1 /* $OpenBSD: kex.c,v 1.109 2015/07/30 00:01:34 djm Exp $ */
2 /*
3 * Copyright (c) 2000, 2001 Markus Friedl. All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
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.
13 *
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.
24 */
25
26 #include "includes.h"
27
28 #include <sys/param.h> /* MAX roundup */
29
30 #include <signal.h>
31 #include <stdarg.h>
32 #include <stdio.h>
33 #include <stdlib.h>
34 #include <string.h>
35
36 #ifdef WITH_OPENSSL
37 #include <openssl/crypto.h>
38 #include <openssl/dh.h>
39 #endif
40
41 #include "ssh2.h"
42 #include "packet.h"
43 #include "compat.h"
44 #include "cipher.h"
45 #include "sshkey.h"
46 #include "kex.h"
47 #include "log.h"
48 #include "mac.h"
49 #include "match.h"
50 #include "misc.h"
51 #include "dispatch.h"
52 #include "monitor.h"
53 #include "roaming.h"
54
55 #include "ssherr.h"
56 #include "sshbuf.h"
57 #include "digest.h"
58
59 #if OPENSSL_VERSION_NUMBER >= 0x00907000L
60 # if defined(HAVE_EVP_SHA256)
61 # define evp_ssh_sha256 EVP_sha256
62 # else
63 extern const EVP_MD *evp_ssh_sha256(void);
64 # endif
65 #endif
66
67 /* prototype */
68 static int kex_choose_conf(struct ssh *);
69 static int kex_input_newkeys(int, u_int32_t, void *);
70
71 struct kexalg {
72 char *name;
73 u_int type;
74 int ec_nid;
75 int hash_alg;
76 };
77 static const struct kexalg kexalgs[] = {
78 #ifdef WITH_OPENSSL
79 { KEX_DH1, KEX_DH_GRP1_SHA1, 0, SSH_DIGEST_SHA1 },
80 { KEX_DH14, KEX_DH_GRP14_SHA1, 0, SSH_DIGEST_SHA1 },
81 { KEX_DHGEX_SHA1, KEX_DH_GEX_SHA1, 0, SSH_DIGEST_SHA1 },
82 #ifdef HAVE_EVP_SHA256
83 { KEX_DHGEX_SHA256, KEX_DH_GEX_SHA256, 0, SSH_DIGEST_SHA256 },
84 #endif /* HAVE_EVP_SHA256 */
85 #ifdef OPENSSL_HAS_ECC
86 { KEX_ECDH_SHA2_NISTP256, KEX_ECDH_SHA2,
87 NID_X9_62_prime256v1, SSH_DIGEST_SHA256 },
88 { KEX_ECDH_SHA2_NISTP384, KEX_ECDH_SHA2, NID_secp384r1,
89 SSH_DIGEST_SHA384 },
90 # ifdef OPENSSL_HAS_NISTP521
91 { KEX_ECDH_SHA2_NISTP521, KEX_ECDH_SHA2, NID_secp521r1,
92 SSH_DIGEST_SHA512 },
93 # endif /* OPENSSL_HAS_NISTP521 */
94 #endif /* OPENSSL_HAS_ECC */
95 #endif /* WITH_OPENSSL */
96 #if defined(HAVE_EVP_SHA256) || !defined(WITH_OPENSSL)
97 { KEX_CURVE25519_SHA256, KEX_C25519_SHA256, 0, SSH_DIGEST_SHA256 },
98 #endif /* HAVE_EVP_SHA256 || !WITH_OPENSSL */
99 { NULL, -1, -1, -1},
100 };
101
102 char *
kex_alg_list(char sep)103 kex_alg_list(char sep)
104 {
105 char *ret = NULL, *tmp;
106 size_t nlen, rlen = 0;
107 const struct kexalg *k;
108
109 for (k = kexalgs; k->name != NULL; k++) {
110 if (ret != NULL)
111 ret[rlen++] = sep;
112 nlen = strlen(k->name);
113 if ((tmp = realloc(ret, rlen + nlen + 2)) == NULL) {
114 free(ret);
115 return NULL;
116 }
117 ret = tmp;
118 memcpy(ret + rlen, k->name, nlen + 1);
119 rlen += nlen;
120 }
121 return ret;
122 }
123
124 static const struct kexalg *
kex_alg_by_name(const char * name)125 kex_alg_by_name(const char *name)
126 {
127 const struct kexalg *k;
128
129 for (k = kexalgs; k->name != NULL; k++) {
130 if (strcmp(k->name, name) == 0)
131 return k;
132 }
133 return NULL;
134 }
135
136 /* Validate KEX method name list */
137 int
kex_names_valid(const char * names)138 kex_names_valid(const char *names)
139 {
140 char *s, *cp, *p;
141
142 if (names == NULL || strcmp(names, "") == 0)
143 return 0;
144 if ((s = cp = strdup(names)) == NULL)
145 return 0;
146 for ((p = strsep(&cp, ",")); p && *p != '\0';
147 (p = strsep(&cp, ","))) {
148 if (kex_alg_by_name(p) == NULL) {
149 error("Unsupported KEX algorithm \"%.100s\"", p);
150 free(s);
151 return 0;
152 }
153 }
154 debug3("kex names ok: [%s]", names);
155 free(s);
156 return 1;
157 }
158
159 /*
160 * Concatenate algorithm names, avoiding duplicates in the process.
