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I have created TCP Client/Server application using MSDN sslstream Article. Both Client and server working correctly. I have also attached ssl certificate to both Client and Server.

When I run client and server programs, server always define "RemoteCertificate= null". I want to read client certificate and copy/store that certificate to store.

I also have demo program to store certificate using X509Store Class. Now the only issue is to get client certificate.

Here is the code for server :

using System;
using System.Collections;
using System.Net;
using System.Net.Sockets;
using System.Net.Security;
using System.Security.Authentication;
using System.Text;
using System.Security.Cryptography.X509Certificates;
using System.IO;

namespace Examples.System.Net
{
    public sealed class SslTcpServer
    {
        static X509Certificate serverCertificate = null;

        public static void RunServer(string certificate)
        {
            serverCertificate = X509Certificate.CreateFromCertFile(certificate);

            TcpListener listener = new TcpListener(IPAddress.Any, 8080);
            listener.Start();
            while (true)
            {
                Console.WriteLine("Waiting for a client to connect...");

                TcpClient client = listener.AcceptTcpClient();
                ProcessClient(client);
            }
        }
        static void ProcessClient(TcpClient client)
        {

            SslStream sslStream = new SslStream(
                client.GetStream(), false);

            try
            {
                sslStream.AuthenticateAsServer(serverCertificate,
                    false, SslProtocols.Tls, true);

                DisplaySecurityLevel(sslStream);
                DisplaySecurityServices(sslStream);
                DisplayCertificateInformation(sslStream);
                DisplayStreamProperties(sslStream);


                sslStream.ReadTimeout = 5000;
                sslStream.WriteTimeout = 5000;

                Console.WriteLine("Waiting for client message...");
                string messageData = ReadMessage(sslStream);
                Console.WriteLine("Received: {0}", messageData);


                byte[] message = Encoding.UTF8.GetBytes("Hello from the server.<EOF>");
                Console.WriteLine("Sending hello message.");
                sslStream.Write(message);
            }
            catch (AuthenticationException e)
            {
                Console.WriteLine("Exception: {0}", e.Message);
                if (e.InnerException != null)
                {
                    Console.WriteLine("Inner exception: {0}", e.InnerException.Message);
                }
                Console.WriteLine("Authentication failed - closing the connection.");
                sslStream.Close();
                client.Close();
                return;
            }
            finally
            {

                sslStream.Close();
                client.Close();
            }
        }
        static string ReadMessage(SslStream sslStream)
        {

            byte[] buffer = new byte[2048];
            StringBuilder messageData = new StringBuilder();
            int bytes = -1;
            do
            {

                bytes = sslStream.Read(buffer, 0, buffer.Length);


                Decoder decoder = Encoding.UTF8.GetDecoder();
                char[] chars = new char[decoder.GetCharCount(buffer, 0, bytes)];
                decoder.GetChars(buffer, 0, bytes, chars, 0);
                messageData.Append(chars);

                if (messageData.ToString().IndexOf("<EOF>") != -1)
                {
                    break;
                }
            } while (bytes != 0);

            return messageData.ToString();
        }
        static void DisplaySecurityLevel(SslStream stream)
        {
            Console.WriteLine("Cipher: {0} strength {1}", stream.CipherAlgorithm, stream.CipherStrength);
            Console.WriteLine("Hash: {0} strength {1}", stream.HashAlgorithm, stream.HashStrength);
            Console.WriteLine("Key exchange: {0} strength {1}", stream.KeyExchangeAlgorithm, stream.KeyExchangeStrength);
            Console.WriteLine("Protocol: {0}", stream.SslProtocol);
        }
        static void DisplaySecurityServices(SslStream stream)
        {
            Console.WriteLine("Is authenticated: {0} as server? {1}", stream.IsAuthenticated, stream.IsServer);
            Console.WriteLine("IsSigned: {0}", stream.IsSigned);
            Console.WriteLine("Is Encrypted: {0}", stream.IsEncrypted);
        }
        static void DisplayStreamProperties(SslStream stream)
        {
            Console.WriteLine("Can read: {0}, write {1}", stream.CanRead, stream.CanWrite);
            Console.WriteLine("Can timeout: {0}", stream.CanTimeout);
        }
        static void DisplayCertificateInformation(SslStream stream)
        {
            Console.WriteLine("Certificate revocation list checked: {0}", stream.CheckCertRevocationStatus);

