crypto/openssh-4/kex.c

   1 /* $OpenBSD: kex.c,v 1.77 2007/01/21 01:41:54 stevesk 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         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 %d ", 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 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 void
 198 kex_input_kexinit(int type, u_int32_t seq, void *ctxt)
 199 {
 200         char *ptr;
 201         u_int i, dlen;
 202         Kex *kex = (Kex *)ctxt;
 203
 204         debug("SSH2_MSG_KEXINIT received");
 205         if (kex == NULL)
 206                 fatal("kex_input_kexinit: no kex, cannot rekey");
 207
 208         ptr = packet_get_raw(&dlen);
 209         buffer_append(&kex->peer, ptr, dlen);
 210
 211         /* discard packet */
 212         for (i = 0; i < KEX_COOKIE_LEN; i++)
 213                 packet_get_char();
 214         for (i = 0; i < PROPOSAL_MAX; i++)
 215                 xfree(packet_get_string(NULL));
 216         (void) packet_get_char();
 217         (void) packet_get_int();
 218         packet_check_eom();
 219
 220         kex_kexinit_finish(kex);
 221 }
 222
 223 Kex *
 224 kex_setup(char *proposal[PROPOSAL_MAX])
 225 {
 226         Kex *kex;
 227
 228         kex = xcalloc(1, sizeof(*kex));
 229         buffer_init(&kex->peer);
 230         buffer_init(&kex->my);
 231         kex_prop2buf(&kex->my, proposal);
 232         kex->done = 0;
 233
 234         kex_send_kexinit(kex);                                  /* we start */
 235         kex_reset_dispatch();
 236
 237         return kex;
 238 }
 239
 240 static void
 241 kex_kexinit_finish(Kex *kex)
 242 {
 243         if (!(kex->flags & KEX_INIT_SENT))
 244                 kex_send_kexinit(kex);
 245
 246         kex_choose_conf(kex);
 247
 248         if (kex->kex_type >= 0 && kex->kex_type < KEX_MAX &&
 249             kex->kex[kex->kex_type] != NULL) {
 250                 (kex->kex[kex->kex_type])(kex);
 251         } else {
 252                 fatal("Unsupported key exchange %d", kex->kex_type);
 253         }
 254 }
 255
 256 static void
 257 choose_enc(Enc *enc, char *client, char *server)
 258 {
 259         char *name = match_list(client, server, NULL);
 260         if (name == NULL)
 261                 fatal("no matching cipher found: client %s server %s", client, server);
 262         if ((enc->cipher = cipher_by_name(name)) == NULL)
 263                 fatal("matching cipher is not supported: %s", name);
 264         enc->name = name;
 265         enc->enabled = 0;
 266         enc->iv = NULL;
 267         enc->key = NULL;
 268         enc->key_len = cipher_keylen(enc->cipher);
 269         enc->block_size = cipher_blocksize(enc->cipher);
 270 }
 271
 272 static void
 273 choose_mac(Mac *mac, char *client, char *server)
 274 {
 275         char *name = match_list(client, server, NULL);
 276         if (name == NULL)
 277                 fatal("no matching mac found: client %s server %s", client, server);
 278         if (mac_init(mac, name) < 0)
 279                 fatal("unsupported mac %s", name);
 280         /* truncate the key */
 281         if (datafellows & SSH_BUG_HMAC)
 282                 mac->key_len = 16;
 283         mac->name = name;
 284         mac->key = NULL;
 285         mac->enabled = 0;
 286 }
 287
 288 static void
 289 choose_comp(Comp *comp, char *client, char *server)
 290 {
 291         char *name = match_list(client, server, NULL);
 292         if (name == NULL)
 293                 fatal("no matching comp found: client %s server %s", client, server);
 294         if (strcmp(name, "zlib@openssh.com") == 0) {
 295                 comp->type = COMP_DELAYED;
 296         } else if (strcmp(name, "zlib") == 0) {
 297                 comp->type = COMP_ZLIB;
 298         } else if (strcmp(name, "none") == 0) {
 299                 comp->type = COMP_NONE;
 300         } else {
 301                 fatal("unsupported comp %s", name);
 302         }
 303         comp->name = name;
 304 }
 305
 306 static void
 307 choose_kex(Kex *k, char *client, char *server)
 308 {
 309         k->name = match_list(client, server, NULL);
 310         if (k->name == NULL)
 311                 fatal("no kex alg");
 312         if (strcmp(k->name, KEX_DH1) == 0) {
 313                 k->kex_type = KEX_DH_GRP1_SHA1;
 314                 k->evp_md = EVP_sha1();
 315         } else if (strcmp(k->name, KEX_DH14) == 0) {
 316                 k->kex_type = KEX_DH_GRP14_SHA1;
 317                 k->evp_md = EVP_sha1();
 318         } else if (strcmp(k->name, KEX_DHGEX_SHA1) == 0) {
