- substr: documentation ( source)
- chr: documentation ( source)
- ord: documentation ( source)
<?php
$sInp = "°©±ª±«©±«±©jbjc";
$sKey = "8519293193919192153";
$s = "";
$j = 0;
for ($i=0;$i< strlen($sInp);$i++)
{
$s .= chr( ord(substr($sInp,$i,1)) - ord(substr($sKey,$j++,1)) );
if($j==strlen($sKey))
$j=0;
}
echo $s;