161 * Caller must free returned string.
162 */
163 char *
kex_names_cat(const char * a,const char * b)164 kex_names_cat(const char *a, const char *b)
165 {
166 char *ret = NULL, *tmp = NULL, *cp, *p;
167 size_t len;
168
169 if (a == NULL || *a == '\0')
170 return NULL;
171 if (b == NULL || *b == '\0')
172 return strdup(a);
173 if (strlen(b) > 1024*1024)
174 return NULL;
175 len = strlen(a) + strlen(b) + 2;
176 if ((tmp = cp = strdup(b)) == NULL ||
177 (ret = calloc(1, len)) == NULL) {
178 free(tmp);
179 return NULL;
180 }
181 strlcpy(ret, a, len);
182 for ((p = strsep(&cp, ",")); p && *p != '\0'; (p = strsep(&cp, ","))) {
183 if (match_list(ret, p, NULL) != NULL)
184 continue; /* Algorithm already present */
185 if (strlcat(ret, ",", len) >= len ||
186 strlcat(ret, p, len) >= len) {
187 free(tmp);
188 free(ret);
189 return NULL; /* Shouldn't happen */
190 }
191 }
192 free(tmp);
193 return ret;
194 }
195
196 /*
197 * Assemble a list of algorithms from a default list and a string from a
198 * configuration file. The user-provided string may begin with '+' to
199 * indicate that it should be appended to the default.
200 */
201 int
kex_assemble_names(const char * def,char ** list)202 kex_assemble_names(const char *def, char **list)
203 {
204 char *ret;
205
206 if (list == NULL || *list == NULL || **list == '\0') {
207 *list = strdup(def);
208 return 0;
209 }
210 if (**list != '+') {
211 return 0;
212 }
213
214 if ((ret = kex_names_cat(def, *list + 1)) == NULL)
215 return SSH_ERR_ALLOC_FAIL;
216 free(*list);
217 *list = ret;
218 return 0;
219 }
220
221 /* put algorithm proposal into buffer */
222 int
kex_prop2buf(struct sshbuf * b,char * proposal[PROPOSAL_MAX])223 kex_prop2buf(struct sshbuf *b, char *proposal[PROPOSAL_MAX])
224 {
225 u_int i;
226 int r;
227
228 sshbuf_reset(b);
229
230 /*
231 * add a dummy cookie, the cookie will be overwritten by
232 * kex_send_kexinit(), each time a kexinit is set
233 */
234 for (i = 0; i < KEX_COOKIE_LEN; i++) {
235 if ((r = sshbuf_put_u8(b, 0)) != 0)
236 return r;
237 }
238 for (i = 0; i < PROPOSAL_MAX; i++) {
239 if ((r = sshbuf_put_cstring(b, proposal[i])) != 0)
240 return r;
241 }
242 if ((r = sshbuf_put_u8(b, 0)) != 0 || /* first_kex_packet_follows */
243 (r = sshbuf_put_u32(b, 0)) != 0) /* uint32 reserved */
244 return r;
245 return 0;
246 }
247
248 /* parse buffer and return algorithm proposal */
249 int
kex_buf2prop(struct sshbuf * raw,int * first_kex_follows,char *** propp)250 kex_buf2prop(struct sshbuf *raw, int *first_kex_follows, char ***propp)
251 {
252 struct sshbuf *b = NULL;
253 u_char v;
254 u_int i;
255 char **proposal = NULL;
256 int r;
257
258 *propp = NULL;
259 if ((proposal = calloc(PROPOSAL_MAX, sizeof(char *))) == NULL)
260 return SSH_ERR_ALLOC_FAIL;
261 if ((b = sshbuf_fromb(raw)) == NULL) {
262 r = SSH_ERR_ALLOC_FAIL;
263 goto out;
264 }
265 if ((r = sshbuf_consume(b, KEX_COOKIE_LEN)) != 0) /* skip cookie */
266 goto out;
267 /* extract kex init proposal strings */
268 for (i = 0; i < PROPOSAL_MAX; i++) {
269 if ((r = sshbuf_get_cstring(b, &(proposal[i]), NULL)) != 0)
270 goto out;
271 debug2("kex_parse_kexinit: %s", proposal[i]);
272 }
273 /* first kex follows / reserved */
