Powerful PHP encryption and decryption class

http://blog.ddian.cn/?post=923

class Ender{
 private $enkey;//Key used for encryption and decryption
 //The construction parameter is the key
 public function __construct($key=''){
 if(!$ key){
 $this->enkey=$key;
 }
 }
 //Set the key
 public function set_key($key){
 $this->enkey=$key;
 }
 private function keyED ($txt,$encrypt_key)
 {
 $encrypt_key = md5($encrypt_key);
 $ctr=0;
 $tmp = "";
 for ($i=0;$i {
 if ($ctr==strlen($encrypt_key)) $ctr=0;
 $tmp.= substr($txt,$i,1) ^ substr($encrypt_key,$ctr,1);
 $ctr++;
 }
 return $tmp;
 }
 //Encrypt string
 public function encrypt($txt,$key='')
 {
 if(!$key){
 $key=$this-> ;enkey;
 }
 srand((double)microtime()*1000000);
 $encrypt_key = md5(rand(0,32000));
 $ctr=0;
 $tmp = "";
 for ($i =0;$i {
 if ($ctr==strlen($encrypt_key)) $ctr=0;
 $tmp.= substr($encrypt_key,$ctr,1) .
 (substr($txt,$i,1) ^ substr($encrypt_key,$ctr,1));
 $ctr++;
 }
 return base64_encode($this->keyED($tmp,$key)) ;
 }
 //Decrypt string
 public function decrypt($txt,$key='')
 {
 $txt=base64_decode($txt);
 if(!$key){
 $key=$this- >enkey;
 }
 $txt = $this->keyED($txt,$key);
 $tmp = "";
 for ($i=0;$i {
 $md5 = substr($txt,$i,1);
 $i++;
 $tmp.= (substr($txt,$i,1) ^ $md5);
 }
 return $tmp; //http://blog.ddian.cn
 }

}