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EAP-pwd: Remove unused checks for cofactor > 1 cases

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None of the ECC groups supported in the implementation had a cofactor
greater than 1, so these checks are unreachable and for all cases, the
cofactor is known to be 1. Furthermore, RFC 5931 explicitly disallow use
of ECC groups with cofactor larger than 1, so this checks cannot be
needed for any curve that is compliant with the RFC.

Remove the unneeded group cofactor checks to simplify the
implementation.

Signed-off-by: Jouni Malinen <j@w1.fi>
This commit is contained in:
Jouni Malinen 2019-04-13 17:30:22 +03:00
parent c7c267fa51
commit 8b093db2c3
3 changed files with 7 additions and 92 deletions
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23
src/eap_peer/eap_pwd.c
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@ -309,7 +309,7 @@ eap_pwd_perform_commit_exchange(struct eap_sm *sm, struct eap_pwd_data *data,
const u8 *payload, size_t payload_len)
{
struct crypto_ec_point *K = NULL;
struct crypto_bignum *mask = NULL, *cofactor = NULL;
struct crypto_bignum *mask = NULL;
const u8 *ptr = payload;
u8 *scalar, *element;
size_t prime_len, order_len;
@ -527,21 +527,14 @@ eap_pwd_perform_commit_exchange(struct eap_sm *sm, struct eap_pwd_data *data,
data->private_value = crypto_bignum_init();
data->my_element = crypto_ec_point_init(data->grp->group);
cofactor = crypto_bignum_init();
data->my_scalar = crypto_bignum_init();
mask = crypto_bignum_init();
if (!data->private_value || !data->my_element || !cofactor ||
if (!data->private_value || !data->my_element ||
!data->my_scalar || !mask) {
wpa_printf(MSG_INFO, "EAP-PWD (peer): scalar allocation fail");
goto fin;
}
if (crypto_ec_cofactor(data->grp->group, cofactor) < 0) {
wpa_printf(MSG_INFO, "EAP-pwd (peer): unable to get cofactor "
"for curve");
goto fin;
}
if (eap_pwd_get_rand_mask(data->grp, data->private_value, mask,
data->my_scalar) < 0)
goto fin;
@ -595,17 +588,8 @@ eap_pwd_perform_commit_exchange(struct eap_sm *sm, struct eap_pwd_data *data,
goto fin;
}
/* ensure that the shared key isn't in a small sub-group */
if (!crypto_bignum_is_one(cofactor)) {
if (crypto_ec_point_mul(data->grp->group, K, cofactor, K) < 0) {
wpa_printf(MSG_INFO, "EAP-PWD (peer): cannot multiply "
"shared key point by order");
goto fin;
}
}
/*
* This check is strictly speaking just for the case above where
* This check is strictly speaking just for the case where
* co-factor > 1 but it was suggested that even though this is probably
* never going to happen it is a simple and safe check "just to be
* sure" so let's be safe.
@ -644,7 +628,6 @@ eap_pwd_perform_commit_exchange(struct eap_sm *sm, struct eap_pwd_data *data,
fin:
crypto_bignum_deinit(mask, 1);
crypto_bignum_deinit(cofactor, 1);
crypto_ec_point_deinit(K, 1);
if (data->outbuf == NULL)
eap_pwd_state(data, FAILURE);