contrib/wpa/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 #ifndef OPENSSL_IS_BORINGSSL
 110         case 25:
 111                 nid = NID_X9_62_prime192v1;
 112                 break;
 113 #endif /* OPENSSL_IS_BORINGSSL */
 114         case 26:
 115                 nid = NID_secp224r1;
 116                 break;
 117         default:
 118                 wpa_printf(MSG_INFO, "EAP-pwd: unsupported group %d", num);
 119                 return -1;
 120         }
 121
 122         grp->pwe = NULL;
 123         grp->order = NULL;
 124         grp->prime = NULL;
 125
 126         if ((grp->group = EC_GROUP_new_by_curve_name(nid)) == NULL) {
 127                 wpa_printf(MSG_INFO, "EAP-pwd: unable to create EC_GROUP");
 128                 goto fail;
 129         }
 130
 131         if (((rnd = BN_new()) == NULL) ||
 132             ((cofactor = BN_new()) == NULL) ||
 133             ((grp->pwe = EC_POINT_new(grp->group)) == NULL) ||
 134             ((grp->order = BN_new()) == NULL) ||
 135             ((grp->prime = BN_new()) == NULL) ||
 136             ((x_candidate = BN_new()) == NULL)) {
 137                 wpa_printf(MSG_INFO, "EAP-pwd: unable to create bignums");
 138                 goto fail;
 139         }
 140
 141         if (!EC_GROUP_get_curve_GFp(grp->group, grp->prime, NULL, NULL, NULL))
 142         {
 143                 wpa_printf(MSG_INFO, "EAP-pwd: unable to get prime for GFp "
 144                            "curve");
 145                 goto fail;
 146         }
 147         if (!EC_GROUP_get_order(grp->group, grp->order, NULL)) {
 148                 wpa_printf(MSG_INFO, "EAP-pwd: unable to get order for curve");
 149                 goto fail;
 150         }
 151         if (!EC_GROUP_get_cofactor(grp->group, cofactor, NULL)) {
 152                 wpa_printf(MSG_INFO, "EAP-pwd: unable to get cofactor for "
 153                            "curve");
 154                 goto fail;
 155         }
 156         primebitlen = BN_num_bits(grp->prime);
 157         primebytelen = BN_num_bytes(grp->prime);
 158         if ((prfbuf = os_malloc(primebytelen)) == NULL) {
 159                 wpa_printf(MSG_INFO, "EAP-pwd: unable to malloc space for prf "
 160                            "buffer");
 161                 goto fail;
 162         }
 163         os_memset(prfbuf, 0, primebytelen);
 164         ctr = 0;
 165         while (1) {
 166                 if (ctr > 30) {
 167                         wpa_printf(MSG_INFO, "EAP-pwd: unable to find random "
 168                                    "point on curve for group %d, something's "
 169                                    "fishy", num);
 170                         goto fail;
 171                 }
 172                 ctr++;
 173
 174                 /*
 175                  * compute counter-mode password value and stretch to prime
 176                  *    pwd-seed = H(token | peer-id | server-id | password |
 177                  *                 counter)
 178                  */
 179                 hash = eap_pwd_h_init();
 180                 if (hash == NULL)
 181                         goto fail;
 182                 eap_pwd_h_update(hash, token, sizeof(u32));
 183                 eap_pwd_h_update(hash, id_peer, id_peer_len);
 184                 eap_pwd_h_update(hash, id_server, id_server_len);
 185                 eap_pwd_h_update(hash, password, password_len);
 186                 eap_pwd_h_update(hash, &ctr, sizeof(ctr));
 187                 eap_pwd_h_final(hash, pwe_digest);
 188
 189                 BN_bin2bn(pwe_digest, SHA256_MAC_LEN, rnd);
 190
 191                 if (eap_pwd_kdf(pwe_digest, SHA256_MAC_LEN,
 192                                 (u8 *) "EAP-pwd Hunting And Pecking",
 193                                 os_strlen("EAP-pwd Hunting And Pecking"),
 194                                 prfbuf, primebitlen) < 0)
 195                         goto fail;
 196
 197                 BN_bin2bn(prfbuf, primebytelen, x_candidate);
 198
 199                 /*
 200                  * eap_pwd_kdf() returns a string of bits 0..primebitlen but
 201                  * BN_bin2bn will treat that string of bits as a big endian
 202                  * number. If the primebitlen is not an even multiple of 8
 203                  * then excessive bits-- those _after_ primebitlen-- so now
 204                  * we have to shift right the amount we masked off.
 205                  */
 206                 if (primebitlen % 8)
 207                         BN_rshift(x_candidate, x_candidate,
 208                                   (8 - (primebitlen % 8)));
 209
 210                 if (BN_ucmp(x_candidate, grp->prime) >= 0)
 211                         continue;
 212
 213                 wpa_hexdump(MSG_DEBUG, "EAP-pwd: x_candidate",
 214                             prfbuf, primebytelen);
 215
 216                 /*
 217                  * need to unambiguously identify the solution, if there is
 218                  * one...
 219                  */
 220                 if (BN_is_odd(rnd))
 221                         is_odd = 1;
 222                 else
 223                         is_odd = 0;
 224
 225                 /*
 226                  * solve the quadratic equation, if it's not solvable then we
 227                  * don't have a point
 228                  */
 229                 if (!EC_POINT_set_compressed_coordinates_GFp(grp->group,
 230                                                              grp->pwe,
 231                                                              x_candidate,
 232                                                              is_odd, NULL))
 233                         continue;
 234                 /*
 235                  * If there's a solution to the equation then the point must be
 236                  * on the curve so why check again explicitly? OpenSSL code
 237                  * says this is required by X9.62. We're not X9.62 but it can't
 238                  * hurt just to be sure.
