jpake.c

   1 /* $OpenBSD: jpake.c,v 1.2 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  * Shared components 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 #include "includes.h"
  29
  30 #include <sys/types.h>
  31
  32 #include <stdio.h>
  33 #include <string.h>
  34 #include <stdarg.h>
  35
  36 #include <openssl/bn.h>
  37 #include <openssl/evp.h>
  38
  39 #include "xmalloc.h"
  40 #include "ssh2.h"
  41 #include "key.h"
  42 #include "hostfile.h"
  43 #include "auth.h"
  44 #include "buffer.h"
  45 #include "packet.h"
  46 #include "dispatch.h"
  47 #include "log.h"
  48
  49 #include "jpake.h"
  50 #include "schnorr.h"
  51
  52 #ifdef JPAKE
  53
  54 /* RFC3526 group 5, 1536 bits */
  55 #define JPAKE_GROUP_G "2"
  56 #define JPAKE_GROUP_P \
  57         "FFFFFFFFFFFFFFFFC90FDAA22168C234C4C6628B80DC1CD129024E088A67CC74" \
  58         "020BBEA63B139B22514A08798E3404DDEF9519B3CD3A431B302B0A6DF25F1437" \
  59         "4FE1356D6D51C245E485B576625E7EC6F44C42E9A637ED6B0BFF5CB6F406B7ED" \
  60         "EE386BFB5A899FA5AE9F24117C4B1FE649286651ECE45B3DC2007CB8A163BF05" \
  61         "98DA48361C55D39A69163FA8FD24CF5F83655D23DCA3AD961C62F356208552BB" \
  62         "9ED529077096966D670C354E4ABC9804F1746C08CA237327FFFFFFFFFFFFFFFF"
  63
  64 struct modp_group *
  65 jpake_default_group(void)
  66 {
  67         return modp_group_from_g_and_safe_p(JPAKE_GROUP_G, JPAKE_GROUP_P);
  68 }
  69
  70 struct jpake_ctx *
  71 jpake_new(void)
  72 {
  73         struct jpake_ctx *ret;
  74
  75         ret = xcalloc(1, sizeof(*ret));
  76
  77         ret->grp = jpake_default_group();
  78
  79         ret->s = ret->k = NULL;
  80         ret->x1 = ret->x2 = ret->x3 = ret->x4 = NULL;
  81         ret->g_x1 = ret->g_x2 = ret->g_x3 = ret->g_x4 = NULL;
  82         ret->a = ret->b = NULL;
  83
  84         ret->client_id = ret->server_id = NULL;
  85         ret->h_k_cid_sessid = ret->h_k_sid_sessid = NULL;
  86
  87         debug3("%s: alloc %p", __func__, ret);
  88
  89         return ret;
  90 }
  91
  92 void
  93 jpake_free(struct jpake_ctx *pctx)
  94 {
  95         debug3("%s: free %p", __func__, pctx);
  96
  97 #define JPAKE_BN_CLEAR_FREE(v)                  \
  98         do {                                    \
  99                 if ((v) != NULL) {              \
 100                         BN_clear_free(v);       \
 101                         (v) = NULL;             \
 102                 }                               \
 103         } while (0)
 104 #define JPAKE_BUF_CLEAR_FREE(v, l)              \
 105         do {                                    \
 106                 if ((v) != NULL) {              \
 107                         bzero((v), (l));        \
 108                         xfree(v);               \
 109                         (v) = NULL;             \
 110                         (l) = 0;                \
 111                 }                               \
 112         } while (0)
 113
 114         JPAKE_BN_CLEAR_FREE(pctx->s);
 115         JPAKE_BN_CLEAR_FREE(pctx->k);
 116         JPAKE_BN_CLEAR_FREE(pctx->x1);
 117         JPAKE_BN_CLEAR_FREE(pctx->x2);
 118         JPAKE_BN_CLEAR_FREE(pctx->x3);
 119         JPAKE_BN_CLEAR_FREE(pctx->x4);
 120         JPAKE_BN_CLEAR_FREE(pctx->g_x1);
 121         JPAKE_BN_CLEAR_FREE(pctx->g_x2);
 122         JPAKE_BN_CLEAR_FREE(pctx->g_x3);
 123         JPAKE_BN_CLEAR_FREE(pctx->g_x4);
 124         JPAKE_BN_CLEAR_FREE(pctx->a);
 125         JPAKE_BN_CLEAR_FREE(pctx->b);
 126
 127         JPAKE_BUF_CLEAR_FREE(pctx->client_id, pctx->client_id_len);
 128         JPAKE_BUF_CLEAR_FREE(pctx->server_id, pctx->server_id_len);
 129         JPAKE_BUF_CLEAR_FREE(pctx->h_k_cid_sessid, pctx->h_k_cid_sessid_len);
 130         JPAKE_BUF_CLEAR_FREE(pctx->h_k_sid_sessid, pctx->h_k_sid_sessid_len);
 131
 132 #undef JPAKE_BN_CLEAR_FREE
 133 #undef JPAKE_BUF_CLEAR_FREE
 134
 135         bzero(pctx, sizeof(pctx));
 136         xfree(pctx);
 137 }
 138
 139 /* dump entire jpake_ctx. NB. includes private values! */
 140 void
 141 jpake_dump(struct jpake_ctx *pctx, const char *fmt, ...)
