kex.c

   1 /* $OpenBSD: kex.c,v 1.76 2006/08/03 03:34:42 deraadt 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 <stdio.h>
  32 #include <stdlib.h>
  33 #include <string.h>
  34
  35 #include <openssl/crypto.h>
  36
  37 #include "xmalloc.h"
  38 #include "ssh2.h"
  39 #include "buffer.h"
  40 #include "packet.h"
  41 #include "compat.h"
  42 #include "cipher.h"
  43 #include "key.h"
  44 #include "kex.h"
  45 #include "log.h"
  46 #include "mac.h"
  47 #include "match.h"
  48 #include "dispatch.h"
  49 #include "monitor.h"
  50
  51 #define KEX_COOKIE_LEN  16
  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         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 %d ", 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 static void
 126 kex_protocol_error(int type, u_int32_t seq, void *ctxt)
 127 {
 128         error("Hm, kex protocol error: type %d seq %u", type, seq);
 129 }
 130
 131 static void
 132 kex_reset_dispatch(void)
 133 {
 134         dispatch_range(SSH2_MSG_TRANSPORT_MIN,
 135             SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error);
 136         dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit);
 137 }
 138
 139 void
 140 kex_finish(Kex *kex)
 141 {
 142         kex_reset_dispatch();
 143
 144         packet_start(SSH2_MSG_NEWKEYS);
 145         packet_send();
 146         /* packet_write_wait(); */
 147         debug("SSH2_MSG_NEWKEYS sent");
 148
 149         debug("expecting SSH2_MSG_NEWKEYS");
 150         packet_read_expect(SSH2_MSG_NEWKEYS);
 151         packet_check_eom();
 152         debug("SSH2_MSG_NEWKEYS received");
 153
 154         kex->done = 1;
 155         buffer_clear(&kex->peer);
 156         /* buffer_clear(&kex->my); */
 157         kex->flags &= ~KEX_INIT_SENT;
 158         xfree(kex->name);
 159         kex->name = NULL;
 160 }
 161
 162 void
 163 kex_send_kexinit(Kex *kex)
 164 {
 165         u_int32_t rnd = 0;
 166         u_char *cookie;
 167         u_int i;
 168
 169         if (kex == NULL) {
 170                 error("kex_send_kexinit: no kex, cannot rekey");
 171                 return;
 172         }
 173         if (kex->flags & KEX_INIT_SENT) {
 174                 debug("KEX_INIT_SENT");
 175                 return;
 176         }
 177         kex->done = 0;
 178
 179         /* generate a random cookie */
 180         if (buffer_len(&kex->my) < KEX_COOKIE_LEN)
 181                 fatal("kex_send_kexinit: kex proposal too short");
 182         cookie = buffer_ptr(&kex->my);
 183         for (i = 0; i < KEX_COOKIE_LEN; i++) {
 184                 if (i % 4 == 0)
 185                         rnd = arc4random();
 186                 cookie[i] = rnd;
 187                 rnd >>= 8;
 188         }
 189         packet_start(SSH2_MSG_KEXINIT);
 190         packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my));
 191         packet_send();
 192         debug("SSH2_MSG_KEXINIT sent");
 193         kex->flags |= KEX_INIT_SENT;
 194 }
 195
 196 void
 197 kex_input_kexinit(int type, u_int32_t seq, void *ctxt)
 198 {
 199         char *ptr;
 200         u_int i, dlen;
 201         Kex *kex = (Kex *)ctxt;
 202
 203         debug("SSH2_MSG_KEXINIT received");
 204         if (kex == NULL)
 205                 fatal("kex_input_kexinit: no kex, cannot rekey");
 206
 207         ptr = packet_get_raw(&dlen);
 208         buffer_append(&kex->peer, ptr, dlen);
 209
 210         /* discard packet */
 211         for (i = 0; i < KEX_COOKIE_LEN; i++)
 212                 packet_get_char();
 213         for (i = 0; i < PROPOSAL_MAX; i++)
 214                 xfree(packet_get_string(NULL));
 215         (void) packet_get_char();
 216         (void) packet_get_int();
 217         packet_check_eom();
 218
 219         kex_kexinit_finish(kex);
 220 }
 221
 222 Kex *
 223 kex_setup(char *proposal[PROPOSAL_MAX])
 224 {
 225         Kex *kex;
 226
 227         kex = xcalloc(1, sizeof(*kex));
 228         buffer_init(&kex->peer);
 229         buffer_init(&kex->my);
 230         kex_prop2buf(&kex->my, proposal);
 231         kex->done = 0;
 232
 233         kex_send_kexinit(kex);                                  /* we start */
