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.
29 #include <sys/param.h>
37 #include <openssl/crypto.h>
55 #if OPENSSL_VERSION_NUMBER >= 0x00907000L
56 # if defined(HAVE_EVP_SHA256)
57 # define evp_ssh_sha256 EVP_sha256
59 extern const EVP_MD *evp_ssh_sha256(void);
64 static void kex_kexinit_finish(Kex *);
65 static void kex_choose_conf(Kex *);
73 static const struct kexalg kexalgs[] = {
74 { KEX_DH1, KEX_DH_GRP1_SHA1, 0, SSH_DIGEST_SHA1 },
75 { KEX_DH14, KEX_DH_GRP14_SHA1, 0, SSH_DIGEST_SHA1 },
76 { KEX_DHGEX_SHA1, KEX_DH_GEX_SHA1, 0, SSH_DIGEST_SHA1 },
77 #ifdef HAVE_EVP_SHA256
78 { KEX_DHGEX_SHA256, KEX_DH_GEX_SHA256, 0, SSH_DIGEST_SHA256 },
80 #ifdef OPENSSL_HAS_ECC
81 { KEX_ECDH_SHA2_NISTP256, KEX_ECDH_SHA2,
82 NID_X9_62_prime256v1, SSH_DIGEST_SHA256 },
83 { KEX_ECDH_SHA2_NISTP384, KEX_ECDH_SHA2, NID_secp384r1,
85 # ifdef OPENSSL_HAS_NISTP521
86 { KEX_ECDH_SHA2_NISTP521, KEX_ECDH_SHA2, NID_secp521r1,
90 { KEX_DH1, KEX_DH_GRP1_SHA1, 0, SSH_DIGEST_SHA1 },
91 #ifdef HAVE_EVP_SHA256
92 { KEX_CURVE25519_SHA256, KEX_C25519_SHA256, 0, SSH_DIGEST_SHA256 },
98 kex_alg_list(char sep)
101 size_t nlen, rlen = 0;
102 const struct kexalg *k;
104 for (k = kexalgs; k->name != NULL; k++) {
107 nlen = strlen(k->name);
108 ret = xrealloc(ret, 1, rlen + nlen + 2);
109 memcpy(ret + rlen, k->name, nlen + 1);
115 static const struct kexalg *
116 kex_alg_by_name(const char *name)
118 const struct kexalg *k;
120 for (k = kexalgs; k->name != NULL; k++) {
121 if (strcmp(k->name, name) == 0)
127 /* Validate KEX method name list */
129 kex_names_valid(const char *names)
133 if (names == NULL || strcmp(names, "") == 0)
135 s = cp = xstrdup(names);
136 for ((p = strsep(&cp, ",")); p && *p != '\0';
137 (p = strsep(&cp, ","))) {
138 if (kex_alg_by_name(p) == NULL) {
139 error("Unsupported KEX algorithm \"%.100s\"", p);
144 debug3("kex names ok: [%s]", names);
149 /* put algorithm proposal into buffer. */
150 #ifndef NONE_CIPHER_ENABLED
153 /* Also used in sshconnect2.c. */
156 kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX])
162 * add a dummy cookie, the cookie will be overwritten by
163 * kex_send_kexinit(), each time a kexinit is set
165 for (i = 0; i < KEX_COOKIE_LEN; i++)
166 buffer_put_char(b, 0);
167 for (i = 0; i < PROPOSAL_MAX; i++)
168 buffer_put_cstring(b, proposal[i]);
169 buffer_put_char(b, 0); /* first_kex_packet_follows */
170 buffer_put_int(b, 0); /* uint32 reserved */
173 /* parse buffer and return algorithm proposal */
175 kex_buf2prop(Buffer *raw, int *first_kex_follows)
181 proposal = xcalloc(PROPOSAL_MAX, sizeof(char *));
184 buffer_append(&b, buffer_ptr(raw), buffer_len(raw));
