jpake.c

   1 /* $OpenBSD: jpake.c,v 1.6 2010/09/20 04:54:07 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 #include "misc.h"
  49
  50 #include "jpake.h"
  51 #include "schnorr.h"
  52
  53 #ifdef JPAKE
  54
  55 /* RFC3526 group 5, 1536 bits */
  56 #define JPAKE_GROUP_G "2"
  57 #define JPAKE_GROUP_P \
  58         "FFFFFFFFFFFFFFFFC90FDAA22168C234C4C6628B80DC1CD129024E088A67CC74" \
  59         "020BBEA63B139B22514A08798E3404DDEF9519B3CD3A431B302B0A6DF25F1437" \
  60         "4FE1356D6D51C245E485B576625E7EC6F44C42E9A637ED6B0BFF5CB6F406B7ED" \
  61         "EE386BFB5A899FA5AE9F24117C4B1FE649286651ECE45B3DC2007CB8A163BF05" \
  62         "98DA48361C55D39A69163FA8FD24CF5F83655D23DCA3AD961C62F356208552BB" \
  63         "9ED529077096966D670C354E4ABC9804F1746C08CA237327FFFFFFFFFFFFFFFF"
  64
  65 struct modp_group *
  66 jpake_default_group(void)
  67 {
  68         return modp_group_from_g_and_safe_p(JPAKE_GROUP_G, JPAKE_GROUP_P);
  69 }
  70
  71 struct jpake_ctx *
  72 jpake_new(void)
  73 {
  74         struct jpake_ctx *ret;
  75
  76         ret = xcalloc(1, sizeof(*ret));
  77
  78         ret->grp = jpake_default_group();
  79
  80         ret->s = ret->k = NULL;
  81         ret->x1 = ret->x2 = ret->x3 = ret->x4 = NULL;
  82         ret->g_x1 = ret->g_x2 = ret->g_x3 = ret->g_x4 = NULL;
  83         ret->a = ret->b = NULL;
  84
  85         ret->client_id = ret->server_id = NULL;
  86         ret->h_k_cid_sessid = ret->h_k_sid_sessid = NULL;
  87
  88         debug3("%s: alloc %p", __func__, ret);
  89
  90         return ret;
  91 }
  92
  93 void
  94 jpake_free(struct jpake_ctx *pctx)
  95 {
  96         debug3("%s: free %p", __func__, pctx);
  97
  98 #define JPAKE_BN_CLEAR_FREE(v)                  \
  99         do {                                    \
 100                 if ((v) != NULL) {              \
 101                         BN_clear_free(v);       \
 102                         (v) = NULL;             \
 103                 }                               \
 104         } while (0)
 105 #define JPAKE_BUF_CLEAR_FREE(v, l)              \
 106         do {                                    \
 107                 if ((v) != NULL) {              \
 108                         bzero((v), (l));        \
 109                         xfree(v);               \
 110                         (v) = NULL;             \
 111                         (l) = 0;                \
 112                 }                               \
 113         } while (0)
 114
 115         JPAKE_BN_CLEAR_FREE(pctx->s);
 116         JPAKE_BN_CLEAR_FREE(pctx->k);
 117         JPAKE_BN_CLEAR_FREE(pctx->x1);
 118         JPAKE_BN_CLEAR_FREE(pctx->x2);
 119         JPAKE_BN_CLEAR_FREE(pctx->x3);
 120         JPAKE_BN_CLEAR_FREE(pctx->x4);
 121         JPAKE_BN_CLEAR_FREE(pctx->g_x1);
 122         JPAKE_BN_CLEAR_FREE(pctx->g_x2);
 123         JPAKE_BN_CLEAR_FREE(pctx->g_x3);
 124         JPAKE_BN_CLEAR_FREE(pctx->g_x4);
 125         JPAKE_BN_CLEAR_FREE(pctx->a);
 126         JPAKE_BN_CLEAR_FREE(pctx->b);
 127
 128         JPAKE_BUF_CLEAR_FREE(pctx->client_id, pctx->client_id_len);
 129         JPAKE_BUF_CLEAR_FREE(pctx->server_id, pctx->server_id_len);
 130         JPAKE_BUF_CLEAR_FREE(pctx->h_k_cid_sessid, pctx->h_k_cid_sessid_len);
 131         JPAKE_BUF_CLEAR_FREE(pctx->h_k_sid_sessid, pctx->h_k_sid_sessid_len);
 132
 133 #undef JPAKE_BN_CLEAR_FREE
 134 #undef JPAKE_BUF_CLEAR_FREE
 135
 136         bzero(pctx, sizeof(pctx));
 137         xfree(pctx);
 138 }
 139
 140 /* dump entire jpake_ctx. NB. includes private values! */
 141 void
 142 jpake_dump(struct jpake_ctx *pctx, const char *fmt, ...)