 234         kex_reset_dispatch();
 235
 236         return kex;
 237 }
 238
 239 static void
 240 kex_kexinit_finish(Kex *kex)
 241 {
 242         if (!(kex->flags & KEX_INIT_SENT))
 243                 kex_send_kexinit(kex);
 244
 245         kex_choose_conf(kex);
 246
 247         if (kex->kex_type >= 0 && kex->kex_type < KEX_MAX &&
 248             kex->kex[kex->kex_type] != NULL) {
 249                 (kex->kex[kex->kex_type])(kex);
 250         } else {
 251                 fatal("Unsupported key exchange %d", kex->kex_type);
 252         }
 253 }
 254
 255 static void
 256 choose_enc(Enc *enc, char *client, char *server)
 257 {
 258         char *name = match_list(client, server, NULL);
 259         if (name == NULL)
 260                 fatal("no matching cipher found: client %s server %s", client, server);
 261         if ((enc->cipher = cipher_by_name(name)) == NULL)
 262                 fatal("matching cipher is not supported: %s", name);
 263         enc->name = name;
 264         enc->enabled = 0;
 265         enc->iv = NULL;
 266         enc->key = NULL;
 267         enc->key_len = cipher_keylen(enc->cipher);
 268         enc->block_size = cipher_blocksize(enc->cipher);
 269 }
 270
 271 static void
 272 choose_mac(Mac *mac, char *client, char *server)
 273 {
 274         char *name = match_list(client, server, NULL);
 275         if (name == NULL)
 276                 fatal("no matching mac found: client %s server %s", client, server);
 277         if (mac_init(mac, name) < 0)
 278                 fatal("unsupported mac %s", name);
 279         /* truncate the key */
 280         if (datafellows & SSH_BUG_HMAC)
 281                 mac->key_len = 16;
 282         mac->name = name;
 283         mac->key = NULL;
 284         mac->enabled = 0;
 285 }
 286
 287 static void
 288 choose_comp(Comp *comp, char *client, char *server)
 289 {
 290         char *name = match_list(client, server, NULL);
 291         if (name == NULL)
 292                 fatal("no matching comp found: client %s server %s", client, server);
 293         if (strcmp(name, "zlib@openssh.com") == 0) {
 294                 comp->type = COMP_DELAYED;
 295         } else if (strcmp(name, "zlib") == 0) {
 296                 comp->type = COMP_ZLIB;
 297         } else if (strcmp(name, "none") == 0) {
 298                 comp->type = COMP_NONE;
 299         } else {
 300                 fatal("unsupported comp %s", name);
 301         }
 302         comp->name = name;
 303 }
 304
 305 static void
 306 choose_kex(Kex *k, char *client, char *server)
 307 {
 308         k->name = match_list(client, server, NULL);
 309         if (k->name == NULL)
 310                 fatal("no kex alg");
 311         if (strcmp(k->name, KEX_DH1) == 0) {
 312                 k->kex_type = KEX_DH_GRP1_SHA1;
 313                 k->evp_md = EVP_sha1();
 314         } else if (strcmp(k->name, KEX_DH14) == 0) {
 315                 k->kex_type = KEX_DH_GRP14_SHA1;
 316                 k->evp_md = EVP_sha1();
 317         } else if (strcmp(k->name, KEX_DHGEX_SHA1) == 0) {
 318                 k->kex_type = KEX_DH_GEX_SHA1;
 319                 k->evp_md = EVP_sha1();
 320 #if OPENSSL_VERSION_NUMBER >= 0x00907000L
 321         } else if (strcmp(k->name, KEX_DHGEX_SHA256) == 0) {
 322                 k->kex_type = KEX_DH_GEX_SHA256;
 323                 k->evp_md = evp_ssh_sha256();
 324 #endif
 325         } else
 326                 fatal("bad kex alg %s", k->name);
 327 }
 328
 329 static void
 330 choose_hostkeyalg(Kex *k, char *client, char *server)
 331 {
 332         char *hostkeyalg = match_list(client, server, NULL);
 333         if (hostkeyalg == NULL)
 334                 fatal("no hostkey alg");
 335         k->hostkey_type = key_type_from_name(hostkeyalg);
 336         if (k->hostkey_type == KEY_UNSPEC)
 337                 fatal("bad hostkey alg '%s'", hostkeyalg);
 338         xfree(hostkeyalg);
 339 }
 340
 341 static int
 342 proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX])
 343 {
 344         static int check[] = {
 345                 PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1