 142 {
 143         char *out;
 144         va_list args;
 145
 146         out = NULL;
 147         va_start(args, fmt);
 148         vasprintf(&out, fmt, args);
 149         va_end(args);
 150         if (out == NULL)
 151                 fatal("%s: vasprintf failed", __func__);
 152
 153         debug3("%s: %s (ctx at %p)", __func__, out, pctx);
 154         if (pctx == NULL) {
 155                 free(out);
 156                 return;
 157         }
 158
 159 #define JPAKE_DUMP_BN(a)        do { \
 160                 if ((a) != NULL) \
 161                         JPAKE_DEBUG_BN(((a), "%s = ", #a)); \
 162         } while (0)
 163 #define JPAKE_DUMP_BUF(a, b)    do { \
 164                 if ((a) != NULL) \
 165                         JPAKE_DEBUG_BUF((a, b, "%s", #a)); \
 166         } while (0)
 167
 168         JPAKE_DUMP_BN(pctx->s);
 169         JPAKE_DUMP_BN(pctx->k);
 170         JPAKE_DUMP_BN(pctx->x1);
 171         JPAKE_DUMP_BN(pctx->x2);
 172         JPAKE_DUMP_BN(pctx->x3);
 173         JPAKE_DUMP_BN(pctx->x4);
 174         JPAKE_DUMP_BN(pctx->g_x1);
 175         JPAKE_DUMP_BN(pctx->g_x2);
 176         JPAKE_DUMP_BN(pctx->g_x3);
 177         JPAKE_DUMP_BN(pctx->g_x4);
 178         JPAKE_DUMP_BN(pctx->a);
 179         JPAKE_DUMP_BN(pctx->b);
 180
 181         JPAKE_DUMP_BUF(pctx->client_id, pctx->client_id_len);
 182         JPAKE_DUMP_BUF(pctx->server_id, pctx->server_id_len);
 183         JPAKE_DUMP_BUF(pctx->h_k_cid_sessid, pctx->h_k_cid_sessid_len);
 184         JPAKE_DUMP_BUF(pctx->h_k_sid_sessid, pctx->h_k_sid_sessid_len);
 185
 186         debug3("%s: %s done", __func__, out);
 187         free(out);
 188 }
 189
 190 /* Shared parts of step 1 exchange calculation */
 191 void
 192 jpake_step1(struct modp_group *grp,
 193     u_char **id, u_int *id_len,
 194     BIGNUM **priv1, BIGNUM **priv2, BIGNUM **g_priv1, BIGNUM **g_priv2,
 195     u_char **priv1_proof, u_int *priv1_proof_len,
 196     u_char **priv2_proof, u_int *priv2_proof_len)
 197 {
 198         BN_CTX *bn_ctx;
 199
 200         if ((bn_ctx = BN_CTX_new()) == NULL)
 201                 fatal("%s: BN_CTX_new", __func__);
 202
 203         /* Random nonce to prevent replay */
 204         *id = xmalloc(KZP_ID_LEN);
 205         *id_len = KZP_ID_LEN;
 206         arc4random_buf(*id, *id_len);
 207
 208         /*
 209          * x1/x3 is a random element of Zq
 210          * x2/x4 is a random element of Z*q
 211          * We also exclude [1] from x1/x3 candidates and [0, 1] from
 212          * x2/x4 candiates to avoid possible degeneracy (i.e. g^0, g^1).
