Session Start

authenticate_user.php

<?php
function authenticate_user($login, $password, $key)
{
	$val = set_codes();
	$query = "select * from users where login='$login' and password = encode('$password', '$key')";
	$result = mysql_query ($query);
	$row = mysql_fetch_row($result);
	
	if (mysql_num_rows($result) > 0)
	{
		$_SESSION['auth'] = $val;
		$_SESSION['id'] = $row[0];
	}
	else 
	{
		$_SESSION['auth'] = "Incorrect Login";
	}
}
?>

session_authenticate.php

<?php 
	$val = set_codes();
	if (!isset ($_SESSION['auth']) || $_SESSION['auth'] != $val)
	{
		if (isset($_POST['username']))
		{
			authenticate_user (mysql_prep($_POST['username']), mysql_prep($_POST['password']), KEY);
		}
	}
?>

session_start.php

<?php 
	session_start();
	if(isset($_GET['killsession']))
	{
		session_destroy();
		session_start();
	}
?>

set_codes.php

<?php
function set_codes()
{
	if (!isset($_SESSION['validcode']))
	{
		$_SESSION['validcode'] = rand (1000000, 9000000);
		$val = $_SESSION['validcode'];
		return $val;
	}
	else
	{
		$val = $_SESSION['validcode'];
		return $val;
	}
}
?>