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EAP-pwd: Enforce 1 < rand,mask < r and rand+mask mod r > 1

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RFC 5931 has these conditions as MUST requirements, so better follow
them explicitly even if the rand,mask == 0 or rand+mask == 0 or 1 cases
are very unlikely to occur in practice while generating random values
locally.

Signed-off-by: Jouni Malinen <jouni@codeaurora.org>
This commit is contained in:
Jouni Malinen 2019-04-05 12:37:21 +03:00 • committed by Jouni Malinen
parent 2e3849bcf5
commit 4396f74a36
4 changed files with 35 additions and 23 deletions
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28
src/eap_common/eap_pwd_common.c
View file

@ -534,3 +534,31 @@ struct crypto_bignum * eap_pwd_get_scalar(EAP_PWD_group *group, const u8 *buf)
return scalar;
}
int eap_pwd_get_rand_mask(EAP_PWD_group *group, struct crypto_bignum *_rand,
struct crypto_bignum *_mask,
struct crypto_bignum *scalar)
{
const struct crypto_bignum *order;
int count;
order = crypto_ec_get_order(group->group);
/* Select two random values rand,mask such that 1 < rand,mask < r and
* rand + mask mod r > 1. */
for (count = 0; count < 100; count++) {
if (crypto_bignum_rand(_rand, order) == 0 &&
!crypto_bignum_is_zero(_rand) &&
crypto_bignum_rand(_mask, order) == 0 &&
!crypto_bignum_is_zero(_mask) &&
crypto_bignum_add(_rand, _mask, scalar) == 0 &&
crypto_bignum_mod(scalar, order, scalar) == 0 &&
!crypto_bignum_is_zero(scalar) &&
!crypto_bignum_is_one(scalar))
return 0;
}
wpa_printf(MSG_INFO, "EAP-pwd: unable to get randomness");
return -1;
}

3
src/eap_common/eap_pwd_common.h
View file

@ -70,5 +70,8 @@ void eap_pwd_h_final(struct crypto_hash *hash, u8 *digest);
struct crypto_ec_point * eap_pwd_get_element(EAP_PWD_group *group,
const u8 *buf);
struct crypto_bignum * eap_pwd_get_scalar(EAP_PWD_group *group, const u8 *buf);
int eap_pwd_get_rand_mask(EAP_PWD_group *group, struct crypto_bignum *_rand,
struct crypto_bignum *_mask,
struct crypto_bignum *scalar);
#endif /* EAP_PWD_COMMON_H */