kex.c

   1 /* $OpenBSD: kex.c,v 1.79 2007/06/05 06:52:37 djm 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
  52 #define KEX_COOKIE_LEN  16
  53
  54 #if OPENSSL_VERSION_NUMBER >= 0x00907000L
  55 # if defined(HAVE_EVP_SHA256)
  56 # define evp_ssh_sha256 EVP_sha256
  57 # else
  58 extern const EVP_MD *evp_ssh_sha256(void);
  59 # endif
  60 #endif
  61
  62 /* prototype */
  63 static void kex_kexinit_finish(Kex *);
  64 static void kex_choose_conf(Kex *);
  65
  66 /* put algorithm proposal into buffer */
  67 static void
  68 kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX])
  69 {
  70         u_int i;
  71
  72         buffer_clear(b);
  73         /*
  74          * add a dummy cookie, the cookie will be overwritten by
  75          * kex_send_kexinit(), each time a kexinit is set
  76          */
  77         for (i = 0; i < KEX_COOKIE_LEN; i++)
  78                 buffer_put_char(b, 0);
  79         for (i = 0; i < PROPOSAL_MAX; i++)
  80                 buffer_put_cstring(b, proposal[i]);
  81         buffer_put_char(b, 0);                  /* first_kex_packet_follows */
  82         buffer_put_int(b, 0);                   /* uint32 reserved */
  83 }
  84
  85 /* parse buffer and return algorithm proposal */
  86 static char **
  87 kex_buf2prop(Buffer *raw, int *first_kex_follows)
  88 {
  89         Buffer b;
  90         u_int i;
  91         char **proposal;
  92
  93         proposal = xcalloc(PROPOSAL_MAX, sizeof(char *));
  94
  95         buffer_init(&b);
  96         buffer_append(&b, buffer_ptr(raw), buffer_len(raw));
  97         /* skip cookie */
  98         for (i = 0; i < KEX_COOKIE_LEN; i++)
  99                 buffer_get_char(&b);
 100         /* extract kex init proposal strings */
 101         for (i = 0; i < PROPOSAL_MAX; i++) {
 102                 proposal[i] = buffer_get_string(&b,NULL);
 103                 debug2("kex_parse_kexinit: %s", proposal[i]);
 104         }
 105         /* first kex follows / reserved */
 106         i = buffer_get_char(&b);
 107         if (first_kex_follows != NULL)
 108                 *first_kex_follows = i;
 109         debug2("kex_parse_kexinit: first_kex_follows %d ", i);
 110         i = buffer_get_int(&b);
 111         debug2("kex_parse_kexinit: reserved %u ", i);
 112         buffer_free(&b);
 113         return proposal;
 114 }
 115
 116 static void
 117 kex_prop_free(char **proposal)
 118 {
 119         u_int i;
 120
 121         for (i = 0; i < PROPOSAL_MAX; i++)
 122                 xfree(proposal[i]);
 123         xfree(proposal);
 124 }
 125
 126 /* ARGSUSED */
 127 static void
 128 kex_protocol_error(int type, u_int32_t seq, void *ctxt)
 129 {
 130         error("Hm, kex protocol error: type %d seq %u", type, seq);
 131 }
 132
 133 static void
 134 kex_reset_dispatch(void)
 135 {
 136         dispatch_range(SSH2_MSG_TRANSPORT_MIN,
 137             SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error);
 138         dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit);
 139 }
 140
 141 void
 142 kex_finish(Kex *kex)
 143 {
 144         kex_reset_dispatch();
 145
 146         packet_start(SSH2_MSG_NEWKEYS);
 147         packet_send();
 148         /* packet_write_wait(); */
 149         debug("SSH2_MSG_NEWKEYS sent");
 150
 151         debug("expecting SSH2_MSG_NEWKEYS");
 152         packet_read_expect(SSH2_MSG_NEWKEYS);
 153         packet_check_eom();
 154         debug("SSH2_MSG_NEWKEYS received");
 155
 156         kex->done = 1;
 157         buffer_clear(&kex->peer);
 158         /* buffer_clear(&kex->my); */
 159         kex->flags &= ~KEX_INIT_SENT;
 160         xfree(kex->name);
 161         kex->name = NULL;
 162 }
 163
 164 void
