protected virtual void ReportServerVersion(ClientHandshakeState state, ProtocolVersion server_version)
        {
            TlsClientContextImpl clientContext        = state.clientContext;
            ProtocolVersion      currentServerVersion = clientContext.ServerVersion;

            if (null == currentServerVersion)
            {
                clientContext.SetServerVersion(server_version);
                state.client.NotifyServerVersion(server_version);
            }
            else if (!currentServerVersion.Equals(server_version))
            {
                throw new TlsFatalAlert(AlertDescription.illegal_parameter);
            }
        }
        /**
         * Initiates a TLS handshake in the role of client.<br/>
         * <br/>
         * In blocking mode, this will not return until the handshake is complete.
         * In non-blocking mode, use {@link TlsPeer#NotifyHandshakeComplete()} to
         * receive a callback when the handshake is complete.
         *
         * @param tlsClient The {@link TlsClient} to use for the handshake.
         * @throws IOException If in blocking mode and handshake was not successful.
         */
        public virtual void Connect(TlsClient tlsClient)
        {
            if (tlsClient == null)
            {
                throw new ArgumentNullException("tlsClient");
            }
            if (this.mTlsClient != null)
            {
                throw new InvalidOperationException("'Connect' can only be called once");
            }

            this.mTlsClient = tlsClient;

            this.mSecurityParameters        = new SecurityParameters();
            this.mSecurityParameters.entity = ConnectionEnd.client;

            this.mTlsClientContext = new TlsClientContextImpl(mSecureRandom, mSecurityParameters);

            this.mSecurityParameters.clientRandom = CreateRandomBlock(tlsClient.ShouldUseGmtUnixTime(),
                                                                      mTlsClientContext.NonceRandomGenerator);

            this.mTlsClient.Init(mTlsClientContext);
            this.mRecordStream.Init(mTlsClientContext);

            TlsSession sessionToResume = tlsClient.GetSessionToResume();

            if (sessionToResume != null && sessionToResume.IsResumable)
            {
                SessionParameters sessionParameters = sessionToResume.ExportSessionParameters();
                if (sessionParameters != null)
                {
                    this.mTlsSession        = sessionToResume;
                    this.mSessionParameters = sessionParameters;
                }
            }

            SendClientHelloMessage();
            this.mConnectionState = CS_CLIENT_HELLO;

            BlockForHandshake();
        }
        protected virtual byte[] GenerateClientHello(ClientHandshakeState state, TlsClient client)
        {
            MemoryStream buf = new MemoryStream();

            ProtocolVersion client_version = client.ClientVersion;

            if (!client_version.IsDtls)
            {
                throw new TlsFatalAlert(AlertDescription.internal_error);
            }

            TlsClientContextImpl context = state.clientContext;

            context.SetClientVersion(client_version);
            TlsUtilities.WriteVersion(client_version, buf);

            SecurityParameters securityParameters = context.SecurityParameters;

            buf.Write(securityParameters.ClientRandom, 0, securityParameters.ClientRandom.Length);

            // Session ID
            byte[] session_id = TlsUtilities.EmptyBytes;
            if (state.tlsSession != null)
            {
                session_id = state.tlsSession.SessionID;
                if (session_id == null || session_id.Length > 32)
                {
                    session_id = TlsUtilities.EmptyBytes;
                }
            }
            TlsUtilities.WriteOpaque8(session_id, buf);

            // Cookie
            TlsUtilities.WriteOpaque8(TlsUtilities.EmptyBytes, buf);

            bool fallback = client.IsFallback;

            /*
             * Cipher suites
             */
            state.offeredCipherSuites = client.GetCipherSuites();

            // Integer -> byte[]
            state.clientExtensions = client.GetClientExtensions();

            // Cipher Suites (and SCSV)
            {
                /*
                 * RFC 5746 3.4. The client MUST include either an empty "renegotiation_info" extension,
                 * or the TLS_EMPTY_RENEGOTIATION_INFO_SCSV signaling cipher suite value in the
                 * ClientHello. Including both is NOT RECOMMENDED.
                 */
                byte[] renegExtData = TlsUtilities.GetExtensionData(state.clientExtensions, ExtensionType.renegotiation_info);
                bool   noRenegExt   = (null == renegExtData);

                bool noRenegSCSV = !Arrays.Contains(state.offeredCipherSuites, CipherSuite.TLS_EMPTY_RENEGOTIATION_INFO_SCSV);

                if (noRenegExt && noRenegSCSV)
                {
                    // TODO Consider whether to default to a client extension instead
                    state.offeredCipherSuites = Arrays.Append(state.offeredCipherSuites, CipherSuite.TLS_EMPTY_RENEGOTIATION_INFO_SCSV);
                }

                /*
                 * draft-ietf-tls-downgrade-scsv-00 4. If a client sends a ClientHello.client_version
                 * containing a lower value than the latest (highest-valued) version supported by the
                 * client, it SHOULD include the TLS_FALLBACK_SCSV cipher suite value in
                 * ClientHello.cipher_suites.
                 */
                if (fallback && !Arrays.Contains(state.offeredCipherSuites, CipherSuite.TLS_FALLBACK_SCSV))
                {
                    state.offeredCipherSuites = Arrays.Append(state.offeredCipherSuites, CipherSuite.TLS_FALLBACK_SCSV);
                }

                TlsUtilities.WriteUint16ArrayWithUint16Length(state.offeredCipherSuites, buf);
            }

            // TODO Add support for compression
            // Compression methods
            // state.offeredCompressionMethods = client.getCompressionMethods();
            state.offeredCompressionMethods = new byte[] { CompressionMethod.cls_null };

            TlsUtilities.WriteUint8ArrayWithUint8Length(state.offeredCompressionMethods, buf);

            // Extensions
            if (state.clientExtensions != null)
            {
                TlsProtocol.WriteExtensions(buf, state.clientExtensions);
            }

            return(buf.ToArray());
        }