public function getRandomBytes(
        $numberOfBytes = PHP_INT_MAX,
        $source = null
    )
    {
        switch ($source) {

            case self::MODE_OPEN_SSL:
                $randomBytes = $this->getRandomBytesFromOpenSSL($numberOfBytes);
                break;

            default:
                // http://php.net/manual/de/function.random-bytes.php - POLYFILL used for PHP < 7
                $randomBytes = random_bytes($numberOfBytes);
                break;
        }

        return $randomBytes;
    }