 319                 k->kex_type = KEX_DH_GEX_SHA1;
 320                 k->evp_md = EVP_sha1();
 321 #if OPENSSL_VERSION_NUMBER >= 0x00907000L
 322         } else if (strcmp(k->name, KEX_DHGEX_SHA256) == 0) {
 323                 k->kex_type = KEX_DH_GEX_SHA256;
 324                 k->evp_md = evp_ssh_sha256();
 325 #endif
 326         } else
 327                 fatal("bad kex alg %s", k->name);
 328 }
 329
 330 static void
 331 choose_hostkeyalg(Kex *k, char *client, char *server)
 332 {
 333         char *hostkeyalg = match_list(client, server, NULL);
 334         if (hostkeyalg == NULL)
 335                 fatal("no hostkey alg");
 336         k->hostkey_type = key_type_from_name(hostkeyalg);
 337         if (k->hostkey_type == KEY_UNSPEC)
 338                 fatal("bad hostkey alg '%s'", hostkeyalg);
 339         xfree(hostkeyalg);
 340 }
 341
 342 static int
 343 proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX])
 344 {
 345         static int check[] = {
 346                 PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1
 347         };
 348         int *idx;
 349         char *p;
 350
 351         for (idx = &check[0]; *idx != -1; idx++) {
 352                 if ((p = strchr(my[*idx], ',')) != NULL)
 353                         *p = '\0';
 354                 if ((p = strchr(peer[*idx], ',')) != NULL)
 355                         *p = '\0';
 356                 if (strcmp(my[*idx], peer[*idx]) != 0) {
 357                         debug2("proposal mismatch: my %s peer %s",
 358                             my[*idx], peer[*idx]);
 359                         return (0);
 360                 }
 361         }
 362         debug2("proposals match");
 363         return (1);
 364 }
 365
 366 static void
 367 kex_choose_conf(Kex *kex)
 368 {
 369         Newkeys *newkeys;
 370         char **my, **peer;
 371         char **cprop, **sprop;
 372         int nenc, nmac, ncomp;
 373         u_int mode, ctos, need;
 374         int first_kex_follows, type;
 375
 376         my   = kex_buf2prop(&kex->my, NULL);
 377         peer = kex_buf2prop(&kex->peer, &first_kex_follows);
 378
 379         if (kex->server) {
 380                 cprop=peer;
 381                 sprop=my;
 382         } else {
 383                 cprop=my;
 384                 sprop=peer;
 385         }
 386
 387         /* Algorithm Negotiation */
 388         for (mode = 0; mode < MODE_MAX; mode++) {
 389                 newkeys = xcalloc(1, sizeof(*newkeys));
 390                 kex->newkeys[mode] = newkeys;
 391                 ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN);
 392                 nenc  = ctos ? PROPOSAL_ENC_ALGS_CTOS  : PROPOSAL_ENC_ALGS_STOC;
 393                 nmac  = ctos ? PROPOSAL_MAC_ALGS_CTOS  : PROPOSAL_MAC_ALGS_STOC;
 394                 ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC;
 395                 choose_enc (&newkeys->enc,  cprop[nenc],  sprop[nenc]);
 396                 choose_mac (&newkeys->mac,  cprop[nmac],  sprop[nmac]);
 397                 choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]);
 398                 debug("kex: %s %s %s %s",
 399                     ctos ? "client->server" : "server->client",
 400                     newkeys->enc.name,
 401                     newkeys->mac.name,
 402                     newkeys->comp.name);
 403         }
 404         choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]);
 405         choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
 406             sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]);
 407         need = 0;
 408         for (mode = 0; mode < MODE_MAX; mode++) {
 409                 newkeys = kex->newkeys[mode];
 410                 if (need < newkeys->enc.key_len)
 411                         need = newkeys->enc.key_len;
 412                 if (need < newkeys->enc.block_size)
 413                         need = newkeys->enc.block_size;
 414                 if (need < newkeys->mac.key_len)
 415                         need = newkeys->mac.key_len;
 416         }
 417         /* XXX need runden? */
 418         kex->we_need = need;
 419
 420         /* ignore the next message if the proposals do not match */
 421         if (first_kex_follows && !proposals_match(my, peer) &&
 422             !(datafellows & SSH_BUG_FIRSTKEX)) {
 423                 type = packet_read();
 424                 debug2("skipping next packet (type %u)", type);
 425         }
 426
 427         kex_prop_free(my);
 428         kex_prop_free(peer);
