1 /* $OpenBSD: kex.c,v 1.86 2010/09/22 05:01:29 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>
57 #if OPENSSL_VERSION_NUMBER >= 0x00907000L
58 # if defined(HAVE_EVP_SHA256)
59 # define evp_ssh_sha256 EVP_sha256
61 extern const EVP_MD *evp_ssh_sha256(void);
66 static void kex_kexinit_finish(Kex *);
67 static void kex_choose_conf(Kex *);
69 /* Validate KEX method name list */
71 kex_names_valid(const char *names)
75 if (names == NULL || strcmp(names, "") == 0)
77 s = cp = xstrdup(names);
78 for ((p = strsep(&cp, ",")); p && *p != '\0';
79 (p = strsep(&cp, ","))) {
80 if (strcmp(p, KEX_DHGEX_SHA256) != 0 &&
81 strcmp(p, KEX_DHGEX_SHA1) != 0 &&
82 strcmp(p, KEX_DH14) != 0 &&
83 strcmp(p, KEX_DH1) != 0 &&
84 (strncmp(p, KEX_ECDH_SHA2_STEM,
85 sizeof(KEX_ECDH_SHA2_STEM) - 1) != 0 ||
86 kex_ecdh_name_to_nid(p) == -1)) {
87 error("Unsupported KEX algorithm \"%.100s\"", p);
92 debug3("kex names ok: [%s]", names);
97 /* put algorithm proposal into buffer */
99 kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX])
105 * add a dummy cookie, the cookie will be overwritten by
106 * kex_send_kexinit(), each time a kexinit is set
108 for (i = 0; i < KEX_COOKIE_LEN; i++)
109 buffer_put_char(b, 0);
110 for (i = 0; i < PROPOSAL_MAX; i++)
111 buffer_put_cstring(b, proposal[i]);
112 buffer_put_char(b, 0); /* first_kex_packet_follows */
113 buffer_put_int(b, 0); /* uint32 reserved */
116 /* parse buffer and return algorithm proposal */
118 kex_buf2prop(Buffer *raw, int *first_kex_follows)
124 proposal = xcalloc(PROPOSAL_MAX, sizeof(char *));
127 buffer_append(&b, buffer_ptr(raw), buffer_len(raw));
129 for (i = 0; i < KEX_COOKIE_LEN; i++)
131 /* extract kex init proposal strings */
132 for (i = 0; i < PROPOSAL_MAX; i++) {
133 proposal[i] = buffer_get_cstring(&b,NULL);
134 debug2("kex_parse_kexinit: %s", proposal[i]);
136 /* first kex follows / reserved */
137 i = buffer_get_char(&b);
138 if (first_kex_follows != NULL)
139 *first_kex_follows = i;
140 debug2("kex_parse_kexinit: first_kex_follows %d ", i);
141 i = buffer_get_int(&b);
142 debug2("kex_parse_kexinit: reserved %u ", i);
148 kex_prop_free(char **proposal)
152 for (i = 0; i < PROPOSAL_MAX; i++)
159 kex_protocol_error(int type, u_int32_t seq, void *ctxt)
161 error("Hm, kex protocol error: type %d seq %u", type, seq);
165 kex_reset_dispatch(void)
167 dispatch_range(SSH2_MSG_TRANSPORT_MIN,
168 SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error);
169 dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit);
175 kex_reset_dispatch();
177 packet_start(SSH2_MSG_NEWKEYS);
179 /* packet_write_wait(); */
180 debug("SSH2_MSG_NEWKEYS sent");
182 debug("expecting SSH2_MSG_NEWKEYS");
183 packet_read_expect(SSH2_MSG_NEWKEYS);
185 debug("SSH2_MSG_NEWKEYS received");
188 buffer_clear(&kex->peer);
189 /* buffer_clear(&kex->my); */
190 kex->flags &= ~KEX_INIT_SENT;
196 kex_send_kexinit(Kex *kex)
203 error("kex_send_kexinit: no kex, cannot rekey");
206 if (kex->flags & KEX_INIT_SENT) {
207 debug("KEX_INIT_SENT");
212 /* generate a random cookie */
213 if (buffer_len(&kex->my) < KEX_COOKIE_LEN)
214 fatal("kex_send_kexinit: kex proposal too short");