274 if ((r = sshbuf_get_u8(b, &v)) != 0 || /* first_kex_follows */
275 (r = sshbuf_get_u32(b, &i)) != 0) /* reserved */
276 goto out;
277 if (first_kex_follows != NULL)
278 *first_kex_follows = v;
279 debug2("first_kex_follows %d ", v);
280 debug2("reserved %u ", i);
281 r = 0;
282 *propp = proposal;
283 out:
284 if (r != 0 && proposal != NULL)
285 kex_prop_free(proposal);
286 sshbuf_free(b);
287 return r;
288 }
289
290 void
kex_prop_free(char ** proposal)291 kex_prop_free(char **proposal)
292 {
293 u_int i;
294
295 if (proposal == NULL)
296 return;
297 for (i = 0; i < PROPOSAL_MAX; i++)
298 free(proposal[i]);
299 free(proposal);
300 }
301
302 /* ARGSUSED */
303 static int
kex_protocol_error(int type,u_int32_t seq,void * ctxt)304 kex_protocol_error(int type, u_int32_t seq, void *ctxt)
305 {
306 error("Hm, kex protocol error: type %d seq %u", type, seq);
307 return 0;
308 }
309
310 static void
kex_reset_dispatch(struct ssh * ssh)311 kex_reset_dispatch(struct ssh *ssh)
312 {
313 ssh_dispatch_range(ssh, SSH2_MSG_TRANSPORT_MIN,
314 SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error);
315 ssh_dispatch_set(ssh, SSH2_MSG_KEXINIT, &kex_input_kexinit);
316 }
317
318 int
kex_send_newkeys(struct ssh * ssh)319 kex_send_newkeys(struct ssh *ssh)
320 {
321 int r;
322
323 kex_reset_dispatch(ssh);
324 if ((r = sshpkt_start(ssh, SSH2_MSG_NEWKEYS)) != 0 ||
325 (r = sshpkt_send(ssh)) != 0)
326 return r;
327 debug("SSH2_MSG_NEWKEYS sent");
328 debug("expecting SSH2_MSG_NEWKEYS");
329 ssh_dispatch_set(ssh, SSH2_MSG_NEWKEYS, &kex_input_newkeys);
330 return 0;
331 }
332
333 static int
kex_input_newkeys(int type,u_int32_t seq,void * ctxt)334 kex_input_newkeys(int type, u_int32_t seq, void *ctxt)
335 {
336 struct ssh *ssh = ctxt;
337 struct kex *kex = ssh->kex;
338 int r;
339
340 debug("SSH2_MSG_NEWKEYS received");
341 ssh_dispatch_set(ssh, SSH2_MSG_NEWKEYS, &kex_protocol_error);
342 if ((r = sshpkt_get_end(ssh)) != 0)
343 return r;
344 kex->done = 1;
345 sshbuf_reset(kex->peer);
346 /* sshbuf_reset(kex->my); */
347 kex->flags &= ~KEX_INIT_SENT;
348 free(kex->name);
349 kex->name = NULL;
350 return 0;
351 }
352
353 int
kex_send_kexinit(struct ssh * ssh)354 kex_send_kexinit(struct ssh *ssh)
355 {
356 u_char *cookie;
357 struct kex *kex = ssh->kex;
358 int r;
359
360 if (kex == NULL)
361 return SSH_ERR_INTERNAL_ERROR;
362 if (kex->flags & KEX_INIT_SENT)
363 return 0;
364 kex->done = 0;
365
366 /* generate a random cookie */
367 if (sshbuf_len(kex->my) < KEX_COOKIE_LEN)
368 return SSH_ERR_INVALID_FORMAT;
369 if ((cookie = sshbuf_mutable_ptr(kex->my)) == NULL)
370 return SSH_ERR_INTERNAL_ERROR;
371 arc4random_buf(cookie, KEX_COOKIE_LEN);
372
373 if ((r = sshpkt_start(ssh, SSH2_MSG_KEXINIT)) != 0 ||
374 (r = sshpkt_putb(ssh, kex->my)) != 0 ||
375 (r = sshpkt_send(ssh)) != 0)
376 return r;
377 debug("SSH2_MSG_KEXINIT sent");
378 kex->flags |= KEX_INIT_SENT;
379 return 0;
380 }
381
382 /* ARGSUSED */
383 int
kex_input_kexinit(int type,u_int32_t seq,void * ctxt)384 kex_input_kexinit(int type, u_int32_t seq, void *ctxt)
385 {
386 struct ssh *ssh = ctxt;
387 struct kex *kex = ssh->kex;
388 const u_char *ptr;
389 u_int i;
390 size_t dlen;
391 int r;
392
