Share a PHP encryption and decryption class

class ption
{

    private static $original = array('=', '+', '/');
    private static $later = array('O0O0O', 'o0O0o', 'oo00o');

    function __construct()
    {

    }

    private static function md5($skey = '')
    {
        $skey = $skey ? $skey : 'ui' ; //uicms::_config('security/authkey');
        return md5(substr($skey, 0, 16));
    }

    /**
 * @use ption::en($string, $key);
 * @param String $string The string that needs to be encrypted
 * @param String $skey The key
 * @param int $expiry The validity period of the ciphertext, when encrypted Valid, unit is second, 0 is permanently valid
 * @return String
*/
    static public function en($string = '', $skey = '', $expiry=0)
    {
        if( is_array( $string ) )
        {
            $string = json_encode($string); // uicms::json($string, true, 'en');
        }
        $string = str_pad($expiry ? $expiry + TIME : 0, 10, 0).$string;
        $strArr = str_split(base64_encode($string));
        $strCount = count($strArr);
        $skey = static::md5($skey);
        foreach (str_split($skey) as $key => $value)
        {
            $key < $strCount && $strArr[$key].=$value;
        }
        return str_replace(self::$original, self::$later, join('', $strArr));
    }

    /**
 * @use ption::de($string, $key);
 * @param String $string The string that needs to be decrypted
 * @param String $skey The key
 * @return String
*/
    static public function de($string = '', $skey = '')
    {
        $strArr = str_split(str_replace(self::$later, self::$original, $string), 2);
        $strCount = count($strArr);
        $skey = static::md5($skey);
        foreach (str_split($skey) as $key => $value)
        {
            $key <= $strCount && $strArr[$key][1] === $value && $strArr[$key] = $strArr[$key][0];
        }
        $result = base64_decode(join('', $strArr));
        if(substr($result, 0, 10) == 0 || substr($result, 0, 10) - TIME > 0)
        {
            return substr($result, 10);
        }
        else
        {
            return false;
        }
    }
}

加密解密, PHP