Monday, 22 September 2008

Counter-steganography research?

In the context of a national research fund, I recently stumbled across a project that deals with counter-steganography research. From an academic point of view, it is healthy to have security technology research and research trying to break these technologies. But when I had a closer look what kind of counter-steganography they were actually working on, I got worried.

The most common security breach in telecommunications is eavesdropping. Steganography and cryptography applied to telecommunication would both prevent that, the first by hiding the information, the second by talking in a language unknown to a third party listening. However, steganography is obviously more bandwidth demanding than cryptography, so why would anyone favour steganography over cryptography, when both achieve the same goals? Steganography has advantage that you can deny the existence of a hide message. Cryptographers call that plausible denial or deniable encryption.

StegIT (german) is a project that aims to prevent steganography in telecommunications (they aim for GSM/UMTS/VoIP). It works by mixing inauditable white noise into the conversation, so these "low bit" channels become unavailable for encoding hidden messages. StegIt does not aim to detect steganography, but its approach is to add this white noise to all conversations by installing equipment at your phone carrier. (To the german-speaking reader: Notice the wording they use in the project description. They speak of "steganographic attacks", and preventing these "attacks". Do they just desperately try to get funding or do they actually believe that?)

My initial reaction to StegIT was: "Why should I bother to use the low bandwidth channels at all? I would just drop those inaudible parts from my data channel and use regular encryption". I would loose the plausible denial property though, but is there is scenario where I would need that property? Yes, when encryption itself is outlawed (or made useless by laws for on-demand decryption).

This would only serve the purpose that eavesdropping is always available to law enforcement. But the idea to outlaw encryption sounded to remote to me... until I started googling that topic. Legislation concerning encryption is far from uncommon, see Crypto Law Survey by Bert-Japp Koops, who also provides us with some nice graphics.

Do I want my national security research fund to support a project that only make scene in a scenario where the right to encrypt -- your own personal guarantee for privacy -- is restricted? Definitely not.


Ron said...


I stumbled onto your blog and enjoyed reading your post. But this statement is incorrect: "However, steganography is obviously more bandwidth demanding than cryptography".

Changing the LSB in a bmp file does not use any more bandwidth. Same for changing the DCT coefficients in a jpg file. Was there a specific stego method you were thinking of?



Clemens Fruhwirth said...

By definition steganography hides information (hidden message) within other information (container).

Assuming the most trivial model, that a fixed portion of the container is dedicated to the hidden message -- lsbs of bmp files -- we see that the rest of the container does not contribute the hidden message and therefore is of no value to the user (of course that rests on the assumption that reason for communication is solely the hidden message)

If he had used cryptography, you don't have the overhead of the container. Hence it's more efficient. That was my point.