eap_pwd_common.c revision 351611
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) */ 22struct 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 31void 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 37void 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 */ 45static 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 89EAP_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 */ 118int 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 struct crypto_bignum *tmp2 = NULL; 131 struct crypto_hash *hash; 132 unsigned char pwe_digest[SHA256_MAC_LEN], *prfbuf = NULL, ctr; 133 int ret = 0, res; 134 u8 found = 0; /* 0 (false) or 0xff (true) to be used as const_time_* 135 * mask */ 136 size_t primebytelen = 0, primebitlen; 137 struct crypto_bignum *x_candidate = NULL; 138 const struct crypto_bignum *prime; 139 u8 found_ctr = 0, is_odd = 0; 140 int cmp_prime; 141 unsigned int in_range; 142 143 if (grp->pwe) 144 return -1; 145 146 os_memset(x_bin, 0, sizeof(x_bin)); 147 148 prime = crypto_ec_get_prime(grp->group); 149 primebitlen = crypto_ec_prime_len_bits(grp->group); 150 primebytelen = crypto_ec_prime_len(grp->group); 151 if (crypto_bignum_to_bin(prime, prime_bin, sizeof(prime_bin), 152 primebytelen) < 0) 153 return -1; 154 grp->pwe = crypto_ec_point_init(grp->group); 155 if (!grp->pwe) { 156 wpa_printf(MSG_INFO, "EAP-pwd: unable to create bignums"); 157 goto fail; 158 } 159 160 if ((prfbuf = os_malloc(primebytelen)) == NULL) { 161 wpa_printf(MSG_INFO, "EAP-pwd: unable to malloc space for prf " 162 "buffer"); 163 goto fail; 164 } 165 166 /* get a random quadratic residue and nonresidue */ 167 if (dragonfly_get_random_qr_qnr(prime, &qr, &qnr) < 0 || 168 crypto_bignum_to_bin(qr, qr_bin, sizeof(qr_bin), 169 primebytelen) < 0 || 170 crypto_bignum_to_bin(qnr, qnr_bin, sizeof(qnr_bin), 171 primebytelen) < 0) 172 goto fail; 173 174 os_memset(prfbuf, 0, primebytelen); 175 ctr = 0; 176 177 /* 178 * Run through the hunting-and-pecking loop 40 times to mask the time 179 * necessary to find PWE. The odds of PWE not being found in 40 loops is 180 * roughly 1 in 1 trillion. 181 */ 182 while (ctr < 40) { 183 ctr++; 184 185 /* 186 * compute counter-mode password value and stretch to prime 187 * pwd-seed = H(token | peer-id | server-id | password | 188 * counter) 189 */ 190 hash = eap_pwd_h_init(); 191 if (hash == NULL) 192 goto fail; 193 eap_pwd_h_update(hash, token, sizeof(u32)); 194 eap_pwd_h_update(hash, id_peer, id_peer_len); 195 eap_pwd_h_update(hash, id_server, id_server_len); 196 eap_pwd_h_update(hash, password, password_len); 197 eap_pwd_h_update(hash, &ctr, sizeof(ctr)); 198 eap_pwd_h_final(hash, pwe_digest); 199 200 is_odd = const_time_select_u8( 201 found, is_odd, pwe_digest[SHA256_MAC_LEN - 1] & 0x01); 202 if (eap_pwd_kdf(pwe_digest, SHA256_MAC_LEN, 203 (u8 *) "EAP-pwd Hunting And Pecking", 204 os_strlen("EAP-pwd Hunting And Pecking"), 205 prfbuf, primebitlen) < 0) 206 goto fail; 207 if (primebitlen % 8) 208 buf_shift_right(prfbuf, primebytelen, 209 8 - primebitlen % 8); 210 cmp_prime = const_time_memcmp(prfbuf, prime_bin, primebytelen); 211 /* Create a const_time mask for selection based on prf result 212 * being smaller than prime. */ 213 in_range = const_time_fill_msb((unsigned int) cmp_prime); 214 /* The algorithm description would skip the next steps if 215 * cmp_prime >= 0, but go through them regardless to minimize 216 * externally observable differences in behavior. */ 217 218 crypto_bignum_deinit(x_candidate, 