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3c0ef626 | 1 | /* |
2 | * Copyright (c) 2000 Niels Provos. All rights reserved. | |
3 | * Copyright (c) 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 | RCSID("$OpenBSD: kexgex.c,v 1.9 2001/09/17 19:27:15 stevesk Exp $"); | |
28 | ||
29 | #include <openssl/bn.h> | |
30 | ||
31 | #include "xmalloc.h" | |
32 | #include "buffer.h" | |
33 | #include "bufaux.h" | |
34 | #include "key.h" | |
35 | #include "kex.h" | |
36 | #include "log.h" | |
37 | #include "packet.h" | |
38 | #include "dh.h" | |
39 | #include "ssh2.h" | |
40 | #include "compat.h" | |
41 | ||
42 | static u_char * | |
43 | kexgex_hash( | |
44 | char *client_version_string, | |
45 | char *server_version_string, | |
46 | char *ckexinit, int ckexinitlen, | |
47 | char *skexinit, int skexinitlen, | |
48 | u_char *serverhostkeyblob, int sbloblen, | |
49 | int min, int wantbits, int max, BIGNUM *prime, BIGNUM *gen, | |
50 | BIGNUM *client_dh_pub, | |
51 | BIGNUM *server_dh_pub, | |
52 | BIGNUM *shared_secret) | |
53 | { | |
54 | Buffer b; | |
55 | static u_char digest[EVP_MAX_MD_SIZE]; | |
56 | EVP_MD *evp_md = EVP_sha1(); | |
57 | EVP_MD_CTX md; | |
58 | ||
59 | buffer_init(&b); | |
60 | buffer_put_cstring(&b, client_version_string); | |
61 | buffer_put_cstring(&b, server_version_string); | |
62 | ||
63 | /* kexinit messages: fake header: len+SSH2_MSG_KEXINIT */ | |
64 | buffer_put_int(&b, ckexinitlen+1); | |
65 | buffer_put_char(&b, SSH2_MSG_KEXINIT); | |
66 | buffer_append(&b, ckexinit, ckexinitlen); | |
67 | buffer_put_int(&b, skexinitlen+1); | |
68 | buffer_put_char(&b, SSH2_MSG_KEXINIT); | |
69 | buffer_append(&b, skexinit, skexinitlen); | |
70 | ||
71 | buffer_put_string(&b, serverhostkeyblob, sbloblen); | |
72 | if (min == -1 || max == -1) | |
73 | buffer_put_int(&b, wantbits); | |
74 | else { | |
75 | buffer_put_int(&b, min); | |
76 | buffer_put_int(&b, wantbits); | |
77 | buffer_put_int(&b, max); | |
78 | } | |
79 | buffer_put_bignum2(&b, prime); | |
80 | buffer_put_bignum2(&b, gen); | |
81 | buffer_put_bignum2(&b, client_dh_pub); | |
82 | buffer_put_bignum2(&b, server_dh_pub); | |
83 | buffer_put_bignum2(&b, shared_secret); | |
84 | ||
85 | #ifdef DEBUG_KEXDH | |
86 | buffer_dump(&b); | |
87 | #endif | |
88 | EVP_DigestInit(&md, evp_md); | |
89 | EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); | |
90 | EVP_DigestFinal(&md, digest, NULL); | |
91 | ||
92 | buffer_free(&b); | |
93 | ||
94 | #ifdef DEBUG_KEXDH | |
95 | dump_digest("hash", digest, evp_md->md_size); | |
96 | #endif | |
97 | return digest; | |
98 | } | |
99 | ||
100 | /* client */ | |
101 | ||
102 | static void | |
103 | kexgex_client(Kex *kex) | |
104 | { | |
105 | BIGNUM *dh_server_pub = NULL, *shared_secret = NULL; | |
106 | BIGNUM *p = NULL, *g = NULL; | |
107 | Key *server_host_key; | |
108 | u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL; | |
109 | u_int klen, kout, slen, sbloblen; | |
110 | int dlen, plen, min, max, nbits; | |
111 | DH *dh; | |
112 | ||
113 | nbits = dh_estimate(kex->we_need * 8); | |
114 | ||
115 | if (datafellows & SSH_OLD_DHGEX) { | |
116 | debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD sent"); | |
117 | ||
118 | /* Old GEX request */ | |
119 | packet_start(SSH2_MSG_KEX_DH_GEX_REQUEST_OLD); | |
