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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" | |
26 | RCSID("$OpenBSD: kexdh.c,v 1.7 2001/09/17 19:27:15 stevesk Exp $"); | |
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" | |
40 | ||
41 | static u_char * | |
42 | kex_dh_hash( | |
43 | char *client_version_string, | |
44 | char *server_version_string, | |
45 | char *ckexinit, int ckexinitlen, | |
46 | char *skexinit, int skexinitlen, | |
47 | u_char *serverhostkeyblob, int sbloblen, | |
48 | 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); | |
58 | buffer_put_cstring(&b, client_version_string); | |
59 | buffer_put_cstring(&b, server_version_string); | |
60 | ||
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 | ||
91 | static void | |
92 | kexdh_client(Kex *kex) | |
93 | { | |
94 | BIGNUM *dh_server_pub = NULL, *shared_secret = NULL; | |
95 | DH *dh; | |
96 | Key *server_host_key; | |
97 | u_char *server_host_key_blob = NULL, *signature = NULL; | |
98 | 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 | ||
126 | 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"); | |
130 | ||
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); | |
174 | BN_free(dh_server_pub); | |
175 | DH_free(dh); | |
176 | ||
177 | if (key_verify(server_host_key, signature, slen, hash, 20) != 1) | |
178 | 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); | |
191 | kex_finish(kex); | |
192 | } | |
193 | ||
194 | /* server */ | |
195 | ||
196 | static void | |
197 | kexdh_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), | |
260 | server_host_key_blob, sbloblen, | |
261 | 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); | |
283 | packet_put_string(server_host_key_blob, sbloblen); | |
284 | packet_put_bignum2(dh->pub_key); /* f */ | |
285 | packet_put_string(signature, slen); | |
286 | packet_send(); | |
287 | ||
288 | xfree(signature); | |
289 | xfree(server_host_key_blob); | |
290 | /* have keys, free DH */ | |
291 | DH_free(dh); | |
292 | ||
293 | kex_derive_keys(kex, hash, shared_secret); | |
294 | BN_clear_free(shared_secret); | |
295 | kex_finish(kex); | |
296 | } | |
297 | ||
298 | void | |
299 | kexdh(Kex *kex) | |
300 | { | |
301 | if (kex->server) | |
302 | kexdh_server(kex); | |
303 | else | |
304 | kexdh_client(kex); | |
305 | } |