393 debug("SSH2_MSG_KEXINIT received");
394 if (kex == NULL)
395 return SSH_ERR_INVALID_ARGUMENT;
396
397 ptr = sshpkt_ptr(ssh, &dlen);
398 if ((r = sshbuf_put(kex->peer, ptr, dlen)) != 0)
399 return r;
400
401 /* discard packet */
402 for (i = 0; i < KEX_COOKIE_LEN; i++)
403 if ((r = sshpkt_get_u8(ssh, NULL)) != 0)
404 return r;
405 for (i = 0; i < PROPOSAL_MAX; i++)
406 if ((r = sshpkt_get_string(ssh, NULL, NULL)) != 0)
407 return r;
408 /*
409 * XXX RFC4253 sec 7: "each side MAY guess" - currently no supported
410 * KEX method has the server move first, but a server might be using
411 * a custom method or one that we otherwise don't support. We should
412 * be prepared to remember first_kex_follows here so we can eat a
413 * packet later.
414 * XXX2 - RFC4253 is kind of ambiguous on what first_kex_follows means
415 * for cases where the server *doesn't* go first. I guess we should
416 * ignore it when it is set for these cases, which is what we do now.
417 */
418 if ((r = sshpkt_get_u8(ssh, NULL)) != 0 || /* first_kex_follows */
419 (r = sshpkt_get_u32(ssh, NULL)) != 0 || /* reserved */
420 (r = sshpkt_get_end(ssh)) != 0)
421 return r;
422
423 if (!(kex->flags & KEX_INIT_SENT))
424 if ((r = kex_send_kexinit(ssh)) != 0)
425 return r;
426 if ((r = kex_choose_conf(ssh)) != 0)
427 return r;
428
429 if (kex->kex_type < KEX_MAX && kex->kex[kex->kex_type] != NULL)
430 return (kex->kex[kex->kex_type])(ssh);
431
432 return SSH_ERR_INTERNAL_ERROR;
433 }
434
435 int
kex_new(struct ssh * ssh,char * proposal[PROPOSAL_MAX],struct kex ** kexp)436 kex_new(struct ssh *ssh, char *proposal[PROPOSAL_MAX], struct kex **kexp)
437 {
438 struct kex *kex;
439 int r;
440
441 *kexp = NULL;
442 if ((kex = calloc(1, sizeof(*kex))) == NULL)
443 return SSH_ERR_ALLOC_FAIL;
444 if ((kex->peer = sshbuf_new()) == NULL ||
445 (kex->my = sshbuf_new()) == NULL) {
446 r = SSH_ERR_ALLOC_FAIL;
447 goto out;
448 }
449 if ((r = kex_prop2buf(kex->my, proposal)) != 0)
450 goto out;
451 kex->done = 0;
452 kex_reset_dispatch(ssh);
453 r = 0;
454 *kexp = kex;
455 out:
456 if (r != 0)
457 kex_free(kex);
458 return r;
459 }
460
461 void
kex_free_newkeys(struct newkeys * newkeys)462 kex_free_newkeys(struct newkeys *newkeys)
463 {
464 if (newkeys == NULL)
465 return;
466 if (newkeys->enc.key) {
467 explicit_bzero(newkeys->enc.key, newkeys->enc.key_len);
468 free(newkeys->enc.key);
469 newkeys->enc.key = NULL;
470 }
471 if (newkeys->enc.iv) {
472 explicit_bzero(newkeys->enc.iv, newkeys->enc.block_size);
473 free(newkeys->enc.iv);
474 newkeys->enc.iv = NULL;
475 }
476 free(newkeys->enc.name);
477 explicit_bzero(&newkeys->enc, sizeof(newkeys->enc));
478 free(newkeys->comp.name);
479 explicit_bzero(&newkeys->comp, sizeof(newkeys->comp));
480 mac_clear(&newkeys->mac);
481 if (newkeys->mac.key) {
482 explicit_bzero(newkeys->mac.key, newkeys->mac.key_len);
483 free(newkeys->mac.key);
484 newkeys->mac.key = NULL;
485 }
486 free(newkeys->mac.name);
487 explicit_bzero(&newkeys->mac, sizeof(newkeys->mac));
488 explicit_bzero(newkeys, sizeof(*newkeys));
489 free(newkeys);
490 }
491
492 void
kex_free(struct kex * kex)493 kex_free(struct kex *kex)
494 {
495 u_int mode;
496
497 #ifdef WITH_OPENSSL
498 if (kex->dh)
