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3c0ef626 | 1 | /* |
2 | * Copyright (c) 2000, 2001 Markus Friedl. All rights reserved. | |
3 | * | |
4 | * Redistribution and use in source and binary forms, with or without | |
5 | * modification, are permitted provided that the following conditions | |
6 | * are met: | |
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. | |
12 | * | |
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. | |
23 | */ | |
24 | ||
25 | #include "includes.h" | |
416fd2a8 | 26 | RCSID("$OpenBSD: kex.c,v 1.56 2003/11/21 11:57:03 djm Exp $"); |
3c0ef626 | 27 | |
28 | #include <openssl/crypto.h> | |
29 | ||
30 | #include "ssh2.h" | |
31 | #include "xmalloc.h" | |
32 | #include "buffer.h" | |
33 | #include "bufaux.h" | |
34 | #include "packet.h" | |
35 | #include "compat.h" | |
36 | #include "cipher.h" | |
37 | #include "kex.h" | |
38 | #include "key.h" | |
39 | #include "log.h" | |
40 | #include "mac.h" | |
41 | #include "match.h" | |
42 | #include "dispatch.h" | |
2980ea68 | 43 | #include "monitor.h" |
44 | ||
45 | #ifdef GSSAPI | |
46 | #include "ssh-gss.h" | |
47 | #endif | |
3c0ef626 | 48 | |
49 | #define KEX_COOKIE_LEN 16 | |
50 | ||
51 | /* prototype */ | |
52 | static void kex_kexinit_finish(Kex *); | |
53 | static void kex_choose_conf(Kex *); | |
54 | ||
55 | /* put algorithm proposal into buffer */ | |
56 | static void | |
57 | kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX]) | |
58 | { | |
3c0ef626 | 59 | int i; |
60 | ||
61 | buffer_clear(b); | |
2980ea68 | 62 | /* |
63 | * add a dummy cookie, the cookie will be overwritten by | |
64 | * kex_send_kexinit(), each time a kexinit is set | |
65 | */ | |
66 | for (i = 0; i < KEX_COOKIE_LEN; i++) | |
67 | buffer_put_char(b, 0); | |
3c0ef626 | 68 | for (i = 0; i < PROPOSAL_MAX; i++) |
69 | buffer_put_cstring(b, proposal[i]); | |
70 | buffer_put_char(b, 0); /* first_kex_packet_follows */ | |
71 | buffer_put_int(b, 0); /* uint32 reserved */ | |
72 | } | |
73 | ||
74 | /* parse buffer and return algorithm proposal */ | |
75 | static char ** | |
1c14df9e | 76 | kex_buf2prop(Buffer *raw, int *first_kex_follows) |
3c0ef626 | 77 | { |
78 | Buffer b; | |
79 | int i; | |
80 | char **proposal; | |
81 | ||
82 | proposal = xmalloc(PROPOSAL_MAX * sizeof(char *)); | |
83 | ||
84 | buffer_init(&b); | |
85 | buffer_append(&b, buffer_ptr(raw), buffer_len(raw)); | |
86 | /* skip cookie */ | |
87 | for (i = 0; i < KEX_COOKIE_LEN; i++) | |
88 | buffer_get_char(&b); | |
89 | /* extract kex init proposal strings */ | |
90 | for (i = 0; i < PROPOSAL_MAX; i++) { | |
91 | proposal[i] = buffer_get_string(&b,NULL); | |
92 | debug2("kex_parse_kexinit: %s", proposal[i]); | |
93 | } | |
94 | /* first kex follows / reserved */ | |
95 | i = buffer_get_char(&b); | |
1c14df9e | 96 | if (first_kex_follows != NULL) |
97 | *first_kex_follows = i; | |
3c0ef626 | 98 | debug2("kex_parse_kexinit: first_kex_follows %d ", i); |
99 | i = buffer_get_int(&b); | |
100 | debug2("kex_parse_kexinit: reserved %d ", i); | |
101 | buffer_free(&b); | |
102 | return proposal; | |
103 | } | |
104 | ||
105 | static void | |
106 | kex_prop_free(char **proposal) | |
