contrib/hostapd/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                              u8 *password, int password_len,
  90                              u8 *id_server, int id_server_len,
  91                              u8 *id_peer, int id_peer_len, u8 *token)
  92 {
  93         BIGNUM *x_candidate = NULL, *rnd = NULL, *cofactor = NULL;
  94         struct crypto_hash *hash;
  95         unsigned char pwe_digest[SHA256_MAC_LEN], *prfbuf = NULL, ctr;
  96         int nid, is_odd, ret = 0;
  97         size_t primebytelen, primebitlen;
  98
  99         switch (num) { /* from IANA registry for IKE D-H groups */
 100         case 19:
 101                 nid = NID_X9_62_prime256v1;
 102                 break;
 103         case 20:
 104                 nid = NID_secp384r1;
 105                 break;
 106         case 21:
 107                 nid = NID_secp521r1;
 108                 break;
 109         case 25:
 110                 nid = NID_X9_62_prime192v1;
 111                 break;
 112         case 26:
 113                 nid = NID_secp224r1;
 114                 break;
 115         default:
 116                 wpa_printf(MSG_INFO, "EAP-pwd: unsupported group %d", num);
 117                 return -1;
 118         }
 119
 120         grp->pwe = NULL;
 121         grp->order = NULL;
 122         grp->prime = NULL;
 123
 124         if ((grp->group = EC_GROUP_new_by_curve_name(nid)) == NULL) {
 125                 wpa_printf(MSG_INFO, "EAP-pwd: unable to create EC_GROUP");
 126                 goto fail;
 127         }
 128
 129         if (((rnd = BN_new()) == NULL) ||
 130             ((cofactor = BN_new()) == NULL) ||
 131             ((grp->pwe = EC_POINT_new(grp->group)) == NULL) ||
 132             ((grp->order = BN_new()) == NULL) ||
 133             ((grp->prime = BN_new()) == NULL) ||
 134             ((x_candidate = BN_new()) == NULL)) {
 135                 wpa_printf(MSG_INFO, "EAP-pwd: unable to create bignums");
 136                 goto fail;
 137         }
 138
 139         if (!EC_GROUP_get_curve_GFp(grp->group, grp->prime, NULL, NULL, NULL))
 140         {
 141                 wpa_printf(MSG_INFO, "EAP-pwd: unable to get prime for GFp "
 142                            "curve");
 143                 goto fail;
 144         }
 145         if (!EC_GROUP_get_order(grp->group, grp->order, NULL)) {
 146                 wpa_printf(MSG_INFO, "EAP-pwd: unable to get order for curve");
 147                 goto fail;
 148         }
 149         if (!EC_GROUP_get_cofactor(grp->group, cofactor, NULL)) {
 150                 wpa_printf(MSG_INFO, "EAP-pwd: unable to get cofactor for "
 151                            "curve");
 152                 goto fail;
 153         }
 154         primebitlen = BN_num_bits(grp->prime);
 155         primebytelen = BN_num_bytes(grp->prime);
 156         if ((prfbuf = os_malloc(primebytelen)) == NULL) {
 157                 wpa_printf(MSG_INFO, "EAP-pwd: unable to malloc space for prf "
 158                            "buffer");
 159                 goto fail;
 160         }
 161         os_memset(prfbuf, 0, primebytelen);
 162         ctr = 0;
 163         while (1) {
 164                 if (ctr > 30) {
 165                         wpa_printf(MSG_INFO, "EAP-pwd: unable to find random "
 166                                    "point on curve for group %d, something's "
 167                                    "fishy", num);
 168                         goto fail;
 169                 }
 170                 ctr++;
 171
 172                 /*
 173                  * compute counter-mode password value and stretch to prime
 174                  *    pwd-seed = H(token | peer-id | server-id | password |
 175                  *                 counter)
 176                  */
 177                 hash = eap_pwd_h_init();