186 for (i = 0; i < KEX_COOKIE_LEN; i++)
188 /* extract kex init proposal strings */
189 for (i = 0; i < PROPOSAL_MAX; i++) {
190 proposal[i] = buffer_get_cstring(&b,NULL);
191 debug2("kex_parse_kexinit: %s", proposal[i]);
193 /* first kex follows / reserved */
194 i = buffer_get_char(&b);
195 if (first_kex_follows != NULL)
196 *first_kex_follows = i;
197 debug2("kex_parse_kexinit: first_kex_follows %d ", i);
198 i = buffer_get_int(&b);
199 debug2("kex_parse_kexinit: reserved %u ", i);
205 kex_prop_free(char **proposal)
209 for (i = 0; i < PROPOSAL_MAX; i++)
216 kex_protocol_error(int type, u_int32_t seq, void *ctxt)
218 error("Hm, kex protocol error: type %d seq %u", type, seq);
222 kex_reset_dispatch(void)
224 dispatch_range(SSH2_MSG_TRANSPORT_MIN,
225 SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error);
226 dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit);
232 kex_reset_dispatch();
234 packet_start(SSH2_MSG_NEWKEYS);
236 /* packet_write_wait(); */
237 debug("SSH2_MSG_NEWKEYS sent");
239 debug("expecting SSH2_MSG_NEWKEYS");
240 packet_read_expect(SSH2_MSG_NEWKEYS);
242 debug("SSH2_MSG_NEWKEYS received");
245 buffer_clear(&kex->peer);
246 /* buffer_clear(&kex->my); */
247 kex->flags &= ~KEX_INIT_SENT;
253 kex_send_kexinit(Kex *kex)
260 error("kex_send_kexinit: no kex, cannot rekey");
263 if (kex->flags & KEX_INIT_SENT) {
264 debug("KEX_INIT_SENT");
269 /* generate a random cookie */
270 if (buffer_len(&kex->my) < KEX_COOKIE_LEN)
271 fatal("kex_send_kexinit: kex proposal too short");
272 cookie = buffer_ptr(&kex->my);
273 for (i = 0; i < KEX_COOKIE_LEN; i++) {
279 packet_start(SSH2_MSG_KEXINIT);
280 packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my));
282 debug("SSH2_MSG_KEXINIT sent");
283 kex->flags |= KEX_INIT_SENT;
288 kex_input_kexinit(int type, u_int32_t seq, void *ctxt)
292 Kex *kex = (Kex *)ctxt;
294 debug("SSH2_MSG_KEXINIT received");
296 fatal("kex_input_kexinit: no kex, cannot rekey");
298 ptr = packet_get_raw(&dlen);
299 buffer_append(&kex->peer, ptr, dlen);
302 for (i = 0; i < KEX_COOKIE_LEN; i++)
304 for (i = 0; i < PROPOSAL_MAX; i++)
305 free(packet_get_string(NULL));
307 * XXX RFC4253 sec 7: "each side MAY guess" - currently no supported
308 * KEX method has the server move first, but a server might be using
309 * a custom method or one that we otherwise don't support. We should
310 * be prepared to remember first_kex_follows here so we can eat a
312 * XXX2 - RFC4253 is kind of ambiguous on what first_kex_follows means
313 * for cases where the server *doesn't* go first. I guess we should
314 * ignore it when it is set for these cases, which is what we do now.
