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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" | |
26 | RCSID("$OpenBSD: kex.c,v 1.50 2002/05/15 15:47:49 mouring Exp $"); | |
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" | |
43 | #include "monitor.h" | |
44 | ||
45 | #define KEX_COOKIE_LEN 16 | |
46 | ||
47 | /* Use privilege separation for sshd */ | |
48 | int use_privsep; | |
49 | struct monitor *pmonitor; | |
50 | ||
51 | ||
52 | /* prototype */ | |
53 | static void kex_kexinit_finish(Kex *); | |
54 | static void kex_choose_conf(Kex *); | |
55 | ||
56 | /* put algorithm proposal into buffer */ | |
57 | static void | |
58 | kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX]) | |
59 | { | |
60 | int i; | |
61 | ||
62 | buffer_clear(b); | |
63 | /* | |
64 | * add a dummy cookie, the cookie will be overwritten by | |
65 | * kex_send_kexinit(), each time a kexinit is set | |
66 | */ | |
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 */ | |
73 | } | |
74 | ||
75 | /* parse buffer and return algorithm proposal */ | |
76 | static char ** | |
77 | kex_buf2prop(Buffer *raw) | |
78 | { | |
79 | Buffer b; | |
80 | int i; | |
81 | char **proposal; | |
82 | ||
83 | proposal = xmalloc(PROPOSAL_MAX * sizeof(char *)); | |
84 | ||
85 | buffer_init(&b); | |
86 | buffer_append(&b, buffer_ptr(raw), buffer_len(raw)); | |
87 | /* skip cookie */ | |
88 | for (i = 0; i < KEX_COOKIE_LEN; i++) | |
89 | buffer_get_char(&b); | |
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]); | |
94 | } | |
95 | /* first kex follows / reserved */ | |
96 | i = buffer_get_char(&b); | |
97 | debug2("kex_parse_kexinit: first_kex_follows %d ", i); | |
98 | i = buffer_get_int(&b); | |
99 | debug2("kex_parse_kexinit: reserved %d ", i); | |
100 | buffer_free(&b); | |
101 | return proposal; | |
102 | } | |
103 | ||
104 | static void | |
105 | kex_prop_free(char **proposal) | |
106 | { | |
107 | int i; | |
108 | ||
109 | for (i = 0; i < PROPOSAL_MAX; i++) | |
110 | xfree(proposal[i]); | |
111 | xfree(proposal); | |
112 | } | |
113 | ||
114 | static void | |
115 | kex_protocol_error(int type, u_int32_t seq, void *ctxt) | |
116 | { | |
117 | error("Hm, kex protocol error: type %d seq %u", type, seq); | |
118 | } | |
119 | ||
120 | static void | |
121 | kex_reset_dispatch(void) | |
122 | { | |
123 | dispatch_range(SSH2_MSG_TRANSPORT_MIN, | |
124 | SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error); | |
125 | dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit); | |
126 | } | |
127 | ||
128 | void | |
129 | kex_finish(Kex *kex) | |
130 | { | |
131 | kex_reset_dispatch(); | |
132 | ||
133 | packet_start(SSH2_MSG_NEWKEYS); | |
134 | packet_send(); | |
135 | /* packet_write_wait(); */ | |
136 | debug("SSH2_MSG_NEWKEYS sent"); | |
137 | ||
138 | debug("waiting for SSH2_MSG_NEWKEYS"); | |
139 | packet_read_expect(SSH2_MSG_NEWKEYS); | |
140 | packet_check_eom(); | |
141 | debug("SSH2_MSG_NEWKEYS received"); | |
142 | ||
143 | kex->done = 1; | |
144 | buffer_clear(&kex->peer); | |
145 | /* buffer_clear(&kex->my); */ | |
146 | kex->flags &= ~KEX_INIT_SENT; | |
147 | xfree(kex->name); | |
148 | kex->name = NULL; | |
149 | } | |
150 | ||
151 | void | |
152 | kex_send_kexinit(Kex *kex) | |
153 | { | |
154 | u_int32_t rand = 0; | |
155 | u_char *cookie; | |
156 | int i; | |
157 | ||
