1 /* $OpenBSD: kex.c,v 1.98 2014/02/02 03:44:31 djm 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.
30 #include <sys/param.h>
38 #include <openssl/crypto.h>
56 #if OPENSSL_VERSION_NUMBER >= 0x00907000L
57 # if defined(HAVE_EVP_SHA256)
58 # define evp_ssh_sha256 EVP_sha256
60 extern const EVP_MD *evp_ssh_sha256(void);
65 static void kex_kexinit_finish(Kex *);
66 static void kex_choose_conf(Kex *);
74 static const struct kexalg kexalgs[] = {
75 { KEX_DH1, KEX_DH_GRP1_SHA1, 0, SSH_DIGEST_SHA1 },
76 { KEX_DH14, KEX_DH_GRP14_SHA1, 0, SSH_DIGEST_SHA1 },
77 { KEX_DHGEX_SHA1, KEX_DH_GEX_SHA1, 0, SSH_DIGEST_SHA1 },
78 #ifdef HAVE_EVP_SHA256
79 { KEX_DHGEX_SHA256, KEX_DH_GEX_SHA256, 0, SSH_DIGEST_SHA256 },
81 #ifdef OPENSSL_HAS_ECC
82 { KEX_ECDH_SHA2_NISTP256, KEX_ECDH_SHA2,
83 NID_X9_62_prime256v1, SSH_DIGEST_SHA256 },
84 { KEX_ECDH_SHA2_NISTP384, KEX_ECDH_SHA2, NID_secp384r1,
86 # ifdef OPENSSL_HAS_NISTP521
87 { KEX_ECDH_SHA2_NISTP521, KEX_ECDH_SHA2, NID_secp521r1,
91 { KEX_DH1, KEX_DH_GRP1_SHA1, 0, SSH_DIGEST_SHA1 },
92 #ifdef HAVE_EVP_SHA256
93 { KEX_CURVE25519_SHA256, KEX_C25519_SHA256, 0, SSH_DIGEST_SHA256 },
99 kex_alg_list(char sep)
102 size_t nlen, rlen = 0;
103 const struct kexalg *k;
105 for (k = kexalgs; k->name != NULL; k++) {
108 nlen = strlen(k->name);
109 ret = xrealloc(ret, 1, rlen + nlen + 2);
110 memcpy(ret + rlen, k->name, nlen + 1);
116 static const struct kexalg *
117 kex_alg_by_name(const char *name)
119 const struct kexalg *k;
121 for (k = kexalgs; k->name != NULL; k++) {
122 if (strcmp(k->name, name) == 0)
128 /* Validate KEX method name list */
130 kex_names_valid(const char *names)
134 if (names == NULL || strcmp(names, "") == 0)
136 s = cp = xstrdup(names);
137 for ((p = strsep(&cp, ",")); p && *p != '\0';
138 (p = strsep(&cp, ","))) {
139 if (kex_alg_by_name(p) == NULL) {
140 error("Unsupported KEX algorithm \"%.100s\"", p);
145 debug3("kex names ok: [%s]", names);
150 /* put algorithm proposal into buffer. */
151 #ifndef NONE_CIPHER_ENABLED
154 /* Also used in sshconnect2.c. */
157 kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX])
163 * add a dummy cookie, the cookie will be overwritten by
164 * kex_send_kexinit(), each time a kexinit is set
166 for (i = 0; i < KEX_COOKIE_LEN; i++)
167 buffer_put_char(b, 0);
168 for (i = 0; i < PROPOSAL_MAX; i++)
169 buffer_put_cstring(b, proposal[i]);
170 buffer_put_char(b, 0); /* first_kex_packet_follows */
171 buffer_put_int(b, 0); /* uint32 reserved */
174 /* parse buffer and return algorithm proposal */
176 kex_buf2prop(Buffer *raw, int *first_kex_follows)
182 proposal = xcalloc(PROPOSAL_MAX, sizeof(char *));
185 buffer_append(&b, buffer_ptr(raw), buffer_len(raw));