316 (void) packet_get_char(); /* first_kex_follows */
317 (void) packet_get_int(); /* reserved */
320 kex_kexinit_finish(kex);
324 kex_setup(char *proposal[PROPOSAL_MAX])
328 kex = xcalloc(1, sizeof(*kex));
329 buffer_init(&kex->peer);
330 buffer_init(&kex->my);
331 kex_prop2buf(&kex->my, proposal);
334 kex_send_kexinit(kex); /* we start */
335 kex_reset_dispatch();
341 kex_kexinit_finish(Kex *kex)
343 if (!(kex->flags & KEX_INIT_SENT))
344 kex_send_kexinit(kex);
346 kex_choose_conf(kex);
348 if (kex->kex_type >= 0 && kex->kex_type < KEX_MAX &&
349 kex->kex[kex->kex_type] != NULL) {
350 (kex->kex[kex->kex_type])(kex);
352 fatal("Unsupported key exchange %d", kex->kex_type);
357 choose_enc(Enc *enc, char *client, char *server)
359 char *name = match_list(client, server, NULL);
361 fatal("no matching cipher found: client %s server %s",
363 if ((enc->cipher = cipher_by_name(name)) == NULL)
364 fatal("matching cipher is not supported: %s", name);
368 enc->iv_len = cipher_ivlen(enc->cipher);
370 enc->key_len = cipher_keylen(enc->cipher);
371 enc->block_size = cipher_blocksize(enc->cipher);
375 choose_mac(Mac *mac, char *client, char *server)
377 char *name = match_list(client, server, NULL);
379 fatal("no matching mac found: client %s server %s",
381 if (mac_setup(mac, name) < 0)
382 fatal("unsupported mac %s", name);
383 /* truncate the key */
384 if (datafellows & SSH_BUG_HMAC)
392 choose_comp(Comp *comp, char *client, char *server)
394 char *name = match_list(client, server, NULL);
396 fatal("no matching comp found: client %s server %s", client, server);
397 if (strcmp(name, "zlib@openssh.com") == 0) {
398 comp->type = COMP_DELAYED;
399 } else if (strcmp(name, "zlib") == 0) {
400 comp->type = COMP_ZLIB;
401 } else if (strcmp(name, "none") == 0) {
402 comp->type = COMP_NONE;
404 fatal("unsupported comp %s", name);
410 choose_kex(Kex *k, char *client, char *server)
412 const struct kexalg *kexalg;
414 k->name = match_list(client, server, NULL);
416 fatal("Unable to negotiate a key exchange method");
417 if ((kexalg = kex_alg_by_name(k->name)) == NULL)
418 fatal("unsupported kex alg %s", k->name);
419 k->kex_type = kexalg->type;
420 k->hash_alg = kexalg->hash_alg;
421 k->ec_nid = kexalg->ec_nid;
425 choose_hostkeyalg(Kex *k, char *client, char *server)
427 char *hostkeyalg = match_list(client, server, NULL);
428 if (hostkeyalg == NULL)
429 fatal("no hostkey alg");
430 k->hostkey_type = key_type_from_name(hostkeyalg);
431 if (k->hostkey_type == KEY_UNSPEC)
432 fatal("bad hostkey alg '%s'", hostkeyalg);
437 proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX])
439 static int check[] = {
440 PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1
445 for (idx = &check[0]; *idx != -1; idx++) {
446 if ((p = strchr(my[*idx], ',')) != NULL)
448 if ((p = strchr(peer[*idx], ',')) != NULL)
450 if (strcmp(my[*idx], peer[*idx]) != 0) {
451 debug2("proposal mismatch: my %s peer %s",
452 my[*idx], peer[*idx]);
456 debug2("proposals match");
461 kex_choose_conf(Kex *kex)
465 char **cprop, **sprop;
466 int nenc, nmac, ncomp;
467 u_int mode, ctos, need, dh_need, authlen;
468 int first_kex_follows, type;
469 #ifdef NONE_CIPHER_ENABLED
473 my = kex_buf2prop(&kex->my, NULL);
474 peer = kex_buf2prop(&kex->peer, &first_kex_follows);
