public function __construct(array $config = []) {
		if (!isset($config['secret'])) {
			throw new ConfigException('Encrypt strategy requires a secret key.');
		}

		if ($this->_mcrypt = $this->_mcrypt($config)) {
			if (!extension_loaded('mcrypt')) {
				throw new ConfigException('The mcrypt extension is not installed or enabled.');
			}
			parent::__construct($config + $this->_defaults + [
				'cipher' => MCRYPT_RIJNDAEL_128,
				'mode' => MCRYPT_MODE_CBC
			]);
			$this->_mcryptResource = mcrypt_module_open(
				$this->_config['cipher'], '', $this->_config['mode'], ''
			);
		} else {
			if (!extension_loaded('openssl')) {
				throw new ConfigException('The `openssl` extension is not installed or enabled.');
			}
			parent::__construct($config + $this->_defaults);
		}
	}