158 | if (kex == NULL) { | |
159 | error("kex_send_kexinit: no kex, cannot rekey"); | |
160 | return; | |
161 | } | |
162 | if (kex->flags & KEX_INIT_SENT) { | |
163 | debug("KEX_INIT_SENT"); | |
164 | return; | |
165 | } | |
166 | kex->done = 0; | |
167 | ||
168 | /* generate a random cookie */ | |
169 | if (buffer_len(&kex->my) < KEX_COOKIE_LEN) | |
170 | fatal("kex_send_kexinit: kex proposal too short"); | |
171 | cookie = buffer_ptr(&kex->my); | |
172 | for (i = 0; i < KEX_COOKIE_LEN; i++) { | |
173 | if (i % 4 == 0) | |
174 | rand = arc4random(); | |
175 | cookie[i] = rand; | |
176 | rand >>= 8; | |
177 | } | |
178 | packet_start(SSH2_MSG_KEXINIT); | |
179 | packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my)); | |
180 | packet_send(); | |
181 | debug("SSH2_MSG_KEXINIT sent"); | |
182 | kex->flags |= KEX_INIT_SENT; | |
183 | } | |
184 | ||
185 | void | |
186 | kex_input_kexinit(int type, u_int32_t seq, void *ctxt) | |
187 | { | |
188 | char *ptr; | |
189 | int dlen; | |
190 | int i; | |
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 | packet_get_char(); | |
206 | packet_get_int(); | |
207 | packet_check_eom(); | |
208 | ||
209 | kex_kexinit_finish(kex); | |
210 | } | |
211 | ||
212 | Kex * | |
213 | kex_setup(char *proposal[PROPOSAL_MAX]) | |
214 | { | |
215 | Kex *kex; | |
216 | ||
217 | kex = xmalloc(sizeof(*kex)); | |
218 | memset(kex, 0, sizeof(*kex)); | |
219 | buffer_init(&kex->peer); | |
220 | buffer_init(&kex->my); | |
221 | kex_prop2buf(&kex->my, proposal); | |
222 | kex->done = 0; | |
223 | ||
224 | kex_send_kexinit(kex); /* we start */ | |
225 | kex_reset_dispatch(); | |
226 | ||
227 | return kex; | |
228 | } | |
229 | ||
230 | static void | |
231 | kex_kexinit_finish(Kex *kex) | |
232 | { | |
233 | if (!(kex->flags & KEX_INIT_SENT)) | |
234 | kex_send_kexinit(kex); | |
235 | ||
236 | kex_choose_conf(kex); | |
237 | ||
238 | switch (kex->kex_type) { | |
239 | case DH_GRP1_SHA1: | |
240 | kexdh(kex); | |
241 | break; | |
242 | case DH_GEX_SHA1: | |
243 | kexgex(kex); | |
244 | break; | |
245 | default: | |
246 | fatal("Unsupported key exchange %d", kex->kex_type); | |
247 | } | |
248 | } | |
249 | ||
250 | static void | |
251 | choose_enc(Enc *enc, char *client, char *server) | |
252 | { | |
253 | char *name = match_list(client, server, NULL); | |
254 | if (name == NULL) | |
255 | fatal("no matching cipher found: client %s server %s", client, server); | |
256 | if ((enc->cipher = cipher_by_name(name)) == NULL) | |
257 | fatal("matching cipher is not supported: %s", name); | |
258 | enc->name = name; | |
259 | enc->enabled = 0; | |
260 | enc->iv = NULL; | |
261 | enc->key = NULL; | |
262 | enc->key_len = cipher_keylen(enc->cipher); | |
263 | enc->block_size = cipher_blocksize(enc->cipher); | |
264 | } | |
265 | static void | |
266 | choose_mac(Mac *mac, char *client, char *server) | |
267 | { | |
268 | char *name = match_list(client, server, NULL); | |
269 | if (name == NULL) | |
270 | fatal("no matching mac found: client %s server %s", client, server); | |
271 | if (mac_init(mac, name) < 0) | |
272 | fatal("unsupported mac %s", name); | |
273 | /* truncate the key */ | |
274 | if (datafellows & SSH_BUG_HMAC) | |
275 | mac->key_len = 16; | |
276 | mac->name = name; | |
277 | mac->key = NULL; | |
278 | mac->enabled = 0; | |
279 | } | |
280 | static void | |
