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Ben Lindstrom22b19b42001-04-04 17:39:19 +00001/*
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"
Ben Lindstrom664408d2001-06-09 01:42:01 +000027RCSID("$OpenBSD: kexgex.c,v 1.6 2001/06/07 20:23:04 markus Exp $");
Ben Lindstrom22b19b42001-04-04 17:39:19 +000028
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
42u_char *
43kexgex_hash(
44 char *client_version_string,
45 char *server_version_string,
46 char *ckexinit, int ckexinitlen,
47 char *skexinit, int skexinitlen,
48 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);
Ben Lindstrom664408d2001-06-09 01:42:01 +000060 buffer_put_cstring(&b, client_version_string);
61 buffer_put_cstring(&b, server_version_string);
Ben Lindstrom22b19b42001-04-04 17:39:19 +000062
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);
Ben Lindstroma3700052001-04-05 23:26:32 +000072 if (min == -1 || max == -1)
Ben Lindstrom22b19b42001-04-04 17:39:19 +000073 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
102void
103kexgex_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->check_host_key == NULL)
181 fatal("cannot check server_host_key");
182 kex->check_host_key(server_host_key);
183
184 /* DH paramter f, server public DH key */
185 dh_server_pub = BN_new();
186 if (dh_server_pub == NULL)
187 fatal("dh_server_pub == NULL");
188 packet_get_bignum2(dh_server_pub, &dlen);
189
190#ifdef DEBUG_KEXDH
191 fprintf(stderr, "dh_server_pub= ");
192 BN_print_fp(stderr, dh_server_pub);
193 fprintf(stderr, "\n");
194 debug("bits %d", BN_num_bits(dh_server_pub));
195#endif
196
197 /* signed H */
198 signature = packet_get_string(&slen);
199 packet_done();
200
201 if (!dh_pub_is_valid(dh, dh_server_pub))
202 packet_disconnect("bad server public DH value");
203
204 klen = DH_size(dh);
205 kbuf = xmalloc(klen);
206 kout = DH_compute_key(kbuf, dh_server_pub, dh);
207#ifdef DEBUG_KEXDH
Ben Lindstroma3700052001-04-05 23:26:32 +0000208 dump_digest("shared secret", kbuf, kout);
Ben Lindstrom22b19b42001-04-04 17:39:19 +0000209#endif
210 shared_secret = BN_new();
211 BN_bin2bn(kbuf, kout, shared_secret);
212 memset(kbuf, 0, klen);
213 xfree(kbuf);
214
215 if (datafellows & SSH_OLD_DHGEX)
216 min = max = -1;
217
218 /* calc and verify H */
219 hash = kexgex_hash(
220 kex->client_version_string,
221 kex->server_version_string,
222 buffer_ptr(&kex->my), buffer_len(&kex->my),
223 buffer_ptr(&kex->peer), buffer_len(&kex->peer),
224 server_host_key_blob, sbloblen,
225 min, nbits, max,
226 dh->p, dh->g,
227 dh->pub_key,
228 dh_server_pub,
229 shared_secret
230 );
Ben Lindstrom238abf62001-04-04 17:52:53 +0000231 /* have keys, free DH */
232 DH_free(dh);
Ben Lindstrom22b19b42001-04-04 17:39:19 +0000233 xfree(server_host_key_blob);
234 BN_free(dh_server_pub);
235
236 if (key_verify(server_host_key, (u_char *)signature, slen, hash, 20) != 1)
237 fatal("key_verify failed for server_host_key");
238 key_free(server_host_key);
239 xfree(signature);
240
241 /* save session id */
242 if (kex->session_id == NULL) {
243 kex->session_id_len = 20;
244 kex->session_id = xmalloc(kex->session_id_len);
245 memcpy(kex->session_id, hash, kex->session_id_len);
246 }
Ben Lindstrom22b19b42001-04-04 17:39:19 +0000247 kex_derive_keys(kex, hash, shared_secret);
248 BN_clear_free(shared_secret);
249
Ben Lindstrom238abf62001-04-04 17:52:53 +0000250 kex_finish(kex);
Ben Lindstrom22b19b42001-04-04 17:39:19 +0000251}
252
253/* server */
254
255void
256kexgex_server(Kex *kex)
257{
258 BIGNUM *shared_secret = NULL, *dh_client_pub = NULL;
259 Key *server_host_key;
260 DH *dh = dh;
261 u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
262 u_int sbloblen, klen, kout;
263 int min = -1, max = -1, nbits = -1, type, plen, dlen, slen;
264
265 if (kex->load_host_key == NULL)
266 fatal("Cannot load hostkey");
267 server_host_key = kex->load_host_key(kex->hostkey_type);
268 if (server_host_key == NULL)
269 fatal("Unsupported hostkey type %d", kex->hostkey_type);
270
271 type = packet_read(&plen);
272 switch(type){
273 case SSH2_MSG_KEX_DH_GEX_REQUEST:
274 debug("SSH2_MSG_KEX_DH_GEX_REQUEST received");
