1 /* 2 * Copyright (c) 2000, 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: kex.c,v 1.36 2001/06/25 08:25:37 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 /* prototype */ 47 static void kex_kexinit_finish(Kex *); 48 static void kex_choose_conf(Kex *); 49 50 /* put algorithm proposal into buffer */ 51 static void 52 kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX]) 53 { 54 u_int32_t rand = 0; 55 int i; 56 57 buffer_clear(b); 58 for (i = 0; i < KEX_COOKIE_LEN; i++) { 59 if (i % 4 == 0) 60 rand = arc4random(); 61 buffer_put_char(b, rand & 0xff); 62 rand >>= 8; 63 } 64 for (i = 0; i < PROPOSAL_MAX; i++) 65 buffer_put_cstring(b, proposal[i]); 66 buffer_put_char(b, 0); /* first_kex_packet_follows */ 67 buffer_put_int(b, 0); /* uint32 reserved */ 68 } 69 70 /* parse buffer and return algorithm proposal */ 71 static char ** 72 kex_buf2prop(Buffer *raw) 73 { 74 Buffer b; 75 int i; 76 char **proposal; 77 78 proposal = xmalloc(PROPOSAL_MAX * sizeof(char *)); 79 80 buffer_init(&b); 81 buffer_append(&b, buffer_ptr(raw), buffer_len(raw)); 82 /* skip cookie */ 83 for (i = 0; i < KEX_COOKIE_LEN; i++) 84 buffer_get_char(&b); 85 /* extract kex init proposal strings */ 86 for (i = 0; i < PROPOSAL_MAX; i++) { 87 proposal[i] = buffer_get_string(&b,NULL); 88 debug2("kex_parse_kexinit: %s", proposal[i]); 89 } 90 /* first kex follows / reserved */ 91 i = buffer_get_char(&b); 92 debug2("kex_parse_kexinit: first_kex_follows %d ", i); 93 i = buffer_get_int(&b); 94 debug2("kex_parse_kexinit: reserved %d ", i); 95 buffer_free(&b); 96 return proposal; 97 } 98 99 static void 100 kex_prop_free(char **proposal) 101 { 102 int i; 103 104 for (i = 0; i < PROPOSAL_MAX; i++) 105 xfree(proposal[i]); 106 xfree(proposal); 107 } 108 109 static void 110 kex_protocol_error(int type, int plen, void *ctxt) 111 { 112 error("Hm, kex protocol error: type %d plen %d", type, plen); 113 } 114 115 static void 116 kex_clear_dispatch(void) 117 { 118 int i; 119 120 /* Numbers 30-49 are used for kex packets */ 121 for (i = 30; i <= 49; i++) 122 dispatch_set(i, &kex_protocol_error); 123 } 124 125 void 126 kex_finish(Kex *kex) 127 { 128 int plen; 129 130 kex_clear_dispatch(); 131 132 packet_start(SSH2_MSG_NEWKEYS); 133 packet_send(); 134 /* packet_write_wait(); */ 135 debug("SSH2_MSG_NEWKEYS sent"); 136 137 debug("waiting for SSH2_MSG_NEWKEYS"); 138 packet_read_expect(&plen, SSH2_MSG_NEWKEYS); 139 debug("SSH2_MSG_NEWKEYS received"); 140 141 kex->done = 1; 142 buffer_clear(&kex->peer); 143 /* buffer_clear(&kex->my); */ 144 kex->flags &= ~KEX_INIT_SENT; 145 xfree(kex->name); 146 kex->name = NULL; 147 } 148 149 void 150 kex_send_kexinit(Kex *kex) 151 { 152 if (kex == NULL) { 153 error("kex_send_kexinit: no kex, cannot rekey"); 154 return; 155 } 156 if (kex->flags & KEX_INIT_SENT) { 157 debug("KEX_INIT_SENT"); 158 return; 159 } 160 kex->done = 0; 161 packet_start(SSH2_MSG_KEXINIT); 162 packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my)); 163 packet_send(); 164 debug("SSH2_MSG_KEXINIT sent"); 165 kex->flags |= KEX_INIT_SENT; 166 } 167 168 void 169 kex_input_kexinit(int type, int plen, void *ctxt) 170 { 171 char *ptr; 172 int dlen; 173 int i; 174 Kex *kex = (Kex *)ctxt; 175 176 debug("SSH2_MSG_KEXINIT received"); 177 if (kex == NULL) 178 fatal("kex_input_kexinit: no kex, cannot rekey"); 179 180 ptr = packet_get_raw(&dlen); 181 buffer_append(&kex->peer, ptr, dlen); 182 183 /* discard packet */ 184 for (i = 0; i < KEX_COOKIE_LEN; i++) 185 packet_get_char(); 186 for (i = 0; i < PROPOSAL_MAX; i++) 187 xfree(packet_get_string(NULL)); 188 packet_get_char(); 189 packet_get_int(); 190 packet_done(); 191 192 kex_kexinit_finish(kex); 193 } 194 195 Kex * 196 kex_setup(char *proposal[PROPOSAL_MAX]) 197 { 198 Kex *kex; 199 200 kex = xmalloc(sizeof(*kex)); 201 memset(kex, 0, sizeof(*kex)); 202 buffer_init(&kex->peer); 203 buffer_init(&kex->my); 204 kex_prop2buf(&kex->my, proposal); 205 kex->done = 0; 206 207 kex_send_kexinit(kex); /* we start */ 208 kex_clear_dispatch(); 209 dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit); 210 211 return kex; 212 } 213 214 static void 215 kex_kexinit_finish(Kex *kex) 216 { 217 if (!