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1 | /* | |
2 | * Copyright (c) 2000 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 1.34 2001/04/30 15:50:46 markus 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 | ||
44 | #define KEX_COOKIE_LEN 16 | |
45 | ||
46 | void kex_kexinit_finish(Kex *kex); | |
47 | void kex_choose_conf(Kex *k); | |
48 | ||
49 | /* put algorithm proposal into buffer */ | |
50 | void | |
51 | kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX]) | |
52 | { | |
53 | u_int32_t rand = 0; | |
54 | int i; | |
55 | ||
56 | buffer_clear(b); | |
57 | for (i = 0; i < KEX_COOKIE_LEN; i++) { | |
58 | if (i % 4 == 0) | |
59 | rand = arc4random(); | |
60 | buffer_put_char(b, rand & 0xff); | |
61 | rand >>= 8; | |
62 | } | |
63 | for (i = 0; i < PROPOSAL_MAX; i++) | |
64 | buffer_put_cstring(b, proposal[i]); | |
65 | buffer_put_char(b, 0); /* first_kex_packet_follows */ | |
66 | buffer_put_int(b, 0); /* uint32 reserved */ | |
67 | } | |
68 | ||
69 | /* parse buffer and return algorithm proposal */ | |
70 | char ** | |
71 | kex_buf2prop(Buffer *raw) | |
72 | { | |
73 | Buffer b; | |
74 | int i; | |
75 | char **proposal; | |
76 | ||
77 | proposal = xmalloc(PROPOSAL_MAX * sizeof(char *)); | |
78 | ||
79 | buffer_init(&b); | |
80 | buffer_append(&b, buffer_ptr(raw), buffer_len(raw)); | |
81 | /* skip cookie */ | |
82 | for (i = 0; i < KEX_COOKIE_LEN; i++) | |
83 | buffer_get_char(&b); | |
84 | /* extract kex init proposal strings */ | |
85 | for (i = 0; i < PROPOSAL_MAX; i++) { | |
86 | proposal[i] = buffer_get_string(&b,NULL); | |
87 | debug2("kex_parse_kexinit: %s", proposal[i]); | |
88 | } | |
89 | /* first kex follows / reserved */ | |
90 | i = buffer_get_char(&b); | |
91 | debug2("kex_parse_kexinit: first_kex_follows %d ", i); | |
92 | i = buffer_get_int(&b); | |
93 | debug2("kex_parse_kexinit: reserved %d ", i); | |
94 | buffer_free(&b); | |
95 | return proposal; | |
96 | } | |
97 | ||
98 | void | |
99 | kex_prop_free(char **proposal) | |
100 | { | |
101 | int i; | |
102 | ||
103 | for (i = 0; i < PROPOSAL_MAX; i++) | |
104 | xfree(proposal[i]); | |
105 | xfree(proposal); | |
106 | } | |
107 | ||
108 | void | |
109 | kex_protocol_error(int type, int plen, void *ctxt) | |
110 | { | |
111 | error("Hm, kex protocol error: type %d plen %d", type, plen); | |
112 | } | |
113 | ||
114 | void | |
115 | kex_clear_dispatch(void) | |
116 | { | |
117 | int i; | |
118 | ||
119 | /* Numbers 30-49 are used for kex packets */ | |
120 | for (i = 30; i <= 49; i++) | |
121 | dispatch_set(i, &kex_protocol_error); | |
122 | } | |
123 | ||
124 | void | |
125 | kex_finish(Kex *kex) | |
126 | { | |
127 | int plen; | |
128 | ||
129 | kex_clear_dispatch(); | |
130 | ||
131 | packet_start(SSH2_MSG_NEWKEYS); | |
132 | packet_send(); | |
133 | /* packet_write_wait(); */ | |
134 | debug("SSH2_MSG_NEWKEYS sent"); | |
135 | ||
136 | debug("waiting for SSH2_MSG_NEWKEYS"); | |
137 | packet_read_expect(&plen, SSH2_MSG_NEWKEYS); | |
138 | debug("SSH2_MSG_NEWKEYS received"); | |
139 | ||
140 | kex->done = 1; | |
141 | buffer_clear(&kex->peer); | |
142 | /* buffer_clear(&kex->my); */ | |
143 | kex->flags &= ~KEX_INIT_SENT; | |
144 | xfree(kex->name); | |
145 | kex->name = NULL; | |
146 | } | |
147 | ||
148 | void | |
149 | kex_send_kexinit(Kex *kex) | |
150 | { | |
151 | if (kex == NULL) { | |
