/*
* EAP server/peer: EAP-pwd shared routines
* Copyright (c) 2010, Dan Harkins <dharkins@lounge.org>
*
* This software may be distributed under the terms of the BSD license.
* See README for more details.
*/
#include "includes.h"
#include "common.h"
#include "eap_defs.h"
#include "eap_pwd_common.h"
/* The random function H(x) = HMAC-SHA256(0^32, x) */
void H_Init(HMAC_CTX *ctx)
{
u8 allzero[SHA256_DIGEST_LENGTH];
os_memset(allzero, 0, SHA256_DIGEST_LENGTH);
HMAC_Init(ctx, allzero, SHA256_DIGEST_LENGTH, EVP_sha256());
}
void H_Update(HMAC_CTX *ctx, const u8 *data, int len)
{
HMAC_Update(ctx, data, len);
}
void H_Final(HMAC_CTX *ctx, u8 *digest)
{
unsigned int mdlen = SHA256_DIGEST_LENGTH;
HMAC_Final(ctx, digest, &mdlen);
HMAC_CTX_cleanup(ctx);
}
/* a counter-based KDF based on NIST SP800-108 */
void eap_pwd_kdf(u8 *key, int keylen, u8 *label, int labellen,
u8 *result, int resultbitlen)
{
HMAC_CTX hctx;
unsigned char digest[SHA256_DIGEST_LENGTH];
u16 i, ctr, L;
int resultbytelen, len = 0;
unsigned int mdlen = SHA256_DIGEST_LENGTH;
unsigned char mask = 0xff;
resultbytelen = (resultbitlen + 7)/8;
ctr = 0;
L = htons(resultbitlen);
while (len < resultbytelen) {
ctr++; i = htons(ctr);
HMAC_Init(&hctx, key, keylen, EVP_sha256());
if (ctr > 1)
HMAC_Update(&hctx, digest, mdlen);
HMAC_Update(&hctx, (u8 *) &i, sizeof(u16));
HMAC_Update(&hctx, label, labellen);
HMAC_Update(&hctx, (u8 *) &L, sizeof(u16));
HMAC_Final(&hctx, digest, &mdlen);
if ((len + (int) mdlen) > resultbytelen)
os_memcpy(result + len, digest, resultbytelen - len);
else
os_memcpy(result + len, digest, mdlen);
len += mdlen;
HMAC_CTX_cleanup(&hctx);
}
/* since we're expanding to a bit length, mask off the excess */
if (resultbitlen % 8) {
mask <<= (8 - (resultbitlen % 8));
result[resultbytelen - 1] &= mask;
}
}
/*
* 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,
u8 *password, int password_len,
u8 *id_server, int id_server_len,
u8 *id_peer, int id_peer_len, u8 *token)
{
BIGNUM *x_candidate = NULL, *rnd = NULL, *cofactor = NULL;
HMAC_CTX ctx;
unsigned char pwe_digest[SHA256_DIGEST_LENGTH], *prfbuf = NULL, ctr;
int nid, is_odd, primebitlen, primebytelen, ret = 0;
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;
case 25:
nid = NID_X9_62_prime192v1;
break;
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 > 10) {
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)
*/
H_Init(&ctx);
H_Update(&ctx, token, sizeof(u32));
H_Update(&ctx, id_peer, id_peer_len);
H_Update(&ctx, id_server, id_server_len);
H_Update(&ctx, password, password_len);
H_Update(&ctx, &ctr, sizeof(ctr));
H_Final(&ctx, pwe_digest);
BN_bin2bn(pwe_digest, SHA256_DIGEST_LENGTH, rnd);
eap_pwd_kdf(pwe_digest, SHA256_DIGEST_LENGTH,
(unsigned char *) "EAP-pwd Hunting And Pecking",
os_strlen("EAP-pwd Hunting And Pecking"),
prfbuf, primebitlen);
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);
EC_POINT_free(grp->pwe);
BN_free(grp->order);
BN_free(grp->prime);
os_free(grp);
grp = NULL;
ret = 1;
}
/* cleanliness and order.... */
BN_free(cofactor);
BN_free(x_candidate);
BN_free(rnd);
os_free(prfbuf);
return ret;
}
int compute_keys(EAP_PWD_group *grp, BN_CTX *bnctx, BIGNUM *k,
BIGNUM *peer_scalar, BIGNUM *server_scalar,
u8 *confirm_peer, u8 *confirm_server,
u32 *ciphersuite, u8 *msk, u8 *emsk)
{
HMAC_CTX ctx;
u8 mk[SHA256_DIGEST_LENGTH], *cruft;
u8 session_id[SHA256_DIGEST_LENGTH + 1];
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;
H_Init(&ctx);
H_Update(&ctx, (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);
H_Update(&ctx, 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);
H_Update(&ctx, cruft, BN_num_bytes(grp->order));
H_Final(&ctx, &session_id[1]);
/* then compute MK = H(k | confirm-peer | confirm-server) */
H_Init(&ctx);
offset = BN_num_bytes(grp->prime) - BN_num_bytes(k);
os_memset(cruft, 0, BN_num_bytes(grp->prime));
BN_bn2bin(k, cruft + offset);
H_Update(&ctx, cruft, BN_num_bytes(grp->prime));
H_Update(&ctx, confirm_peer, SHA256_DIGEST_LENGTH);
H_Update(&ctx, confirm_server, SHA256_DIGEST_LENGTH);
H_Final(&ctx, mk);
/* stretch the mk with the session-id to get MSK | EMSK */
eap_pwd_kdf(mk, SHA256_DIGEST_LENGTH,
session_id, SHA256_DIGEST_LENGTH+1,
msk_emsk, (EAP_MSK_LEN + EAP_EMSK_LEN) * 8);
os_memcpy(msk, msk_emsk, EAP_MSK_LEN);
os_memcpy(emsk, msk_emsk + EAP_MSK_LEN, EAP_EMSK_LEN);
os_free(cruft);
return 1;
}