code: private function getOpenSslEncryptionOptions()
      {
          $options = self::DEFAULT_OPENSSL_OPTIONS;
  
          if ($this->zero_pad) {
              $options = $options | OPENSSL_ZERO_PADDING;
          }
  
          return $options;
      }
docs: Gets the OpenSSL encryption options.
  
  @return int The options to use in an OpenSSL encryption call.