1 /* 2 * EAP server/peer: EAP-pwd shared routines 3 * Copyright (c) 2010, Dan Harkins <dharkins@lounge.org> 4 * 5 * This software may be distributed under the terms of the BSD license. 6 * See README for more details. 7 */ 8 9 #include "includes.h" 10 #include "common.h" 11 #include "utils/const_time.h" 12 #include "common/dragonfly.h" 13 #include "crypto/sha256.h" 14 #include "crypto/crypto.h" 15 #include "eap_defs.h" 16 #include "eap_pwd_common.h" 17 18 #define MAX_ECC_PRIME_LEN 66 19 20 21 /* The random function H(x) = HMAC-SHA256(0^32, x) */ 22 struct crypto_hash * eap_pwd_h_init(void) 23 { 24 u8 allzero[SHA256_MAC_LEN]; 25 os_memset(allzero, 0, SHA256_MAC_LEN); 26 return crypto_hash_init(CRYPTO_HASH_ALG_HMAC_SHA256, allzero, 27 SHA256_MAC_LEN); 28 } 29 30 31 void eap_pwd_h_update(struct crypto_hash *hash, const u8 *data, size_t len) 32 { 33 crypto_hash_update(hash, data, len); 34 } 35 36 37 void eap_pwd_h_final(struct crypto_hash *hash, u8 *digest) 38 { 39 size_t len = SHA256_MAC_LEN; 40 crypto_hash_finish(hash, digest, &len); 41 } 42 43 44 /* a counter-based KDF based on NIST SP800-108 */ 45 static int eap_pwd_kdf(const u8 *key, size_t keylen, const u8 *label, 46 size_t labellen, u8 *result, size_t resultbitlen) 47 { 48 struct crypto_hash *hash; 49 u8 digest[SHA256_MAC_LEN]; 50 u16 i, ctr, L; 51 size_t resultbytelen, len = 0, mdlen; 52 53 resultbytelen = (resultbitlen + 7) / 8; 54 ctr = 0; 55 L = htons(resultbitlen); 56 while (len < resultbytelen) { 57 ctr++; 58 i = htons(ctr); 59 hash = crypto_hash_init(CRYPTO_HASH_ALG_HMAC_SHA256, 60 key, keylen); 61 if (hash == NULL) 62 return -1; 63 if (ctr > 1) 64 crypto_hash_update(hash, digest, SHA256_MAC_LEN); 65 crypto_hash_update(hash, (u8 *) &i, sizeof(u16)); 66 crypto_hash_update(hash, label, labellen); 67 crypto_hash_update(hash, (u8 *) &L, sizeof(u16)); 68 mdlen = SHA256_MAC_LEN; 69 if (crypto_hash_finish(hash, digest, &mdlen) < 0) 70 return -1; 71 if ((len + mdlen) > resultbytelen) 72 os_memcpy(result + len, digest, resultbytelen - len); 73 else 74 os_memcpy(result + len, digest, mdlen); 75 len += mdlen; 76 } 77 78 /* since we're expanding to a bit length, mask off the excess */ 79 if (resultbitlen % 8) { 80 u8 mask = 0xff; 81 mask <<= (8 - (resultbitlen % 8)); 82 result[resultbytelen - 1] &= mask; 83 } 84 85 return 0; 86 } 87 88 89 EAP_PWD_group * get_eap_pwd_group(u16 num) 90 { 91 EAP_PWD_group *grp; 92 93 if (!dragonfly_suitable_group(num, 1)) { 94 wpa_printf(MSG_INFO, "EAP-pwd: unsuitable group %u", num); 95 return NULL; 96 } 97 grp = os_zalloc(sizeof(EAP_PWD_group)); 98 if (!grp) 99 return NULL; 100 grp->group = crypto_ec_init(num); 101 if (!grp->group) { 102 wpa_printf(MSG_INFO, "EAP-pwd: unable to create EC group"); 103 os_free(grp); 104 return NULL; 105 } 106 107 grp->group_num = num; 108 wpa_printf(MSG_INFO, "EAP-pwd: provisioned group %d", num); 109 110 return grp; 111 } 112 113 114 /* 115 * compute a "random" secret point on an elliptic curve based 116 * on the password and identities. 