Falcon::get_hash PHP Method

    public static function get_hash($post_id, $user, $site_id)
    {
        return hash_hmac('sha1', $post_id . '|' . $site_id . '|' . $user->ID, 'bbsub_reply_by_email');
    }

 public function is_valid()
 {
     $user = $this->get_user();
     return $this->nonce === Falcon::get_hash($this->post, $user, $this->site);
 }