auth2-jpake.c

   1 /* $OpenBSD: auth2-jpake.c,v 1.3 2009/03/05 07:18:19 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         default:
 166                 fatal("%s: unknown key type %d", __func__, k->type);
 167         }
 168         if (hash_buffer(buffer_ptr(&b), buffer_len(&b), EVP_sha256(),
 169             &digest, &digest_len) != 0)
 170                 fatal("%s: hash_buffer", __func__);
 171         buffer_free(&b);
 172         if (len > digest_len)
 173                 fatal("%s: not enough bytes for rawsalt (want %u have %u)",
 174                     __func__, len, digest_len);
 175         memcpy(rawsalt, digest, len);
 176         bzero(digest, digest_len);
 177         xfree(digest);
 178 }
 179
 180 /* ASCII an integer [0, 64) for inclusion in a password/salt */
 181 static char
 182 pw_encode64(u_int i64)
 183 {
 184         const u_char e64[] =
 185             "./0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
 186         return e64[i64 % 64];
 187 }
 188
 189 /* Generate ASCII salt bytes for user */
 190 static char *
 191 makesalt(u_int want, const char *user)
 192 {
 193         u_char rawsalt[32];
 194         static char ret[33];
 195         u_int i;
 196
 197         if (want > sizeof(ret) - 1)
 198                 fatal("%s: want %u", __func__, want);
 199
 200         derive_rawsalt(user, rawsalt, sizeof(rawsalt));
 201         bzero(ret, sizeof(ret));
 202         for (i = 0; i < want; i++)
 203                 ret[i] = pw_encode64(rawsalt[i]);
 204         bzero(rawsalt, sizeof(rawsalt));
 205
 206         return ret;
 207 }
 208
 209 /*
 210  * Select the system's default password hashing scheme and generate
 211  * a stable fake salt under it for use by a non-existent account.
 212  * Prevents jpake method being used to infer the validity of accounts.
 213  */
 214 static void
 215 fake_salt_and_scheme(Authctxt *authctxt, char **salt, char **scheme)
 216 {
 217         char *rounds_s, *style;
 218         long long rounds;
 219         login_cap_t *lc;
 220
 221
 222         if ((lc = login_getclass(authctxt->pw->pw_class)) == NULL &&
 223             (lc = login_getclass(NULL)) == NULL)
 224                 fatal("%s: login_getclass failed", __func__);
 225         style = login_getcapstr(lc, "localcipher", NULL, NULL);
 226         if (style == NULL)
 227                 style = xstrdup("blowfish,6");
 228         login_close(lc);
 229
 230         if ((rounds_s = strchr(style, ',')) != NULL)
 231                 *rounds_s++ = '\0';
 232         rounds = strtonum(rounds_s, 1, 1<<31, NULL);
 233
 234         if (strcmp(style, "md5") == 0) {
 235                 xasprintf(salt, "$1$%s$", makesalt(8, authctxt->user));
 236                 *scheme = xstrdup("md5");
 237         } else if (strcmp(style, "old") == 0) {
 238                 *salt = xstrdup(makesalt(2, authctxt->user));
 239                 *scheme = xstrdup("crypt");
 240         } else if (strcmp(style, "newsalt") == 0) {
 241                 rounds = MAX(rounds, 7250);
 242                 rounds = MIN(rounds, (1<<24) - 1);
 243                 xasprintf(salt, "_%c%c%c%c%s",
 244                     pw_encode64(rounds), pw_encode64(rounds >> 6),
 245                     pw_encode64(rounds >> 12), pw_encode64(rounds >> 18),
 246                     makesalt(4, authctxt->user));
 247                 *scheme = xstrdup("crypt-extended");
 248         } else {
 249                 /* Default to blowfish */
 250                 rounds = MAX(rounds, 3);
 251                 rounds = MIN(rounds, 31);
 252                 xasprintf(salt, "$2a$%02lld$%s", rounds,
 253                     makesalt(22, authctxt->user));
 254                 *scheme = xstrdup("bcrypt");
 255         }
 256         xfree(style);
 257         debug3("%s: fake %s salt for user %s: %s",
 258             __func__, *scheme, authctxt->user, *salt);
 259 }
 260
 261 /*
 262  * Fetch password hashing scheme, password salt and derive shared secret
 263  * for user. If user does not exist, a fake but stable and user-unique
 264  * salt will be returned.
