1 /* $OpenBSD: kex.c,v 1.91 2013/05/17 00:13:13 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>
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 *);
70 const EVP_MD *(*mdfunc)(void);
72 static const struct kexalg kexalgs[] = {
73 { KEX_DH1, KEX_DH_GRP1_SHA1, 0, EVP_sha1 },
74 { KEX_DH14, KEX_DH_GRP14_SHA1, 0, EVP_sha1 },
75 { KEX_DHGEX_SHA1, KEX_DH_GEX_SHA1, 0, EVP_sha1 },
76 #ifdef HAVE_EVP_SHA256
77 { KEX_DHGEX_SHA256, KEX_DH_GEX_SHA256, 0, EVP_sha256 },
79 #ifdef OPENSSL_HAS_ECC
80 { KEX_ECDH_SHA2_NISTP256, KEX_ECDH_SHA2, NID_X9_62_prime256v1, EVP_sha256 },
81 { KEX_ECDH_SHA2_NISTP384, KEX_ECDH_SHA2, NID_secp384r1, EVP_sha384 },
82 { KEX_ECDH_SHA2_NISTP521, KEX_ECDH_SHA2, NID_secp521r1, EVP_sha512 },
84 { NULL, -1, -1, NULL},
91 size_t nlen, rlen = 0;
92 const struct kexalg *k;
94 for (k = kexalgs; k->name != NULL; k++) {
97 nlen = strlen(k->name);
98 ret = xrealloc(ret, 1, rlen + nlen + 2);
99 memcpy(ret + rlen, k->name, nlen + 1);
105 static const struct kexalg *
106 kex_alg_by_name(const char *name)
108 const struct kexalg *k;
110 for (k = kexalgs; k->name != NULL; k++) {
111 if (strcmp(k->name, name) == 0)
117 /* Validate KEX method name list */
119 kex_names_valid(const char *names)
123 if (names == NULL || strcmp(names, "") == 0)
125 s = cp = xstrdup(names);
126 for ((p = strsep(&cp, ",")); p && *p != '\0';
127 (p = strsep(&cp, ","))) {
128 if (kex_alg_by_name(p) == NULL) {
129 error("Unsupported KEX algorithm \"%.100s\"", p);
134 debug3("kex names ok: [%s]", names);
139 /* put algorithm proposal into buffer. */
140 #ifndef NONE_CIPHER_ENABLED
143 /* Also used in sshconnect2.c. */
146 kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX])
152 * add a dummy cookie, the cookie will be overwritten by
153 * kex_send_kexinit(), each time a kexinit is set
155 for (i = 0; i < KEX_COOKIE_LEN; i++)
156 buffer_put_char(b, 0);
157 for (i = 0; i < PROPOSAL_MAX; i++)
158 buffer_put_cstring(b, proposal[i]);
159 buffer_put_char(b, 0); /* first_kex_packet_follows */
160 buffer_put_int(b, 0); /* uint32 reserved */
163 /* parse buffer and return algorithm proposal */
165 kex_buf2prop(Buffer *raw, int *first_kex_follows)
171 proposal = xcalloc(PROPOSAL_MAX, sizeof(char *));
174 buffer_append(&b, buffer_ptr(raw), buffer_len(raw));
176 for (i = 0; i < KEX_COOKIE_LEN; i++)
178 /* extract kex init proposal strings */
179 for (i = 0; i < PROPOSAL_MAX; i++) {
180 proposal[i] = buffer_get_cstring(&b,NULL);
181 debug2("kex_parse_kexinit: %s", proposal[i]);
183 /* first kex follows / reserved */
184 i = buffer_get_char(&b);
185 if (first_kex_follows != NULL)
186 *first_kex_follows = i;
187 debug2("kex_parse_kexinit: first_kex_follows %d ", i);
188 i = buffer_get_int(&b);
189 debug2("kex_parse_kexinit: reserved %u ", i);
195 kex_prop_free(char **proposal)
199 for (i = 0; i < PROPOSAL_MAX; i++)
206 kex_protocol_error(int type, u_int32_t seq, void *ctxt)
208 error("Hm, kex protocol error: type %d seq %u", type, seq);
212 kex_reset_dispatch(void)
214 dispatch_range(SSH2_MSG_TRANSPORT_MIN,
215 SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error);
216 dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit);
222 kex_reset_dispatch();
224 packet_start(SSH2_MSG_NEWKEYS);
226 /* packet_write_wait(); */
227 debug("SSH2_MSG_NEWKEYS sent");
229 debug("expecting SSH2_MSG_NEWKEYS");
230 packet_read_expect(SSH2_MSG_NEWKEYS);
