1 /* $OpenBSD: kex.c,v 1.81 2009/05/27 06:34:36 andreas Exp $ */
2 /*
3 * Copyright © 2013
4 * Thorsten “mirabilos” Glaser <tg@mirbsd.org>
5 * Copyright (c) 2000, 2001 Markus Friedl. All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 * notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 * notice, this list of conditions and the following disclaimer in the
14 * documentation and/or other materials provided with the distribution.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
17 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
18 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
19 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
21 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
22 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
23 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
24 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
25 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
26 */
27
28 #include <sys/param.h>
29
30 #include <signal.h>
31 #include <stdio.h>
32 #include <stdlib.h>
33 #include <string.h>
34
35 #include <openssl/crypto.h>
36
37 #include "xmalloc.h"
38 #include "ssh2.h"
39 #include "buffer.h"
40 #include "packet.h"
41 #include "compat.h"
42 #include "cipher.h"
43 #include "key.h"
44 #include "kex.h"
45 #include "log.h"
46 #include "mac.h"
47 #include "match.h"
48 #include "dispatch.h"
49 #include "monitor.h"
50
51 __RCSID("$MirOS: src/usr.bin/ssh/kex.c,v 1.11 2013/10/31 20:07:12 tg Exp $");
52
53 extern const EVP_MD *evp_ssh_sha256(void);
54
55 /* prototype */
56 static void kex_kexinit_finish(Kex *);
57 static void kex_choose_conf(Kex *);
58
59 /* put algorithm proposal into buffer */
60 static void
kex_prop2buf(Buffer * b,const char * proposal[PROPOSAL_MAX])61 kex_prop2buf(Buffer *b, const char *proposal[PROPOSAL_MAX])
62 {
63 u_int i;
64
65 buffer_clear(b);
66 /*
67 * add a dummy cookie, the cookie will be overwritten by
68 * kex_send_kexinit(), each time a kexinit is set
69 */
70 for (i = 0; i < KEX_COOKIE_LEN; i++)
71 buffer_put_char(b, 0);
72 for (i = 0; i < PROPOSAL_MAX; i++)
73 buffer_put_cstring(b, proposal[i]);
74 buffer_put_char(b, 0); /* first_kex_packet_follows */
75 buffer_put_int(b, 0); /* uint32 reserved */
76 }
77
78 /* parse buffer and return algorithm proposal */
79 static char **
kex_buf2prop(Buffer * raw,int * first_kex_follows)80 kex_buf2prop(Buffer *raw, int *first_kex_follows)
81 {
82 Buffer b;
83 u_int i;
84 char **proposal;
85
86 proposal = xcalloc(PROPOSAL_MAX, sizeof(char *));
87
88 buffer_init(&b);
89 buffer_append(&b, buffer_ptr(raw), buffer_len(raw));
90 /* skip cookie */
91 for (i = 0; i < KEX_COOKIE_LEN; i++)
92 buffer_get_char(&b);
93 /* extract kex init proposal strings */
94 for (i = 0; i < PROPOSAL_MAX; i++) {
95 proposal[i] = buffer_get_string(&b,NULL);
96 debug2("kex_parse_kexinit: %s", proposal[i]);
97 }
98 /* first kex follows / reserved */
99 i = buffer_get_char(&b);
100 if (first_kex_follows != NULL)
101 *first_kex_follows = i;
102 debug2("kex_parse_kexinit: first_kex_follows %d ", i);
103 i = buffer_get_int(&b);
104 debug2("kex_parse_kexinit: reserved %u ", i);
105 buffer_free(&b);
106 return proposal;
107 }
108
109 static void
kex_prop_free(char ** proposal)110 kex_prop_free(char **proposal)