 346         };
 347         int *idx;
 348         char *p;
 349
 350         for (idx = &check[0]; *idx != -1; idx++) {
 351                 if ((p = strchr(my[*idx], ',')) != NULL)
 352                         *p = '\0';
 353                 if ((p = strchr(peer[*idx], ',')) != NULL)
 354                         *p = '\0';
 355                 if (strcmp(my[*idx], peer[*idx]) != 0) {
 356                         debug2("proposal mismatch: my %s peer %s",
 357                             my[*idx], peer[*idx]);
 358                         return (0);
 359                 }
 360         }
 361         debug2("proposals match");
 362         return (1);
 363 }
 364
 365 static void
 366 kex_choose_conf(Kex *kex)
 367 {
 368         Newkeys *newkeys;
 369         char **my, **peer;
 370         char **cprop, **sprop;
 371         int nenc, nmac, ncomp;
 372         u_int mode, ctos, need;
 373         int first_kex_follows, type;
 374
 375         my   = kex_buf2prop(&kex->my, NULL);
 376         peer = kex_buf2prop(&kex->peer, &first_kex_follows);
 377
 378         if (kex->server) {
 379                 cprop=peer;
 380                 sprop=my;
 381         } else {
 382                 cprop=my;
 383                 sprop=peer;
 384         }
 385
 386         /* Algorithm Negotiation */
 387         for (mode = 0; mode < MODE_MAX; mode++) {
 388                 newkeys = xcalloc(1, sizeof(*newkeys));
 389                 kex->newkeys[mode] = newkeys;
 390                 ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN);
 391                 nenc  = ctos ? PROPOSAL_ENC_ALGS_CTOS  : PROPOSAL_ENC_ALGS_STOC;
 392                 nmac  = ctos ? PROPOSAL_MAC_ALGS_CTOS  : PROPOSAL_MAC_ALGS_STOC;
 393                 ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC;
 394                 choose_enc (&newkeys->enc,  cprop[nenc],  sprop[nenc]);
 395                 choose_mac (&newkeys->mac,  cprop[nmac],  sprop[nmac]);
 396                 choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]);
 397                 debug("kex: %s %s %s %s",
 398                     ctos ? "client->server" : "server->client",
 399                     newkeys->enc.name,
 400                     newkeys->mac.name,
 401                     newkeys->comp.name);
 402         }
 403         choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]);
 404         choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
 405             sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]);
 406         need = 0;
 407         for (mode = 0; mode < MODE_MAX; mode++) {
 408                 newkeys = kex->newkeys[mode];
 409                 if (need < newkeys->enc.key_len)
 410                         need = newkeys->enc.key_len;
 411                 if (need < newkeys->enc.block_size)
 412                         need = newkeys->enc.block_size;
 413                 if (need < newkeys->mac.key_len)
 414                         need = newkeys->mac.key_len;
 415         }
 416         /* XXX need runden? */
 417         kex->we_need = need;
 418
 419         /* ignore the next message if the proposals do not match */
 420         if (first_kex_follows && !proposals_match(my, peer) &&
 421             !(datafellows & SSH_BUG_FIRSTKEX)) {
 422                 type = packet_read();
 423                 debug2("skipping next packet (type %u)", type);
 424         }
 425
 426         kex_prop_free(my);
 427         kex_prop_free(peer);
 428 }
 429
 430 static u_char *
 431 derive_key(Kex *kex, int id, u_int need, u_char *hash, u_int hashlen,
 432     BIGNUM *shared_secret)
 433 {
 434         Buffer b;
 435         EVP_MD_CTX md;
 436         char c = id;
 437         u_int have;
 438         int mdsz;
 439         u_char *digest;
 440
 441         if ((mdsz = EVP_MD_size(kex->evp_md)) <= 0)
 442                 fatal("bad kex md size %d", mdsz);
 443         digest = xmalloc(roundup(need, mdsz));
 444
 445         buffer_init(&b);
 446         buffer_put_bignum2(&b, shared_secret);
 447
 448         /* K1 = HASH(K || H || "A" || session_id) */
