auth2-jpake.c

   1 /* $OpenBSD: auth2-jpake.c,v 1.4 2010/08/31 11:54:45 djm Exp $ */
   2 /*
   3  * Copyright (c) 2008 Damien Miller.  All rights reserved.
   4  *
   5  * Permission to use, copy, modify, and distribute this software for any
   6  * purpose with or without fee is hereby granted, provided that the above
   7  * copyright notice and this permission notice appear in all copies.
   8  *
   9  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
  10  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
  11  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
  12  * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
  13  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
  14  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
  15  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  16  */
  17
  18 /*
  19  * Server side of zero-knowledge password auth using J-PAKE protocol
  20  * as described in:
  21  *
  22  * F. Hao, P. Ryan, "Password Authenticated Key Exchange by Juggling",
  23  * 16th Workshop on Security Protocols, Cambridge, April 2008
  24  *
  25  * http://grouper.ieee.org/groups/1363/Research/contributions/hao-ryan-2008.pdf
  26  */
  27
  28 #ifdef JPAKE
  29
  30 #include <sys/types.h>
  31 #include <sys/param.h>
  32
  33 #include <pwd.h>
  34 #include <stdio.h>
  35 #include <string.h>
  36 #include <login_cap.h>
  37
  38 #include <openssl/bn.h>
  39 #include <openssl/evp.h>
  40
  41 #include "xmalloc.h"
  42 #include "ssh2.h"
  43 #include "key.h"
  44 #include "hostfile.h"
  45 #include "auth.h"
  46 #include "buffer.h"
  47 #include "packet.h"
  48 #include "dispatch.h"
  49 #include "log.h"
  50 #include "servconf.h"
  51 #include "auth-options.h"
  52 #include "canohost.h"
  53 #ifdef GSSAPI
  54 #include "ssh-gss.h"
  55 #endif
  56 #include "monitor_wrap.h"
  57
  58 #include "schnorr.h"
  59 #include "jpake.h"
  60
  61 /*
  62  * XXX options->permit_empty_passwd (at the moment, they will be refused
  63  * anyway because they will mismatch on fake salt.
  64  */
  65
  66 /* Dispatch handlers */
  67 static void input_userauth_jpake_client_step1(int, u_int32_t, void *);
  68 static void input_userauth_jpake_client_step2(int, u_int32_t, void *);
  69 static void input_userauth_jpake_client_confirm(int, u_int32_t, void *);
  70
  71 static int auth2_jpake_start(Authctxt *);
  72
  73 /* import */
  74 extern ServerOptions options;
  75 extern u_char *session_id2;
  76 extern u_int session_id2_len;
  77
  78 /*
  79  * Attempt J-PAKE authentication.
  80  */
  81 static int
  82 userauth_jpake(Authctxt *authctxt)
  83 {
  84         int authenticated = 0;
  85
  86         packet_check_eom();
  87
  88         debug("jpake-01@openssh.com requested");
  89
  90         if (authctxt->user != NULL) {
  91                 if (authctxt->jpake_ctx == NULL)
  92                         authctxt->jpake_ctx = jpake_new();
  93                 if (options.zero_knowledge_password_authentication)
  94                         authenticated = auth2_jpake_start(authctxt);
  95         }
  96
  97         return authenticated;
  98 }
  99
 100 Authmethod method_jpake = {
 101         "jpake-01@openssh.com",
 102         userauth_jpake,
 103         &options.zero_knowledge_password_authentication
 104 };
 105
 106 /* Clear context and callbacks */
 107 void
 108 auth2_jpake_stop(Authctxt *authctxt)
 109 {
 110         /* unregister callbacks */
 111         dispatch_set(SSH2_MSG_USERAUTH_JPAKE_CLIENT_STEP1, NULL);
 112         dispatch_set(SSH2_MSG_USERAUTH_JPAKE_CLIENT_STEP2, NULL);
 113         dispatch_set(SSH2_MSG_USERAUTH_JPAKE_CLIENT_CONFIRM, NULL);
 114         if (authctxt->jpake_ctx != NULL) {
 115                 jpake_free(authctxt->jpake_ctx);
 116                 authctxt->jpake_ctx = NULL;
 117         }
 118 }
 119
 120 /* Returns 1 if 'c' is a valid crypt(3) salt character, 0 otherwise */
 121 static int
 122 valid_crypt_salt(int c)
 123 {
 124         if (c >= 'A' && c <= 'Z')
 125                 return 1;
 126         if (c >= 'a' && c <= 'z')
 127                 return 1;
 128         if (c >= '.' && c <= '9')
 129                 return 1;
 130         return 0;
 131 }
 132
 133 /*
 134  * Derive fake salt as H(username || first_private_host_key)
 135  * This provides relatively stable fake salts for non-existent
 136  * users and avoids the jpake method becoming an account validity
 137  * oracle.