152 | error("kex_send_kexinit: no kex, cannot rekey"); | |
153 | return; | |
154 | } | |
155 | if (kex->flags & KEX_INIT_SENT) { | |
156 | debug("KEX_INIT_SENT"); | |
157 | return; | |
158 | } | |
159 | kex->done = 0; | |
160 | packet_start(SSH2_MSG_KEXINIT); | |
161 | packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my)); | |
162 | packet_send(); | |
163 | debug("SSH2_MSG_KEXINIT sent"); | |
164 | kex->flags |= KEX_INIT_SENT; | |
165 | } | |
166 | ||
167 | void | |
168 | kex_input_kexinit(int type, int plen, void *ctxt) | |
169 | { | |
170 | char *ptr; | |
171 | int dlen; | |
172 | int i; | |
173 | Kex *kex = (Kex *)ctxt; | |
174 | ||
175 | debug("SSH2_MSG_KEXINIT received"); | |
176 | if (kex == NULL) | |
177 | fatal("kex_input_kexinit: no kex, cannot rekey"); | |
178 | ||
179 | ptr = packet_get_raw(&dlen); | |
180 | buffer_append(&kex->peer, ptr, dlen); | |
181 | ||
182 | /* discard packet */ | |
183 | for (i = 0; i < KEX_COOKIE_LEN; i++) | |
184 | packet_get_char(); | |
185 | for (i = 0; i < PROPOSAL_MAX; i++) | |
186 | xfree(packet_get_string(NULL)); | |
187 | packet_get_char(); | |
188 | packet_get_int(); | |
189 | packet_done(); | |
190 | ||
191 | kex_kexinit_finish(kex); | |
192 | } | |
193 | ||
194 | Kex * | |
195 | kex_setup(char *proposal[PROPOSAL_MAX]) | |
196 | { | |
197 | Kex *kex; | |
198 | ||
199 | kex = xmalloc(sizeof(*kex)); | |
200 | memset(kex, 0, sizeof(*kex)); | |
201 | buffer_init(&kex->peer); | |
202 | buffer_init(&kex->my); | |
203 | kex_prop2buf(&kex->my, proposal); | |
204 | kex->done = 0; | |
205 | ||
206 | kex_send_kexinit(kex); /* we start */ | |
207 | kex_clear_dispatch(); | |
208 | dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit); | |
209 | ||
210 | return kex; | |
211 | } | |
212 | ||
213 | void | |
214 | kex_kexinit_finish(Kex *kex) | |
215 | { | |
216 | if (!(kex->flags & KEX_INIT_SENT)) | |
217 | kex_send_kexinit(kex); | |
218 | ||
219 | kex_choose_conf(kex); | |
220 | ||
221 | switch(kex->kex_type) { | |
222 | case DH_GRP1_SHA1: | |
223 | kexdh(kex); | |
224 | break; | |
225 | case DH_GEX_SHA1: | |
226 | kexgex(kex); | |
227 | break; | |
228 | default: | |
229 | fatal("Unsupported key exchange %d", kex->kex_type); | |
230 | } | |
231 | } | |
232 | ||
233 | void | |
234 | choose_enc(Enc *enc, char *client, char *server) | |
235 | { | |
236 | char *name = match_list(client, server, NULL); | |
237 | if (name == NULL) | |
238 | fatal("no matching cipher found: client %s server %s", client, server); | |
239 | enc->cipher = cipher_by_name(name); | |
240 | if (enc->cipher == NULL) | |
241 | fatal("matching cipher is not supported: %s", name); | |
242 | enc->name = name; | |
243 | enc->enabled = 0; | |
244 | enc->iv = NULL; | |
245 | enc->key = NULL; | |
246 | } | |
247 | void | |
248 | choose_mac(Mac *mac, char *client, char *server) | |
249 | { | |
250 | char *name = match_list(client, server, NULL); | |
251 | if (name == NULL) | |
252 | fatal("no matching mac found: client %s server %s", client, server); | |
253 | if (mac_init(mac, name) < 0) | |
254 | fatal("unsupported mac %s", name); | |
255 | /* truncate the key */ | |
256 | if (datafellows & SSH_BUG_HMAC) | |
257 | mac->key_len = 16; | |
258 | mac->name = name; | |
259 | mac->key = NULL; | |
260 | mac->enabled = 0; | |
261 | } | |
262 | void | |
