一段php加密解密的代码

<?php $key = “This is supposed to be a secret key !!!”; function keyED($txt,$encrypt_key) { $encrypt_key = md5($encrypt_key); $ctr=0; $tmp = “”; for ($i=0;$i<strlen($txt);$i++) { if ($ctr==strlen($encrypt_key)) $ctr=0; $tmp.= substr($txt,$i,1) ^ substr($encrypt_key,$ctr,1);