 213          */
 214         if ((*priv1 = bn_rand_range_gt_one(grp->q)) == NULL ||
 215             (*priv2 = bn_rand_range_gt_one(grp->q)) == NULL)
 216                 fatal("%s: bn_rand_range_gt_one", __func__);
 217
 218         /*
 219          * client: g_x1 = g^x1 mod p / server: g_x3 = g^x3 mod p
 220          * client: g_x2 = g^x2 mod p / server: g_x4 = g^x4 mod p
 221          */
 222         if ((*g_priv1 = BN_new()) == NULL ||
 223             (*g_priv2 = BN_new()) == NULL)
 224                 fatal("%s: BN_new", __func__);
 225         if (BN_mod_exp(*g_priv1, grp->g, *priv1, grp->p, bn_ctx) == -1)
 226                 fatal("%s: BN_mod_exp", __func__);
 227         if (BN_mod_exp(*g_priv2, grp->g, *priv2, grp->p, bn_ctx) == -1)
 228                 fatal("%s: BN_mod_exp", __func__);
 229
 230         /* Generate proofs for holding x1/x3 and x2/x4 */
 231         if (schnorr_sign_buf(grp->p, grp->q, grp->g,
 232             *priv1, *g_priv1, *id, *id_len,
 233             priv1_proof, priv1_proof_len) != 0)
 234                 fatal("%s: schnorr_sign", __func__);
 235         if (schnorr_sign_buf(grp->p, grp->q, grp->g,
 236             *priv2, *g_priv2, *id, *id_len,
 237             priv2_proof, priv2_proof_len) != 0)
 238                 fatal("%s: schnorr_sign", __func__);
 239
 240         BN_CTX_free(bn_ctx);
 241 }
 242
 243 /* Shared parts of step 2 exchange calculation */
 244 void
 245 jpake_step2(struct modp_group *grp, BIGNUM *s,
 246     BIGNUM *mypub1, BIGNUM *theirpub1, BIGNUM *theirpub2, BIGNUM *mypriv2,
 247     const u_char *theirid, u_int theirid_len,
 248     const u_char *myid, u_int myid_len,
 249     const u_char *theirpub1_proof, u_int theirpub1_proof_len,
 250     const u_char *theirpub2_proof, u_int theirpub2_proof_len,
 251     BIGNUM **newpub,
 252     u_char **newpub_exponent_proof, u_int *newpub_exponent_proof_len)
 253 {
 254         BN_CTX *bn_ctx;
 255         BIGNUM *tmp, *exponent;
 256
 257         /* Validate peer's step 1 values */
 258         if (BN_cmp(theirpub1, BN_value_one()) <= 0)
 259                 fatal("%s: theirpub1 <= 1", __func__);
 260         if (BN_cmp(theirpub2, BN_value_one()) <= 0)
 261                 fatal("%s: theirpub2 <= 1", __func__);
 262
 263         if (schnorr_verify_buf(grp->p, grp->q, grp->g, theirpub1,
 264             theirid, theirid_len, theirpub1_proof, theirpub1_proof_len) != 1)
 265                 fatal("%s: schnorr_verify theirpub1 failed", __func__);
 266         if (schnorr_verify_buf(grp->p, grp->q, grp->g, theirpub2,
 267             theirid, theirid_len, theirpub2_proof, theirpub2_proof_len) != 1)
 268                 fatal("%s: schnorr_verify theirpub2 failed", __func__);
 269
 270         if ((bn_ctx = BN_CTX_new()) == NULL)
 271                 fatal("%s: BN_CTX_new", __func__);
 272
 273         if ((*newpub = BN_new()) == NULL ||
 274             (tmp = BN_new()) == NULL ||
 275             (exponent = BN_new()) == NULL)
 276                 fatal("%s: BN_new", __func__);
 277
 278         /*
 279          * client: exponent = x2 * s mod p
 280          * server: exponent = x4 * s mod p
 281          */
 282         if (BN_mod_mul(exponent, mypriv2, s, grp->q, bn_ctx) != 1)
 283                 fatal("%s: BN_mod_mul (exponent = mypriv2 * s mod p)",
 284                     __func__);
 285
 286         /*
 287          * client: tmp = g^(x1 + x3 + x4) mod p
 288          * server: tmp = g^(x1 + x2 + x3) mod p
 289          */
