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Ben Lindstrom22b19b42001-04-04 17:39:19 +00001/*
2 * Copyright (c) 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"
Ben Lindstrom9e0ddd42001-09-18 05:41:19 +000026RCSID("$OpenBSD: kexdh.c,v 1.7 2001/09/17 19:27:15 stevesk Exp $");
Ben Lindstrom22b19b42001-04-04 17:39:19 +000027
28#include <openssl/crypto.h>
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
Ben Lindstrombba81212001-06-25 05:01:22 +000041static u_char *
Ben Lindstrom22b19b42001-04-04 17:39:19 +000042kex_dh_hash(
43 char *client_version_string,
44 char *server_version_string,
45 char *ckexinit, int ckexinitlen,
46 char *skexinit, int skexinitlen,
Ben Lindstrom9e0ddd42001-09-18 05:41:19 +000047 u_char *serverhostkeyblob, int sbloblen,
Ben Lindstrom22b19b42001-04-04 17:39:19 +000048 BIGNUM *client_dh_pub,
49 BIGNUM *server_dh_pub,
50 BIGNUM *shared_secret)
51{
52 Buffer b;
53 static u_char digest[EVP_MAX_MD_SIZE];
54 EVP_MD *evp_md = EVP_sha1();
55 EVP_MD_CTX md;
56
57 buffer_init(&b);
Ben Lindstrom664408d2001-06-09 01:42:01 +000058 buffer_put_cstring(&b, client_version_string);
59 buffer_put_cstring(&b, server_version_string);
Ben Lindstrom22b19b42001-04-04 17:39:19 +000060
61 /* kexinit messages: fake header: len+SSH2_MSG_KEXINIT */
62 buffer_put_int(&b, ckexinitlen+1);
63 buffer_put_char(&b, SSH2_MSG_KEXINIT);
64 buffer_append(&b, ckexinit, ckexinitlen);
65 buffer_put_int(&b, skexinitlen+1);
66 buffer_put_char(&b, SSH2_MSG_KEXINIT);
67 buffer_append(&b, skexinit, skexinitlen);
68
69 buffer_put_string(&b, serverhostkeyblob, sbloblen);
70 buffer_put_bignum2(&b, client_dh_pub);
71 buffer_put_bignum2(&b, server_dh_pub);
72 buffer_put_bignum2(&b, shared_secret);
73
74#ifdef DEBUG_KEX
75 buffer_dump(&b);
76#endif
77 EVP_DigestInit(&md, evp_md);
78 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
79 EVP_DigestFinal(&md, digest, NULL);
80
81 buffer_free(&b);
82
83#ifdef DEBUG_KEX
84 dump_digest("hash", digest, evp_md->md_size);
85#endif
86 return digest;
87}
88
89/* client */
90
Ben Lindstrombba81212001-06-25 05:01:22 +000091static void
Ben Lindstrom22b19b42001-04-04 17:39:19 +000092kexdh_client(Kex *kex)
93{
94 BIGNUM *dh_server_pub = NULL, *shared_secret = NULL;
95 DH *dh;
96 Key *server_host_key;
Ben Lindstrom9e0ddd42001-09-18 05:41:19 +000097 u_char *server_host_key_blob = NULL, *signature = NULL;
Ben Lindstrom22b19b42001-04-04 17:39:19 +000098 u_char *kbuf, *hash;
99 u_int klen, kout, slen, sbloblen;
100 int dlen, plen;
101
102 /* generate and send 'e', client DH public key */
103 dh = dh_new_group1();
104 dh_gen_key(dh, kex->we_need * 8);
105 packet_start(SSH2_MSG_KEXDH_INIT);
106 packet_put_bignum2(dh->pub_key);
107 packet_send();
108
109 debug("sending SSH2_MSG_KEXDH_INIT");
110#ifdef DEBUG_KEXDH
111 DHparams_print_fp(stderr, dh);
112 fprintf(stderr, "pub= ");
113 BN_print_fp(stderr, dh->pub_key);
114 fprintf(stderr, "\n");
115#endif
116
117 debug("expecting SSH2_MSG_KEXDH_REPLY");
118 packet_read_expect(&plen, SSH2_MSG_KEXDH_REPLY);
119
120 /* key, cert */
121 server_host_key_blob = packet_get_string(&sbloblen);
