1 /* $OpenBSD: kex.c,v 1.98 2014/02/02 03:44:31 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>
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 *);
72 static const struct kexalg kexalgs[] = {
73 { KEX_DH1, KEX_DH_GRP1_SHA1, 0, SSH_DIGEST_SHA1 },
74 { KEX_DH14, KEX_DH_GRP14_SHA1, 0, SSH_DIGEST_SHA1 },
75 { KEX_DHGEX_SHA1, KEX_DH_GEX_SHA1, 0, SSH_DIGEST_SHA1 },
76 #ifdef HAVE_EVP_SHA256
77 { KEX_DHGEX_SHA256, KEX_DH_GEX_SHA256, 0, SSH_DIGEST_SHA256 },
79 #ifdef OPENSSL_HAS_ECC
80 { KEX_ECDH_SHA2_NISTP256, KEX_ECDH_SHA2,
81 NID_X9_62_prime256v1, SSH_DIGEST_SHA256 },
82 { KEX_ECDH_SHA2_NISTP384, KEX_ECDH_SHA2, NID_secp384r1,
84 # ifdef OPENSSL_HAS_NISTP521
85 { KEX_ECDH_SHA2_NISTP521, KEX_ECDH_SHA2, NID_secp521r1,
89 { KEX_DH1, KEX_DH_GRP1_SHA1, 0, SSH_DIGEST_SHA1 },
90 #ifdef HAVE_EVP_SHA256
91 { KEX_CURVE25519_SHA256, KEX_C25519_SHA256, 0, SSH_DIGEST_SHA256 },
97 kex_alg_list(char sep)
100 size_t nlen, rlen = 0;
101 const struct kexalg *k;
103 for (k = kexalgs; k->name != NULL; k++) {
106 nlen = strlen(k->name);
107 ret = xrealloc(ret, 1, rlen + nlen + 2);
108 memcpy(ret + rlen, k->name, nlen + 1);
114 static const struct kexalg *
115 kex_alg_by_name(const char *name)
117 const struct kexalg *k;
119 for (k = kexalgs; k->name != NULL; k++) {
120 if (strcmp(k->name, name) == 0)
126 /* Validate KEX method name list */
128 kex_names_valid(const char *names)
132 if (names == NULL || strcmp(names, "") == 0)
134 s = cp = xstrdup(names);
135 for ((p = strsep(&cp, ",")); p && *p != '\0';
136 (p = strsep(&cp, ","))) {
137 if (kex_alg_by_name(p) == NULL) {
138 error("Unsupported KEX algorithm \"%.100s\"", p);
143 debug3("kex names ok: [%s]", names);
148 /* put algorithm proposal into buffer */
150 kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX])
156 * add a dummy cookie, the cookie will be overwritten by
157 * kex_send_kexinit(), each time a kexinit is set
159 for (i = 0; i < KEX_COOKIE_LEN; i++)
160 buffer_put_char(b, 0);
161 for (i = 0; i < PROPOSAL_MAX; i++)
162 buffer_put_cstring(b, proposal[i]);
163 buffer_put_char(b, 0); /* first_kex_packet_follows */
164 buffer_put_int(b, 0); /* uint32 reserved */
167 /* parse buffer and return algorithm proposal */
169 kex_buf2prop(Buffer *raw, int *first_kex_follows)
175 proposal = xcalloc(PROPOSAL_MAX, sizeof(char *));
178 buffer_append(&b, buffer_ptr(raw), buffer_len(raw));
180 for (i = 0; i < KEX_COOKIE_LEN; i++)
182 /* extract kex init proposal strings */
183 for (i = 0; i < PROPOSAL_MAX; i++) {
184 proposal[i] = buffer_get_cstring(&b,NULL);
185 debug2("kex_parse_kexinit: %s", proposal[i]);
187 /* first kex follows / reserved */
188 i = buffer_get_char(&b);
189 if (first_kex_follows != NULL)
190 *first_kex_follows = i;
191 debug2("kex_parse_kexinit: first_kex_follows %d ", i);
192 i = buffer_get_int(&b);
193 debug2("kex_parse_kexinit: reserved %u ", i);
199 kex_prop_free(char **proposal)
203 for (i = 0; i < PROPOSAL_MAX; i++)
210 kex_protocol_error(int type, u_int32_t seq, void *ctxt)
212 error("Hm, kex protocol error: type %d seq %u", type, seq);
216 kex_reset_dispatch(void)
218 dispatch_range(SSH2_MSG_TRANSPORT_MIN,
219 SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error);
220 dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit);
226 kex_reset_dispatch();
228 packet_start(SSH2_MSG_NEWKEYS);
230 /* packet_write_wait(); */
231 debug("SSH2_MSG_NEWKEYS sent");
233 debug("expecting SSH2_MSG_NEWKEYS");
234 packet_read_expect(SSH2_MSG_NEWKEYS);
236 debug("SSH2_MSG_NEWKEYS received");
239 buffer_clear(&kex->peer);
240 /* buffer_clear(&kex->my); */
241 kex->flags &= ~KEX_INIT_SENT;