 290         if (BN_mod_mul(tmp, mypub1, theirpub1, grp->p, bn_ctx) != 1)
 291                 fatal("%s: BN_mod_mul (tmp = mypub1 * theirpub1 mod p)",
 292                     __func__);
 293         if (BN_mod_mul(tmp, tmp, theirpub2, grp->p, bn_ctx) != 1)
 294                 fatal("%s: BN_mod_mul (tmp = tmp * theirpub2 mod p)", __func__);
 295
 296         /*
 297          * client: a = tmp^exponent = g^((x1+x3+x4) * x2 * s) mod p
 298          * server: b = tmp^exponent = g^((x1+x2+x3) * x4 * s) mod p
 299          */
 300         if (BN_mod_exp(*newpub, tmp, exponent, grp->p, bn_ctx) != 1)
 301                 fatal("%s: BN_mod_mul (newpub = tmp^exponent mod p)", __func__);
 302
 303         JPAKE_DEBUG_BN((tmp, "%s: tmp = ", __func__));
 304         JPAKE_DEBUG_BN((exponent, "%s: exponent = ", __func__));
 305
 306         /* Note the generator here is 'tmp', not g */
 307         if (schnorr_sign_buf(grp->p, grp->q, tmp, exponent, *newpub,
 308             myid, myid_len,
 309             newpub_exponent_proof, newpub_exponent_proof_len) != 0)
 310                 fatal("%s: schnorr_sign newpub", __func__);
 311
 312         BN_clear_free(tmp); /* XXX stash for later use? */
 313         BN_clear_free(exponent); /* XXX stash for later use? (yes, in conf) */
 314
 315         BN_CTX_free(bn_ctx);
 316 }
 317
 318 /* Confirmation hash calculation */
 319 void
 320 jpake_confirm_hash(const BIGNUM *k,
 321     const u_char *endpoint_id, u_int endpoint_id_len,
 322     const u_char *sess_id, u_int sess_id_len,
 323     u_char **confirm_hash, u_int *confirm_hash_len)
 324 {
 325         Buffer b;
 326
 327         /*
 328          * Calculate confirmation proof:
 329          *     client: H(k || client_id || session_id)
 330          *     server: H(k || server_id || session_id)
 331          */
 332         buffer_init(&b);
 333         buffer_put_bignum2(&b, k);
 334         buffer_put_string(&b, endpoint_id, endpoint_id_len);
 335         buffer_put_string(&b, sess_id, sess_id_len);
 336         if (hash_buffer(buffer_ptr(&b), buffer_len(&b), EVP_sha256(),
 337             confirm_hash, confirm_hash_len) != 0)
 338                 fatal("%s: hash_buffer", __func__);
 339         buffer_free(&b);
 340 }
 341
 342 /* Shared parts of key derivation and confirmation calculation */
 343 void
 344 jpake_key_confirm(struct modp_group *grp, BIGNUM *s, BIGNUM *step2_val,
 345     BIGNUM *mypriv2, BIGNUM *mypub1, BIGNUM *mypub2,
 346     BIGNUM *theirpub1, BIGNUM *theirpub2,
 347     const u_char *my_id, u_int my_id_len,
 348     const u_char *their_id, u_int their_id_len,
 349     const u_char *sess_id, u_int sess_id_len,
 350     const u_char *theirpriv2_s_proof, u_int theirpriv2_s_proof_len,
 351     BIGNUM **k,
 352     u_char **confirm_hash, u_int *confirm_hash_len)
 353 {
 354         BN_CTX *bn_ctx;
 355         BIGNUM *tmp;
 356
 357         if ((bn_ctx = BN_CTX_new()) == NULL)
 358                 fatal("%s: BN_CTX_new", __func__);
 359         if ((tmp = BN_new()) == NULL ||
 360             (*k = BN_new()) == NULL)
 361                 fatal("%s: BN_new", __func__);
 362
 363         /* Validate step 2 values */
 364         if (BN_cmp(step2_val, BN_value_one()) <= 0)
 365                 fatal("%s: step2_val <= 1", __func__);
 366
 367         /*
 368          * theirpriv2_s_proof is calculated with a different generator:
 369          * tmp = g^(mypriv1+mypriv2+theirpub1) = g^mypub1*g^mypub2*g^theirpub1
 370          * Calculate it here so we can check the signature.