 165 kex_send_kexinit(Kex *kex)
 166 {
 167         u_int32_t rnd = 0;
 168         u_char *cookie;
 169         u_int i;
 170
 171         if (kex == NULL) {
 172                 error("kex_send_kexinit: no kex, cannot rekey");
 173                 return;
 174         }
 175         if (kex->flags & KEX_INIT_SENT) {
 176                 debug("KEX_INIT_SENT");
 177                 return;
 178         }
 179         kex->done = 0;
 180
 181         /* generate a random cookie */
 182         if (buffer_len(&kex->my) < KEX_COOKIE_LEN)
 183                 fatal("kex_send_kexinit: kex proposal too short");
 184         cookie = buffer_ptr(&kex->my);
 185         for (i = 0; i < KEX_COOKIE_LEN; i++) {
 186                 if (i % 4 == 0)
 187                         rnd = arc4random();
 188                 cookie[i] = rnd;
 189                 rnd >>= 8;
 190         }
 191         packet_start(SSH2_MSG_KEXINIT);
 192         packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my));
 193         packet_send();
 194         debug("SSH2_MSG_KEXINIT sent");
 195         kex->flags |= KEX_INIT_SENT;
 196 }
 197
 198 /* ARGSUSED */
 199 void
 200 kex_input_kexinit(int type, u_int32_t seq, void *ctxt)
 201 {
 202         char *ptr;
 203         u_int i, dlen;
 204         Kex *kex = (Kex *)ctxt;
 205
 206         debug("SSH2_MSG_KEXINIT received");
 207         if (kex == NULL)
 208                 fatal("kex_input_kexinit: no kex, cannot rekey");
 209
 210         ptr = packet_get_raw(&dlen);
 211         buffer_append(&kex->peer, ptr, dlen);
 212
 213         /* discard packet */
 214         for (i = 0; i < KEX_COOKIE_LEN; i++)
 215                 packet_get_char();
 216         for (i = 0; i < PROPOSAL_MAX; i++)
 217                 xfree(packet_get_string(NULL));
 218         (void) packet_get_char();
 219         (void) packet_get_int();
 220         packet_check_eom();
 221
 222         kex_kexinit_finish(kex);
 223 }
 224
 225 Kex *
 226 kex_setup(char *proposal[PROPOSAL_MAX])
 227 {
 228         Kex *kex;
 229
 230         kex = xcalloc(1, sizeof(*kex));
 231         buffer_init(&kex->peer);
 232         buffer_init(&kex->my);
 233         kex_prop2buf(&kex->my, proposal);
 234         kex->done = 0;
 235
 236         kex_send_kexinit(kex);                                  /* we start */
 237         kex_reset_dispatch();
 238
 239         return kex;
 240 }
 241
 242 static void
 243 kex_kexinit_finish(Kex *kex)
 244 {
 245         if (!(kex->flags & KEX_INIT_SENT))
 246                 kex_send_kexinit(kex);
 247
 248         kex_choose_conf(kex);
 249
 250         if (kex->kex_type >= 0 && kex->kex_type < KEX_MAX &&
 251             kex->kex[kex->kex_type] != NULL) {
 252                 (kex->kex[kex->kex_type])(kex);
 253         } else {
 254                 fatal("Unsupported key exchange %d", kex->kex_type);
 255         }
 256 }
 257
 258 static void
 259 choose_enc(Enc *enc, char *client, char *server)
 260 {
 261         char *name = match_list(client, server, NULL);
 262         if (name == NULL)
 263                 fatal("no matching cipher found: client %s server %s",
 264                     client, server);
 265         if ((enc->cipher = cipher_by_name(name)) == NULL)
 266                 fatal("matching cipher is not supported: %s", name);
 267         enc->name = name;
 268         enc->enabled = 0;
 269         enc->iv = NULL;
 270         enc->key = NULL;
 271         enc->key_len = cipher_keylen(enc->cipher);
 272         enc->block_size = cipher_blocksize(enc->cipher);
 273 }
 274
 275 static void
 276 choose_mac(Mac *mac, char *client, char *server)
 277 {
 278         char *name = match_list(client, server, NULL);
