1 /* $OpenBSD: kex.c,v 1.88 2013/01/08 18:49:04 markus Exp $ */
4 * Copyright (c) 2000, 2001 Markus Friedl. All rights reserved.
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
9 * 1. Redistributions of source code must retain the above copyright
10 * notice, this list of conditions and the following disclaimer.
11 * 2. Redistributions in binary form must reproduce the above copyright
12 * notice, this list of conditions and the following disclaimer in the
13 * documentation and/or other materials provided with the distribution.
15 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
16 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
17 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
18 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
19 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
20 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
21 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
22 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
23 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
24 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
29 #include <sys/param.h>
37 #include <openssl/crypto.h>
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 /* Validate KEX method name list */
68 kex_names_valid(const char *names)
72 if (names == NULL || strcmp(names, "") == 0)
74 s = cp = xstrdup(names);
75 for ((p = strsep(&cp, ",")); p && *p != '\0';
76 (p = strsep(&cp, ","))) {
77 if (strcmp(p, KEX_DHGEX_SHA256) != 0 &&
78 strcmp(p, KEX_DHGEX_SHA1) != 0 &&
79 strcmp(p, KEX_DH14) != 0 &&
80 strcmp(p, KEX_DH1) != 0 &&
81 (strncmp(p, KEX_ECDH_SHA2_STEM,
82 sizeof(KEX_ECDH_SHA2_STEM) - 1) != 0 ||
83 kex_ecdh_name_to_nid(p) == -1)) {
84 error("Unsupported KEX algorithm \"%.100s\"", p);
89 debug3("kex names ok: [%s]", names);
94 /* put algorithm proposal into buffer. */
95 #ifndef NONE_CIPHER_ENABLED
98 /* Also used in sshconnect2.c. */
101 kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX])
107 * add a dummy cookie, the cookie will be overwritten by
108 * kex_send_kexinit(), each time a kexinit is set
110 for (i = 0; i < KEX_COOKIE_LEN; i++)
111 buffer_put_char(b, 0);
112 for (i = 0; i < PROPOSAL_MAX; i++)
113 buffer_put_cstring(b, proposal[i]);
114 buffer_put_char(b, 0); /* first_kex_packet_follows */
115 buffer_put_int(b, 0); /* uint32 reserved */
118 /* parse buffer and return algorithm proposal */
120 kex_buf2prop(Buffer *raw, int *first_kex_follows)
126 proposal = xcalloc(PROPOSAL_MAX, sizeof(char *));
129 buffer_append(&b, buffer_ptr(raw), buffer_len(raw));
131 for (i = 0; i < KEX_COOKIE_LEN; i++)
133 /* extract kex init proposal strings */
134 for (i = 0; i < PROPOSAL_MAX; i++) {
135 proposal[i] = buffer_get_cstring(&b,NULL);
136 debug2("kex_parse_kexinit: %s", proposal[i]);
138 /* first kex follows / reserved */
139 i = buffer_get_char(&b);
140 if (first_kex_follows != NULL)
141 *first_kex_follows = i;
142 debug2("kex_parse_kexinit: first_kex_follows %d ", i);
143 i = buffer_get_int(&b);
144 debug2("kex_parse_kexinit: reserved %u ", i);
150 kex_prop_free(char **proposal)
154 for (i = 0; i < PROPOSAL_MAX; i++)
161 kex_protocol_error(int type, u_int32_t seq, void *ctxt)
163 error("Hm, kex protocol error: type %d seq %u", type, seq);
167 kex_reset_dispatch(void)
169 dispatch_range(SSH2_MSG_TRANSPORT_MIN,
170 SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error);
171 dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit);
177 kex_reset_dispatch();
179 packet_start(SSH2_MSG_NEWKEYS);
181 /* packet_write_wait(); */
