Secure Covert Channels in Multiplayer Games

Steganography is the art of hidden communication. In recent years, some publications presented approaches to transmit hidden information for different purposes via covert channels provided by games. These approaches used rather ad-hoc techniques to reach their objectives without establishing notions of steganographic security in their domain and applying them to review their solution. Therefore, this paper both theoretically and practically tackles the question how to implement secure steganography for games. First, we recall the necessary game-theoretic basics from which we derive a notion of steganographic security for game-based methods that depends on strategy imitation. This is followed by a general information-theoretic analysis of games to calculate the total amount of information that is sent during a game and the share that can be used securely for game-theoretic steganography. Second, based on our game-theoretic framework, we present a secure steganographic system for a simplified version of poker that serves as a proof of concept. Its features are evaluated and compared to the theoretical results. Despite its security, the system can replace over 50% of the cover data with steganographic information. Further advantages of our method are that no large cover messages are needed and that it can be used for steganographic streaming.