flags |= KEX_INIT_SENT;
204 kex_input_kexinit(int type, u_int32_t seq, void *ctxt)
208 Kex *kex = (Kex *)ctxt;
210 debug("SSH2_MSG_KEXINIT received");
212 fatal("kex_input_kexinit: no kex, cannot rekey");
214 ptr = packet_get_raw(&dlen);
215 buffer_append(&kex->peer, ptr, dlen);
218 for (i = 0; i < KEX_COOKIE_LEN; i++)
220 for (i = 0; i < PROPOSAL_MAX; i++)
221 xfree(packet_get_string(NULL));
222 (void) packet_get_char();
223 (void) packet_get_int();
226 kex_kexinit_finish(kex);
230 kex_setup(char *proposal[PROPOSAL_MAX])
234 kex = xcalloc(1, sizeof(*kex));
235 buffer_init(&kex->peer);
236 buffer_init(&kex->my);
237 kex_prop2buf(&kex->my, proposal);
240 kex_send_kexinit(kex); /* we start */
241 kex_reset_dispatch();
247 kex_kexinit_finish(Kex *kex)
249 if (!(kex->flags & KEX_INIT_SENT))
250 kex_send_kexinit(kex);
252 kex_choose_conf(kex);
254 if (kex->kex_type >= 0 && kex->kex_type < KEX_MAX &&
255 kex->kex[kex->kex_type] != NULL) {
256 (kex->kex[kex->kex_type])(kex);
258 fatal("Unsupported key exchange %d", kex->kex_type);
263 choose_enc(Enc *enc, char *client, char *server)
265 char *name = match_list(client, server, NULL);
267 fatal("no matching cipher found: client %s server %s",
269 if ((enc->cipher = cipher_by_name(name)) == NULL)
270 fatal("matching cipher is not supported: %s", name);
275 enc->key_len = cipher_keylen(enc->cipher);
276 enc->block_size = cipher_blocksize(enc->cipher);
280 choose_mac(Mac *mac, char *client, char *server)
282 char *name = match_list(client, server, NULL);
284 fatal("no matching mac found: client %s server %s",
286 if (mac_setup(mac, name) < 0)
287 fatal("unsupported mac %s", name);
288 /* truncate the key */
289 if (datafellows & SSH_BUG_HMAC)
297 choose_comp(Comp *comp, char *client, char *server)
299 char *name = match_list(client, server, NULL);
301 fatal("no matching comp found: client %s server %s", client, server);
302 if (strcmp(name, "zlib@openssh.com") == 0) {
303 comp->type = COMP_DELAYED;
304 } else if (strcmp(name, "zlib") == 0) {
305 comp->type = COMP_ZLIB;
306 } else if (strcmp(name, "none") == 0) {
307 comp->type = COMP_NONE;
309 fatal("unsupported comp %s", name);
315 choose_kex(Kex *k, char *client, char *server)
317 k->name = match_list(client, server, NULL);
319 fatal("Unable to negotiate a key exchange method");
320 if (strcmp(k->name, KEX_DH1) == 0) {
321 k->kex_type = KEX_DH_GRP1_SHA1;
322 k->evp_md = EVP_sha1();
323 } else if (strcmp(k->name, KEX_DH14) == 0) {
324 k->kex_type = KEX_DH_GRP14_SHA1;
325 k->evp_md = EVP_sha1();
326 } else if (strcmp(k->name, KEX_DHGEX_SHA1) == 0) {
327 k->kex_type = KEX_DH_GEX_SHA1;
328 k->evp_md = EVP_sha1();
329 #if OPENSSL_VERSION_NUMBER >= 0x00907000L
330 } else if (strcmp(k->name, KEX_DHGEX_SHA256) == 0) {
331 k->kex_type = KEX_DH_GEX_SHA256;
332 k->evp_md = evp_ssh_sha256();
335 } else if (strncmp(k->name, KEX_GSS_GEX_SHA1_ID,
336 sizeof(KEX_GSS_GEX_SHA1_ID) - 1) == 0) {
337 k->kex_type = KEX_GSS_GEX_SHA1;
338 k->evp_md = EVP_sha1();
339 } else if (strncmp(k->name, KEX_GSS_GRP1_SHA1_ID,
340 sizeof(KEX_GSS_GRP1_SHA1_ID) - 1) == 0) {
341 k->kex_type = KEX_GSS_GRP1_SHA1;
342 k->evp_md = EVP_sha1();
343 } else if (strncmp(k->name, KEX_GSS_GRP14_SHA1_ID,
344 sizeof(KEX_GSS_GRP14_SHA1_ID) - 1) == 0) {
345 k->kex_type = KEX_GSS_GRP14_SHA1;
346 k->evp_md = EVP_sha1();
349 fatal("bad kex alg %s", k->name);
353 choose_hostkeyalg(Kex *k, char *client, char *server)
355 char *hostkeyalg = match_list(client, server, NULL);
356 if (hostkeyalg == NULL)
357 fatal("no hostkey alg");
358 k->hostkey_type = key_type_from_name(hostkeyalg);
359 if (k->hostkey_type == KEY_UNSPEC)
360 fatal("bad hostkey alg '%s'", hostkeyalg);
365 proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX])
367 static int check[] = {
368 PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1
373 for (idx = &check[0]; *idx != -1; idx++) {
374 if ((p = strchr(my[*idx], ',')) != NULL)
376 if ((p = strchr(peer[*idx], ',')) != NULL)
378 if (strcmp(my[*idx], peer[*idx]) != 0) {
379 debug2("proposal mismatch: my %s peer %s",
380 my[*idx], peer[*idx]);
384 debug2("proposals match");
389 kex_choose_conf(Kex *kex)
393 char **cprop, **sprop;
394 int nenc, nmac, ncomp;
395 u_int mode, ctos, need;
396 int first_kex_follows, type;
398 my = kex_buf2prop(&kex->my, NULL);
399 peer = kex_buf2prop(&kex->peer, &first_kex_follows);
409 /* Algorithm Negotiation */
410 for (mode = 0; mode < MODE_MAX; mode++) {
