<?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);   $ctr++;   }   return $tmp;   }   function encrypt($txt,$key)   {   srand((double)microtime()*1000000);   $encrypt_key = md5(rand(0,32000));   $ctr=0;   $tmp = "";   for ($i=0;$i<strlen($txt);$i++)   {   if ($ctr==strlen($encrypt_key)) $ctr=0;   $tmp.= substr($encrypt_key,$ctr,1) .   (substr($txt,$i,1) ^ substr($encrypt_key,$ctr,1));   $ctr++;   }   return keyED($tmp,$key);   }   function decrypt($txt,$key)   {   $txt = keyED($txt,$key);   $tmp = "";   for ($i=0;$i<strlen($txt);$i++)   {   $md5 = substr($txt,$i,1);   $i++;   $tmp.= (substr($txt,$i,1) ^ $md5);   }   return $tmp;   }   $string = "Hello World !!!";   // encrypt $string, and store it in $enc_text   $enc_text = encrypt($string,$key);   // decrypt the encrypted text $enc_text, and store it in $dec_text   $dec_text = decrypt($enc_text,$key);   print "Original text : $string <Br>n";   print "Encrypted text : $enc_text <Br>n";   print "Decrypted text : $dec_text <Br>n";   ?>