215 cookie = buffer_ptr(&kex->my);
216 for (i = 0; i < KEX_COOKIE_LEN; i++) {
222 packet_start(SSH2_MSG_KEXINIT);
223 packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my));
225 debug("SSH2_MSG_KEXINIT sent");
226 kex->flags |= KEX_INIT_SENT;
231 kex_input_kexinit(int type, u_int32_t seq, void *ctxt)
235 Kex *kex = (Kex *)ctxt;
237 debug("SSH2_MSG_KEXINIT received");
239 fatal("kex_input_kexinit: no kex, cannot rekey");
241 ptr = packet_get_raw(&dlen);
242 buffer_append(&kex->peer, ptr, dlen);
245 for (i = 0; i < KEX_COOKIE_LEN; i++)
247 for (i = 0; i < PROPOSAL_MAX; i++)
248 xfree(packet_get_string(NULL));
249 (void) packet_get_char();
250 (void) packet_get_int();
253 kex_kexinit_finish(kex);
257 kex_setup(char *proposal[PROPOSAL_MAX])
261 kex = xcalloc(1, sizeof(*kex));
262 buffer_init(&kex->peer);
263 buffer_init(&kex->my);
264 kex_prop2buf(&kex->my, proposal);
267 kex_send_kexinit(kex); /* we start */
268 kex_reset_dispatch();
274 kex_kexinit_finish(Kex *kex)
276 if (!(kex->flags & KEX_INIT_SENT))
277 kex_send_kexinit(kex);
279 kex_choose_conf(kex);
281 if (kex->kex_type >= 0 && kex->kex_type < KEX_MAX &&
282 kex->kex[kex->kex_type] != NULL) {
283 (kex->kex[kex->kex_type])(kex);
285 fatal("Unsupported key exchange %d", kex->kex_type);
290 choose_enc(Enc *enc, char *client, char *server)
292 char *name = match_list(client, server, NULL);
294 fatal("no matching cipher found: client %s server %s",
296 if ((enc->cipher = cipher_by_name(name)) == NULL)
297 fatal("matching cipher is not supported: %s", name);
302 enc->key_len = cipher_keylen(enc->cipher);
303 enc->block_size = cipher_blocksize(enc->cipher);
307 choose_mac(Mac *mac, char *client, char *server)
309 char *name = match_list(client, server, NULL);
311 fatal("no matching mac found: client %s server %s",
313 if (mac_setup(mac, name) < 0)
314 fatal("unsupported mac %s", name);
315 /* truncate the key */
316 if (datafellows & SSH_BUG_HMAC)
324 choose_comp(Comp *comp, char *client, char *server)
326 char *name = match_list(client, server, NULL);
328 fatal("no matching comp found: client %s server %s", client, server);
329 if (strcmp(name, "zlib@openssh.com") == 0) {
330 comp->type = COMP_DELAYED;
331 } else if (strcmp(name, "zlib") == 0) {
332 comp->type = COMP_ZLIB;
333 } else if (strcmp(name, "none") == 0) {
334 comp->type = COMP_NONE;
336 fatal("unsupported comp %s", name);
342 choose_kex(Kex *k, char *client, char *server)
344 k->name = match_list(client, server, NULL);
346 fatal("Unable to negotiate a key exchange method");
347 if (strcmp(k->name, KEX_DH1) == 0) {
348 k->kex_type = KEX_DH_GRP1_SHA1;
349 k->evp_md = EVP_sha1();
350 } else if (strcmp(k->name, KEX_DH14) == 0) {
351 k->kex_type = KEX_DH_GRP14_SHA1;
352 k->evp_md = EVP_sha1();
353 } else if (strcmp(k->name, KEX_DHGEX_SHA1) == 0) {
354 k->kex_type = KEX_DH_GEX_SHA1;
355 k->evp_md = EVP_sha1();
356 #if OPENSSL_VERSION_NUMBER >= 0x00907000L
357 } else if (strcmp(k->name, KEX_DHGEX_SHA256) == 0) {
358 k->kex_type = KEX_DH_GEX_SHA256;
359 k->evp_md = evp_ssh_sha256();
360 } else if (strncmp(k->name, KEX_ECDH_SHA2_STEM,
