From 7150af6b9e21ed7802202702b1dac3a3df1998c0 Mon Sep 17 00:00:00 2001
From: Shish <shish@shishnet.org>
Date: Fri, 21 Jun 2024 19:18:21 +0100
Subject: [PATCH] [core] use sha3 instead of md5 for csrf tokens

---
 core/user.php | 16 ++++++----------
 1 file changed, 6 insertions(+), 10 deletions(-)

diff --git a/core/user.php b/core/user.php
index 0b7b556d..225f0b38 100644
--- a/core/user.php
+++ b/core/user.php
@@ -238,20 +238,16 @@ class User
     /**
      * Get an auth token to be used in POST forms
      *
-     * password = secret, avoid storing directly
-     * passhash = bcrypt(password), so someone who gets to the database can't get passwords
-     * sesskey  = md5(passhash . IP), so if it gets sniffed it can't be used from another IP,
-     *            and it can't be used to get the passhash to generate new sesskeys
-     * authtok  = md5(sesskey, salt), presented to the user in web forms, to make sure that
-     *            the form was generated within the session. Salted and re-hashed so that
-     *            reading a web page from the user's cache doesn't give access to the session key
+     * the token is based on
+     * - the user's password, so that only this user can use the token
+     * - the session IP, to reduce the blast radius of guessed passwords
+     * - a salt known only to the server, so that clients or attackers
+     *   can't generate their own tokens even if they know the first two
      */
     public function get_auth_token(): string
     {
         global $config;
-        $salt = SECRET;
-        $addr = get_session_ip($config);
-        return md5(md5($this->passhash . $addr) . "salty-csrf-" . $salt);
+        return hash("sha3-256", $this->passhash . get_session_ip($config) . SECRET);
     }