int compute_keys(EAP_PWD_group *grp, BN_CTX *bnctx, const BIGNUM *k,
const BIGNUM *peer_scalar, const BIGNUM *server_scalar,
const u8 *confirm_peer, const u8 *confirm_server,
const u32 *ciphersuite, u8 *msk, u8 *emsk, u8 *session_id)
{
struct crypto_hash *hash;
u8 mk[SHA256_MAC_LEN], *cruft;
u8 msk_emsk[EAP_MSK_LEN + EAP_EMSK_LEN];
int offset;
if ((cruft = os_malloc(BN_num_bytes(grp->prime))) == NULL)
return -1;
/*
* first compute the session-id = TypeCode | H(ciphersuite | scal_p |
* scal_s)
*/
session_id[0] = EAP_TYPE_PWD;
hash = eap_pwd_h_init();
if (hash == NULL) {
os_free(cruft);
return -1;
}
eap_pwd_h_update(hash, (const u8 *) ciphersuite, sizeof(u32));
offset = BN_num_bytes(grp->order) - BN_num_bytes(peer_scalar);
os_memset(cruft, 0, BN_num_bytes(grp->prime));
BN_bn2bin(peer_scalar, cruft + offset);
eap_pwd_h_update(hash, cruft, BN_num_bytes(grp->order));
offset = BN_num_bytes(grp->order) - BN_num_bytes(server_scalar);
os_memset(cruft, 0, BN_num_bytes(grp->prime));
BN_bn2bin(server_scalar, cruft + offset);
eap_pwd_h_update(hash, cruft, BN_num_bytes(grp->order));
eap_pwd_h_final(hash, &session_id[1]);
/* then compute MK = H(k | confirm-peer | confirm-server) */
hash = eap_pwd_h_init();
if (hash == NULL) {
os_free(cruft);
return -1;
}
offset = BN_num_bytes(grp->prime) - BN_num_bytes(k);
os_memset(cruft, 0, BN_num_bytes(grp->prime));
BN_bn2bin(k, cruft + offset);
eap_pwd_h_update(hash, cruft, BN_num_bytes(grp->prime));
os_free(cruft);
eap_pwd_h_update(hash, confirm_peer, SHA256_MAC_LEN);
eap_pwd_h_update(hash, confirm_server, SHA256_MAC_LEN);
eap_pwd_h_final(hash, mk);
/* stretch the mk with the session-id to get MSK | EMSK */
if (eap_pwd_kdf(mk, SHA256_MAC_LEN,
session_id, SHA256_MAC_LEN + 1,
msk_emsk, (EAP_MSK_LEN + EAP_EMSK_LEN) * 8) < 0) {
return -1;
}
os_memcpy(msk, msk_emsk, EAP_MSK_LEN);
os_memcpy(emsk, msk_emsk + EAP_MSK_LEN, EAP_EMSK_LEN);
return 1;
}
/*
* compute a "random" secret point on an elliptic curve based
* on the password and identities.
*/
int compute_password_element(EAP_PWD_group *grp, u16 num, const u8 *password, size_t password_len, const u8 *id_server, size_t id_server_len, const u8 *id_peer, size_t id_peer_len, const u8 *token)
{
BIGNUM *x_candidate = NULL, *rnd = NULL, *cofactor = NULL;
struct crypto_hash *hash;
unsigned char pwe_digest[SHA256_MAC_LEN], *prfbuf = NULL, ctr;
int nid, is_odd, ret = 0;
size_t primebytelen, primebitlen;
switch (num) { /* from IANA registry for IKE D-H groups */
case 19:
nid = NID_X9_62_prime256v1;
break;
case 20:
nid = NID_secp384r1;
break;
case 21:
nid = NID_secp521r1;
break;
#ifndef OPENSSL_IS_BORINGSSL
case 25:
nid = NID_X9_62_prime192v1;
break;
#endif /* OPENSSL_IS_BORINGSSL */
case 26:
nid = NID_secp224r1;
break;
default:
wpa_printf(MSG_INFO, "EAP-pwd: unsupported group %d", num);
return -1;
}
grp->pwe = NULL;
grp->order = NULL;
grp->prime = NULL;
if ((grp->group = EC_GROUP_new_by_curve_name(nid)) == NULL) {
wpa_printf(MSG_INFO, "EAP-pwd: unable to create EC_GROUP");
goto fail;
}
if (((rnd = BN_new()) == NULL) || ((cofactor = BN_new()) == NULL) || ((grp->pwe = EC_POINT_new(grp->group)) == NULL) || ((grp->order = BN_new()) == NULL) || ((grp->prime = BN_new()) == NULL) || ((x_candidate = BN_new()) == NULL)) {
wpa_printf(MSG_INFO, "EAP-pwd: unable to create bignums");
goto fail;
}
if (!EC_GROUP_get_curve_GFp(grp->group, grp->prime, NULL, NULL, NULL)) {
wpa_printf(MSG_INFO, "EAP-pwd: unable to get prime for GFp " "curve");
goto fail;