187 for (i = 0; i < KEX_COOKIE_LEN; i++)
189 /* extract kex init proposal strings */
190 for (i = 0; i < PROPOSAL_MAX; i++) {
191 proposal[i] = buffer_get_cstring(&b,NULL);
192 debug2("kex_parse_kexinit: %s", proposal[i]);
194 /* first kex follows / reserved */
195 i = buffer_get_char(&b);
196 if (first_kex_follows != NULL)
197 *first_kex_follows = i;
198 debug2("kex_parse_kexinit: first_kex_follows %d ", i);
199 i = buffer_get_int(&b);
200 debug2("kex_parse_kexinit: reserved %u ", i);
206 kex_prop_free(char **proposal)
210 for (i = 0; i < PROPOSAL_MAX; i++)
217 kex_protocol_error(int type, u_int32_t seq, void *ctxt)
219 error("Hm, kex protocol error: type %d seq %u", type, seq);
223 kex_reset_dispatch(void)
225 dispatch_range(SSH2_MSG_TRANSPORT_MIN,
226 SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error);
227 dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit);
233 kex_reset_dispatch();
235 packet_start(SSH2_MSG_NEWKEYS);
237 /* packet_write_wait(); */
238 debug("SSH2_MSG_NEWKEYS sent");
240 debug("expecting SSH2_MSG_NEWKEYS");
241 packet_read_expect(SSH2_MSG_NEWKEYS);
243 debug("SSH2_MSG_NEWKEYS received");
246 buffer_clear(&kex->peer);
247 /* buffer_clear(&kex->my); */
248 kex->flags &= ~KEX_INIT_SENT;
254 kex_send_kexinit(Kex *kex)
261 error("kex_send_kexinit: no kex, cannot rekey");
264 if (kex->flags & KEX_INIT_SENT) {
265 debug("KEX_INIT_SENT");
270 /* generate a random cookie */
271 if (buffer_len(&kex->my) < KEX_COOKIE_LEN)
272 fatal("kex_send_kexinit: kex proposal too short");
273 cookie = buffer_ptr(&kex->my);
274 for (i = 0; i < KEX_COOKIE_LEN; i++) {
280 packet_start(SSH2_MSG_KEXINIT);
281 packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my));
283 debug("SSH2_MSG_KEXINIT sent");
284 kex->flags |= KEX_INIT_SENT;
289 kex_input_kexinit(int type, u_int32_t seq, void *ctxt)
293 Kex *kex = (Kex *)ctxt;
295 debug("SSH2_MSG_KEXINIT received");
297 fatal("kex_input_kexinit: no kex, cannot rekey");
299 ptr = packet_get_raw(&dlen);
300 buffer_append(&kex->peer, ptr, dlen);
303 for (i = 0; i < KEX_COOKIE_LEN; i++)
305 for (i = 0; i < PROPOSAL_MAX; i++)
306 free(packet_get_string(NULL));
308 * XXX RFC4253 sec 7: "each side MAY guess" - currently no supported
309 * KEX method has the server move first, but a server might be using
310 * a custom method or one that we otherwise don't support. We should
311 * be prepared to remember first_kex_follows here so we can eat a
313 * XXX2 - RFC4253 is kind of ambiguous on what first_kex_follows means
314 * for cases where the server *doesn't* go first. I guess we should
315 * ignore it when it is set for these cases, which is what we do now.
