KEYWORDS: Digital watermarking, Wavelets, Information security, Barium, Denoising, Multimedia, Single crystal X-ray diffraction, Signal processing, Distortion, Image processing
This paper deals with the security of the robust zero-bit watermarking technique "Broken Arrows" (BA),1
which was invented and tested for the international challenge
BOWS-2.2 The results of the first episode of the
challenge showed that BA is very robust and we proposed last year an enhancement called "Averaging Wavelet
Coefficients" (AWC),3 which further strengthens the robustness against the worst attack disclosed during this
BOWS-2's first episode.4 However, in the second and third episodes of the challenge, during which the pirates
could observe plenty of pictures watermarked with the same secret key, security flaws have been revealed and
discussed.5 Here we propose counterattacks to these security flaws, investigating BA and its variant AWC. We
propose two counterattack directions: to use the embedding technique AWC instead of BA, and to regulate
the system parameters to lighten the watermarking embedding footprint. We also discuss these directions in
the context of traitor tracing.6 Experimental results show that following these recommendations is sufficient to
counter these attacks.
KEYWORDS: Multimedia, Digital watermarking, Expectation maximization algorithms, Forensic science, Electronic imaging, Current controlled current source
This paper presents our recent works on multimedia fingerprinting, which consists in improving both the fingerprinting code and the watermarking scheme. The fingerprinting code is the well known Tardos code. Our contributions only focus on deriving a better accusation process.
It appears that Tardos orginal decoding is very conservative: its performances are guaranteed whatever the collusion strategy. Indeed, major improvements stems from the knowledge of the collusion strategy. Therefore, this paper investigates whether it is possible to learn and adapt to the collusion strategy. This done with an iterative algorithm a la EM, where a better estimation of their strategy yields a better tracing of the colluders, which in return yields a better estimation of their strategy etc.
The second part focuses on the multimedia watermarking scheme. In a previous paper, we already used the `Broken Arrows' technique as the watermarking layer for multimedia fingerprinting. However, a recent paper from A. Westfeld discloses a flaw in this technique. We just present a counter-measure which blocks this security hole while preserving the robustness of the original technique.
The Good is Blondie, a wandering gunman with a strong personal sense of honor. The Bad is Angel Eyes, a sadistic hitman who always hits his mark. The Ugly is Tuco, a Mexican bandit who's always only looking out for himself. Against the backdrop of the BOWS contest, they search for a watermark in gold buried in three images. Each knows only a portion of the gold's exact location, so for the moment they're dependent on each other. However, none are particularly inclined to share...
This paper considers watermarking detection, also known as zero-bit watermarking. A watermark, carrying no hidden message, is inserted in content. The watermark detector checks for the presence of this particular weak signal in content. The paper aims at looking to this problem from a classical detection theory point of view, but with side information enabled at the embedding side. This means that the watermarking signal is a function of the host content. Our study is twofold. The first issue is to design the best embedding function for a given detection function (a Neyman-Pearson detector structure is assumed). The second issue is to find the best detection function for a given embedding function. This yields two conditions, which are mixed into one 'fundamental' differential equation. Solutions to this equation are optimal in these two senses. Interestingly, there are other solutions than the regular quantization index modulation scheme. The JANIS scheme, for instance, invented in a heuristic manner several years ago, is justified as it is one of these solutions.
KEYWORDS: Digital watermarking, Independent component analysis, Information security, Principal component analysis, Expectation maximization algorithms, Distortion, Algorithms, Computer security, Signal processing, Information theory
This second part focuses on estimation of secret parameters of some practical watermarking techniques. The first part reveals some theoretical bounds of information leakage about secret keys from observations. However, as usual in information theory, nothing has been said about practical algorithms which pirates use in real life application. Whereas Part One deals with the necessary number of observations to disclose secret keys (see definitions of security levels), this part focuses on the complexity or the computing power of practical estimators. Again, we are inspired here by the work of Shannon as in his famous article, he has already made a clear cut between the unicity distance and the work of opponents' algorithm. Our experimental work also illustrates how Blind Source Separation (especially Independent Component Analysis) algorithms help the opponent exploiting this information leakage to disclose the secret carriers in the spread spectrum case. Simulations assess the security levels theoretically derived in Part One.
KEYWORDS: Digital watermarking, Information security, Information theory, Cryptography, Computer security, Cryptanalysis, Binary data, Modulation, Defense and security, Wavelets
This article proposes a theory of watermarking security based on a cryptanalysis point of view. The main idea is that information about the secret key leaks from the observations, for instance watermarked pieces of content, available to the opponent. Tools from information theory (Shannon's mutual information and Fisher's information matrix) can measure this leakage of information. The security level is then defined as the number of observations the attacker needs to successfully estimate the secret key. This theory is applied to common watermarking methods: the substitutive scheme and spread spectrum based techniques. Their security levels are calculated against three kinds of attack.
In spread-spectrum watermarking, the watermarked document is obtained from the addition of an attenuated watermark signal to a
cover multimedia document. A traditional strategy consists of
optimizing the detector for a given embedding function. In
general, this leads to sub-optimal detection and much improvement
can be obtained by exploiting side-information available at the
embedder. In some prior art, the authors showed that for blind
detection of small signals, maximum detection power is obtained to
first order by setting the watermark signal to the gradient of the
detector. Recently, Malvar et al. improved the performance of direct-sequence spread-spectrum watermarking by using a signal dependent modulation. In the first part of the paper, we develop this idea further and extend Costa's decoding theory to the problem of watermarking detection. In the second part, we propose a practical implementation of this work using non-linear detectors based on our family of polynomial functions. We show some improved performance of the technique.
KEYWORDS: Digital watermarking, Sensors, Signal to noise ratio, Signal detection, Optical correlators, Stereolithography, Video, Distortion, Feature extraction, Receivers
This paper deals with some detection issues of watermark signals. We propose an easy way to implement an informed watermarking embedder whatever the detection function. This method shows that a linear detection function is not suitable for side information. This is the reason why we build a family of non-linear functions based on nth-order statistics. Used with a side-informed embedder, its performance is much better than the classical direct sequence spread spectrum method.
We consider the problem of hiding information in a steganographic framework, i.e. embedding a binary message within an apparently innocuous content, in order to establish a suspicion-free digital communication channel. The adversary is passive as no intentional attack is foreseen. The only threat is that she discovers the presence of a hidden communication. The main goal of this article is to find if the Scalar Costa Scheme, a recently published embedding method exploiting side information at the encoder, is suitable for that framework. We justify its use assessing its security level with respect to the Cachin's criterion. We derive a public-key stego-system following the ideas of R. Anderson and P. Petitcolas. This technique is eventually applied to PCM audio contents. Experimental performances are detailed in terms of bit-rate and Kullback-Leibler distance.
KEYWORDS: Digital watermarking, Sensors, Signal processing, Signal detection, Information security, Fourier transforms, Electronic filtering, Statistical analysis, Calculus, Atrial fibrillation
Asymmetric schemes belong to second generation of watermarking. Whereas their need and advantage are well understood, many doubts have been raised about their robustness and security. Four different asymmetric schemes have been proposed up to now. Whereas they were seemingly relying on completely different concepts, they share the same performances. Exploring in detail these concepts, the authors propose a common formulation of the four different detector processes. This allows to stress common features about security of asymmetric schemes.
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