2 * Copyright (c) 2000, 2001 Markus Friedl. All rights reserved.
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions
7 * 1. Redistributions of source code must retain the above copyright
8 * notice, this list of conditions and the following disclaimer.
9 * 2. Redistributions in binary form must reproduce the above copyright
10 * notice, this list of conditions and the following disclaimer in the
11 * documentation and/or other materials provided with the distribution.
13 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
14 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
15 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
16 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
17 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
18 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
19 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
20 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
21 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
22 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
26 RCSID("$OpenBSD: kex.c,v 1.53 2003/02/02 10:56:08 markus Exp $");
28 #include <openssl/crypto.h>
45 #define KEX_COOKIE_LEN 16
47 /* Use privilege separation for sshd */
49 struct monitor *pmonitor;
53 static void kex_kexinit_finish(Kex *);
54 static void kex_choose_conf(Kex *);
56 /* put algorithm proposal into buffer */
58 kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX])
64 * add a dummy cookie, the cookie will be overwritten by
65 * kex_send_kexinit(), each time a kexinit is set
67 for (i = 0; i < KEX_COOKIE_LEN; i++)
68 buffer_put_char(b, 0);
69 for (i = 0; i < PROPOSAL_MAX; i++)
70 buffer_put_cstring(b, proposal[i]);
71 buffer_put_char(b, 0); /* first_kex_packet_follows */
72 buffer_put_int(b, 0); /* uint32 reserved */
75 /* parse buffer and return algorithm proposal */
77 kex_buf2prop(Buffer *raw, int *first_kex_follows)
83 proposal = xmalloc(PROPOSAL_MAX * sizeof(char *));
86 buffer_append(&b, buffer_ptr(raw), buffer_len(raw));
88 for (i = 0; i < KEX_COOKIE_LEN; i++)
90 /* extract kex init proposal strings */
91 for (i = 0; i < PROPOSAL_MAX; i++) {
92 proposal[i] = buffer_get_string(&b,NULL);
93 debug2("kex_parse_kexinit: %s", proposal[i]);
95 /* first kex follows / reserved */
96 i = buffer_get_char(&b);
97 if (first_kex_follows != NULL)
98 *first_kex_follows = i;
99 debug2("kex_parse_kexinit: first_kex_follows %d ", i);
100 i = buffer_get_int(&b);
101 debug2("kex_parse_kexinit: reserved %d ", i);
107 kex_prop_free(char **proposal)
111 for (i = 0; i < PROPOSAL_MAX; i++)
117 kex_protocol_error(int type, u_int32_t seq, void *ctxt)
119 error("Hm, kex protocol error: type %d seq %u", type, seq);
123 kex_reset_dispatch(void)
125 dispatch_range(SSH2_MSG_TRANSPORT_MIN,
126 SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error);
127 dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit);
133 kex_reset_dispatch();
135 packet_start(SSH2_MSG_NEWKEYS);
137 /* packet_write_wait(); */
138 debug("SSH2_MSG_NEWKEYS sent");
140 debug("expecting SSH2_MSG_NEWKEYS");
141 packet_read_expect(SSH2_MSG_NEWKEYS);
143 debug("SSH2_MSG_NEWKEYS received");
146 buffer_clear(&kex->peer);
147 /* buffer_clear(&kex->my); */
148 kex->flags &= ~KEX_INIT_SENT;
154 kex_send_kexinit(Kex *kex)
161 error("kex_send_kexinit: no kex, cannot rekey");
164 if (kex->flags & KEX_INIT_SENT) {
165 debug("KEX_INIT_SENT");
170 /* generate a random cookie */
171 if (buffer_len(&kex->my) < KEX_COOKIE_LEN)
172 fatal("kex_send_kexinit: kex proposal too short");
