public function generateKey($length = null) {
		if (!$length) {
			$length = $this->defaultLength;
		}

		if (version_compare(PHP_VERSION, '7.0.0') >= 0) {
			$function = 'random_bytes';
		} elseif (extension_loaded('openssl')) {
			$function = 'openssl_random_pseudo_bytes';
		} else {
			trigger_error('Not secure', E_USER_DEPRECATED);
			return Random::pwd($length);
		}

		$value = bin2hex($function($length / 2));
		if (strlen($value) !== $length) {
			$value = str_pad($value, $length, '0');
		}
		return $value;
	}