}
if (!EC_GROUP_get_order(grp->group, grp->order, NULL)) {
wpa_printf(MSG_INFO, "EAP-pwd: unable to get order for curve");
goto fail;
}
if (!EC_GROUP_get_cofactor(grp->group, cofactor, NULL)) {
wpa_printf(MSG_INFO, "EAP-pwd: unable to get cofactor for " "curve");
goto fail;
}
primebitlen = BN_num_bits(grp->prime);
primebytelen = BN_num_bytes(grp->prime);
if ((prfbuf = os_malloc(primebytelen)) == NULL) {
wpa_printf(MSG_INFO, "EAP-pwd: unable to malloc space for prf " "buffer");
goto fail;
}
os_memset(prfbuf, 0, primebytelen);
ctr = 0;
while (1) {
if (ctr > 30) {
wpa_printf(MSG_INFO, "EAP-pwd: unable to find random " "point on curve for group %d, something's " "fishy", num);
goto fail;
}
ctr++;
/*
* compute counter-mode password value and stretch to prime
* pwd-seed = H(token | peer-id | server-id | password |
* counter)
*/
hash = eap_pwd_h_init();
if (hash == NULL) {
goto fail;
}
eap_pwd_h_update(hash, token, sizeof(u32));
eap_pwd_h_update(hash, id_peer, id_peer_len);
eap_pwd_h_update(hash, id_server, id_server_len);
eap_pwd_h_update(hash, password, password_len);
eap_pwd_h_update(hash, &ctr, sizeof(ctr));
eap_pwd_h_final(hash, pwe_digest);
BN_bin2bn(pwe_digest, SHA256_MAC_LEN, rnd);
if (eap_pwd_kdf(pwe_digest, SHA256_MAC_LEN, (u8 *)"EAP-pwd Hunting And Pecking", os_strlen("EAP-pwd Hunting And Pecking"), prfbuf, primebitlen) < 0) {
goto fail;
}
BN_bin2bn(prfbuf, primebytelen, x_candidate);
/*
* eap_pwd_kdf() returns a string of bits 0..primebitlen but
* BN_bin2bn will treat that string of bits as a big endian
* number. If the primebitlen is not an even multiple of 8
* then excessive bits-- those _after_ primebitlen-- so now
* we have to shift right the amount we masked off.
*/
if (primebitlen % 8) {
BN_rshift(x_candidate, x_candidate, (8 - (primebitlen % 8)));
}
if (BN_ucmp(x_candidate, grp->prime) >= 0) {
continue;
}
wpa_hexdump(MSG_DEBUG, "EAP-pwd: x_candidate", prfbuf, primebytelen);
/*
* need to unambiguously identify the solution, if there is
* one...
*/
if (BN_is_odd(rnd)) {
is_odd = 1;
} else {
is_odd = 0;
}
/*
* solve the quadratic equation, if it's not solvable then we
* don't have a point
*/
if (!EC_POINT_set_compressed_coordinates_GFp(grp->group, grp->pwe, x_candidate, is_odd, NULL)) {
continue;
}
/*
* If there's a solution to the equation then the point must be
* on the curve so why check again explicitly? OpenSSL code
* says this is required by X9.62. We're not X9.62 but it can't
* hurt just to be sure.
*/
if (!EC_POINT_is_on_curve(grp->group, grp->pwe, NULL)) {
wpa_printf(MSG_INFO, "EAP-pwd: point is not on curve");
continue;
}
if (BN_cmp(cofactor, BN_value_one())) {
/* make sure the point is not in a small sub-group */
if (!EC_POINT_mul(grp->group, grp->pwe, NULL, grp->pwe, cofactor, NULL)) {
wpa_printf(MSG_INFO, "EAP-pwd: cannot " "multiply generator by order");
continue;
}
if (EC_POINT_is_at_infinity(grp->group, grp->pwe)) {
wpa_printf(MSG_INFO, "EAP-pwd: point is at " "infinity");
continue;
}
}
/* if we got here then we have a new generator. */
break;
}
wpa_printf(MSG_DEBUG, "EAP-pwd: found a PWE in %d tries", ctr);
grp->group_num = num;
if (0) {
fail:
EC_GROUP_free(grp->group);
grp->group = NULL;
EC_POINT_clear_free(grp->pwe);
grp->pwe = NULL;
BN_clear_free(grp->order);
grp->order = NULL;
BN_clear_free(grp->prime);
grp->prime = NULL;
ret = 1;
}
/* cleanliness and order.... */
BN_clear_free(cofactor);
BN_clear_free(x_candidate);
BN_clear_free(rnd);
os_free(prfbuf);
return ret;
}
