Adding a key to decryption and encryption functions

[omerbar]

*please forgive me if this is a repost, I've carefully looked around forum before posting*

So I am willing to broadcast over LAN from one computer, and be able to play the video from another computer.
Broadcasting is done via the UDP port 1234. The problem is, I want to encrypt the message on the server side before broadcasting, and give the decryption key only to specific users so that they can use that key in order to play the video.

What is the best / most simple way to get this done?
1. write a lua/c++ plugin for vlc
2. use the VLC open source code and compile it on each machine
3. any other ideas would be highly appreciated.

I thank you in advance.

[Jean-Baptiste Kempf]

Use DVB-CSA keys?