 138  */
 139 static void
 140 derive_rawsalt(const char *username, u_char *rawsalt, u_int len)
 141 {
 142         u_char *digest;
 143         u_int digest_len;
 144         Buffer b;
 145         Key *k;
 146
 147         buffer_init(&b);
 148         buffer_put_cstring(&b, username);
 149         if ((k = get_hostkey_by_index(0)) == NULL ||
 150             (k->flags & KEY_FLAG_EXT))
 151                 fatal("%s: no hostkeys", __func__);
 152         switch (k->type) {
 153         case KEY_RSA1:
 154         case KEY_RSA:
 155                 if (k->rsa->p == NULL || k->rsa->q == NULL)
 156                         fatal("%s: RSA key missing p and/or q", __func__);
 157                 buffer_put_bignum2(&b, k->rsa->p);
 158                 buffer_put_bignum2(&b, k->rsa->q);
 159                 break;
 160         case KEY_DSA:
 161                 if (k->dsa->priv_key == NULL)
 162                         fatal("%s: DSA key missing priv_key", __func__);
 163                 buffer_put_bignum2(&b, k->dsa->priv_key);
 164                 break;
 165         case KEY_ECDSA:
 166                 if (EC_KEY_get0_private_key(k->ecdsa) == NULL)
 167                         fatal("%s: ECDSA key missing priv_key", __func__);
 168                 buffer_put_bignum2(&b, EC_KEY_get0_private_key(k->ecdsa));
 169                 break;
 170         default:
 171                 fatal("%s: unknown key type %d", __func__, k->type);
 172         }
 173         if (hash_buffer(buffer_ptr(&b), buffer_len(&b), EVP_sha256(),
 174             &digest, &digest_len) != 0)
 175                 fatal("%s: hash_buffer", __func__);
 176         buffer_free(&b);
 177         if (len > digest_len)
 178                 fatal("%s: not enough bytes for rawsalt (want %u have %u)",
 179                     __func__, len, digest_len);
 180         memcpy(rawsalt, digest, len);
 181         bzero(digest, digest_len);
 182         xfree(digest);
 183 }
 184
 185 /* ASCII an integer [0, 64) for inclusion in a password/salt */
 186 static char
 187 pw_encode64(u_int i64)
 188 {
 189         const u_char e64[] =
 190             "./0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
 191         return e64[i64 % 64];
 192 }
 193
 194 /* Generate ASCII salt bytes for user */
 195 static char *
 196 makesalt(u_int want, const char *user)
 197 {
 198         u_char rawsalt[32];
 199         static char ret[33];
 200         u_int i;
 201
 202         if (want > sizeof(ret) - 1)
 203                 fatal("%s: want %u", __func__, want);
 204
 205         derive_rawsalt(user, rawsalt, sizeof(rawsalt));
 206         bzero(ret, sizeof(ret));
 207         for (i = 0; i < want; i++)
 208                 ret[i] = pw_encode64(rawsalt[i]);
 209         bzero(rawsalt, sizeof(rawsalt));
 210
 211         return ret;
 212 }
 213
 214 /*
 215  * Select the system's default password hashing scheme and generate
 216  * a stable fake salt under it for use by a non-existent account.
 217  * Prevents jpake method being used to infer the validity of accounts.
