Como desenvolver no C# um sistema que expire a cada 30 dias?

private void Expiracao_Sistema()
        {
            try
            {
                Microsoft.Win32.RegistryKey EncryptedKey;
                RSACryptoServiceProvider crypto = new RSACryptoServiceProvider();
                EncryptedKey = Microsoft.Win32.Registry.CurrentUser.CreateSubKey(@"HKEY_LOCAL_MACHINE\\SOFTWARE\\Microsoft\\EncryptedDate");

                object value = EncryptedKey.GetValue("EncryptedDate");

                if (value == null)
                {
                    EncryptedKey = Microsoft.Win32.Registry.CurrentUser.CreateSubKey(@"HKEY_LOCAL_MACHINE\\SOFTWARE\\Microsoft\\EncryptedDate");

                    string keyvalue = DateTime.Now.ToString("dd-MMM-yyyy");
                    byte[] messageBytes = Encoding.Unicode.GetBytes(keyvalue);

                    string encryptedMessage = Convert.ToBase64String(messageBytes);

                    EncryptedKey.SetValue("EncryptedDate", encryptedMessage);
                }
                else
                {
                    byte[] encryptedMessage1 = Convert.FromBase64String(value.ToString());

                    string key = System.Text.Encoding.Unicode.GetString(encryptedMessage1);

                    DateTime date = Convert.ToDateTime(key);

                    dataDaExpiracao = date.AddDays(30);

                    dataExpirou = dataDaExpiracao;

                    if (dataAtual >= dataDaExpiracao)
                    {
                        btnFechar.Visible = true;
                        lblMensagem.Visible = true;
                    }
                    else
                    {
                        pbWIDTH = picBoxPB.Width;
                        pbHEIGTH = picBoxPB.Height;

                        pbUnit = pbWIDTH / 100.0;

                        pbCompleto = 0;

                        bmp = new Bitmap(pbWIDTH, pbHEIGTH);

                        t.Interval = 40;
                        t.Tick += new EventHandler(this.t_Tick);
                        t.Start();
                    }
                }
            }
            catch (Exception e)
            {
                MessageBox.Show(e.Message);
            }
        }