 143 {
 144         char *out;
 145         va_list args;
 146
 147         out = NULL;
 148         va_start(args, fmt);
 149         vasprintf(&out, fmt, args);
 150         va_end(args);
 151         if (out == NULL)
 152                 fatal("%s: vasprintf failed", __func__);
 153
 154         debug3("%s: %s (ctx at %p)", __func__, out, pctx);
 155         if (pctx == NULL) {
 156                 free(out);
 157                 return;
 158         }
 159
 160 #define JPAKE_DUMP_BN(a)        do { \
 161                 if ((a) != NULL) \
 162                         JPAKE_DEBUG_BN(((a), "%s = ", #a)); \
 163         } while (0)
 164 #define JPAKE_DUMP_BUF(a, b)    do { \
 165                 if ((a) != NULL) \
 166                         JPAKE_DEBUG_BUF((a, b, "%s", #a)); \
 167         } while (0)
 168
 169         JPAKE_DUMP_BN(pctx->s);
 170         JPAKE_DUMP_BN(pctx->k);
 171         JPAKE_DUMP_BN(pctx->x1);
 172         JPAKE_DUMP_BN(pctx->x2);
 173         JPAKE_DUMP_BN(pctx->x3);
 174         JPAKE_DUMP_BN(pctx->x4);
 175         JPAKE_DUMP_BN(pctx->g_x1);
 176         JPAKE_DUMP_BN(pctx->g_x2);
 177         JPAKE_DUMP_BN(pctx->g_x3);
 178         JPAKE_DUMP_BN(pctx->g_x4);
 179         JPAKE_DUMP_BN(pctx->a);
 180         JPAKE_DUMP_BN(pctx->b);
 181
 182         JPAKE_DUMP_BUF(pctx->client_id, pctx->client_id_len);
 183         JPAKE_DUMP_BUF(pctx->server_id, pctx->server_id_len);
 184         JPAKE_DUMP_BUF(pctx->h_k_cid_sessid, pctx->h_k_cid_sessid_len);
 185         JPAKE_DUMP_BUF(pctx->h_k_sid_sessid, pctx->h_k_sid_sessid_len);
 186
 187         debug3("%s: %s done", __func__, out);
 188         free(out);
 189 }
 190
 191 /* Shared parts of step 1 exchange calculation */
 192 void
 193 jpake_step1(struct modp_group *grp,
 194     u_char **id, u_int *id_len,
 195     BIGNUM **priv1, BIGNUM **priv2, BIGNUM **g_priv1, BIGNUM **g_priv2,
 196     u_char **priv1_proof, u_int *priv1_proof_len,
 197     u_char **priv2_proof, u_int *priv2_proof_len)
 198 {
 199         BN_CTX *bn_ctx;
 200
 201         if ((bn_ctx = BN_CTX_new()) == NULL)
 202                 fatal("%s: BN_CTX_new", __func__);
 203
 204         /* Random nonce to prevent replay */
 205         *id = xmalloc(KZP_ID_LEN);
 206         *id_len = KZP_ID_LEN;
 207         arc4random_buf(*id, *id_len);
 208
 209         /*
 210          * x1/x3 is a random element of Zq
 211          * x2/x4 is a random element of Z*q
 212          * We also exclude [1] from x1/x3 candidates and [0, 1] from
 213          * x2/x4 candiates to avoid possible degeneracy (i.e. g^0, g^1).