263 | choose_comp(Comp *comp, char *client, char *server) | |
264 | { | |
265 | char *name = match_list(client, server, NULL); | |
266 | if (name == NULL) | |
267 | fatal("no matching comp found: client %s server %s", client, server); | |
268 | if (strcmp(name, "zlib") == 0) { | |
269 | comp->type = 1; | |
270 | } else if (strcmp(name, "none") == 0) { | |
271 | comp->type = 0; | |
272 | } else { | |
273 | fatal("unsupported comp %s", name); | |
274 | } | |
275 | comp->name = name; | |
276 | } | |
277 | void | |
278 | choose_kex(Kex *k, char *client, char *server) | |
279 | { | |
280 | k->name = match_list(client, server, NULL); | |
281 | if (k->name == NULL) | |
282 | fatal("no kex alg"); | |
283 | if (strcmp(k->name, KEX_DH1) == 0) { | |
284 | k->kex_type = DH_GRP1_SHA1; | |
285 | } else if (strcmp(k->name, KEX_DHGEX) == 0) { | |
286 | k->kex_type = DH_GEX_SHA1; | |
287 | } else | |
288 | fatal("bad kex alg %s", k->name); | |
289 | } | |
290 | void | |
291 | choose_hostkeyalg(Kex *k, char *client, char *server) | |
292 | { | |
293 | char *hostkeyalg = match_list(client, server, NULL); | |
294 | if (hostkeyalg == NULL) | |
295 | fatal("no hostkey alg"); | |
296 | k->hostkey_type = key_type_from_name(hostkeyalg); | |
297 | if (k->hostkey_type == KEY_UNSPEC) | |
298 | fatal("bad hostkey alg '%s'", hostkeyalg); | |
299 | xfree(hostkeyalg); | |
300 | } | |
301 | ||
302 | void | |
303 | kex_choose_conf(Kex *kex) | |
304 | { | |
305 | Newkeys *newkeys; | |
306 | char **my, **peer; | |
307 | char **cprop, **sprop; | |
308 | int nenc, nmac, ncomp; | |
309 | int mode; | |
310 | int ctos; /* direction: if true client-to-server */ | |
311 | int need; | |
312 | ||
313 | my = kex_buf2prop(&kex->my); | |
314 | peer = kex_buf2prop(&kex->peer); | |
315 | ||
316 | if (kex->server) { | |
317 | cprop=peer; | |
318 | sprop=my; | |
319 | } else { | |
320 | cprop=my; | |
321 | sprop=peer; | |
322 | } | |
323 | ||
324 | /* Algorithm Negotiation */ | |
325 | for (mode = 0; mode < MODE_MAX; mode++) { | |
326 | newkeys = xmalloc(sizeof(*newkeys)); | |
327 | memset(newkeys, 0, sizeof(*newkeys)); | |
328 | kex->newkeys[mode] = newkeys; | |
329 | ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN); | |
330 | nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC; | |
331 | nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC; | |
332 | ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC; | |
333 | choose_enc (&newkeys->enc, cprop[nenc], sprop[nenc]); | |
334 | choose_mac (&newkeys->mac, cprop[nmac], sprop[nmac]); | |
335 | choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]); | |
336 | debug("kex: %s %s %s %s", | |
337 | ctos ? "client->server" : "server->client", | |
338 | newkeys->enc.name, | |
339 | newkeys->mac.name, | |
340 | newkeys->comp.name); | |
341 | } | |
342 | choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]); | |
343 | choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS], | |
344 | sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]); | |
345 | need = 0; | |
346 | for (mode = 0; mode < MODE_MAX; mode++) { | |
347 | newkeys = kex->newkeys[mode]; | |
348 | if (need < newkeys->enc.cipher->key_len) | |
349 | need = newkeys->enc.cipher->key_len; | |
350 | if (need < newkeys->enc.cipher->block_size) | |
351 | need = newkeys->enc.cipher->block_size; | |
352 | if (need < newkeys->mac.key_len) | |