120 | packet_put_int(nbits); | |
121 | min = DH_GRP_MIN; | |
122 | max = DH_GRP_MAX; | |
123 | } else { | |
124 | debug("SSH2_MSG_KEX_DH_GEX_REQUEST sent"); | |
125 | ||
126 | /* New GEX request */ | |
127 | min = DH_GRP_MIN; | |
128 | max = DH_GRP_MAX; | |
129 | packet_start(SSH2_MSG_KEX_DH_GEX_REQUEST); | |
130 | packet_put_int(min); | |
131 | packet_put_int(nbits); | |
132 | packet_put_int(max); | |
133 | } | |
134 | #ifdef DEBUG_KEXDH | |
135 | fprintf(stderr, "\nmin = %d, nbits = %d, max = %d\n", | |
136 | min, nbits, max); | |
137 | #endif | |
138 | packet_send(); | |
139 | ||
140 | debug("expecting SSH2_MSG_KEX_DH_GEX_GROUP"); | |
141 | packet_read_expect(&plen, SSH2_MSG_KEX_DH_GEX_GROUP); | |
142 | ||
143 | if ((p = BN_new()) == NULL) | |
144 | fatal("BN_new"); | |
145 | packet_get_bignum2(p, &dlen); | |
146 | if ((g = BN_new()) == NULL) | |
147 | fatal("BN_new"); | |
148 | packet_get_bignum2(g, &dlen); | |
149 | packet_done(); | |
150 | ||
151 | if (BN_num_bits(p) < min || BN_num_bits(p) > max) | |
152 | fatal("DH_GEX group out of range: %d !< %d !< %d", | |
153 | min, BN_num_bits(p), max); | |
154 | ||
155 | dh = dh_new_group(g, p); | |
156 | dh_gen_key(dh, kex->we_need * 8); | |
157 | ||
158 | #ifdef DEBUG_KEXDH | |
159 | DHparams_print_fp(stderr, dh); | |
160 | fprintf(stderr, "pub= "); | |
161 | BN_print_fp(stderr, dh->pub_key); | |
162 | fprintf(stderr, "\n"); | |
163 | #endif | |
164 | ||
165 | debug("SSH2_MSG_KEX_DH_GEX_INIT sent"); | |
166 | /* generate and send 'e', client DH public key */ | |
167 | packet_start(SSH2_MSG_KEX_DH_GEX_INIT); | |
168 | packet_put_bignum2(dh->pub_key); | |
169 | packet_send(); | |
170 | ||
171 | debug("expecting SSH2_MSG_KEX_DH_GEX_REPLY"); | |
172 | packet_read_expect(&plen, SSH2_MSG_KEX_DH_GEX_REPLY); | |
173 | ||
174 | /* key, cert */ | |
175 | server_host_key_blob = packet_get_string(&sbloblen); | |
176 | server_host_key = key_from_blob(server_host_key_blob, sbloblen); | |
177 | if (server_host_key == NULL) | |
178 | fatal("cannot decode server_host_key_blob"); | |
179 | ||
180 | if (kex->verify_host_key == NULL) | |
181 | fatal("cannot verify server_host_key"); | |
182 | if (kex->verify_host_key(server_host_key) == -1) | |
183 | fatal("server_host_key verification failed"); | |
184 | ||
185 | /* DH paramter f, server public DH key */ | |
186 | dh_server_pub = BN_new(); | |
187 | if (dh_server_pub == NULL) | |
188 | fatal("dh_server_pub == NULL"); | |
189 | packet_get_bignum2(dh_server_pub, &dlen); | |
190 | ||
191 | #ifdef DEBUG_KEXDH | |
192 | fprintf(stderr, "dh_server_pub= "); | |
193 | BN_print_fp(stderr, dh_server_pub); | |
194 | fprintf(stderr, "\n"); | |
195 | debug("bits %d", BN_num_bits(dh_server_pub)); | |
196 | #endif | |
197 | ||
198 | /* signed H */ | |
199 | signature = packet_get_string(&slen); | |
200 | packet_done(); | |
201 | ||
202 | if (!dh_pub_is_valid(dh, dh_server_pub)) | |
203 | packet_disconnect("bad server public DH value"); | |
204 | ||
205 | klen = DH_size(dh); | |
206 | kbuf = xmalloc(klen); | |
207 | kout = DH_compute_key(kbuf, dh_server_pub, dh); | |
208 | #ifdef DEBUG_KEXDH | |
209 | dump_digest("shared secret", kbuf, kout); | |
210 | #endif | |
211 | shared_secret = BN_new(); | |
212 | BN_bin2bn(kbuf, kout, shared_secret); | |
213 | memset(kbuf, 0, klen); | |
214 | xfree(kbuf); | |