484 /* Check whether server offers roaming */
487 roaming = match_list(KEX_RESUME, peer[PROPOSAL_KEX_ALGS], NULL);
494 /* Algorithm Negotiation */
495 #ifdef NONE_CIPHER_ENABLED
496 auth_flag = packet_get_authentication_state();
497 debug ("AUTH STATE is %d", auth_flag);
499 for (mode = 0; mode < MODE_MAX; mode++) {
500 newkeys = xcalloc(1, sizeof(*newkeys));
501 kex->newkeys[mode] = newkeys;
502 ctos = (!kex->server && mode == MODE_OUT) ||
503 (kex->server && mode == MODE_IN);
504 nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC;
505 nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC;
506 ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC;
507 choose_enc(&newkeys->enc, cprop[nenc], sprop[nenc]);
508 /* ignore mac for authenticated encryption */
509 authlen = cipher_authlen(newkeys->enc.cipher);
511 choose_mac(&newkeys->mac, cprop[nmac], sprop[nmac]);
512 choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]);
513 #ifdef NONE_CIPHER_ENABLED
514 debug("REQUESTED ENC.NAME is '%s'", newkeys->enc.name);
515 if (strcmp(newkeys->enc.name, "none") == 0) {
516 debug("Requesting NONE. Authflag is %d", auth_flag);
518 debug("None requested post authentication.");
520 fatal("Pre-authentication none cipher requests "
524 debug("kex: %s %s %s %s",
525 ctos ? "client->server" : "server->client",
527 authlen == 0 ? newkeys->mac.name : "<implicit>",
530 choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]);
531 choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
532 sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]);
534 for (mode = 0; mode < MODE_MAX; mode++) {
535 newkeys = kex->newkeys[mode];
536 need = MAX(need, newkeys->enc.key_len);
537 need = MAX(need, newkeys->enc.block_size);
538 need = MAX(need, newkeys->enc.iv_len);
539 need = MAX(need, newkeys->mac.key_len);
540 dh_need = MAX(dh_need, cipher_seclen(newkeys->enc.cipher));
541 dh_need = MAX(dh_need, newkeys->enc.block_size);
542 dh_need = MAX(dh_need, newkeys->enc.iv_len);
543 dh_need = MAX(dh_need, newkeys->mac.key_len);
545 /* XXX need runden? */
547 kex->dh_need = dh_need;
549 /* ignore the next message if the proposals do not match */
550 if (first_kex_follows && !proposals_match(my, peer) &&
551 !(datafellows & SSH_BUG_FIRSTKEX)) {
552 type = packet_read();
553 debug2("skipping next packet (type %u)", type);
561 derive_key(Kex *kex, int id, u_int need, u_char *hash, u_int hashlen,
562 const u_char *shared_secret, u_int slen)
565 struct ssh_digest_ctx *hashctx;
571 if ((mdsz = ssh_digest_bytes(kex->hash_alg)) == 0)
572 fatal("bad kex md size %zu", mdsz);
573 digest = xmalloc(roundup(need, mdsz));
576 buffer_append(&b, shared_secret, slen);
578 /* K1 = HASH(K || H || "A" || session_id) */
579 if ((hashctx = ssh_digest_start(kex->hash_alg)) == NULL)
580 fatal("%s: ssh_digest_start failed", __func__);
581 if (ssh_digest_update_buffer(hashctx, &b) != 0 ||
582 ssh_digest_update(hashctx, hash, hashlen) != 0 ||
583 ssh_digest_update(hashctx, &c, 1) != 0 ||
584 ssh_digest_update(hashctx, kex->session_id,
585 kex->session_id_len) != 0)
586 fatal("%s: ssh_digest_update failed", __func__);
587 if (ssh_digest_final(hashctx, digest, mdsz) != 0)
588 fatal("%s: ssh_digest_final failed", __func__);
589 ssh_digest_free(hashctx);
593 * Kn = HASH(K || H || K1 || K2 || ... || Kn-1)