232 debug("SSH2_MSG_NEWKEYS received");
235 buffer_clear(&kex->peer);
236 /* buffer_clear(&kex->my); */
237 kex->flags &= ~KEX_INIT_SENT;
243 kex_send_kexinit(Kex *kex)
250 error("kex_send_kexinit: no kex, cannot rekey");
253 if (kex->flags & KEX_INIT_SENT) {
254 debug("KEX_INIT_SENT");
259 /* generate a random cookie */
260 if (buffer_len(&kex->my) < KEX_COOKIE_LEN)
261 fatal("kex_send_kexinit: kex proposal too short");
262 cookie = buffer_ptr(&kex->my);
263 for (i = 0; i < KEX_COOKIE_LEN; i++) {
269 packet_start(SSH2_MSG_KEXINIT);
270 packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my));
272 debug("SSH2_MSG_KEXINIT sent");
273 kex->flags |= KEX_INIT_SENT;
278 kex_input_kexinit(int type, u_int32_t seq, void *ctxt)
282 Kex *kex = (Kex *)ctxt;
284 debug("SSH2_MSG_KEXINIT received");
286 fatal("kex_input_kexinit: no kex, cannot rekey");
288 ptr = packet_get_raw(&dlen);
289 buffer_append(&kex->peer, ptr, dlen);
292 for (i = 0; i < KEX_COOKIE_LEN; i++)
294 for (i = 0; i < PROPOSAL_MAX; i++)
295 free(packet_get_string(NULL));
297 * XXX RFC4253 sec 7: "each side MAY guess" - currently no supported
298 * KEX method has the server move first, but a server might be using
299 * a custom method or one that we otherwise don't support. We should
300 * be prepared to remember first_kex_follows here so we can eat a
302 * XXX2 - RFC4253 is kind of ambiguous on what first_kex_follows means
303 * for cases where the server *doesn't* go first. I guess we should
304 * ignore it when it is set for these cases, which is what we do now.
306 (void) packet_get_char(); /* first_kex_follows */
307 (void) packet_get_int(); /* reserved */
310 kex_kexinit_finish(kex);
314 kex_setup(char *proposal[PROPOSAL_MAX])
318 kex = xcalloc(1, sizeof(*kex));
319 buffer_init(&kex->peer);
320 buffer_init(&kex->my);
321 kex_prop2buf(&kex->my, proposal);
324 kex_send_kexinit(kex); /* we start */
325 kex_reset_dispatch();
331 kex_kexinit_finish(Kex *kex)
333 if (!(kex->flags & KEX_INIT_SENT))
334 kex_send_kexinit(kex);
336 kex_choose_conf(kex);
338 if (kex->kex_type >= 0 && kex->kex_type < KEX_MAX &&
339 kex->kex[kex->kex_type] != NULL) {
340 (kex->kex[kex->kex_type])(kex);
342 fatal("Unsupported key exchange %d", kex->kex_type);
347 choose_enc(Enc *enc, char *client, char *server)
349 char *name = match_list(client, server, NULL);
351 fatal("no matching cipher found: client %s server %s",
353 if ((enc->cipher = cipher_by_name(name)) == NULL)
354 fatal("matching cipher is not supported: %s", name);
358 enc->iv_len = cipher_ivlen(enc->cipher);
360 enc->key_len = cipher_keylen(enc->cipher);
361 enc->block_size = cipher_blocksize(enc->cipher);
365 choose_mac(Mac *mac, char *client, char *server)
367 char *name = match_list(client, server, NULL);
369 fatal("no matching mac found: client %s server %s",
371 if (mac_setup(mac, name) < 0)
372 fatal("unsupported mac %s", name);
373 /* truncate the key */
374 if (datafellows & SSH_BUG_HMAC)
382 choose_comp(Comp *comp, char *client, char *server)
384 char *name = match_list(client, server, NULL);
386 fatal("no matching comp found: client %s server %s", client, server);
387 if (strcmp(name, "zlib@openssh.com") == 0) {
388 comp->type = COMP_DELAYED;
389 } else if (strcmp(name, "zlib") == 0) {
390 comp->type = COMP_ZLIB;
391 } else if (strcmp(name, "none") == 0) {
392 comp->type = COMP_NONE;
