Emre Topak

On reversibility of random binning techniques: multimedia perspectives

In this paper, we analyze a possibility of reversibility of data-hiding techniques based on random binning from multimedia perspectives. We demonstrate the capabilities of unauthorized users to perform hidden data removal using solely a signal processing approach based on optimal estimation as well as consider reversibility on the side of authorized users who have the knowledge of key used for the message hiding.

Security analysis of robust data-hiding with geometrically structured codebooks

In digital media transfer, geometrical transformations desynchronize the communications between the encoder and the decoder. Therefore, an attempt to decode the message based on the direct output of the channel with random geometrical state fails. The main goal of this paper is to analyze the conditions of reliable communications based on structured codebooks in channels with geometrical transformations. Structured codebooks include codewords that have some features or statistics designed for synchronization purposes. In the design of capacity approaching data-hiding codes, host interference problem should be resolved. The solution to this problem is to perform the message coding based on random binning dependent on host-state. On the other hand, to achieve robustness to geometrical transformations, the codewords should have host independent statistics and encoding should be performed using random coding. To satisfy these conflicting requirements we propose Multiple Access Channel (MAC) framework where the message is split between two encoders designed based on the random binning and random coding principles. The message encoded according to random coding additionally serves for synchronization purposes. Sequentially, all existing methods that are proposed for reliable communications in channels with geometrical transformations are analyzed within the proposed MAC set-up. Depending on the particular codebook design, we classify these methods into two main groups: template-based codebooks and redundant codebooks. Finally, we perform the analysis of security leaks of each codebook structure in terms of complexity of the worst case attack.

Towards geometrically robust data-hiding with structured codebooks

In this paper we analyze performance of practical robust data-hiding in channels with geometrical transformations. By applying information-theoretic argument we show that performance of a system designed based on both random coding and random binning principles is bounded by the same maximal achievable rate for the cases when communication channel includes geometrical transformations or not. Targeting to provide theoretic performance limits of practical robust data-hiding we model it using a multiple access channel (MAC) with side information (SI) available at one of encoders and present the bounds on achievable rates of reliable communications to such a protocol. Finally, considering template-based and redundant-based design of geometrically robust data-hiding systems, we perform security analysis of their performance and present results in terms of number of trial efforts the attacker needs to completely remove hidden information.

Tangible interactive system for document browsing and visualisation of multimedia data

In this paper we introduce and develop a framework for document interactive navigation in multimodal databases. First, we analyze the main open issues of existing multimodal interfaces and then discuss two applications that include interaction with documents in several human environments, i.e., the so-called smart rooms. Second, we propose a system set-up dedicated to the efficient navigation in the printed documents. This set-up is based on the fusion of data from several modalities that include images and text. Both modalities can be used as cover data for hidden indexes using data-hiding technologies as well as source data for robust visual hashing. The particularities of the proposed robust visual hashing are described in the paper. Finally, we address two practical applications of smart rooms for tourism and education and demonstrate the advantages of the proposed solution.

E-capacity analysis of data hiding channels with geometrical attacks

In a data hiding communications scenario, geometrical attacks lead to a loss of reliable communications due to synchronization problems when the applied attack is unknown. In our previous work, information-theoretic analysis of this problem was performed for theoretic setups, i.e., when the length of communicated data sequences asymptotically approaches infinity. Assuming that the applied geometrical attack belongs to a set of finite cardinality, it is demonstrated that it does not asymptotically affect the achievable rate in comparison to the scenario without any attack. The main goal of this paper is to investigate the upper and lower bounds on the rate reliability function that can be achieved in the data hiding channel with some geometrical state. In particular, we investigate the random coding and sphere packing bounds in channels with random parameter for the case when the interference (channel state) is not taken into account at the encoder. Furthermore, only those geometrical transformations that preserve the input dimensionality and input type class are considered. For this case we are showing that similar conclusion obtained in the asymptotic case is valid, meaning that within the class of considered geometrical attacks the rate reliability function is bounded in the same way as in the case with no geometrical distortions.

Asymmetrically informed data-hiding optimization of achievable rate for Laplacian host

In data-hiding the issue of the achievable rate maximization is closely related to the problem of host interference cancellation. The optimal host interference cancellation relies on the knowledge of the host realization and the channel statistics (the additive white Gaussian noise (AWGN) variance) available at the encoder a priori to the transmission. The latter assumption can be rarely met in practical situations. Contrarily to the Costa set-up where the encoder is optimized for the particular state of the independent and identically distributed (i.i.d.) Gaussian attacking channel, we address the problem of asymmetrically informed data-hiding optimal encoder design assuming that the host interference probability density function (pdf) is an i.i.d. Laplacian and the channel variance lies on some known interval. The presented experimental results advocate the advantages of the developed embedding strategy.

On reversibility of random binning based data-hiding techniques: security perspectives

Reversibility of data-hiding refers to the reconstruction of original host data at the decoder from the stego data. Previous works on the subject are concentrated on the reversibility of data-hiding techniques from multimedia perspectives. However, from the security point of view, that at our knowledge was not exploited in existing studies, reversibility could be used by an attacker to remove the complete trace of watermark data from the stego data in the sense of designing the worst case attack. Thus, the aim of this paper is to analyze the reversibility of data-hiding techniques based on random binning from the security perspectives.