 218  */
 219 static void
 220 fake_salt_and_scheme(Authctxt *authctxt, char **salt, char **scheme)
 221 {
 222         char *rounds_s, *style;
 223         long long rounds;
 224         login_cap_t *lc;
 225
 226
 227         if ((lc = login_getclass(authctxt->pw->pw_class)) == NULL &&
 228             (lc = login_getclass(NULL)) == NULL)
 229                 fatal("%s: login_getclass failed", __func__);
 230         style = login_getcapstr(lc, "localcipher", NULL, NULL);
 231         if (style == NULL)
 232                 style = xstrdup("blowfish,6");
 233         login_close(lc);
 234
 235         if ((rounds_s = strchr(style, ',')) != NULL)
 236                 *rounds_s++ = '\0';
 237         rounds = strtonum(rounds_s, 1, 1<<31, NULL);
 238
 239         if (strcmp(style, "md5") == 0) {
 240                 xasprintf(salt, "$1$%s$", makesalt(8, authctxt->user));
 241                 *scheme = xstrdup("md5");
 242         } else if (strcmp(style, "old") == 0) {
 243                 *salt = xstrdup(makesalt(2, authctxt->user));
 244                 *scheme = xstrdup("crypt");
 245         } else if (strcmp(style, "newsalt") == 0) {
 246                 rounds = MAX(rounds, 7250);
 247                 rounds = MIN(rounds, (1<<24) - 1);
 248                 xasprintf(salt, "_%c%c%c%c%s",
 249                     pw_encode64(rounds), pw_encode64(rounds >> 6),
 250                     pw_encode64(rounds >> 12), pw_encode64(rounds >> 18),
 251                     makesalt(4, authctxt->user));
 252                 *scheme = xstrdup("crypt-extended");
 253         } else {
 254                 /* Default to blowfish */
 255                 rounds = MAX(rounds, 3);
 256                 rounds = MIN(rounds, 31);
 257                 xasprintf(salt, "$2a$%02lld$%s", rounds,
 258                     makesalt(22, authctxt->user));
 259                 *scheme = xstrdup("bcrypt");
 260         }
 261         xfree(style);
 262         debug3("%s: fake %s salt for user %s: %s",
 263             __func__, *scheme, authctxt->user, *salt);
 264 }
 265
 266 /*
 267  * Fetch password hashing scheme, password salt and derive shared secret
 268  * for user. If user does not exist, a fake but stable and user-unique
 269  * salt will be returned.
 270  */
 271 void
 272 auth2_jpake_get_pwdata(Authctxt *authctxt, BIGNUM **s,
 273     char **hash_scheme, char **salt)
 274 {
 275         char *cp;
 276         u_char *secret;
 277         u_int secret_len, salt_len;
 278
 279 #ifdef JPAKE_DEBUG
 280         debug3("%s: valid %d pw %.5s...", __func__,
 281             authctxt->valid, authctxt->pw->pw_passwd);
 282 #endif
 283
 284         *salt = NULL;
 285         *hash_scheme = NULL;
 286         if (authctxt->valid) {
 287                 if (strncmp(authctxt->pw->pw_passwd, "$2$", 3) == 0 &&
 288                     strlen(authctxt->pw->pw_passwd) > 28) {
 289                         /*
 290                          * old-variant bcrypt:
 291                          *     "$2$", 2 digit rounds, "$", 22 bytes salt
 292                          */
 293                         salt_len = 3 + 2 + 1 + 22 + 1;
 294                         *salt = xmalloc(salt_len);
 295                         strlcpy(*salt, authctxt->pw->pw_passwd, salt_len);
 296                         *hash_scheme = xstrdup("bcrypt");
 297                 } else if (strncmp(authctxt->pw->pw_passwd, "$2a$", 4) == 0 &&
 298                     strlen(authctxt->pw->pw_passwd) > 29) {
 299                         /*