107 | { | |
108 | int i; | |
109 | ||
110 | for (i = 0; i < PROPOSAL_MAX; i++) | |
111 | xfree(proposal[i]); | |
112 | xfree(proposal); | |
113 | } | |
114 | ||
115 | static void | |
e9a17296 | 116 | kex_protocol_error(int type, u_int32_t seq, void *ctxt) |
3c0ef626 | 117 | { |
e9a17296 | 118 | error("Hm, kex protocol error: type %d seq %u", type, seq); |
3c0ef626 | 119 | } |
120 | ||
121 | static void | |
e9a17296 | 122 | kex_reset_dispatch(void) |
3c0ef626 | 123 | { |
e9a17296 | 124 | dispatch_range(SSH2_MSG_TRANSPORT_MIN, |
125 | SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error); | |
126 | dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit); | |
3c0ef626 | 127 | } |
128 | ||
129 | void | |
130 | kex_finish(Kex *kex) | |
131 | { | |
e9a17296 | 132 | kex_reset_dispatch(); |
3c0ef626 | 133 | |
134 | packet_start(SSH2_MSG_NEWKEYS); | |
135 | packet_send(); | |
136 | /* packet_write_wait(); */ | |
137 | debug("SSH2_MSG_NEWKEYS sent"); | |
138 | ||
1c14df9e | 139 | debug("expecting SSH2_MSG_NEWKEYS"); |
e9a17296 | 140 | packet_read_expect(SSH2_MSG_NEWKEYS); |
141 | packet_check_eom(); | |
3c0ef626 | 142 | debug("SSH2_MSG_NEWKEYS received"); |
143 | ||
144 | kex->done = 1; | |
145 | buffer_clear(&kex->peer); | |
146 | /* buffer_clear(&kex->my); */ | |
147 | kex->flags &= ~KEX_INIT_SENT; | |
148 | xfree(kex->name); | |
149 | kex->name = NULL; | |
150 | } | |
151 | ||
152 | void | |
153 | kex_send_kexinit(Kex *kex) | |
154 | { | |
2980ea68 | 155 | u_int32_t rand = 0; |
156 | u_char *cookie; | |
157 | int i; | |
158 | ||
3c0ef626 | 159 | if (kex == NULL) { |
160 | error("kex_send_kexinit: no kex, cannot rekey"); | |
161 | return; | |
162 | } | |
163 | if (kex->flags & KEX_INIT_SENT) { | |
164 | debug("KEX_INIT_SENT"); | |
165 | return; | |
166 | } | |
167 | kex->done = 0; | |
2980ea68 | 168 | |
169 | /* generate a random cookie */ | |
170 | if (buffer_len(&kex->my) < KEX_COOKIE_LEN) | |
171 | fatal("kex_send_kexinit: kex proposal too short"); | |
172 | cookie = buffer_ptr(&kex->my); | |
173 | for (i = 0; i < KEX_COOKIE_LEN; i++) { | |
174 | if (i % 4 == 0) | |
175 | rand = arc4random(); | |
176 | cookie[i] = rand; | |
177 | rand >>= 8; | |
178 | } | |
3c0ef626 | 179 | packet_start(SSH2_MSG_KEXINIT); |
180 | packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my)); | |
181 | packet_send(); | |
182 | debug("SSH2_MSG_KEXINIT sent"); | |
183 | kex->flags |= KEX_INIT_SENT; | |
184 | } | |
185 | ||
186 | void | |
e9a17296 | 187 | kex_input_kexinit(int type, u_int32_t seq, void *ctxt) |
3c0ef626 | 188 | { |
189 | char *ptr; | |
190 | int dlen; | |
191 | int i; | |
192 | Kex *kex = (Kex *)ctxt; | |
193 | ||
194 | debug("SSH2_MSG_KEXINIT received"); | |
195 | if (kex == NULL) | |
196 | fatal("kex_input_kexinit: no kex, cannot rekey"); | |
197 | ||
198 | ptr = packet_get_raw(&dlen); | |
199 | buffer_append(&kex->peer, ptr, dlen); | |
200 | ||
201 | /* discard packet */ | |
202 | for (i = 0; i < KEX_COOKIE_LEN; i++) | |
203 | packet_get_char(); | |
204 | for (i = 0; i < PROPOSAL_MAX; i++) | |
205 | xfree(packet_get_string(NULL)); | |
ff2d7a98 | 206 | (void) packet_get_char(); |