594 * Key = K1 || K2 || ... || Kn
596 for (have = mdsz; need > have; have += mdsz) {
597 if ((hashctx = ssh_digest_start(kex->hash_alg)) == NULL)
598 fatal("%s: ssh_digest_start failed", __func__);
599 if (ssh_digest_update_buffer(hashctx, &b) != 0 ||
600 ssh_digest_update(hashctx, hash, hashlen) != 0 ||
601 ssh_digest_update(hashctx, digest, have) != 0)
602 fatal("%s: ssh_digest_update failed", __func__);
603 if (ssh_digest_final(hashctx, digest + have, mdsz) != 0)
604 fatal("%s: ssh_digest_final failed", __func__);
605 ssh_digest_free(hashctx);
609 fprintf(stderr, "key '%c'== ", c);
610 dump_digest("key", digest, need);
615 Newkeys *current_keys[MODE_MAX];
619 kex_derive_keys(Kex *kex, u_char *hash, u_int hashlen,
620 const u_char *shared_secret, u_int slen)
625 for (i = 0; i < NKEYS; i++) {
626 keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, hashlen,
627 shared_secret, slen);
630 debug2("kex_derive_keys");
631 for (mode = 0; mode < MODE_MAX; mode++) {
632 current_keys[mode] = kex->newkeys[mode];
633 kex->newkeys[mode] = NULL;
634 ctos = (!kex->server && mode == MODE_OUT) ||
635 (kex->server && mode == MODE_IN);
636 current_keys[mode]->enc.iv = keys[ctos ? 0 : 1];
637 current_keys[mode]->enc.key = keys[ctos ? 2 : 3];
638 current_keys[mode]->mac.key = keys[ctos ? 4 : 5];
643 kex_derive_keys_bn(Kex *kex, u_char *hash, u_int hashlen, const BIGNUM *secret)
645 Buffer shared_secret;
647 buffer_init(&shared_secret);
648 buffer_put_bignum2(&shared_secret, secret);
649 kex_derive_keys(kex, hash, hashlen,
650 buffer_ptr(&shared_secret), buffer_len(&shared_secret));
651 buffer_free(&shared_secret);
655 kex_get_newkeys(int mode)
659 ret = current_keys[mode];
660 current_keys[mode] = NULL;
665 derive_ssh1_session_id(BIGNUM *host_modulus, BIGNUM *server_modulus,
666 u_int8_t cookie[8], u_int8_t id[16])
668 u_int8_t nbuf[2048], obuf[SSH_DIGEST_MAX_LENGTH];
670 struct ssh_digest_ctx *hashctx;
672 if ((hashctx = ssh_digest_start(SSH_DIGEST_MD5)) == NULL)
673 fatal("%s: ssh_digest_start", __func__);
675 len = BN_num_bytes(host_modulus);
676 if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
677 fatal("%s: bad host modulus (len %d)", __func__, len);
678 BN_bn2bin(host_modulus, nbuf);
679 if (ssh_digest_update(hashctx, nbuf, len) != 0)
680 fatal("%s: ssh_digest_update failed", __func__);
682 len = BN_num_bytes(server_modulus);
683 if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
684 fatal("%s: bad server modulus (len %d)", __func__, len);
685 BN_bn2bin(server_modulus, nbuf);
686 if (ssh_digest_update(hashctx, nbuf, len) != 0 ||
687 ssh_digest_update(hashctx, cookie, 8) != 0)
688 fatal("%s: ssh_digest_update failed", __func__);
689 if (ssh_digest_final(hashctx, obuf, sizeof(obuf)) != 0)
690 fatal("%s: ssh_digest_final failed", __func__);
691 memcpy(id, obuf, ssh_digest_bytes(SSH_DIGEST_MD5));
693 explicit_bzero(nbuf, sizeof(nbuf));
694 explicit_bzero(obuf, sizeof(obuf));
697 #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH) || defined(DEBUG_KEXECDH)
699 dump_digest(char *msg, u_char *digest, int len)
703 fprintf(stderr, "%s\n", msg);
704 for (i = 0; i < len; i++) {
705 fprintf(stderr, "%02x", digest[i]);
707 fprintf(stderr, "\n");
709 fprintf(stderr, " ");
711 fprintf(stderr, "\n");