 239                  */
 240                 if (!EC_POINT_is_on_curve(grp->group, grp->pwe, NULL)) {
 241                         wpa_printf(MSG_INFO, "EAP-pwd: point is not on curve");
 242                         continue;
 243                 }
 244
 245                 if (BN_cmp(cofactor, BN_value_one())) {
 246                         /* make sure the point is not in a small sub-group */
 247                         if (!EC_POINT_mul(grp->group, grp->pwe, NULL, grp->pwe,
 248                                           cofactor, NULL)) {
 249                                 wpa_printf(MSG_INFO, "EAP-pwd: cannot "
 250                                            "multiply generator by order");
 251                                 continue;
 252                         }
 253                         if (EC_POINT_is_at_infinity(grp->group, grp->pwe)) {
 254                                 wpa_printf(MSG_INFO, "EAP-pwd: point is at "
 255                                            "infinity");
 256                                 continue;
 257                         }
 258                 }
 259                 /* if we got here then we have a new generator. */
 260                 break;
 261         }
 262         wpa_printf(MSG_DEBUG, "EAP-pwd: found a PWE in %d tries", ctr);
 263         grp->group_num = num;
 264         if (0) {
 265  fail:
 266                 EC_GROUP_free(grp->group);
 267                 grp->group = NULL;
 268                 EC_POINT_clear_free(grp->pwe);
 269                 grp->pwe = NULL;
 270                 BN_clear_free(grp->order);
 271                 grp->order = NULL;
 272                 BN_clear_free(grp->prime);
 273                 grp->prime = NULL;
 274                 ret = 1;
 275         }
 276         /* cleanliness and order.... */
 277         BN_clear_free(cofactor);
 278         BN_clear_free(x_candidate);
 279         BN_clear_free(rnd);
 280         os_free(prfbuf);
 281
 282         return ret;
 283 }
 284
 285
 286 int compute_keys(EAP_PWD_group *grp, BN_CTX *bnctx, BIGNUM *k,
 287                  BIGNUM *peer_scalar, BIGNUM *server_scalar,
 288                  u8 *confirm_peer, u8 *confirm_server,
 289                  u32 *ciphersuite, u8 *msk, u8 *emsk, u8 *session_id)
 290 {
 291         struct crypto_hash *hash;
 292         u8 mk[SHA256_MAC_LEN], *cruft;
 293         u8 msk_emsk[EAP_MSK_LEN + EAP_EMSK_LEN];
 294         int offset;
 295
 296         if ((cruft = os_malloc(BN_num_bytes(grp->prime))) == NULL)
 297                 return -1;
 298
 299         /*
 300          * first compute the session-id = TypeCode | H(ciphersuite | scal_p |
 301          *      scal_s)
 302          */
 303         session_id[0] = EAP_TYPE_PWD;
 304         hash = eap_pwd_h_init();
 305         if (hash == NULL) {
 306                 os_free(cruft);
 307                 return -1;
 308         }
 309         eap_pwd_h_update(hash, (u8 *) ciphersuite, sizeof(u32));
 310         offset = BN_num_bytes(grp->order) - BN_num_bytes(peer_scalar);
 311         os_memset(cruft, 0, BN_num_bytes(grp->prime));
 312         BN_bn2bin(peer_scalar, cruft + offset);
 313         eap_pwd_h_update(hash, cruft, BN_num_bytes(grp->order));
 314         offset = BN_num_bytes(grp->order) - BN_num_bytes(server_scalar);
 315         os_memset(cruft, 0, BN_num_bytes(grp->prime));
 316         BN_bn2bin(server_scalar, cruft + offset);
 317         eap_pwd_h_update(hash, cruft, BN_num_bytes(grp->order));
 318         eap_pwd_h_final(hash, &session_id[1]);
 319
 320         /* then compute MK = H(k | confirm-peer | confirm-server) */
 321         hash = eap_pwd_h_init();
 322         if (hash == NULL) {
 323                 os_free(cruft);
 324                 return -1;
 325         }
 326         offset = BN_num_bytes(grp->prime) - BN_num_bytes(k);
 327         os_memset(cruft, 0, BN_num_bytes(grp->prime));
 328         BN_bn2bin(k, cruft + offset);
 329         eap_pwd_h_update(hash, cruft, BN_num_bytes(grp->prime));
 330         os_free(cruft);
 331         eap_pwd_h_update(hash, confirm_peer, SHA256_MAC_LEN);
 332         eap_pwd_h_update(hash, confirm_server, SHA256_MAC_LEN);
 333         eap_pwd_h_final(hash, mk);
 334
 335         /* stretch the mk with the session-id to get MSK | EMSK */
 336         if (eap_pwd_kdf(mk, SHA256_MAC_LEN,
 337                         session_id, SHA256_MAC_LEN + 1,
 338                         msk_emsk, (EAP_MSK_LEN + EAP_EMSK_LEN) * 8) < 0) {
 339                 return -1;
 340         }
 341
 342         os_memcpy(msk, msk_emsk, EAP_MSK_LEN);
 343         os_memcpy(emsk, msk_emsk + EAP_MSK_LEN, EAP_EMSK_LEN);
 344
 345         return 1;
 346 }