PHP-CSRF

Cross-Site Request Forgery protection PHP library

PHP-CSRF manage, generate and validate hashes, on the user's session, to provide a basic protection from Cross-Site Request Forgery.

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Download

• Direct download php-csrf.php file (right click save as).
• Using wget wget -O php-csrf.php https://raw.githubusercontent.com/GramThanos/php-csrf/master/php-csrf.php

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Example usage

<?php
    // Include the PHP-CSRF library
    include('php-csrf.php');
    // Start or Resume a session
    session_start();
    // Initialize an instance
    $csrf = new CSRF();

    // If form was submitted
    if ($_SERVER['REQUEST_METHOD'] === 'POST') {
        // Validate that a correct token was given
        if ($csrf->validate('my-form')) {
            // Success
        }
        else {
            // Failure
        }
    }
?>

<!-- Your normal HTML form -->
<form method="POST">
    <!-- Print a hidden hash input -->
    <?=$csrf->input('my-form');?>
    ...
    <input type="submit" value="Submit"/>
</form>

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API

Create a csrf object

• $csrf = new CSRF($session_name='csrf-lib', $input_name='key-awesome', $hashTime2Live=0, $hashSize=64);
  • $session_name the name to be used for the session variable.
  • $input_name the name to be used on the HTML input with the hash.
  • $hashTime2Live the default hash live time of each hash in seconds. Should be >=0. If zero, by default the hash will not expire.
  • $hashSize the default hash size in chars. Should be >0.

Clear excess hashes

• $deleted = $csrf->clearHashes($context='', $max_hashes=0);
  • $context the name of the group to clear
  • $max_hashes the number of hashes to keep. If the hash population is bigger, the oldest hashes will be deleted.
  • returns the number of deleted hashes.

Generate HTML input element code

• echo $csrf->input($context='', $time2Live=-1, $max_hashes=5)
  • $context the name of the group to save the hash to. Usually, it is different for each form.
  • $time2Live the hash live time in seconds. If zero, the hash will not expire. If negative, the default value will be used.
  • $max_hashes the hash limit of the group. If the group has already reached this limit, the oldest hash will be discarded.
  • returns a string with the HTML code. Example return value '<input type="hidden" name="key-awesome" value="1234567890ABCDEF1234567890ABCDEF"/>'.

Generate javascript script element code (alternative)

• echo $csrf->script($context='', $name='', $declaration='var', $time2Live=-1, $max_hashes=5)
  • $context the name of the group to save the hash to. Usually, it is different for each form.
  • $name the name of the javascript variable. If it is empty string, the name of the input_name will be used, but the default one is an invalid variable name.
  • $declaration the declaration key word of the variable, usually var, let or const.
  • $time2Live the hash live time in seconds. If zero, the hash will not expire. If negative, the default value will be used.
  • $max_hashes the hash limit of the group. If the group has already reached this limit, the oldest hash will be discarded.
  • returns a string with the HTML script code. Example return value '<script type="text/javascript">var name = "1234567890ABCDEF1234567890ABCDEF";</script>'.

Generate javascript variable code (alternative)

• echo $csrf->javascript($context='', $name='', $declaration='var', $time2Live=-1, $max_hashes=5)
  • $context the name of the group to save the hash to. Usually, it is different for each form.
  • $name the name of the javascript variable. If it is empty string, the name of the input_name will be used, but the default one is an invalid variable name.
  • $declaration the declaration key word of the variable, usually var, let or const.
  • $time2Live the hash live time in seconds. If zero, the hash will not expire. If negative, the default value will be used.
  • $max_hashes the hash limit of the group. If the group has already reached this limit, the oldest hash will be discarded.
  • returns a string with the javascript code. Example return value 'var name = "1234567890ABCDEF1234567890ABCDEF";'.

Generate hash as a string (alternative)

• echo $csrf->string($context='', $time2Live=-1, $max_hashes=5)
  • $context the name of the group to save the hash to. Usually, it is different for each form.
  • $time2Live the hash live time in seconds. If zero, the hash will not expire. If negative, the default value will be used.
  • $max_hashes the hash limit of the group. If the group has already reached this limit, the oldest hash will be discarded.
  • returns a string with the hash. Example return value '1234567890ABCDEF1234567890ABCDEF'.

Check if a valid hash was posted

• $is_valid = $csrf->validate($context='', $hash=null)
  • $context the name of the group to search for the hash into.
  • $hash the hash to validate. If null, the hash will be retrieved by the $_POST or the $_GET objects.
  • returns true if the validation was successful or false otherwise.

Get the hashes of a context

• $is_valid = $csrf->getHashes($context='', $max_hashes=-1)
  • $context the name of the group to get its hashes.
  • $max_hashes max number of hashes to get. If negative value, all the hashes will be returned.
  • returns an array of string hashes.

The hashes are saved on the $_SESSION under the a single variable using serialize and unserialize. Thus, if the session expires or get destroyed, the hashes would too.

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About the Security

This library uses the openssl_random_pseudo_bytes function to generate random hashes. In order to be sure that your system can produce cryptographically strong hashes, you should run the following PHP code and check the result.

<?php
	// Test if random_pseudo is cryptographically strong in your system
	$hash = openssl_random_pseudo_bytes(32, $crypto_strong);
?>
<!DOCTYPE html>
<html lang="en">
	<head>
		<meta charset="utf-8">
		<title>PHP-CSRF Test</title>
	</head>
	<body>
		Is cryptographically strong: <?=($crypto_strong ? 'yes' : 'no');?><br>
	</body>
</html>

This library was created to provide a basic protection from Cross-Site Request Forgery attacks. Thus, sophisticated attacks like a timing attack may break the protection.

By using relative big hash sizes, relative short hash expiration times and small group hash limits, you can strengthen the security.

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License

This project is under The MIT license. I do although appreciate attribute.

Copyright (c) 2020 Grammatopoulos Athanasios Vasileios

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