Minoru Kuribayashi

Fingerprinting protocol for images based on additive homomorphic property

Homomorphic property of public-key cryptosystems is applied for several cryptographic protocols, such as electronic cash, voting system, bidding protocols, etc. Several fingerprinting protocols also exploit the property to achieve an asymmetric system. However, their enciphering rate is extremely low and the implementation of watermarking technique is difficult. In this paper, we propose a new fingerprinting protocol applying additive homomorphic property of Okamoto-Uchiyama encryption scheme. Exploiting the property ingenuously, the enciphering rate of our fingerprinting scheme can be close to the corresponding cryptosystem. We study the problem of implementation of watermarking technique and propose a successful method to embed an encrypted information without knowing the plain value. The security can also be protected for both a buyer and a merchant in our scheme.

Collusion-resistant fingerprinting scheme based on the CDMA-technique

Digital fingerprinting is a scheme to insert users own ID information into digital contents in order to identify illegal users who distribute unauthorized copy. One of the important problems is a collusion attack such that several users combine their copies of a same content to modify/delete the embedded fingerprint. In this paper, we propose a collusion-resilient fingerprinting scheme based on the CDMA technique. By combining spread spectrum sequence with orthogonal transform, we allocate the combination of spectrum components to users as their fingerprints. At a detector side, a threshold for the detection of colluded users is determined considering the false positive probability. We then estimate the parameters in the scheme for both optimal embedding and detection, and improve the accuracy of the detection of colluders. Experimental results show the effectiveness of proposed scheme.

On the implementation of spread spectrum fingerprinting in asymmetric cryptographic protocol

Digital fingerprinting of multimedia contents involves the generation of a fingerprint, the embedding operation, and the realization of traceability from redistributed contents. Considering a buyers right, the asymmetric property in the transaction between a buyer and a seller must be achieved using a cryptographic protocol. In the conventional schemes, the implementation of a watermarking algorithm into the cryptographic protocol is not deeply discussed. In this paper, we propose the method for implementing the spread spectrum watermarking technique in the fingerprinting protocol based on the homomorphic encryption scheme. We first develop a rounding operation which converts real values into integer and its compensation, and then explore the tradeoff between the robustness and communication overhead. Experimental results show that our system can simulate Coxs spread spectrum watermarking method into asymmetric fingerprinting protocol.

Adaptive reversible data hiding for JPEG images

This paper presents an improved method of the reversible data hiding for JPEG images proposed by Xuan, et al. The conventional method embeds data into the JPEG quantized 8 times 8 block DCT coefficients. In this method, we found that the blocks, located in the noisy part of the image, are not suitable for embedding data. The proposed method can judge whether a block consisted of 8 times 8 DCT coefficients is located in smooth part of image by using the DC coefficient of neighboring blocks. Our method can avoid the noisy part for embedding. It results in a better performance in terms of capacity-distortion behavior.

Reversible Watermark with Large Capacity Based on the Prediction Error Expansion

A reversible watermark algorithm with large capacity has been developed by applying the difference expansion of a generalized integer transform. In this algorithm, a watermark signal is inserted in the LSB of the difference values among pixels. In this paper, we apply the prediction errors calculated by a predictor in JPEG-LS for embedding watermark, which contributes to increase the amount of embedded information with less degradation. As one of the drawbacks discovered in the above conventional method is the large size of the embedded location map introduced to make it reversible, we decrease the large size of the location map by vectorization, and then modify the composition of the map using the local characteristics. We also exclude the positions such that the modification in the embedding operation cannot increase the capacity but merely degrade the image quality, which can be applicable to the conventional methods.

Hierarchical Spread Spectrum Fingerprinting Scheme Based on the CDMA Technique

Digital fingerprinting is a method to insert users own ID into digital contents in order to identify illegal users who distribute unauthorized copies. One of the serious problems in a fingerprinting system is the collusion attack such that several users combine their copies of the same content to modify/delete the embedded fingerprints. In this paper, we propose a collusion-resistant fingerprinting scheme based on the CDMA technique. Our fingerprint sequences are orthogonal sequences of DCT basic vectors modulated by PN sequence. In order to increase the number of users, a hierarchical structure is produced by assigning a pair of the fingerprint sequences to a user. Under the assumption that the frequency components of detected sequences modulated by PN sequence follow Gaussian distribution, the design of thresholds and the weighting of parameters are studied to improve the performance. The robustness against collusion attack and the computational costs required for the detection are estimated in our simulation.

