Plaintext cookie : name=guest;admin=0;password=guest;userid=1337

<?php

require('key.php');

function source()
{
    echo "<pre>";
    highlight_string(file_get_contents(__FILE__));
    echo "</pre>";
}

function quit()
{
    source();
    die();
}

function encrypt($input) {
    $res = openssl_encrypt($input, "AES-128-ECB", KEY, OPENSSL_RAW_DATA);
    return $res;
}

function decrypt($input) {
    $res = openssl_decrypt($input, "AES-128-ECB", KEY, OPENSSL_RAW_DATA);
    return $res;
}

if(!isset($_COOKIE['key'])) {
    $username=(isset($_GET['username'])) ? $_GET['username'] : "guest";
    $password=(isset($_GET['password'])) ? $_GET['password'] : "guest";
    if(preg_match("/admin=1/i", $username) || preg_match("/admin=1/i", $password) ) quit();
    $cookieenc = encrypt("name=$username;admin=0;password=$password;userid=1337");
    setcookie('key', base64_encode($cookieenc));
    $_COOKIE['key'] = base64_encode($cookieenc);
}

if(strpos(decrypt(base64_decode($_COOKIE['key'])), 'admin=1') !== false)
{
    echo "<img src='https://media.giphy.com/media/H6CDICYUiPAwE/giphy.gif' /><br>";
    echo "Bravo, tu peux valider avec le flag suivant : ".FLAG ;
    die();
}
else
{
    echo "Plaintext cookie : ".decrypt(base64_decode($_COOKIE['key']))."<br>";
    quit();
}
source();