111 {
112 u_int i;
113
114 for (i = 0; i < PROPOSAL_MAX; i++)
115 xfree(proposal[i]);
116 xfree(proposal);
117 }
118
119 /* ARGSUSED */
120 static void
kex_protocol_error(int type,u_int32_t seq,void * ctxt)121 kex_protocol_error(int type, u_int32_t seq, void *ctxt __attribute__((__unused__)))
122 {
123 error("Hm, kex protocol error: type %d seq %u", type, seq);
124 }
125
126 static void
kex_reset_dispatch(void)127 kex_reset_dispatch(void)
128 {
129 dispatch_range(SSH2_MSG_TRANSPORT_MIN,
130 SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error);
131 dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit);
132 }
133
134 void
kex_finish(Kex * kex)135 kex_finish(Kex *kex)
136 {
137 kex_reset_dispatch();
138
139 packet_start(SSH2_MSG_NEWKEYS);
140 packet_send();
141 /* packet_write_wait(); */
142 debug("SSH2_MSG_NEWKEYS sent");
143
144 debug("expecting SSH2_MSG_NEWKEYS");
145 packet_read_expect(SSH2_MSG_NEWKEYS);
146 packet_check_eom();
147 debug("SSH2_MSG_NEWKEYS received");
148
149 kex->done = 1;
150 buffer_clear(&kex->peer);
151 /* buffer_clear(&kex->my); */
152 kex->flags &= ~KEX_INIT_SENT;
153 xfree(kex->name);
154 kex->name = NULL;
155 }
156
157 void
kex_send_kexinit(Kex * kex)158 kex_send_kexinit(Kex *kex)
159 {
160 u_char *cookie;
161
162 if (kex == NULL) {
163 error("kex_send_kexinit: no kex, cannot rekey");
164 return;
165 }
166 if (kex->flags & KEX_INIT_SENT) {
167 debug("KEX_INIT_SENT");
168 return;
169 }
170 kex->done = 0;
171
172 /* generate a random cookie */
173 if (buffer_len(&kex->my) < KEX_COOKIE_LEN)
174 fatal("kex_send_kexinit: kex proposal too short");
175 cookie = buffer_ptr(&kex->my);
176 arc4random_buf(cookie, KEX_COOKIE_LEN);
177 packet_start(SSH2_MSG_KEXINIT);
178 packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my));
179 packet_send();
180 debug("SSH2_MSG_KEXINIT sent");
181 kex->flags |= KEX_INIT_SENT;
182 }
183
184 /* ARGSUSED */
185 void
kex_input_kexinit(int type,u_int32_t seq,void * ctxt)186 kex_input_kexinit(int type __attribute__((__unused__)),
187 u_int32_t seq __attribute__((__unused__)), void *ctxt)
188 {
189 char *ptr;
190 u_int i, dlen;
191 Kex *kex = (Kex *)ctxt;
192
193 debug("SSH2_MSG_KEXINIT received");
194 if (kex == NULL)
195 fatal("kex_input_kexinit: no kex, cannot rekey");
196
197 ptr = packet_get_raw(&dlen);
198 buffer_append(&kex->peer, ptr, dlen);
199
200 /* discard packet */
201 for (i = 0; i < KEX_COOKIE_LEN; i++)
202 packet_get_char();
203 for (i = 0; i < PROPOSAL_MAX; i++)
204 xfree(packet_get_string(NULL));
205 (void) packet_get_char();
206 (void) packet_get_int();
207 packet_check_eom();
208
209 kex_kexinit_finish(kex);
210 }
211
212 Kex *
kex_setup(const char * proposal[PROPOSAL_MAX])213 kex_setup(const char *proposal[PROPOSAL_MAX])
214 {
215 Kex *kex;
216
217 kex = xcalloc(1, sizeof(*kex));
218 buffer_init(&kex->peer);
219 buffer_init(&kex->my);
220 kex_prop2buf(&kex->my, proposal);
221 kex->done = 0;
222
223 kex_send_kexinit(kex); /* we start */
224 kex_reset_dispatch();
225
226 return kex;
227 }
228
229 static void
kex_kexinit_finish(Kex * kex)230 kex_kexinit_finish(Kex *kex)
231 {
232 if (!(kex->flags & KEX_INIT_SENT))
233 kex_send_kexinit(kex);
234
235 kex_choose_conf(kex);
236
237 if (kex->kex_type >= 0 && kex->kex_type < KEX_MAX &&
