kex.c

   1 /* $OpenBSD: kex.c,v 1.82 2009/10/24 11:13:54 andreas Exp $ */
   2 /*
   3  * Copyright (c) 2000, 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"
  27
  28 #include <sys/param.h>
  29
  30 #include <signal.h>
  31 #include <stdarg.h>
  32 #include <stdio.h>
  33 #include <stdlib.h>
  34 #include <string.h>
  35
  36 #include <openssl/crypto.h>
  37
  38 #include "xmalloc.h"
  39 #include "ssh2.h"
  40 #include "buffer.h"
  41 #include "packet.h"
  42 #include "compat.h"
  43 #include "cipher.h"
  44 #include "key.h"
  45 #include "kex.h"
  46 #include "log.h"
  47 #include "mac.h"
  48 #include "match.h"
  49 #include "dispatch.h"
  50 #include "monitor.h"
  51 #include "roaming.h"
  52
  53 #if OPENSSL_VERSION_NUMBER >= 0x00907000L
  54 # if defined(HAVE_EVP_SHA256)
  55 # define evp_ssh_sha256 EVP_sha256
  56 # else
  57 extern const EVP_MD *evp_ssh_sha256(void);
  58 # endif
  59 #endif
  60
  61 /* prototype */
  62 static void kex_kexinit_finish(Kex *);
  63 static void kex_choose_conf(Kex *);
  64
  65 /* put algorithm proposal into buffer */
  66 static void
  67 kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX])
  68 {
  69         u_int i;
  70
  71         buffer_clear(b);
  72         /*
  73          * add a dummy cookie, the cookie will be overwritten by
  74          * kex_send_kexinit(), each time a kexinit is set
  75          */
  76         for (i = 0; i < KEX_COOKIE_LEN; i++)
  77                 buffer_put_char(b, 0);
  78         for (i = 0; i < PROPOSAL_MAX; i++)
  79                 buffer_put_cstring(b, proposal[i]);
  80         buffer_put_char(b, 0);                  /* first_kex_packet_follows */
  81         buffer_put_int(b, 0);                   /* uint32 reserved */
  82 }
  83
  84 /* parse buffer and return algorithm proposal */
  85 static char **
  86 kex_buf2prop(Buffer *raw, int *first_kex_follows)
  87 {
  88         Buffer b;
  89         u_int i;
  90         char **proposal;
  91
  92         proposal = xcalloc(PROPOSAL_MAX, sizeof(char *));
  93
  94         buffer_init(&b);
  95         buffer_append(&b, buffer_ptr(raw), buffer_len(raw));
  96         /* skip cookie */
  97         for (i = 0; i < KEX_COOKIE_LEN; i++)
  98                 buffer_get_char(&b);
  99         /* extract kex init proposal strings */
 100         for (i = 0; i < PROPOSAL_MAX; i++) {
 101                 proposal[i] = buffer_get_string(&b,NULL);
 102                 debug2("kex_parse_kexinit: %s", proposal[i]);
 103         }
 104         /* first kex follows / reserved */
 105         i = buffer_get_char(&b);
 106         if (first_kex_follows != NULL)
 107                 *first_kex_follows = i;
 108         debug2("kex_parse_kexinit: first_kex_follows %d ", i);
 109         i = buffer_get_int(&b);
 110         debug2("kex_parse_kexinit: reserved %u ", i);
 111         buffer_free(&b);
 112         return proposal;
 113 }
 114
 115 static void
 116 kex_prop_free(char **proposal)
 117 {
 118         u_int i;
 119
 120         for (i = 0; i < PROPOSAL_MAX; i++)
 121                 xfree(proposal[i]);
 122         xfree(proposal);
 123 }
 124
 125 /* ARGSUSED */
 126 static void
 127 kex_protocol_error(int type, u_int32_t seq, void *ctxt)
 128 {
 129         error("Hm, kex protocol error: type %d seq %u", type, seq);
 130 }
 131
 132 static void
 133 kex_reset_dispatch(void)
 134 {
 135         dispatch_range(SSH2_MSG_TRANSPORT_MIN,
 136             SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error);
 137         dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit);
 138 }
 139
 140 void
 141 kex_finish(Kex *kex)
 142 {
 143         kex_reset_dispatch();
 144
 145         packet_start(SSH2_MSG_NEWKEYS);
 146         packet_send();
 147         /* packet_write_wait(); */
 148         debug("SSH2_MSG_NEWKEYS sent");
 149
 150         debug("expecting SSH2_MSG_NEWKEYS");