247 kex_send_kexinit(Kex *kex)
254 error("kex_send_kexinit: no kex, cannot rekey");
257 if (kex->flags & KEX_INIT_SENT) {
258 debug("KEX_INIT_SENT");
263 /* generate a random cookie */
264 if (buffer_len(&kex->my) < KEX_COOKIE_LEN)
265 fatal("kex_send_kexinit: kex proposal too short");
266 cookie = buffer_ptr(&kex->my);
267 for (i = 0; i < KEX_COOKIE_LEN; i++) {
273 packet_start(SSH2_MSG_KEXINIT);
274 packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my));
276 debug("SSH2_MSG_KEXINIT sent");
277 kex->flags |= KEX_INIT_SENT;
282 kex_input_kexinit(int type, u_int32_t seq, void *ctxt)
286 Kex *kex = (Kex *)ctxt;
288 debug("SSH2_MSG_KEXINIT received");
290 fatal("kex_input_kexinit: no kex, cannot rekey");
292 ptr = packet_get_raw(&dlen);
293 buffer_append(&kex->peer, ptr, dlen);
296 for (i = 0; i < KEX_COOKIE_LEN; i++)
298 for (i = 0; i < PROPOSAL_MAX; i++)
299 free(packet_get_string(NULL));
301 * XXX RFC4253 sec 7: "each side MAY guess" - currently no supported
302 * KEX method has the server move first, but a server might be using
303 * a custom method or one that we otherwise don't support. We should
304 * be prepared to remember first_kex_follows here so we can eat a
306 * XXX2 - RFC4253 is kind of ambiguous on what first_kex_follows means
307 * for cases where the server *doesn't* go first. I guess we should
308 * ignore it when it is set for these cases, which is what we do now.
310 (void) packet_get_char(); /* first_kex_follows */
311 (void) packet_get_int(); /* reserved */
314 kex_kexinit_finish(kex);
318 kex_setup(char *proposal[PROPOSAL_MAX])
322 kex = xcalloc(1, sizeof(*kex));
323 buffer_init(&kex->peer);
324 buffer_init(&kex->my);
325 kex_prop2buf(&kex->my, proposal);
328 kex_send_kexinit(kex); /* we start */
329 kex_reset_dispatch();
335 kex_kexinit_finish(Kex *kex)
337 if (!(kex->flags & KEX_INIT_SENT))
338 kex_send_kexinit(kex);
340 kex_choose_conf(kex);
342 if (kex->kex_type >= 0 && kex->kex_type < KEX_MAX &&
343 kex->kex[kex->kex_type] != NULL) {
344 (kex->kex[kex->kex_type])(kex);
346 fatal("Unsupported key exchange %d", kex->kex_type);
351 choose_enc(Enc *enc, char *client, char *server)
353 char *name = match_list(client, server, NULL);
355 fatal("no matching cipher found: client %s server %s",
357 if ((enc->cipher = cipher_by_name(name)) == NULL)
358 fatal("matching cipher is not supported: %s", name);
362 enc->iv_len = cipher_ivlen(enc->cipher);
364 enc->key_len = cipher_keylen(enc->cipher);
365 enc->block_size = cipher_blocksize(enc->cipher);
369 choose_mac(Mac *mac, char *client, char *server)
371 char *name = match_list(client, server, NULL);
373 fatal("no matching mac found: client %s server %s",
375 if (mac_setup(mac, name) < 0)
376 fatal("unsupported mac %s", name);
377 /* truncate the key */
378 if (datafellows & SSH_BUG_HMAC)
386 choose_comp(Comp *comp, char *client, char *server)
388 char *name = match_list(client, server, NULL);
390 fatal("no matching comp found: client %s server %s", client, server);
391 if (strcmp(name, "zlib@openssh.com") == 0) {
392 comp->type = COMP_DELAYED;
393 } else if (strcmp(name, "zlib") == 0) {
394 comp->type = COMP_ZLIB;
395 } else if (strcmp(name, "none") == 0) {
396 comp->type = COMP_NONE;
398 fatal("unsupported comp %s", name);
404 choose_kex(Kex *k, char *client, char *server)
406 const struct kexalg *kexalg;
408 k->name = match_list(client, server, NULL);
410 fatal("Unable to negotiate a key exchange method");
411 if ((kexalg = kex_alg_by_name(k->name)) == NULL)
412 fatal("unsupported kex alg %s", k->name);
413 k->kex_type = kexalg->type;
