1 /* 2 * EAP server/peer: EAP-pwd shared routines 3 * Copyright (c) 2010, Dan Harkins <dharkins (at) 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 "crypto/sha256.h" 12 #include "crypto/crypto.h" 13 #include "eap_defs.h" 14 #include "eap_pwd_common.h" 15 16 /* The random function H(x) = HMAC-SHA256(0^32, x) */ 17 struct crypto_hash * eap_pwd_h_init(void) 18 { 19 u8 allzero[SHA256_MAC_LEN]; 20 os_memset(allzero, 0, SHA256_MAC_LEN); 21 return crypto_hash_init(CRYPTO_HASH_ALG_HMAC_SHA256, allzero, 22 SHA256_MAC_LEN); 23 } 24 25 26 void eap_pwd_h_update(struct crypto_hash *hash, const u8 *data, size_t len) 27 { 28 crypto_hash_update(hash, data, len); 29 } 30 31 32 void eap_pwd_h_final(struct crypto_hash *hash, u8 *digest) 33 { 34 size_t len = SHA256_MAC_LEN; 35 crypto_hash_finish(hash, digest, &len); 36 } 37 38 39 /* a counter-based KDF based on NIST SP800-108 */ 40 static int eap_pwd_kdf(const u8 *key, size_t keylen, const u8 *label, 41 size_t labellen, u8 *result, size_t resultbitlen) 42 { 43 struct crypto_hash *hash; 44 u8 digest[SHA256_MAC_LEN]; 45 u16 i, ctr, L; 46 size_t resultbytelen, len = 0, mdlen; 47 48 resultbytelen = (resultbitlen + 7) / 8; 49 ctr = 0; 50 L = htons(resultbitlen); 51 while (len < resultbytelen) { 52 ctr++; 53 i = htons(ctr); 54 hash = crypto_hash_init(CRYPTO_HASH_ALG_HMAC_SHA256, 55 key, keylen); 56 if (hash == NULL) 57 return -1; 58 if (ctr > 1) 59 crypto_hash_update(hash, digest, SHA256_MAC_LEN); 60 crypto_hash_update(hash, (u8 *) &i, sizeof(u16)); 61 crypto_hash_update(hash, label, labellen); 62 crypto_hash_update(hash, (u8 *) &L, sizeof(u16)); 63 mdlen = SHA256_MAC_LEN; 64 if (crypto_hash_finish(hash, digest, &mdlen) < 0) 65 return -1; 66 if ((len + mdlen) > resultbytelen) 67 os_memcpy(result + len, digest, resultbytelen - len); 68 else 69 os_memcpy(result + len, digest, mdlen); 70 len += mdlen; 71 } 72 73 /* since we're expanding to a bit length, mask off the excess */ 74 if (resultbitlen % 8) { 75 u8 mask = 0xff; 76 mask <<= (8 - (resultbitlen % 8)); 77 result[resultbytelen - 1] &= mask; 78 } 79 80 return 0; 81 } 82 83 84 /* 85 * compute a "random" secret point on an elliptic curve based 86 * on the password and identities. 87 */ 88 int compute_password_element(EAP_PWD_group *grp, u16 num, 89 const u8 *password, size_t password_len, 90 const u8 *id_server, size_t id_server_len, 91 const u8 *id_peer, size_t id_peer_len, 92 const u8 *token) 93 { 94 BIGNUM *x_candidate = NULL, *rnd = NULL, *cofactor = NULL; 95 struct crypto_hash *hash; 96 unsigned char pwe_digest[SHA256_MAC_LEN], *prfbuf = NULL, ctr; 97 int nid, is_odd, ret = 0; 98 size_t primebytelen, primebitlen; 99 100 switch (num) { /* from IANA registry for IKE D-H groups */ 101 case 19: 102 nid = NID_X9_62_prime256v1; 103 break; 104 case 20: 105 nid = NID_secp384r1; 106 break; 107 case 21: 108 nid = NID_secp521r1; 109 break; 110 #ifndef OPENSSL_IS_BORINGSSL 111 case 25: 112 nid = NID_X9_62_prime192v1; 113 break; 114 #endif /* OPENSSL_IS_BORINGSSL */ 115 case 26: 116 nid = NID_secp224r1; 117 break; 118 default: 119 wpa_printf(MSG_INFO, "EAP-pwd: unsupported group %d", num); 120 return -1; 121 } 122 123 grp->pwe = NULL; 124 grp->order = NULL; 125 grp->prime = NULL; 126 127 if ((grp->group = EC_GROUP_new_by_curve_name(nid)) == NULL) { 128 wpa_printf(MSG_INFO, "EAP-pwd: unable to create EC_GROUP"); 