238 kex->kex[kex->kex_type] != NULL) {
239 (kex->kex[kex->kex_type])(kex);
240 } else {
241 fatal("Unsupported key exchange %d", kex->kex_type);
242 }
243 }
244
245 static void
choose_enc(Enc * enc,char * client,char * server)246 choose_enc(Enc *enc, char *client, char *server)
247 {
248 char *name = match_list(client, server, NULL);
249 if (name == NULL)
250 fatal("no matching cipher found: client %s server %s",
251 client, server);
252 if ((enc->cipher = cipher_by_name(name)) == NULL)
253 fatal("matching cipher is not supported: %s", name);
254 enc->name = name;
255 enc->enabled = 0;
256 enc->iv = NULL;
257 enc->key = NULL;
258 enc->key_len = cipher_keylen(enc->cipher);
259 enc->block_size = cipher_blocksize(enc->cipher);
260 }
261
262 static void
choose_mac(Mac * mac,char * client,char * server)263 choose_mac(Mac *mac, char *client, char *server)
264 {
265 char *name = match_list(client, server, NULL);
266 if (name == NULL)
267 fatal("no matching mac found: client %s server %s",
268 client, server);
269 if (mac_setup(mac, name) < 0)
270 fatal("unsupported mac %s", name);
271 /* truncate the key */
272 if (datafellows & SSH_BUG_HMAC)
273 mac->key_len = 16;
274 mac->name = name;
275 mac->key = NULL;
276 mac->enabled = 0;
277 }
278
279 static void
choose_comp(Comp * comp,char * client,char * server)280 choose_comp(Comp *comp, char *client, char *server)
281 {
282 char *name = match_list(client, server, NULL);
283 if (name == NULL)
284 fatal("no matching comp found: client %s server %s", client, server);
285 if (strcmp(name, "zlib@openssh.com") == 0) {
286 comp->type = COMP_DELAYED;
287 } else if (strcmp(name, "zlib") == 0) {
288 comp->type = COMP_ZLIB;
289 } else if (strcmp(name, "none") == 0) {
290 comp->type = COMP_NONE;
291 } else {
292 fatal("unsupported comp %s", name);
293 }
294 comp->name = name;
295 }
296
297 static void
choose_kex(Kex * k,char * client,char * server)298 choose_kex(Kex *k, char *client, char *server)
299 {
300 k->name = match_list(client, server, NULL);
301 if (k->name == NULL)
302 fatal("Unable to negotiate a key exchange method");
303 if (strcmp(k->name, KEX_DH1) == 0) {
304 k->kex_type = KEX_DH_GRP1_SHA1;
305 k->evp_md = EVP_sha1();
306 } else if (strcmp(k->name, KEX_DH14) == 0) {
307 k->kex_type = KEX_DH_GRP14_SHA1;
308 k->evp_md = EVP_sha1();
309 } else if (strcmp(k->name, KEX_DHGEX_SHA1) == 0) {
310 k->kex_type = KEX_DH_GEX_SHA1;
311 k->evp_md = EVP_sha1();
312 } else if (strcmp(k->name, KEX_DHGEX_SHA256) == 0) {
313 k->kex_type = KEX_DH_GEX_SHA256;
314 k->evp_md = evp_ssh_sha256();
315 } else
316 fatal("bad kex alg %s", k->name);
317 }
318
319 static void
choose_hostkeyalg(Kex * k,char * client,char * server)320 choose_hostkeyalg(Kex *k, char *client, char *server)
321 {
322 char *hostkeyalg = match_list(client, server, NULL);
323 if (hostkeyalg == NULL)
324 fatal("no hostkey alg");
325 k->hostkey_type = key_type_from_name(hostkeyalg);
326 if (k->hostkey_type == KEY_UNSPEC)
327 fatal("bad hostkey alg '%s'", hostkeyalg);
328 xfree(hostkeyalg);
329 }
330
331 static int
proposals_match(char * my[PROPOSAL_MAX],char * peer[PROPOSAL_MAX])332 proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX])
333 {
334 static int check[] = {
335 PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1