 449         EVP_DigestInit(&md, kex->evp_md);
 450         if (!(datafellows & SSH_BUG_DERIVEKEY))
 451                 EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
 452         EVP_DigestUpdate(&md, hash, hashlen);
 453         EVP_DigestUpdate(&md, &c, 1);
 454         EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len);
 455         EVP_DigestFinal(&md, digest, NULL);
 456
 457         /*
 458          * expand key:
 459          * Kn = HASH(K || H || K1 || K2 || ... || Kn-1)
 460          * Key = K1 || K2 || ... || Kn
 461          */
 462         for (have = mdsz; need > have; have += mdsz) {
 463                 EVP_DigestInit(&md, kex->evp_md);
 464                 if (!(datafellows & SSH_BUG_DERIVEKEY))
 465                         EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
 466                 EVP_DigestUpdate(&md, hash, hashlen);
 467                 EVP_DigestUpdate(&md, digest, have);
 468                 EVP_DigestFinal(&md, digest + have, NULL);
 469         }
 470         buffer_free(&b);
 471 #ifdef DEBUG_KEX
 472         fprintf(stderr, "key '%c'== ", c);
 473         dump_digest("key", digest, need);
 474 #endif
 475         return digest;
 476 }
 477
 478 Newkeys *current_keys[MODE_MAX];
 479
 480 #define NKEYS   6
 481 void
 482 kex_derive_keys(Kex *kex, u_char *hash, u_int hashlen, BIGNUM *shared_secret)
 483 {
 484         u_char *keys[NKEYS];
 485         u_int i, mode, ctos;
 486
 487         for (i = 0; i < NKEYS; i++) {
 488                 keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, hashlen,
 489                     shared_secret);
 490         }
 491
 492         debug2("kex_derive_keys");
 493         for (mode = 0; mode < MODE_MAX; mode++) {
 494                 current_keys[mode] = kex->newkeys[mode];
 495                 kex->newkeys[mode] = NULL;
 496                 ctos = (!kex->server && mode == MODE_OUT) ||
 497                     (kex->server && mode == MODE_IN);
 498                 current_keys[mode]->enc.iv  = keys[ctos ? 0 : 1];
 499                 current_keys[mode]->enc.key = keys[ctos ? 2 : 3];
 500                 current_keys[mode]->mac.key = keys[ctos ? 4 : 5];
 501         }
 502 }
 503
 504 Newkeys *
 505 kex_get_newkeys(int mode)
 506 {
 507         Newkeys *ret;
 508
 509         ret = current_keys[mode];
 510         current_keys[mode] = NULL;
 511         return ret;
 512 }
 513
 514 void
 515 derive_ssh1_session_id(BIGNUM *host_modulus, BIGNUM *server_modulus,
 516     u_int8_t cookie[8], u_int8_t id[16])
 517 {
 518         const EVP_MD *evp_md = EVP_md5();
 519         EVP_MD_CTX md;
 520         u_int8_t nbuf[2048], obuf[EVP_MAX_MD_SIZE];
 521         int len;
 522
 523         EVP_DigestInit(&md, evp_md);
 524
 525         len = BN_num_bytes(host_modulus);
 526         if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
 527                 fatal("%s: bad host modulus (len %d)", __func__, len);
 528         BN_bn2bin(host_modulus, nbuf);
 529         EVP_DigestUpdate(&md, nbuf, len);
 530
 531         len = BN_num_bytes(server_modulus);
 532         if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
 533                 fatal("%s: bad server modulus (len %d)", __func__, len);
 534         BN_bn2bin(server_modulus, nbuf);
 535         EVP_DigestUpdate(&md, nbuf, len);
 536
 537         EVP_DigestUpdate(&md, cookie, 8);
 538
 539         EVP_DigestFinal(&md, obuf, NULL);
 540         memcpy(id, obuf, 16);
 541
 542         memset(nbuf, 0, sizeof(nbuf));
 543         memset(obuf, 0, sizeof(obuf));
 544         memset(&md, 0, sizeof(md));
 545 }
 546
 547 #if defined(DEBUG_KEX) || defined(DEBUG_KEXDH)
 548 void
 549 dump_digest(char *msg, u_char *digest, int len)
 550 {
 551         u_int i;
 552
 553         fprintf(stderr, "%s\n", msg);
 554         for (i = 0; i< len; i++) {
 555                 fprintf(stderr, "%02x", digest[i]);
 556                 if (i%32 == 31)
 557                         fprintf(stderr, "\n");
 558                 else if (i%8 == 7)
 559                         fprintf(stderr, " ");
 560         }
 561         fprintf(stderr, "\n");
 562 }
 563 #endif