 151         packet_read_expect(SSH2_MSG_NEWKEYS);
 152         packet_check_eom();
 153         debug("SSH2_MSG_NEWKEYS received");
 154
 155         kex->done = 1;
 156         buffer_clear(&kex->peer);
 157         /* buffer_clear(&kex->my); */
 158         kex->flags &= ~KEX_INIT_SENT;
 159         xfree(kex->name);
 160         kex->name = NULL;
 161 }
 162
 163 void
 164 kex_send_kexinit(Kex *kex)
 165 {
 166         u_int32_t rnd = 0;
 167         u_char *cookie;
 168         u_int i;
 169
 170         if (kex == NULL) {
 171                 error("kex_send_kexinit: no kex, cannot rekey");
 172                 return;
 173         }
 174         if (kex->flags & KEX_INIT_SENT) {
 175                 debug("KEX_INIT_SENT");
 176                 return;
 177         }
 178         kex->done = 0;
 179
 180         /* generate a random cookie */
 181         if (buffer_len(&kex->my) < KEX_COOKIE_LEN)
 182                 fatal("kex_send_kexinit: kex proposal too short");
 183         cookie = buffer_ptr(&kex->my);
 184         for (i = 0; i < KEX_COOKIE_LEN; i++) {
 185                 if (i % 4 == 0)
 186                         rnd = arc4random();
 187                 cookie[i] = rnd;
 188                 rnd >>= 8;
 189         }
 190         packet_start(SSH2_MSG_KEXINIT);
 191         packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my));
 192         packet_send();
 193         debug("SSH2_MSG_KEXINIT sent");
 194         kex->flags |= KEX_INIT_SENT;
 195 }
 196
 197 /* ARGSUSED */
 198 void
 199 kex_input_kexinit(int type, u_int32_t seq, void *ctxt)
 200 {
 201         char *ptr;
 202         u_int i, dlen;
 203         Kex *kex = (Kex *)ctxt;
 204
 205         debug("SSH2_MSG_KEXINIT received");
 206         if (kex == NULL)
 207                 fatal("kex_input_kexinit: no kex, cannot rekey");
 208
 209         ptr = packet_get_raw(&dlen);
 210         buffer_append(&kex->peer, ptr, dlen);
 211
 212         /* discard packet */
 213         for (i = 0; i < KEX_COOKIE_LEN; i++)
 214                 packet_get_char();
 215         for (i = 0; i < PROPOSAL_MAX; i++)
 216                 xfree(packet_get_string(NULL));
 217         (void) packet_get_char();
 218         (void) packet_get_int();
 219         packet_check_eom();
 220
 221         kex_kexinit_finish(kex);
 222 }
 223
 224 Kex *
 225 kex_setup(char *proposal[PROPOSAL_MAX])
 226 {
 227         Kex *kex;
 228
 229         kex = xcalloc(1, sizeof(*kex));
 230         buffer_init(&kex->peer);
 231         buffer_init(&kex->my);
 232         kex_prop2buf(&kex->my, proposal);
 233         kex->done = 0;
 234
 235         kex_send_kexinit(kex);                                  /* we start */
 236         kex_reset_dispatch();
 237
 238         return kex;
 239 }
 240
 241 static void
 242 kex_kexinit_finish(Kex *kex)
 243 {
 244         if (!(kex->flags & KEX_INIT_SENT))
 245                 kex_send_kexinit(kex);
 246
 247         kex_choose_conf(kex);
 248
 249         if (kex->kex_type >= 0 && kex->kex_type < KEX_MAX &&
 250             kex->kex[kex->kex_type] != NULL) {
 251                 (kex->kex[kex->kex_type])(kex);
 252         } else {
 253                 fatal("Unsupported key exchange %d", kex->kex_type);
 254         }
 255 }
 256
 257 static void
 258 choose_enc(Enc *enc, char *client, char *server)
 259 {
 260         char *name = match_list(client, server, NULL);
 261         if (name == NULL)
 262                 fatal("no matching cipher found: client %s server %s",
 263                     client, server);
 264         if ((enc->cipher = cipher_by_name(name)) == NULL)
 265                 fatal("matching cipher is not supported: %s", name);
 266         enc->name = name;
 267         enc->enabled = 0;
 268         enc->iv = NULL;
 269         enc->key = NULL;
 270         enc->key_len = cipher_keylen(enc->cipher);
 271         enc->block_size = cipher_blocksize(enc->cipher);
