php实现base64的编码和解码

<?
class encryptCalss
{
    var $key=12;
    function encode($txt){
        for($i=0;$i<strlen($txt);$i++){
            $txt[$i]=chr(ord($txt[$i])+$this->key);
        }
        return $txt=urlencode(base64_encode(urlencode($txt)));
    }
    function decode($txt){
        $txt=urldecode(base64_decode($txt));
        for($i=0;$i<strlen($txt);$i++){
            $txt[$i]=chr(ord($txt[$i])-$this->key);
        }
        return $txt;
    }
}
?>