361 sizeof(KEX_ECDH_SHA2_STEM) - 1) == 0) {
362 k->kex_type = KEX_ECDH_SHA2;
363 k->evp_md = kex_ecdh_name_to_evpmd(k->name);
366 } else if (strncmp(k->name, KEX_GSS_GEX_SHA1_ID,
367 sizeof(KEX_GSS_GEX_SHA1_ID) - 1) == 0) {
368 k->kex_type = KEX_GSS_GEX_SHA1;
369 k->evp_md = EVP_sha1();
370 } else if (strncmp(k->name, KEX_GSS_GRP1_SHA1_ID,
371 sizeof(KEX_GSS_GRP1_SHA1_ID) - 1) == 0) {
372 k->kex_type = KEX_GSS_GRP1_SHA1;
373 k->evp_md = EVP_sha1();
374 } else if (strncmp(k->name, KEX_GSS_GRP14_SHA1_ID,
375 sizeof(KEX_GSS_GRP14_SHA1_ID) - 1) == 0) {
376 k->kex_type = KEX_GSS_GRP14_SHA1;
377 k->evp_md = EVP_sha1();
380 fatal("bad kex alg %s", k->name);
384 choose_hostkeyalg(Kex *k, char *client, char *server)
386 char *hostkeyalg = match_list(client, server, NULL);
387 if (hostkeyalg == NULL)
388 fatal("no hostkey alg");
389 k->hostkey_type = key_type_from_name(hostkeyalg);
390 if (k->hostkey_type == KEY_UNSPEC)
391 fatal("bad hostkey alg '%s'", hostkeyalg);
396 proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX])
398 static int check[] = {
399 PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1
404 for (idx = &check[0]; *idx != -1; idx++) {
405 if ((p = strchr(my[*idx], ',')) != NULL)
407 if ((p = strchr(peer[*idx], ',')) != NULL)
409 if (strcmp(my[*idx], peer[*idx]) != 0) {
410 debug2("proposal mismatch: my %s peer %s",
411 my[*idx], peer[*idx]);
415 debug2("proposals match");
420 kex_choose_conf(Kex *kex)
424 char **cprop, **sprop;
425 int nenc, nmac, ncomp;
426 u_int mode, ctos, need;
427 int first_kex_follows, type;
429 my = kex_buf2prop(&kex->my, NULL);
430 peer = kex_buf2prop(&kex->peer, &first_kex_follows);
440 /* Check whether server offers roaming */
443 roaming = match_list(KEX_RESUME, peer[PROPOSAL_KEX_ALGS], NULL);
450 /* Algorithm Negotiation */
451 for (mode = 0; mode < MODE_MAX; mode++) {
452 newkeys = xcalloc(1, sizeof(*newkeys));
453 kex->newkeys[mode] = newkeys;
454 ctos = (!kex->server && mode == MODE_OUT) ||
455 (kex->server && mode == MODE_IN);
456 nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC;
457 nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC;
458 ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC;
459 choose_enc (&newkeys->enc, cprop[nenc], sprop[nenc]);
460 choose_mac (&newkeys->mac, cprop[nmac], sprop[nmac]);
461 choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]);
462 debug("kex: %s %s %s %s",
463 ctos ? "client->server" : "server->client",
468 choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]);
469 choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
470 sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]);
472 for (mode = 0; mode < MODE_MAX; mode++) {
473 newkeys = kex->newkeys[mode];
474 if (need < newkeys->enc.key_len)
475 need = newkeys->enc.key_len;
476 if (need < newkeys->enc.block_size)
477 need = newkeys->enc.block_size;
478 if (need < newkeys->mac.key_len)
479 need = newkeys->mac.key_len;
481 /* XXX need runden? */
484 /* ignore the next message if the proposals do not match */
485 if (first_kex_follows && !proposals_match(my, peer) &&
486 !(datafellows & SSH_BUG_FIRSTKEX)) {
487 type = packet_read();