 214          */
 215         if ((*priv1 = bn_rand_range_gt_one(grp->q)) == NULL ||
 216             (*priv2 = bn_rand_range_gt_one(grp->q)) == NULL)
 217                 fatal("%s: bn_rand_range_gt_one", __func__);
 218
 219         /*
 220          * client: g_x1 = g^x1 mod p / server: g_x3 = g^x3 mod p
 221          * client: g_x2 = g^x2 mod p / server: g_x4 = g^x4 mod p
 222          */
 223         if ((*g_priv1 = BN_new()) == NULL ||
 224             (*g_priv2 = BN_new()) == NULL)
 225                 fatal("%s: BN_new", __func__);
 226         if (BN_mod_exp(*g_priv1, grp->g, *priv1, grp->p, bn_ctx) == -1)
 227                 fatal("%s: BN_mod_exp", __func__);
 228         if (BN_mod_exp(*g_priv2, grp->g, *priv2, grp->p, bn_ctx) == -1)
 229                 fatal("%s: BN_mod_exp", __func__);
 230
 231         /* Generate proofs for holding x1/x3 and x2/x4 */
 232         if (schnorr_sign_buf(grp->p, grp->q, grp->g,
 233             *priv1, *g_priv1, *id, *id_len,
 234             priv1_proof, priv1_proof_len) != 0)
 235                 fatal("%s: schnorr_sign", __func__);
 236         if (schnorr_sign_buf(grp->p, grp->q, grp->g,
 237             *priv2, *g_priv2, *id, *id_len,
 238             priv2_proof, priv2_proof_len) != 0)
 239                 fatal("%s: schnorr_sign", __func__);
 240
 241         BN_CTX_free(bn_ctx);
 242 }
 243
 244 /* Shared parts of step 2 exchange calculation */
 245 void
 246 jpake_step2(struct modp_group *grp, BIGNUM *s,
 247     BIGNUM *mypub1, BIGNUM *theirpub1, BIGNUM *theirpub2, BIGNUM *mypriv2,
 248     const u_char *theirid, u_int theirid_len,
 249     const u_char *myid, u_int myid_len,
 250     const u_char *theirpub1_proof, u_int theirpub1_proof_len,
 251     const u_char *theirpub2_proof, u_int theirpub2_proof_len,
 252     BIGNUM **newpub,
 253     u_char **newpub_exponent_proof, u_int *newpub_exponent_proof_len)
 254 {
 255         BN_CTX *bn_ctx;
 256         BIGNUM *tmp, *exponent;
 257
 258         /* Validate peer's step 1 values */
 259         if (BN_cmp(theirpub1, BN_value_one()) <= 0)
 260                 fatal("%s: theirpub1 <= 1", __func__);
 261         if (BN_cmp(theirpub1, grp->p) >= 0)
 262                 fatal("%s: theirpub1 >= p", __func__);
 263         if (BN_cmp(theirpub2, BN_value_one()) <= 0)
 264                 fatal("%s: theirpub2 <= 1", __func__);
 265         if (BN_cmp(theirpub2, grp->p) >= 0)
 266                 fatal("%s: theirpub2 >= p", __func__);
 267
 268         if (schnorr_verify_buf(grp->p, grp->q, grp->g, theirpub1,
 269             theirid, theirid_len, theirpub1_proof, theirpub1_proof_len) != 1)
 270                 fatal("%s: schnorr_verify theirpub1 failed", __func__);
 271         if (schnorr_verify_buf(grp->p, grp->q, grp->g, theirpub2,
 272             theirid, theirid_len, theirpub2_proof, theirpub2_proof_len) != 1)
 273                 fatal("%s: schnorr_verify theirpub2 failed", __func__);
 274
 275         if ((bn_ctx = BN_CTX_new()) == NULL)
 276                 fatal("%s: BN_CTX_new", __func__);
 277
 278         if ((*newpub = BN_new()) == NULL ||
 279             (tmp = BN_new()) == NULL ||
 280             (exponent = BN_new()) == NULL)
 281                 fatal("%s: BN_new", __func__);
 282
 283         /*
 284          * client: exponent = x2 * s mod p
 285          * server: exponent = x4 * s mod p
 286          */
 287         if (BN_mod_mul(exponent, mypriv2, s, grp->q, bn_ctx) != 1)
 288                 fatal("%s: BN_mod_mul (exponent = mypriv2 * s mod p)",
 289                     __func__);
 290
 291         /*
 292          * client: tmp = g^(x1 + x3 + x4) mod p
 293          * server: tmp = g^(x1 + x2 + x3) mod p