317 (void) packet_get_char(); /* first_kex_follows */
318 (void) packet_get_int(); /* reserved */
321 kex_kexinit_finish(kex);
325 kex_setup(char *proposal[PROPOSAL_MAX])
329 kex = xcalloc(1, sizeof(*kex));
330 buffer_init(&kex->peer);
331 buffer_init(&kex->my);
332 kex_prop2buf(&kex->my, proposal);
335 kex_send_kexinit(kex); /* we start */
336 kex_reset_dispatch();
342 kex_kexinit_finish(Kex *kex)
344 if (!(kex->flags & KEX_INIT_SENT))
345 kex_send_kexinit(kex);
347 kex_choose_conf(kex);
349 if (kex->kex_type >= 0 && kex->kex_type < KEX_MAX &&
350 kex->kex[kex->kex_type] != NULL) {
351 (kex->kex[kex->kex_type])(kex);
353 fatal("Unsupported key exchange %d", kex->kex_type);
358 choose_enc(Enc *enc, char *client, char *server)
360 char *name = match_list(client, server, NULL);
362 fatal("no matching cipher found: client %s server %s",
364 if ((enc->cipher = cipher_by_name(name)) == NULL)
365 fatal("matching cipher is not supported: %s", name);
369 enc->iv_len = cipher_ivlen(enc->cipher);
371 enc->key_len = cipher_keylen(enc->cipher);
372 enc->block_size = cipher_blocksize(enc->cipher);
376 choose_mac(Mac *mac, char *client, char *server)
378 char *name = match_list(client, server, NULL);
380 fatal("no matching mac found: client %s server %s",
382 if (mac_setup(mac, name) < 0)
383 fatal("unsupported mac %s", name);
384 /* truncate the key */
385 if (datafellows & SSH_BUG_HMAC)
393 choose_comp(Comp *comp, char *client, char *server)
395 char *name = match_list(client, server, NULL);
397 fatal("no matching comp found: client %s server %s", client, server);
398 if (strcmp(name, "zlib@openssh.com") == 0) {
399 comp->type = COMP_DELAYED;
400 } else if (strcmp(name, "zlib") == 0) {
401 comp->type = COMP_ZLIB;
402 } else if (strcmp(name, "none") == 0) {
403 comp->type = COMP_NONE;
405 fatal("unsupported comp %s", name);
411 choose_kex(Kex *k, char *client, char *server)
413 const struct kexalg *kexalg;
415 k->name = match_list(client, server, NULL);
417 fatal("Unable to negotiate a key exchange method");
418 if ((kexalg = kex_alg_by_name(k->name)) == NULL)
419 fatal("unsupported kex alg %s", k->name);
420 k->kex_type = kexalg->type;
421 k->hash_alg = kexalg->hash_alg;
422 k->ec_nid = kexalg->ec_nid;
426 choose_hostkeyalg(Kex *k, char *client, char *server)
428 char *hostkeyalg = match_list(client, server, NULL);
429 if (hostkeyalg == NULL)
430 fatal("no hostkey alg");
431 k->hostkey_type = key_type_from_name(hostkeyalg);
432 if (k->hostkey_type == KEY_UNSPEC)
433 fatal("bad hostkey alg '%s'", hostkeyalg);
438 proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX])
440 static int check[] = {
441 PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1
446 for (idx = &check[0]; *idx != -1; idx++) {
447 if ((p = strchr(my[*idx], ',')) != NULL)
449 if ((p = strchr(peer[*idx], ',')) != NULL)
451 if (strcmp(my[*idx], peer[*idx]) != 0) {
452 debug2("proposal mismatch: my %s peer %s",
453 my[*idx], peer[*idx]);
457 debug2("proposals match");
462 kex_choose_conf(Kex *kex)
466 char **cprop, **sprop;
467 int nenc, nmac, ncomp;
468 u_int mode, ctos, need, dh_need, authlen;
469 int first_kex_follows, type;
470 #ifdef NONE_CIPHER_ENABLED
474 my = kex_buf2prop(&kex->my, NULL);
475 peer = kex_buf2prop(&kex->peer, &first_kex_follows);
