Catálogo de publicaciones - libros

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.

In this paper we introduce the problem of watermark security for systems in which an implementation of a watermark detector is available to an attacker. This paper serves as an introduction to a keynote talk at IWDW 2006. This talk will review two homomorphic encryption methods, viz. Paillier and Goldwasser & Micali, and their application to secure detection of Quantization Index Modulation (QIM) watermarks.

Steganography is often combined with cryptographic mechanisms. This enhances steganography by valuable properties that are originally left to cryptographic systems. However, new problems for cryptographic mechanisms arise from the context of steganography. There are two sorts of steganographic tools: commercial tools with insecure or badly implemented cryptography and academic proof-of-concepts that abstain from the actual implementation of the cryptographic part. Comparably to cryptography, steganography evolves in an iterative process of designing and breaking new methods. In this paper we examine the encoding properties and cryptographic functionality of steganographic tools to enable the detection of embedded information in steganograms even if the embedding part was otherwise secure.

In this paper, we propose a new method for the detection of LSB embedding in JPEG images. We are motivated by a need to further research the idea of the chi-square attack. The new method simply use the first-order statistics of DCT coefficients, but is more powerful to detect the random embedding in JPEG images. For evaluation, we used versions of Jsteg and Jphide with randomized embedding path to generate stego images in our experiments. In results, the proposed method outperforms the method of Zhang and Ping and is applicable to Jphide. The detection power of both proposed methods is compared to the blind classifier by Fridrich that uses 23 DCT features.

This paper presents a novel steganalysis scheme with high-dimensional feature vectors derived from co-occurrence matrix in either spatial domain or JPEG coefficient domain, which is sensitive to data embedding process. The class-wise non-principal components analysis (CNPCA) is proposed to solve the problem of the classification in the high-dimensional feature vector space. The experimental results have demonstrated that the proposed scheme outperforms the existing steganalysis techniques in attacking the commonly used steganographic schemes applied to spatial domain (Spread-Spectrum, LSB, QIM) or JPEG domain (OutGuess, F5, Model-Based).

This paper addresses a novel steganography method for images. Most statistical steganalysis algorithms are strong to defeat previous steganography algorithms. RS steganalysis and pixel difference histogram analysis are two well-known statistical steganalysis algorithms which detect non-random changes caused by embedding a secret message into cover image. In this paper, we first explain how two steganalysis algorithms exploit the effect of the non-random changes and then propose a new steganography method that avoids the non-random changes to evade statistical analysis methods. For this purpose, we adjust the embedding process to be more adaptive to cover image by considering embedding in Gray code bit planes, not natural binary bit planes, of cover images, and two parameters: (1) similarity threshold for selecting non-flat area in lower bit planes, and (2) size of flat blocks n × n in embedding bit planes. Experimental results show that the secret messages embedded by our method are undetectable under RS steganalysis and pixel difference histogram analysis.

This paper proposes a reversible watermarking scheme for error diffused halftone images. It exploits statistical features of 2×2 binary patterns in halftone images to embed data. According to a small look-up table constructed in advance, a state sequence is extracted and losslessly compressed, and the saved space is filled up with the watermark and some side information. We modulate the extracted state sequence into a new concatenated sequence by similar pair toggling, and meanwhile the watermark and the LUT are embedded. The proposed scheme can provide a considerable capacity and the original image can be recovered if its watermarked version is intact.

In this paper we present a print-scan resilient method to embed multibit messages into images. Multilevel watermarking principles are applied in order to embed a reference watermark and the message bits. Methods to embed a robust spatial domain reference watermark, utilizing HVS are proposed and methods to improve the estimation of affine transformation parameters from a periodic reference watermark are considered. The multibit message is embedded on the approximation coefficients of the wavelet transform, utilizing JND profile estimation and additive spread spectrum techniques. A blind correlation based detection method is made use of to recover the message. In the experiments the imperceptuality issues related to multilevel watermarking are considered with different parameter settings and the robustness against print-scan attack and JPEG compression is measured and the results are shown.

In this paper we propose a multi-set modulation technique to increase the hiding capacity within a binary document image. As part of this technique we propose an Automatic Threshold Calculation and Threshold Buffering, Shifted Space Distribution and Letter Space Compensation technique. The Automatic Threshold Calculation is used to distinguish word spaces from letter spaces. The Threshold Buffering is used to reduce the chance of misinterpretation of spaces during the detection phase, following printing and scanning. The Shifted Space Distribution and Letter Space Compensation techniques robustly embed a watermark into the binary document image. The Automatic Threshold Calculation has been shown to be successful in identifying word spaces for different types of fonts and font sizes. The combination of the Shifted Space Distribution, Letter Space Compensation and Threshold Buffering techniques have been shown to create a watermark that is robust to printing and scanning.

This paper presents a new multibit watermarking method. The method uses multiple orthonormalized watermark patterns of the same size as the host signal. In particular, the elements of each watermark pattern follow independent normal distribution. Each bit of the transmitted message is hidden using the dither quantizers to modify the projection of the host signal onto its corresponding watermark pattern. As a result, every hidden bit is spread over all elements of the host data and the extracting procedure is blind. Meanwhile, we consider how to choose a suitable quantization step size under the given distortion constraint. It is also proved mathematically that the upper bound of the bit error probability of our method is equal to one of the spread-transform dithered modulation (STDM) under the same situations. Experimental results show our scheme performs better than STDM in terms of bit error probability.