499 DH_free(kex->dh);
500 #ifdef OPENSSL_HAS_ECC
501 if (kex->ec_client_key)
502 EC_KEY_free(kex->ec_client_key);
503 #endif /* OPENSSL_HAS_ECC */
504 #endif /* WITH_OPENSSL */
505 for (mode = 0; mode < MODE_MAX; mode++) {
506 kex_free_newkeys(kex->newkeys[mode]);
507 kex->newkeys[mode] = NULL;
508 }
509 sshbuf_free(kex->peer);
510 sshbuf_free(kex->my);
511 free(kex->session_id);
512 free(kex->client_version_string);
513 free(kex->server_version_string);
514 free(kex->failed_choice);
515 free(kex);
516 }
517
518 int
kex_setup(struct ssh * ssh,char * proposal[PROPOSAL_MAX])519 kex_setup(struct ssh *ssh, char *proposal[PROPOSAL_MAX])
520 {
521 int r;
522
523 if ((r = kex_new(ssh, proposal, &ssh->kex)) != 0)
524 return r;
525 if ((r = kex_send_kexinit(ssh)) != 0) { /* we start */
526 kex_free(ssh->kex);
527 ssh->kex = NULL;
528 return r;
529 }
530 return 0;
531 }
532
533 static int
choose_enc(struct sshenc * enc,char * client,char * server)534 choose_enc(struct sshenc *enc, char *client, char *server)
535 {
536 char *name = match_list(client, server, NULL);
537
538 if (name == NULL)
539 return SSH_ERR_NO_CIPHER_ALG_MATCH;
540 if ((enc->cipher = cipher_by_name(name)) == NULL)
541 return SSH_ERR_INTERNAL_ERROR;
542 enc->name = name;
543 enc->enabled = 0;
544 enc->iv = NULL;
545 enc->iv_len = cipher_ivlen(enc->cipher);
546 enc->key = NULL;
547 enc->key_len = cipher_keylen(enc->cipher);
548 enc->block_size = cipher_blocksize(enc->cipher);
549 return 0;
550 }
551
552 static int
choose_mac(struct ssh * ssh,struct sshmac * mac,char * client,char * server)553 choose_mac(struct ssh *ssh, struct sshmac *mac, char *client, char *server)
554 {
555 char *name = match_list(client, server, NULL);
556
557 if (name == NULL)
558 return SSH_ERR_NO_MAC_ALG_MATCH;
559 if (mac_setup(mac, name) < 0)
560 return SSH_ERR_INTERNAL_ERROR;
561 /* truncate the key */
562 if (ssh->compat & SSH_BUG_HMAC)
563 mac->key_len = 16;
564 mac->name = name;
565 mac->key = NULL;
566 mac->enabled = 0;
567 return 0;
568 }
569
570 static int
choose_comp(struct sshcomp * comp,char * client,char * server)571 choose_comp(struct sshcomp *comp, char *client, char *server)
572 {
573 char *name = match_list(client, server, NULL);
574
575 if (name == NULL)
576 return SSH_ERR_NO_COMPRESS_ALG_MATCH;
577 if (strcmp(name, "zlib@openssh.com") == 0) {
578 comp->type = COMP_DELAYED;
579 } else if (strcmp(name, "zlib") == 0) {
580 comp->type = COMP_ZLIB;
581 } else if (strcmp(name, "none") == 0) {
582 comp->type = COMP_NONE;
583 } else {
584 return SSH_ERR_INTERNAL_ERROR;
585 }
586 comp->name = name;
587 return 0;
588 }
589
590 static int
choose_kex(struct kex * k,char * client,char * server)591 choose_kex(struct kex *k, char *client, char *server)
592 {
593 const struct kexalg *kexalg;
594
595 k->name = match_list(client, server, NULL);
596
597 if (k->name == NULL)
598 return SSH_ERR_NO_KEX_ALG_MATCH;
599 if ((kexalg = kex_alg_by_name(k->name)) == NULL)
600 return SSH_ERR_INTERNAL_ERROR;
601 k->kex_type = kexalg->type;
602 k->hash_alg = kexalg->hash_alg;
603 k->ec_nid = kexalg->ec_nid;
604 return 0;
605 }
606
607 static int
choose_hostkeyalg(struct kex * k,char * client,char * server)608 choose_hostkeyalg(struct kex *k, char *client, char *server)