            X509Certificate localCertificate = stream.LocalCertificate;
            if (stream.LocalCertificate != null)
            {
                Console.WriteLine("Local cert was issued to {0} and is valid from {1} until {2}.",
                    localCertificate.Subject,
                    localCertificate.GetEffectiveDateString(),
                    localCertificate.GetExpirationDateString());
            }
            else
            {
                Console.WriteLine("Local certificate is null.");
            }

            X509Certificate remoteCertificate = stream.RemoteCertificate;
            if (stream.RemoteCertificate != null)
            {
                Console.WriteLine("Remote cert was issued to {0} and is valid from {1} until {2}.",
                    remoteCertificate.Subject,
                    remoteCertificate.GetEffectiveDateString(),
                    remoteCertificate.GetExpirationDateString());
            }
            else
            {
                Console.WriteLine("Remote certificate is null.");
            }
        }
        public static void Main(string[] args)
        {
            string certificate = "c:/Test.cer";
            SslTcpServer.RunServer(certificate);
        }
    }
}

Here is the code for client :

using System;
using System.Collections;
using System.Net;
using System.Net.Security;
using System.Net.Sockets;
using System.Security.Authentication;
using System.Text;
using System.Security.Cryptography.X509Certificates;
using System.IO;

namespace Examples.System.Net
{
    public class SslTcpClient
    {
        private static Hashtable certificateErrors = new Hashtable();

        // The following method is invoked by the RemoteCertificateValidationDelegate. 
        public static bool ValidateServerCertificate(
              object sender,
              X509Certificate certificate,
              X509Chain chain,
              SslPolicyErrors sslPolicyErrors)
        {
            if (sslPolicyErrors == SslPolicyErrors.None)
                return true;

            Console.WriteLine("Certificate error: {0}", sslPolicyErrors);

            // Do not allow this client to communicate with unauthenticated servers. 
            return false;
        }
        public static void RunClient(string machineName, string serverName)
        {
            // Create a TCP/IP client socket. 
            // machineName is the host running the server application.
            TcpClient client = new TcpClient(machineName, 8080);
            Console.WriteLine("Client connected.");
            // Create an SSL stream that will close the client's stream.
            SslStream sslStream = new SslStream(
                client.GetStream(),
                false,
                new RemoteCertificateValidationCallback(ValidateServerCertificate),
                null
                );
            // The server name must match the name on the server certificate. 
            try
            {
                sslStream.AuthenticateAsClient(serverName);
            }
            catch (AuthenticationException e)
            {
                Console.WriteLine("Exception: {0}", e.Message);
                if (e.InnerException != null)
                {
                    Console.WriteLine("Inner exception: {0}", e.InnerException.Message);
                }
                Console.WriteLine("Authentication failed - closing the connection.");
                client.Close();
                return;
            }

            X509Certificate remoteCertificate = sslStream.RemoteCertificate;
            if (sslStream.RemoteCertificate != null)
            {
                Console.WriteLine("Remote cert was issued to {0} and is valid from {1} until {2}.",
                    remoteCertificate.Subject,
                    remoteCertificate.GetEffectiveDateString(),
                    remoteCertificate.GetExpirationDateString());
            }
            else
            {
                Console.WriteLine("Remote certificate is null.");
            }

            // Encode a test message into a byte array. 
            // Signal the end of the message using the "<EOF>".
            byte[] messsage = Encoding.UTF8.GetBytes("Hello from the client.<EOF>");
            // Send hello message to the server. 
            sslStream.Write(messsage);
            sslStream.Flush();
            // Read message from the server. 
            string serverMessage = ReadMessage(sslStream);
            Console.WriteLine("Server says: {0}", serverMessage);
            // Close the client connection.
            client.Close();
            Console.WriteLine("Client closed.");
        }
        static string ReadMessage(SslStream sslStream)
        {
            // Read the  message sent by the server. 
            // The end of the message is signaled using the 
            // "<EOF>" marker.
            byte[] buffer = new byte[2048];
            StringBuilder messageData = new StringBuilder();
            int bytes = -1;
            do
            {
                bytes = sslStream.Read(buffer, 0, buffer.Length);

