Prova

// userName and password sent from form
$myusername=$_POST['username'];
$mypassword=$_POST['password'];

// To protect MySQL injection (more detail about MySQL injection)
$myusername = stripslashes($myusername);
$mypassword = stripslashes($mypassword);
$myusername = mysql_real_escape_string($myusername);
$mypassword = mysql_real_escape_string($mypassword);
$salt = createSalt();
$hash = hash('sha256', $mypassword);
$mypassword = hash('sha256', $salt . $hash);

$sql="SELECT * FROM $tbl_name WHERE username='$myusername' and password='$mypassword'";
$result=mysql_query($sql);

// Mysql_num_row is counting table row
$count=mysql_num_rows($result);

// If result matched $myusername and $mypassword, table row must be 1 row

if($count==1 ){
    if(crypt($password, $row['Password']) == $row['Password'])
    {
        header("location:index.php");
        exit();
    }
}
else {
    //echo "Wrong Username or Password";
    header("Location:login.php?errorMssg=".urlencode("Wrong Username or Password"));
}

function createSalt()
{
    return '2123293dsj2hu2besdbsjdsd';
}