.....
           TcpClient client = null;
            try
            {
                client = new TcpClient(Kde_remote_host, Kde_remote_port);
            }
            catch (SocketException s)
            {
                Log.Error(s.ToString());
                message_error = "Соединение не установлено. Проверьте строку соединения и доступность сервера";
                throw;
            }

            Log.Debug("Соединение установлено");
            SslStream sslStream = new SslStream(client.GetStream(),
                                                false,
                                                new RemoteCertificateValidationCallback(ValidateServerCertificate),
                                                new LocalCertificateSelectionCallback(ValidateClientCertificate)
                                               );
            try
            {
                X509Store store = new X509Store(StoreName.My, StoreLocation.CurrentUser);
                try
                {
                    store.Open(OpenFlags.ReadOnly);
                }
                catch (SecurityException s)
                {
                    Log.ErrorFormat("(store.Open): {0}", s.ToString());
                    throw;
                }
                catch (ArgumentException a)
                {
                    Log.ErrorFormat("(store.Open): {0}", a.ToString());
                    throw;
                }
                catch (Exception e)
                {
                    Log.ErrorFormat("(store.Open): {0}", e.ToString());
                    throw;
                }
                X509Certificate2Collection cert = store.Certificates.Find(X509FindType.FindBySubjectName, "KDEC", false);
                if (cert == null||cert.Count ==0)
                {
                    X509Certificate2Collection collection = new X509Certificate2Collection();
                    X509Certificate2 sert = new X509Certificate2("Мойсерт.pfx", "123456");
                    collection.Add(sert);
                    store.Add(sert);
                    cert = store.Certificates.Find(X509FindType.FindBySubjectName, "KKKK", false);
                }
                sslStream.AuthenticateAsClient(serverName, cert, SslProtocols.Default, false);
            }
            catch (AuthenticationException e)
            {
                if (e.InnerException != null)
                {
                    Log.ErrorFormat("Inner exception: {0}", e.InnerException.Message);
                }
                Log.Error(e.ToString());
                sslStream.Close();
                client.Close();
                message_error = "Ошибка сертификата. Обратитесть к системному администратору";
                throw;
            }
.....