 279         if (name == NULL)
 280                 fatal("no matching mac found: client %s server %s",
 281                     client, server);
 282         if (mac_setup(mac, name) < 0)
 283                 fatal("unsupported mac %s", name);
 284         /* truncate the key */
 285         if (datafellows & SSH_BUG_HMAC)
 286                 mac->key_len = 16;
 287         mac->name = name;
 288         mac->key = NULL;
 289         mac->enabled = 0;
 290 }
 291
 292 static void
 293 choose_comp(Comp *comp, char *client, char *server)
 294 {
 295         char *name = match_list(client, server, NULL);
 296         if (name == NULL)
 297                 fatal("no matching comp found: client %s server %s", client, server);
 298         if (strcmp(name, "zlib@openssh.com") == 0) {
 299                 comp->type = COMP_DELAYED;
 300         } else if (strcmp(name, "zlib") == 0) {
 301                 comp->type = COMP_ZLIB;
 302         } else if (strcmp(name, "none") == 0) {
 303                 comp->type = COMP_NONE;
 304         } else {
 305                 fatal("unsupported comp %s", name);
 306         }
 307         comp->name = name;
 308 }
 309
 310 static void
 311 choose_kex(Kex *k, char *client, char *server)
 312 {
 313         k->name = match_list(client, server, NULL);
 314         if (k->name == NULL)
 315                 fatal("Unable to negotiate a key exchange method");
 316         if (strcmp(k->name, KEX_DH1) == 0) {
 317                 k->kex_type = KEX_DH_GRP1_SHA1;
 318                 k->evp_md = EVP_sha1();
 319         } else if (strcmp(k->name, KEX_DH14) == 0) {
 320                 k->kex_type = KEX_DH_GRP14_SHA1;
 321                 k->evp_md = EVP_sha1();
 322         } else if (strcmp(k->name, KEX_DHGEX_SHA1) == 0) {
 323                 k->kex_type = KEX_DH_GEX_SHA1;
 324                 k->evp_md = EVP_sha1();
 325 #if OPENSSL_VERSION_NUMBER >= 0x00907000L
 326         } else if (strcmp(k->name, KEX_DHGEX_SHA256) == 0) {
 327                 k->kex_type = KEX_DH_GEX_SHA256;
 328                 k->evp_md = evp_ssh_sha256();
 329 #endif
 330         } else
 331                 fatal("bad kex alg %s", k->name);
 332 }
 333
 334 static void
 335 choose_hostkeyalg(Kex *k, char *client, char *server)
 336 {
 337         char *hostkeyalg = match_list(client, server, NULL);
 338         if (hostkeyalg == NULL)
 339                 fatal("no hostkey alg");
 340         k->hostkey_type = key_type_from_name(hostkeyalg);
 341         if (k->hostkey_type == KEY_UNSPEC)
 342                 fatal("bad hostkey alg '%s'", hostkeyalg);
 343         xfree(hostkeyalg);
 344 }
 345
 346 static int
 347 proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX])
 348 {
 349         static int check[] = {
 350                 PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1
 351         };
 352         int *idx;
 353         char *p;
 354
 355         for (idx = &check[0]; *idx != -1; idx++) {
 356                 if ((p = strchr(my[*idx], ',')) != NULL)
 357                         *p = '\0';
 358                 if ((p = strchr(peer[*idx], ',')) != NULL)
 359                         *p = '\0';
 360                 if (strcmp(my[*idx], peer[*idx]) != 0) {
 361                         debug2("proposal mismatch: my %s peer %s",
 362                             my[*idx], peer[*idx]);
 363                         return (0);
 364                 }
 365         }
 366         debug2("proposals match");
 367         return (1);
 368 }
 369
 370 static void
 371 kex_choose_conf(Kex *kex)
 372 {
 373         Newkeys *newkeys;
 374         char **my, **peer;
 375         char **cprop, **sprop;
 376         int nenc, nmac, ncomp;