207 | (void) packet_get_int(); | |
e9a17296 | 208 | packet_check_eom(); |
3c0ef626 | 209 | |
210 | kex_kexinit_finish(kex); | |
211 | } | |
212 | ||
213 | Kex * | |
214 | kex_setup(char *proposal[PROPOSAL_MAX]) | |
215 | { | |
216 | Kex *kex; | |
217 | ||
218 | kex = xmalloc(sizeof(*kex)); | |
219 | memset(kex, 0, sizeof(*kex)); | |
220 | buffer_init(&kex->peer); | |
221 | buffer_init(&kex->my); | |
222 | kex_prop2buf(&kex->my, proposal); | |
223 | kex->done = 0; | |
224 | ||
225 | kex_send_kexinit(kex); /* we start */ | |
e9a17296 | 226 | kex_reset_dispatch(); |
3c0ef626 | 227 | |
228 | return kex; | |
229 | } | |
230 | ||
231 | static void | |
232 | kex_kexinit_finish(Kex *kex) | |
233 | { | |
234 | if (!(kex->flags & KEX_INIT_SENT)) | |
235 | kex_send_kexinit(kex); | |
236 | ||
237 | kex_choose_conf(kex); | |
238 | ||
1c14df9e | 239 | if (kex->kex_type >= 0 && kex->kex_type < KEX_MAX && |
240 | kex->kex[kex->kex_type] != NULL) { | |
241 | (kex->kex[kex->kex_type])(kex); | |
242 | } else { | |
3c0ef626 | 243 | fatal("Unsupported key exchange %d", kex->kex_type); |
244 | } | |
245 | } | |
246 | ||
247 | static void | |
248 | choose_enc(Enc *enc, char *client, char *server) | |
249 | { | |
250 | char *name = match_list(client, server, NULL); | |
251 | if (name == NULL) | |
252 | fatal("no matching cipher found: client %s server %s", client, server); | |
e9a17296 | 253 | if ((enc->cipher = cipher_by_name(name)) == NULL) |
3c0ef626 | 254 | fatal("matching cipher is not supported: %s", name); |
255 | enc->name = name; | |
256 | enc->enabled = 0; | |
257 | enc->iv = NULL; | |
258 | enc->key = NULL; | |
e9a17296 | 259 | enc->key_len = cipher_keylen(enc->cipher); |
260 | enc->block_size = cipher_blocksize(enc->cipher); | |
3c0ef626 | 261 | } |
262 | static void | |
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", client, server); | |
268 | if (mac_init(mac, name) < 0) | |
269 | fatal("unsupported mac %s", name); | |
270 | /* truncate the key */ | |
271 | if (datafellows & SSH_BUG_HMAC) | |
272 | mac->key_len = 16; | |
273 | mac->name = name; | |
274 | mac->key = NULL; | |
275 | mac->enabled = 0; | |
276 | } | |
277 | static void | |
278 | choose_comp(Comp *comp, char *client, char *server) | |
279 | { | |
280 | char *name = match_list(client, server, NULL); | |
281 | if (name == NULL) | |
282 | fatal("no matching comp found: client %s server %s", client, server); | |
283 | if (strcmp(name, "zlib") == 0) { | |
284 | comp->type = 1; | |
285 | } else if (strcmp(name, "none") == 0) { | |
286 | comp->type = 0; | |
287 | } else { | |
288 | fatal("unsupported comp %s", name); | |
289 | } | |
290 | comp->name = name; | |
291 | } | |
292 | static void | |
293 | choose_kex(Kex *k, char *client, char *server) | |
294 | { | |
295 | k->name = match_list(client, server, NULL); | |
296 | if (k->name == NULL) | |
70791e56 | 297 | fatal("no kex alg"); |
3c0ef626 | 298 | if (strcmp(k->name, KEX_DH1) == 0) { |
1c14df9e | 299 | k->kex_type = KEX_DH_GRP1_SHA1; |
3c0ef626 | 300 | } else if (strcmp(k->name, KEX_DHGEX) == 0) { |
1c14df9e | 301 | k->kex_type = KEX_DH_GEX_SHA1; |
2980ea68 | 302 | #ifdef GSSAPI |