117 */ 118 int compute_password_element(EAP_PWD_group *grp, u16 num, 119 const u8 *password, size_t password_len, 120 const u8 *id_server, size_t id_server_len, 121 const u8 *id_peer, size_t id_peer_len, 122 const u8 *token) 123 { 124 struct crypto_bignum *qr = NULL, *qnr = NULL; 125 u8 qr_bin[MAX_ECC_PRIME_LEN]; 126 u8 qnr_bin[MAX_ECC_PRIME_LEN]; 127 u8 qr_or_qnr_bin[MAX_ECC_PRIME_LEN]; 128 u8 x_bin[MAX_ECC_PRIME_LEN]; 129 u8 prime_bin[MAX_ECC_PRIME_LEN]; 130 u8 x_y[2 * MAX_ECC_PRIME_LEN]; 131 struct crypto_bignum *tmp2 = NULL, *y = NULL; 132 struct crypto_hash *hash; 133 unsigned char pwe_digest[SHA256_MAC_LEN], *prfbuf = NULL, ctr; 134 int ret = 0, res; 135 u8 found = 0; /* 0 (false) or 0xff (true) to be used as const_time_* 136 * mask */ 137 size_t primebytelen = 0, primebitlen; 138 struct crypto_bignum *x_candidate = NULL; 139 const struct crypto_bignum *prime; 140 u8 found_ctr = 0, is_odd = 0; 141 int cmp_prime; 142 unsigned int in_range; 143 unsigned int is_eq; 144 145 if (grp->pwe) 146 return -1; 147 148 os_memset(x_bin, 0, sizeof(x_bin)); 149 150 prime = crypto_ec_get_prime(grp->group); 151 primebitlen = crypto_ec_prime_len_bits(grp->group); 152 primebytelen = crypto_ec_prime_len(grp->group); 153 if (crypto_bignum_to_bin(prime, prime_bin, sizeof(prime_bin), 154 primebytelen) < 0) 155 return -1; 156 157 if ((prfbuf = os_malloc(primebytelen)) == NULL) { 158 wpa_printf(MSG_INFO, "EAP-pwd: unable to malloc space for prf " 159 "buffer"); 160 goto fail; 161 } 162 163 /* get a random quadratic residue and nonresidue */ 164 if (dragonfly_get_random_qr_qnr(prime, &qr, &qnr) < 0 || 165 crypto_bignum_to_bin(qr, qr_bin, sizeof(qr_bin), 166 primebytelen) < 0 || 167 crypto_bignum_to_bin(qnr, qnr_bin, sizeof(qnr_bin), 168 primebytelen) < 0) 169 goto fail; 170 171 os_memset(prfbuf, 0, primebytelen); 172 ctr = 0; 173 174 /* 175 * Run through the hunting-and-pecking loop 40 times to mask the time 176 * necessary to find PWE. The odds of PWE not being found in 40 loops is 177 * roughly 1 in 1 trillion. 178 */ 179 while (ctr < 40) { 180 ctr++; 181 182 /* 183 * compute counter-mode password value and stretch to prime 184 * pwd-seed = H(token | peer-id | server-id | password | 185 * counter) 186 */ 187 hash = eap_pwd_h_init(); 188 if (hash == NULL) 189 goto fail; 190 eap_pwd_h_update(hash, token, sizeof(u32)); 191 eap_pwd_h_update(hash, id_peer, id_peer_len); 192 eap_pwd_h_update(hash, id_server, id_server_len); 193 eap_pwd_h_update(hash, password, password_len); 194 eap_pwd_h_update(hash, &ctr, sizeof(ctr)); 195 eap_pwd_h_final(hash, pwe_digest); 196 197 is_odd = const_time_select_u8( 198 found, is_odd, pwe_digest[SHA256_MAC_LEN - 1] & 0x01); 199 if (eap_pwd_kdf(pwe_digest, SHA256_MAC_LEN, 200 (u8 *) "EAP-pwd Hunting And Pecking", 201 os_strlen("EAP-pwd