336 };
337 int *idx;
338 char *p;
339
340 for (idx = &check[0]; *idx != -1; idx++) {
341 if ((p = strchr(my[*idx], ',')) != NULL)
342 *p = '\0';
343 if ((p = strchr(peer[*idx], ',')) != NULL)
344 *p = '\0';
345 if (strcmp(my[*idx], peer[*idx]) != 0) {
346 debug2("proposal mismatch: my %s peer %s",
347 my[*idx], peer[*idx]);
348 return (0);
349 }
350 }
351 debug2("proposals match");
352 return (1);
353 }
354
355 static void
kex_choose_conf(Kex * kex)356 kex_choose_conf(Kex *kex)
357 {
358 Newkeys *newkeys;
359 char **my, **peer;
360 char **cprop, **sprop;
361 int nenc, nmac, ncomp;
362 u_int mode, ctos, need;
363 int first_kex_follows, type;
364
365 my = kex_buf2prop(&kex->my, NULL);
366 peer = kex_buf2prop(&kex->peer, &first_kex_follows);
367
368 if (kex->server) {
369 cprop=peer;
370 sprop=my;
371 } else {
372 cprop=my;
373 sprop=peer;
374 }
375
376 /* Algorithm Negotiation */
377 for (mode = 0; mode < MODE_MAX; mode++) {
378 newkeys = xcalloc(1, sizeof(*newkeys));
379 kex->newkeys[mode] = newkeys;
380 ctos = (!kex->server && mode == MODE_OUT) ||
381 (kex->server && mode == MODE_IN);
382 nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC;
383 nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC;
384 ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC;
385 choose_enc (&newkeys->enc, cprop[nenc], sprop[nenc]);
386 choose_mac (&newkeys->mac, cprop[nmac], sprop[nmac]);
387 choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]);
388 debug("kex: %s %s %s %s",
389 ctos ? "client->server" : "server->client",
390 newkeys->enc.name,
391 newkeys->mac.name,
392 newkeys->comp.name);
393 }
394 choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]);
395 choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
396 sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]);
397 need = 0;
398 for (mode = 0; mode < MODE_MAX; mode++) {
399 newkeys = kex->newkeys[mode];
400 if (need < newkeys->enc.key_len)
401 need = newkeys->enc.key_len;
402 if (need < newkeys->enc.block_size)
403 need = newkeys->enc.block_size;
404 if (need < newkeys->mac.key_len)
405 need = newkeys->mac.key_len;
406 }
407 /* XXX need runden? */
408 kex->we_need = need;
409
410 /* ignore the next message if the proposals do not match */
411 if (first_kex_follows && !proposals_match(my, peer) &&
412 !(datafellows & SSH_BUG_FIRSTKEX)) {
413 type = packet_read();
414 debug2("skipping next packet (type %u)", type);
415 }
416
417 kex_prop_free(my);
418 kex_prop_free(peer);
419 }
420
421 static u_char *
derive_key(Kex * kex,int id,u_int need,u_char * hash,u_int hashlen,BIGNUM * shared_secret)422 derive_key(Kex *kex, int id, u_int need, u_char *hash, u_int hashlen,
423 BIGNUM *shared_secret)
424 {
425 Buffer b;
426 EVP_MD_CTX md;
427 char c = id;
428 u_int have;
429 int mdsz;
430 u_char *digest;
431
432 if ((mdsz = EVP_MD_size(kex->evp_md)) <= 0)
433 fatal("bad kex md size %d", mdsz);
434 digest = xmalloc(roundup(need, mdsz));
435
436 buffer_init(&b);
437 buffer_put_bignum2(&b, shared_secret);
438
439 /* K1 = HASH(K || H || "A" || session_id) */
440 EVP_DigestInit(&md, kex->evp_md);
441 if (!(datafellows & SSH_BUG_DERIVEKEY))
442 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
443 EVP_DigestUpdate(&md, hash, hashlen);
444 EVP_DigestUpdate(&md, &c, 1);