 371          */
 372         if (BN_mod_mul(tmp, mypub1, mypub2, grp->p, bn_ctx) != 1)
 373                 fatal("%s: BN_mod_mul (tmp = mypub1 * mypub2 mod p)", __func__);
 374         if (BN_mod_mul(tmp, tmp, theirpub1, grp->p, bn_ctx) != 1)
 375                 fatal("%s: BN_mod_mul (tmp = tmp * theirpub1 mod p)", __func__);
 376
 377         JPAKE_DEBUG_BN((tmp, "%s: tmp = ", __func__));
 378
 379         if (schnorr_verify_buf(grp->p, grp->q, tmp, step2_val,
 380             their_id, their_id_len,
 381             theirpriv2_s_proof, theirpriv2_s_proof_len) != 1)
 382                 fatal("%s: schnorr_verify theirpriv2_s_proof failed", __func__);
 383
 384         /*
 385          * Derive shared key:
 386          *     client: k = (b / g^(x2*x4*s))^x2 = g^((x1+x3)*x2*x4*s)
 387          *     server: k = (a / g^(x2*x4*s))^x4 = g^((x1+x3)*x2*x4*s)
 388          *
 389          * Computed as:
 390          *     client: k = (g_x4^(q - (x2 * s)) * b)^x2 mod p
 391          *     server: k = (g_x2^(q - (x4 * s)) * b)^x4 mod p
 392          */
 393         if (BN_mul(tmp, mypriv2, s, bn_ctx) != 1)
 394                 fatal("%s: BN_mul (tmp = mypriv2 * s)", __func__);
 395         if (BN_mod_sub(tmp, grp->q, tmp, grp->q, bn_ctx) != 1)
 396                 fatal("%s: BN_mod_sub (tmp = q - tmp mod q)", __func__);
 397         if (BN_mod_exp(tmp, theirpub2, tmp, grp->p, bn_ctx) != 1)
 398                 fatal("%s: BN_mod_exp (tmp = theirpub2^tmp) mod p", __func__);
 399         if (BN_mod_mul(tmp, tmp, step2_val, grp->p, bn_ctx) != 1)
 400                 fatal("%s: BN_mod_mul (tmp = tmp * step2_val) mod p", __func__);
 401         if (BN_mod_exp(*k, tmp, mypriv2, grp->p, bn_ctx) != 1)
 402                 fatal("%s: BN_mod_exp (k = tmp^mypriv2) mod p", __func__);
 403
 404         BN_CTX_free(bn_ctx);
 405         BN_clear_free(tmp);
 406
 407         jpake_confirm_hash(*k, my_id, my_id_len, sess_id, sess_id_len,
 408             confirm_hash, confirm_hash_len);
 409 }
 410
 411 /*
 412  * Calculate and check confirmation hash from peer. Returns 1 on success
 413  * 0 on failure/mismatch.
 414  */
 415 int
 416 jpake_check_confirm(const BIGNUM *k,
 417     const u_char *peer_id, u_int peer_id_len,
 418     const u_char *sess_id, u_int sess_id_len,
 419     const u_char *peer_confirm_hash, u_int peer_confirm_hash_len)
 420 {
 421         u_char *expected_confirm_hash;
 422         u_int expected_confirm_hash_len;
 423         int success = 0;
 424
 425         /* Calculate and verify expected confirmation hash */
 426         jpake_confirm_hash(k, peer_id, peer_id_len, sess_id, sess_id_len,
 427             &expected_confirm_hash, &expected_confirm_hash_len);
 428
 429         JPAKE_DEBUG_BUF((expected_confirm_hash, expected_confirm_hash_len,
 430             "%s: expected confirm hash", __func__));
 431         JPAKE_DEBUG_BUF((peer_confirm_hash, peer_confirm_hash_len,
 432             "%s: received confirm hash", __func__));
 433
 434         if (peer_confirm_hash_len != expected_confirm_hash_len)
 435                 error("%s: confirmation length mismatch (my %u them %u)",
 436                     __func__, expected_confirm_hash_len, peer_confirm_hash_len);
 437         else if (memcmp(peer_confirm_hash, expected_confirm_hash,
 438             expected_confirm_hash_len) == 0)
 439                 success = 1;
 440         bzero(expected_confirm_hash, expected_confirm_hash_len);
 441         xfree(expected_confirm_hash);
 442         debug3("%s: success = %d", __func__, success);
 443         return success;
 444 }
 445
 446 /* XXX main() function with tests */
 447
 448 #endif /* JPAKE */
 449