In this paper, a novel method for detection in quantization-based watermarking is introduced. This method basically works by quantizing a projection of the host signal onto a subspace of smaller dimensionality. A theoretical performance analysis under AWGN and fixed gain attacks is carried out, showing great improvements over traditional spread-spectrum-based methods operating under the same conditions of embedding distortion and attacking noise. A security analysis for oracle-like attacks is also accomplished, proposing a sensitivity attack suited to quantization-based methods for the first time in the literature, and showing a trade-off between security level and performance; anyway, this new method o#ers significant improvements in security, once again, over spread-spectrum-based methods facing the same kind of attacks.

Abstract—Security of quantization index modulation (QIM) watermarking methods is usually sought through a pseudorandom dither signal which randomizes the codebook. This dither plays the role of the secret key (i.e., a parameter only shared by the watermarking embedder and decoder), which prevents unauthorized embedding and/or decoding. However, if the same dither signal is reused, the observation of several watermarked signals can provide sufficient information for an attacker to estimate the dither signal. This paper focuses on the cases when the embedded messages are either known or constant. In the first part of this paper, a theoretical security analysis of QIM data hiding measures the information leakage about the secret dither as the mutual information between the dither and the watermarked signals. In the second part, we show how set-membership estimation techniques successfully provide accurate estimates of the dither from observed watermarked signals. The conclusion of this twofold study is that current QIM watermarking schemes have a relative low security level against this scenario because a small number of observed watermarked signals yields a sufficiently accurate estimate of the secret dither. The analysis presented in this paper also serves as the basis for more involved scenarios. Index Terms—Equivocation, lattice data hiding, mutual information, quantization index modulation, set-membership estimation, watermarking security. I.

In this paper we consider the problem of document authentication in electronic and printed forms. We formulate this problem from the information-theoretic perspectives and present the joint source-channel coding theorems showing the performance limits in such protocols. We analyze the security of document authentication methods and present the optimal attacking strategies with corresponding complexity estimates that, contrarily to the existing studies, crucially rely on the information leaked by the authentication protocol. Finally, we present the results of experimental validation of the developed concept that justifies the practical efficiency of the elaborated framework.

This paper presents a security analysis for data hiding methods based on nested lattice codes, extending the analysis provided by previous works. The security is quantified in an information-theoretic sense by means of the information leakage between the watermarked signals seen by the attacker and the secret key used in the embedding process. The theoretical analysis accomplished in the first part of the paper addresses important issues such as the possibility of achieving perfect secrecy and the impact of the embedding rate and channel coding in the security level. In the second part, a practical algorithm for estimating the secret key is proposed, and the information extracted is used for implementing a reversibility attack on real images.

We extend the square root law of steganographic capacity, for the simplest case of iid covers, in two ways. First, we show that the law still holds under a more realistic embedding assumption, where the payload is of fixed length (instead of, in the classic result, independent embedding at each location). Second, we consider the case of nonuniform embedding paths, which is forced when the stegosystem’s secret key is of limited size: we show that the secret key must be of length at least linear in the payload size, if a square root law is to hold. The latter is parallel to Shannon’s perfect cryptography bound. Categories and Subject Descriptors D.2.11 [Software Engineering]: Software Architectures— information hiding; H.1.1 [Models and Principles]: Systems

This paper presents an information-theoretic analysis of security for data hiding methods based on spread spectrum. The security is quantified by means of the mutual information between the observed watermarked signals and the secret carrier (a.k.a. spreading vector) that conveys the watermark, a measure that can be used to bound the number of observations needed to estimate the carrier up to a certain accuracy. The main results of this paper permit to establish fundamental security limits for this kind of methods and to draw conclusions about the tradeoffs between robustness and security. Specifically, the impact of the dimensionality of the embedding function, the host rejection, and the embedding distortion in the security level is investigated, and in some cases explicitly quantified.

Abstract. A number of analogies to cryptographic concepts have been made about watermarking. In this paper, we argue that these analogies are misleading or incorrect, and highlight several analogies to support our argument. We believe that the fundamental role of watermarking is the reliable embedding and detection of information and should therefore be considered a form of communications. We note that the fields of communications and cryptography are quite distinct and while communications systems often combine technologies from the two fields, a layered architecture is applied that requires no knowledge of the layers above. We discuss how this layered approach can be applied to watermarking applications. 1

Abstract. Steganography has been studied extensively in the light of information, complexity, probability and signal processing theory. This paper adds epistemology to the list and argues that Simmon’s seminal prisoner’s problem has an empirical dimension, which cannot be ignored (or defined away) without simplifying the problem substantially. An introduction to the epistemological perspective on steganography is given along with a structured discussion on how the novel perspective fits into the existing body of literature. 1 Steganography and steganalysis as empirical sciences A broad definition of steganography includes all endeavours to communicate in such a way that the existence of the message cannot be detected. A more specific problem description that triggered research in modern digital steganography is given in the prisoner’s problem formulated by Gustavus Simmons [1] in 1983: Two prisoners want to cook up an escape plan together. They may communicate with each other, but all their communication is monitored by a warden. As soon

In this paper, security of lattice-quantization data hiding is considered under a cryptanalytic point of view. Security in this family of methods is implemented by means of a pseudorandom dither signal which randomizes the codebook, preventing unauthorized embedding and/or decoding. However, the theoretical analysis shows that the observation of several watermarked signals can provide sufficient information for an attacker willing to estimate the dither signal, quantifying information leakages in different scenarios. The practical algorithms proposed in this paper show that such information leakage may be successfully exploited with manageable complexity, providing accurate estimates of the dither using a small number of observations. The aim of this work is to highlight the security weaknesses of lattice data hiding schemes whose security relies only on secret dithering.

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