Catálogo de publicaciones - libros

It is well known that all information hiding methods that modify the least significant bits introduce distortions into the cover objects. Those distortions have been utilized by steganalysis algorithms to detect that the objects had been modified. It has been proposed that only coefficients whose modification does not introduce large distortions should be used for embedding. In this paper we propose an efficient algorithm for information hiding in the LSBs of JPEG coefficients. Our algorithm uses modified matrix encoding to choose the coefficients whose modifications introduce minimal embedding distortion. We derive the expected value of the embedding distortion as a function of the message length and the probability distribution of the JPEG quantization errors of cover images. Our experiments show close agreement between the theoretical prediction and the actual embedding distortion. Our algorithm can be used for both steganography and fragile watermarking as well as in other applications in which it is necessary to keep the distortion as low as possible.

Digital fingerprinting is a technique to prevent customers from redistributing multimedia contents illegally. Main attack for fingerprinting is the collusion attack, where multiple users collude by creating an average or median of their individual fingerprinted copies, and escape identification. Previous research such as ACC (anti-collusion code) cannot support large number of users, and also vulnerable to LCCA (linear combination collusion attack). We present a practical SACC (scalable ACC) scheme to generate codebooks for supporting large number of users; and angular decoding scheme to be robust on LCCA. We implemented the SACC codebook using a Gaussian distributed random variable for various attack robustness, and the fingerprint embedding using human visual system based watermarking scheme. We experimented with standard test images for collusion detection performance, and it shows good collusion detection performance over average, median attacks. For LCCA collusion attack on SACC, our angular decoding scheme identifies the correct colluder set under various WNR (watermark to noise ratio).

A video watermarking scheme is proposed in this paper using the concept of the secret sharing scheme. The owner’s mark is split into twin shares, where the shares are inserted into the video frames in the spatial domain in a simple manner. The detection algorithm uses a linear function applied to the twin shares to reconstruct the secret. This makes the watermarked video sequence robust against pirate attacks, such as frame averaging and frame swapping. Due to the compatibility of the exploited secret sharing scheme to geometrical distortions, the watermarking system is also robust to this kind of processing schemes. On account of insertion of various marks into different frames, which are linearly related, the watermarked sequence is robust to collusion attack that is a major concern in the field of video watermarking.

We present the first (1,2)-SETUP algorithm for the RSA digital signature scheme with appendix. A SETUP algorithm ′ is an algorithmic modification of algorithm that (1) contains an asymmetric backdoor that can only be used by the designer, even if the backdoor algorithm is fully public, and (2) ensures that the public outputs of and ′ are computationally indistinguishable under black-box queries. The SETUP is presented in RSASSA-PSS and it transmits the RSA private key within two w.l.o.g consecutive digital signatures. This problem has been solved for DSA and other discrete-log based digital signature algorithms, but not RSA. We therefore solve a long-standing problem in kleptography.

A mode of operation of the Elliptic Curve Digital Signature Algorithm (ECDSA) is presented which provably excludes subliminal communication through ECDSA signatures. For this, the notion of a signature scheme that is is introduced which can be seen as generalizing and being intermediate to the established concepts of and .

Motivated by the proposed use of ECDSA for signing passports, our focus is not on proving the mere existence of a subliminal-free ECDSA mode of operation, but on demonstrating its practical potential. The proposed construction relies on the availability of a party acting as warden and on a reasonably-sized non-interactive proof of subliminal-freeness. For instance, in the passport scenario, the passport holder plays the role of the warden, and we show that a suitable combination of the pseudo random function of Naor and Reingold with bit commitments and non-interactive zero-knowledge proofs can be used for accomplishing the required proof of subliminal-freeness with acceptable efficiency.