 294          */
 295         if (BN_mod_mul(tmp, mypub1, theirpub1, grp->p, bn_ctx) != 1)
 296                 fatal("%s: BN_mod_mul (tmp = mypub1 * theirpub1 mod p)",
 297                     __func__);
 298         if (BN_mod_mul(tmp, tmp, theirpub2, grp->p, bn_ctx) != 1)
 299                 fatal("%s: BN_mod_mul (tmp = tmp * theirpub2 mod p)", __func__);
 300
 301         /*
 302          * client: a = tmp^exponent = g^((x1+x3+x4) * x2 * s) mod p
 303          * server: b = tmp^exponent = g^((x1+x2+x3) * x4 * s) mod p
 304          */
 305         if (BN_mod_exp(*newpub, tmp, exponent, grp->p, bn_ctx) != 1)
 306                 fatal("%s: BN_mod_mul (newpub = tmp^exponent mod p)", __func__);
 307
 308         JPAKE_DEBUG_BN((tmp, "%s: tmp = ", __func__));
 309         JPAKE_DEBUG_BN((exponent, "%s: exponent = ", __func__));
 310
 311         /* Note the generator here is 'tmp', not g */
 312         if (schnorr_sign_buf(grp->p, grp->q, tmp, exponent, *newpub,
 313             myid, myid_len,
 314             newpub_exponent_proof, newpub_exponent_proof_len) != 0)
 315                 fatal("%s: schnorr_sign newpub", __func__);
 316
 317         BN_clear_free(tmp); /* XXX stash for later use? */
 318         BN_clear_free(exponent); /* XXX stash for later use? (yes, in conf) */
 319
 320         BN_CTX_free(bn_ctx);
 321 }
 322
 323 /* Confirmation hash calculation */
 324 void
 325 jpake_confirm_hash(const BIGNUM *k,
 326     const u_char *endpoint_id, u_int endpoint_id_len,
 327     const u_char *sess_id, u_int sess_id_len,
 328     u_char **confirm_hash, u_int *confirm_hash_len)
 329 {
 330         Buffer b;
 331
 332         /*
 333          * Calculate confirmation proof:
 334          *     client: H(k || client_id || session_id)
 335          *     server: H(k || server_id || session_id)
 336          */
 337         buffer_init(&b);
 338         buffer_put_bignum2(&b, k);
 339         buffer_put_string(&b, endpoint_id, endpoint_id_len);
 340         buffer_put_string(&b, sess_id, sess_id_len);
 341         if (hash_buffer(buffer_ptr(&b), buffer_len(&b), EVP_sha256(),
 342             confirm_hash, confirm_hash_len) != 0)
 343                 fatal("%s: hash_buffer", __func__);
 344         buffer_free(&b);
 345 }
 346
 347 /* Shared parts of key derivation and confirmation calculation */
 348 void
 349 jpake_key_confirm(struct modp_group *grp, BIGNUM *s, BIGNUM *step2_val,
 350     BIGNUM *mypriv2, BIGNUM *mypub1, BIGNUM *mypub2,
 351     BIGNUM *theirpub1, BIGNUM *theirpub2,
 352     const u_char *my_id, u_int my_id_len,
 353     const u_char *their_id, u_int their_id_len,
 354     const u_char *sess_id, u_int sess_id_len,
 355     const u_char *theirpriv2_s_proof, u_int theirpriv2_s_proof_len,
 356     BIGNUM **k,
 357     u_char **confirm_hash, u_int *confirm_hash_len)
 358 {
 359         BN_CTX *bn_ctx;
 360         BIGNUM *tmp;
 361
 362         if ((bn_ctx = BN_CTX_new()) == NULL)
 363                 fatal("%s: BN_CTX_new", __func__);
 364         if ((tmp = BN_new()) == NULL ||
 365             (*k = BN_new()) == NULL)
 366                 fatal("%s: BN_new", __func__);
 367
 368         /* Validate step 2 values */
 369         if (BN_cmp(step2_val, BN_value_one()) <= 0)
 370                 fatal("%s: step2_val <= 1", __func__);
 371         if (BN_cmp(step2_val, grp->p) >= 0)
 372                 fatal("%s: step2_val >= p", __func__);
 373
 374         /*
 375          * theirpriv2_s_proof is calculated with a different generator:
 376          * tmp = g^(mypriv1+mypriv2+theirpub1) = g^mypub1*g^mypub2*g^theirpub1
 377          * Calculate it here so we can check the signature.
