Sep 142014

IPv6 Talk 2014Today I gave a talk at the Seattle Code Camp.
Wonderful atmosphere, excellent organization, and a plenty of fun. Only bad thing was that it ended too soon (single day only).

My session was mostly geared toward the beginners and it covered just the basics of IPv6 and how we can use it from C#. I can only hope I lit some IPv6 fire in the great crowd that came.

I went to many other sessions myself and, while they did vary in quality, there was not a single bad one. My day was definitely fulfilled.

Feel free to download slides and examples.

Sep 092014

In my last post I described how to do the client-authenticated TLS and one of magic ingredients there was a certificate with the private key in the form of .pfx files.

Server and client certificates are essentially the same but I’ll show creating of both anyhow. For this I will assume that your Windows SDK files are in the C:\Program Files (x86)\Microsoft SDKs\Windows\v7.1A\Bin\ and that we are storing files in the root of the drive D:

> cd "C:\Program Files (x86)\Microsoft SDKs\Windows\v7.1A\Bin\"

> makecert -n "CN=MyServer" -r -sv D:\server.pvk D:\server.cer

> makecert -n "CN=MyClient" -pe -r -sv D:\client.pvk D:\client.cer

> pvk2pfx -pvk D:\server.pvk -spc D:\server.cer -pfx D:\server.pfx

> pvk2pfx -pvk D:\client.pvk -spc D:\client.cer -pfx D:\client.pfx

> DEL D:\client.cer D:\client.pvk D:\server.cer D:\server.pvk

This results in the server.pfx and client.pfx files. We can opt to import them into the Windows Certificate Store (also possible with makecert command) or to use them directly as in this example.

Sep 022014

Thanks to NSA, most probably every developer is aware of the HTTPS and the underlying TLS (or older SSL). While most scenarios involve authentication of a server, authentication of a client is often overlooked.

If you wonder what you gain, just be reminded of key-based authentication in the SSH. No need to exchange username/password with every client. You just exchange a (safely stored) key and you know who is on the other side.

Distribution and a safe storage of the client certificate is a non-trivial problem but easily handable on a smaller scale. Windows certificate store is not too bad and the client authentication makes it easy to block keys that aren’t trusted any more.

Here is the example code of a simple TLS encrypted TCP client/server with a self-signed certificates. Of course, one would expect proper certificates to be used in any production environment, but these will do in a pinch.

First we need to setup a server using just a standard TCP listener with a twist:

var serverCertificate = new X509Certificate2(ServerCertificateFile);

var listener = new TcpListener(IPAddress.Any, ServerPort);

while (true) {
    using (var client = listener.AcceptTcpClient())
    using (var sslStream = new SslStream(client.GetStream(), false, App_CertificateValidation)) {
        sslStream.AuthenticateAsServer(serverCertificate, true, SslProtocols.Tls12, false);

        //send/receive from the sslStream

Client is equally simple:

var clientCertificate = new X509Certificate2(ClientCertificateFile);
var clientCertificateCollection = new X509CertificateCollection(new X509Certificate[] { clientCertificate });

using (var client = new TcpClient(ServerHostName, ServerPort))
using (var sslStream = new SslStream(client.GetStream(), false, App_CertificateValidation)) {
    sslStream.AuthenticateAsClient(ServerCertificateName, clientCertificateCollection, SslProtocols.Tls12, false);

    //send/receive from the sslStream

Only trick in validation is to allow certificate chain errors. That is needed for self-signed certificates to work:

bool App_CertificateValidation(Object sender, X509Certificate certificate, X509Chain chain, SslPolicyErrors sslPolicyErrors) {
    if (sslPolicyErrors == SslPolicyErrors.None) { return true; }
    if (sslPolicyErrors == SslPolicyErrors.RemoteCertificateChainErrors) { return true; } //we don't have a proper certificate tree
    return false;

It is really this simple to convert any TCP socket code into the encrypted TLS.

Full example is available for download.

Aug 262014

Making a minimal C# video player in the Linux ought to be easy. I mean, both platforms are mature and something so basic should not present a problem.

GStreamer C# bindings seemed as a perfect choice at first. All needed was to “make” it. Simple enough – just use followed by make and enjoy the fruits of your labor.

That was a plan until I started the dependency dance. First I had to make GtkSharp myself since my latest library versions were too low for GStreamer. Then I had to get GStreamer. Then I had to get GStreamer plugins. And then I gave up.

Between compiling, downloading, and resolving dependencies I have installed around 50 packages, manually compiled multiple libraries, and I was still on the “just one more” stage. Call me spoiled, but I find this unacceptable.

Fortunately Linux is full of choices and my next try was with the MPlayerControl. It too needed a few packets on the top of a clean Mint 17 installation but nowhere close to the dependency hell:

# sudo apt-get install mono-complete monodevelop mplayer git

After that I had to get the latest MPlayerControl source:

# git clone MPlayerControl

And that was it. Shockingly, example within the source was working perfectly albeit it was not the smallest one they could make. I created my own sample form (with a reference to the LibMPlayerCommon) to play a single file as simply as possible:

using System;
using System.Collections.Generic;
using System.IO;
using System.Windows.Forms;
using LibMPlayerCommon;

namespace TestMedia {
  public class MainForm : Form {
    private MPlayer mPlayer;

    public MainForm() {
      this.WindowState = FormWindowState.Maximized;
      this.mPlayer = new MPlayer(this.Handle.ToInt32(), MplayerBackends.GL2);

      this.Load += delegate(object sender, EventArgs e) {
      this.Text = this.fileQueue.Peek();
      this.mPlayer.VideoExited += delegate(object sender, MplayerEvent e) {

While GStreamer more complete solution by far, I found MPlayerControl infinitely easier to use and setup.