RSA_set_method
int RSA_set_method(RSA *rsa, const RSA_METHOD *meth);
RSA_set_method(rsa, rsa_method) == 0) {
RSA_set_method(k->rsa, helper->rsa_meth);
RSA_set_method(ret->rsa, helper->rsa_meth);
RSA_set_method(rsa, rsa_method);