<?php
require("dbconn.php");
function check($username, $password) {
    $query = "SELECT ID, username, password, serial FROM users WHERE username=".mysql_real_escape_string($username);
    $result = mysql_query($query);
    if(mysql_num_rows($result) > 0) {
        $password = mysql_result($result, 0, "password");
        $id = mysql_result($result, 0, "ID");
        if ($pass != $password) {
            return false;
        } else {
            return $id;
        }
    } else {
        return false;
    }
}
if(isset($_POST['submitted'])) {
    $user = $_POST['username'];
    $pass = $_POST['password'];
    $serial = $_POST['serial'];
    $pass = hash('sha256', $pass);
    $id = check($user, $pass);
    if($id != false) {
        $_SESSION['username'] = $user;
        $_SESSION['password'] = $pass;
        $_SESSION['id'] = $id;
    }
}

if(check($_SESSION['username'], $_SESSION['password']) == false) {
    echo '<table border="0">';
    echo '<form action="'.$_SERVER['PHP_SELF'].'" method="post">';
    echo '<tr><td>Username:</td><td><input class="tbLogin" type="text" name="username"></td></tr>';
    echo '<tr><td>Password:</td><td><input class="tbLogin" type="password" name="password"></td></tr>';
    echo '<tr><td>&nbsp;</td><td></td></tr>';
    echo '<tr><td></td><td><input class="btnLogin" type="submit" name="submitted" value="Log in">&nbsp;<input class="btnLogin" style="float: right" type="button" value="Register" onClick="document.location = \'register.php\'"></td></tr>';
    echo '</form>';
    echo '</table>';
    exit;
}
?>