Decrypting the URL and Getting the Resource Name

decode

byte[] encryptedData = HttpServerUtility.UrlTokenDecode(urlEncodedData);

        Type machineKeySection = typeof(MachineKeySection);
        Type[] paramTypes = new Type[] { typeof(bool), typeof(byte[]), typeof(byte[]), typeof(int), typeof(int) };
        MethodInfo encryptOrDecryptData = machineKeySection.GetMethod("EncryptOrDecryptData", BindingFlags.Static | BindingFlags.NonPublic, null, paramTypes, null);

        try
        {
            byte[] decryptedData = (byte[])encryptOrDecryptData.Invoke(null, new object[] { false, encryptedData, null, 0, encryptedData.Length });
            string decrypted = Encoding.UTF8.GetString(decryptedData);

            decryptedLabel.BackColor = Color.Lime;
            decryptedLabel.Text = decrypted;
        }
        catch (TargetInvocationException)
        {
            decryptedLabel.BackColor = Color.Red;
            decryptedLabel.Text = "Error decrypting data. Are you running your page on the same server and inside the same application as the web resource URL that was generated?";
        }

from:http://blogs.telerik.com/hristodeshev/posts/07-03-27/debugging-asp-net-2-0-web-resources-decrypting-the-url-and-getting-the-resource-name.aspx