                // Use Decoder class to convert from bytes to UTF8 
                // in case a character spans two buffers.
                Decoder decoder = Encoding.UTF8.GetDecoder();
                char[] chars = new char[decoder.GetCharCount(buffer, 0, bytes)];
                decoder.GetChars(buffer, 0, bytes, chars, 0);
                messageData.Append(chars);
                // Check for EOF. 
                if (messageData.ToString().IndexOf("<EOF>") != -1)
                {
                    break;
                }
            } while (bytes != 0);

            return messageData.ToString();
        }
        public static void Main(string[] args)
        {
            string serverCertificateName = null;
            string machineName = null;
            /*
            // User can specify the machine name and server name. 
            // Server name must match the name on the server's certificate. 
            machineName = args[0];
            if (args.Length < 2)
            {
                serverCertificateName = machineName;
            }
            else
            {
                serverCertificateName = args[1];
            }*/
            machineName = "127.0.0.1";
            serverCertificateName = "David-PC";// tried Test, LocalMachine and 127.0.0.1
            SslTcpClient.RunClient(machineName, serverCertificateName);
            Console.ReadKey();
        }
    }
}

Anyone Help? Thanks!

Jaimesh
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2 Answers2

2

After our conversation, using SSL Stream you are able to authenticate fine. To actually pull the server public key you will need to try another solution. So to answer your question you cannot get the public key or store it with ssl stream. You will need to follow something like this.

Also you are not going to be able to store the private key, only the public key. This is the nature of how the key pair works.

Community
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Nick McGinnis
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  • +1 For your Support. So it is not possible to get client certificate? And Using MSDN Ssl stream article(Link available in Question), I always receive "RemoteCertificate= null". Another question is : How to get client's public certificate?@Nick McGinnis – Jaimesh May 27 '16 at 05:41
  • @Jaimesh it is possible to use their public key yes, can you post some of your code so I can see what you are trying to do. If the code is running correctly I believe the issue is with what certificate the client is offering up. If you are using the example in the MSDN page for ssl stream you're setting RemoteCertificate = stream.remotecertificate. If the client either doesn't have a cert or is offering up the wrong one it could cause the null issue. – Nick McGinnis May 27 '16 at 11:48
  • yes. I am using the example of MSDN page. Not a single line of code edited. I just put code in question so you can better understand. – Jaimesh May 27 '16 at 11:52
  • @ Nick McGinnis : I also want to read server's Public/Private Key at client side. I have used RemoteCertificate at client side and get success to read server certificate but not able to read Public/Private key of server. – Jaimesh May 27 '16 at 11:59
  • I am comparing your code to the MSDN page code, you added another RemoteCertificate to your client code as well. Is this the section that is null? Try going back to just the code on the MSDN example, get that working first. Looking at your code it would seem your server is pulling the client certs fine, but the client can pull the servers. This might be a security setting on the server. So I would try to only do what the example shows first then try to add on. – Nick McGinnis May 27 '16 at 13:10
  • ya. MSDN Page code is working correctly. I just add RemoteCertificate at client side to read server certificate data, And it's also Working fine. I am able to read server certificate using RemoteCertificate at client side but not able to read server public/private key. – Jaimesh May 27 '16 at 13:16
  • According to your suggestion of security setting setting on server, How can I allow server to send it's Public/Private key to client? – Jaimesh May 27 '16 at 13:17
  • @Jaimesh What do you need the public/private key for? Is your goal to just authenticate or are you trying to encrypt something using the servers public key? – Nick McGinnis May 27 '16 at 13:30
  • Let me clear my task first. My task is to read server's Public/Private key at server side and Client's Public/Private Key at server side. Is this Possible? You have any suggestion to explore this? – Jaimesh May 27 '16 at 13:36
1

In server code change:

slStream.AuthenticateAsServer(serverCertificate, false, SslProtocols.Tls, true);

To

slStream.AuthenticateAsServer(serverCertificate, true, SslProtocols.Tls, true);
Anatoly
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