 265  */
 266 void
 267 auth2_jpake_get_pwdata(Authctxt *authctxt, BIGNUM **s,
 268     char **hash_scheme, char **salt)
 269 {
 270         char *cp;
 271         u_char *secret;
 272         u_int secret_len, salt_len;
 273
 274 #ifdef JPAKE_DEBUG
 275         debug3("%s: valid %d pw %.5s...", __func__,
 276             authctxt->valid, authctxt->pw->pw_passwd);
 277 #endif
 278
 279         *salt = NULL;
 280         *hash_scheme = NULL;
 281         if (authctxt->valid) {
 282                 if (strncmp(authctxt->pw->pw_passwd, "$2$", 3) == 0 &&
 283                     strlen(authctxt->pw->pw_passwd) > 28) {
 284                         /*
 285                          * old-variant bcrypt:
 286                          *     "$2$", 2 digit rounds, "$", 22 bytes salt
 287                          */
 288                         salt_len = 3 + 2 + 1 + 22 + 1;
 289                         *salt = xmalloc(salt_len);
 290                         strlcpy(*salt, authctxt->pw->pw_passwd, salt_len);
 291                         *hash_scheme = xstrdup("bcrypt");
 292                 } else if (strncmp(authctxt->pw->pw_passwd, "$2a$", 4) == 0 &&
 293                     strlen(authctxt->pw->pw_passwd) > 29) {
 294                         /*
 295                          * current-variant bcrypt:
 296                          *     "$2a$", 2 digit rounds, "$", 22 bytes salt
 297                          */
 298                         salt_len = 4 + 2 + 1 + 22 + 1;
 299                         *salt = xmalloc(salt_len);
 300                         strlcpy(*salt, authctxt->pw->pw_passwd, salt_len);
 301                         *hash_scheme = xstrdup("bcrypt");
 302                 } else if (strncmp(authctxt->pw->pw_passwd, "$1$", 3) == 0 &&
 303                     strlen(authctxt->pw->pw_passwd) > 5) {
 304                         /*
 305                          * md5crypt:
 306                          *     "$1$", salt until "$"
 307                          */
 308                         cp = strchr(authctxt->pw->pw_passwd + 3, '$');
 309                         if (cp != NULL) {
 310                                 salt_len = (cp - authctxt->pw->pw_passwd) + 1;
 311                                 *salt = xmalloc(salt_len);
 312                                 strlcpy(*salt, authctxt->pw->pw_passwd,
 313                                     salt_len);
 314                                 *hash_scheme = xstrdup("md5crypt");
 315                         }
 316                 } else if (strncmp(authctxt->pw->pw_passwd, "_", 1) == 0 &&
 317                     strlen(authctxt->pw->pw_passwd) > 9) {
 318                         /*
 319                          * BSDI extended crypt:
 320                          *     "_", 4 digits count, 4 chars salt
 321                          */
 322                         salt_len = 1 + 4 + 4 + 1;
 323                         *salt = xmalloc(salt_len);
 324                         strlcpy(*salt, authctxt->pw->pw_passwd, salt_len);
 325                         *hash_scheme = xstrdup("crypt-extended");
 326                 } else if (strlen(authctxt->pw->pw_passwd) == 13  &&
 327                     valid_crypt_salt(authctxt->pw->pw_passwd[0]) &&
 328                     valid_crypt_salt(authctxt->pw->pw_passwd[1])) {
 329                         /*
 330                          * traditional crypt:
 331                          *     2 chars salt
 332                          */
 333                         salt_len = 2 + 1;
 334                         *salt = xmalloc(salt_len);
 335                         strlcpy(*salt, authctxt->pw->pw_passwd, salt_len);
 336                         *hash_scheme = xstrdup("crypt");
 337                 }
 338                 if (*salt == NULL) {
 339                         debug("%s: unrecognised crypt scheme for user %s",
 340                             __func__, authctxt->pw->pw_name);
 341                 }
 342         }
 343         if (*salt == NULL)
 344                 fake_salt_and_scheme(authctxt, salt, hash_scheme);
 345
 346         if (hash_buffer(authctxt->pw->pw_passwd,
 347             strlen(authctxt->pw->pw_passwd), EVP_sha256(),
 348             &secret, &secret_len) != 0)
 349                 fatal("%s: hash_buffer", __func__);
 350         if ((*s = BN_bin2bn(secret, secret_len, NULL)) == NULL)
 351                 fatal("%s: BN_bin2bn (secret)", __func__);
 352 #ifdef JPAKE_DEBUG
 353         debug3("%s: salt = %s (len %u)", __func__,
 354             *salt, (u_int)strlen(*salt));
 355         debug3("%s: scheme = %s", __func__, *hash_scheme);
 356         JPAKE_DEBUG_BN((*s, "%s: s = ", __func__));
 357 #endif
 358         bzero(secret, secret_len);
 359         xfree(secret);
 360 }
 361
 362 /*
 363  * Begin authentication attempt.
