Ben Lindstrom | 22b19b4 | 2001-04-04 17:39:19 +0000 | [diff] [blame] | 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" |
Ben Lindstrom | bba8121 | 2001-06-25 05:01:22 +0000 | [diff] [blame] | 27 | RCSID("$OpenBSD: kexgex.c,v 1.8 2001/06/23 15:12:19 itojun Exp $"); |
Ben Lindstrom | 22b19b4 | 2001-04-04 17:39:19 +0000 | [diff] [blame] | 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 | |
Ben Lindstrom | bba8121 | 2001-06-25 05:01:22 +0000 | [diff] [blame] | 42 | static u_char * |
Ben Lindstrom | 22b19b4 | 2001-04-04 17:39:19 +0000 | [diff] [blame] | 43 | kexgex_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 Lindstrom | 664408d | 2001-06-09 01:42:01 +0000 | [diff] [blame] | 60 | buffer_put_cstring(&b, client_version_string); |
| 61 | buffer_put_cstring(&b, server_version_string); |
Ben Lindstrom | 22b19b4 | 2001-04-04 17:39:19 +0000 | [diff] [blame] | 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); |
Ben Lindstrom | a370005 | 2001-04-05 23:26:32 +0000 | [diff] [blame] | 72 | if (min == -1 || max == -1) |
Ben Lindstrom | 22b19b4 | 2001-04-04 17:39:19 +0000 | [diff] [blame] | 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 | |
Ben Lindstrom | bba8121 | 2001-06-25 05:01:22 +0000 | [diff] [blame] | 102 | static void |
Ben Lindstrom | 22b19b4 | 2001-04-04 17:39:19 +0000 | [diff] [blame] | 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 | |
Ben Lindstrom | d6481ea | 2001-06-25 04:37:41 +0000 | [diff] [blame] | 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"); |
Ben Lindstrom | 22b19b4 | 2001-04-04 17:39:19 +0000 | [diff] [blame] | 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 |
Ben Lindstrom | a370005 | 2001-04-05 23:26:32 +0000 | [diff] [blame] | 209 | dump_digest("shared secret", kbuf, kout); |
Ben Lindstrom | 22b19b4 | 2001-04-04 17:39:19 +0000 | [diff] [blame] | 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 | ); |
Ben Lindstrom | 238abf6 | 2001-04-04 17:52:53 +0000 | [diff] [blame] | 232 | /* have keys, free DH */ |
| 233 | DH_free(dh); |
Ben Lindstrom | 22b19b4 | 2001-04-04 17:39:19 +0000 | [diff] [blame] | 234 | xfree(server_host_key_blob); |
| 235 | BN_free(dh_server_pub); |
| 236 | |
| 237 | if (key_verify(server_host_key, (u_char *)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 | } |
Ben Lindstrom | 22b19b4 | 2001-04-04 17:39:19 +0000 | [diff] [blame] | 248 | kex_derive_keys(kex, hash, shared_secret); |
| 249 | BN_clear_free(shared_secret); |
| 250 | |
Ben Lindstrom | 238abf6 | 2001-04-04 17:52:53 +0000 | [diff] [blame] | 251 | kex_finish(kex); |
Ben Lindstrom | 22b19b4 | 2001-04-04 17:39:19 +0000 | [diff] [blame] | 252 | } |
| 253 | |
| 254 | /* server */ |
| 255 | |
Ben Lindstrom | bba8121 | 2001-06-25 05:01:22 +0000 | [diff] [blame] | 256 | static void |
Ben Lindstrom | 22b19b4 | 2001-04-04 17:39:19 +0000 | [diff] [blame] | 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: |
Ben Lindstrom | 8e312f3 | 2001-04-04 23:50:21 +0000 | [diff] [blame] | 290 | fatal("protocol error during kex, no DH_GEX_REQUEST: %d", type); |
Ben Lindstrom | 22b19b4 | 2001-04-04 17:39:19 +0000 | [diff] [blame] | 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 |
Ben Lindstrom | a370005 | 2001-04-05 23:26:32 +0000 | [diff] [blame] | 343 | dump_digest("shared secret", kbuf, kout); |
Ben Lindstrom | 22b19b4 | 2001-04-04 17:39:19 +0000 | [diff] [blame] | 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 | (char *)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((char *)server_host_key_blob, sbloblen); |
| 388 | packet_put_bignum2(dh->pub_key); /* f */ |
| 389 | packet_put_string((char *)signature, slen); |
| 390 | packet_send(); |
| 391 | xfree(signature); |
| 392 | xfree(server_host_key_blob); |
Ben Lindstrom | 238abf6 | 2001-04-04 17:52:53 +0000 | [diff] [blame] | 393 | /* have keys, free DH */ |
| 394 | DH_free(dh); |
Ben Lindstrom | 22b19b4 | 2001-04-04 17:39:19 +0000 | [diff] [blame] | 395 | |
| 396 | kex_derive_keys(kex, hash, shared_secret); |
| 397 | BN_clear_free(shared_secret); |
| 398 | |
Ben Lindstrom | 238abf6 | 2001-04-04 17:52:53 +0000 | [diff] [blame] | 399 | kex_finish(kex); |
Ben Lindstrom | 22b19b4 | 2001-04-04 17:39:19 +0000 | [diff] [blame] | 400 | } |
| 401 | |
| 402 | void |
| 403 | kexgex(Kex *kex) |
| 404 | { |
| 405 | if (kex->server) |
| 406 | kexgex_server(kex); |
| 407 | else |
| 408 | kexgex_client(kex); |
| 409 | } |