215 | ||
216 | if (datafellows & SSH_OLD_DHGEX) | |
217 | min = max = -1; | |
218 | ||
219 | /* calc and verify H */ | |
220 | hash = kexgex_hash( | |
221 | kex->client_version_string, | |
222 | kex->server_version_string, | |
223 | buffer_ptr(&kex->my), buffer_len(&kex->my), | |
224 | buffer_ptr(&kex->peer), buffer_len(&kex->peer), | |
225 | server_host_key_blob, sbloblen, | |
226 | min, nbits, max, | |
227 | dh->p, dh->g, | |
228 | dh->pub_key, | |
229 | dh_server_pub, | |
230 | shared_secret | |
231 | ); | |
232 | /* have keys, free DH */ | |
233 | DH_free(dh); | |
234 | xfree(server_host_key_blob); | |
235 | BN_free(dh_server_pub); | |
236 | ||
237 | if (key_verify(server_host_key, signature, slen, hash, 20) != 1) | |
238 | fatal("key_verify failed for server_host_key"); | |
239 | key_free(server_host_key); | |
240 | xfree(signature); | |
241 | ||
242 | /* save session id */ | |
243 | if (kex->session_id == NULL) { | |
244 | kex->session_id_len = 20; | |
245 | kex->session_id = xmalloc(kex->session_id_len); | |
246 | memcpy(kex->session_id, hash, kex->session_id_len); | |
247 | } | |
248 | kex_derive_keys(kex, hash, shared_secret); | |
249 | BN_clear_free(shared_secret); | |
250 | ||
251 | kex_finish(kex); | |
252 | } | |
253 | ||
254 | /* server */ | |
255 | ||
256 | static void | |
257 | kexgex_server(Kex *kex) | |
258 | { | |
259 | BIGNUM *shared_secret = NULL, *dh_client_pub = NULL; | |
260 | Key *server_host_key; | |
261 | DH *dh = dh; | |
262 | u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL; | |
263 | u_int sbloblen, klen, kout; | |
264 | int min = -1, max = -1, nbits = -1, type, plen, dlen, slen; | |
265 | ||
266 | if (kex->load_host_key == NULL) | |
267 | fatal("Cannot load hostkey"); | |
268 | server_host_key = kex->load_host_key(kex->hostkey_type); | |
269 | if (server_host_key == NULL) | |
270 | fatal("Unsupported hostkey type %d", kex->hostkey_type); | |
271 | ||
272 | type = packet_read(&plen); | |
273 | switch(type){ | |
274 | case SSH2_MSG_KEX_DH_GEX_REQUEST: | |
275 | debug("SSH2_MSG_KEX_DH_GEX_REQUEST received"); | |
276 | min = packet_get_int(); | |
277 | nbits = packet_get_int(); | |
278 | max = packet_get_int(); | |
279 | min = MAX(DH_GRP_MIN, min); | |
280 | max = MIN(DH_GRP_MAX, max); | |
281 | break; | |
282 | case SSH2_MSG_KEX_DH_GEX_REQUEST_OLD: | |
283 | debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD received"); | |
284 | nbits = packet_get_int(); | |
285 | min = DH_GRP_MIN; | |
286 | max = DH_GRP_MAX; | |
287 | /* unused for old GEX */ | |
288 | break; | |
289 | default: | |
290 | fatal("protocol error during kex, no DH_GEX_REQUEST: %d", type); | |
291 | } | |
292 | packet_done(); | |
293 | ||
294 | if (max < min || nbits < min || max < nbits) | |
295 | fatal("DH_GEX_REQUEST, bad parameters: %d !< %d !< %d", | |
296 | min, nbits, max); | |
297 | ||
298 | dh = choose_dh(min, nbits, max); | |
299 | if (dh == NULL) | |
300 | packet_disconnect("Protocol error: no matching DH grp found"); | |
301 | ||
302 | debug("SSH2_MSG_KEX_DH_GEX_GROUP sent"); | |
303 | packet_start(SSH2_MSG_KEX_DH_GEX_GROUP); | |
304 | packet_put_bignum2(dh->p); | |
305 | packet_put_bignum2(dh->g); | |
306 | packet_send(); | |
307 | ||
308 | /* flush */ | |
309 | packet_write_wait(); | |
310 | ||