173 cookie = buffer_ptr(&kex->my);
174 for (i = 0; i < KEX_COOKIE_LEN; i++) {
180 packet_start(SSH2_MSG_KEXINIT);
181 packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my));
183 debug("SSH2_MSG_KEXINIT sent");
184 kex->flags |= KEX_INIT_SENT;
188 kex_input_kexinit(int type, u_int32_t seq, void *ctxt)
193 Kex *kex = (Kex *)ctxt;
195 debug("SSH2_MSG_KEXINIT received");
197 fatal("kex_input_kexinit: no kex, cannot rekey");
199 ptr = packet_get_raw(&dlen);
200 buffer_append(&kex->peer, ptr, dlen);
203 for (i = 0; i < KEX_COOKIE_LEN; i++)
205 for (i = 0; i < PROPOSAL_MAX; i++)
206 xfree(packet_get_string(NULL));
207 (void) packet_get_char();
208 (void) packet_get_int();
211 kex_kexinit_finish(kex);
215 kex_setup(char *proposal[PROPOSAL_MAX])
219 kex = xmalloc(sizeof(*kex));
220 memset(kex, 0, sizeof(*kex));
221 buffer_init(&kex->peer);
222 buffer_init(&kex->my);
223 kex_prop2buf(&kex->my, proposal);
226 kex_send_kexinit(kex); /* we start */
227 kex_reset_dispatch();
233 kex_kexinit_finish(Kex *kex)
235 if (!(kex->flags & KEX_INIT_SENT))
236 kex_send_kexinit(kex);
238 kex_choose_conf(kex);
240 switch (kex->kex_type) {
248 fatal("Unsupported key exchange %d", kex->kex_type);
253 choose_enc(Enc *enc, char *client, char *server)
255 char *name = match_list(client, server, NULL);
257 fatal("no matching cipher found: client %s server %s", client, server);
258 if ((enc->cipher = cipher_by_name(name)) == NULL)
259 fatal("matching cipher is not supported: %s", name);
264 enc->key_len = cipher_keylen(enc->cipher);
265 enc->block_size = cipher_blocksize(enc->cipher);
268 choose_mac(Mac *mac, char *client, char *server)
270 char *name = match_list(client, server, NULL);
272 fatal("no matching mac found: client %s server %s", client, server);
273 if (mac_init(mac, name) < 0)
274 fatal("unsupported mac %s", name);
275 /* truncate the key */
276 if (datafellows & SSH_BUG_HMAC)
283 choose_comp(Comp *comp, char *client, char *server)
285 char *name = match_list(client, server, NULL);
287 fatal("no matching comp found: client %s server %s", client, server);
288 if (strcmp(name, "zlib") == 0) {
290 } else if (strcmp(name, "none") == 0) {
293 fatal("unsupported comp %s", name);
298 choose_kex(Kex *k, char *client, char *server)
300 k->name = match_list(client, server, NULL);
303 if (strcmp(k->name, KEX_DH1) == 0) {
304 k->kex_type = DH_GRP1_SHA1;
305 } else if (strcmp(k->name, KEX_DHGEX) == 0) {
306 k->kex_type = DH_GEX_SHA1;
308 fatal("bad kex alg %s", k->name);
311 choose_hostkeyalg(Kex *k, char *client, char *server)
313 char *hostkeyalg = match_list(client, server, NULL);
314 if (hostkeyalg == NULL)
315 fatal("no hostkey alg");
316 k->hostkey_type = key_type_from_name(hostkeyalg);
317 if (k->hostkey_type == KEY_UNSPEC)
318 fatal("bad hostkey alg '%s'", hostkeyalg);
323 proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX])
325 static int check[] = {
326 PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1
331 for (idx = &check[0]; *idx != -1; idx++) {
332 if ((p = strchr(my[*idx], ',')) != NULL)
334 if ((p = strchr(peer[*idx], ',')) != NULL)
336 if (strcmp(my[*idx], peer[*idx]) != 0) {
337 debug2("proposal mismatch: my %s peer %s",
338 my[*idx], peer[*idx]);
342 debug2("proposals match");
347 kex_choose_conf(Kex *kex)
351 char **cprop, **sprop;
352 int nenc, nmac, ncomp;
354 int ctos; /* direction: if true client-to-server */
356 int first_kex_follows, type;
358 my = kex_buf2prop(&kex->my, NULL);
