Sofiane Braci

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 sosta 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.

Security evaluation of informed watermarking schemes

In this paper, security evaluation of an important watermarking class based on quantization is given. Theoretical developments and practical simulations are used to measure the security level of watermarking techniques. We give the contribution of each observation available to the attacker on the total gathered information about the watermarking secrecy. By leading on watermarking technique weaknesses, we find that using the Quantization Index Modulation (QIM) with continuous secret key is equivalent to using a secret key with two states. The latter is easier to estimate than a continuous key. Then, we propose a secure version of a classical trellis coded quantization watermarking. The security is guaranteed thanks to the trellis path generated from the discrete key and the message. We show that the spread transform can represent a second or alternative security level for watermarking systems. It allows to increase the watermarking security level and to keep the embedded message hard to read for unauthorise user.

Quantized based image watermarking in an independent domain

This paper presents a performance study for two well known quantized based watermarking schemes Scalar Costa Scheme (SCS), and Trellis Coded Quantization scheme (TCQ) in an independent domain. For our study, the independent domain is obtained by the combination of the cited schemes with Independent Component Analysis (ICA). The Independent Component Analysis is used while inserting and extracting the message. Thus a performance compromise improvement of the original SCS and TCQ schemes in terms of robustness, capacity, and security is shown. Then the obtained schemes performances are compared to the Spread Transform (ST) based scheme well known for its proven good robustness properties. Our results show that, using watermarking with side information in independent domain permits to improve the global SCS and TCQ schemes performances. For example, in the case of SCS, by studying the Bit Error Rate (BER) in function of the watermark to noise ratio (WNR), the robustness has been improved by 20dB (1 decade) when WNR is equal to 0dB. Moreover, the capacity study shows for the same WNR=0dB, the amount of information to be transmitted without error for a given noise level of the proposed SCS combined with ICA scheme (SCS-ICA) is much higher than that of the existing schemes. Finally, the study of the probability density functions (PDF) of the original and marked signals has shown that the Cachin-security level of the TCQ in an independent domain scheme (TCQ-ICA) is the best one compared to the other known schemes.

On the tradeoff between security and Robustness of the Trellis Coded Quantization scheme

The steganographic security in the Cachins work is defined as the statistical invisibility between the host signal and its marked version. At contrary, the robustness to an attack is not a prime goal. In robust watermarking, this is exactly the inverse. The scalar costa scheme (SCS) is a typical example of this fact. Indeed, this scheme is robust to additive white Gaussian noise (AWGN) attack but is drastically insecure since its probability density function for Gaussian host signal is severely discontinuous. An improved scheme has been proposed by Guillon et al. which increases the security to the detriment of the robustness. In this paper, we propose a new watermarking scheme, based on the combination of the spread transform (ST) and the trellis coded quantization (TCQ) which is secure and robust to AWGN attack.

Analysis of the resistance of the Spread Transform against Temporal Frame Averaging attack

The Spread Transform (ST) robustness facing a Temporal Frame Averaging (TFA) is studied in this paper. Our analysis provides new insights on the effect of the TFA attack in the context of video watermarking when the ST is used. To remove the interferences and the attenuation of the watermark caused by the TFA attack, an adaptation of the Spread Transform is proposed. Our solution is based on the embedding of the watermark thanks to different orthogonal directions and by exploiting the temporal diversity of the video signal, i.e. the message is spread over several video frames. Finally, we show that the robustness and decoding performances are close to the ones before the attack.

Hidden QIM Watermarking on Compressed Data Using Channel Coding and Lifting

This paper investigates the scope of application of channel coding on compressed host data for watermarking using dither modulation (DM) based quantization index modulation (QIM). Lifting based wavelet is used to decompose the encoded compressed data in integer coefficients. The relative gain on imperceptibility and robustness performance are reported for direct watermark embedding on entropy decoded host, using repetition code, convolution code, and finally the combined use of channel codes and lifting. Simulation results show that 6.24 dB (9.50 dB) improvement in document- to-watermark ratio (DWR) for watermark power at 12. 73 dB (16.81 dB) and 15 dB gain in noise power for watermark decoding at bit error rate (BER) of 10? 2 are achieved, respectively over direct watermarking on entropy decoded data.

Improved performances of Scalar Costa Scheme for images watermarking in an independent domain

In this paper, we studied the performances of the well known side information watermarking scheme, Scalar Costa Scheme (SCS), in independent domain. We have used the Independent Component Analysis (ICA) to insert and extract the message. Thus, we improve the performances compromise of the original SCS scheme in terms of robustness, capacity, and undetectability. In our study, we also compare the obtained scheme performances to the well known Spread Transform (ST) based scheme for its proven good properties. We show that using watermarking with side information in independent domain permits to improve the global SCS scheme performances. For example, by studying the bit error rate (BER) in function of the watermark to noise ratio (WNR), we show that the robustness is improved by 1 decade when WNR is equal to 0dB. We also show by studying the capacity (amount of information to be transmitted without error for a given noise level) for the same WNR = 0dB, the capacity of our watermarking scheme is much higher than that of the existing schemes. Finally, the study of probability density functions (PDF) of the original signals and marked ones, allowed us to show that the Cachin-security level of the proposed scheme is satisfied through the use of Independent Component Analysis.

Trellis Coded Quantization based watermarking scheme performances in an independent domain

In applications to secured diffusion of digital images, several watermarking solutions have been studied in the field of Data Hiding. For this aim, the main idea consists in embedding an information in the digital media with good properties in terms of robustness, capacity and invisibility (perceptual transparency and statistical undetectability). Recent studies has highlighted the importance of statistical undetectability which is unfortunately not often evaluated. We propose in this work to study a watermarking scheme with side-information at the encoder and based on Treillis Coded Quantization (TCQ). The main particularity of our approach is that we propose to apply the embedding process in an independent domain (by the way of Independent Component Analysis: ICA). We then show the improvement of the robustness and statistical undetectability properties with our proposal. The comparison with well known watermarking approaches, of the performances obtained, is done. This highlight the wide improvement of the obtained performances: high robustness without reducing the capacity, good security level or very low distorsions on the watermarked signals probability density functions.

Watermarking scar as an ultimate copy protection

Strong and powerful attacks are able to make the watermark extraction impossible even if there is some watermarking. In this work, we call this residual information the scar and we use it to prove the existence of an attacked watermark. We evaluate the Scar by the mutual information between the embedded watermark and the attacked copies. It is well known that the mutual information between two random variables gives an evaluation of the shared information between the two variables. Thus, the attack can compromise the correct decoding by removing partialy the watermarking information. However, it is possible to make the watermarking existence proof possible when the mutual information between the embedded message and the attacked copies is above a certain threshold. We propose a practical way to use the scar by measuring the correlation between the attacked watermark and the original one.