 378          */
 379         if (BN_mod_mul(tmp, mypub1, mypub2, grp->p, bn_ctx) != 1)
 380                 fatal("%s: BN_mod_mul (tmp = mypub1 * mypub2 mod p)", __func__);
 381         if (BN_mod_mul(tmp, tmp, theirpub1, grp->p, bn_ctx) != 1)
 382                 fatal("%s: BN_mod_mul (tmp = tmp * theirpub1 mod p)", __func__);
 383
 384         JPAKE_DEBUG_BN((tmp, "%s: tmp = ", __func__));
 385
 386         if (schnorr_verify_buf(grp->p, grp->q, tmp, step2_val,
 387             their_id, their_id_len,
 388             theirpriv2_s_proof, theirpriv2_s_proof_len) != 1)
 389                 fatal("%s: schnorr_verify theirpriv2_s_proof failed", __func__);
 390
 391         /*
 392          * Derive shared key:
 393          *     client: k = (b / g^(x2*x4*s))^x2 = g^((x1+x3)*x2*x4*s)
 394          *     server: k = (a / g^(x2*x4*s))^x4 = g^((x1+x3)*x2*x4*s)
 395          *
 396          * Computed as:
 397          *     client: k = (g_x4^(q - (x2 * s)) * b)^x2 mod p
 398          *     server: k = (g_x2^(q - (x4 * s)) * b)^x4 mod p
 399          */
 400         if (BN_mul(tmp, mypriv2, s, bn_ctx) != 1)
 401                 fatal("%s: BN_mul (tmp = mypriv2 * s)", __func__);
 402         if (BN_mod_sub(tmp, grp->q, tmp, grp->q, bn_ctx) != 1)
 403                 fatal("%s: BN_mod_sub (tmp = q - tmp mod q)", __func__);
 404         if (BN_mod_exp(tmp, theirpub2, tmp, grp->p, bn_ctx) != 1)
 405                 fatal("%s: BN_mod_exp (tmp = theirpub2^tmp) mod p", __func__);
 406         if (BN_mod_mul(tmp, tmp, step2_val, grp->p, bn_ctx) != 1)
 407                 fatal("%s: BN_mod_mul (tmp = tmp * step2_val) mod p", __func__);
 408         if (BN_mod_exp(*k, tmp, mypriv2, grp->p, bn_ctx) != 1)
 409                 fatal("%s: BN_mod_exp (k = tmp^mypriv2) mod p", __func__);
 410
 411         BN_CTX_free(bn_ctx);
 412         BN_clear_free(tmp);
 413
 414         jpake_confirm_hash(*k, my_id, my_id_len, sess_id, sess_id_len,
 415             confirm_hash, confirm_hash_len);
 416 }
 417
 418 /*
 419  * Calculate and check confirmation hash from peer. Returns 1 on success
 420  * 0 on failure/mismatch.
 421  */
 422 int
 423 jpake_check_confirm(const BIGNUM *k,
 424     const u_char *peer_id, u_int peer_id_len,
 425     const u_char *sess_id, u_int sess_id_len,
 426     const u_char *peer_confirm_hash, u_int peer_confirm_hash_len)
 427 {
 428         u_char *expected_confirm_hash;
 429         u_int expected_confirm_hash_len;
 430         int success = 0;
 431
 432         /* Calculate and verify expected confirmation hash */
 433         jpake_confirm_hash(k, peer_id, peer_id_len, sess_id, sess_id_len,
 434             &expected_confirm_hash, &expected_confirm_hash_len);
 435
 436         JPAKE_DEBUG_BUF((expected_confirm_hash, expected_confirm_hash_len,
 437             "%s: expected confirm hash", __func__));
 438         JPAKE_DEBUG_BUF((peer_confirm_hash, peer_confirm_hash_len,
 439             "%s: received confirm hash", __func__));
 440
 441         if (peer_confirm_hash_len != expected_confirm_hash_len)
 442                 error("%s: confirmation length mismatch (my %u them %u)",
 443                     __func__, expected_confirm_hash_len, peer_confirm_hash_len);
 444         else if (timingsafe_bcmp(peer_confirm_hash, expected_confirm_hash,
 445             expected_confirm_hash_len) == 0)
 446                 success = 1;
 447         bzero(expected_confirm_hash, expected_confirm_hash_len);
 448         xfree(expected_confirm_hash);
 449         debug3("%s: success = %d", __func__, success);
 450         return success;
 451 }
 452
 453 /* XXX main() function with tests */
 454
 455 #endif /* JPAKE */
 456