1); 219 x_candidate = crypto_bignum_init_set(prfbuf, primebytelen); 220 if (!x_candidate) { 221 wpa_printf(MSG_INFO, 222 "EAP-pwd: unable to create x_candidate"); 223 goto fail; 224 } 225 226 wpa_hexdump_key(MSG_DEBUG, "EAP-pwd: x_candidate", 227 prfbuf, primebytelen); 228 const_time_select_bin(found, x_bin, prfbuf, primebytelen, 229 x_bin); 230 231 /* 232 * compute y^2 using the equation of the curve 233 * 234 * y^2 = x^3 + ax + b 235 */ 236 crypto_bignum_deinit(tmp2, 1); 237 tmp2 = crypto_ec_point_compute_y_sqr(grp->group, x_candidate); 238 if (!tmp2) 239 goto fail; 240 241 res = dragonfly_is_quadratic_residue_blind(grp->group, qr_bin, 242 qnr_bin, tmp2); 243 if (res < 0) 244 goto fail; 245 found_ctr = const_time_select_u8(found, found_ctr, ctr); 246 /* found is 0 or 0xff here and res is 0 or 1. Bitwise OR of them 247 * (with res converted to 0/0xff and masked with prf being below 248 * prime) handles this in constant time. 249 */ 250 found |= (res & in_range) * 0xff; 251 } 252 if (found == 0) { 253 wpa_printf(MSG_INFO, 254 "EAP-pwd: unable to find random point on curve for group %d, something's fishy", 255 num); 256 goto fail; 257 } 258 259 /* 260 * We know x_candidate is a quadratic residue so set it here. 261 */ 262 crypto_bignum_deinit(x_candidate, 1); 263 x_candidate = crypto_bignum_init_set(x_bin, primebytelen); 264 if (!x_candidate || 265 crypto_ec_point_solve_y_coord(grp->group, grp->pwe, x_candidate, 266 is_odd) != 0) { 267 wpa_printf(MSG_INFO, "EAP-pwd: Could not solve for y"); 268 goto fail; 269 } 270 271 /* 272 * If there's a solution to the equation then the point must be on the 273 * curve so why check again explicitly? OpenSSL code says this is 274 * required by X9.62. We're not X9.62 but it can't hurt just to be sure. 275 */ 276 if (!crypto_ec_point_is_on_curve(grp->group, grp->pwe)) { 277 wpa_printf(MSG_INFO, "EAP-pwd: point is not on curve"); 278 goto fail; 279 } 280 281 wpa_printf(MSG_DEBUG, "EAP-pwd: found a PWE in %02d tries", found_ctr); 282 283 if (0) { 284 fail: 285 crypto_ec_point_deinit(grp->pwe, 1); 286 grp->pwe = NULL; 287 ret = 1; 288 } 289 /* cleanliness and order.... */ 290 crypto_bignum_deinit(x_candidate, 1); 291 crypto_bignum_deinit(tmp2, 1); 292 crypto_bignum_deinit(qr, 1); 293 crypto_bignum_deinit(qnr, 1); 294 bin_clear_free(prfbuf, primebytelen); 295 os_memset(qr_bin, 0, sizeof(qr_bin)); 296 os_memset(qnr_bin, 0, sizeof(qnr_bin)); 297 os_memset(qr_or_qnr_bin, 0, sizeof(qr_or_qnr_bin)); 298 os_memset(pwe_digest, 0, sizeof(pwe_digest)); 299 300 return ret; 301} 302 303 304int compute_keys(EAP_PWD_group *grp, const struct crypto_bignum *k, 305 const struct crypto_bignum *peer_scalar, 306 const struct crypto_bignum *server_scalar, 307 const u8 *confirm_peer, const u8 *confirm_server, 308 const u32 *ciphersuite, u8 *msk, u8 *emsk, u8 *session_id) 309{ 310 struct crypto_hash *hash; 311 u8 mk[SHA256_MAC_LEN], *cruft; 312 u8 msk_emsk[EAP_MSK_LEN + EAP_EMSK_LEN]; 313 size_t prime_len, order_len; 314 315 prime_len = crypto_ec_prime_len(grp->group); 316 order_len = crypto_ec_order_len(grp->group); 317 318 cruft = os_malloc(prime_len); 319 if (!cruft) 320 return -1; 321 322 /* 323 * first compute the session-id = TypeCode | H(ciphersuite | scal_p | 324 * scal_s) 325 */ 326 session_id[0] = EAP_TYPE_PWD; 327 hash = eap_pwd_h_init(); 328 if (hash == NULL) { 329 os_free(cruft); 330 return -1; 331 } 332 eap_pwd_h_update(hash, (const u8 *) ciphersuite, sizeof(u32)); 333 