gisostallenberg / fixed-token

1.0.0 2017-01-27 15:41 UTC

Requires (Dev)

• phpunit/phpunit: ^5.7

Unknown License

• Giso Stallenberg

Published on Packagist.org on 2017-01-27 15:50 UTC

README

Generate and verify tokens based on a secret and some public data

⚠️ Do not use this package

It is insecure and unnecessary. Two flaws, both fatal for a security token:

1. Length-extension attack. generate() returns sha1($secret . $data). SHA-1 is a Merkle–Damgård hash, so anyone holding a single valid (data, token) pair can forge a valid token for extended data without knowing the secret. The construction that prevents this is HMAC.
2. Timing attack. verify() compares with ===, which stops at the first differing byte and leaks the match length, allowing a byte-by-byte forgery. MAC comparison must be constant-time (hash_equals()).

Both are solved by PHP's standard library — no dependency needed. hash_hmac and hash_equals are built in (hash_equals since PHP 5.6):

$payload = http_build_query($data); // ksort($data) first for a stable order

// generate
$token = hash_hmac('sha256', $payload, $secret);

// verify (constant-time)
hash_equals($token, $givenToken); // bool

If you need expiry, claims or revocation rather than a bare tag, use a maintained, reviewed library such as paragonie/paseto or firebase/php-jwt.

Installation

composer require gisostallenberg/fixed-token

Usage example

<?php

use GisoStallenberg\FixedToken\FixedToken;

$secret = 'oxQu/H2FZLOK2elkfle8bg./eg';
$data = array(
    'username' => 'giso',
);

$token = FixedToken::create($secret)
    ->addData($data)
    ->generate();

FixedToken::create($secret)
    ->addData($data)
    ->verify($token); // should return true