Hey! I am one of the authors of this paper. I'd be happy to answer any questions about Castle. fcxSanya is right about the general idea behind the system. The idea is to use video games to establish covert communication channels that are hard to detect. This WIRED article did a good job of explaining the ideas behind our system: http://www.wired.com/2015/04/app-hides-secret-messages-starcraft-style-games/ There's more to come from Castle! We're specifically targeting making Castle a Tor pluggable transport by the end of this year. A little note on the relationship between 0 A.D. and Castle: 0 A.D. is our go to game for demos. While we have Castle working over other big titles, we cannot release that code for legal reasons. However, we do not recommend using Castle over 0 A.D. in the real world, due to the lack of encryption and authentication of the move communication channel. The good news is, Castle is highly adaptable and can be moved over other RTS-games in about a day, if required.