- if (EC_GROUP_get_mont_data(group) != NULL) {
- /*
- * We want inverse in constant time, therefore we utilize the fact
- * order must be prime and use Fermats Little Theorem instead.
- */
- if (!BN_set_word(X, 2)) {
- ECerr(EC_F_ECDSA_SIGN_SETUP, ERR_R_BN_LIB);
- goto err;
- }
- if (!BN_mod_sub(X, order, X, order, ctx)) {
- ECerr(EC_F_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))) {
- ECerr(EC_F_ECDSA_SIGN_SETUP, ERR_R_BN_LIB);
- goto err;
- }
- } else {
- if (!BN_mod_inverse(k, k, order, ctx)) {
- ECerr(EC_F_ECDSA_SIGN_SETUP, ERR_R_BN_LIB);
- goto err;
- }
+ if (!ec_group_do_inverse_ord(group, k, k, ctx)) {
+ ECerr(EC_F_ECDSA_SIGN_SETUP, ERR_R_BN_LIB);
+ goto err;