logon.php

<?php
//login.php
session_start();

if (isset($_SESSION['username'])){
	if (isset($_GET['logout'])) unset($_SESSION['username']);
	header("location: index.php");
} else {
	if ($_POST){
		//asumsi username and password hasil fetched form database
		$username = "admin";
		$password = "21232f297a57a5a743894a0e4a801fc3"; //admin
		//password di atas hasil md5("admin");

		if ($_POST['uname']==$username){ //bandingkan username
			if (md5($_POST['passwd'])==$password){ //bandingkan password
				//sukses
				unset($_SESSION['failed']); //hapus failed
				unset($_SESSION['delayto']); //hapus delayto
				$_SESSION['username']=$username; //catat username
				header("location: index.php"); //ke halaman utama
			}
		}
		//failed catat sudah berapa kali
		$message = "Username/password tidak match";
		if (!isset($_SESSION['failed'])) $_SESSION['failed']=0;
		$_SESSION['failed']++; //faileb bertambah

		//delay sebanyak 2 pangkat gagal
		$delay = pow(2,$_SESSION['failed']);
		$_SESSION['delayto'] = strtotime("+ {$delay} seconds");
	}
}
?>
<h2>Login</h2>
<?php
if (isset($message)) echo $message."<br/>";
if (isset($_SESSION['delayto'])) $delay = $_SESSION['delayto'] - time();
else $delay = 0;

if ($delay > 0): ?>

<p>
Sudah <?php echo $_SESSION['failed'];?> kali gagal.<br/>
Silakan coba
<span id="delay"><?php echo $delay;?></span>.
</p>
<script type="text/javascript">
  var seconds;
  var temp;

  function countdown() {
    seconds = document.getElementById('delay').innerHTML;
    seconds = parseInt(seconds, 10);

    if (seconds == 1) {
      temp = document.getElementById('delay');
      temp.innerHTML = "<a href='login.php'>login</a>";
      return;
    }

    seconds--;
    temp = document.getElementById('delay');
    temp.innerHTML = seconds+" detik lagi";
    timeoutMyOswego = setTimeout(countdown, 1000);
  }

  countdown();
</script>

<?php else: ?>

<form method="POST">
	Username: <br/>
	<input type="text" name="uname"><br/>
	Password :<br/>
	<input type="password" name="passwd"><br/>
	<input type="submit" value="Submit">
</form>

<?php endif; ?>