1 /* 2 * Copyright (c) 2000 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: kex.c,v 1.33 2001/04/05 10:42:50 markus Exp $"); 27 28 #include <openssl/crypto.h> 29 30 #include "ssh2.h" 31 #include "xmalloc.h" 32 #include "buffer.h" 33 #include "bufaux.h" 34 #include "packet.h" 35 #include "compat.h" 36 #include "cipher.h" 37 #include "kex.h" 38 #include "key.h" 39 #include "log.h" 40 #include "mac.h" 41 #include "match.h" 42 #include "dispatch.h" 43 44 #define KEX_COOKIE_LEN 16 45 46 void kex_kexinit_finish(Kex *kex); 47 void kex_choose_conf(Kex *k); 48 49 /* put algorithm proposal into buffer */ 50 void 51 kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX]) 52 { 53 u_int32_t rand = 0; 54 int i; 55 56 buffer_clear(b); 57 for (i = 0; i < KEX_COOKIE_LEN; i++) { 58 if (i % 4 == 0) 59 rand = arc4random(); 60 buffer_put_char(b, rand & 0xff); 61 rand >>= 8; 62 } 63 for (i = 0; i < PROPOSAL_MAX; i++) 64 buffer_put_cstring(b, proposal[i]); 65 buffer_put_char(b, 0); /* first_kex_packet_follows */ 66 buffer_put_int(b, 0); /* uint32 reserved */ 67 } 68 69 /* parse buffer and return algorithm proposal */ 70 char ** 71 kex_buf2prop(Buffer *raw) 72 { 73 Buffer b; 74 int i; 75 char **proposal; 76 77 proposal = xmalloc(PROPOSAL_MAX * sizeof(char *)); 78 79 buffer_init(&b); 80 buffer_append(&b, buffer_ptr(raw), buffer_len(raw)); 81 /* skip cookie */ 82 for (i = 0; i < KEX_COOKIE_LEN; i++) 83 buffer_get_char(&b); 84 /* extract kex init proposal strings */ 85 for (i = 0; i < PROPOSAL_MAX; i++) { 86 proposal[i] = buffer_get_string(&b,NULL); 87 debug2("kex_parse_kexinit: %s", proposal[i]); 88 } 89 /* first kex follows / reserved */ 90 i = buffer_get_char(&b); 91 debug2("kex_parse_kexinit: first_kex_follows %d ", i); 92 i = buffer_get_int(&b); 93 debug2("kex_parse_kexinit: reserved %d ", i); 94 buffer_free(&b); 95 return proposal; 96 } 97 98 void 99 kex_prop_free(char **proposal) 100 { 101 int i; 102 103 for (i = 0; i < PROPOSAL_MAX; i++) 104 xfree(proposal[i]); 105 xfree(proposal); 106 } 107 108 void 109 kex_protocol_error(int type, int plen, void *ctxt) 110 { 111 error("Hm, kex protocol error: type %d plen %d", type, plen); 112 } 113 114 void 115 kex_clear_dispatch(void) 116 { 117 int i; 118 119 /* Numbers 30-49 are used for kex packets */ 120 for (i = 30; i <= 49; i++) 121 dispatch_set(i, &kex_protocol_error); 122 } 123 124 void 125 kex_finish(Kex *kex) 126 { 127 int plen; 128 129 kex_clear_dispatch(); 130 131 packet_start(SSH2_MSG_NEWKEYS); 132 packet_send(); 133 /* packet_write_wait(); */ 134 debug("SSH2_MSG_NEWKEYS sent"); 135 136 debug("waiting for SSH2_MSG_NEWKEYS"); 137 packet_read_expect(&plen, SSH2_MSG_NEWKEYS); 138 debug("SSH2_MSG_NEWKEYS received"); 139 140 kex->done = 1; 141 buffer_clear(&kex->peer); 142 /* buffer_clear(&kex->my); */ 143 kex->flags &= ~KEX_INIT_SENT; 144 xfree(kex->name); 145 kex->name = NULL; 146 } 147 148 void 149 kex_send_kexinit(Kex *kex) 150 { 151 if (kex == NULL) { 152 error("kex_send_kexinit: no kex, cannot rekey"); 153 return; 154 } 155 if (kex->flags & KEX_INIT_SENT) { 156 debug("KEX_INIT_SENT"); 157 return; 158 } 159 kex->done = 0; 160 packet_start(SSH2_MSG_KEXINIT); 161 packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my)); 162 packet_send(); 163 debug("SSH2_MSG_KEXINIT sent"); 164 kex->flags |= KEX_INIT_SENT; 165 } 166 167 void 168 kex_input_kexinit(int type, int plen, void *ctxt) 169 { 170 char *ptr; 171 int dlen; 172 int i; 173 Kex *kex = (Kex *)ctxt; 174 175 debug("SSH2_MSG_KEXINIT received"); 176 if (kex == NULL) 177 fatal("kex_input_kexinit: no kex, cannot rekey"); 178 179 ptr = packet_get_raw(&dlen); 180 buffer_append(&kex->peer, ptr, dlen); 181 182 /* discard packet */ 183 for (i = 0; i < KEX_COOKIE_LEN; i++) 184 packet_get_char(); 185 for (i = 0; i < PROPOSAL_MAX; i++) 186 xfree(packet_get_string(NULL)); 187 packet_get_char(); 188 packet_get_int(); 189 packet_done(); 190 191 kex_kexinit_finish(kex); 192 } 193 194 Kex * 195 kex_setup(char *proposal[PROPOSAL_MAX]) 196 { 197 Kex *kex; 198 199 kex = xmalloc(sizeof(*kex)); 200 memset(kex, 0, sizeof(*kex)); 201 buffer_init(&kex->peer); 202 buffer_init(&kex->my); 203 kex_prop2buf(&kex->my, proposal); 204 kex->done = 0; 205 206 kex_send_kexinit(kex); /* we start */ 207 kex_clear_dispatch(); 208 dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit); 209 210 return kex; 211 } 212 213 void 214 kex_kexinit_finish(Kex *kex) 215 { 216 if (!(kex->flags & KEX_INIT_SENT)) 217 kex_send_kexinit(kex); 218 219 kex_choose_conf(kex); 220 221 switch(kex->kex_type) { 222 case DH_GRP1_SHA1: 223 kexdh(kex); 224 break; 225 case DH_GEX_SHA1: 226 kexgex(kex); 227 break; 228 default: 229 fatal("Unsupported key exchange %d", kex->kex_type); 230 } 231 } 232 233 void 234 choose_enc(Enc *enc, char *client, char *server) 235 { 236 char *name = match_list(client, server, NULL); 237 if (name == NULL) 238 fatal("no matching cipher found: client %s server %s", client, server); 239 enc->cipher = cipher_by_name(name); 240 if (enc->cipher == NULL) 241 fatal("matching cipher is not supported: %s", name); 242 enc->name = name; 243 enc->enabled = 0; 244 enc->iv = NULL; 245 enc->key = NULL; 246 } 247 void 248 choose_mac(Mac *mac, char *client, char *server) 249 { 250 char *name = match_list(client, server, NULL); 251 if (name == NULL) 252 fatal("no matching mac found: client %s server %s", client, server); 253 if (mac_init(mac, name) < 0) 254 fatal("unsupported mac %s", name); 255 /* truncate the key */ 256 if (datafellows & SSH_BUG_HMAC) 257 mac->key_len = 16; 258 mac->name = name; 259 mac->key = NULL; 260 mac->enabled = 0; 261 } 262 void 263 choose_comp(Comp *comp, char *client, char *server) 264 { 265 char *name = match_list(client, server, NULL); 266 if (name == NULL) 267 fatal("no matching comp found: client %s server %s", client, server); 268 if (strcmp(name, "zlib") == 0) { 269 comp->type = 1; 270 } else if (strcmp(name, "none") == 0) { 271 comp->type = 0; 272 } else { 273 fatal("unsupported comp %s", name); 274 } 275 comp->name = name; 276 } 277 void 278 choose_kex(Kex *k, char *client, char *server) 279 { 280 k->name = match_list(client, server, NULL); 281 if (k->name == NULL) 282 fatal("no kex alg"); 283 if (strcmp(k->name, KEX_DH1) == 0) { 284 k->kex_type = DH_GRP1_SHA1; 285 } else if (strcmp(k->name, KEX_DHGEX) == 0) { 286 k->kex_type = DH_GEX_SHA1; 287 } else 288 fatal("bad kex alg %s", k->name); 289 } 290 void 291 choose_hostkeyalg(Kex *k, char *client, char *server) 292 { 293 char *hostkeyalg = match_list(client, server, NULL); 294 if (hostkeyalg == NULL) 295 fatal("no hostkey alg"); 296 k->hostkey_type = key_type_from_name(hostkeyalg); 297 if (k->hostkey_type == KEY_UNSPEC) 298 fatal("bad hostkey alg '%s'", hostkeyalg); 299 xfree(hostkeyalg); 300 } 301 302 void 303 kex_choose_conf(Kex *kex) 304 { 305 Newkeys *newkeys; 306 char **my, **peer; 307 char **cprop, **sprop; 308 int nenc, nmac, ncomp; 309 int mode; 310 int ctos; /* direction: if true client-to-server */ 311 int need; 312 313 my = kex_buf2prop(&kex->my); 314 peer = kex_buf2prop(&kex->peer); 315 316 if (kex->server) { 317 cprop=peer; 318 sprop=my; 319 } else { 320 cprop=my; 321 sprop=peer; 322 } 323 324 /* Algorithm Negotiation */ 325 for (mode = 0; mode < MODE_MAX; mode++) { 326 newkeys = xmalloc(sizeof(*newkeys)); 327 memset(newkeys, 0, sizeof(*newkeys)); 328 kex->newkeys[mode] = newkeys; 329 ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN); 330 nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC; 331 nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC; 332 ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC; 333 choose_enc (&newkeys->enc, cprop[nenc], sprop[nenc]); 334 choose_mac (&newkeys->mac, cprop[nmac], sprop[nmac]); 335 choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]); 336 debug("kex: %s %s %s %s", 337 ctos ? "client->server" : "server->client", 338 newkeys->enc.name, 339 newkeys->mac.name, 340 newkeys->comp.name); 341 } 342 choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]); 343 choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS], 344 sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]); 345 need = 0; 346 for (mode = 0; mode < MODE_MAX; mode++) { 347 newkeys = kex->newkeys[mode]; 348 if (need < newkeys->enc.cipher->key_len) 349 need = newkeys->enc.cipher->key_len; 350 if (need < newkeys->enc.cipher->block_size) 351 need = newkeys->enc.cipher->block_size; 352 if (need < newkeys->mac.key_len) 353 need = newkeys->mac.key_len; 354 } 355 /* XXX need runden? */ 356 kex->we_need = need; 357 358 kex_prop_free(my); 359 kex_prop_free(peer); 360 } 361 362 u_char * 363 derive_key(Kex *kex, int id, int need, u_char *hash, BIGNUM *shared_secret) 364 { 365 Buffer b; 366 EVP_MD *evp_md = EVP_sha1(); 367 EVP_MD_CTX md; 368 char c = id; 369 int have; 370 int mdsz = evp_md->md_size; 371 u_char *digest = xmalloc(roundup(need, mdsz)); 372 373 buffer_init(&b); 374 buffer_put_bignum2(&b, shared_secret); 375 376 /* K1 = HASH(K || H || "A" || session_id) */ 377 EVP_DigestInit(&md, evp_md); 378 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); 379 EVP_DigestUpdate(&md, hash, mdsz); 380 EVP_DigestUpdate(&md, &c, 1); 381 EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len); 382 EVP_DigestFinal(&md, digest, NULL); 383 384 /* 385 * expand key: 386 * Kn = HASH(K || H || K1 || K2 || ... || Kn-1) 387 * Key = K1 || K2 || ... || Kn 388 */ 389 for (have = mdsz; need > have; have += mdsz) { 390 EVP_DigestInit(&md, evp_md); 391 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); 392 EVP_DigestUpdate(&md, hash, mdsz); 393 EVP_DigestUpdate(&md, digest, have); 394 EVP_DigestFinal(&md, digest + have, NULL); 395 } 396 buffer_free(&b); 397 #ifdef DEBUG_KEX 398 fprintf(stderr, "key '%c'== ", c); 399 dump_digest("key", digest, need); 400 #endif 401 return digest; 402 } 403 404 Newkeys *current_keys[MODE_MAX]; 405 406 #define NKEYS 6 407 void 408 kex_derive_keys(Kex *kex, u_char *hash, BIGNUM *shared_secret) 409 { 410 u_char *keys[NKEYS]; 411 int i, mode, ctos; 412 413 for (i = 0; i < NKEYS; i++) 414 keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, shared_secret); 415 416 debug("kex_derive_keys"); 417 for (mode = 0; mode < MODE_MAX; mode++) { 418 current_keys[mode] = kex->newkeys[mode]; 419 kex->newkeys[mode] = NULL; 420 ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN); 421 current_keys[mode]->enc.iv = keys[ctos ? 0 : 1]; 422 current_keys[mode]->enc.key = keys[ctos ? 2 : 3]; 423 current_keys[mode]->mac.key = keys[ctos ? 4 : 5]; 424 } 425 } 426 427 Newkeys * 428 kex_get_newkeys(int mode) 429 { 430 Newkeys *ret; 431 432 ret = current_keys[mode]; 433 current_keys[mode] = NULL; 434 return ret; 435 } 436 437 #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH) 438 void 439 dump_digest(char *msg, u_char *digest, int len) 440 { 441 int i; 442 443 fprintf(stderr, "%s\n", msg); 444 for (i = 0; i< len; i++){ 445 fprintf(stderr, "%02x", digest[i]); 446 if (i%32 == 31) 447 fprintf(stderr, "\n"); 448 else if (i%8 == 7) 449 fprintf(stderr, " "); 450 } 451 fprintf(stderr, "\n"); 452 } 453 #endif 454