609 {
610 char *hostkeyalg = match_list(client, server, NULL);
611
612 if (hostkeyalg == NULL)
613 return SSH_ERR_NO_HOSTKEY_ALG_MATCH;
614 k->hostkey_type = sshkey_type_from_name(hostkeyalg);
615 if (k->hostkey_type == KEY_UNSPEC)
616 return SSH_ERR_INTERNAL_ERROR;
617 k->hostkey_nid = sshkey_ecdsa_nid_from_name(hostkeyalg);
618 free(hostkeyalg);
619 return 0;
620 }
621
622 static int
proposals_match(char * my[PROPOSAL_MAX],char * peer[PROPOSAL_MAX])623 proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX])
624 {
625 static int check[] = {
626 PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1
627 };
628 int *idx;
629 char *p;
630
631 for (idx = &check[0]; *idx != -1; idx++) {
632 if ((p = strchr(my[*idx], ',')) != NULL)
633 *p = '\0';
634 if ((p = strchr(peer[*idx], ',')) != NULL)
635 *p = '\0';
636 if (strcmp(my[*idx], peer[*idx]) != 0) {
637 debug2("proposal mismatch: my %s peer %s",
638 my[*idx], peer[*idx]);
639 return (0);
640 }
641 }
642 debug2("proposals match");
643 return (1);
644 }
645
646 static int
kex_choose_conf(struct ssh * ssh)647 kex_choose_conf(struct ssh *ssh)
648 {
649 struct kex *kex = ssh->kex;
650 struct newkeys *newkeys;
651 char **my = NULL, **peer = NULL;
652 char **cprop, **sprop;
653 int nenc, nmac, ncomp;
654 u_int mode, ctos, need, dh_need, authlen;
655 int r, first_kex_follows;
656
657 if ((r = kex_buf2prop(kex->my, NULL, &my)) != 0 ||
658 (r = kex_buf2prop(kex->peer, &first_kex_follows, &peer)) != 0)
659 goto out;
660
661 if (kex->server) {
662 cprop=peer;
663 sprop=my;
664 } else {
665 cprop=my;
666 sprop=peer;
667 }
668
669 /* Check whether server offers roaming */
670 if (!kex->server) {
671 char *roaming = match_list(KEX_RESUME,
672 peer[PROPOSAL_KEX_ALGS], NULL);
673
674 if (roaming) {
675 kex->roaming = 1;
676 free(roaming);
677 }
678 }
679
680 /* Algorithm Negotiation */
681 for (mode = 0; mode < MODE_MAX; mode++) {
682 if ((newkeys = calloc(1, sizeof(*newkeys))) == NULL) {
683 r = SSH_ERR_ALLOC_FAIL;
684 goto out;
685 }
686 kex->newkeys[mode] = newkeys;
687 ctos = (!kex->server && mode == MODE_OUT) ||
688 (kex->server && mode == MODE_IN);
689 nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC;
690 nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC;
691 ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC;
692 if ((r = choose_enc(&newkeys->enc, cprop[nenc],
693 sprop[nenc])) != 0) {
694 kex->failed_choice = peer[nenc];
695 peer[nenc] = NULL;
696 goto out;
697 }
698 authlen = cipher_authlen(newkeys->enc.cipher);
699 /* ignore mac for authenticated encryption */
700 if (authlen == 0 &&
701 (r = choose_mac(ssh, &newkeys->mac, cprop[nmac],
702 sprop[nmac])) != 0) {
703 kex->failed_choice = peer[nmac];
704 peer[nmac] = NULL;
705 goto out;
706 }
707 if ((r = choose_comp(&newkeys->comp, cprop[ncomp],
708 sprop[ncomp])) != 0) {
709 kex->failed_choice = peer[ncomp];
710 peer[ncomp] = NULL;
711 goto out;
712 }
713 debug("kex: %s %s %s %s",
714 ctos ? "client->server" : "server->client",
715 newkeys->enc.name,
716 authlen == 0 ? newkeys->mac.name : "<implicit>",
717 newkeys->comp.name);
718 }
719 if ((r = choose_kex(kex, cprop[PROPOSAL_KEX_ALGS],
