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3c0ef626 | 1 | /* |
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" | |
700318f3 | 26 | RCSID("$OpenBSD: kexdh.c,v 1.18 2002/03/18 17:50:31 provos Exp $"); |
3c0ef626 | 27 | |
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" | |
700318f3 | 40 | #include "monitor_wrap.h" |
3c0ef626 | 41 | |
42 | static u_char * | |
43 | kex_dh_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 | BIGNUM *client_dh_pub, | |
50 | BIGNUM *server_dh_pub, | |
51 | BIGNUM *shared_secret) | |
52 | { | |
53 | Buffer b; | |
54 | static u_char digest[EVP_MAX_MD_SIZE]; | |
e9a17296 | 55 | const EVP_MD *evp_md = EVP_sha1(); |
3c0ef626 | 56 | EVP_MD_CTX md; |
57 | ||
58 | buffer_init(&b); | |
59 | buffer_put_cstring(&b, client_version_string); | |
60 | buffer_put_cstring(&b, server_version_string); | |
61 | ||
62 | /* kexinit messages: fake header: len+SSH2_MSG_KEXINIT */ | |
63 | buffer_put_int(&b, ckexinitlen+1); | |
64 | buffer_put_char(&b, SSH2_MSG_KEXINIT); | |
65 | buffer_append(&b, ckexinit, ckexinitlen); | |
66 | buffer_put_int(&b, skexinitlen+1); | |
67 | buffer_put_char(&b, SSH2_MSG_KEXINIT); | |
68 | buffer_append(&b, skexinit, skexinitlen); | |
69 | ||
70 | buffer_put_string(&b, serverhostkeyblob, sbloblen); | |
71 | buffer_put_bignum2(&b, client_dh_pub); | |
72 | buffer_put_bignum2(&b, server_dh_pub); | |
73 | buffer_put_bignum2(&b, shared_secret); | |
74 | ||
75 | #ifdef DEBUG_KEX | |
76 | buffer_dump(&b); | |
77 | #endif | |
78 | EVP_DigestInit(&md, evp_md); | |
79 | EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); | |
80 | EVP_DigestFinal(&md, digest, NULL); | |
81 | ||
82 | buffer_free(&b); | |
83 | ||
84 | #ifdef DEBUG_KEX | |
e9a17296 | 85 | dump_digest("hash", digest, EVP_MD_size(evp_md)); |
3c0ef626 | 86 | #endif |
87 | return digest; | |
88 | } | |
89 | ||
90 | /* client */ | |
91 | ||
92 | static void | |
93 | kexdh_client(Kex *kex) | |
94 | { | |
95 | BIGNUM *dh_server_pub = NULL, *shared_secret = NULL; | |
96 | DH *dh; | |
97 | Key *server_host_key; | |
98 | u_char *server_host_key_blob = NULL, *signature = NULL; | |
99 | u_char *kbuf, *hash; | |
100 | u_int klen, kout, slen, sbloblen; | |
3c0ef626 | 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"); | |
e9a17296 | 118 | packet_read_expect(SSH2_MSG_KEXDH_REPLY); |
3c0ef626 | 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"); | |
e9a17296 | 125 | if (server_host_key->type != kex->hostkey_type) |
126 | fatal("type mismatch for decoded server_host_key_blob"); | |
3c0ef626 | 127 | if (kex->verify_host_key == NULL) |
128 | fatal("cannot verify server_host_key"); | |
129 | if (kex->verify_host_key(server_host_key) == -1) | |
130 | fatal("server_host_key verification failed"); | |
131 | ||
132 | /* DH paramter f, server public DH key */ | |
e9a17296 | 133 | if ((dh_server_pub = BN_new()) == NULL) |
3c0ef626 | 134 | fatal("dh_server_pub == NULL"); |
e9a17296 | 135 | packet_get_bignum2(dh_server_pub); |
3c0ef626 | 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); | |
e9a17296 | 146 | packet_check_eom(); |
3c0ef626 | 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 | |
e9a17296 | 157 | if ((shared_secret = BN_new()) == NULL) |
158 | fatal("kexdh_client: BN_new failed"); | |
3c0ef626 | 159 | BN_bin2bn(kbuf, kout, shared_secret); |
160 | memset(kbuf, 0, klen); | |
161 | xfree(kbuf); | |
162 | ||
163 | /* calc and verify H */ | |
164 | hash = kex_dh_hash( | |
165 | kex->client_version_string, | |
166 | kex->server_version_string, | |
167 | buffer_ptr(&kex->my), buffer_len(&kex->my), | |
168 | buffer_ptr(&kex->peer), buffer_len(&kex->peer), | |
169 | server_host_key_blob, sbloblen, | |
170 | dh->pub_key, | |
171 | dh_server_pub, | |
172 | shared_secret | |
173 | ); | |
174 | xfree(server_host_key_blob); | |
e9a17296 | 175 | BN_clear_free(dh_server_pub); |
3c0ef626 | 176 | DH_free(dh); |
177 | ||
178 | if (key_verify(server_host_key, signature, slen, hash, 20) != 1) | |
179 | fatal("key_verify failed for server_host_key"); | |
180 | key_free(server_host_key); | |
181 | xfree(signature); | |
182 | ||
183 | /* save session id */ | |
184 | if (kex->session_id == NULL) { | |
185 | kex->session_id_len = 20; | |