359 peer = kex_buf2prop(&kex->peer, &first_kex_follows);
369 /* Algorithm Negotiation */
370 for (mode = 0; mode < MODE_MAX; mode++) {
371 newkeys = xmalloc(sizeof(*newkeys));
372 memset(newkeys, 0, sizeof(*newkeys));
373 kex->newkeys[mode] = newkeys;
374 ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN);
375 nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC;
376 nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC;
377 ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC;
378 choose_enc (&newkeys->enc, cprop[nenc], sprop[nenc]);
379 choose_mac (&newkeys->mac, cprop[nmac], sprop[nmac]);
380 choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]);
381 debug("kex: %s %s %s %s",
382 ctos ? "client->server" : "server->client",
387 choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]);
388 choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
389 sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]);
391 for (mode = 0; mode < MODE_MAX; mode++) {
392 newkeys = kex->newkeys[mode];
393 if (need < newkeys->enc.key_len)
394 need = newkeys->enc.key_len;
395 if (need < newkeys->enc.block_size)
396 need = newkeys->enc.block_size;
397 if (need < newkeys->mac.key_len)
398 need = newkeys->mac.key_len;
400 /* XXX need runden? */
403 /* ignore the next message if the proposals do not match */
404 if (first_kex_follows && !proposals_match(my, peer)) {
405 type = packet_read();
406 debug2("skipping next packet (type %u)", type);
414 derive_key(Kex *kex, int id, int need, u_char *hash, BIGNUM *shared_secret)
417 const EVP_MD *evp_md = EVP_sha1();
421 int mdsz = EVP_MD_size(evp_md);
422 u_char *digest = xmalloc(roundup(need, mdsz));
425 buffer_put_bignum2(&b, shared_secret);
427 /* K1 = HASH(K || H || "A" || session_id) */
428 EVP_DigestInit(&md, evp_md);
429 if (!(datafellows & SSH_BUG_DERIVEKEY))
430 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
431 EVP_DigestUpdate(&md, hash, mdsz);
432 EVP_DigestUpdate(&md, &c, 1);
433 EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len);
434 EVP_DigestFinal(&md, digest, NULL);
438 * Kn = HASH(K || H || K1 || K2 || ... || Kn-1)
439 * Key = K1 || K2 || ... || Kn
441 for (have = mdsz; need > have; have += mdsz) {
442 EVP_DigestInit(&md, evp_md);
443 if (!(datafellows & SSH_BUG_DERIVEKEY))
444 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
445 EVP_DigestUpdate(&md, hash, mdsz);
446 EVP_DigestUpdate(&md, digest, have);
447 EVP_DigestFinal(&md, digest + have, NULL);
451 fprintf(stderr, "key '%c'== ", c);
452 dump_digest("key", digest, need);
457 Newkeys *current_keys[MODE_MAX];
461 kex_derive_keys(Kex *kex, u_char *hash, BIGNUM *shared_secret)
466 for (i = 0; i < NKEYS; i++)
467 keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, shared_secret);
469 debug2("kex_derive_keys");
470 for (mode = 0; mode < MODE_MAX; mode++) {
471 current_keys[mode] = kex->newkeys[mode];
472 kex->newkeys[mode] = NULL;
473 ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN);
474 current_keys[mode]->enc.iv = keys[ctos ? 0 : 1];
475 current_keys[mode]->enc.key = keys[ctos ? 2 : 3];
476 current_keys[mode]->mac.key = keys[ctos ? 4 : 5];
481 kex_get_newkeys(int mode)
485 ret = current_keys[mode];
486 current_keys[mode] = NULL;
490 #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH)
492 dump_digest(char *msg, u_char *digest, int len)
496 fprintf(stderr, "%s\n", msg);
497 for (i = 0; i< len; i++) {
498 fprintf(stderr, "%02x", digest[i]);
500 fprintf(stderr, "\n");
502 fprintf(stderr, " ");
504 fprintf(stderr, "\n");