Informed stego-systems in active warden context: statistical undetectability and capacity

Several authors have studied stego-systems based on Costa scheme, but just a few ones gave both theoretical and experimental justifications of these schemes performance in an active warden context. We provide in this paper a steganographic and comparative study of three informed stego-systems in active warden context: scalar Costa scheme, trellis-coded quantization and spread transform scalar Costa scheme. By leading on analytical formulations and on experimental evaluations, we show the advantages and limits of each scheme in term of statistical undetectability and capacity in the case of active warden. Such as the undetectability is given by the distance between the stego-signal and the cover distance. It is measured by the Kullback-Leibler distance.Comment: 6 pages, 8 figure

TCQ Practical Evaluation in the Hyper-Cube Watermarking Framework

International audienceThe Hyper-Cube watermarking has shown a high potential for high-rate robust watermarking. In this paper, we carry on the study and the evaluation of this quantization-based approach. We especially focus on the use of a Trellis Coded Quantization (TCQ) and its impact on the Hyper-Cube performances. First, we recall the TCQ functioning principle andwe propose adapted quantizers. Second, we analyze the integration of the TCQ module in a cascade of two coders (resp. two decoders). Finally, we experimentally compare the proposed approach with the state-of-the-art of high-rate watermarking schemes. The obtained results show that our Multi-Hyper-Cube scheme always provides good average performance

Nested turbo codes for the costa problem

Driven by applications in data-hiding, MIMO broadcast channel coding, precoding for interference cancellation, and transmitter cooperation in wireless networks, Costa coding has lately become a very active research area. In this paper, we first offer code design guidelines in terms of source- channel coding for algebraic binning. We then address practical code design based on nested lattice codes and propose nested turbo codes using turbo-like trellis-coded quantization (TCQ) for source coding and turbo trellis-coded modulation (TTCM) for channel coding. Compared to TCQ, turbo-like TCQ offers structural similarity between the source and channel coding components, leading to more efficient nesting with TTCM and better source coding performance. Due to the difference in effective dimensionality between turbo-like TCQ and TTCM, there is a performance tradeoff between these two components when they are nested together, meaning that the performance of turbo-like TCQ worsens as the TTCM code becomes stronger and vice versa. Optimization of this performance tradeoff leads to our code design that outperforms existing TCQ/TCM and TCQ/TTCM constructions and exhibits a gap of 0.94, 1.42 and 2.65 dB to the Costa capacity at 2.0, 1.0, and 0.5 bits/sample, respectively

Watermarking security part II: practice

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 [15], 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