129 goto fail; 130 } 131 132 if (((rnd = BN_new()) == NULL) || 133 ((cofactor = BN_new()) == NULL) || 134 ((grp->pwe = EC_POINT_new(grp->group)) == NULL) || 135 ((grp->order = BN_new()) == NULL) || 136 ((grp->prime = BN_new()) == NULL) || 137 ((x_candidate = BN_new()) == NULL)) { 138 wpa_printf(MSG_INFO, "EAP-pwd: unable to create bignums"); 139 goto fail; 140 } 141 142 if (!EC_GROUP_get_curve_GFp(grp->group, grp->prime, NULL, NULL, NULL)) 143 { 144 wpa_printf(MSG_INFO, "EAP-pwd: unable to get prime for GFp " 145 "curve"); 146 goto fail; 147 } 148 if (!EC_GROUP_get_order(grp->group, grp->order, NULL)) { 149 wpa_printf(MSG_INFO, "EAP-pwd: unable to get order for curve"); 150 goto fail; 151 } 152 if (!EC_GROUP_get_cofactor(grp->group, cofactor, NULL)) { 153 wpa_printf(MSG_INFO, "EAP-pwd: unable to get cofactor for " 154 "curve"); 155 goto fail; 156 } 157 primebitlen = BN_num_bits(grp->prime); 158 primebytelen = BN_num_bytes(grp->prime); 159 if ((prfbuf = os_malloc(primebytelen)) == NULL) { 160 wpa_printf(MSG_INFO, "EAP-pwd: unable to malloc space for prf " 161 "buffer"); 162 goto fail; 163 } 164 os_memset(prfbuf, 0, primebytelen); 165 ctr = 0; 166 while (1) { 167 if (ctr > 30) { 168 wpa_printf(MSG_INFO, "EAP-pwd: unable to find random " 169 "point on curve for group %d, something's " 170 "fishy", num); 171 goto fail; 172 } 173 ctr++; 174 175 /* 176 * compute counter-mode password value and stretch to prime 177 * pwd-seed = H(token | peer-id | server-id | password | 178 * counter) 179 */ 180 hash = eap_pwd_h_init(); 181 if (hash == NULL) 182 goto fail; 183 eap_pwd_h_update(hash, token, sizeof(u32)); 184 eap_pwd_h_update(hash, id_peer, id_peer_len); 185 eap_pwd_h_update(hash, id_server, id_server_len); 186 eap_pwd_h_update(hash, password, password_len); 187 eap_pwd_h_update(hash, &ctr, sizeof(ctr)); 188 eap_pwd_h_final(hash, pwe_digest); 189 190 BN_bin2bn(pwe_digest, SHA256_MAC_LEN, rnd); 191 192 if (eap_pwd_kdf(pwe_digest, SHA256_MAC_LEN, 193 (u8 *) "EAP-pwd Hunting And Pecking", 194 os_strlen("EAP-pwd Hunting And Pecking"), 195 prfbuf, primebitlen) < 0) 196 goto fail; 197 198 BN_bin2bn(prfbuf, primebytelen, x_candidate); 199 200 /* 201 * eap_pwd_kdf() returns a string of bits 0..primebitlen but 202 * BN_bin2bn will treat that string of bits as a big endian 203 * number. If the primebitlen is not an even multiple of 8 204 * then excessive bits-- those _after_ primebitlen-- so now 205 * we have to shift right the amount we masked off. 206 */ 207 if (primebitlen % 8) 208 BN_rshift(x_candidate, x_candidate, 209 (8 - (primebitlen % 8))); 210 211 if (BN_ucmp(x_candidate, grp->prime) >= 0) 212 continue; 213 214 wpa_hexdump(MSG_DEBUG, "EAP-pwd: x_candidate", 215 prfbuf, primebytelen); 216 217 /* 218 * need to unambiguously identify the solution, if there is 219 * one... 220 */ 221 if (BN_is_odd(rnd)) 222 is_odd = 1; 223 else 224 is_odd = 0; 225 226 /* 227 * solve the quadratic equation, if it's not solvable then we 228 * don't have a point 229 */ 230 if (!EC_POINT_set_compressed_coordinates_GFp(grp->group, 231 grp->pwe, 232 x_candidate, 233 is_odd, NULL)) 234 continue; 235 /* 236 * If there's a solution to the equation then the point must be 237 * on the curve so why check again explicitly? OpenSSL code 238 * says this is required by X9.62. We're not X9.62 but it can't 239 * hurt just to