414 k->hash_alg = kexalg->hash_alg;
415 k->ec_nid = kexalg->ec_nid;
419 choose_hostkeyalg(Kex *k, char *client, char *server)
421 char *hostkeyalg = match_list(client, server, NULL);
422 if (hostkeyalg == NULL)
423 fatal("no hostkey alg");
424 k->hostkey_type = key_type_from_name(hostkeyalg);
425 if (k->hostkey_type == KEY_UNSPEC)
426 fatal("bad hostkey alg '%s'", hostkeyalg);
431 proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX])
433 static int check[] = {
434 PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1
439 for (idx = &check[0]; *idx != -1; idx++) {
440 if ((p = strchr(my[*idx], ',')) != NULL)
442 if ((p = strchr(peer[*idx], ',')) != NULL)
444 if (strcmp(my[*idx], peer[*idx]) != 0) {
445 debug2("proposal mismatch: my %s peer %s",
446 my[*idx], peer[*idx]);
450 debug2("proposals match");
455 kex_choose_conf(Kex *kex)
459 char **cprop, **sprop;
460 int nenc, nmac, ncomp;
461 u_int mode, ctos, need, dh_need, authlen;
462 int first_kex_follows, type;
464 my = kex_buf2prop(&kex->my, NULL);
465 peer = kex_buf2prop(&kex->peer, &first_kex_follows);
475 /* Check whether server offers roaming */
478 roaming = match_list(KEX_RESUME, peer[PROPOSAL_KEX_ALGS], NULL);
485 /* Algorithm Negotiation */
486 for (mode = 0; mode < MODE_MAX; mode++) {
487 newkeys = xcalloc(1, sizeof(*newkeys));
488 kex->newkeys[mode] = newkeys;
489 ctos = (!kex->server && mode == MODE_OUT) ||
490 (kex->server && mode == MODE_IN);
491 nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC;
492 nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC;
493 ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC;
494 choose_enc(&newkeys->enc, cprop[nenc], sprop[nenc]);
495 /* ignore mac for authenticated encryption */
496 authlen = cipher_authlen(newkeys->enc.cipher);
498 choose_mac(&newkeys->mac, cprop[nmac], sprop[nmac]);
499 choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]);
500 debug("kex: %s %s %s %s",
501 ctos ? "client->server" : "server->client",
503 authlen == 0 ? newkeys->mac.name : "<implicit>",
506 choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]);
507 choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
508 sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]);
510 for (mode = 0; mode < MODE_MAX; mode++) {
511 newkeys = kex->newkeys[mode];
512 need = MAX(need, newkeys->enc.key_len);
513 need = MAX(need, newkeys->enc.block_size);
514 need = MAX(need, newkeys->enc.iv_len);
515 need = MAX(need, newkeys->mac.key_len);
516 dh_need = MAX(dh_need, cipher_seclen(newkeys->enc.cipher));
517 dh_need = MAX(dh_need, newkeys->enc.block_size);
518 dh_need = MAX(dh_need, newkeys->enc.iv_len);
519 dh_need = MAX(dh_need, newkeys->mac.key_len);
521 /* XXX need runden? */
523 kex->dh_need = dh_need;
525 /* ignore the next message if the proposals do not match */
526 if (first_kex_follows && !proposals_match(my, peer) &&
527 !(datafellows & SSH_BUG_FIRSTKEX)) {
528 type = packet_read();
529 debug2("skipping next packet (type %u)", type);
537 derive_key(Kex *kex, int id, u_int need, u_char *hash, u_int hashlen,
538 const u_char *shared_secret, u_int slen)
541 struct ssh_digest_ctx *hashctx;
547 if ((mdsz = ssh_digest_bytes(kex->hash_alg)) == 0)
548 fatal("bad kex md size %zu", mdsz);
549 digest = xmalloc(roundup(need, mdsz));
552 buffer_append(&b, shared_secret, slen);
554 /* K1 = HASH(K || H || "A" || session_id) */
555 if ((hashctx = ssh_digest_start(kex->hash_alg)) == NULL)
556 fatal("%s: ssh_digest_start failed", __func__);
557 if (ssh_digest_update_buffer(hashctx, &b) != 0 ||
558 ssh_digest_update(hashctx, hash, hashlen) != 0 ||
