<?php

    if(!isset($_SESSION['signed_in'])) {

        header('Location: index.php');
        exit();

            }else{

            if(!isset($_SESSION['signed_in'])) {

                session_regenerate_id();
                $_SESSION['signed_in'] = TRUE;
                }

            if(isset($_SESSION['REMOTE_ADDR'])) {

                if($_SESSION['REMOTE_ADDR'] != $_SERVER['REMOTE_ADDR']) {
                exit;
                }

            }else{

            $_SESSION['REMOTE_ADDR'] = $_SERVER['REMOTE_ADDR'];
            }

            if(isset($_SESSION['HTTP_USER_AGENT'])) {

                if($_SESSION['HTTP_USER_AGENT'] != sha1($_SERVER['HTTP_USER_AGENT'])) {
                exit;
                }

        }else{

        $_SESSION['HTTP_USER_AGENT'] = sha1($_SERVER['HTTP_USER_AGENT']);
        }
    }

?>