488 debug2("skipping next packet (type %u)", type);
496 derive_key(Kex *kex, int id, u_int need, u_char *hash, u_int hashlen,
497 BIGNUM *shared_secret)
506 if ((mdsz = EVP_MD_size(kex->evp_md)) <= 0)
507 fatal("bad kex md size %d", mdsz);
508 digest = xmalloc(roundup(need, mdsz));
511 buffer_put_bignum2(&b, shared_secret);
513 /* K1 = HASH(K || H || "A" || session_id) */
514 EVP_DigestInit(&md, kex->evp_md);
515 if (!(datafellows & SSH_BUG_DERIVEKEY))
516 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
517 EVP_DigestUpdate(&md, hash, hashlen);
518 EVP_DigestUpdate(&md, &c, 1);
519 EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len);
520 EVP_DigestFinal(&md, digest, NULL);
524 * Kn = HASH(K || H || K1 || K2 || ... || Kn-1)
525 * Key = K1 || K2 || ... || Kn
527 for (have = mdsz; need > have; have += mdsz) {
528 EVP_DigestInit(&md, kex->evp_md);
529 if (!(datafellows & SSH_BUG_DERIVEKEY))
530 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
531 EVP_DigestUpdate(&md, hash, hashlen);
532 EVP_DigestUpdate(&md, digest, have);
533 EVP_DigestFinal(&md, digest + have, NULL);
537 fprintf(stderr, "key '%c'== ", c);
538 dump_digest("key", digest, need);
543 Newkeys *current_keys[MODE_MAX];
547 kex_derive_keys(Kex *kex, u_char *hash, u_int hashlen, BIGNUM *shared_secret)
552 for (i = 0; i < NKEYS; i++) {
553 keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, hashlen,
557 debug2("kex_derive_keys");
558 for (mode = 0; mode < MODE_MAX; mode++) {
559 current_keys[mode] = kex->newkeys[mode];
560 kex->newkeys[mode] = NULL;
561 ctos = (!kex->server && mode == MODE_OUT) ||
562 (kex->server && mode == MODE_IN);
563 current_keys[mode]->enc.iv = keys[ctos ? 0 : 1];
564 current_keys[mode]->enc.key = keys[ctos ? 2 : 3];
565 current_keys[mode]->mac.key = keys[ctos ? 4 : 5];
570 kex_get_newkeys(int mode)
574 ret = current_keys[mode];
575 current_keys[mode] = NULL;
580 derive_ssh1_session_id(BIGNUM *host_modulus, BIGNUM *server_modulus,
581 u_int8_t cookie[8], u_int8_t id[16])
583 const EVP_MD *evp_md = EVP_md5();
585 u_int8_t nbuf[2048], obuf[EVP_MAX_MD_SIZE];
588 EVP_DigestInit(&md, evp_md);
590 len = BN_num_bytes(host_modulus);
591 if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
592 fatal("%s: bad host modulus (len %d)", __func__, len);
593 BN_bn2bin(host_modulus, nbuf);
594 EVP_DigestUpdate(&md, nbuf, len);
596 len = BN_num_bytes(server_modulus);
597 if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
598 fatal("%s: bad server modulus (len %d)", __func__, len);
599 BN_bn2bin(server_modulus, nbuf);
600 EVP_DigestUpdate(&md, nbuf, len);
602 EVP_DigestUpdate(&md, cookie, 8);
604 EVP_DigestFinal(&md, obuf, NULL);
605 memcpy(id, obuf, 16);
607 memset(nbuf, 0, sizeof(nbuf));
608 memset(obuf, 0, sizeof(obuf));
609 memset(&md, 0, sizeof(md));
612 #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH) || defined(DEBUG_KEXECDH)
614 dump_digest(char *msg, u_char *digest, int len)
618 fprintf(stderr, "%s\n", msg);
619 for (i = 0; i < len; i++) {
620 fprintf(stderr, "%02x", digest[i]);
622 fprintf(stderr, "\n");
624 fprintf(stderr, " ");
626 fprintf(stderr, "\n");