182 debug("SSH2_MSG_NEWKEYS sent");
184 debug("expecting SSH2_MSG_NEWKEYS");
185 packet_read_expect(SSH2_MSG_NEWKEYS);
187 debug("SSH2_MSG_NEWKEYS received");
190 buffer_clear(&kex->peer);
191 /* buffer_clear(&kex->my); */
192 kex->flags &= ~KEX_INIT_SENT;
198 kex_send_kexinit(Kex *kex)
205 error("kex_send_kexinit: no kex, cannot rekey");
208 if (kex->flags & KEX_INIT_SENT) {
209 debug("KEX_INIT_SENT");
214 /* generate a random cookie */
215 if (buffer_len(&kex->my) < KEX_COOKIE_LEN)
216 fatal("kex_send_kexinit: kex proposal too short");
217 cookie = buffer_ptr(&kex->my);
218 for (i = 0; i < KEX_COOKIE_LEN; i++) {
224 packet_start(SSH2_MSG_KEXINIT);
225 packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my));
227 debug("SSH2_MSG_KEXINIT sent");
228 kex->flags |= KEX_INIT_SENT;
233 kex_input_kexinit(int type, u_int32_t seq, void *ctxt)
237 Kex *kex = (Kex *)ctxt;
239 debug("SSH2_MSG_KEXINIT received");
241 fatal("kex_input_kexinit: no kex, cannot rekey");
243 ptr = packet_get_raw(&dlen);
244 buffer_append(&kex->peer, ptr, dlen);
247 for (i = 0; i < KEX_COOKIE_LEN; i++)
249 for (i = 0; i < PROPOSAL_MAX; i++)
250 xfree(packet_get_string(NULL));
252 * XXX RFC4253 sec 7: "each side MAY guess" - currently no supported
253 * KEX method has the server move first, but a server might be using
254 * a custom method or one that we otherwise don't support. We should
255 * be prepared to remember first_kex_follows here so we can eat a
257 * XXX2 - RFC4253 is kind of ambiguous on what first_kex_follows means
258 * for cases where the server *doesn't* go first. I guess we should
259 * ignore it when it is set for these cases, which is what we do now.
261 (void) packet_get_char(); /* first_kex_follows */
262 (void) packet_get_int(); /* reserved */
265 kex_kexinit_finish(kex);
269 kex_setup(char *proposal[PROPOSAL_MAX])
273 kex = xcalloc(1, sizeof(*kex));
274 buffer_init(&kex->peer);
275 buffer_init(&kex->my);
276 kex_prop2buf(&kex->my, proposal);
279 kex_send_kexinit(kex); /* we start */
280 kex_reset_dispatch();
286 kex_kexinit_finish(Kex *kex)
288 if (!(kex->flags & KEX_INIT_SENT))
289 kex_send_kexinit(kex);
291 kex_choose_conf(kex);
293 if (kex->kex_type >= 0 && kex->kex_type < KEX_MAX &&
294 kex->kex[kex->kex_type] != NULL) {
295 (kex->kex[kex->kex_type])(kex);
297 fatal("Unsupported key exchange %d", kex->kex_type);
302 choose_enc(Enc *enc, char *client, char *server)
304 char *name = match_list(client, server, NULL);
306 fatal("no matching cipher found: client %s server %s",
308 if ((enc->cipher = cipher_by_name(name)) == NULL)
309 fatal("matching cipher is not supported: %s", name);
313 enc->iv_len = cipher_ivlen(enc->cipher);
315 enc->key_len = cipher_keylen(enc->cipher);
316 enc->block_size = cipher_blocksize(enc->cipher);
320 choose_mac(Mac *mac, char *client, char *server)
322 char *name = match_list(client, server, NULL);
324 fatal("no matching mac found: client %s server %s",
326 if (mac_setup(mac, name) < 0)
327 fatal("unsupported mac %s", name);
328 /* truncate the key */
329 if (datafellows & SSH_BUG_HMAC)
337 choose_comp(Comp *comp, char *client, char *server)
339 char *name = match_list(client, server, NULL);
341 fatal("no matching comp found: client %s server %s", client, server);
342 if (strcmp(name, "zlib@openssh.com") == 0) {
343 comp->type = COMP_DELAYED;
344 } else if (strcmp(name, "zlib") == 0) {
345 comp->type = COMP_ZLIB;
346 } else if (strcmp(name, "none") == 0) {
347 comp->type = COMP_NONE;
349 fatal("unsupported comp %s", name);
355 choose_kex(Kex *k, char *client, char *server)