 178                 if (hash == NULL)
 179                         goto fail;
 180                 eap_pwd_h_update(hash, token, sizeof(u32));
 181                 eap_pwd_h_update(hash, id_peer, id_peer_len);
 182                 eap_pwd_h_update(hash, id_server, id_server_len);
 183                 eap_pwd_h_update(hash, password, password_len);
 184                 eap_pwd_h_update(hash, &ctr, sizeof(ctr));
 185                 eap_pwd_h_final(hash, pwe_digest);
 186
 187                 BN_bin2bn(pwe_digest, SHA256_MAC_LEN, rnd);
 188
 189                 if (eap_pwd_kdf(pwe_digest, SHA256_MAC_LEN,
 190                                 (u8 *) "EAP-pwd Hunting And Pecking",
 191                                 os_strlen("EAP-pwd Hunting And Pecking"),
 192                                 prfbuf, primebitlen) < 0)
 193                         goto fail;
 194
 195                 BN_bin2bn(prfbuf, primebytelen, x_candidate);
 196
 197                 /*
 198                  * eap_pwd_kdf() returns a string of bits 0..primebitlen but
 199                  * BN_bin2bn will treat that string of bits as a big endian
 200                  * number. If the primebitlen is not an even multiple of 8
 201                  * then excessive bits-- those _after_ primebitlen-- so now
 202                  * we have to shift right the amount we masked off.
 203                  */
 204                 if (primebitlen % 8)
 205                         BN_rshift(x_candidate, x_candidate,
 206                                   (8 - (primebitlen % 8)));
 207
 208                 if (BN_ucmp(x_candidate, grp->prime) >= 0)
 209                         continue;
 210
 211                 wpa_hexdump(MSG_DEBUG, "EAP-pwd: x_candidate",
 212                             prfbuf, primebytelen);
 213
 214                 /*
 215                  * need to unambiguously identify the solution, if there is
 216                  * one...
 217                  */
 218                 if (BN_is_odd(rnd))
 219                         is_odd = 1;
 220                 else
 221                         is_odd = 0;
 222
 223                 /*
 224                  * solve the quadratic equation, if it's not solvable then we
 225                  * don't have a point
 226                  */
 227                 if (!EC_POINT_set_compressed_coordinates_GFp(grp->group,
 228                                                              grp->pwe,
 229                                                              x_candidate,
 230                                                              is_odd, NULL))
 231                         continue;
 232                 /*
 233                  * If there's a solution to the equation then the point must be
 234                  * on the curve so why check again explicitly? OpenSSL code
 235                  * says this is required by X9.62. We're not X9.62 but it can't
 236                  * hurt just to be sure.
 237                  */
 238                 if (!EC_POINT_is_on_curve(grp->group, grp->pwe, NULL)) {
 239                         wpa_printf(MSG_INFO, "EAP-pwd: point is not on curve");
 240                         continue;
 241                 }
 242
 243                 if (BN_cmp(cofactor, BN_value_one())) {
 244                         /* make sure the point is not in a small sub-group */
 245                         if (!EC_POINT_mul(grp->group, grp->pwe, NULL, grp->pwe,
 246                                           cofactor, NULL)) {
 247                                 wpa_printf(MSG_INFO, "EAP-pwd: cannot "
 248                                            "multiply generator by order");
 249                                 continue;
 250                         }
 251                         if (EC_POINT_is_at_infinity(grp->group, grp->pwe)) {
