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 114static void buf_shift_right(u8 *buf, size_t len, size_t bits) 115{ 116 size_t i; 117 for (i = len - 1; i > 0; i--) 118 buf[i] = (buf[i - 1] << (8 - bits)) | (buf[i] >> bits); 119 buf[0] >>= bits; 120} 121 122 123/* 124 * compute a "random" secret point on an elliptic curve based 125 * on the password and identities. 126 */ 127int compute_password_element(EAP_PWD_group *grp, u16 num, 128 const u8 *password, size_t password_len, 129 const u8 *id_server, size_t id_server_len, 130 const u8 *id_peer, size_t id_peer_len, 131 const u8 *token) 132{ 133 struct crypto_bignum *qr = NULL, *qnr = NULL; 134 u8 qr_bin[MAX_ECC_PRIME_LEN]; 135 u8 qnr_bin[MAX_ECC_PRIME_LEN]; 136 u8 qr_or_qnr_bin[MAX_ECC_PRIME_LEN]; 137 u8 x_bin[MAX_ECC_PRIME_LEN]; 138 u8 prime_bin[MAX_ECC_PRIME_LEN]; 139 struct crypto_bignum *tmp2 = NULL; 140 struct crypto_hash *hash; 141 unsigned char pwe_digest[SHA256_MAC_LEN], *prfbuf = NULL, ctr; 142 int ret = 0, res; 143 u8 found = 0; /* 0 (false) or 0xff (true) to be used as const_time_* 144 * mask */ 145 size_t primebytelen = 0, primebitlen; 146 struct crypto_bignum *x_candidate = NULL; 147 const struct crypto_bignum *prime; 148 u8 found_ctr = 0, is_odd = 0; 149 int cmp_prime; 150 unsigned int in_range; 151 152 if (grp->pwe) 153 return -1; 154 155 os_memset(x_bin, 0, sizeof(x_bin)); 156 157 prime = crypto_ec_get_prime(grp->group); 158 primebitlen = crypto_ec_prime_len_bits(grp->group); 159 primebytelen = crypto_ec_prime_len(grp->group); 160 if (crypto_bignum_to_bin(prime, prime_bin, sizeof(prime_bin), 161 primebytelen) < 0) 162 return -1; 163 grp->pwe = crypto_ec_point_init(grp->group); 164 if (!grp->pwe) { 165 wpa_printf(MSG_INFO, "EAP-pwd: unable to create bignums"); 166 goto fail; 167 } 168 169 if ((prfbuf = os_malloc(primebytelen)) == NULL) { 170 wpa_printf(MSG_INFO, "EAP-pwd: unable to malloc space for prf " 171 "buffer"); 172 goto fail; 173 } 174 175 /* get a random quadratic residue and nonresidue */ 176 if (dragonfly_get_random_qr_qnr(prime, &qr, &qnr) < 0 || 177 crypto_bignum_to_bin(qr, qr_bin, sizeof(qr_bin), 178 primebytelen) < 0 || 179 crypto_bignum_to_bin(qnr, qnr_bin, sizeof(qnr_bin), 180 primebytelen) < 0) 181 goto fail; 182 183 os_memset(prfbuf, 0, primebytelen); 184 ctr = 0; 185 186 /* 187 * Run through the hunting-and-pecking loop 40 times to mask the time 188 * necessary to find PWE. The odds of PWE not being found in 40 loops is 189 * roughly 1 in 1 trillion. 190 */ 191 while (ctr < 40) { 192 ctr++; 193 194 /* 195 * compute counter-mode password value and stretch to prime 196 * pwd-seed = H(token | peer-id | server-id | password | 197 * counter) 198 */ 199 hash = eap_pwd_h_init(); 200 if (hash == NULL) 201 goto fail; 202 eap_pwd_h_update(hash, token, sizeof(u32)); 203 eap_pwd_h_update(hash, id_peer, id_peer_len); 204 eap_pwd_h_update(hash, id_server, id_server_len); 205 eap_pwd_h_update(hash, password, password_len); 206 eap_pwd_h_update(hash, &ctr, sizeof(ctr)); 207 eap_pwd_h_final(hash, pwe_digest); 208 209 is_odd = const_time_select_u8( 210 found, is_odd, pwe_digest[SHA256_MAC_LEN - 1] & 0x01); 211 if (eap_pwd_kdf(pwe_digest, SHA256_MAC_LEN, 212 (u8 *) "EAP-pwd Hunting And Pecking", 213 os_strlen("EAP-pwd Hunting And Pecking"), 214 prfbuf, primebitlen) < 0) 215 goto fail; 216 if (primebitlen % 8) 217 buf_shift_right(prfbuf, primebytelen, 218 8 - primebitlen % 8); 219 cmp_prime = const_time_memcmp(prfbuf, prime_bin, primebytelen); 220 /* Create a const_time mask for selection based on prf result 221 * being smaller than prime. */ 222 in_range = const_time_fill_msb((unsigned int) cmp_prime); 223 /* The algorithm description would skip the next steps if 224 * cmp_prime >= 0, but go through them regardless to minimize 225 * externally observable differences in behavior. */ 226 227 crypto_bignum_deinit(x_candidate, 1); 228 x_candidate = crypto_bignum_init_set(prfbuf, primebytelen); 229 if (!x_candidate) { 230 wpa_printf(MSG_INFO, 231 "EAP-pwd: unable to create x_candidate"); 232 goto fail; 233 } 234 235 wpa_hexdump_key(MSG_DEBUG, "EAP-pwd: x_candidate", 236 prfbuf, primebytelen); 237 const_time_select_bin(found, x_bin, prfbuf, primebytelen, 238 x_bin); 239 240 /* 241 * compute y^2 using the equation of the curve 242 * 243 * y^2 = x^3 + ax + b 244 */ 245 crypto_bignum_deinit(tmp2, 1); 246 tmp2 = crypto_ec_point_compute_y_sqr(grp->group, x_candidate); 247 if (!tmp2) 248 goto fail; 249 250 res = dragonfly_is_quadratic_residue_blind(grp->group, qr_bin, 251 qnr_bin, tmp2); 252 if (res < 0) 253 goto fail; 254 found_ctr = const_time_select_u8(found, found_ctr, ctr); 255 /* found is 0 or 0xff here and res is 0 or 1. Bitwise OR of them 256 * (with res converted to 0/0xff and masked with prf being below 257 * prime) handles this in constant time. 258 */ 259 found |= (res & in_range) * 0xff; 260 } 261 if (found == 0) { 262 wpa_printf(MSG_INFO, 263 "EAP-pwd: unable to find random point on curve for group %d, something's fishy", 264 num); 265 goto fail; 266 } 267 268 /* 269 * We know x_candidate is a quadratic residue so set it here. 270 */ 271 crypto_bignum_deinit(x_candidate, 1); 272 x_candidate = crypto_bignum_init_set(x_bin, primebytelen); 273 if (!x_candidate || 274 crypto_ec_point_solve_y_coord(grp->group, grp->pwe, x_candidate, 275 is_odd) != 0) { 276 wpa_printf(MSG_INFO, "EAP-pwd: Could not solve for y"); 277 goto fail; 278 } 279 280 /* 281 * If there's a solution to the equation then the point must be on the 282 * curve so why check again explicitly? OpenSSL code says this is 283 * required by X9.62. We're not X9.62 but it can't hurt just to be sure. 284 */ 285 if (!crypto_ec_point_is_on_curve(grp->group, grp->pwe)) { 286 wpa_printf(MSG_INFO, "EAP-pwd: point is not on curve"); 287 goto fail; 288 } 289 290 wpa_printf(MSG_DEBUG, "EAP-pwd: found a PWE in %02d tries", found_ctr); 291 292 if (0) { 293 fail: 294 crypto_ec_point_deinit(grp->pwe, 1); 295 grp->pwe = NULL; 296 ret = 1; 297 } 298 /* cleanliness and order.... */ 299 crypto_bignum_deinit(x_candidate, 1); 300 crypto_bignum_deinit(tmp2, 1); 301 crypto_bignum_deinit(qr, 1); 302 crypto_bignum_deinit(qnr, 1); 303 bin_clear_free(prfbuf, primebytelen); 304 os_memset(qr_bin, 0, sizeof(qr_bin)); 305 os_memset(qnr_bin, 0, sizeof(qnr_bin)); 306 os_memset(qr_or_qnr_bin, 0, sizeof(qr_or_qnr_bin)); 307 os_memset(pwe_digest, 0, sizeof(pwe_digest)); 308 309 return ret; 310} 311 312 313int compute_keys(EAP_PWD_group *grp, const struct crypto_bignum *k, 314 const struct crypto_bignum *peer_scalar, 315 const struct crypto_bignum *server_scalar, 316 const u8 *confirm_peer, const u8 *confirm_server, 317 const u32 *ciphersuite, u8 *msk, u8 *emsk, u8 *session_id) 318{ 319 struct crypto_hash *hash; 320 u8 mk[SHA256_MAC_LEN], *cruft; 321 u8 msk_emsk[EAP_MSK_LEN + EAP_EMSK_LEN]; 322 size_t prime_len, order_len; 323 324 prime_len = crypto_ec_prime_len(grp->group); 325 order_len = crypto_ec_order_len(grp->group); 326 327 cruft = os_malloc(prime_len); 328 if (!cruft) 329 return -1; 330 331 /* 332 * first compute the session-id = TypeCode | H(ciphersuite | scal_p | 333 * scal_s) 334 */ 335 session_id[0] = EAP_TYPE_PWD; 336 hash = eap_pwd_h_init(); 337 if (hash == NULL) { 338 