88928908 | 303 | } else if (strncmp(k->name, KEX_GSS_SHA1, sizeof(KEX_GSS_SHA1)-1) == 0) { |
1c14df9e | 304 | k->kex_type = KEX_GSS_GRP1_SHA1; |
2980ea68 | 305 | #endif |
3c0ef626 | 306 | } else |
307 | fatal("bad kex alg %s", k->name); | |
308 | } | |
309 | static void | |
310 | choose_hostkeyalg(Kex *k, char *client, char *server) | |
311 | { | |
312 | char *hostkeyalg = match_list(client, server, NULL); | |
313 | if (hostkeyalg == NULL) | |
314 | fatal("no hostkey alg"); | |
315 | k->hostkey_type = key_type_from_name(hostkeyalg); | |
316 | if (k->hostkey_type == KEY_UNSPEC) | |
317 | fatal("bad hostkey alg '%s'", hostkeyalg); | |
318 | xfree(hostkeyalg); | |
319 | } | |
320 | ||
416fd2a8 | 321 | static int |
1c14df9e | 322 | proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX]) |
323 | { | |
324 | static int check[] = { | |
325 | PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1 | |
326 | }; | |
327 | int *idx; | |
328 | char *p; | |
329 | ||
330 | for (idx = &check[0]; *idx != -1; idx++) { | |
331 | if ((p = strchr(my[*idx], ',')) != NULL) | |
332 | *p = '\0'; | |
333 | if ((p = strchr(peer[*idx], ',')) != NULL) | |
334 | *p = '\0'; | |
335 | if (strcmp(my[*idx], peer[*idx]) != 0) { | |
336 | debug2("proposal mismatch: my %s peer %s", | |
337 | my[*idx], peer[*idx]); | |
338 | return (0); | |
339 | } | |
340 | } | |
341 | debug2("proposals match"); | |
342 | return (1); | |
343 | } | |
344 | ||
3c0ef626 | 345 | static void |
346 | kex_choose_conf(Kex *kex) | |
347 | { | |
348 | Newkeys *newkeys; | |
349 | char **my, **peer; | |
350 | char **cprop, **sprop; | |
351 | int nenc, nmac, ncomp; | |
352 | int mode; | |
353 | int ctos; /* direction: if true client-to-server */ | |
354 | int need; | |
1c14df9e | 355 | int first_kex_follows, type; |
3c0ef626 | 356 | |
1c14df9e | 357 | my = kex_buf2prop(&kex->my, NULL); |
358 | peer = kex_buf2prop(&kex->peer, &first_kex_follows); | |
3c0ef626 | 359 | |
360 | if (kex->server) { | |
361 | cprop=peer; | |
362 | sprop=my; | |
363 | } else { | |
364 | cprop=my; | |
365 | sprop=peer; | |
366 | } | |
367 | ||
368 | /* Algorithm Negotiation */ | |
369 | for (mode = 0; mode < MODE_MAX; mode++) { | |
370 | newkeys = xmalloc(sizeof(*newkeys)); | |
371 | memset(newkeys, 0, sizeof(*newkeys)); | |
372 | kex->newkeys[mode] = newkeys; | |
373 | ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN); | |
374 | nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC; | |
375 | nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC; | |
376 | ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC; | |
377 | choose_enc (&newkeys->enc, cprop[nenc], sprop[nenc]); | |
378 | choose_mac (&newkeys->mac, cprop[nmac], sprop[nmac]); | |
379 | choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]); | |
380 | debug("kex: %s %s %s %s", | |
381 | ctos ? "client->server" : "server->client", | |
382 | newkeys->enc.name, | |
383 | newkeys->mac.name, | |
384 | newkeys->comp.name); | |
385 | } | |
386 | choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]); | |
387 | choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS], | |