122 server_host_key = key_from_blob(server_host_key_blob, sbloblen);
123 if (server_host_key == NULL)
124 fatal("cannot decode server_host_key_blob");
125
Ben Lindstromd6481ea2001-06-25 04:37:41 +0000126 if (kex->verify_host_key == NULL)
127 fatal("cannot verify server_host_key");
128 if (kex->verify_host_key(server_host_key) == -1)
129 fatal("server_host_key verification failed");
Ben Lindstrom22b19b42001-04-04 17:39:19 +0000130
131 /* DH paramter f, server public DH key */
132 dh_server_pub = BN_new();
133 if (dh_server_pub == NULL)
134 fatal("dh_server_pub == NULL");
135 packet_get_bignum2(dh_server_pub, &dlen);
136
137#ifdef DEBUG_KEXDH
138 fprintf(stderr, "dh_server_pub= ");
139 BN_print_fp(stderr, dh_server_pub);
140 fprintf(stderr, "\n");
141 debug("bits %d", BN_num_bits(dh_server_pub));
142#endif
143
144 /* signed H */
145 signature = packet_get_string(&slen);
146 packet_done();
147
148 if (!dh_pub_is_valid(dh, dh_server_pub))
149 packet_disconnect("bad server public DH value");
150
151 klen = DH_size(dh);
152 kbuf = xmalloc(klen);
153 kout = DH_compute_key(kbuf, dh_server_pub, dh);
154#ifdef DEBUG_KEXDH
155 dump_digest("shared secret", kbuf, kout);
156#endif
157 shared_secret = BN_new();
158 BN_bin2bn(kbuf, kout, shared_secret);
159 memset(kbuf, 0, klen);
160 xfree(kbuf);
161
162 /* calc and verify H */
163 hash = kex_dh_hash(
164 kex->client_version_string,
165 kex->server_version_string,
166 buffer_ptr(&kex->my), buffer_len(&kex->my),
167 buffer_ptr(&kex->peer), buffer_len(&kex->peer),
168 server_host_key_blob, sbloblen,
169 dh->pub_key,
170 dh_server_pub,
171 shared_secret
172 );
173 xfree(server_host_key_blob);
Ben Lindstrom22b19b42001-04-04 17:39:19 +0000174 BN_free(dh_server_pub);
Ben Lindstrom238abf62001-04-04 17:52:53 +0000175 DH_free(dh);
Ben Lindstrom22b19b42001-04-04 17:39:19 +0000176
Ben Lindstrom9e0ddd42001-09-18 05:41:19 +0000177 if (key_verify(server_host_key, signature, slen, hash, 20) != 1)
Ben Lindstrom22b19b42001-04-04 17:39:19 +0000178 fatal("key_verify failed for server_host_key");
179 key_free(server_host_key);
180 xfree(signature);
181
182 /* save session id */
183 if (kex->session_id == NULL) {
184 kex->session_id_len = 20;
185 kex->session_id = xmalloc(kex->session_id_len);
186 memcpy(kex->session_id, hash, kex->session_id_len);
187 }
188
189 kex_derive_keys(kex, hash, shared_secret);
190 BN_clear_free(shared_secret);
Ben Lindstrom238abf62001-04-04 17:52:53 +0000191 kex_finish(kex);
Ben Lindstrom22b19b42001-04-04 17:39:19 +0000192}
193
194/* server */
195
Ben Lindstrombba81212001-06-25 05:01:22 +0000196static void
Ben Lindstrom22b19b42001-04-04 17:39:19 +0000197kexdh_server(Kex *kex)
198{
199 BIGNUM *shared_secret = NULL, *dh_client_pub = NULL;
200 DH *dh;
201 Key *server_host_key;
202 u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
203 u_int sbloblen, klen, kout;
204 int dlen, slen, plen;
205
206 /* generate server DH public key */
207 dh = dh_new_group1();
208 dh_gen_key(dh, kex->we_need * 8);
209
210 debug("expecting SSH2_MSG_KEXDH_INIT");
211 packet_read_expect(&plen, SSH2_MSG_KEXDH_INIT);
212
