- var_dump: documentation ( source)
- chr: documentation ( source)
- hexdec: documentation ( source)
- ord: documentation ( source)
<?php
$str = "COe1rdm1";
$str[0] = chr(ord($str[0]) + hexdec('6b') - hexdec('42'));
$str[1] = chr(ord($str[1]) + hexdec('61') - hexdec('65'));
$str[2] = chr(ord($str[2]) + hexdec('61') - hexdec('65'));
$str[3] = chr(ord($str[3]) + hexdec('79') - hexdec('47'));
$str[4] = chr(ord($str[4]) - hexdec('79') + hexdec('47'));
$str[5] = chr(ord($str[5]) - hexdec('62') + hexdec('65'));
$str[6] = chr(ord($str[6]) - hexdec('61') + hexdec('65'));
$str[7] = chr(ord($str[7]) - hexdec('42') + hexdec('6B'));
var_dump($str);