Luis Pérez-Freire

Spread-Spectrum Watermarking Security

This paper presents both theoretical and practical analyses of the security offered by watermarking and data hiding methods based on spread spectrum. In this context, security is understood as the difficulty of estimating the secret parameters of the embedding function based on the observation of watermarked signals. On the theoretical side, the security is quantified from an information-theoretic point of view by means of the equivocation about the secret parameters. The main results reveal fundamental limits and bounds on security and provide insight into other properties, such as the impact of the embedding parameters, and the tradeoff between robustness and security. On the practical side, workable estimators of the secret parameters are proposed and theoretically analyzed for a variety of scenarios, providing a comparison with previous approaches, and showing that the security of many schemes used in practice can be fairly low.

Watermarking security: a survey

Watermarking security has emerged in the last years as as a new subject in the watermarking area. As it brings new challenges to the design of watermarking systems, a good understanding of the problem is fundamental. This paper is intended to clarify the concepts related to watermarking security, provide an exhaustive literature overview, and serve as a starting point for newcomers interested in carrying out research on this topic.

Fundamentals of data hiding security and their application to spread-spectrum analysis

This paper puts in consideration the concepts of security and robustness in watermarking, in order to be able to establish a clear frontier between them. A new information-theoretic framework to study data-hiding and watermarking security is proposed, using the mutual information to quantify the information about the secret key that leaks from the observation of watermarked objects. This framework is applied to the analysis of a Spread-Spectrum data-hiding scheme in different scenarios. Finally, we show some interesting links between a measure proposed in previous works in the literature, which is based on Fisher Information Matrix, and our proposed measure.

The return of the sensitivity attack

The sensitivity attack is considered as a serious threat to the security of spread-spectrum-based schemes, since it provides a practical method of removing watermarks with minimum attacking distortion. This paper is intended as a tutorial on this problem, presenting an overview of previous research and introducing a new method based on a general formulation. This new method does not require any knowledge about the detection function nor any other system parameter, but just the binary output of the detector, being suitable for attacking most known watermarking methods. Finally, the soundness of this new approach is tested by attacking several of those methods.

Information-theoretic analysis of security in side-informed data hiding

In this paper a novel theoretical security analysis will be presented for data hiding methods with side-information, based on Costas dirty paper scheme. We quantify the information about the secret key that leaks from the observation of watermarked signals, using the mutual information as analytic tool for providing a fair comparison between the original Costas scheme, Distortion Compensated – Dither Modulation and Spread Spectrum.

Security of Lattice-Based Data Hiding Against the Watermarked-Only Attack

This paper presents a security analysis for data-hiding methods based on nested lattice codes, extending the analysis provided by previous works to a more general scenario. The security is quantified as the difficulty of estimating the secret key used in the embedding process, assuming that the attacker has several signals watermarked available with the same secret key. The theoretical analysis accomplished in the first part of this paper quantifies security in an information-theoretic sense by means of the mutual information between the watermarked signals and the secret key, addressing important issues, such as the possibility of achieving perfect secrecy and the impact of the embedding rate 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.

A multimedia approach for audio segmentation in TV broadcast news

The paper deals with the task of audio segmentation in TV broadcast news. A multimedia approach for this purpose, by means of audio and video processing, is proposed. Thus, the segmentation system is composed by two differentiated parts: one analyzes the audio stream, and is based on the well-known Bayesian information criterion (BIC), whereas the other part extracts useful information from the video stream to improve the performance of BIC. An investigation of parameters involved in BIC formulation is also accomplished, in order to achieve the best results possible in our experimental framework: the database Transcrigal-DB. The final system provides significative improvements in both overall performance and robustness.

Secret dither estimation in lattice-quantization data hiding : a set-membership approach

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.

Exploiting security holes in lattice data hiding

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.

Security of spread-spectrum-based data hiding

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.