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 */ 456 457