357 k->name = match_list(client, server, NULL);
359 fatal("Unable to negotiate a key exchange method");
360 if (strcmp(k->name, KEX_DH1) == 0) {
361 k->kex_type = KEX_DH_GRP1_SHA1;
362 k->evp_md = EVP_sha1();
363 } else if (strcmp(k->name, KEX_DH14) == 0) {
364 k->kex_type = KEX_DH_GRP14_SHA1;
365 k->evp_md = EVP_sha1();
366 } else if (strcmp(k->name, KEX_DHGEX_SHA1) == 0) {
367 k->kex_type = KEX_DH_GEX_SHA1;
368 k->evp_md = EVP_sha1();
369 #if OPENSSL_VERSION_NUMBER >= 0x00907000L
370 } else if (strcmp(k->name, KEX_DHGEX_SHA256) == 0) {
371 k->kex_type = KEX_DH_GEX_SHA256;
372 k->evp_md = evp_ssh_sha256();
373 } else if (strncmp(k->name, KEX_ECDH_SHA2_STEM,
374 sizeof(KEX_ECDH_SHA2_STEM) - 1) == 0) {
375 k->kex_type = KEX_ECDH_SHA2;
376 k->evp_md = kex_ecdh_name_to_evpmd(k->name);
379 fatal("bad kex alg %s", k->name);
383 choose_hostkeyalg(Kex *k, char *client, char *server)
385 char *hostkeyalg = match_list(client, server, NULL);
386 if (hostkeyalg == NULL)
387 fatal("no hostkey alg");
388 k->hostkey_type = key_type_from_name(hostkeyalg);
389 if (k->hostkey_type == KEY_UNSPEC)
390 fatal("bad hostkey alg '%s'", hostkeyalg);
395 proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX])
397 static int check[] = {
398 PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1
403 for (idx = &check[0]; *idx != -1; idx++) {
404 if ((p = strchr(my[*idx], ',')) != NULL)
406 if ((p = strchr(peer[*idx], ',')) != NULL)
408 if (strcmp(my[*idx], peer[*idx]) != 0) {
409 debug2("proposal mismatch: my %s peer %s",
410 my[*idx], peer[*idx]);
414 debug2("proposals match");
419 kex_choose_conf(Kex *kex)
423 char **cprop, **sprop;
424 int nenc, nmac, ncomp;
425 u_int mode, ctos, need, authlen;
426 int first_kex_follows, type;
427 #ifdef NONE_CIPHER_ENABLED
431 my = kex_buf2prop(&kex->my, NULL);
432 peer = kex_buf2prop(&kex->peer, &first_kex_follows);
442 /* Check whether server offers roaming */
445 roaming = match_list(KEX_RESUME, peer[PROPOSAL_KEX_ALGS], NULL);
452 /* Algorithm Negotiation */
453 #ifdef NONE_CIPHER_ENABLED
454 auth_flag = packet_get_authentication_state();
455 debug ("AUTH STATE is %d", auth_flag);
457 for (mode = 0; mode < MODE_MAX; mode++) {
458 newkeys = xcalloc(1, sizeof(*newkeys));
459 kex->newkeys[mode] = newkeys;
460 ctos = (!kex->server && mode == MODE_OUT) ||
461 (kex->server && mode == MODE_IN);
462 nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC;
463 nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC;
464 ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC;
465 choose_enc(&newkeys->enc, cprop[nenc], sprop[nenc]);
466 /* ignore mac for authenticated encryption */
467 authlen = cipher_authlen(newkeys->enc.cipher);
469 choose_mac(&newkeys->mac, cprop[nmac], sprop[nmac]);
470 choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]);
471 #ifdef NONE_CIPHER_ENABLED
472 debug("REQUESTED ENC.NAME is '%s'", newkeys->enc.name);
473 if (strcmp(newkeys->enc.name, "none") == 0) {
474 debug("Requesting NONE. Authflag is %d", auth_flag);
476 debug("None requested post authentication.");
478 fatal("Pre-authentication none cipher requests "
482 debug("kex: %s %s %s %s",
483 ctos ? "client->server" : "server->client",
485 authlen == 0 ? newkeys->mac.name : "<implicit>",
488 choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]);
489 choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
490 sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]);
492 for (mode = 0; mode < MODE_MAX; mode++) {
493 newkeys = kex->newkeys[mode];
494 if (need < newkeys->enc.key_len)
495 need = newkeys->enc.key_len;