213 if (kex->load_host_key == NULL)
214 fatal("Cannot load hostkey");
215 server_host_key = kex->load_host_key(kex->hostkey_type);
216 if (server_host_key == NULL)
217 fatal("Unsupported hostkey type %d", kex->hostkey_type);
218
219 /* key, cert */
220 dh_client_pub = BN_new();
221 if (dh_client_pub == NULL)
222 fatal("dh_client_pub == NULL");
223 packet_get_bignum2(dh_client_pub, &dlen);
224
225#ifdef DEBUG_KEXDH
226 fprintf(stderr, "dh_client_pub= ");
227 BN_print_fp(stderr, dh_client_pub);
228 fprintf(stderr, "\n");
229 debug("bits %d", BN_num_bits(dh_client_pub));
230#endif
231
232#ifdef DEBUG_KEXDH
233 DHparams_print_fp(stderr, dh);
234 fprintf(stderr, "pub= ");
235 BN_print_fp(stderr, dh->pub_key);
236 fprintf(stderr, "\n");
237#endif
238 if (!dh_pub_is_valid(dh, dh_client_pub))
239 packet_disconnect("bad client public DH value");
240
241 klen = DH_size(dh);
242 kbuf = xmalloc(klen);
243 kout = DH_compute_key(kbuf, dh_client_pub, dh);
244#ifdef DEBUG_KEXDH
245 dump_digest("shared secret", kbuf, kout);
246#endif
247 shared_secret = BN_new();
248 BN_bin2bn(kbuf, kout, shared_secret);
249 memset(kbuf, 0, klen);
250 xfree(kbuf);
251
252 key_to_blob(server_host_key, &server_host_key_blob, &sbloblen);
253
254 /* calc H */
255 hash = kex_dh_hash(
256 kex->client_version_string,
257 kex->server_version_string,
258 buffer_ptr(&kex->peer), buffer_len(&kex->peer),
259 buffer_ptr(&kex->my), buffer_len(&kex->my),
Ben Lindstrom9e0ddd42001-09-18 05:41:19 +0000260 server_host_key_blob, sbloblen,
Ben Lindstrom22b19b42001-04-04 17:39:19 +0000261 dh_client_pub,
262 dh->pub_key,
263 shared_secret
264 );
265 BN_free(dh_client_pub);
266
267 /* save session id := H */
268 /* XXX hashlen depends on KEX */
269 if (kex->session_id == NULL) {
270 kex->session_id_len = 20;
271 kex->session_id = xmalloc(kex->session_id_len);
272 memcpy(kex->session_id, hash, kex->session_id_len);
273 }
274
275 /* sign H */
276 /* XXX hashlen depends on KEX */
277 key_sign(server_host_key, &signature, &slen, hash, 20);
278
279 /* destroy_sensitive_data(); */
280
281 /* send server hostkey, DH pubkey 'f' and singed H */
282 packet_start(SSH2_MSG_KEXDH_REPLY);
Ben Lindstrom9e0ddd42001-09-18 05:41:19 +0000283 packet_put_string(server_host_key_blob, sbloblen);
Ben Lindstrom22b19b42001-04-04 17:39:19 +0000284 packet_put_bignum2(dh->pub_key); /* f */
Ben Lindstrom9e0ddd42001-09-18 05:41:19 +0000285 packet_put_string(signature, slen);
Ben Lindstrom22b19b42001-04-04 17:39:19 +0000286 packet_send();
Ben Lindstrom238abf62001-04-04 17:52:53 +0000287
Ben Lindstrom22b19b42001-04-04 17:39:19 +0000288 xfree(signature);
289 xfree(server_host_key_blob);
Ben Lindstrom238abf62001-04-04 17:52:53 +0000290 /* have keys, free DH */
291 DH_free(dh);
Ben Lindstrom22b19b42001-04-04 17:39:19 +0000292
293 kex_derive_keys(kex, hash, shared_secret);
294 BN_clear_free(shared_secret);
Ben Lindstrom238abf62001-04-04 17:52:53 +0000295 kex_finish(kex);
Ben Lindstrom22b19b42001-04-04 17:39:19 +0000296}
297
298void
299kexdh(Kex *kex)
300{
301 if (kex->server)
302 kexdh_server(kex);
303 else
304 kexdh_client(kex);
305}