485 /* Check whether server offers roaming */
488 roaming = match_list(KEX_RESUME, peer[PROPOSAL_KEX_ALGS], NULL);
495 /* Algorithm Negotiation */
496 #ifdef NONE_CIPHER_ENABLED
497 auth_flag = packet_get_authentication_state();
498 debug ("AUTH STATE is %d", auth_flag);
500 for (mode = 0; mode < MODE_MAX; mode++) {
501 newkeys = xcalloc(1, sizeof(*newkeys));
502 kex->newkeys[mode] = newkeys;
503 ctos = (!kex->server && mode == MODE_OUT) ||
504 (kex->server && mode == MODE_IN);
505 nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC;
506 nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC;
507 ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC;
508 choose_enc(&newkeys->enc, cprop[nenc], sprop[nenc]);
509 /* ignore mac for authenticated encryption */
510 authlen = cipher_authlen(newkeys->enc.cipher);
512 choose_mac(&newkeys->mac, cprop[nmac], sprop[nmac]);
513 choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]);
514 #ifdef NONE_CIPHER_ENABLED
515 debug("REQUESTED ENC.NAME is '%s'", newkeys->enc.name);
516 if (strcmp(newkeys->enc.name, "none") == 0) {
517 debug("Requesting NONE. Authflag is %d", auth_flag);
519 debug("None requested post authentication.");
521 fatal("Pre-authentication none cipher requests "
525 debug("kex: %s %s %s %s",
526 ctos ? "client->server" : "server->client",
528 authlen == 0 ? newkeys->mac.name : "<implicit>",
531 choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]);
532 choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
533 sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]);
535 for (mode = 0; mode < MODE_MAX; mode++) {
536 newkeys = kex->newkeys[mode];
537 need = MAX(need, newkeys->enc.key_len);
538 need = MAX(need, newkeys->enc.block_size);
539 need = MAX(need, newkeys->enc.iv_len);
540 need = MAX(need, newkeys->mac.key_len);
541 dh_need = MAX(dh_need, cipher_seclen(newkeys->enc.cipher));
542 dh_need = MAX(dh_need, newkeys->enc.block_size);
543 dh_need = MAX(dh_need, newkeys->enc.iv_len);
544 dh_need = MAX(dh_need, newkeys->mac.key_len);
546 /* XXX need runden? */
548 kex->dh_need = dh_need;
550 /* ignore the next message if the proposals do not match */
551 if (first_kex_follows && !proposals_match(my, peer) &&
552 !(datafellows & SSH_BUG_FIRSTKEX)) {
553 type = packet_read();
554 debug2("skipping next packet (type %u)", type);
562 derive_key(Kex *kex, int id, u_int need, u_char *hash, u_int hashlen,
563 const u_char *shared_secret, u_int slen)
566 struct ssh_digest_ctx *hashctx;
572 if ((mdsz = ssh_digest_bytes(kex->hash_alg)) == 0)
573 fatal("bad kex md size %zu", mdsz);
574 digest = xmalloc(roundup(need, mdsz));
577 buffer_append(&b, shared_secret, slen);
579 /* K1 = HASH(K || H || "A" || session_id) */
580 if ((hashctx = ssh_digest_start(kex->hash_alg)) == NULL)
581 fatal("%s: ssh_digest_start failed", __func__);
582 if (ssh_digest_update_buffer(hashctx, &b) != 0 ||
583 ssh_digest_update(hashctx, hash, hashlen) != 0 ||
584 ssh_digest_update(hashctx, &c, 1) != 0 ||
585 ssh_digest_update(hashctx, kex->session_id,
586 kex->session_id_len) != 0)
587 fatal("%s: ssh_digest_update failed", __func__);
588 if (ssh_digest_final(hashctx, digest, mdsz) != 0)
589 fatal("%s: ssh_digest_final failed", __func__);
590 ssh_digest_free(hashctx);
594 * Kn = HASH(K || H || K1 || K2 || ... || Kn-1)