311 | /* Compute our exchange value in parallel with the client */ | |
312 | dh_gen_key(dh, kex->we_need * 8); | |
313 | ||
314 | debug("expecting SSH2_MSG_KEX_DH_GEX_INIT"); | |
315 | packet_read_expect(&plen, SSH2_MSG_KEX_DH_GEX_INIT); | |
316 | ||
317 | /* key, cert */ | |
318 | dh_client_pub = BN_new(); | |
319 | if (dh_client_pub == NULL) | |
320 | fatal("dh_client_pub == NULL"); | |
321 | packet_get_bignum2(dh_client_pub, &dlen); | |
322 | ||
323 | #ifdef DEBUG_KEXDH | |
324 | fprintf(stderr, "dh_client_pub= "); | |
325 | BN_print_fp(stderr, dh_client_pub); | |
326 | fprintf(stderr, "\n"); | |
327 | debug("bits %d", BN_num_bits(dh_client_pub)); | |
328 | #endif | |
329 | ||
330 | #ifdef DEBUG_KEXDH | |
331 | DHparams_print_fp(stderr, dh); | |
332 | fprintf(stderr, "pub= "); | |
333 | BN_print_fp(stderr, dh->pub_key); | |
334 | fprintf(stderr, "\n"); | |
335 | #endif | |
336 | if (!dh_pub_is_valid(dh, dh_client_pub)) | |
337 | packet_disconnect("bad client public DH value"); | |
338 | ||
339 | klen = DH_size(dh); | |
340 | kbuf = xmalloc(klen); | |
341 | kout = DH_compute_key(kbuf, dh_client_pub, dh); | |
342 | #ifdef DEBUG_KEXDH | |
343 | dump_digest("shared secret", kbuf, kout); | |
344 | #endif | |
345 | shared_secret = BN_new(); | |
346 | BN_bin2bn(kbuf, kout, shared_secret); | |
347 | memset(kbuf, 0, klen); | |
348 | xfree(kbuf); | |
349 | ||
350 | key_to_blob(server_host_key, &server_host_key_blob, &sbloblen); | |
351 | ||
352 | if (type == SSH2_MSG_KEX_DH_GEX_REQUEST_OLD) | |
353 | min = max = -1; | |
354 | ||
355 | /* calc H */ /* XXX depends on 'kex' */ | |
356 | hash = kexgex_hash( | |
357 | kex->client_version_string, | |
358 | kex->server_version_string, | |
359 | buffer_ptr(&kex->peer), buffer_len(&kex->peer), | |
360 | buffer_ptr(&kex->my), buffer_len(&kex->my), | |
361 | server_host_key_blob, sbloblen, | |
362 | min, nbits, max, | |
363 | dh->p, dh->g, | |
364 | dh_client_pub, | |
365 | dh->pub_key, | |
366 | shared_secret | |
367 | ); | |
368 | BN_free(dh_client_pub); | |
369 | ||
370 | /* save session id := H */ | |
371 | /* XXX hashlen depends on KEX */ | |
372 | if (kex->session_id == NULL) { | |
373 | kex->session_id_len = 20; | |
374 | kex->session_id = xmalloc(kex->session_id_len); | |
375 | memcpy(kex->session_id, hash, kex->session_id_len); | |
376 | } | |
377 | ||
378 | /* sign H */ | |
379 | /* XXX hashlen depends on KEX */ | |
380 | key_sign(server_host_key, &signature, &slen, hash, 20); | |
381 | ||
382 | /* destroy_sensitive_data(); */ | |
383 | ||
384 | /* send server hostkey, DH pubkey 'f' and singed H */ | |
385 | debug("SSH2_MSG_KEX_DH_GEX_REPLY sent"); | |
386 | packet_start(SSH2_MSG_KEX_DH_GEX_REPLY); | |
387 | packet_put_string(server_host_key_blob, sbloblen); | |
388 | packet_put_bignum2(dh->pub_key); /* f */ | |
389 | packet_put_string(signature, slen); | |
390 | packet_send(); | |
391 | xfree(signature); | |
392 | xfree(server_host_key_blob); | |
393 | /* have keys, free DH */ | |
394 | DH_free(dh); | |
395 | ||
396 | kex_derive_keys(kex, hash, shared_secret); | |
397 | BN_clear_free(shared_secret); | |
398 | ||
399 | kex_finish(kex); | |
400 | } | |
401 | ||
402 | void | |
403 | kexgex(Kex *kex) | |
404 | { | |
405 | if (kex->server) | |
406 | kexgex_server(kex); | |
407 | else | |
408 | kexgex_client(kex); | |
409 | } |