445 EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len);
446 EVP_DigestFinal(&md, digest, NULL);
447
448 /*
449 * expand key:
450 * Kn = HASH(K || H || K1 || K2 || ... || Kn-1)
451 * Key = K1 || K2 || ... || Kn
452 */
453 for (have = mdsz; need > have; have += mdsz) {
454 EVP_DigestInit(&md, kex->evp_md);
455 if (!(datafellows & SSH_BUG_DERIVEKEY))
456 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
457 EVP_DigestUpdate(&md, hash, hashlen);
458 EVP_DigestUpdate(&md, digest, have);
459 EVP_DigestFinal(&md, digest + have, NULL);
460 }
461 buffer_free(&b);
462 #ifdef DEBUG_KEX
463 fprintf(stderr, "key '%c'== ", c);
464 dump_digest("key", digest, need);
465 #endif
466 return digest;
467 }
468
469 Newkeys *current_keys[MODE_MAX];
470
471 #define NKEYS 6
472 void
kex_derive_keys(Kex * kex,u_char * hash,u_int hashlen,BIGNUM * shared_secret)473 kex_derive_keys(Kex *kex, u_char *hash, u_int hashlen, BIGNUM *shared_secret)
474 {
475 u_char *keys[NKEYS];
476 u_int i, mode, ctos;
477
478 for (i = 0; i < NKEYS; i++) {
479 keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, hashlen,
480 shared_secret);
481 }
482
483 debug2("kex_derive_keys");
484 for (mode = 0; mode < MODE_MAX; mode++) {
485 current_keys[mode] = kex->newkeys[mode];
486 kex->newkeys[mode] = NULL;
487 ctos = (!kex->server && mode == MODE_OUT) ||
488 (kex->server && mode == MODE_IN);
489 current_keys[mode]->enc.iv = keys[ctos ? 0 : 1];
490 current_keys[mode]->enc.key = keys[ctos ? 2 : 3];
491 current_keys[mode]->mac.key = keys[ctos ? 4 : 5];
492 }
493 }
494
495 Newkeys *
kex_get_newkeys(int mode)496 kex_get_newkeys(int mode)
497 {
498 Newkeys *ret;
499
500 ret = current_keys[mode];
501 current_keys[mode] = NULL;
502 return ret;
503 }
504
505 void
derive_ssh1_session_id(BIGNUM * host_modulus,BIGNUM * server_modulus,u_int8_t cookie[8],u_int8_t id[16])506 derive_ssh1_session_id(BIGNUM *host_modulus, BIGNUM *server_modulus,
507 u_int8_t cookie[8], u_int8_t id[16])
508 {
509 const EVP_MD *evp_md = EVP_md5();
510 EVP_MD_CTX md;
511 u_int8_t nbuf[2048], obuf[EVP_MAX_MD_SIZE];
512 int len;
513
514 EVP_DigestInit(&md, evp_md);
515
516 len = BN_num_bytes(host_modulus);
517 if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
518 fatal("%s: bad host modulus (len %d)", __func__, len);
519 BN_bn2bin(host_modulus, nbuf);
520 EVP_DigestUpdate(&md, nbuf, len);
521
522 len = BN_num_bytes(server_modulus);
523 if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
524 fatal("%s: bad server modulus (len %d)", __func__, len);
525 BN_bn2bin(server_modulus, nbuf);
526 EVP_DigestUpdate(&md, nbuf, len);
527
528 EVP_DigestUpdate(&md, cookie, 8);
529
530 EVP_DigestFinal(&md, obuf, NULL);
531 memcpy(id, obuf, 16);
532
533 memset(nbuf, 0, sizeof(nbuf));
534 memset(obuf, 0, sizeof(obuf));
535 memset(&md, 0, sizeof(md));
536 }
537
538 #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH)
539 void
dump_digest(char * msg,u_char * digest,int len)540 dump_digest(char *msg, u_char *digest, int len)
541 {
542 u_int i;
543
544 fprintf(stderr, "%s\n", msg);
545 for (i = 0; i < len; i++) {
546 fprintf(stderr, "%02x", digest[i]);
547 if (i%32 == 31)
548 fprintf(stderr, "\n");
549 else if (i%8 == 7)
550 fprintf(stderr, " ");
551 }
552 fprintf(stderr, "\n");
553 }
554 #endif
555