394 fatal("unsupported comp %s", name);
400 choose_kex(Kex *k, char *client, char *server)
402 const struct kexalg *kexalg;
404 k->name = match_list(client, server, NULL);
406 fatal("Unable to negotiate a key exchange method");
407 if ((kexalg = kex_alg_by_name(k->name)) == NULL)
408 fatal("unsupported kex alg %s", k->name);
409 k->kex_type = kexalg->type;
410 k->evp_md = kexalg->mdfunc();
411 k->ec_nid = kexalg->ec_nid;
415 choose_hostkeyalg(Kex *k, char *client, char *server)
417 char *hostkeyalg = match_list(client, server, NULL);
418 if (hostkeyalg == NULL)
419 fatal("no hostkey alg");
420 k->hostkey_type = key_type_from_name(hostkeyalg);
421 if (k->hostkey_type == KEY_UNSPEC)
422 fatal("bad hostkey alg '%s'", hostkeyalg);
427 proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX])
429 static int check[] = {
430 PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1
435 for (idx = &check[0]; *idx != -1; idx++) {
436 if ((p = strchr(my[*idx], ',')) != NULL)
438 if ((p = strchr(peer[*idx], ',')) != NULL)
440 if (strcmp(my[*idx], peer[*idx]) != 0) {
441 debug2("proposal mismatch: my %s peer %s",
442 my[*idx], peer[*idx]);
446 debug2("proposals match");
451 kex_choose_conf(Kex *kex)
455 char **cprop, **sprop;
456 int nenc, nmac, ncomp;
457 u_int mode, ctos, need, authlen;
458 int first_kex_follows, type;
459 #ifdef NONE_CIPHER_ENABLED
463 my = kex_buf2prop(&kex->my, NULL);
464 peer = kex_buf2prop(&kex->peer, &first_kex_follows);
474 /* Check whether server offers roaming */
477 roaming = match_list(KEX_RESUME, peer[PROPOSAL_KEX_ALGS], NULL);
484 /* Algorithm Negotiation */
485 #ifdef NONE_CIPHER_ENABLED
486 auth_flag = packet_get_authentication_state();
487 debug ("AUTH STATE is %d", auth_flag);
489 for (mode = 0; mode < MODE_MAX; mode++) {
490 newkeys = xcalloc(1, sizeof(*newkeys));
491 kex->newkeys[mode] = newkeys;
492 ctos = (!kex->server && mode == MODE_OUT) ||
493 (kex->server && mode == MODE_IN);
494 nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC;
495 nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC;
496 ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC;
497 choose_enc(&newkeys->enc, cprop[nenc], sprop[nenc]);
498 /* ignore mac for authenticated encryption */
499 authlen = cipher_authlen(newkeys->enc.cipher);
501 choose_mac(&newkeys->mac, cprop[nmac], sprop[nmac]);
502 choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]);
503 #ifdef NONE_CIPHER_ENABLED
504 debug("REQUESTED ENC.NAME is '%s'", newkeys->enc.name);
505 if (strcmp(newkeys->enc.name, "none") == 0) {
506 debug("Requesting NONE. Authflag is %d", auth_flag);
508 debug("None requested post authentication.");
510 fatal("Pre-authentication none cipher requests "
514 debug("kex: %s %s %s %s",
515 ctos ? "client->server" : "server->client",
517 authlen == 0 ? newkeys->mac.name : "<implicit>",
520 choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]);
521 choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
522 sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]);
524 for (mode = 0; mode < MODE_MAX; mode++) {
525 newkeys = kex->newkeys[mode];
526 if (need < newkeys->enc.key_len)
527 need = newkeys->enc.key_len;
528 if (need < newkeys->enc.block_size)
529 need = newkeys->enc.block_size;
530 if (need < newkeys->enc.iv_len)
531 need = newkeys->enc.iv_len;
532 if (need < newkeys->mac.key_len)
