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EAP-pwd: Check element x,y coordinates explicitly

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This adds an explicit check for 0 < x,y < prime based on RFC 5931,
2.8.5.2.2 requirement. The earlier checks might have covered this
implicitly, but it is safer to avoid any dependency on implicit checks
and specific crypto library behavior. (CVE-2019-9498 and CVE-2019-9499)

Furthermore, this moves the EAP-pwd element and scalar parsing and
validation steps into shared helper functions so that there is no need
to maintain two separate copies of this common functionality between the
server and peer implementations.

Signed-off-by: Jouni Malinen <jouni@codeaurora.org>
This commit is contained in:
Jouni Malinen 2019-04-05 02:12:50 +03:00 • committed by Jouni Malinen
parent 8ad8585f91
commit 16d4f10691
4 changed files with 117 additions and 82 deletions
Download patch file Download diff file Expand all files Collapse all files

106
src/eap_common/eap_pwd_common.c
View file

@ -428,3 +428,109 @@ int compute_keys(EAP_PWD_group *grp, const struct crypto_bignum *k,
return 1;
}
static int eap_pwd_element_coord_ok(const struct crypto_bignum *prime,
const u8 *buf, size_t len)
{
struct crypto_bignum *val;
int ok = 1;
val = crypto_bignum_init_set(buf, len);
if (!val || crypto_bignum_is_zero(val) ||
crypto_bignum_cmp(val, prime) >= 0)
ok = 0;
crypto_bignum_deinit(val, 0);
return ok;
}
struct crypto_ec_point * eap_pwd_get_element(EAP_PWD_group *group,
const u8 *buf)
{
struct crypto_ec_point *element;
const struct crypto_bignum *prime;
size_t prime_len;
struct crypto_bignum *cofactor = NULL;
prime = crypto_ec_get_prime(group->group);
prime_len = crypto_ec_prime_len(group->group);
/* RFC 5931, 2.8.5.2.2: 0 < x,y < p */
if (!eap_pwd_element_coord_ok(prime, buf, prime_len) ||
!eap_pwd_element_coord_ok(prime, buf + prime_len, prime_len)) {
wpa_printf(MSG_INFO, "EAP-pwd: Invalid coordinate in element");
return NULL;
}
element = crypto_ec_point_from_bin(group->group, buf);
if (!element) {
wpa_printf(MSG_INFO, "EAP-pwd: EC point from element failed");
return NULL;
}
/* RFC 5931, 2.8.5.2.2: on curve and not the point at infinity */
if (!crypto_ec_point_is_on_curve(group->group, element) ||
crypto_ec_point_is_at_infinity(group->group, element)) {
wpa_printf(MSG_INFO, "EAP-pwd: Invalid element");
goto fail;
}
cofactor = crypto_bignum_init();
if (!cofactor || crypto_ec_cofactor(group->group, cofactor) < 0) {
wpa_printf(MSG_INFO,
"EAP-pwd: Unable to get cofactor for curve");
goto fail;
}
if (!crypto_bignum_is_one(cofactor)) {
struct crypto_ec_point *point;
int ok = 1;
/* check to ensure peer's element is not in a small sub-group */
point = crypto_ec_point_init(group->group);
if (!point ||
crypto_ec_point_mul(group->group, element,
cofactor, point) != 0 ||
crypto_ec_point_is_at_infinity(group->group, point))
ok = 0;
crypto_ec_point_deinit(point, 0);
if (!ok) {
wpa_printf(MSG_INFO,
"EAP-pwd: Small sub-group check on peer element failed");
goto fail;
}
}
out:
crypto_bignum_deinit(cofactor, 0);
return element;
fail:
crypto_ec_point_deinit(element, 0);
element = NULL;
goto out;
}
struct crypto_bignum * eap_pwd_get_scalar(EAP_PWD_group *group, const u8 *buf)
{
struct crypto_bignum *scalar;
const struct crypto_bignum *order;
size_t order_len;
order = crypto_ec_get_order(group->group);
order_len = crypto_ec_order_len(group->group);
/* RFC 5931, 2.8.5.2: 1 < scalar < r */
scalar = crypto_bignum_init_set(buf, order_len);
if (!scalar || crypto_bignum_is_zero(scalar) ||
crypto_bignum_is_one(scalar) ||
crypto_bignum_cmp(scalar, order) >= 0) {
wpa_printf(MSG_INFO, "EAP-pwd: received scalar is invalid");
crypto_bignum_deinit(scalar, 0);
scalar = NULL;
}
return scalar;
}

3
src/eap_common/eap_pwd_common.h
View file

@ -67,5 +67,8 @@ int compute_keys(EAP_PWD_group *grp, const struct crypto_bignum *k,
struct crypto_hash * eap_pwd_h_init(void);
void eap_pwd_h_update(struct crypto_hash *hash, const u8 *data, size_t len);
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);
#endif /* EAP_PWD_COMMON_H */