275 min = packet_get_int();
276 nbits = packet_get_int();
277 max = packet_get_int();
278 min = MAX(DH_GRP_MIN, min);
279 max = MIN(DH_GRP_MAX, max);
280 break;
281 case SSH2_MSG_KEX_DH_GEX_REQUEST_OLD:
282 debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD received");
283 nbits = packet_get_int();
284 min = DH_GRP_MIN;
285 max = DH_GRP_MAX;
286 /* unused for old GEX */
287 break;
288 default:
Ben Lindstrom8e312f32001-04-04 23:50:21 +0000289 fatal("protocol error during kex, no DH_GEX_REQUEST: %d", type);
Ben Lindstrom22b19b42001-04-04 17:39:19 +0000290 }
291 packet_done();
292
293 if (max < min || nbits < min || max < nbits)
294 fatal("DH_GEX_REQUEST, bad parameters: %d !< %d !< %d",
295 min, nbits, max);
296
297 dh = choose_dh(min, nbits, max);
298 if (dh == NULL)
299 packet_disconnect("Protocol error: no matching DH grp found");
300
301 debug("SSH2_MSG_KEX_DH_GEX_GROUP sent");
302 packet_start(SSH2_MSG_KEX_DH_GEX_GROUP);
303 packet_put_bignum2(dh->p);
304 packet_put_bignum2(dh->g);
305 packet_send();
306
307 /* flush */
308 packet_write_wait();
309
310 /* Compute our exchange value in parallel with the client */
311 dh_gen_key(dh, kex->we_need * 8);
312
313 debug("expecting SSH2_MSG_KEX_DH_GEX_INIT");
314 packet_read_expect(&plen, SSH2_MSG_KEX_DH_GEX_INIT);
315
316 /* key, cert */
317 dh_client_pub = BN_new();
318 if (dh_client_pub == NULL)
319 fatal("dh_client_pub == NULL");
320 packet_get_bignum2(dh_client_pub, &dlen);
321
322#ifdef DEBUG_KEXDH
323 fprintf(stderr, "dh_client_pub= ");
324 BN_print_fp(stderr, dh_client_pub);
325 fprintf(stderr, "\n");
326 debug("bits %d", BN_num_bits(dh_client_pub));
327#endif
328
329#ifdef DEBUG_KEXDH
330 DHparams_print_fp(stderr, dh);
331 fprintf(stderr, "pub= ");
332 BN_print_fp(stderr, dh->pub_key);
333 fprintf(stderr, "\n");
334#endif
335 if (!dh_pub_is_valid(dh, dh_client_pub))
336 packet_disconnect("bad client public DH value");
337
338 klen = DH_size(dh);
339 kbuf = xmalloc(klen);
340 kout = DH_compute_key(kbuf, dh_client_pub, dh);
341#ifdef DEBUG_KEXDH
Ben Lindstroma3700052001-04-05 23:26:32 +0000342 dump_digest("shared secret", kbuf, kout);
Ben Lindstrom22b19b42001-04-04 17:39:19 +0000343#endif
344 shared_secret = BN_new();
345 BN_bin2bn(kbuf, kout, shared_secret);
346 memset(kbuf, 0, klen);
347 xfree(kbuf);
348
349 key_to_blob(server_host_key, &server_host_key_blob, &sbloblen);
350
351 if (type == SSH2_MSG_KEX_DH_GEX_REQUEST_OLD)
352 min = max = -1;
353
354 /* calc H */ /* XXX depends on 'kex' */
355 hash = kexgex_hash(
356 kex->client_version_string,
357 kex->server_version_string,
358 buffer_ptr(&kex->peer), buffer_len(&kex->peer),
359 buffer_ptr(&kex->my), buffer_len(&kex->my),
360 (char *)server_host_key_blob, sbloblen,
361 min, nbits, max,
362 dh->p, dh->g,
363 dh_client_pub,
364 dh->pub_key,
365 shared_secret
366 );
367 BN_free(dh_client_pub);
368
369 /* save session id := H */
370 /* XXX hashlen depends on KEX */
371 if (kex->session_id == NULL) {
372 kex->session_id_len = 20;
373 kex->session_id = xmalloc(kex->session_id_len);
374 memcpy(kex->session_id, hash, kex->session_id_len);
375 }
376
377 /* sign H */
378 /* XXX hashlen depends on KEX */
379 key_sign(server_host_key, &signature, &slen, hash, 20);
380
381 /* destroy_sensitive_data(); */
382
383 /* send server hostkey, DH pubkey 'f' and singed H */
384 debug("SSH2_MSG_KEX_DH_GEX_REPLY sent");
385 packet_start(SSH2_MSG_KEX_DH_GEX_REPLY);
386 packet_put_string((char *)server_host_key_blob, sbloblen);
387 packet_put_bignum2(dh->pub_key); /* f */
388 packet_put_string((char *)signature, slen);
389 packet_send();
390 xfree(signature);
391 xfree(server_host_key_blob);
Ben Lindstrom238abf62001-04-04 17:52:53 +0000392 /* have keys, free DH */
393 DH_free(dh);
Ben Lindstrom22b19b42001-04-04 17:39:19 +0000394
395 kex_derive_keys(kex, hash, shared_secret);
396 BN_clear_free(shared_secret);
397
Ben Lindstrom238abf62001-04-04 17:52:53 +0000398 kex_finish(kex);
Ben Lindstrom22b19b42001-04-04 17:39:19 +0000399}
400
401void
402kexgex(Kex *kex)
403{
404 if (kex->server)
405 kexgex_server(kex);
406 else
407 kexgex_client(kex);
408}