Tuesday, September 15, 2009

ACM mmsec 09, the hidden (and fun) parts

By Tsatsiki
Miss cucumber is right, there were interesting papers in the ACM workshop on Multimedia and Security. And the participants had some fun as well. This is mainly thanks to one guy: Scoot Craver, the co-chair of the conference.

Scott is born data-hider, let me tell you why.
Firstly, when the participants arrived to register, they were offered a nice usb key like this one:


- these were the two first hidden messages. (look at it upside down)







Secondly, Scoot launched the workshop saying that there was a hidden (and cyphered) message on the building of the conference (the Friend Center in Princeton). This was true indeed since during the next coffee break the participants were able to see this:

- this was the second hidden message! Did Scoot add the bricks just for the conference? François Cayre, knowing ASCII code by heart, succeeded to decipher the message, while some others asked Google for the solutions.


Of course the talks of the workshop were also filled with hidden information (it was voluntary or not) and two of them were rather fun:
- the magic display cable (Atakli et al.) which is able to recognize, descramble and display encrypted images of a computer desktop on the fly,
- during the rump session, a teaser of the first contest on steganography was presented by T. Pevny. According to him it will be launch in 2010 and called BOSS (for Break Our Steganographic Scheme). I think that this contest is going to be rather popular.

Let's hope that WIFS 2009, the next conference on data-hiding, will be as fun as this one.

Monday, September 14, 2009

ACM mmsec 2009: the rise of the dragon?


ACM mmsec took place under the black and orange flags of the amazing campus of Princeton University, 7-8 september.
The general chair was Ed Felten, Prof. of Computer Science and Public Affairs (might be the only one to have this title), and the director of the brand new Center for Information Technology Policy.
He made a very good introduction speech calling for more discussions between computer scientists and law makers, and then, he almost disappeared from the conference (I could understand, after all, Monday was Labor day)! Never mind, Scott Craver organized a very good social event between nowhere and goodbye in a house near the lake and the lunch in Prospect House was also terrific.

Helas, there were only 40 to 50 attendees! Scott Craver defended the idea that, despite the decline of submissions, their overall quality was good. Therefore, good papers don't fear the financial crisis (if this is the real reason for the submission number decrease).
Like in IH'09, there were indeed quite few papers of lower interest so that the idea of S. Craver holds.

So, what is hot? MP3 quality assessment! The scenario is as follows: a low bitrate MP3 file is transcoded at a higher bitrate and sold as a pretendedly high quality tune. How to detect this? By revealing the signs of a double compression. Actually, H. Farid also presented a talk about double compression to detect video edition. Three speeches, three different approaches: from the "I don't know what happens, but my SVM will tell" heuristic to a more convincing statistical modeling.

The asian dragon? The era of old asian professors reading with difficulty their slides full of approximative english long sentences is over. We are witnessing, in multimedia security (it is probably the case for a long time in other fields), a new generation of young, convincing communicator and quite good researchers. Among the speakers but also in the audience. Some aggressive but very relevant questions were asked.

We also met the future leaders in steganalysis: Jan Kodovsky and Jan Judas replacing the two Tomas evil twins leaving Binghamton (Tomas has already left for Grenoble and soon Praha, while Tomas is finishing his ph.D). The Czech eagle vs. the asian dragon... An interesting battle is coming.

Talks I liked:

- "Two Key Estimation for the Borken Arrows watermarking Scheme", P. Bas and A. Westfeld. Another evil twin couple is born. How to break Broken Arrows (the watermarking technique used for BOWS-2) again and again. I guess, since P. Bas is one of the inventor, it is easier to analyze one's own scheme.

- "Additive Spread-spectrum watermarking detection in demosaicked images", P. Meerwald and A. Uhl. Hack your camera! The Austrian team modified the firmware of a camera so that watermark embedding is done in the device just after the CFA capture. Cool hack! This rises the challenge of watermark detection after demosaicking.

- "Exposing digital forgeries in video by detecting double quantization", W. Wang and H. Farid.
The best paper of all the "double compression" works in this conference. Nice but oversimple talk (as always), which plays the role of a teaser to read the paper for further information. The paper is indeed good: statistical model, identification of the parameters with an 'E-M' like algorithm, hypothesis test.

- "Calibration revisited" J. Kodovsky and J. Fridrich. My understanding about calibration is that natural images follow no statistical model or a so flat pdf p(X) that no hypothesis test will work with so few discrimination. Calibration is about estimating a set of parameters P specializing the model, switching from the flat marginal p(X) to the much more contrasted conditional p(X|P). Calibration is about statistical modeling. Whereas this paper uses calibration with SVM, which is, IMHO, the contrary of statistical modeling. SVM means "I don't know how to model things but, once trained, the SVM will find its way". Therefore, I was a little confused by this approach. But the results are there.

- "Square Root Law" A. Ker. During IH'09, I was not convinced by the talks about the square root law: It is was not enough formalized, the assumptions were not clearly delimited, so that if the law indeed holds, we could not tell the real reasons. This is exactly what Andrew Ker did in between the two conferences, and now, this became serious math with theorem (conditions and results) and proofs.

- "Detection of seam carving and localization of seam insertions an digital images" A. Sarkar, L. Natarj, and B. Manjunath. Seam carving is this image processing tool. It a priori seems a 'mission impossible' to detect seam carving, but a heavy tool (a 324 Markov features classifier) starts producing good results. Work in progress. A maybe too dense presentation.

Miss Cucumber