 300                          * current-variant bcrypt:
 301                          *     "$2a$", 2 digit rounds, "$", 22 bytes salt
 302                          */
 303                         salt_len = 4 + 2 + 1 + 22 + 1;
 304                         *salt = xmalloc(salt_len);
 305                         strlcpy(*salt, authctxt->pw->pw_passwd, salt_len);
 306                         *hash_scheme = xstrdup("bcrypt");
 307                 } else if (strncmp(authctxt->pw->pw_passwd, "$1$", 3) == 0 &&
 308                     strlen(authctxt->pw->pw_passwd) > 5) {
 309                         /*
 310                          * md5crypt:
 311                          *     "$1$", salt until "$"
 312                          */
 313                         cp = strchr(authctxt->pw->pw_passwd + 3, '$');
 314                         if (cp != NULL) {
 315                                 salt_len = (cp - authctxt->pw->pw_passwd) + 1;
 316                                 *salt = xmalloc(salt_len);
 317                                 strlcpy(*salt, authctxt->pw->pw_passwd,
 318                                     salt_len);
 319                                 *hash_scheme = xstrdup("md5crypt");
 320                         }
 321                 } else if (strncmp(authctxt->pw->pw_passwd, "_", 1) == 0 &&
 322                     strlen(authctxt->pw->pw_passwd) > 9) {
 323                         /*
 324                          * BSDI extended crypt:
 325                          *     "_", 4 digits count, 4 chars salt
 326                          */
 327                         salt_len = 1 + 4 + 4 + 1;
 328                         *salt = xmalloc(salt_len);
 329                         strlcpy(*salt, authctxt->pw->pw_passwd, salt_len);
 330                         *hash_scheme = xstrdup("crypt-extended");
 331                 } else if (strlen(authctxt->pw->pw_passwd) == 13  &&
 332                     valid_crypt_salt(authctxt->pw->pw_passwd[0]) &&
 333                     valid_crypt_salt(authctxt->pw->pw_passwd[1])) {
 334                         /*
 335                          * traditional crypt:
 336                          *     2 chars salt
 337                          */
 338                         salt_len = 2 + 1;
 339                         *salt = xmalloc(salt_len);
 340                         strlcpy(*salt, authctxt->pw->pw_passwd, salt_len);
 341                         *hash_scheme = xstrdup("crypt");
 342                 }
 343                 if (*salt == NULL) {
 344                         debug("%s: unrecognised crypt scheme for user %s",
 345                             __func__, authctxt->pw->pw_name);
 346                 }
 347         }
 348         if (*salt == NULL)
 349                 fake_salt_and_scheme(authctxt, salt, hash_scheme);
 350
 351         if (hash_buffer(authctxt->pw->pw_passwd,
 352             strlen(authctxt->pw->pw_passwd), EVP_sha256(),
 353             &secret, &secret_len) != 0)
 354                 fatal("%s: hash_buffer", __func__);
 355         if ((*s = BN_bin2bn(secret, secret_len, NULL)) == NULL)
 356                 fatal("%s: BN_bin2bn (secret)", __func__);
 357 #ifdef JPAKE_DEBUG
 358         debug3("%s: salt = %s (len %u)", __func__,
 359             *salt, (u_int)strlen(*salt));
 360         debug3("%s: scheme = %s", __func__, *hash_scheme);
 361         JPAKE_DEBUG_BN((*s, "%s: s = ", __func__));
 362 #endif
 363         bzero(secret, secret_len);
 364         xfree(secret);
 365 }
 366
 367 /*
 368  * Begin authentication attempt.