os_free(cruft); 339 return -1; 340 } 341 eap_pwd_h_update(hash, (const u8 *) ciphersuite, sizeof(u32)); 342 crypto_bignum_to_bin(peer_scalar, cruft, order_len, order_len); 343 eap_pwd_h_update(hash, cruft, order_len); 344 crypto_bignum_to_bin(server_scalar, cruft, order_len, order_len); 345 eap_pwd_h_update(hash, cruft, order_len); 346 eap_pwd_h_final(hash, &session_id[1]); 347 348 /* then compute MK = H(k | confirm-peer | confirm-server) */ 349 hash = eap_pwd_h_init(); 350 if (hash == NULL) { 351 os_free(cruft); 352 return -1; 353 } 354 crypto_bignum_to_bin(k, cruft, prime_len, prime_len); 355 eap_pwd_h_update(hash, cruft, prime_len); 356 os_free(cruft); 357 eap_pwd_h_update(hash, confirm_peer, SHA256_MAC_LEN); 358 eap_pwd_h_update(hash, confirm_server, SHA256_MAC_LEN); 359 eap_pwd_h_final(hash, mk); 360 361 /* stretch the mk with the session-id to get MSK | EMSK */ 362 if (eap_pwd_kdf(mk, SHA256_MAC_LEN, 363 session_id, SHA256_MAC_LEN + 1, 364 msk_emsk, (EAP_MSK_LEN + EAP_EMSK_LEN) * 8) < 0) { 365 return -1; 366 } 367 368 os_memcpy(msk, msk_emsk, EAP_MSK_LEN); 369 os_memcpy(emsk, msk_emsk + EAP_MSK_LEN, EAP_EMSK_LEN); 370 371 return 1; 372} 373 374 375static int eap_pwd_element_coord_ok(const struct crypto_bignum *prime, 376 const u8 *buf, size_t len) 377{ 378 struct crypto_bignum *val; 379 int ok = 1; 380 381 val = crypto_bignum_init_set(buf, len); 382 if (!val || crypto_bignum_is_zero(val) || 383 crypto_bignum_cmp(val, prime) >= 0) 384 ok = 0; 385 crypto_bignum_deinit(val, 0); 386 return ok; 387} 388 389 390struct crypto_ec_point * eap_pwd_get_element(EAP_PWD_group *group, 391 const u8 *buf) 392{ 393 struct crypto_ec_point *element; 394 const struct crypto_bignum *prime; 395 size_t prime_len; 396 397 prime = crypto_ec_get_prime(group->group); 398 prime_len = crypto_ec_prime_len(group->group); 399 400 /* RFC 5931, 2.8.5.2.2: 0 < x,y < p */ 401 if (!eap_pwd_element_coord_ok(prime, buf, prime_len) || 402 !eap_pwd_element_coord_ok(prime, buf + prime_len, prime_len)) { 403 wpa_printf(MSG_INFO, "EAP-pwd: Invalid coordinate in element"); 404 return NULL; 405 } 406 407 element = crypto_ec_point_from_bin(group->group, buf); 408 if (!element) { 409 wpa_printf(MSG_INFO, "EAP-pwd: EC point from element failed"); 410 return NULL; 411 } 412 413 /* RFC 5931, 2.8.5.2.2: on curve and not the point at infinity */ 414 if (!crypto_ec_point_is_on_curve(group->group, element) || 415 crypto_ec_point_is_at_infinity(group->group, element)) { 416 wpa_printf(MSG_INFO, "EAP-pwd: Invalid element"); 417 goto fail; 418 } 419 420out: 421 return element; 422fail: 423 crypto_ec_point_deinit(element, 0); 424 element = NULL; 425 goto out; 426} 427 428 429struct crypto_bignum * eap_pwd_get_scalar(EAP_PWD_group *group, const u8 *buf) 430{ 431 struct crypto_bignum *scalar; 432 const struct crypto_bignum *order; 433 size_t order_len; 434 435 order = crypto_ec_get_order(group->group); 436 order_len = crypto_ec_order_len(group->group); 437 438 /* RFC 5931, 2.8.5.2: 1 < scalar < r */ 439 scalar = crypto_bignum_init_set(buf, order_len); 440 if (!scalar || crypto_bignum_is_zero(scalar) || 441 crypto_bignum_is_one(scalar) || 442 crypto_bignum_cmp(scalar, order) >= 0) { 443 wpa_printf(MSG_INFO, "EAP-pwd: received scalar is invalid"); 444 crypto_bignum_deinit(scalar, 0); 445 scalar = NULL; 446 } 447 448 return scalar; 449} 450 451 452int eap_pwd_get_rand_mask(EAP_PWD_group *group, struct crypto_bignum *_rand, 453 struct crypto_bignum *_mask, 454 struct crypto_bignum *scalar) 455{ 456 return dragonfly_generate_scalar(crypto_ec_get_order(group->group), 457 _rand, _mask, scalar); 458} 459