libeap/src/eap_common/eap_pwd_common.c

   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 "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 }