be sure. 240 */ 241 if (!EC_POINT_is_on_curve(grp->group, grp->pwe, NULL)) { 242 wpa_printf(MSG_INFO, "EAP-pwd: point is not on curve"); 243 continue; 244 } 245 246 if (BN_cmp(cofactor, BN_value_one())) { 247 /* make sure the point is not in a small sub-group */ 248 if (!EC_POINT_mul(grp->group, grp->pwe, NULL, grp->pwe, 249 cofactor, NULL)) { 250 wpa_printf(MSG_INFO, "EAP-pwd: cannot " 251 "multiply generator by order"); 252 continue; 253 } 254 if (EC_POINT_is_at_infinity(grp->group, grp->pwe)) { 255 wpa_printf(MSG_INFO, "EAP-pwd: point is at " 256 "infinity"); 257 continue; 258 } 259 } 260 /* if we got here then we have a new generator. */ 261 break; 262 } 263 wpa_printf(MSG_DEBUG, "EAP-pwd: found a PWE in %d tries", ctr); 264 grp->group_num = num; 265 if (0) { 266 fail: 267 EC_GROUP_free(grp->group); 268 grp->group = NULL; 269 EC_POINT_clear_free(grp->pwe); 270 grp->pwe = NULL; 271 BN_clear_free(grp->order); 272 grp->order = NULL; 273 BN_clear_free(grp->prime); 274 grp->prime = NULL; 275 ret = 1; 276 } 277 /* cleanliness and order.... */ 278 BN_clear_free(cofactor); 279 BN_clear_free(x_candidate); 280 BN_clear_free(rnd); 281 os_free(prfbuf); 282 283 return ret; 284 } 285 286 287 int compute_keys(EAP_PWD_group *grp, BN_CTX *bnctx, const BIGNUM *k, 288 const BIGNUM *peer_scalar, const BIGNUM *server_scalar, 289 const u8 *confirm_peer, const u8 *confirm_server, 290 const u32 *ciphersuite, u8 *msk, u8 *emsk, u8 *session_id) 291 { 292 struct crypto_hash *hash; 293 u8 mk[SHA256_MAC_LEN], *cruft; 294 u8 msk_emsk[EAP_MSK_LEN + EAP_EMSK_LEN]; 295 int offset; 296 297 if ((cruft = os_malloc(BN_num_bytes(grp->prime))) == NULL) 298 return -1; 299 300 /* 301 * first compute the session-id = TypeCode | H(ciphersuite | scal_p | 302 * scal_s) 303 */ 304 session_id[0] = EAP_TYPE_PWD; 305 hash = eap_pwd_h_init(); 306 if (hash == NULL) { 307 os_free(cruft); 308 return -1; 309 } 310 eap_pwd_h_update(hash, (const u8 *) ciphersuite, sizeof(u32)); 311 offset = BN_num_bytes(grp->order) - BN_num_bytes(peer_scalar); 312 os_memset(cruft, 0, BN_num_bytes(grp->prime)); 313 BN_bn2bin(peer_scalar, cruft + offset); 314 eap_pwd_h_update(hash, cruft, BN_num_bytes(grp->order)); 315 offset = BN_num_bytes(grp->order) - BN_num_bytes(server_scalar); 316 os_memset(cruft, 0, BN_num_bytes(grp->prime)); 317 BN_bn2bin(server_scalar, cruft + offset); 318 eap_pwd_h_update(hash, cruft, BN_num_bytes(grp->order)); 319 eap_pwd_h_final(hash, &session_id[1]); 320 321 /* then compute MK = H(k | confirm-peer | confirm-server) */ 322 hash = eap_pwd_h_init(); 323 if (hash == NULL) { 324 os_free(cruft); 325 return -1; 326 } 327 offset = BN_num_bytes(grp->prime) - BN_num_bytes(k); 328 os_memset(cruft, 0, BN_num_bytes(grp->prime)); 329 BN_bn2bin(k, cruft + offset); 330 eap_pwd_h_update(hash, cruft, BN_num_bytes(grp->prime)); 331 os_free(cruft); 332 eap_pwd_h_update(hash, confirm_peer, SHA256_MAC_LEN); 333 eap_pwd_h_update(hash, confirm_server, SHA256_MAC_LEN); 334 eap_pwd_h_final(hash, mk); 335 336 /* stretch the mk with the session-id to get MSK | EMSK */ 337 if (eap_pwd_kdf(mk, SHA256_MAC_LEN, 338 session_id, SHA256_MAC_LEN + 1, 339 msk_emsk, (EAP_MSK_LEN + EAP_EMSK_LEN) * 8) < 0) { 340 return -1; 341 } 342 343 os_memcpy(msk, msk_emsk, EAP_MSK_LEN); 344 os_memcpy(emsk, msk_emsk + EAP_MSK_LEN, EAP_EMSK_LEN); 345 346 return 1; 347 } 348