 364  * Note, sets authctxt->postponed while in subprotocol
 365  */
 366 static int
 367 auth2_jpake_start(Authctxt *authctxt)
 368 {
 369         struct jpake_ctx *pctx = authctxt->jpake_ctx;
 370         u_char *x3_proof, *x4_proof;
 371         u_int x3_proof_len, x4_proof_len;
 372         char *salt, *hash_scheme;
 373
 374         debug("%s: start", __func__);
 375
 376         PRIVSEP(jpake_step1(pctx->grp,
 377             &pctx->server_id, &pctx->server_id_len,
 378             &pctx->x3, &pctx->x4, &pctx->g_x3, &pctx->g_x4,
 379             &x3_proof, &x3_proof_len,
 380             &x4_proof, &x4_proof_len));
 381
 382         PRIVSEP(auth2_jpake_get_pwdata(authctxt, &pctx->s,
 383             &hash_scheme, &salt));
 384
 385         if (!use_privsep)
 386                 JPAKE_DEBUG_CTX((pctx, "step 1 sending in %s", __func__));
 387
 388         packet_start(SSH2_MSG_USERAUTH_JPAKE_SERVER_STEP1);
 389         packet_put_cstring(hash_scheme);
 390         packet_put_cstring(salt);
 391         packet_put_string(pctx->server_id, pctx->server_id_len);
 392         packet_put_bignum2(pctx->g_x3);
 393         packet_put_bignum2(pctx->g_x4);
 394         packet_put_string(x3_proof, x3_proof_len);
 395         packet_put_string(x4_proof, x4_proof_len);
 396         packet_send();
 397         packet_write_wait();
 398
 399         bzero(hash_scheme, strlen(hash_scheme));
 400         bzero(salt, strlen(salt));
 401         xfree(hash_scheme);
 402         xfree(salt);
 403         bzero(x3_proof, x3_proof_len);
 404         bzero(x4_proof, x4_proof_len);
 405         xfree(x3_proof);
 406         xfree(x4_proof);
 407
 408         /* Expect step 1 packet from peer */
 409         dispatch_set(SSH2_MSG_USERAUTH_JPAKE_CLIENT_STEP1,
 410             input_userauth_jpake_client_step1);
 411
 412         authctxt->postponed = 1;
 413         return 0;
 414 }
 415
 416 /* ARGSUSED */
 417 static void
 418 input_userauth_jpake_client_step1(int type, u_int32_t seq, void *ctxt)
 419 {
 420         Authctxt *authctxt = ctxt;
 421         struct jpake_ctx *pctx = authctxt->jpake_ctx;
 422         u_char *x1_proof, *x2_proof, *x4_s_proof;
 423         u_int x1_proof_len, x2_proof_len, x4_s_proof_len;
 424
 425         /* Disable this message */
 426         dispatch_set(SSH2_MSG_USERAUTH_JPAKE_CLIENT_STEP1, NULL);
 427
 428         /* Fetch step 1 values */
 429         if ((pctx->g_x1 = BN_new()) == NULL ||
 430             (pctx->g_x2 = BN_new()) == NULL)
 431                 fatal("%s: BN_new", __func__);
 432         pctx->client_id = packet_get_string(&pctx->client_id_len);
 433         packet_get_bignum2(pctx->g_x1);
 434         packet_get_bignum2(pctx->g_x2);
 435         x1_proof = packet_get_string(&x1_proof_len);
 436         x2_proof = packet_get_string(&x2_proof_len);
 437         packet_check_eom();
 438
 439         if (!use_privsep)
 440                 JPAKE_DEBUG_CTX((pctx, "step 1 received in %s", __func__));
 441
 442         PRIVSEP(jpake_step2(pctx->grp, pctx->s, pctx->g_x3,
 443             pctx->g_x1, pctx->g_x2, pctx->x4,
 444             pctx->client_id, pctx->client_id_len,
 445             pctx->server_id, pctx->server_id_len,
 446             x1_proof, x1_proof_len,
 447             x2_proof, x2_proof_len,
 448             &pctx->b,
 449             &x4_s_proof, &x4_s_proof_len));
 450
 451         bzero(x1_proof, x1_proof_len);
 452         bzero(x2_proof, x2_proof_len);
 453         xfree(x1_proof);
 454         xfree(x2_proof);
 455
 456         if (!use_privsep)
 457                 JPAKE_DEBUG_CTX((pctx, "step 2 sending in %s", __func__));
 458
 459         /* Send values for step 2 */
 460         packet_start(SSH2_MSG_USERAUTH_JPAKE_SERVER_STEP2);