(kex->flags & KEX_INIT_SENT)) 218 kex_send_kexinit(kex); 219 220 kex_choose_conf(kex); 221 222 switch(kex->kex_type) { 223 case DH_GRP1_SHA1: 224 kexdh(kex); 225 break; 226 case DH_GEX_SHA1: 227 kexgex(kex); 228 break; 229 default: 230 fatal("Unsupported key exchange %d", kex->kex_type); 231 } 232 } 233 234 static void 235 choose_enc(Enc *enc, char *client, char *server) 236 { 237 char *name = match_list(client, server, NULL); 238 if (name == NULL) 239 fatal("no matching cipher found: client %s server %s", client, server); 240 enc->cipher = cipher_by_name(name); 241 if (enc->cipher == NULL) 242 fatal("matching cipher is not supported: %s", name); 243 enc->name = name; 244 enc->enabled = 0; 245 enc->iv = NULL; 246 enc->key = NULL; 247 } 248 static void 249 choose_mac(Mac *mac, char *client, char *server) 250 { 251 char *name = match_list(client, server, NULL); 252 if (name == NULL) 253 fatal("no matching mac found: client %s server %s", client, server); 254 if (mac_init(mac, name) < 0) 255 fatal("unsupported mac %s", name); 256 /* truncate the key */ 257 if (datafellows & SSH_BUG_HMAC) 258 mac->key_len = 16; 259 mac->name = name; 260 mac->key = NULL; 261 mac->enabled = 0; 262 } 263 static void 264 choose_comp(Comp *comp, char *client, char *server) 265 { 266 char *name = match_list(client, server, NULL); 267 if (name == NULL) 268 fatal("no matching comp found: client %s server %s", client, server); 269 if (strcmp(name, "zlib") == 0) { 270 comp->type = 1; 271 } else if (strcmp(name, "none") == 0) { 272 comp->type = 0; 273 } else { 274 fatal("unsupported comp %s", name); 275 } 276 comp->name = name; 277 } 278 static void 279 choose_kex(Kex *k, char *client, char *server) 280 { 281 k->name = match_list(client, server, NULL); 282 if (k->name == NULL) 283 fatal("no kex alg"); 284 if (strcmp(k->name, KEX_DH1) == 0) { 285 k->kex_type = DH_GRP1_SHA1; 286 } else if (strcmp(k->name, KEX_DHGEX) == 0) { 287 k->kex_type = DH_GEX_SHA1; 288 } else 289 fatal("bad kex alg %s", k->name); 290 } 291 static void 292 choose_hostkeyalg(Kex *k, char *client, char *server) 293 { 294 char *hostkeyalg = match_list(client, server, NULL); 295 if (hostkeyalg == NULL) 296 fatal("no hostkey alg"); 297 k->hostkey_type = key_type_from_name(hostkeyalg); 298 if (k->hostkey_type == KEY_UNSPEC) 299 fatal("bad hostkey alg '%s'", hostkeyalg); 300 xfree(hostkeyalg); 301 } 302 303 static void 304 kex_choose_conf(Kex *kex) 305 { 306 Newkeys *newkeys; 307 char **my, **peer; 308 char **cprop, **sprop; 309 int nenc, nmac, ncomp; 310 int mode; 311 int ctos; /* direction: if true client-to-server */ 312 int need; 313 314 my = kex_buf2prop(&kex->my); 315 peer = kex_buf2prop(&kex->peer); 316 317 if (kex->server) { 318 cprop=peer; 319 sprop=my; 320 } else { 321 cprop=my; 322 sprop=peer; 323 } 324 325 /* Algorithm Negotiation */ 326 for (mode = 0; mode < MODE_MAX; mode++) { 327 newkeys = xmalloc(sizeof(*newkeys)); 328 memset(newkeys, 0, sizeof(*newkeys)); 329 kex->newkeys[mode] = newkeys; 330 ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN); 331 nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC; 332 nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC; 333 ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC; 334 choose_enc (&newkeys->enc, cprop[nenc], sprop[nenc]); 335 choose_mac (&newkeys->mac, cprop[nmac], sprop[nmac]); 336 choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]); 337 debug("kex: %s %s %s %s", 338 ctos ? "client->server" : "server->client", 339 newkeys->enc.name, 340 newkeys->mac.name, 341 newkeys->comp.name); 342 } 343 choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]); 344 choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS], 345 sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]); 346 need = 0; 347 for (mode = 0; mode < MODE_MAX; mode++) { 348 newkeys = kex->newkeys[mode]; 349 if (need < newkeys->enc.cipher->key_len) 350 need = newkeys->enc.cipher->key_len; 351 if (need < newkeys->enc.cipher->block_size) 352 need = newkeys->enc.cipher->block_size; 353 if (need < newkeys->mac.key_len) 354 need = newkeys->mac.key_len; 355 } 356 /* XXX need runden? */ 357 kex->we_need = need; 358 359 kex_prop_free(my); 360 kex_prop_free(peer); 361 } 362 363 static u_char * 364 derive_key(Kex *kex, int id, int need, u_char *hash, BIGNUM *shared_secret) 365 { 366 Buffer b; 367 EVP_MD *evp_md = EVP_sha1(); 368 EVP_MD_CTX md; 369 char c = id; 370 int have; 371 int mdsz = evp_md->md_size; 372 u_char *digest = xmalloc(roundup(need, mdsz)); 373 374 buffer_init(&b); 375 buffer_put_bignum2(&b, shared_secret); 376 377 /* K1 = HASH(K || H || "A" || session_id) */ 378 EVP_DigestInit(&md, evp_md); 379 if (!(datafellows & SSH_BUG_DERIVEKEY)) 380 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); 381 EVP_DigestUpdate(&md, hash, mdsz); 382 EVP_DigestUpdate(&md, &c, 1); 383 EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len); 384 EVP_DigestFinal(&md, digest, NULL); 385 386 /* 387 * expand key: 388 * Kn = HASH(K || H || K1 || K2 || ... || Kn-1) 389 * Key = K1 || K2 || ... || Kn 390 */ 391 for (have = mdsz; need > have; have += mdsz) { 392 EVP_DigestInit(&md, evp_md); 393 if (!(datafellows & SSH_BUG_DERIVEKEY)) 394 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); 395 EVP_DigestUpdate(&md, hash, mdsz); 396 EVP_DigestUpdate(&md, digest, have); 397 EVP_DigestFinal(&md, digest + have, NULL); 398 } 399 buffer_free(&b); 400 #ifdef DEBUG_KEX 401 fprintf(stderr, "key '%c'== ", c); 402 dump_digest("key", digest, need); 403 #endif 404 return digest; 405 } 406 407 Newkeys *current_keys[MODE_MAX]; 408 409 #define NKEYS 6 410 void 411 kex_derive_keys(Kex *kex, u_char *hash, BIGNUM *shared_secret) 412 { 413 u_char *keys[NKEYS]; 414 int i, mode, ctos; 415 416 for (i = 0; i < NKEYS; i++) 417 keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, shared_secret); 418 419 debug("kex_derive_keys"); 420 for (mode = 0; mode < MODE_MAX; mode++) { 421 current_keys[mode] = kex->newkeys[mode]; 422 kex->newkeys[mode] = NULL; 423 ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN); 424 current_keys[mode]->enc.iv = keys[ctos ? 0 : 1]; 425 current_keys[mode]->enc.key = keys[ctos ? 2 : 3]; 426 current_keys[mode]->mac.key = keys[ctos ? 4 : 5]; 427 } 428 } 429 430 Newkeys * 431 kex_get_newkeys(int mode) 432 { 433 Newkeys *ret; 434 435 ret = current_keys[mode]; 436 current_keys[mode] = NULL; 437 return ret; 438 } 439 440 #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH) 441 void 442 dump_digest(char *msg, u_char *digest, int len) 443 { 444 int i; 445 446 fprintf(stderr, "%s\n", msg); 447 for (i = 0; i< len; i++){ 448 fprintf(stderr, "%02x", digest[i]); 449 if (i%32 == 31) 450 fprintf(stderr, "\n"); 451 else if (i%8 == 7) 452 fprintf(stderr, " "); 453 } 454 fprintf(stderr, "\n"); 455 } 456 #endif 457