 429 }
 430
 431 static u_char *
 432 derive_key(Kex *kex, int id, u_int need, u_char *hash, u_int hashlen,
 433     BIGNUM *shared_secret)
 434 {
 435         Buffer b;
 436         EVP_MD_CTX md;
 437         char c = id;
 438         u_int have;
 439         int mdsz;
 440         u_char *digest;
 441
 442         if ((mdsz = EVP_MD_size(kex->evp_md)) <= 0)
 443                 fatal("bad kex md size %d", mdsz);
 444         digest = xmalloc(roundup(need, mdsz));
 445
 446         buffer_init(&b);
 447         buffer_put_bignum2(&b, shared_secret);
 448
 449         /* K1 = HASH(K || H || "A" || session_id) */
 450         EVP_DigestInit(&md, kex->evp_md);
 451         if (!(datafellows & SSH_BUG_DERIVEKEY))
 452                 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
 453         EVP_DigestUpdate(&md, hash, hashlen);
 454         EVP_DigestUpdate(&md, &c, 1);
 455         EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len);
 456         EVP_DigestFinal(&md, digest, NULL);
 457
 458         /*
 459          * expand key:
 460          * Kn = HASH(K || H || K1 || K2 || ... || Kn-1)
 461          * Key = K1 || K2 || ... || Kn
 462          */
 463         for (have = mdsz; need > have; have += mdsz) {
 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, digest, have);
 469                 EVP_DigestFinal(&md, digest + have, NULL);
 470         }
 471         buffer_free(&b);
 472 #ifdef DEBUG_KEX
 473         fprintf(stderr, "key '%c'== ", c);
 474         dump_digest("key", digest, need);
 475 #endif
 476         return digest;
 477 }
 478
 479 Newkeys *current_keys[MODE_MAX];
 480
 481 #define NKEYS   6
 482 void
 483 kex_derive_keys(Kex *kex, u_char *hash, u_int hashlen, BIGNUM *shared_secret)
 484 {
 485         u_char *keys[NKEYS];
 486         u_int i, mode, ctos;
 487
 488         for (i = 0; i < NKEYS; i++) {
 489                 keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, hashlen,
 490                     shared_secret);
 491         }
 492
 493         debug2("kex_derive_keys");
 494         for (mode = 0; mode < MODE_MAX; mode++) {
 495                 current_keys[mode] = kex->newkeys[mode];
 496                 kex->newkeys[mode] = NULL;
 497                 ctos = (!kex->server && mode == MODE_OUT) ||
 498                     (kex->server && mode == MODE_IN);
 499                 current_keys[mode]->enc.iv  = keys[ctos ? 0 : 1];
 500                 current_keys[mode]->enc.key = keys[ctos ? 2 : 3];
 501                 current_keys[mode]->mac.key = keys[ctos ? 4 : 5];
 502         }
 503 }
 504
 505 Newkeys *
 506 kex_get_newkeys(int mode)
 507 {
 508         Newkeys *ret;
 509
 510         ret = current_keys[mode];
 511         current_keys[mode] = NULL;
 512         return ret;
 513 }
 514
 515 void
 516 derive_ssh1_session_id(BIGNUM *host_modulus, BIGNUM *server_modulus,
 517     u_int8_t cookie[8], u_int8_t id[16])
 518 {
 519         const EVP_MD *evp_md = EVP_md5();
 520         EVP_MD_CTX md;
 521         u_int8_t nbuf[2048], obuf[EVP_MAX_MD_SIZE];
 522         int len;
 523
 524         EVP_DigestInit(&md, evp_md);
 525
 526         len = BN_num_bytes(host_modulus);
 527         if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
 528                 fatal("%s: bad host modulus (len %d)", __func__, len);
 529         BN_bn2bin(host_modulus, nbuf);
 530         EVP_DigestUpdate(&md, nbuf, len);
 531
 532         len = BN_num_bytes(server_modulus);
 533         if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
 534                 fatal("%s: bad server modulus (len %d)", __func__, len);
 535         BN_bn2bin(server_modulus, nbuf);
 536         EVP_DigestUpdate(&md, nbuf, len);
 537
 538         EVP_DigestUpdate(&md, cookie, 8);
 539
 540         EVP_DigestFinal(&md, obuf, NULL);
 541         memcpy(id, obuf, 16);
 542
 543         memset(nbuf, 0, sizeof(nbuf));
 544         memset(obuf, 0, sizeof(obuf));
 545         memset(&md, 0, sizeof(md));
 546 }
 547
 548 #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH)
 549 void
 550 dump_digest(char *msg, u_char *digest, int len)
 551 {
 552         u_int i;
 553
 554         fprintf(stderr, "%s\n", msg);
 555         for (i = 0; i < len; i++) {
 556                 fprintf(stderr, "%02x", digest[i]);
 557                 if (i%32 == 31)
 558                         fprintf(stderr, "\n");
 559                 else if (i%8 == 7)
 560                         fprintf(stderr, " ");
 561         }
 562         fprintf(stderr, "\n");
 563 }
 564 #endif