crypto_bignum_to_bin(peer_scalar, cruft, order_len, order_len); 334 eap_pwd_h_update(hash, cruft, order_len); 335 crypto_bignum_to_bin(server_scalar, cruft, order_len, order_len); 336 eap_pwd_h_update(hash, cruft, order_len); 337 eap_pwd_h_final(hash, &session_id[1]); 338 339 /* then compute MK = H(k | confirm-peer | confirm-server) */ 340 hash = eap_pwd_h_init(); 341 if (hash == NULL) { 342 os_free(cruft); 343 return -1; 344 } 345 crypto_bignum_to_bin(k, cruft, prime_len, prime_len); 346 eap_pwd_h_update(hash, cruft, prime_len); 347 os_free(cruft); 348 eap_pwd_h_update(hash, confirm_peer, SHA256_MAC_LEN); 349 eap_pwd_h_update(hash, confirm_server, SHA256_MAC_LEN); 350 eap_pwd_h_final(hash, mk); 351 352 /* stretch the mk with the session-id to get MSK | EMSK */ 353 if (eap_pwd_kdf(mk, SHA256_MAC_LEN, 354 session_id, SHA256_MAC_LEN + 1, 355 msk_emsk, (EAP_MSK_LEN + EAP_EMSK_LEN) * 8) < 0) { 356 return -1; 357 } 358 359 os_memcpy(msk, msk_emsk, EAP_MSK_LEN); 360 os_memcpy(emsk, msk_emsk + EAP_MSK_LEN, EAP_EMSK_LEN); 361 362 return 1; 363} 364 365 366static int eap_pwd_element_coord_ok(const struct crypto_bignum *prime, 367 const u8 *buf, size_t len) 368{ 369 struct crypto_bignum *val; 370 int ok = 1; 371 372 val = crypto_bignum_init_set(buf, len); 373 if (!val || crypto_bignum_is_zero(val) || 374 crypto_bignum_cmp(val, prime) >= 0) 375 ok = 0; 376 crypto_bignum_deinit(val, 0); 377 return ok; 378} 379 380 381struct crypto_ec_point * eap_pwd_get_element(EAP_PWD_group *group, 382 const u8 *buf) 383{ 384 struct crypto_ec_point *element; 385 const struct crypto_bignum *prime; 386 size_t prime_len; 387 388 prime = crypto_ec_get_prime(group->group); 389 prime_len = crypto_ec_prime_len(group->group); 390 391 /* RFC 5931, 2.8.5.2.2: 0 < x,y < p */ 392 if (!eap_pwd_element_coord_ok(prime, buf, prime_len) || 393 !eap_pwd_element_coord_ok(prime, buf + prime_len, prime_len)) { 394 wpa_printf(MSG_INFO, "EAP-pwd: Invalid coordinate in element"); 395 return NULL; 396 } 397 398 element = crypto_ec_point_from_bin(group->group, buf); 399 if (!element) { 400 wpa_printf(MSG_INFO, "EAP-pwd: EC point from element failed"); 401 return NULL; 402 } 403 404 /* RFC 5931, 2.8.5.2.2: on curve and not the point at infinity */ 405 if (!crypto_ec_point_is_on_curve(group->group, element) || 406 crypto_ec_point_is_at_infinity(group->group, element)) { 407 wpa_printf(MSG_INFO, "EAP-pwd: Invalid element"); 408 goto fail; 409 } 410 411out: 412 return element; 413fail: 414 crypto_ec_point_deinit(element, 0); 415 element = NULL; 416 goto out; 417} 418 419 420struct crypto_bignum * eap_pwd_get_scalar(EAP_PWD_group *group, const u8 *buf) 421{ 422 struct crypto_bignum *scalar; 423 const struct crypto_bignum *order; 424 size_t order_len; 425 426 order = crypto_ec_get_order(group->group); 427 order_len = crypto_ec_order_len(group->group); 428 429 /* RFC 5931, 2.8.5.2: 1 < scalar < r */ 430 scalar = crypto_bignum_init_set(buf, order_len); 431 if (!scalar || crypto_bignum_is_zero(scalar) || 432 crypto_bignum_is_one(scalar) || 433 crypto_bignum_cmp(scalar, order) >= 0) { 434 wpa_printf(MSG_INFO, "EAP-pwd: received scalar is invalid"); 435 crypto_bignum_deinit(scalar, 0); 436 scalar = NULL; 437 } 438 439 return scalar; 440} 441 442 443int eap_pwd_get_rand_mask(EAP_PWD_group *group, struct crypto_bignum *_rand, 444 struct crypto_bignum *_mask, 445 struct crypto_bignum *scalar) 446{ 447 return dragonfly_generate_scalar(crypto_ec_get_order(group->group), 448 _rand, _mask, scalar); 449} 450