 369  * Note, sets authctxt->postponed while in subprotocol
 370  */
 371 static int
 372 auth2_jpake_start(Authctxt *authctxt)
 373 {
 374         struct jpake_ctx *pctx = authctxt->jpake_ctx;
 375         u_char *x3_proof, *x4_proof;
 376         u_int x3_proof_len, x4_proof_len;
 377         char *salt, *hash_scheme;
 378
 379         debug("%s: start", __func__);
 380
 381         PRIVSEP(jpake_step1(pctx->grp,
 382             &pctx->server_id, &pctx->server_id_len,
 383             &pctx->x3, &pctx->x4, &pctx->g_x3, &pctx->g_x4,
 384             &x3_proof, &x3_proof_len,
 385             &x4_proof, &x4_proof_len));
 386
 387         PRIVSEP(auth2_jpake_get_pwdata(authctxt, &pctx->s,
 388             &hash_scheme, &salt));
 389
 390         if (!use_privsep)
 391                 JPAKE_DEBUG_CTX((pctx, "step 1 sending in %s", __func__));
 392
 393         packet_start(SSH2_MSG_USERAUTH_JPAKE_SERVER_STEP1);
 394         packet_put_cstring(hash_scheme);
 395         packet_put_cstring(salt);
 396         packet_put_string(pctx->server_id, pctx->server_id_len);
 397         packet_put_bignum2(pctx->g_x3);
 398         packet_put_bignum2(pctx->g_x4);
 399         packet_put_string(x3_proof, x3_proof_len);
 400         packet_put_string(x4_proof, x4_proof_len);
 401         packet_send();
 402         packet_write_wait();
 403
 404         bzero(hash_scheme, strlen(hash_scheme));
 405         bzero(salt, strlen(salt));
 406         xfree(hash_scheme);
 407         xfree(salt);
 408         bzero(x3_proof, x3_proof_len);
 409         bzero(x4_proof, x4_proof_len);
 410         xfree(x3_proof);
 411         xfree(x4_proof);
 412
 413         /* Expect step 1 packet from peer */
 414         dispatch_set(SSH2_MSG_USERAUTH_JPAKE_CLIENT_STEP1,
 415             input_userauth_jpake_client_step1);
 416
 417         authctxt->postponed = 1;
 418         return 0;
 419 }
 420
 421 /* ARGSUSED */
 422 static void
 423 input_userauth_jpake_client_step1(int type, u_int32_t seq, void *ctxt)
 424 {
 425         Authctxt *authctxt = ctxt;
 426         struct jpake_ctx *pctx = authctxt->jpake_ctx;
 427         u_char *x1_proof, *x2_proof, *x4_s_proof;
 428         u_int x1_proof_len, x2_proof_len, x4_s_proof_len;
 429
 430         /* Disable this message */
 431         dispatch_set(SSH2_MSG_USERAUTH_JPAKE_CLIENT_STEP1, NULL);
 432
 433         /* Fetch step 1 values */
 434         if ((pctx->g_x1 = BN_new()) == NULL ||
 435             (pctx->g_x2 = BN_new()) == NULL)
 436                 fatal("%s: BN_new", __func__);
 437         pctx->client_id = packet_get_string(&pctx->client_id_len);
 438         packet_get_bignum2(pctx->g_x1);
 439         packet_get_bignum2(pctx->g_x2);
 440         x1_proof = packet_get_string(&x1_proof_len);
 441         x2_proof = packet_get_string(&x2_proof_len);
 442         packet_check_eom();
 443
 444         if (!use_privsep)
 445                 JPAKE_DEBUG_CTX((pctx, "step 1 received in %s", __func__));
 446
 447         PRIVSEP(jpake_step2(pctx->grp, pctx->s, pctx->g_x3,
 448             pctx->g_x1, pctx->g_x2, pctx->x4,
 449             pctx->client_id, pctx->client_id_len,
 450             pctx->server_id, pctx->server_id_len,
 451             x1_proof, x1_proof_len,
 452             x2_proof, x2_proof_len,
 453             &pctx->b,
 454             &x4_s_proof, &x4_s_proof_len));
 455
 456         bzero(x1_proof, x1_proof_len);
 457         bzero(x2_proof, x2_proof_len);
 458         xfree(x1_proof);
 459         xfree(x2_proof);
 460
 461         if (!use_privsep)
 462                 JPAKE_DEBUG_CTX((pctx, "step 2 sending in %s", __func__));
 463
 464         /* Send values for step 2 */
 465         packet_start(SSH2_MSG_USERAUTH_JPAKE_SERVER_STEP2);