 272 }
 273
 274 static void
 275 choose_mac(Mac *mac, char *client, char *server)
 276 {
 277         char *name = match_list(client, server, NULL);
 278         if (name == NULL)
 279                 fatal("no matching mac found: client %s server %s",
 280                     client, server);
 281         if (mac_setup(mac, name) < 0)
 282                 fatal("unsupported mac %s", name);
 283         /* truncate the key */
 284         if (datafellows & SSH_BUG_HMAC)
 285                 mac->key_len = 16;
 286         mac->name = name;
 287         mac->key = NULL;
 288         mac->enabled = 0;
 289 }
 290
 291 static void
 292 choose_comp(Comp *comp, char *client, char *server)
 293 {
 294         char *name = match_list(client, server, NULL);
 295         if (name == NULL)
 296                 fatal("no matching comp found: client %s server %s", client, server);
 297         if (strcmp(name, "zlib@openssh.com") == 0) {
 298                 comp->type = COMP_DELAYED;
 299         } else if (strcmp(name, "zlib") == 0) {
 300                 comp->type = COMP_ZLIB;
 301         } else if (strcmp(name, "none") == 0) {
 302                 comp->type = COMP_NONE;
 303         } else {
 304                 fatal("unsupported comp %s", name);
 305         }
 306         comp->name = name;
 307 }
 308
 309 static void
 310 choose_kex(Kex *k, char *client, char *server)
 311 {
 312         k->name = match_list(client, server, NULL);
 313         if (k->name == NULL)
 314                 fatal("Unable to negotiate a key exchange method");
 315         if (strcmp(k->name, KEX_DH1) == 0) {
 316                 k->kex_type = KEX_DH_GRP1_SHA1;
 317                 k->evp_md = EVP_sha1();
 318         } else if (strcmp(k->name, KEX_DH14) == 0) {
 319                 k->kex_type = KEX_DH_GRP14_SHA1;
 320                 k->evp_md = EVP_sha1();
 321         } else if (strcmp(k->name, KEX_DHGEX_SHA1) == 0) {
 322                 k->kex_type = KEX_DH_GEX_SHA1;
 323                 k->evp_md = EVP_sha1();
 324 #if OPENSSL_VERSION_NUMBER >= 0x00907000L
 325         } else if (strcmp(k->name, KEX_DHGEX_SHA256) == 0) {
 326                 k->kex_type = KEX_DH_GEX_SHA256;
 327                 k->evp_md = evp_ssh_sha256();
 328 #endif
 329         } else
 330                 fatal("bad kex alg %s", k->name);
 331 }
 332
 333 static void
 334 choose_hostkeyalg(Kex *k, char *client, char *server)
 335 {
 336         char *hostkeyalg = match_list(client, server, NULL);
 337         if (hostkeyalg == NULL)
 338                 fatal("no hostkey alg");
 339         k->hostkey_type = key_type_from_name(hostkeyalg);
 340         if (k->hostkey_type == KEY_UNSPEC)
 341                 fatal("bad hostkey alg '%s'", hostkeyalg);
 342         xfree(hostkeyalg);
 343 }
 344
 345 static int
 346 proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX])
 347 {
 348         static int check[] = {
 349                 PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1
 350         };
 351         int *idx;
 352         char *p;
 353
 354         for (idx = &check[0]; *idx != -1; idx++) {
 355                 if ((p = strchr(my[*idx], ',')) != NULL)
 356                         *p = '\0';
 357                 if ((p = strchr(peer[*idx], ',')) != NULL)
 358                         *p = '\0';
 359                 if (strcmp(my[*idx], peer[*idx]) != 0) {
 360                         debug2("proposal mismatch: my %s peer %s",
 361                             my[*idx], peer[*idx]);
 362                         return (0);
 363                 }
 364         }
 365         debug2("proposals match");
 366         return (1);
 367 }
 368
 369 static void
 370 kex_choose_conf(Kex *kex)
 371 {
 372         Newkeys *newkeys;
 373         char **my, **peer;
 374         char **cprop, **sprop;
 375         int nenc, nmac, ncomp;
 376         u_int mode, ctos, need;
