DO NOT MERGE Always use Fermat's Little Theorem in ecdsa_sign_setup.
The case where ec_group_get_mont_data is NULL is only for arbitrary groups
which we now require to be prime order. BN_mod_exp_mont is fine with a NULL
BN_MONT_CTX. It will just compute it. Saves a bit of special-casing.
Also don't mark p-2 as BN_FLG_CONSTTIME as the exponent is public anyway.
(cherry picked from commit 8cf79af7d1497c07bd684764b96c9659e7b32ae1)
FPIIM-672
Bug: 33752052
Change-Id: Ia57cf8b68415742233b5c70e9da901b0f2954e7a
(cherry picked from commit c5f118738a61b533d90b01841664e6480e0692fe)
diff --git a/src/crypto/ec/ec.c b/src/crypto/ec/ec.c
index 1bc2e26..d2be59d 100644
--- a/src/crypto/ec/ec.c
+++ b/src/crypto/ec/ec.c
@@ -361,6 +361,12 @@
return 0;
}
+ /* Require a cofactor of one for custom curves, which implies prime order. */
+ if (!BN_is_one(cofactor)) {
+ OPENSSL_PUT_ERROR(EC, EC_GROUP_new_curve_GFp, EC_R_WRONG_CURVE_PARAMETERS);
+ return 0;
+ }
+
if (group->generator == NULL) {
group->generator = EC_POINT_new(group);
if (group->generator == NULL) {
diff --git a/src/crypto/ecdsa/ecdsa.c b/src/crypto/ecdsa/ecdsa.c
index 86e41bb..4c35983 100644
--- a/src/crypto/ecdsa/ecdsa.c
+++ b/src/crypto/ecdsa/ecdsa.c
@@ -235,7 +235,7 @@
BIGNUM **rp, const uint8_t *digest,
size_t digest_len) {
BN_CTX *ctx = NULL;
- BIGNUM *k = NULL, *r = NULL, *order = NULL, *X = NULL;
+ BIGNUM *k = NULL, *r = NULL, *order = NULL, *tmp = NULL;
EC_POINT *tmp_point = NULL;
const EC_GROUP *group;
int ret = 0;
@@ -257,8 +257,8 @@
k = BN_new(); /* this value is later returned in *kinvp */
r = BN_new(); /* this value is later returned in *rp */
order = BN_new();
- X = BN_new();
- if (!k || !r || !order || !X) {
+ tmp = BN_new();
+ if (!k || !r || !order || !tmp) {
OPENSSL_PUT_ERROR(ECDSA, ecdsa_sign_setup, ERR_R_MALLOC_FAILURE);
goto err;
}
@@ -310,33 +310,25 @@
OPENSSL_PUT_ERROR(ECDSA, ecdsa_sign_setup, ERR_R_EC_LIB);
goto err;
}
- if (!EC_POINT_get_affine_coordinates_GFp(group, tmp_point, X, NULL, ctx)) {
+ if (!EC_POINT_get_affine_coordinates_GFp(group, tmp_point, tmp, NULL,
+ ctx)) {
OPENSSL_PUT_ERROR(ECDSA, ecdsa_sign_setup, ERR_R_EC_LIB);
goto err;
}
- if (!BN_nnmod(r, X, order, ctx)) {
+ if (!BN_nnmod(r, tmp, order, ctx)) {
OPENSSL_PUT_ERROR(ECDSA, ecdsa_sign_setup, ERR_R_BN_LIB);
goto err;
}
} while (BN_is_zero(r));
- /* compute the inverse of k */
- if (ec_group_get_mont_data(group) != NULL) {
- /* We want inverse in constant time, therefore we use that the order must
- * be prime and thus we can use Fermat's Little Theorem. */
- if (!BN_set_word(X, 2) ||
- !BN_sub(X, order, X)) {
- OPENSSL_PUT_ERROR(ECDSA, ecdsa_sign_setup, ERR_R_BN_LIB);
- goto err;
- }
- BN_set_flags(X, BN_FLG_CONSTTIME);
- if (!BN_mod_exp_mont_consttime(k, k, X, order, ctx,
- ec_group_get_mont_data(group))) {
- OPENSSL_PUT_ERROR(ECDSA, ecdsa_sign_setup, ERR_R_BN_LIB);
- goto err;
- }
- } else if (!BN_mod_inverse(k, k, order, ctx)) {
+ /* Compute the inverse of k. The order is a prime, so use Fermat's Little
+ * Theorem. */
+ if (!BN_set_word(tmp, 2) ||
+ !BN_sub(tmp, order, tmp) ||
+ /* Note |ec_group_get_mont_data| may return NULL but |BN_mod_exp_mont|
+ * allows it to be. */
+ !BN_mod_exp_mont(k, k, tmp, order, ctx, ec_group_get_mont_data(group))) {
OPENSSL_PUT_ERROR(ECDSA, ecdsa_sign_setup, ERR_R_BN_LIB);
goto err;
}
@@ -359,7 +351,7 @@
}
BN_free(order);
EC_POINT_free(tmp_point);
- BN_clear_free(X);
+ BN_clear_free(tmp);
return ret;
}