Decrypting non https session cookie Error

问题

I am trying to follow this post to decrypt a session cookie from a Capture the Flag event as a learning exercise

How to decrypt cookie?

Here is my php script that I put together for the very first time in my life in php

#!/usr/bin/php
<?php

    echo 'Hello World!';
    $cookie = 'eyJpdiI6ImFUQ0FvMWFSVlNvTmhlQjdLWGw1Z1E9PSIsInZhbHVlIjoicFh6Q09iTDl0K0huWU1Nc1NYVmxSY2hPRGU5Vk85dDJyYUpRbUVjRWg5R0JxYkVobkF3YkZVcVQrakFFUmxaVnZrTjFST3F3RTZ4akpDZEpvUFJiQXc9PSIsIm1hYyI6IjlhYmJhMTY3MWMxYWI3YjJmNmFjMmNkZWE0MWZmMmVhNTNiMjI5ZWY3NzUwNzQ0ZjAzMGQ1ZGU0YzVhNjJmZGYifQ==';
    $cookie_contents = json_decode( base64_decode( $cookie, true ));
    print_r($cookie_contents);
    $value = base64_decode( $cookie_contents->value );
    var_dump($value);
    $iv = base64_decode( $cookie_contents->iv );
    var_dump($iv);
    $clear = unserialize(openssl_decrypt($value, \Config::get( 'app.cipher' ), \Config::get( 'app.key' ), OPENSSL_RAW_DATA, $iv));
    var_dump($clear);
    echo "Cookie contents (Session ID): $clearn";

    ?>

and here is the output with some Errors

Hello World!stdClass Object
(
    [iv] => aTCAo1aRVSoNheB7KXl5gQ==
    [value] => pXzCObL9t+HnYMMsSXVlRchODe9VO9t2raJQmEcEh9GBqbEhnAwbFUqT+jAERlZVvkN1ROqwE6xjJCdJoPRbAw==
    [mac] => 9abba1671c1ab7b2f6ac2cdea41ff2ea53b229ef7750744f030d5de4c5a62fdf
)
ڶ¢PGс©±! "¥|9²򦡃,IueEǎ
          򃅖U¾CuDꮓ¬c$'I 󙁢
󿹩yy"ng(16) "i0£VU*
PHP Fatal error:  Class 'Config' not found in /home/code/php/test.php on line 12

I am not able to fix the Fatal Error and I need guidance in how to decrypt a flag hidden in the cookie.

来源：https://stackoverflow.com/questions/55165915/decrypting-non-https-session-cookie-error

标签

php

encryption

base64

session-cookies