411 newkeys = xcalloc(1, sizeof(*newkeys));
412 kex->newkeys[mode] = newkeys;
413 ctos = (!kex->server && mode == MODE_OUT) ||
414 (kex->server && mode == MODE_IN);
415 nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC;
416 nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC;
417 ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC;
418 choose_enc (&newkeys->enc, cprop[nenc], sprop[nenc]);
419 choose_mac (&newkeys->mac, cprop[nmac], sprop[nmac]);
420 choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]);
421 debug("kex: %s %s %s %s",
422 ctos ? "client->server" : "server->client",
427 choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]);
428 choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
429 sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]);
431 for (mode = 0; mode < MODE_MAX; mode++) {
432 newkeys = kex->newkeys[mode];
433 if (need < newkeys->enc.key_len)
434 need = newkeys->enc.key_len;
435 if (need < newkeys->enc.block_size)
436 need = newkeys->enc.block_size;
437 if (need < newkeys->mac.key_len)
438 need = newkeys->mac.key_len;
440 /* XXX need runden? */
443 /* ignore the next message if the proposals do not match */
444 if (first_kex_follows && !proposals_match(my, peer) &&
445 !(datafellows & SSH_BUG_FIRSTKEX)) {
446 type = packet_read();
447 debug2("skipping next packet (type %u)", type);
455 derive_key(Kex *kex, int id, u_int need, u_char *hash, u_int hashlen,
456 BIGNUM *shared_secret)
465 if ((mdsz = EVP_MD_size(kex->evp_md)) <= 0)
466 fatal("bad kex md size %d", mdsz);
467 digest = xmalloc(roundup(need, mdsz));
470 buffer_put_bignum2(&b, shared_secret);
472 /* K1 = HASH(K || H || "A" || session_id) */
473 EVP_DigestInit(&md, kex->evp_md);
474 if (!(datafellows & SSH_BUG_DERIVEKEY))
475 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
476 EVP_DigestUpdate(&md, hash, hashlen);
477 EVP_DigestUpdate(&md, &c, 1);
478 EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len);
479 EVP_DigestFinal(&md, digest, NULL);
483 * Kn = HASH(K || H || K1 || K2 || ... || Kn-1)
484 * Key = K1 || K2 || ... || Kn
486 for (have = mdsz; need > have; have += mdsz) {
487 EVP_DigestInit(&md, kex->evp_md);
488 if (!(datafellows & SSH_BUG_DERIVEKEY))
489 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
490 EVP_DigestUpdate(&md, hash, hashlen);
491 EVP_DigestUpdate(&md, digest, have);
492 EVP_DigestFinal(&md, digest + have, NULL);
496 fprintf(stderr, "key '%c'== ", c);
497 dump_digest("key", digest, need);
502 Newkeys *current_keys[MODE_MAX];
506 kex_derive_keys(Kex *kex, u_char *hash, u_int hashlen, BIGNUM *shared_secret)
511 for (i = 0; i < NKEYS; i++) {
512 keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, hashlen,
516 debug2("kex_derive_keys");
517 for (mode = 0; mode < MODE_MAX; mode++) {
518 current_keys[mode] = kex->newkeys[mode];
519 kex->newkeys[mode] = NULL;
520 ctos = (!kex->server && mode == MODE_OUT) ||
521 (kex->server && mode == MODE_IN);
522 current_keys[mode]->enc.iv = keys[ctos ? 0 : 1];
523 current_keys[mode]->enc.key = keys[ctos ? 2 : 3];
524 current_keys[mode]->mac.key = keys[ctos ? 4 : 5];
529 kex_get_newkeys(int mode)
533 ret = current_keys[mode];
534 current_keys[mode] = NULL;
539 derive_ssh1_session_id(BIGNUM *host_modulus, BIGNUM *server_modulus,
540 u_int8_t cookie[8], u_int8_t id[16])
542 const EVP_MD *evp_md = EVP_md5();
544 u_int8_t nbuf[2048], obuf[EVP_MAX_MD_SIZE];
547 EVP_DigestInit(&md, evp_md);
549 len = BN_num_bytes(host_modulus);
550 if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
551 fatal("%s: bad host modulus (len %d)", __func__, len);
552 BN_bn2bin(host_modulus, nbuf);
553 EVP_DigestUpdate(&md, nbuf, len);
555 len = BN_num_bytes(server_modulus);
556 if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
557 fatal("%s: bad server modulus (len %d)", __func__, len);
558 BN_bn2bin(server_modulus, nbuf);
559 EVP_DigestUpdate(&md, nbuf, len);
561 EVP_DigestUpdate(&md, cookie, 8);
563 EVP_DigestFinal(&md, obuf, NULL);
564 memcpy(id, obuf, 16);
566 memset(nbuf, 0, sizeof(nbuf));
567 memset(obuf, 0, sizeof(obuf));
568 memset(&md, 0, sizeof(md));
571 #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH)
573 dump_digest(char *msg, u_char *digest, int len)
577 fprintf(stderr, "%s\n", msg);
578 for (i = 0; i < len; i++) {
579 fprintf(stderr, "%02x", digest[i]);
581 fprintf(stderr, "\n");
583 fprintf(stderr, " ");
585 fprintf(stderr, "\n");