388 | sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]); | |
389 | need = 0; | |
390 | for (mode = 0; mode < MODE_MAX; mode++) { | |
391 | newkeys = kex->newkeys[mode]; | |
e9a17296 | 392 | if (need < newkeys->enc.key_len) |
393 | need = newkeys->enc.key_len; | |
394 | if (need < newkeys->enc.block_size) | |
395 | need = newkeys->enc.block_size; | |
3c0ef626 | 396 | if (need < newkeys->mac.key_len) |
397 | need = newkeys->mac.key_len; | |
398 | } | |
399 | /* XXX need runden? */ | |
400 | kex->we_need = need; | |
401 | ||
1c14df9e | 402 | /* ignore the next message if the proposals do not match */ |
416fd2a8 | 403 | if (first_kex_follows && !proposals_match(my, peer) && |
1c14df9e | 404 | !(datafellows & SSH_BUG_FIRSTKEX)) { |
405 | type = packet_read(); | |
406 | debug2("skipping next packet (type %u)", type); | |
407 | } | |
408 | ||
3c0ef626 | 409 | kex_prop_free(my); |
410 | kex_prop_free(peer); | |
411 | } | |
412 | ||
413 | static u_char * | |
414 | derive_key(Kex *kex, int id, int need, u_char *hash, BIGNUM *shared_secret) | |
415 | { | |
416 | Buffer b; | |
e9a17296 | 417 | const EVP_MD *evp_md = EVP_sha1(); |
3c0ef626 | 418 | EVP_MD_CTX md; |
419 | char c = id; | |
420 | int have; | |
e9a17296 | 421 | int mdsz = EVP_MD_size(evp_md); |
3c0ef626 | 422 | u_char *digest = xmalloc(roundup(need, mdsz)); |
423 | ||
424 | buffer_init(&b); | |
425 | buffer_put_bignum2(&b, shared_secret); | |
426 | ||
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); | |
435 | ||
436 | /* | |
437 | * expand key: | |
438 | * Kn = HASH(K || H || K1 || K2 || ... || Kn-1) | |
439 | * Key = K1 || K2 || ... || Kn | |
440 | */ | |
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); | |
448 | } | |
449 | buffer_free(&b); | |
450 | #ifdef DEBUG_KEX | |
451 | fprintf(stderr, "key '%c'== ", c); | |
452 | dump_digest("key", digest, need); | |
453 | #endif | |
454 | return digest; | |
455 | } | |
456 | ||
457 | Newkeys *current_keys[MODE_MAX]; | |
458 | ||
459 | #define NKEYS 6 | |
460 | void | |
461 | kex_derive_keys(Kex *kex, u_char *hash, BIGNUM *shared_secret) | |
462 | { | |
463 | u_char *keys[NKEYS]; | |
464 | int i, mode, ctos; | |
465 | ||
466 | for (i = 0; i < NKEYS; i++) | |
467 | keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, shared_secret); | |
468 | ||
1c14df9e | 469 | debug2("kex_derive_keys"); |
3c0ef626 | 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]; | |
477 | } | |
478 | } | |
479 | ||
480 | Newkeys * | |
481 | kex_get_newkeys(int mode) | |
482 | { | |
483 | Newkeys *ret; | |
484 | ||
485 | ret = current_keys[mode]; | |
486 | current_keys[mode] = NULL; | |
487 | return ret; | |
488 | } | |
489 | ||
490 | #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH) | |
491 | void | |
492 | dump_digest(char *msg, u_char *digest, int len) | |
493 | { | |
494 | int i; | |
495 | ||
496 | fprintf(stderr, "%s\n", msg); | |
e9a17296 | 497 | for (i = 0; i< len; i++) { |
3c0ef626 | 498 | fprintf(stderr, "%02x", digest[i]); |
499 | if (i%32 == 31) | |
500 | fprintf(stderr, "\n"); | |
501 | else if (i%8 == 7) | |
502 | fprintf(stderr, " "); | |
503 | } | |
504 | fprintf(stderr, "\n"); | |
505 | } | |
506 | #endif |