 377         int first_kex_follows, type;
 378
 379         my   = kex_buf2prop(&kex->my, NULL);
 380         peer = kex_buf2prop(&kex->peer, &first_kex_follows);
 381
 382         if (kex->server) {
 383                 cprop=peer;
 384                 sprop=my;
 385         } else {
 386                 cprop=my;
 387                 sprop=peer;
 388         }
 389
 390         /* Check whether server offers roaming */
 391         if (!kex->server) {
 392                 char *roaming;
 393                 roaming = match_list(KEX_RESUME, peer[PROPOSAL_KEX_ALGS], NULL);
 394                 if (roaming) {
 395                         kex->roaming = 1;
 396                         xfree(roaming);
 397                 }
 398         }
 399
 400         /* Algorithm Negotiation */
 401         for (mode = 0; mode < MODE_MAX; mode++) {
 402                 newkeys = xcalloc(1, sizeof(*newkeys));
 403                 kex->newkeys[mode] = newkeys;
 404                 ctos = (!kex->server && mode == MODE_OUT) ||
 405                     (kex->server && mode == MODE_IN);
 406                 nenc  = ctos ? PROPOSAL_ENC_ALGS_CTOS  : PROPOSAL_ENC_ALGS_STOC;
 407                 nmac  = ctos ? PROPOSAL_MAC_ALGS_CTOS  : PROPOSAL_MAC_ALGS_STOC;
 408                 ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC;
 409                 choose_enc (&newkeys->enc,  cprop[nenc],  sprop[nenc]);
 410                 choose_mac (&newkeys->mac,  cprop[nmac],  sprop[nmac]);
 411                 choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]);
 412                 debug("kex: %s %s %s %s",
 413                     ctos ? "client->server" : "server->client",
 414                     newkeys->enc.name,
 415                     newkeys->mac.name,
 416                     newkeys->comp.name);
 417         }
 418         choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]);
 419         choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
 420             sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]);
 421         need = 0;
 422         for (mode = 0; mode < MODE_MAX; mode++) {
 423                 newkeys = kex->newkeys[mode];
 424                 if (need < newkeys->enc.key_len)
 425                         need = newkeys->enc.key_len;
 426                 if (need < newkeys->enc.block_size)
 427                         need = newkeys->enc.block_size;
 428                 if (need < newkeys->mac.key_len)
 429                         need = newkeys->mac.key_len;
 430         }
 431         /* XXX need runden? */
 432         kex->we_need = need;
 433
 434         /* ignore the next message if the proposals do not match */
 435         if (first_kex_follows && !proposals_match(my, peer) &&
 436             !(datafellows & SSH_BUG_FIRSTKEX)) {
 437                 type = packet_read();
 438                 debug2("skipping next packet (type %u)", type);
 439         }
 440
 441         kex_prop_free(my);
 442         kex_prop_free(peer);
 443 }
 444
 445 static u_char *
 446 derive_key(Kex *kex, int id, u_int need, u_char *hash, u_int hashlen,
 447     BIGNUM *shared_secret)
 448 {
 449         Buffer b;
 450         EVP_MD_CTX md;
 451         char c = id;
 452         u_int have;
 453         int mdsz;
 454         u_char *digest;
 455
 456         if ((mdsz = EVP_MD_size(kex->evp_md)) <= 0)
 457                 fatal("bad kex md size %d", mdsz);
 458         digest = xmalloc(roundup(need, mdsz));
 459
 460         buffer_init(&b);
 461         buffer_put_bignum2(&b, shared_secret);
 462
 463         /* K1 = HASH(K || H || "A" || session_id) */
 464         EVP_DigestInit(&md, kex->evp_md);
 465         if (!(datafellows & SSH_BUG_DERIVEKEY))
 466                 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
 467         EVP_DigestUpdate(&md, hash, hashlen);
 468         EVP_DigestUpdate(&md, &c, 1);
