OPENSSL_EC_EXPLICIT_CURVE
EC_GROUP_set_asn1_flag(group, OPENSSL_EC_EXPLICIT_CURVE);
EC_GROUP_set_asn1_flag(group, OPENSSL_EC_EXPLICIT_CURVE);
NID_X9_62_prime256v1, OPENSSL_EC_EXPLICIT_CURVE,
NID_secp256k1, OPENSSL_EC_EXPLICIT_CURVE,