 461         packet_put_bignum2(pctx->b);
 462         packet_put_string(x4_s_proof, x4_s_proof_len);
 463         packet_send();
 464         packet_write_wait();
 465
 466         bzero(x4_s_proof, x4_s_proof_len);
 467         xfree(x4_s_proof);
 468
 469         /* Expect step 2 packet from peer */
 470         dispatch_set(SSH2_MSG_USERAUTH_JPAKE_CLIENT_STEP2,
 471             input_userauth_jpake_client_step2);
 472 }
 473
 474 /* ARGSUSED */
 475 static void
 476 input_userauth_jpake_client_step2(int type, u_int32_t seq, void *ctxt)
 477 {
 478         Authctxt *authctxt = ctxt;
 479         struct jpake_ctx *pctx = authctxt->jpake_ctx;
 480         u_char *x2_s_proof;
 481         u_int x2_s_proof_len;
 482
 483         /* Disable this message */
 484         dispatch_set(SSH2_MSG_USERAUTH_JPAKE_CLIENT_STEP2, NULL);
 485
 486         if ((pctx->a = BN_new()) == NULL)
 487                 fatal("%s: BN_new", __func__);
 488
 489         /* Fetch step 2 values */
 490         packet_get_bignum2(pctx->a);
 491         x2_s_proof = packet_get_string(&x2_s_proof_len);
 492         packet_check_eom();
 493
 494         if (!use_privsep)
 495                 JPAKE_DEBUG_CTX((pctx, "step 2 received in %s", __func__));
 496
 497         /* Derive shared key and calculate confirmation hash */
 498         PRIVSEP(jpake_key_confirm(pctx->grp, pctx->s, pctx->a,
 499             pctx->x4, pctx->g_x3, pctx->g_x4, pctx->g_x1, pctx->g_x2,
 500             pctx->server_id, pctx->server_id_len,
 501             pctx->client_id, pctx->client_id_len,
 502             session_id2, session_id2_len,
 503             x2_s_proof, x2_s_proof_len,
 504             &pctx->k,
 505             &pctx->h_k_sid_sessid, &pctx->h_k_sid_sessid_len));
 506
 507         bzero(x2_s_proof, x2_s_proof_len);
 508         xfree(x2_s_proof);
 509
 510         if (!use_privsep)
 511                 JPAKE_DEBUG_CTX((pctx, "confirm sending in %s", __func__));
 512
 513         /* Send key confirmation proof */
 514         packet_start(SSH2_MSG_USERAUTH_JPAKE_SERVER_CONFIRM);
 515         packet_put_string(pctx->h_k_sid_sessid, pctx->h_k_sid_sessid_len);
 516         packet_send();
 517         packet_write_wait();
 518
 519         /* Expect confirmation from peer */
 520         dispatch_set(SSH2_MSG_USERAUTH_JPAKE_CLIENT_CONFIRM,
 521             input_userauth_jpake_client_confirm);
 522 }
 523
 524 /* ARGSUSED */
 525 static void
 526 input_userauth_jpake_client_confirm(int type, u_int32_t seq, void *ctxt)
 527 {
 528         Authctxt *authctxt = ctxt;
 529         struct jpake_ctx *pctx = authctxt->jpake_ctx;
 530         int authenticated = 0;
 531
 532         /* Disable this message */
 533         dispatch_set(SSH2_MSG_USERAUTH_JPAKE_CLIENT_CONFIRM, NULL);
 534
 535         pctx->h_k_cid_sessid = packet_get_string(&pctx->h_k_cid_sessid_len);
 536         packet_check_eom();
 537
 538         if (!use_privsep)
 539                 JPAKE_DEBUG_CTX((pctx, "confirm received in %s", __func__));
 540
 541         /* Verify expected confirmation hash */
 542         if (PRIVSEP(jpake_check_confirm(pctx->k,
 543             pctx->client_id, pctx->client_id_len,
 544             session_id2, session_id2_len,
 545             pctx->h_k_cid_sessid, pctx->h_k_cid_sessid_len)) == 1)
 546                 authenticated = authctxt->valid ? 1 : 0;
 547         else
 548                 debug("%s: confirmation mismatch", __func__);
 549
 550         /* done */
 551         authctxt->postponed = 0;
 552         jpake_free(authctxt->jpake_ctx);
 553         authctxt->jpake_ctx = NULL;
 554         userauth_finish(authctxt, authenticated, method_jpake.name);
 555 }
 556
 557 #endif /* JPAKE */
 558