281 | choose_comp(Comp *comp, char *client, char *server) | |
282 | { | |
283 | char *name = match_list(client, server, NULL); | |
284 | if (name == NULL) | |
285 | fatal("no matching comp found: client %s server %s", client, server); | |
286 | if (strcmp(name, "zlib") == 0) { | |
287 | comp->type = 1; | |
288 | } else if (strcmp(name, "none") == 0) { | |
289 | comp->type = 0; | |
290 | } else { | |
291 | fatal("unsupported comp %s", name); | |
292 | } | |
293 | comp->name = name; | |
294 | } | |
295 | static void | |
296 | choose_kex(Kex *k, char *client, char *server) | |
297 | { | |
298 | k->name = match_list(client, server, NULL); | |
299 | if (k->name == NULL) | |
300 | fatal("no kex alg"); | |
301 | if (strcmp(k->name, KEX_DH1) == 0) { | |
302 | k->kex_type = DH_GRP1_SHA1; | |
303 | } else if (strcmp(k->name, KEX_DHGEX) == 0) { | |
304 | k->kex_type = DH_GEX_SHA1; | |
305 | } else | |
306 | fatal("bad kex alg %s", k->name); | |
307 | } | |
308 | static void | |
309 | choose_hostkeyalg(Kex *k, char *client, char *server) | |
310 | { | |
311 | char *hostkeyalg = match_list(client, server, NULL); | |
312 | if (hostkeyalg == NULL) | |
313 | fatal("no hostkey alg"); | |
314 | k->hostkey_type = key_type_from_name(hostkeyalg); | |
315 | if (k->hostkey_type == KEY_UNSPEC) | |
316 | fatal("bad hostkey alg '%s'", hostkeyalg); | |
317 | xfree(hostkeyalg); | |
318 | } | |
319 | ||
320 | static void | |
321 | kex_choose_conf(Kex *kex) | |
322 | { | |
323 | Newkeys *newkeys; | |
324 | char **my, **peer; | |
325 | char **cprop, **sprop; | |
326 | int nenc, nmac, ncomp; | |
327 | int mode; | |
328 | int ctos; /* direction: if true client-to-server */ | |
329 | int need; | |
330 | ||
331 | my = kex_buf2prop(&kex->my); | |
332 | peer = kex_buf2prop(&kex->peer); | |
333 | ||
334 | if (kex->server) { | |
335 | cprop=peer; | |
336 | sprop=my; | |
337 | } else { | |
338 | cprop=my; | |
339 | sprop=peer; | |
340 | } | |
341 | ||
342 | /* Algorithm Negotiation */ | |
343 | for (mode = 0; mode < MODE_MAX; mode++) { | |
344 | newkeys = xmalloc(sizeof(*newkeys)); | |
345 | memset(newkeys, 0, sizeof(*newkeys)); | |
346 | kex->newkeys[mode] = newkeys; | |
347 | ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN); | |
348 | nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC; | |
349 | nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC; | |
350 | ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC; | |
351 | choose_enc (&newkeys->enc, cprop[nenc], sprop[nenc]); | |
352 | choose_mac (&newkeys->mac, cprop[nmac], sprop[nmac]); | |
353 | choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]); | |
354 | debug("kex: %s %s %s %s", | |
355 | ctos ? "client->server" : "server->client", | |
356 | newkeys->enc.name, | |
357 | newkeys->mac.name, | |
358 | newkeys->comp.name); | |
359 | } | |
360 | choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]); | |
361 | choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS], | |
362 | sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]); | |
363 | need = 0; | |
364 | for (mode = 0; mode < MODE_MAX; mode++) { | |
365 | newkeys = kex->newkeys[mode]; | |
366 | if (need < newkeys->enc.key_len) | |
367 | need = newkeys->enc.key_len; | |
368 | if (need < newkeys->enc.block_size) | |
369 | need = newkeys->enc.block_size; | |
370 | if (need < newkeys->mac.key_len) | |
