How to decrypt cookie?

Question

I've just caught a crash reported on sentry, I am trying to debug and see the root cause for the problem.

Luckily, in the cookies panel, I can see the laravel_session value that was used while crash happened.

The question, is, how can decrypt the cookie?

Answer 1

You can decrypt the cookie with the following code:

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

You should end up with a session ID that looks something like this:

• Laravel 5.1: 55782b00dbfcc3f848585ac2cefc66802d773cf5
• Laravel 5.4: yPjeV74joY4MtMNNtTpeOYBP2CMixJBBChc9HRND

I didn't test with Laravel 5.3, but I'm confident it will work.

When using this code, make sure you paste the entire contents of the cookie into the $cookie variable, including the two equals signs at the end.

Answer 2

For laravel 6 I think it's pretty much the same

$base64_key = "base64:ISAcSPwQ0HDqqLygaS9LyPzs5ZujMAKOjBou+gyz9sw=";
$payload = json_decode(base64_decode($_COOKIE["your_cookie_name"]), true);
$iv = base64_decode($payload['iv']);
$key = base64_decode(substr($base64_key, 7));
$sessionId = openssl_decrypt($payload['value'],  'AES-256-CBC', $key, 0, $iv);

echo "Session Id: $sessionId";

But check few things:

• Cipher encoding, mine is 'AES-256-CBC', it can be 'AES-128-CBC' if your key length is 16
• Key format, mine start with "base64:" so I have to remove this part first