353 | need = newkeys->mac.key_len; | |
354 | } | |
355 | /* XXX need runden? */ | |
356 | kex->we_need = need; | |
357 | ||
358 | kex_prop_free(my); | |
359 | kex_prop_free(peer); | |
360 | } | |
361 | ||
362 | u_char * | |
363 | derive_key(Kex *kex, int id, int need, u_char *hash, BIGNUM *shared_secret) | |
364 | { | |
365 | Buffer b; | |
366 | EVP_MD *evp_md = EVP_sha1(); | |
367 | EVP_MD_CTX md; | |
368 | char c = id; | |
369 | int have; | |
370 | int mdsz = evp_md->md_size; | |
371 | u_char *digest = xmalloc(roundup(need, mdsz)); | |
372 | ||
373 | buffer_init(&b); | |
374 | buffer_put_bignum2(&b, shared_secret); | |
375 | ||
376 | /* K1 = HASH(K || H || "A" || session_id) */ | |
377 | EVP_DigestInit(&md, evp_md); | |
378 | if (!(datafellows & SSH_BUG_DERIVEKEY)) | |
379 | EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); | |
380 | EVP_DigestUpdate(&md, hash, mdsz); | |
381 | EVP_DigestUpdate(&md, &c, 1); | |
382 | EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len); | |
383 | EVP_DigestFinal(&md, digest, NULL); | |
384 | ||
385 | /* | |
386 | * expand key: | |
387 | * Kn = HASH(K || H || K1 || K2 || ... || Kn-1) | |
388 | * Key = K1 || K2 || ... || Kn | |
389 | */ | |
390 | for (have = mdsz; need > have; have += mdsz) { | |
391 | EVP_DigestInit(&md, evp_md); | |
392 | if (!(datafellows & SSH_BUG_DERIVEKEY)) | |
393 | EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); | |
394 | EVP_DigestUpdate(&md, hash, mdsz); | |
395 | EVP_DigestUpdate(&md, digest, have); | |
396 | EVP_DigestFinal(&md, digest + have, NULL); | |
397 | } | |
398 | buffer_free(&b); | |
399 | #ifdef DEBUG_KEX | |
400 | fprintf(stderr, "key '%c'== ", c); | |
401 | dump_digest("key", digest, need); | |
402 | #endif | |
403 | return digest; | |
404 | } | |
405 | ||
406 | Newkeys *current_keys[MODE_MAX]; | |
407 | ||
408 | #define NKEYS 6 | |
409 | void | |
410 | kex_derive_keys(Kex *kex, u_char *hash, BIGNUM *shared_secret) | |
411 | { | |
412 | u_char *keys[NKEYS]; | |
413 | int i, mode, ctos; | |
414 | ||
415 | for (i = 0; i < NKEYS; i++) | |
416 | keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, shared_secret); | |
417 | ||
418 | debug("kex_derive_keys"); | |
419 | for (mode = 0; mode < MODE_MAX; mode++) { | |
420 | current_keys[mode] = kex->newkeys[mode]; | |
421 | kex->newkeys[mode] = NULL; | |
422 | ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN); | |
423 | current_keys[mode]->enc.iv = keys[ctos ? 0 : 1]; | |
424 | current_keys[mode]->enc.key = keys[ctos ? 2 : 3]; | |
425 | current_keys[mode]->mac.key = keys[ctos ? 4 : 5]; | |
426 | } | |
427 | } | |
428 | ||
429 | Newkeys * | |
430 | kex_get_newkeys(int mode) | |
431 | { | |
432 | Newkeys *ret; | |
433 | ||
434 | ret = current_keys[mode]; | |
435 | current_keys[mode] = NULL; | |
436 | return ret; | |
437 | } | |
438 | ||
439 | #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH) | |
440 | void | |
441 | dump_digest(char *msg, u_char *digest, int len) | |
442 | { | |
443 | int i; | |
444 | ||
445 | fprintf(stderr, "%s\n", msg); | |
446 | for (i = 0; i< len; i++){ | |
447 | fprintf(stderr, "%02x", digest[i]); | |
448 | if (i%32 == 31) | |
449 | fprintf(stderr, "\n"); | |
450 | else if (i%8 == 7) | |
451 | fprintf(stderr, " "); | |
452 | } | |
453 | fprintf(stderr, "\n"); | |
454 | } | |
455 | #endif |