371 | need = newkeys->mac.key_len; | |
372 | } | |
373 | /* XXX need runden? */ | |
374 | kex->we_need = need; | |
375 | ||
376 | kex_prop_free(my); | |
377 | kex_prop_free(peer); | |
378 | } | |
379 | ||
380 | static u_char * | |
381 | derive_key(Kex *kex, int id, int need, u_char *hash, BIGNUM *shared_secret) | |
382 | { | |
383 | Buffer b; | |
384 | const EVP_MD *evp_md = EVP_sha1(); | |
385 | EVP_MD_CTX md; | |
386 | char c = id; | |
387 | int have; | |
388 | int mdsz = EVP_MD_size(evp_md); | |
389 | u_char *digest = xmalloc(roundup(need, mdsz)); | |
390 | ||
391 | buffer_init(&b); | |
392 | buffer_put_bignum2(&b, shared_secret); | |
393 | ||
394 | /* K1 = HASH(K || H || "A" || session_id) */ | |
395 | EVP_DigestInit(&md, evp_md); | |
396 | if (!(datafellows & SSH_BUG_DERIVEKEY)) | |
397 | EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); | |
398 | EVP_DigestUpdate(&md, hash, mdsz); | |
399 | EVP_DigestUpdate(&md, &c, 1); | |
400 | EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len); | |
401 | EVP_DigestFinal(&md, digest, NULL); | |
402 | ||
403 | /* | |
404 | * expand key: | |
405 | * Kn = HASH(K || H || K1 || K2 || ... || Kn-1) | |
406 | * Key = K1 || K2 || ... || Kn | |
407 | */ | |
408 | for (have = mdsz; need > have; have += mdsz) { | |
409 | EVP_DigestInit(&md, evp_md); | |
410 | if (!(datafellows & SSH_BUG_DERIVEKEY)) | |
411 | EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); | |
412 | EVP_DigestUpdate(&md, hash, mdsz); | |
413 | EVP_DigestUpdate(&md, digest, have); | |
414 | EVP_DigestFinal(&md, digest + have, NULL); | |
415 | } | |
416 | buffer_free(&b); | |
417 | #ifdef DEBUG_KEX | |
418 | fprintf(stderr, "key '%c'== ", c); | |
419 | dump_digest("key", digest, need); | |
420 | #endif | |
421 | return digest; | |
422 | } | |
423 | ||
424 | Newkeys *current_keys[MODE_MAX]; | |
425 | ||
426 | #define NKEYS 6 | |
427 | void | |
428 | kex_derive_keys(Kex *kex, u_char *hash, BIGNUM *shared_secret) | |
429 | { | |
430 | u_char *keys[NKEYS]; | |
431 | int i, mode, ctos; | |
432 | ||
433 | for (i = 0; i < NKEYS; i++) | |
434 | keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, shared_secret); | |
435 | ||
436 | debug("kex_derive_keys"); | |
437 | for (mode = 0; mode < MODE_MAX; mode++) { | |
438 | current_keys[mode] = kex->newkeys[mode]; | |
439 | kex->newkeys[mode] = NULL; | |
440 | ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN); | |
441 | current_keys[mode]->enc.iv = keys[ctos ? 0 : 1]; | |
442 | current_keys[mode]->enc.key = keys[ctos ? 2 : 3]; | |
443 | current_keys[mode]->mac.key = keys[ctos ? 4 : 5]; | |
444 | } | |
445 | } | |
446 | ||
447 | Newkeys * | |
448 | kex_get_newkeys(int mode) | |
449 | { | |
450 | Newkeys *ret; | |
451 | ||
452 | ret = current_keys[mode]; | |
453 | current_keys[mode] = NULL; | |
454 | return ret; | |
455 | } | |
456 | ||
457 | #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH) | |
458 | void | |
459 | dump_digest(char *msg, u_char *digest, int len) | |
460 | { | |
461 | int i; | |
462 | ||
463 | fprintf(stderr, "%s\n", msg); | |
464 | for (i = 0; i< len; i++) { | |
465 | fprintf(stderr, "%02x", digest[i]); | |
466 | if (i%32 == 31) | |
467 | fprintf(stderr, "\n"); | |
468 | else if (i%8 == 7) | |
469 | fprintf(stderr, " "); | |
470 | } | |
471 | fprintf(stderr, "\n"); | |
472 | } | |
473 | #endif |