private function checkKey()
    {
        if (empty($this->key) || empty($this->authentication)) {
            $key = $this->secureRandomKey();
            $message = 'No binary key provided to encrypt/decrypt data.';

            if ($key !== null) {
                $message .= sprintf(" For example: base64_decode('%s')", base64_encode($key));
            }

            throw new RuntimeException($message);
        }
    }