/**
* @brief Set the default key
* @param string $key The default key
* @return void
*/
protected static function _setDefaultKey($key)
{
self::$_default_key = $key = trim($key);
$file_name = _XE_PATH_ . 'files/config/crypto.config.php';
$file_content = '<?php return ' . var_export($key, true) . ';' . PHP_EOL;
FileHandler::writeFile($file_name, $file_content);
}