Assured Supraliminal Steganography in Computer Games

Transcription

1 Assured Supraliminal Steganography in Computer Games Anton Mosunov, Vineet Sinha, Heather Crawford, John Aycock, Daniel Medeiros Nunes de Castro, Rashmi Kumari

2 Subliminal vs. Supraliminal Steganography Subliminal. Making unobtrusive changes to some cover object (e.g. data file); Supraliminal. Information is hidden in plain sight. Cover object Embedded object LSB (subliminal) steganography example from

3 Prisoner s Problem Diagram taken from the paper of S. Craver, On Public-Key Steganography in the Presence of an Active Warden. In Information Hiding 2007, pages 42 47, 2007.

4 Deconstructing Supraliminal What exactly constitutes supraliminal? Problems arise with original definition: o Interpretation. Many supraliminal steganographic techniques can be considered subliminal from a different perspective; o Uncertainty. Sometimes it is not clear whether a steganographic technique is really supra- or subliminal to humans; o Warden Activity. Limits on the warden s possible actions with respect to the channel must be well defined.

5 Application to Computer Games We strengthen original definition to create assured supraliminal steganography (AS²); That is, the channel is robust, blatant, inconspicuous and human-perceptible; A human is able to see enough to extract message manually, if necessary; We demonstrate the concept of AS² on four computer games: Breakout, Solitaire, Pong and Pac-Man.

6 AS² Taxonomy Derives from how a human extracts a message: o Static. The message may be perceived in its entirety initially without starting to play the game; o Dynamic. The message may only be perceived (in whole or part) while the human is actively playing the game. Note. In a static method a message can be split statically across multiple games or levels.

7 Static Methods

8 Breakout Message encoded using the color of blocks; Embedded message E is preceded by a random nonce N; N serves to ensure that E will appear differently each time; Colors are linked to scoring, so the warden cannot destroy the message without altering gameplay.

9 Solitaire (Freecell and Klondike) Freecell. 52 cards face-up; Klondike. 7 cards up + 24 cards in the stock;

10 Solitaire (Freecell and Klondike) Freecell is static, Klondike is dynamic; Encoding considers N cards that are face-up or that may be revealed from the stock; The permutation of the N cards is the basis for encoding. This allows bits per game; A message M can be converted to the card permutation; Alice and Bob must agree on the same unpermuted order.

11 Dynamic Methods

12 Pong Two players: sender and receiver; Sender enters the message in a textbox. After that sender s paddle becomes automated and starts to transmit the message; A paddle is divided on three parts. If the ball hits top (bottom), 1 (0) is transmitted. Ball hitting a middle helps to indicate a beginning or ending of the message. 1 0 Receiver Sender

13 Pac-Man Message encoded into the movement of ghosts; Normally, ghosts move in deterministic way; But, whenever Pac-Man eats a power pill, ghosts get scared and start move randomly. This is when the message gets transmitted. Power pill

14 Pac-Man Drawback. Low embedding rate (scared mode does not last for long); To extract a message, user must watch where ghost turns when it reaches intersection; A single user can follow at most two ghosts. To follow all ghosts, additional software (Pixel Tracker) is used.

15 Experimental Results

16 Extraction accuracy

17 Worst extraction accuracy

18 Conclusion

19 Conclusion The notion of supraliminal steganography is refined to create assured supraliminal steganography (AS²); The best way to prove that the technique is supraliminal is to demonstrate that a human (possibly trained) can extract it; We applied this to computer games; Our experiments involving trained operators showed that our techniques are indeed AS².

20 Assured Supraliminal Steganography in Computer Games Anton Mosunov, Vineet Sinha, Heather Crawford, John Aycock, Daniel Medeiros Nunes de Castro, Rashmi Kumari