720 sprop[PROPOSAL_KEX_ALGS])) != 0) {
721 kex->failed_choice = peer[PROPOSAL_KEX_ALGS];
722 peer[PROPOSAL_KEX_ALGS] = NULL;
723 goto out;
724 }
725 if ((r = choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
726 sprop[PROPOSAL_SERVER_HOST_KEY_ALGS])) != 0) {
727 kex->failed_choice = peer[PROPOSAL_SERVER_HOST_KEY_ALGS];
728 peer[PROPOSAL_SERVER_HOST_KEY_ALGS] = NULL;
729 goto out;
730 }
731 need = dh_need = 0;
732 for (mode = 0; mode < MODE_MAX; mode++) {
733 newkeys = kex->newkeys[mode];
734 need = MAX(need, newkeys->enc.key_len);
735 need = MAX(need, newkeys->enc.block_size);
736 need = MAX(need, newkeys->enc.iv_len);
737 need = MAX(need, newkeys->mac.key_len);
738 dh_need = MAX(dh_need, cipher_seclen(newkeys->enc.cipher));
739 dh_need = MAX(dh_need, newkeys->enc.block_size);
740 dh_need = MAX(dh_need, newkeys->enc.iv_len);
741 dh_need = MAX(dh_need, newkeys->mac.key_len);
742 }
743 /* XXX need runden? */
744 kex->we_need = need;
745 kex->dh_need = dh_need;
746
747 /* ignore the next message if the proposals do not match */
748 if (first_kex_follows && !proposals_match(my, peer) &&
749 !(ssh->compat & SSH_BUG_FIRSTKEX))
750 ssh->dispatch_skip_packets = 1;
751 r = 0;
752 out:
753 kex_prop_free(my);
754 kex_prop_free(peer);
755 return r;
756 }
757
758 static int
derive_key(struct ssh * ssh,int id,u_int need,u_char * hash,u_int hashlen,const struct sshbuf * shared_secret,u_char ** keyp)759 derive_key(struct ssh *ssh, int id, u_int need, u_char *hash, u_int hashlen,
760 const struct sshbuf *shared_secret, u_char **keyp)
761 {
762 struct kex *kex = ssh->kex;
763 struct ssh_digest_ctx *hashctx = NULL;
764 char c = id;
765 u_int have;
766 size_t mdsz;
767 u_char *digest;
768 int r;
769
770 if ((mdsz = ssh_digest_bytes(kex->hash_alg)) == 0)
771 return SSH_ERR_INVALID_ARGUMENT;
772 if ((digest = calloc(1, roundup(need, mdsz))) == NULL) {
773 r = SSH_ERR_ALLOC_FAIL;
774 goto out;
775 }
776
777 /* K1 = HASH(K || H || "A" || session_id) */
778 if ((hashctx = ssh_digest_start(kex->hash_alg)) == NULL ||
779 ssh_digest_update_buffer(hashctx, shared_secret) != 0 ||
780 ssh_digest_update(hashctx, hash, hashlen) != 0 ||
781 ssh_digest_update(hashctx, &c, 1) != 0 ||
782 ssh_digest_update(hashctx, kex->session_id,
783 kex->session_id_len) != 0 ||
784 ssh_digest_final(hashctx, digest, mdsz) != 0) {
785 r = SSH_ERR_LIBCRYPTO_ERROR;
786 goto out;
787 }
788 ssh_digest_free(hashctx);
789 hashctx = NULL;
790
791 /*
792 * expand key:
793 * Kn = HASH(K || H || K1 || K2 || ... || Kn-1)
794 * Key = K1 || K2 || ... || Kn
795 */
796 for (have = mdsz; need > have; have += mdsz) {
797 if ((hashctx = ssh_digest_start(kex->hash_alg)) == NULL ||
798 ssh_digest_update_buffer(hashctx, shared_secret) != 0 ||
799 ssh_digest_update(hashctx, hash, hashlen) != 0 ||
800 ssh_digest_update(hashctx, digest, have) != 0 ||
801 ssh_digest_final(hashctx, digest + have, mdsz) != 0) {
802 r = SSH_ERR_LIBCRYPTO_ERROR;
803 goto out;
804 }
805 ssh_digest_free(hashctx);
806 hashctx = NULL;
807 }
808 #ifdef DEBUG_KEX
809 fprintf(stderr, "key '%c'== ", c);
810 dump_digest("key", digest, need);
811 #endif
812 *keyp = digest;
813 digest = NULL;
814 r = 0;
815 out:
816 if (digest)