559 ssh_digest_update(hashctx, &c, 1) != 0 ||
560 ssh_digest_update(hashctx, kex->session_id,
561 kex->session_id_len) != 0)
562 fatal("%s: ssh_digest_update failed", __func__);
563 if (ssh_digest_final(hashctx, digest, mdsz) != 0)
564 fatal("%s: ssh_digest_final failed", __func__);
565 ssh_digest_free(hashctx);
569 * Kn = HASH(K || H || K1 || K2 || ... || Kn-1)
570 * Key = K1 || K2 || ... || Kn
572 for (have = mdsz; need > have; have += mdsz) {
573 if ((hashctx = ssh_digest_start(kex->hash_alg)) == NULL)
574 fatal("%s: ssh_digest_start failed", __func__);
575 if (ssh_digest_update_buffer(hashctx, &b) != 0 ||
576 ssh_digest_update(hashctx, hash, hashlen) != 0 ||
577 ssh_digest_update(hashctx, digest, have) != 0)
578 fatal("%s: ssh_digest_update failed", __func__);
579 if (ssh_digest_final(hashctx, digest + have, mdsz) != 0)
580 fatal("%s: ssh_digest_final failed", __func__);
581 ssh_digest_free(hashctx);
585 fprintf(stderr, "key '%c'== ", c);
586 dump_digest("key", digest, need);
591 Newkeys *current_keys[MODE_MAX];
595 kex_derive_keys(Kex *kex, u_char *hash, u_int hashlen,
596 const u_char *shared_secret, u_int slen)
601 for (i = 0; i < NKEYS; i++) {
602 keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, hashlen,
603 shared_secret, slen);
606 debug2("kex_derive_keys");
607 for (mode = 0; mode < MODE_MAX; mode++) {
608 current_keys[mode] = kex->newkeys[mode];
609 kex->newkeys[mode] = NULL;
610 ctos = (!kex->server && mode == MODE_OUT) ||
611 (kex->server && mode == MODE_IN);
612 current_keys[mode]->enc.iv = keys[ctos ? 0 : 1];
613 current_keys[mode]->enc.key = keys[ctos ? 2 : 3];
614 current_keys[mode]->mac.key = keys[ctos ? 4 : 5];
619 kex_derive_keys_bn(Kex *kex, u_char *hash, u_int hashlen, const BIGNUM *secret)
621 Buffer shared_secret;
623 buffer_init(&shared_secret);
624 buffer_put_bignum2(&shared_secret, secret);
625 kex_derive_keys(kex, hash, hashlen,
626 buffer_ptr(&shared_secret), buffer_len(&shared_secret));
627 buffer_free(&shared_secret);
631 kex_get_newkeys(int mode)
635 ret = current_keys[mode];
636 current_keys[mode] = NULL;
641 derive_ssh1_session_id(BIGNUM *host_modulus, BIGNUM *server_modulus,
642 u_int8_t cookie[8], u_int8_t id[16])
644 u_int8_t nbuf[2048], obuf[SSH_DIGEST_MAX_LENGTH];
646 struct ssh_digest_ctx *hashctx;
648 if ((hashctx = ssh_digest_start(SSH_DIGEST_MD5)) == NULL)
649 fatal("%s: ssh_digest_start", __func__);
651 len = BN_num_bytes(host_modulus);
652 if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
653 fatal("%s: bad host modulus (len %d)", __func__, len);
654 BN_bn2bin(host_modulus, nbuf);
655 if (ssh_digest_update(hashctx, nbuf, len) != 0)
656 fatal("%s: ssh_digest_update failed", __func__);
658 len = BN_num_bytes(server_modulus);
659 if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
660 fatal("%s: bad server modulus (len %d)", __func__, len);
661 BN_bn2bin(server_modulus, nbuf);
662 if (ssh_digest_update(hashctx, nbuf, len) != 0 ||
663 ssh_digest_update(hashctx, cookie, 8) != 0)
664 fatal("%s: ssh_digest_update failed", __func__);
665 if (ssh_digest_final(hashctx, obuf, sizeof(obuf)) != 0)
666 fatal("%s: ssh_digest_final failed", __func__);
667 memcpy(id, obuf, ssh_digest_bytes(SSH_DIGEST_MD5));
669 explicit_bzero(nbuf, sizeof(nbuf));
670 explicit_bzero(obuf, sizeof(obuf));
673 #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH) || defined(DEBUG_KEXECDH)
675 dump_digest(char *msg, u_char *digest, int len)
679 fprintf(stderr, "%s\n", msg);
680 for (i = 0; i < len; i++) {
681 fprintf(stderr, "%02x", digest[i]);
683 fprintf(stderr, "\n");
685 fprintf(stderr, " ");
687 fprintf(stderr, "\n");