On the systematic generation of Tardos’s fingerprinting codes

Digital fingerprinting is used to trace back illegal users, where unique ID known as digital fingerprints is embedded into a content before distribution. On the generation of such fingerprints, one of the important properties is collusion-resistance. Binary codes for fingerprinting with a code length of theoretically minimum order were proposed by Tardos, and the related works mainly focused on the reduction of the code length were presented. In this paper, we present a concrete and systematic construction of the Tardospsilas fingerprinting code using a chaotic map. Using a statistical model for correlation scores, a proper threshold for detecting colluders is calculated. Furthermore, for the reduction of computational costs required for the detection, a hierarchical structure is introduced on the codewords. The collusion-resistance of the generated fingerprinting codes is evaluated by a computer simulation.

Interference Removal Operation for Spread Spectrum Fingerprinting Scheme

In digital fingerprinting schemes based on the spread spectrum technique, (quasi-)orthogonal sequences are assigned to users as their fingerprints, and they are embedded into digital contents prior to distribution. Owing to the (quasi-) orthogonality, we can uniquely identify the users from a pirated copy, even if dozens of users are involved in the collusion process. Because the number of users accommodated in a fingerprinting system is generally very large, the interference among the sequences involved in a pirated copy becomes non-negligible as the number of colluders increases. In this paper, we investigate the interference from the viewpoint of a communication channel, and we propose an effective removal operation to reduce the interference as far as possible. By iteratively operating the proposed detector, we can sequentially and successively detect colluders from a pirated copy. Furthermore, two kinds of thresholds are introduced in order to perform the removal operation adaptively for detected signals. Experimental results reveal a drastic improvement in the traceability and a reduction in the amount of interference by the removal operation.

A New Anonymous Fingerprinting Scheme with High Enciphering Rate

We propose a new anonymous fingerprinting scheme using Okamoto-Uchiyama cryptosystem [1]. In the previous schemes [2]-[4] the enciphering rate is so small that it seems very difficult to implement for any applications. In order to improve the rate, we have applied the Okamoto-Uchiyama cryptosystem for our fingerprinting protocol. As the results, a buyer can commit a fingerprint to a merchant being embedded in a digital content anonymously and efficiently, and then the amount of encrypted data is controlled in a reasonable size. The security can also be protected for both of a buyer and a merchant in our scheme.

Simplified MAP Detector for Binary Fingerprinting Code Embedded by Spread Spectrum Watermarking Scheme

When a binary fingerprinting codeword is embedded into multimedia content by using a spread-spectrum (SS) watermarking scheme, it is difficult for colluders to perform a symbol-wise attack using their codewords. As discussed in regard to SS fingerprinting schemes, averaging their copies is a cost-effective attack from the signal processing point of view. If the number of colluders is known, an optimal detector can be used against an averaging attack with added white Gaussian noise. The detector first estimates the variance of additive noise, and then calculates correlation scores using a log-likelihood-based approach. However, the number of colluders is not usually known in a real situation. In this paper, we simplify the optimal detector by making statistical approximations and using the characteristics of the parameters for generating codewords. After that, we propose an orthogonal frequency division multiplexing-based SS watermarking scheme to embed the fingerprinting codeword into multimedia content. In a realistic situation, the signal embedded as a fingerprint is in principle attenuated by lossy compression. Because the signal amplitude in a pirated codeword is attenuated, we should adaptively estimate the parameters before calculating the scores. Different from the optimal detector, the simplified detector can easily accommodate changes in signal amplitude by examining the distorted codeword extracted from a pirated copy. We evaluate the performance of the simplified detector through simulation using digital images as well as codewords.