// returns an encrypted string version of an ID suitable for transmission on a URL
    public static string EncryptID(int unencryptedID)
    {
        string encryptedID;

        byte[] bKey = new byte[8];
        byte[] IV = { 0x12, 0x34, 0x56, 0x78, 0x90, 0xAB, 0xCD, 0xEF };

        bKey = System.Text.Encoding.UTF8.GetBytes("!#$a54?3");  // you might want to store the encryption key in an appSetting of your web.config
        DESCryptoServiceProvider des = new DESCryptoServiceProvider();
        Byte[] inputByteArray = System.Text.Encoding.UTF8.GetBytes(unencryptedID.ToString());
        MemoryStream ms = new MemoryStream();
        CryptoStream cs = new CryptoStream(ms, des.CreateEncryptor(bKey, IV), CryptoStreamMode.Write);
        cs.Write(inputByteArray, 0, inputByteArray.Length);
        cs.FlushFinalBlock();

        encryptedID = Convert.ToBase64String(ms.ToArray());

        return HttpContext.Current.Server.UrlEncode(encryptedID);
    }

    public static int DecryptID(string encryptedID)
    {
        try
        {

            byte[] key = System.Text.Encoding.UTF8.GetBytes("!#$a54?3");  // you might want to store the encryption key in an appSetting of your web.config
            byte[] IV = { 0x12, 0x34, 0x56, 0x78, 0x90, 0xAB, 0xCD, 0xEF };
            byte[] inputByteArray = new byte[encryptedID.Length];

            DESCryptoServiceProvider des = new DESCryptoServiceProvider();
            inputByteArray = Convert.FromBase64String(encryptedID);
            MemoryStream ms = new MemoryStream();
            CryptoStream cs = new CryptoStream(ms, des.CreateDecryptor(key, IV), CryptoStreamMode.Write);
            cs.Write(inputByteArray, 0, inputByteArray.Length);
            cs.FlushFinalBlock();
            System.Text.Encoding encoding = System.Text.Encoding.UTF8;

            return int.Parse(encoding.GetString(ms.ToArray()));
        }
        catch
        {
            throw new ApplicationException("An invalid ID was received.");  
        }
    }