 469         EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len);
 470         EVP_DigestFinal(&md, digest, NULL);
 471
 472         /*
 473          * expand key:
 474          * Kn = HASH(K || H || K1 || K2 || ... || Kn-1)
 475          * Key = K1 || K2 || ... || Kn
 476          */
 477         for (have = mdsz; need > have; have += mdsz) {
 478                 EVP_DigestInit(&md, kex->evp_md);
 479                 if (!(datafellows & SSH_BUG_DERIVEKEY))
 480                         EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
 481                 EVP_DigestUpdate(&md, hash, hashlen);
 482                 EVP_DigestUpdate(&md, digest, have);
 483                 EVP_DigestFinal(&md, digest + have, NULL);
 484         }
 485         buffer_free(&b);
 486 #ifdef DEBUG_KEX
 487         fprintf(stderr, "key '%c'== ", c);
 488         dump_digest("key", digest, need);
 489 #endif
 490         return digest;
 491 }
 492
 493 Newkeys *current_keys[MODE_MAX];
 494
 495 #define NKEYS   6
 496 void
 497 kex_derive_keys(Kex *kex, u_char *hash, u_int hashlen, BIGNUM *shared_secret)
 498 {
 499         u_char *keys[NKEYS];
 500         u_int i, mode, ctos;
 501
 502         for (i = 0; i < NKEYS; i++) {
 503                 keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, hashlen,
 504                     shared_secret);
 505         }
 506
 507         debug2("kex_derive_keys");
 508         for (mode = 0; mode < MODE_MAX; mode++) {
 509                 current_keys[mode] = kex->newkeys[mode];
 510                 kex->newkeys[mode] = NULL;
 511                 ctos = (!kex->server && mode == MODE_OUT) ||
 512                     (kex->server && mode == MODE_IN);
 513                 current_keys[mode]->enc.iv  = keys[ctos ? 0 : 1];
 514                 current_keys[mode]->enc.key = keys[ctos ? 2 : 3];
 515                 current_keys[mode]->mac.key = keys[ctos ? 4 : 5];
 516         }
 517 }
 518
 519 Newkeys *
 520 kex_get_newkeys(int mode)
 521 {
 522         Newkeys *ret;
 523
 524         ret = current_keys[mode];
 525         current_keys[mode] = NULL;
 526         return ret;
 527 }
 528
 529 void
 530 derive_ssh1_session_id(BIGNUM *host_modulus, BIGNUM *server_modulus,
 531     u_int8_t cookie[8], u_int8_t id[16])
 532 {
 533         const EVP_MD *evp_md = EVP_md5();
 534         EVP_MD_CTX md;
 535         u_int8_t nbuf[2048], obuf[EVP_MAX_MD_SIZE];
 536         int len;
 537
 538         EVP_DigestInit(&md, evp_md);
 539
 540         len = BN_num_bytes(host_modulus);
 541         if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
 542                 fatal("%s: bad host modulus (len %d)", __func__, len);
 543         BN_bn2bin(host_modulus, nbuf);
 544         EVP_DigestUpdate(&md, nbuf, len);
 545
 546         len = BN_num_bytes(server_modulus);
 547         if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
 548                 fatal("%s: bad server modulus (len %d)", __func__, len);
 549         BN_bn2bin(server_modulus, nbuf);
 550         EVP_DigestUpdate(&md, nbuf, len);
 551
 552         EVP_DigestUpdate(&md, cookie, 8);
 553
 554         EVP_DigestFinal(&md, obuf, NULL);
 555         memcpy(id, obuf, 16);
 556
 557         memset(nbuf, 0, sizeof(nbuf));
 558         memset(obuf, 0, sizeof(obuf));
 559         memset(&md, 0, sizeof(md));
 560 }
 561
 562 #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH)
 563 void
 564 dump_digest(char *msg, u_char *digest, int len)
 565 {
 566         u_int i;
 567
 568         fprintf(stderr, "%s\n", msg);
 569         for (i = 0; i < len; i++) {
 570                 fprintf(stderr, "%02x", digest[i]);
 571                 if (i%32 == 31)
 572                         fprintf(stderr, "\n");
 573                 else if (i%8 == 7)
 574                         fprintf(stderr, " ");
 575         }
 576         fprintf(stderr, "\n");
 577 }
 578 #endif