Hunting And Pecking"), 202 prfbuf, primebitlen) < 0) 203 goto fail; 204 if (primebitlen % 8) 205 buf_shift_right(prfbuf, primebytelen, 206 8 - primebitlen % 8); 207 cmp_prime = const_time_memcmp(prfbuf, prime_bin, primebytelen); 208 /* Create a const_time mask for selection based on prf result 209 * being smaller than prime. */ 210 in_range = const_time_fill_msb((unsigned int) cmp_prime); 211 /* The algorithm description would skip the next steps if 212 * cmp_prime >= 0, but go through them regardless to minimize 213 * externally observable differences in behavior. */ 214 215 crypto_bignum_deinit(x_candidate, 1); 216 x_candidate = crypto_bignum_init_set(prfbuf, primebytelen); 217 if (!x_candidate) { 218 wpa_printf(MSG_INFO, 219 "EAP-pwd: unable to create x_candidate"); 220 goto fail; 221 } 222 223 wpa_hexdump_key(MSG_DEBUG, "EAP-pwd: x_candidate", 224 prfbuf, primebytelen); 225 const_time_select_bin(found, x_bin, prfbuf, primebytelen, 226 x_bin); 227 228 /* 229 * compute y^2 using the equation of the curve 230 * 231 * y^2 = x^3 + ax + b 232 */ 233 crypto_bignum_deinit(tmp2, 1); 234 tmp2 = crypto_ec_point_compute_y_sqr(grp->group, x_candidate); 235 if (!tmp2) 236 goto fail; 237 238 res = dragonfly_is_quadratic_residue_blind(grp->group, qr_bin, 239 qnr_bin, tmp2); 240 if (res < 0) 241 goto fail; 242 found_ctr = const_time_select_u8(found, found_ctr, ctr); 243 /* found is 0 or 0xff here and res is 0 or 1. Bitwise OR of them 244 * (with res converted to 0/0xff and masked with prf being below 245 * prime) handles this in constant time. 246 */ 247 found |= (res & in_range) * 0xff; 248 } 249 if (found == 0) { 250 wpa_printf(MSG_INFO, 251 "EAP-pwd: unable to find random point on curve for group %d, something's fishy", 252 num); 253 goto fail; 254 } 255 256 /* 257 * We know x_candidate is a quadratic residue so set it here. 258 */ 259 crypto_bignum_deinit(x_candidate, 1); 260 x_candidate = crypto_bignum_init_set(x_bin, primebytelen); 261 if (!x_candidate) 262 goto fail; 263 264 /* y = sqrt(x^3 + ax + b) mod p 265 * if LSB(y) == LSB(pwd-seed): PWE = (x, y) 266 * else: PWE = (x, p - y) 267 * 268 * Calculate y and the two possible values for PWE and after that, 269 * use constant time selection to copy the correct alternative. 270 */ 271 y = crypto_ec_point_compute_y_sqr(grp->group, x_candidate); 272 if (!y || 273 dragonfly_sqrt(grp->group, y, y) < 0 || 274 crypto_bignum_to_bin(y, x_y, MAX_ECC_PRIME_LEN, primebytelen) < 0 || 275 crypto_bignum_sub(prime, y, y) < 0 || 276 crypto_bignum_to_bin(y, x_y + MAX_ECC_PRIME_LEN, 277 MAX_ECC_PRIME_LEN, primebytelen) < 0) { 278 wpa_printf(MSG_DEBUG, "SAE: Could not solve y"); 279 goto fail; 280 } 281 282 /* Constant time selection of the y coordinate from the two 283 * options */ 284 is_eq = const_time_eq(is_odd, x_y[primebytelen - 1] & 0x01); 285 const_time_select_bin(is_eq, x_y, x_y + MAX_ECC_PRIME_LEN, 286 primebytelen, x_y + primebytelen); 287 os_memcpy(x_y, x_bin, primebytelen); 288 wpa_hexdump_key(MSG_DEBUG, "EAP-pwd: PWE", x_y, 2 * primebytelen); 289 grp->pwe = crypto_ec_point_from_bin(grp->group, x_y); 290 if (!grp->pwe) { 291 wpa_printf(MSG_DEBUG, "EAP-pwd: Could not generate PWE"); 292 goto fail; 293 } 294 295 /* 296 * If there's a solution to the equation then the point must be on the 297 * curve so why check again explicitly? OpenSSL code says this is 298 * required by X9.62. We're not X9.62 but it can't hurt just to be sure. 299 */ 300 if (!crypto_ec_point_is_on_curve(grp->group, grp->pwe)) { 301 wpa_printf(MSG_INFO, "EAP-pwd: point is not on curve"); 302 goto fail; 303 } 304 305 wpa_printf(MSG_DEBUG, "EAP-pwd: found a PWE in %02d tries", found_ctr); 306 307 if (0) { 308 fail: 309 crypto_ec_point_deinit(grp->pwe, 1); 310 grp->pwe = NULL; 311 ret = 1; 312 } 313 /* cleanliness and order.... */ 314 crypto_bignum_deinit(x_candidate, 1); 315 crypto_bignum_deinit(tmp2, 1); 316 crypto_bignum_deinit(y, 1); 317 crypto_bignum_deinit(qr, 1); 318 crypto_bignum_deinit(qnr, 1); 319 bin_clear_free(prfbuf, primebytelen); 320 os_memset(qr_bin, 0, sizeof(qr_bin)); 321 os_memset(qnr_bin, 0, sizeof(qnr_bin)); 322 os_memset(qr_or_qnr_bin, 0, sizeof(qr_or_qnr_bin)); 323 os_memset(pwe_digest, 0, sizeof(pwe_digest)); 324 forced_memzero(x_y, sizeof(x_y)); 325 326 return ret; 327 } 328 329 330 int compute_keys(EAP_PWD_group *grp, const struct crypto_bignum *k, 331 const struct crypto_bignum *peer_scalar, 332 const struct crypto_bignum *server_scalar, 333 const u8 *confirm_peer, const u8 *confirm_server, 334 const u32 *ciphersuite, u8 *msk, u8 *emsk, u8 *session_id) 335 { 336 struct crypto_hash *hash; 337 u8 mk[SHA256_MAC_LEN], *cruft; 338 u8 msk_emsk[EAP_MSK_LEN + EAP_EMSK_LEN]; 339 size_t prime_len, order_len; 340 341 prime_len = crypto_ec_prime_len(grp->group); 342 order_len = crypto_ec_order_len(grp->group); 343 344 cruft = os_malloc(prime_len); 345 if (!cruft) 346 return -1; 347 348 /* 349 * first compute the session-id = TypeCode | H(ciphersuite | scal_p | 350 * scal_s) 351 */ 352 session_id[0] = EAP_TYPE_PWD; 353 hash = eap_pwd_h_init(); 354 if (hash == NULL) { 355 os_free(cruft); 356 return -1; 357 } 358 eap_pwd_h_update(hash, (const u8 *) ciphersuite, sizeof(u32)); 359 crypto_bignum_to_bin(peer_scalar, cruft, order_len, order_len); 360 eap_pwd_h_update(hash, cruft, order_len); 361 crypto_bignum_to_bin(server_scalar, cruft, order_len, order_len); 362 eap_pwd_h_update(hash, cruft, order_len); 363 eap_pwd_h_final(hash, &session_id[1]); 364 365 /* then compute MK = H(k | confirm-peer | confirm-server) */ 366 hash = eap_pwd_h_init(); 367 if (hash == NULL) { 368 os_free(cruft); 369 return -1; 370 } 371 crypto_bignum_to_bin(k, cruft, prime_len, prime_len); 372 eap_pwd_h_update(hash, cruft, prime_len); 373 os_free(cruft); 374 eap_pwd_h_update(hash, confirm_peer, SHA256_MAC_LEN); 