Davide Cavagnino

Individual single source authentication on the MBONE

Broadcast and multicast communications present new problems with respect to security. In particular the individual authentications of the senders to be efficient require novel solutions with respect to the unicast ones. The paper presents an efficient authentication protocol and discusses its implementation in an audio conferencing application.

A Novel Block-based Watermarking Scheme Using the SVD Transform

In this paper, a block-based watermarking scheme based on the Singular Value Decomposition (SVD) is proposed. Our watermark, a pseudo-random Gaussian sequence, is embedded by modifying the angles formed by the right singular vectors of each block of the original image. The orthogonality property of the right singular vector matrix is preserved during the embedding process. Several experiments have been carried out to test the performance of the proposed scheme against different attack scenarios. We conclude that the proposed scheme is resistant against common signal processing operations and attacks, while it preserves the quality of the original image.

Chained Stream Authentication

We present a protocol for the exchange of individually authenticated data streams among N parties. Our authentication procedure is fast, because it only requires the computation of hash functions - we do not need digital signatures, that are substantially less efficient. The authentication information is also short: two hash values for every block of data. Since there are no shared secrets, this information does not grow with N, the number of parties.

Individual Authentication in Multiparty Communications

In this paper we introduce a new authentication scheme to achieve individual authentication in group communications. The scheme is particularly efficient and suitable for applications where users require to transmit stream of data of undefined length through noisy channels. Our scheme is in fact, robust against loss of packets during the transmission. We present the scheme called chained stream authentication (CSA) and then we prove that the scheme is conditionally secure. We then describe two variations of CSA, one interactive to use when multicast is available and a timed version suitable for broadcast communications. We conclude by describing our implementation of the timed version that is integrated and fully compatible with RAT.

A modular framework for color image watermarking

We present an algorithm for fragile watermarking of color, or multi-channel, images either in uncompressed format, in lossless compressed format, or in compressed format with locally compressed units (like JPEG). The watermark is embedded into the Karhunen-Loeve transform (KLT) coefficients of the host image, and the security of the method is based on the secrecy of the KLT basis computed from a corresponding secret key image. The watermark bits may be embedded with various methods, in particular the use of syndrome coding has proven flexible and effective. Genetic Algorithms (GAs) are used to find the optimum pixel modification leading to the watermark embedding. The resulting watermarked images have shown to have both a high objective quality (in terms of PSNR and SSIM) and a high subjective quality (tested by a group of observers). At the same time, the watermark extraction is very sensitive to small (?1 intensity level for single pixel) modifications, ensuring image authentication with very high probability. We propose an image fragile watermarking framework in the KLT transformed domain.The modular structure of the proposed algorithm makes it flexible and easily extendable.An optimization algorithm saves the use of inverse transformation.It works and produces both lossless and lossy compressed color images.The quality of the resulting images is very high.

Protecting the Content Integrity of Digital Imagery with Fidelity Preservation: An Improved Version

Fragile watermarking has attracted a lot of attention in the last decade. An interesting approach, presented in 2011 by Lin et al., results in very high quality of the watermarked images. However, after a thorough examination of the paper, a few improvements are proposed in our revised version of the algorithm in order to overcome some shortcomings. In particular, changes to the pseudocode and modifications to deal with pixel saturation are suggested, along with a way to improve the scheme security. Finally, a deeper analysis of the security is presented.

Fragile watermarking using Karhunen---Loève transform: the KLT-F approach

The paper presents a fragile watermarking technique that may be used to discover image manipulations at block level. The proposed algorithm, based on the Karhunen–Loève linear transform (KLT), modifies some of the KLT coefficients obtained from a secret base (defined by a secret key image) so that they contain a binary pseudo-random message. A genetic algorithm is used to compensate for rounding errors introduced by inverse transforming in the integer pixel domain. An extensive experimentation has been performed to test the effectiveness of the method and to show the sensitivity of the algorithm to single pixel modifications (also as a function of the number of modified coefficients). A comparison with other fragile watermarking methods is reported. It should be noted that the proposed approach results in both a high PSNR (more than 53 dB on average) and a high subjective quality. The system may be tested online by submitting images to be watermarked and subsequently verifying the presence of modifications in a previously marked image.

Security analysis of SVD-based watermarking techniques

Digital watermarking is a widely adopted solution to ownership protection and authentication of multimedia contents, such as images and videos. In the last years, the well-known numerical tool called singular value decomposition (SVD) received much attention from the watermarking community. Many schemes showing good performances in terms of robustness, capacity and imperceptibility have been devised. However, few of these schemes take into consideration another crucial constraint, the security , which guarantees the usability of the watermarking technology. This paper shows that most of the watermarking schemes based on SVD are insecure and cannot be used for applications that require ownership protection and authentication. This is due to the fact that the space where the watermark resides, i.e., the embedding space, can be estimated and the watermark removed or overwritten. To motivate our findings, two different attacks that remove the watermark while minimising the distortion were developed. The attac...

Image Compression for the Silicon Drift Detectors in the ALICE Experiment

Abstract We describe an algorithm for the zero suppression and data compression for the Silicon Drift Detectors (SDD) in the ALICE experiment. The algorithm operates on 10-bit linear data streams from the SDDs by applying a 10 bit to 8-bit non-linear compression followed by a data reduction based on a two-threshold discrimination and a two-dimensional analysis along both the drift time and the anodes. The proposed scheme allows for a better understanding of the neighborhoods of the SDD signal clusters, thus improving their reconstructability, and also provides a statistical monitoring of the background characteristics for each SDD anode. The entire algorithm is purely combinatorial and thus can be executed in pipeline, without additional clock cycles, during the SDD readout. The hardware coding together with the methods for the expansion to the original 10-bit values in the offline analysis and for the background monitoring are presented.

KL-F: Karhunen-Loève based fragile watermarking

In this paper a fragile watermarking technique based on Karhunen-Loève transform (KLT) and genetic algorithms (GA) is proposed. To achieve high sensibility to content manipulations, the proposed algorithm slightly modifies the middle-frequency KLT coefficients while maintaining the visual imperceptibility of the watermark (i.e., the average peak signal-to-noise ratio reported was 52.49 dB). It uses a GA to compensate the errors in the extraction of the authentication information, which is a pseudo-random generated watermark sequence. The experimental tests carried out show that the scheme is able to detect pixel-level alterations localizing the block in which the pixel(s) was modified.