 377         u_int mode, ctos, need;
 378         int first_kex_follows, type;
 379
 380         my   = kex_buf2prop(&kex->my, NULL);
 381         peer = kex_buf2prop(&kex->peer, &first_kex_follows);
 382
 383         if (kex->server) {
 384                 cprop=peer;
 385                 sprop=my;
 386         } else {
 387                 cprop=my;
 388                 sprop=peer;
 389         }
 390
 391         /* Algorithm Negotiation */
 392         for (mode = 0; mode < MODE_MAX; mode++) {
 393                 newkeys = xcalloc(1, sizeof(*newkeys));
 394                 kex->newkeys[mode] = newkeys;
 395                 ctos = (!kex->server && mode == MODE_OUT) ||
 396                     (kex->server && mode == MODE_IN);
 397                 nenc  = ctos ? PROPOSAL_ENC_ALGS_CTOS  : PROPOSAL_ENC_ALGS_STOC;
 398                 nmac  = ctos ? PROPOSAL_MAC_ALGS_CTOS  : PROPOSAL_MAC_ALGS_STOC;
 399                 ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC;
 400                 choose_enc (&newkeys->enc,  cprop[nenc],  sprop[nenc]);
 401                 choose_mac (&newkeys->mac,  cprop[nmac],  sprop[nmac]);
 402                 choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]);
 403                 debug("kex: %s %s %s %s",
 404                     ctos ? "client->server" : "server->client",
 405                     newkeys->enc.name,
 406                     newkeys->mac.name,
 407                     newkeys->comp.name);
 408         }
 409         choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]);
 410         choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
 411             sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]);
 412         need = 0;
 413         for (mode = 0; mode < MODE_MAX; mode++) {
 414                 newkeys = kex->newkeys[mode];
 415                 if (need < newkeys->enc.key_len)
 416                         need = newkeys->enc.key_len;
 417                 if (need < newkeys->enc.block_size)
 418                         need = newkeys->enc.block_size;
 419                 if (need < newkeys->mac.key_len)
 420                         need = newkeys->mac.key_len;
 421         }
 422         /* XXX need runden? */
 423         kex->we_need = need;
 424
 425         /* ignore the next message if the proposals do not match */
 426         if (first_kex_follows && !proposals_match(my, peer) &&
 427             !(datafellows & SSH_BUG_FIRSTKEX)) {
 428                 type = packet_read();
 429                 debug2("skipping next packet (type %u)", type);
 430         }
 431
 432         kex_prop_free(my);
 433         kex_prop_free(peer);
 434 }
 435
 436 static u_char *
 437 derive_key(Kex *kex, int id, u_int need, u_char *hash, u_int hashlen,
 438     BIGNUM *shared_secret)
 439 {
 440         Buffer b;
 441         EVP_MD_CTX md;
 442         char c = id;
 443         u_int have;
 444         int mdsz;
 445         u_char *digest;
 446
 447         if ((mdsz = EVP_MD_size(kex->evp_md)) <= 0)
 448                 fatal("bad kex md size %d", mdsz);
 449         digest = xmalloc(roundup(need, mdsz));
 450
 451         buffer_init(&b);
 452         buffer_put_bignum2(&b, shared_secret);
 453
 454         /* K1 = HASH(K || H || "A" || session_id) */
 455         EVP_DigestInit(&md, kex->evp_md);
 456         if (!(datafellows & SSH_BUG_DERIVEKEY))
 457                 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
 458         EVP_DigestUpdate(&md, hash, hashlen);
 459         EVP_DigestUpdate(&md, &c, 1);
 460         EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len);
 461         EVP_DigestFinal(&md, digest, NULL);
 462
 463         /*
 464          * expand key:
 465          * Kn = HASH(K || H || K1 || K2 || ... || Kn-1)
 466          * Key = K1 || K2 || ... || Kn
 467          */
 468         for (have = mdsz; need > have; have += mdsz) {
 469                 EVP_DigestInit(&md, kex->evp_md);
 470                 if (!(datafellows & SSH_BUG_DERIVEKEY))
 471                         EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
 472                 EVP_DigestUpdate(&md, hash, hashlen);
 473                 EVP_DigestUpdate(&md, digest, have);
 474                 EVP_DigestFinal(&md, digest + have, NULL);
 475         }
 476         buffer_free(&b);
 477 #ifdef DEBUG_KEX
 478         fprintf(stderr, "key '%c'== ", c);
 479         dump_digest("key", digest, need);
 480 #endif
 481         return digest;
 482 }
 483
 484 Newkeys *current_keys[MODE_MAX];
 485
 486 #define NKEYS   6
 487 void
 488 kex_derive_keys(Kex *kex, u_char *hash, u_int hashlen, BIGNUM *shared_secret)
 489 {
 490         u_char *keys[NKEYS];
 491         u_int i, mode, ctos;
 492
 493         for (i = 0; i < NKEYS; i++) {
 494                 keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, hashlen,
 495                     shared_secret);
 496         }
 497
 498         debug2("kex_derive_keys");
 499         for (mode = 0; mode < MODE_MAX; mode++) {
 500                 current_keys[mode] = kex->newkeys[mode];
 501                 kex->newkeys[mode] = NULL;
 502                 ctos = (!kex->server && mode == MODE_OUT) ||
 503                     (kex->server && mode == MODE_IN);
 504                 current_keys[mode]->enc.iv  = keys[ctos ? 0 : 1];
 505                 current_keys[mode]->enc.key = keys[ctos ? 2 : 3];
 506                 current_keys[mode]->mac.key = keys[ctos ? 4 : 5];
 507         }
 508 }
 509
 510 Newkeys *
 511 kex_get_newkeys(int mode)
 512 {
 513         Newkeys *ret;
 514
 515         ret = current_keys[mode];
 516         current_keys[mode] = NULL;
 517         return ret;
 518 }
 519
 520 void
 521 derive_ssh1_session_id(BIGNUM *host_modulus, BIGNUM *server_modulus,
 522     u_int8_t cookie[8], u_int8_t id[16])
 523 {
 524         const EVP_MD *evp_md = EVP_md5();
 525         EVP_MD_CTX md;
 526         u_int8_t nbuf[2048], obuf[EVP_MAX_MD_SIZE];
 527         int len;
 528
 529         EVP_DigestInit(&md, evp_md);
 530
 531         len = BN_num_bytes(host_modulus);
 532         if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
 533                 fatal("%s: bad host modulus (len %d)", __func__, len);
 534         BN_bn2bin(host_modulus, nbuf);
 535         EVP_DigestUpdate(&md, nbuf, len);
 536
 537         len = BN_num_bytes(server_modulus);
 538         if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
 539                 fatal("%s: bad server modulus (len %d)", __func__, len);
 540         BN_bn2bin(server_modulus, nbuf);
 541         EVP_DigestUpdate(&md, nbuf, len);
 542
 543         EVP_DigestUpdate(&md, cookie, 8);
 544
 545         EVP_DigestFinal(&md, obuf, NULL);
 546         memcpy(id, obuf, 16);
 547
 548         memset(nbuf, 0, sizeof(nbuf));
 549         memset(obuf, 0, sizeof(obuf));
 550         memset(&md, 0, sizeof(md));
 551 }
 552
 553 #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH)
 554 void
 555 dump_digest(char *msg, u_char *digest, int len)
 556 {
 557         u_int i;
 558
 559         fprintf(stderr, "%s\n", msg);
 560         for (i = 0; i < len; i++) {
 561                 fprintf(stderr, "%02x", digest[i]);
 562                 if (i%32 == 31)
 563                         fprintf(stderr, "\n");
 564                 else if (i%8 == 7)
 565                         fprintf(stderr, " ");
 566         }
 567         fprintf(stderr, "\n");
 568 }
 569 #endif