186 | kex->session_id = xmalloc(kex->session_id_len); | |
187 | memcpy(kex->session_id, hash, kex->session_id_len); | |
188 | } | |
189 | ||
190 | kex_derive_keys(kex, hash, shared_secret); | |
191 | BN_clear_free(shared_secret); | |
192 | kex_finish(kex); | |
193 | } | |
194 | ||
195 | /* server */ | |
196 | ||
197 | static void | |
198 | kexdh_server(Kex *kex) | |
199 | { | |
200 | BIGNUM *shared_secret = NULL, *dh_client_pub = NULL; | |
201 | DH *dh; | |
202 | Key *server_host_key; | |
203 | u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL; | |
204 | u_int sbloblen, klen, kout; | |
e9a17296 | 205 | u_int slen; |
3c0ef626 | 206 | |
207 | /* generate server DH public key */ | |
208 | dh = dh_new_group1(); | |
209 | dh_gen_key(dh, kex->we_need * 8); | |
210 | ||
211 | debug("expecting SSH2_MSG_KEXDH_INIT"); | |
e9a17296 | 212 | packet_read_expect(SSH2_MSG_KEXDH_INIT); |
3c0ef626 | 213 | |
214 | if (kex->load_host_key == NULL) | |
215 | fatal("Cannot load hostkey"); | |
216 | server_host_key = kex->load_host_key(kex->hostkey_type); | |
217 | if (server_host_key == NULL) | |
218 | fatal("Unsupported hostkey type %d", kex->hostkey_type); | |
219 | ||
220 | /* key, cert */ | |
e9a17296 | 221 | if ((dh_client_pub = BN_new()) == NULL) |
3c0ef626 | 222 | fatal("dh_client_pub == NULL"); |
e9a17296 | 223 | packet_get_bignum2(dh_client_pub); |
224 | packet_check_eom(); | |
3c0ef626 | 225 | |
226 | #ifdef DEBUG_KEXDH | |
227 | fprintf(stderr, "dh_client_pub= "); | |
228 | BN_print_fp(stderr, dh_client_pub); | |
229 | fprintf(stderr, "\n"); | |
230 | debug("bits %d", BN_num_bits(dh_client_pub)); | |
231 | #endif | |
232 | ||
233 | #ifdef DEBUG_KEXDH | |
234 | DHparams_print_fp(stderr, dh); | |
235 | fprintf(stderr, "pub= "); | |
236 | BN_print_fp(stderr, dh->pub_key); | |
237 | fprintf(stderr, "\n"); | |
238 | #endif | |
239 | if (!dh_pub_is_valid(dh, dh_client_pub)) | |
240 | packet_disconnect("bad client public DH value"); | |
241 | ||
242 | klen = DH_size(dh); | |
243 | kbuf = xmalloc(klen); | |
244 | kout = DH_compute_key(kbuf, dh_client_pub, dh); | |
245 | #ifdef DEBUG_KEXDH | |
246 | dump_digest("shared secret", kbuf, kout); | |
247 | #endif | |
e9a17296 | 248 | if ((shared_secret = BN_new()) == NULL) |
249 | fatal("kexdh_server: BN_new failed"); | |
3c0ef626 | 250 | BN_bin2bn(kbuf, kout, shared_secret); |
251 | memset(kbuf, 0, klen); | |
252 | xfree(kbuf); | |
253 | ||
254 | key_to_blob(server_host_key, &server_host_key_blob, &sbloblen); | |
255 | ||
256 | /* calc H */ | |
257 | hash = kex_dh_hash( | |
258 | kex->client_version_string, | |
259 | kex->server_version_string, | |
260 | buffer_ptr(&kex->peer), buffer_len(&kex->peer), | |
261 | buffer_ptr(&kex->my), buffer_len(&kex->my), | |
262 | server_host_key_blob, sbloblen, | |
263 | dh_client_pub, | |
264 | dh->pub_key, | |
265 | shared_secret | |
266 | ); | |
e9a17296 | 267 | BN_clear_free(dh_client_pub); |
3c0ef626 | 268 | |
269 | /* save session id := H */ | |
270 | /* XXX hashlen depends on KEX */ | |
271 | if (kex->session_id == NULL) { | |
272 | kex->session_id_len = 20; | |
273 | kex->session_id = xmalloc(kex->session_id_len); | |
274 | memcpy(kex->session_id, hash, kex->session_id_len); | |
275 | } | |
276 | ||
277 | /* sign H */ | |
278 | /* XXX hashlen depends on KEX */ | |
700318f3 | 279 | PRIVSEP(key_sign(server_host_key, &signature, &slen, hash, 20)); |
3c0ef626 | 280 | |
281 | /* destroy_sensitive_data(); */ | |
282 | ||
283 | /* send server hostkey, DH pubkey 'f' and singed H */ | |
284 | packet_start(SSH2_MSG_KEXDH_REPLY); | |
285 | packet_put_string(server_host_key_blob, sbloblen); | |
286 | packet_put_bignum2(dh->pub_key); /* f */ | |
287 | packet_put_string(signature, slen); | |
288 | packet_send(); | |
289 | ||
290 | xfree(signature); | |
291 | xfree(server_host_key_blob); | |
292 | /* have keys, free DH */ | |
293 | DH_free(dh); | |
294 | ||
295 | kex_derive_keys(kex, hash, shared_secret); | |
296 | BN_clear_free(shared_secret); | |
297 | kex_finish(kex); | |
298 | } | |
299 | ||
300 | void | |
301 | kexdh(Kex *kex) | |
302 | { | |
303 | if (kex->server) | |
304 | kexdh_server(kex); | |
305 | else | |
306 | kexdh_client(kex); | |
307 | } |