 466         packet_put_bignum2(pctx->b);
 467         packet_put_string(x4_s_proof, x4_s_proof_len);
 468         packet_send();
 469         packet_write_wait();
 470
 471         bzero(x4_s_proof, x4_s_proof_len);
 472         xfree(x4_s_proof);
 473
 474         /* Expect step 2 packet from peer */
 475         dispatch_set(SSH2_MSG_USERAUTH_JPAKE_CLIENT_STEP2,
 476             input_userauth_jpake_client_step2);
 477 }
 478
 479 /* ARGSUSED */
 480 static void
 481 input_userauth_jpake_client_step2(int type, u_int32_t seq, void *ctxt)
 482 {
 483         Authctxt *authctxt = ctxt;
 484         struct jpake_ctx *pctx = authctxt->jpake_ctx;
 485         u_char *x2_s_proof;
 486         u_int x2_s_proof_len;
 487
 488         /* Disable this message */
 489         dispatch_set(SSH2_MSG_USERAUTH_JPAKE_CLIENT_STEP2, NULL);
 490
 491         if ((pctx->a = BN_new()) == NULL)
 492                 fatal("%s: BN_new", __func__);
 493
 494         /* Fetch step 2 values */
 495         packet_get_bignum2(pctx->a);
 496         x2_s_proof = packet_get_string(&x2_s_proof_len);
 497         packet_check_eom();
 498
 499         if (!use_privsep)
 500                 JPAKE_DEBUG_CTX((pctx, "step 2 received in %s", __func__));
 501
 502         /* Derive shared key and calculate confirmation hash */
 503         PRIVSEP(jpake_key_confirm(pctx->grp, pctx->s, pctx->a,
 504             pctx->x4, pctx->g_x3, pctx->g_x4, pctx->g_x1, pctx->g_x2,
 505             pctx->server_id, pctx->server_id_len,
 506             pctx->client_id, pctx->client_id_len,
 507             session_id2, session_id2_len,
 508             x2_s_proof, x2_s_proof_len,
 509             &pctx->k,
 510             &pctx->h_k_sid_sessid, &pctx->h_k_sid_sessid_len));
 511
 512         bzero(x2_s_proof, x2_s_proof_len);
 513         xfree(x2_s_proof);
 514
 515         if (!use_privsep)
 516                 JPAKE_DEBUG_CTX((pctx, "confirm sending in %s", __func__));
 517
 518         /* Send key confirmation proof */
 519         packet_start(SSH2_MSG_USERAUTH_JPAKE_SERVER_CONFIRM);
 520         packet_put_string(pctx->h_k_sid_sessid, pctx->h_k_sid_sessid_len);
 521         packet_send();
 522         packet_write_wait();
 523
 524         /* Expect confirmation from peer */
 525         dispatch_set(SSH2_MSG_USERAUTH_JPAKE_CLIENT_CONFIRM,
 526             input_userauth_jpake_client_confirm);
 527 }
 528
 529 /* ARGSUSED */
 530 static void
 531 input_userauth_jpake_client_confirm(int type, u_int32_t seq, void *ctxt)
 532 {
 533         Authctxt *authctxt = ctxt;
 534         struct jpake_ctx *pctx = authctxt->jpake_ctx;
 535         int authenticated = 0;
 536
 537         /* Disable this message */
 538         dispatch_set(SSH2_MSG_USERAUTH_JPAKE_CLIENT_CONFIRM, NULL);
 539
 540         pctx->h_k_cid_sessid = packet_get_string(&pctx->h_k_cid_sessid_len);
 541         packet_check_eom();
 542
 543         if (!use_privsep)
 544                 JPAKE_DEBUG_CTX((pctx, "confirm received in %s", __func__));
 545
 546         /* Verify expected confirmation hash */
 547         if (PRIVSEP(jpake_check_confirm(pctx->k,
 548             pctx->client_id, pctx->client_id_len,
 549             session_id2, session_id2_len,
 550             pctx->h_k_cid_sessid, pctx->h_k_cid_sessid_len)) == 1)
 551                 authenticated = authctxt->valid ? 1 : 0;
 552         else
 553                 debug("%s: confirmation mismatch", __func__);
 554
 555         /* done */
 556         authctxt->postponed = 0;
 557         jpake_free(authctxt->jpake_ctx);
 558         authctxt->jpake_ctx = NULL;
 559         userauth_finish(authctxt, authenticated, method_jpake.name);
 560 }
 561
 562 #endif /* JPAKE */
 563