595 * Key = K1 || K2 || ... || Kn
597 for (have = mdsz; need > have; have += mdsz) {
598 if ((hashctx = ssh_digest_start(kex->hash_alg)) == NULL)
599 fatal("%s: ssh_digest_start failed", __func__);
600 if (ssh_digest_update_buffer(hashctx, &b) != 0 ||
601 ssh_digest_update(hashctx, hash, hashlen) != 0 ||
602 ssh_digest_update(hashctx, digest, have) != 0)
603 fatal("%s: ssh_digest_update failed", __func__);
604 if (ssh_digest_final(hashctx, digest + have, mdsz) != 0)
605 fatal("%s: ssh_digest_final failed", __func__);
606 ssh_digest_free(hashctx);
610 fprintf(stderr, "key '%c'== ", c);
611 dump_digest("key", digest, need);
616 Newkeys *current_keys[MODE_MAX];
620 kex_derive_keys(Kex *kex, u_char *hash, u_int hashlen,
621 const u_char *shared_secret, u_int slen)
626 for (i = 0; i < NKEYS; i++) {
627 keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, hashlen,
628 shared_secret, slen);
631 debug2("kex_derive_keys");
632 for (mode = 0; mode < MODE_MAX; mode++) {
633 current_keys[mode] = kex->newkeys[mode];
634 kex->newkeys[mode] = NULL;
635 ctos = (!kex->server && mode == MODE_OUT) ||
636 (kex->server && mode == MODE_IN);
637 current_keys[mode]->enc.iv = keys[ctos ? 0 : 1];
638 current_keys[mode]->enc.key = keys[ctos ? 2 : 3];
639 current_keys[mode]->mac.key = keys[ctos ? 4 : 5];
644 kex_derive_keys_bn(Kex *kex, u_char *hash, u_int hashlen, const BIGNUM *secret)
646 Buffer shared_secret;
648 buffer_init(&shared_secret);
649 buffer_put_bignum2(&shared_secret, secret);
650 kex_derive_keys(kex, hash, hashlen,
651 buffer_ptr(&shared_secret), buffer_len(&shared_secret));
652 buffer_free(&shared_secret);
656 kex_get_newkeys(int mode)
660 ret = current_keys[mode];
661 current_keys[mode] = NULL;
666 derive_ssh1_session_id(BIGNUM *host_modulus, BIGNUM *server_modulus,
667 u_int8_t cookie[8], u_int8_t id[16])
669 u_int8_t nbuf[2048], obuf[SSH_DIGEST_MAX_LENGTH];
671 struct ssh_digest_ctx *hashctx;
673 if ((hashctx = ssh_digest_start(SSH_DIGEST_MD5)) == NULL)
674 fatal("%s: ssh_digest_start", __func__);
676 len = BN_num_bytes(host_modulus);
677 if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
678 fatal("%s: bad host modulus (len %d)", __func__, len);
679 BN_bn2bin(host_modulus, nbuf);
680 if (ssh_digest_update(hashctx, nbuf, len) != 0)
681 fatal("%s: ssh_digest_update failed", __func__);
683 len = BN_num_bytes(server_modulus);
684 if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
685 fatal("%s: bad server modulus (len %d)", __func__, len);
686 BN_bn2bin(server_modulus, nbuf);
687 if (ssh_digest_update(hashctx, nbuf, len) != 0 ||
688 ssh_digest_update(hashctx, cookie, 8) != 0)
689 fatal("%s: ssh_digest_update failed", __func__);
690 if (ssh_digest_final(hashctx, obuf, sizeof(obuf)) != 0)
691 fatal("%s: ssh_digest_final failed", __func__);
692 memcpy(id, obuf, ssh_digest_bytes(SSH_DIGEST_MD5));
694 explicit_bzero(nbuf, sizeof(nbuf));
695 explicit_bzero(obuf, sizeof(obuf));
698 #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH) || defined(DEBUG_KEXECDH)
700 dump_digest(char *msg, u_char *digest, int len)
704 fprintf(stderr, "%s\n", msg);
705 for (i = 0; i < len; i++) {
706 fprintf(stderr, "%02x", digest[i]);
708 fprintf(stderr, "\n");
710 fprintf(stderr, " ");
712 fprintf(stderr, "\n");