 252                                 wpa_printf(MSG_INFO, "EAP-pwd: point is at "
 253                                            "infinity");
 254                                 continue;
 255                         }
 256                 }
 257                 /* if we got here then we have a new generator. */
 258                 break;
 259         }
 260         wpa_printf(MSG_DEBUG, "EAP-pwd: found a PWE in %d tries", ctr);
 261         grp->group_num = num;
 262         if (0) {
 263  fail:
 264                 EC_GROUP_free(grp->group);
 265                 grp->group = NULL;
 266                 EC_POINT_free(grp->pwe);
 267                 grp->pwe = NULL;
 268                 BN_free(grp->order);
 269                 grp->order = NULL;
 270                 BN_free(grp->prime);
 271                 grp->prime = NULL;
 272                 ret = 1;
 273         }
 274         /* cleanliness and order.... */
 275         BN_free(cofactor);
 276         BN_free(x_candidate);
 277         BN_free(rnd);
 278         os_free(prfbuf);
 279
 280         return ret;
 281 }
 282
 283
 284 int compute_keys(EAP_PWD_group *grp, BN_CTX *bnctx, BIGNUM *k,
 285                  BIGNUM *peer_scalar, BIGNUM *server_scalar,
 286                  u8 *confirm_peer, u8 *confirm_server,
 287                  u32 *ciphersuite, u8 *msk, u8 *emsk)
 288 {
 289         struct crypto_hash *hash;
 290         u8 mk[SHA256_MAC_LEN], *cruft;
 291         u8 session_id[SHA256_MAC_LEN + 1];
 292         u8 msk_emsk[EAP_MSK_LEN + EAP_EMSK_LEN];
 293         int offset;
 294
 295         if ((cruft = os_malloc(BN_num_bytes(grp->prime))) == NULL)
 296                 return -1;
 297
 298         /*
 299          * first compute the session-id = TypeCode | H(ciphersuite | scal_p |
 300          *      scal_s)
 301          */
 302         session_id[0] = EAP_TYPE_PWD;
 303         hash = eap_pwd_h_init();
 304         if (hash == NULL) {
 305                 os_free(cruft);
 306                 return -1;
 307         }
 308         eap_pwd_h_update(hash, (u8 *) ciphersuite, sizeof(u32));
 309         offset = BN_num_bytes(grp->order) - BN_num_bytes(peer_scalar);
 310         os_memset(cruft, 0, BN_num_bytes(grp->prime));
 311         BN_bn2bin(peer_scalar, cruft + offset);
 312         eap_pwd_h_update(hash, cruft, BN_num_bytes(grp->order));
 313         offset = BN_num_bytes(grp->order) - BN_num_bytes(server_scalar);
 314         os_memset(cruft, 0, BN_num_bytes(grp->prime));
 315         BN_bn2bin(server_scalar, cruft + offset);
 316         eap_pwd_h_update(hash, cruft, BN_num_bytes(grp->order));
 317         eap_pwd_h_final(hash, &session_id[1]);
 318
 319         /* then compute MK = H(k | confirm-peer | confirm-server) */
 320         hash = eap_pwd_h_init();
 321         if (hash == NULL) {
 322                 os_free(cruft);
 323                 return -1;
 324         }
 325         offset = BN_num_bytes(grp->prime) - BN_num_bytes(k);
 326         os_memset(cruft, 0, BN_num_bytes(grp->prime));
 327         BN_bn2bin(k, cruft + offset);
 328         eap_pwd_h_update(hash, cruft, BN_num_bytes(grp->prime));
 329         os_free(cruft);
 330         eap_pwd_h_update(hash, confirm_peer, SHA256_MAC_LEN);
 331         eap_pwd_h_update(hash, confirm_server, SHA256_MAC_LEN);
 332         eap_pwd_h_final(hash, mk);
 333
 334         /* stretch the mk with the session-id to get MSK | EMSK */
 335         if (eap_pwd_kdf(mk, SHA256_MAC_LEN,
 336                         session_id, SHA256_MAC_LEN + 1,
 337                         msk_emsk, (EAP_MSK_LEN + EAP_EMSK_LEN) * 8) < 0) {
 338                 return -1;
 339         }
 340
 341         os_memcpy(msk, msk_emsk, EAP_MSK_LEN);
 342         os_memcpy(emsk, msk_emsk + EAP_MSK_LEN, EAP_EMSK_LEN);
 343
 344         return 1;
 345 }