php – 类的对象..无法转换为字符串

class Cryption
{
    var $data;
    var $salt;

function __construct($data,$salt)
{
    $this->data = $data;
    $this->salt = $salt;
}

function sha512()
{
    $sodium = 'Na';
    return hash_hmac("sha512",$this->data . $this->salt,$sodium);
}

function encrypt()
{
    $salt = substr(sha512(($this->key),'brownies'),30);
    return base64_encode(mcrypt_encrypt(MCRYPT_RIJNDAEL_256,$salt,$this->data,MCRYPT_MODE_CBC,md5($salt)));
}

当我使用它时：

$password = new Cryption(mysql_real_escape_string(trim($_POST['password'])),'pepper');
$password->sha512();

它说’PHP Catchable致命错误：类Cryption的对象无法转换为字符串’

我真的不知道怎么把它重新变成一个字符串.愿有人请帮帮我吗？

谢谢.

编辑：

<?php
require("config.php");
include("includes/cryption/cryption.php");

$username = mysql_real_escape_string(trim($_POST['username']));
$password = new Cryption(mysql_real_escape_string(trim($_POST['password'])),'pepper'); //use a different salt next time such as a special salt for each user
$password->sha512();

$result = mysql_query("SELECT * FROM `administrators` WHERE username='$username' and password='$password'");
$row = mysql_fetch_row($result);
$count = mysql_num_rows($result);

if ($count == 1) {
    if (isset($_POST['remember'])) {
        session_start();
        $_SESSION['user'] = array(
            'id' => $row[0],'username' => $row[1],'password' => $row[2]
        );
        $userid = new Cryption($_SESSION['user']['id'],'kkfishing');
        $session = new Cryption($_SESSION['user']['username'],'kkfishing');
        $validated = new Cryption($_SESSION['user']['password'],'kkfishing');

        setcookie("uniqueid",$userid->encrypt(),time() + 60 * 60 * 24 * 100,"/"); //100 days
        setcookie("kksessionid",$session->encrypt(),"/");
        setcookie("kkuserid",$validated->encrypt(),"/");//disguised cookie name
    }
    session_start();
    $_SESSION['authenticated'] = $row[0];
    echo '1'; //true
    exit;
}
else
{
    echo '0'; //false
    exit;
}
?>