533 need = newkeys->mac.key_len;
535 /* XXX need runden? */
538 /* ignore the next message if the proposals do not match */
539 if (first_kex_follows && !proposals_match(my, peer) &&
540 !(datafellows & SSH_BUG_FIRSTKEX)) {
541 type = packet_read();
542 debug2("skipping next packet (type %u)", type);
550 derive_key(Kex *kex, int id, u_int need, u_char *hash, u_int hashlen,
551 BIGNUM *shared_secret)
560 if ((mdsz = EVP_MD_size(kex->evp_md)) <= 0)
561 fatal("bad kex md size %d", mdsz);
562 digest = xmalloc(roundup(need, mdsz));
565 buffer_put_bignum2(&b, shared_secret);
567 /* K1 = HASH(K || H || "A" || session_id) */
568 EVP_DigestInit(&md, kex->evp_md);
569 if (!(datafellows & SSH_BUG_DERIVEKEY))
570 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
571 EVP_DigestUpdate(&md, hash, hashlen);
572 EVP_DigestUpdate(&md, &c, 1);
573 EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len);
574 EVP_DigestFinal(&md, digest, NULL);
578 * Kn = HASH(K || H || K1 || K2 || ... || Kn-1)
579 * Key = K1 || K2 || ... || Kn
581 for (have = mdsz; need > have; have += mdsz) {
582 EVP_DigestInit(&md, kex->evp_md);
583 if (!(datafellows & SSH_BUG_DERIVEKEY))
584 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
585 EVP_DigestUpdate(&md, hash, hashlen);
586 EVP_DigestUpdate(&md, digest, have);
587 EVP_DigestFinal(&md, digest + have, NULL);
591 fprintf(stderr, "key '%c'== ", c);
592 dump_digest("key", digest, need);
597 Newkeys *current_keys[MODE_MAX];
601 kex_derive_keys(Kex *kex, u_char *hash, u_int hashlen, BIGNUM *shared_secret)
606 for (i = 0; i < NKEYS; i++) {
607 keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, hashlen,
611 debug2("kex_derive_keys");
612 for (mode = 0; mode < MODE_MAX; mode++) {
613 current_keys[mode] = kex->newkeys[mode];
614 kex->newkeys[mode] = NULL;
615 ctos = (!kex->server && mode == MODE_OUT) ||
616 (kex->server && mode == MODE_IN);
617 current_keys[mode]->enc.iv = keys[ctos ? 0 : 1];
618 current_keys[mode]->enc.key = keys[ctos ? 2 : 3];
619 current_keys[mode]->mac.key = keys[ctos ? 4 : 5];
624 kex_get_newkeys(int mode)
628 ret = current_keys[mode];
629 current_keys[mode] = NULL;
634 derive_ssh1_session_id(BIGNUM *host_modulus, BIGNUM *server_modulus,
635 u_int8_t cookie[8], u_int8_t id[16])
637 const EVP_MD *evp_md = EVP_md5();
639 u_int8_t nbuf[2048], obuf[EVP_MAX_MD_SIZE];
642 EVP_DigestInit(&md, evp_md);
644 len = BN_num_bytes(host_modulus);
645 if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
646 fatal("%s: bad host modulus (len %d)", __func__, len);
647 BN_bn2bin(host_modulus, nbuf);
648 EVP_DigestUpdate(&md, nbuf, len);
650 len = BN_num_bytes(server_modulus);
651 if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
652 fatal("%s: bad server modulus (len %d)", __func__, len);
653 BN_bn2bin(server_modulus, nbuf);
654 EVP_DigestUpdate(&md, nbuf, len);
656 EVP_DigestUpdate(&md, cookie, 8);
658 EVP_DigestFinal(&md, obuf, NULL);
659 memcpy(id, obuf, 16);
661 memset(nbuf, 0, sizeof(nbuf));
662 memset(obuf, 0, sizeof(obuf));
663 memset(&md, 0, sizeof(md));
666 #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH) || defined(DEBUG_KEXECDH)
668 dump_digest(char *msg, u_char *digest, int len)
672 fprintf(stderr, "%s\n", msg);
673 for (i = 0; i < len; i++) {
674 fprintf(stderr, "%02x", digest[i]);
676 fprintf(stderr, "\n");
678 fprintf(stderr, " ");
680 fprintf(stderr, "\n");