496 if (need < newkeys->enc.block_size)
497 need = newkeys->enc.block_size;
498 if (need < newkeys->enc.iv_len)
499 need = newkeys->enc.iv_len;
500 if (need < newkeys->mac.key_len)
501 need = newkeys->mac.key_len;
503 /* XXX need runden? */
506 /* ignore the next message if the proposals do not match */
507 if (first_kex_follows && !proposals_match(my, peer) &&
508 !(datafellows & SSH_BUG_FIRSTKEX)) {
509 type = packet_read();
510 debug2("skipping next packet (type %u)", type);
518 derive_key(Kex *kex, int id, u_int need, u_char *hash, u_int hashlen,
519 BIGNUM *shared_secret)
528 if ((mdsz = EVP_MD_size(kex->evp_md)) <= 0)
529 fatal("bad kex md size %d", mdsz);
530 digest = xmalloc(roundup(need, mdsz));
533 buffer_put_bignum2(&b, shared_secret);
535 /* K1 = HASH(K || H || "A" || session_id) */
536 EVP_DigestInit(&md, kex->evp_md);
537 if (!(datafellows & SSH_BUG_DERIVEKEY))
538 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
539 EVP_DigestUpdate(&md, hash, hashlen);
540 EVP_DigestUpdate(&md, &c, 1);
541 EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len);
542 EVP_DigestFinal(&md, digest, NULL);
546 * Kn = HASH(K || H || K1 || K2 || ... || Kn-1)
547 * Key = K1 || K2 || ... || Kn
549 for (have = mdsz; need > have; have += mdsz) {
550 EVP_DigestInit(&md, kex->evp_md);
551 if (!(datafellows & SSH_BUG_DERIVEKEY))
552 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
553 EVP_DigestUpdate(&md, hash, hashlen);
554 EVP_DigestUpdate(&md, digest, have);
555 EVP_DigestFinal(&md, digest + have, NULL);
559 fprintf(stderr, "key '%c'== ", c);
560 dump_digest("key", digest, need);
565 Newkeys *current_keys[MODE_MAX];
569 kex_derive_keys(Kex *kex, u_char *hash, u_int hashlen, BIGNUM *shared_secret)
574 for (i = 0; i < NKEYS; i++) {
575 keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, hashlen,
579 debug2("kex_derive_keys");
580 for (mode = 0; mode < MODE_MAX; mode++) {
581 current_keys[mode] = kex->newkeys[mode];
582 kex->newkeys[mode] = NULL;
583 ctos = (!kex->server && mode == MODE_OUT) ||
584 (kex->server && mode == MODE_IN);
585 current_keys[mode]->enc.iv = keys[ctos ? 0 : 1];
586 current_keys[mode]->enc.key = keys[ctos ? 2 : 3];
587 current_keys[mode]->mac.key = keys[ctos ? 4 : 5];
592 kex_get_newkeys(int mode)
596 ret = current_keys[mode];
597 current_keys[mode] = NULL;
602 derive_ssh1_session_id(BIGNUM *host_modulus, BIGNUM *server_modulus,
603 u_int8_t cookie[8], u_int8_t id[16])
605 const EVP_MD *evp_md = EVP_md5();
607 u_int8_t nbuf[2048], obuf[EVP_MAX_MD_SIZE];
610 EVP_DigestInit(&md, evp_md);
612 len = BN_num_bytes(host_modulus);
613 if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
614 fatal("%s: bad host modulus (len %d)", __func__, len);
615 BN_bn2bin(host_modulus, nbuf);
616 EVP_DigestUpdate(&md, nbuf, len);
618 len = BN_num_bytes(server_modulus);
619 if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
620 fatal("%s: bad server modulus (len %d)", __func__, len);
621 BN_bn2bin(server_modulus, nbuf);
622 EVP_DigestUpdate(&md, nbuf, len);
624 EVP_DigestUpdate(&md, cookie, 8);
626 EVP_DigestFinal(&md, obuf, NULL);
627 memcpy(id, obuf, 16);
629 memset(nbuf, 0, sizeof(nbuf));
630 memset(obuf, 0, sizeof(obuf));
631 memset(&md, 0, sizeof(md));
634 #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH) || defined(DEBUG_KEXECDH)
636 dump_digest(char *msg, u_char *digest, int len)
640 fprintf(stderr, "%s\n", msg);
641 for (i = 0; i < len; i++) {
642 fprintf(stderr, "%02x", digest[i]);
644 fprintf(stderr, "\n");
646 fprintf(stderr, " ");
648 fprintf(stderr, "\n");