375 eap_pwd_h_update(hash, confirm_server, SHA256_MAC_LEN); 376 eap_pwd_h_final(hash, mk); 377 378 /* stretch the mk with the session-id to get MSK | EMSK */ 379 if (eap_pwd_kdf(mk, SHA256_MAC_LEN, 380 session_id, SHA256_MAC_LEN + 1, 381 msk_emsk, (EAP_MSK_LEN + EAP_EMSK_LEN) * 8) < 0) { 382 return -1; 383 } 384 385 os_memcpy(msk, msk_emsk, EAP_MSK_LEN); 386 os_memcpy(emsk, msk_emsk + EAP_MSK_LEN, EAP_EMSK_LEN); 387 388 return 1; 389 } 390 391 392 static int eap_pwd_element_coord_ok(const struct crypto_bignum *prime, 393 const u8 *buf, size_t len) 394 { 395 struct crypto_bignum *val; 396 int ok = 1; 397 398 val = crypto_bignum_init_set(buf, len); 399 if (!val || crypto_bignum_is_zero(val) || 400 crypto_bignum_cmp(val, prime) >= 0) 401 ok = 0; 402 crypto_bignum_deinit(val, 0); 403 return ok; 404 } 405 406 407 struct crypto_ec_point * eap_pwd_get_element(EAP_PWD_group *group, 408 const u8 *buf) 409 { 410 struct crypto_ec_point *element; 411 const struct crypto_bignum *prime; 412 size_t prime_len; 413 414 prime = crypto_ec_get_prime(group->group); 415 prime_len = crypto_ec_prime_len(group->group); 416 417 /* RFC 5931, 2.8.5.2.2: 0 < x,y < p */ 418 if (!eap_pwd_element_coord_ok(prime, buf, prime_len) || 419 !eap_pwd_element_coord_ok(prime, buf + prime_len, prime_len)) { 420 wpa_printf(MSG_INFO, "EAP-pwd: Invalid coordinate in element"); 421 return NULL; 422 } 423 424 element = crypto_ec_point_from_bin(group->group, buf); 425 if (!element) { 426 wpa_printf(MSG_INFO, "EAP-pwd: EC point from element failed"); 427 return NULL; 428 } 429 430 /* RFC 5931, 2.8.5.2.2: on curve and not the point at infinity */ 431 if (!crypto_ec_point_is_on_curve(group->group, element) || 432 crypto_ec_point_is_at_infinity(group->group, element)) { 433 wpa_printf(MSG_INFO, "EAP-pwd: Invalid element"); 434 goto fail; 435 } 436 437 out: 438 return element; 439 fail: 440 crypto_ec_point_deinit(element, 0); 441 element = NULL; 442 goto out; 443 } 444 445 446 struct crypto_bignum * eap_pwd_get_scalar(EAP_PWD_group *group, const u8 *buf) 447 { 448 struct crypto_bignum *scalar; 449 const struct crypto_bignum *order; 450 size_t order_len; 451 452 order = crypto_ec_get_order(group->group); 453 order_len = crypto_ec_order_len(group->group); 454 455 /* RFC 5931, 2.8.5.2: 1 < scalar < r */ 456 scalar = crypto_bignum_init_set(buf, order_len); 457 if (!scalar || crypto_bignum_is_zero(scalar) || 458 crypto_bignum_is_one(scalar) || 459 crypto_bignum_cmp(scalar, order) >= 0) { 460 wpa_printf(MSG_INFO, "EAP-pwd: received scalar is invalid"); 461 crypto_bignum_deinit(scalar, 0); 462 scalar = NULL; 463 } 464 465 return scalar; 466 } 467 468 469 int eap_pwd_get_rand_mask(EAP_PWD_group *group, struct crypto_bignum *_rand, 470 struct crypto_bignum *_mask, 471 struct crypto_bignum *scalar) 472 { 473 return dragonfly_generate_scalar(crypto_ec_get_order(group->group), 474 _rand, _mask, scalar); 475 } 476