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 1.41 2001/12/28 15:06:00 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, u_int32_t seq, void *ctxt) 111 { 112 error("Hm, kex protocol error: type %d seq %u", type, seq); 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 kex_clear_dispatch(); 129 130 packet_start(SSH2_MSG_NEWKEYS); 131 packet_send(); 132 /* packet_write_wait(); */ 133 debug("SSH2_MSG_NEWKEYS sent"); 134 135 debug("waiting for SSH2_MSG_NEWKEYS"); 136 packet_read_expect(SSH2_MSG_NEWKEYS); 137 debug("SSH2_MSG_NEWKEYS received"); 138 139 kex->done = 1; 140 buffer_clear(&kex->peer); 141 /* buffer_clear(&kex->my); */ 142 kex->flags &= ~KEX_INIT_SENT; 143 xfree(kex->name); 144 kex->name = NULL; 145 } 146 147 void 148 kex_send_kexinit(Kex *kex) 149 { 150 if (kex == NULL) { 151 error("kex_send_kexinit: no kex, cannot rekey"); 152 return; 153 } 154 if (kex->flags & KEX_INIT_SENT) { 155 debug("KEX_INIT_SENT"); 156 return; 157 } 158 kex->done = 0; 159 packet_start(SSH2_MSG_KEXINIT); 160 packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my)); 161 packet_send(); 162 debug("SSH2_MSG_KEXINIT sent"); 163 kex->flags |= KEX_INIT_SENT; 164 } 165 166 void 167 kex_input_kexinit(int type, u_int32_t seq, void *ctxt) 168 { 169 char *ptr; 170 int dlen; 171 int i; 172 Kex *kex = (Kex *)ctxt; 173 174 debug("SSH2_MSG_KEXINIT received"); 175 if (kex == NULL) 176 fatal("kex_input_kexinit: no kex, cannot rekey"); 177 178 ptr = packet_get_raw(&dlen); 179 buffer_append(&kex->peer, ptr, dlen); 180 181 /* discard packet */ 182 for (i = 0; i < KEX_COOKIE_LEN; i++) 183 packet_get_char(); 184 for (i = 0; i < PROPOSAL_MAX; i++) 185 xfree(packet_get_string(NULL)); 186 packet_get_char(); 187 packet_get_int(); 188 packet_check_eom(); 189 190 kex_kexinit_finish(kex); 191 } 192 193 Kex * 194 kex_setup(char *proposal[PROPOSAL_MAX]) 195 { 196 Kex *kex; 197 198 kex = xmalloc(sizeof(*kex)); 199 memset(kex, 0, sizeof(*kex)); 200 buffer_init(&kex->peer); 201 buffer_init(&kex->my); 202 kex_prop2buf(&kex->my, proposal); 203 kex->done = 0; 204 205 kex_send_kexinit(kex); /* we start */ 206 kex_clear_dispatch(); 207 dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit); 208 209 return kex; 210 } 211 212 static void 213 kex_kexinit_finish(Kex *kex) 214 { 215 if (!(kex->flags & KEX_INIT_SENT)) 216 kex_send_kexinit(kex); 217 218 kex_choose_conf(kex); 219 220 switch (kex->kex_type) { 221 case DH_GRP1_SHA1: 222 kexdh(kex); 223 break; 224 case DH_GEX_SHA1: 225 kexgex(kex); 226 break; 227 default: 228 fatal("Unsupported key exchange %d", kex->kex_type); 229 } 230 } 231 232 static void 233 choose_enc(Enc *enc, char *client, char *server) 234 { 235 char *name = match_list(client, server, NULL); 236 if (name == NULL) 237 fatal("no matching cipher found: client %s server %s", client, server); 238 enc->cipher = cipher_by_name(name); 239 if (enc->cipher == NULL) 240 fatal("matching cipher is not supported: %s", name); 241 enc->name = name; 242 enc->enabled = 0; 243 enc->iv = NULL; 244 enc->key = NULL; 245 } 246 static void 247 choose_mac(Mac *mac, char *client, char *server) 248 { 249 char *name = match_list(client, server, NULL); 250 if (name == NULL) 251 fatal("no matching mac found: client %s server %s", client, server); 252 if (mac_init(mac, name) < 0) 253 fatal("unsupported mac %s", name); 254 /* truncate the key */ 255 if (datafellows & SSH_BUG_HMAC) 256 mac->key_len = 16; 257 mac->name = name; 258 mac->key = NULL; 259 mac->enabled = 0; 260 } 261 static void 262 choose_comp(Comp *comp, char *client, char *server) 263 { 264 char *name = match_list(client, server, NULL); 265 if (name == NULL) 266 fatal("no matching comp found: client %s server %s", client, server); 267 if (strcmp(name, "zlib") == 0) { 268 comp->type = 1; 269 } else if (strcmp(name, "none") == 0) { 270 comp->type = 0; 271 } else { 272 fatal("unsupported comp %s", name); 273 } 274 comp->name = name; 275 } 276 static void 277 choose_kex(Kex *k, char *client, char *server) 278 { 279 k->name = match_list(client, server, NULL); 280 if (k->name == NULL) 281 fatal("no kex alg"); 282 if (strcmp(k->name, KEX_DH1) == 0) { 283 k->kex_type = DH_GRP1_SHA1; 284 } else if (strcmp(k->name, KEX_DHGEX) == 0) { 285 k->kex_type = DH_GEX_SHA1; 286 } else 287 fatal("bad kex alg %s", k->name); 288 } 289 static void 290 choose_hostkeyalg(Kex *k, char *client, char *server) 291 { 292 char *hostkeyalg = match_list(client, server, NULL); 293 if (hostkeyalg == NULL) 294 fatal("no hostkey alg"); 295 k->hostkey_type = key_type_from_name(hostkeyalg); 296 if (k->hostkey_type == KEY_UNSPEC) 297 fatal("bad hostkey alg '%s'", hostkeyalg); 298 xfree(hostkeyalg); 299 } 300 301 static void 302 kex_choose_conf(Kex *kex) 303 { 304 Newkeys *newkeys; 305 char **my, **peer; 306 char **cprop, **sprop; 307 int nenc, nmac, ncomp; 308 int mode; 309 int ctos; /* direction: if true client-to-server */ 310 int need; 311 312 my = kex_buf2prop(&kex->my); 313 peer = kex_buf2prop(&kex->peer); 314 315 if (kex->server) { 316 cprop=peer; 317 sprop=my; 318 } else { 319 cprop=my; 320 sprop=peer; 321 } 322 323 /* Algorithm Negotiation */ 324 for (mode = 0; mode < MODE_MAX; mode++) { 325 newkeys = xmalloc(sizeof(*newkeys)); 326 memset(newkeys, 0, sizeof(*newkeys)); 327 kex->newkeys[mode] = newkeys; 328 ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN); 329 nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC; 330 nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC; 331 ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC; 332 choose_enc (&newkeys->enc, cprop[nenc], sprop[nenc]); 333 choose_mac (&newkeys->mac, cprop[nmac], sprop[nmac]); 334 choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]); 335 debug("kex: %s %s %s %s", 336 ctos ? "client->server" : "server->client", 337 newkeys->enc.name, 338 newkeys->mac.name, 339 newkeys->comp.name); 340 } 341 choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]); 342 choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS], 343 sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]); 344 need = 0; 345 for (mode = 0; mode < MODE_MAX; mode++) { 346 newkeys = kex->newkeys[mode]; 347 if (need < newkeys->enc.cipher->key_len) 348 need = newkeys->enc.cipher->key_len; 349 if (need < newkeys->enc.cipher->block_size) 350 need = newkeys->enc.cipher->block_size; 351 if (need < newkeys->mac.key_len) 352 need = newkeys->mac.key_len; 353 } 354 /* XXX need runden? */ 355 kex->we_need = need; 356 357 kex_prop_free(my); 358 kex_prop_free(peer); 359 } 360 361 static u_char * 362 derive_key(Kex *kex, int id, int need, u_char *hash, BIGNUM *shared_secret) 363 { 364 Buffer b; 365 EVP_MD *evp_md = EVP_sha1(); 366 EVP_MD_CTX md; 367 char c = id; 368 int have; 369 int mdsz = evp_md->md_size; 370 u_char *digest = xmalloc(roundup(need, mdsz)); 371 372 buffer_init(&b); 373 buffer_put_bignum2(&b, shared_secret); 374 375 /* K1 = HASH(K || H || "A" || session_id) */ 376 EVP_DigestInit(&md, evp_md); 377 if (!(datafellows & SSH_BUG_DERIVEKEY)) 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 if (!(datafellows & SSH_BUG_DERIVEKEY)) 392 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); 393 EVP_DigestUpdate(&md, hash, mdsz); 394 EVP_DigestUpdate(&md, digest, have); 395 EVP_DigestFinal(&md, digest + have, NULL); 396 } 397 buffer_free(&b); 398 #ifdef DEBUG_KEX 399 fprintf(stderr, "key '%c'== ", c); 400 dump_digest("key", digest, need); 401 #endif 402 return digest; 403 } 404 405 Newkeys *current_keys[MODE_MAX]; 406 407 #define NKEYS 6 408 void 409 kex_derive_keys(Kex *kex, u_char *hash, BIGNUM *shared_secret) 410 { 411 u_char *keys[NKEYS]; 412 int i, mode, ctos; 413 414 for (i = 0; i < NKEYS; i++) 415 keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, shared_secret); 416 417 debug("kex_derive_keys"); 418 for (mode = 0; mode < MODE_MAX; mode++) { 419 current_keys[mode] = kex->newkeys[mode]; 420 kex->newkeys[mode] = NULL; 421 ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN); 422 current_keys[mode]->enc.iv = keys[ctos ? 0 : 1]; 423 current_keys[mode]->enc.key = keys[ctos ? 2 : 3]; 424 current_keys[mode]->mac.key = keys[ctos ? 4 : 5]; 425 } 426 } 427 428 Newkeys * 429 kex_get_newkeys(int mode) 430 { 431 Newkeys *ret; 432 433 ret = current_keys[mode]; 434 current_keys[mode] = NULL; 435 return ret; 436 } 437 438 #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH) 439 void 440 dump_digest(char *msg, u_char *digest, int len) 441 { 442 int i; 443 444 fprintf(stderr, "%s\n", msg); 445 for (i = 0; i< len; i++) { 446 fprintf(stderr, "%02x", digest[i]); 447 if (i%32 == 31) 448 fprintf(stderr, "\n"); 449 else if (i%8 == 7) 450 fprintf(stderr, " "); 451 } 452 fprintf(stderr, "\n"); 453 } 454 #endif 455