817 free(digest);
818 ssh_digest_free(hashctx);
819 return r;
820 }
821
822 #define NKEYS 6
823 int
kex_derive_keys(struct ssh * ssh,u_char * hash,u_int hashlen,const struct sshbuf * shared_secret)824 kex_derive_keys(struct ssh *ssh, u_char *hash, u_int hashlen,
825 const struct sshbuf *shared_secret)
826 {
827 struct kex *kex = ssh->kex;
828 u_char *keys[NKEYS];
829 u_int i, j, mode, ctos;
830 int r;
831
832 for (i = 0; i < NKEYS; i++) {
833 if ((r = derive_key(ssh, 'A'+i, kex->we_need, hash, hashlen,
834 shared_secret, &keys[i])) != 0) {
835 for (j = 0; j < i; j++)
836 free(keys[j]);
837 return r;
838 }
839 }
840 for (mode = 0; mode < MODE_MAX; mode++) {
841 ctos = (!kex->server && mode == MODE_OUT) ||
842 (kex->server && mode == MODE_IN);
843 kex->newkeys[mode]->enc.iv = keys[ctos ? 0 : 1];
844 kex->newkeys[mode]->enc.key = keys[ctos ? 2 : 3];
845 kex->newkeys[mode]->mac.key = keys[ctos ? 4 : 5];
846 }
847 return 0;
848 }
849
850 #ifdef WITH_OPENSSL
851 int
kex_derive_keys_bn(struct ssh * ssh,u_char * hash,u_int hashlen,const BIGNUM * secret)852 kex_derive_keys_bn(struct ssh *ssh, u_char *hash, u_int hashlen,
853 const BIGNUM *secret)
854 {
855 struct sshbuf *shared_secret;
856 int r;
857
858 if ((shared_secret = sshbuf_new()) == NULL)
859 return SSH_ERR_ALLOC_FAIL;
860 if ((r = sshbuf_put_bignum2(shared_secret, secret)) == 0)
861 r = kex_derive_keys(ssh, hash, hashlen, shared_secret);
862 sshbuf_free(shared_secret);
863 return r;
864 }
865 #endif
866
867 #ifdef WITH_SSH1
868 int
derive_ssh1_session_id(BIGNUM * host_modulus,BIGNUM * server_modulus,u_int8_t cookie[8],u_int8_t id[16])869 derive_ssh1_session_id(BIGNUM *host_modulus, BIGNUM *server_modulus,
870 u_int8_t cookie[8], u_int8_t id[16])
871 {
872 u_int8_t hbuf[2048], sbuf[2048], obuf[SSH_DIGEST_MAX_LENGTH];
873 struct ssh_digest_ctx *hashctx = NULL;
874 size_t hlen, slen;
875 int r;
876
877 hlen = BN_num_bytes(host_modulus);
878 slen = BN_num_bytes(server_modulus);
879 if (hlen < (512 / 8) || (u_int)hlen > sizeof(hbuf) ||
880 slen < (512 / 8) || (u_int)slen > sizeof(sbuf))
881 return SSH_ERR_KEY_BITS_MISMATCH;
882 if (BN_bn2bin(host_modulus, hbuf) <= 0 ||
883 BN_bn2bin(server_modulus, sbuf) <= 0) {
884 r = SSH_ERR_LIBCRYPTO_ERROR;
885 goto out;
886 }
887 if ((hashctx = ssh_digest_start(SSH_DIGEST_MD5)) == NULL) {
888 r = SSH_ERR_ALLOC_FAIL;
889 goto out;
890 }
891 if (ssh_digest_update(hashctx, hbuf, hlen) != 0 ||
892 ssh_digest_update(hashctx, sbuf, slen) != 0 ||
893 ssh_digest_update(hashctx, cookie, 8) != 0 ||
894 ssh_digest_final(hashctx, obuf, sizeof(obuf)) != 0) {
895 r = SSH_ERR_LIBCRYPTO_ERROR;
896 goto out;
897 }
898 memcpy(id, obuf, ssh_digest_bytes(SSH_DIGEST_MD5));
899 r = 0;
900 out:
901 ssh_digest_free(hashctx);
902 explicit_bzero(hbuf, sizeof(hbuf));
903 explicit_bzero(sbuf, sizeof(sbuf));
904 explicit_bzero(obuf, sizeof(obuf));
905 return r;
906 }
907 #endif
908
909 #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH) || defined(DEBUG_KEXECDH)
910 void
dump_digest(char * msg,u_char * digest,int len)911 dump_digest(char *msg, u_char *digest, int len)
912 {
913 fprintf(stderr, "%s\n", msg);
914 sshbuf_dump_data(digest, len, stderr);
915 }
916 #endif
917