practice 5

practice 5.php

<title>CrypotCrypotCrypot</title>
<pre><h3>
<?php
$FLAG = 'XXXXXXXXXXXXXXX_censored_XXXXXXXXXXXXX';
$LENGTH_FLAG = strlen($FLAG);
$KEY = empty($_GET['key']) ? "TEST" : $_GET['key'];
$sha1_all = hash("sha512","\x00",true); //init

echo "Your KEY : <font color=Green>$KEY</font>\n";
for($i=0; $i < $LENGTH_FLAG; $i++){
    $KEY[$i] = empty($KEY[$i]) ? "\xff" : $KEY[$i];
    $c = $KEY[$i].str_repeat($FLAG[$i],$LENGTH_FLAG - strlen($KEY[$i]));
    $sha1_all ^= hash("sha512",$c,true);
}
echo "Your FLAG: <font color=Red>".bin2hex($sha1_all ^ $FLAG)."</font>\n\n";

?>