Du-Shiau Tsai

Cheating in Visual Cryptography

A secret sharing scheme allows a secret to be shared among a set of participants, P, such that only authorized subsets of P can recover the secret, but any unauthorized subset cannot recover the secret. In 1995, Naor and Shamir proposed a variant of secret sharing, called visual cryptography, where the shares given to participants are xeroxed onto transparencies. If X is an authorized subset of P, then the participants in X can visually recover the secret image by stacking their transparencies together without performing any computation. In this paper, we address the issue of cheating by dishonest participants, called cheaters, in visual cryptography. The experimental results demonstrate that cheating is possible when the cheaters form a coalition in order to deceive honest participants. We also propose two simple cheating prevention visual cryptographic schemes.

A cheating prevention scheme for binary visual cryptography with homogeneous secret images

In 1995, Naor and Shamir proposed the k-out-of-n visual cryptography scheme such that only more than or equal to k participants can visually recover the secret through superimposing their transparencies. Visual cryptography schemes have been extensively investigated since their invention and extended to numerous applications such as visual authentication and identification, steganography, and image encryption. In 2006, Horng et al. proposed that cheating is possible where some participants can deceive the remaining participants by delivering forged transparencies. Meanwhile, Horng et al. also proposed two cheating prevention schemes. One scheme, however, requires extra verification transparencies and the other needs larger transparencies. In other words, compared to visual cryptography, both schemes burden each participant with an additional problem of transparency management. In this paper, a more secure scheme is given to solve the cheating problem without extra burdens by adopting multiple distinct secret images. Moreover, for sharing these secret images simultaneously, the share construction method of visual cryptography is redesigned and extended by generic algorithms. Finally, the results of the experiment and security analysis show that not only the proposed scheme is more secure in comparison with the two previous cheating prevention schemes in the literature, but extra burdens are also eliminated.

A novel secret image sharing scheme for true-color images with size constraint

Rapid development of telecommunication and service has made researchers think of intelligent tools to assist users in delivering critical data securely. When it comes to share digital images, owing to high frequent use of Mega pixel digital cameras or camera phones, true-color images become one common image type. In the last few years, several researches have been devoted to study of secret image sharing. What seems lacking is a scheme for sharing true-color secret images with size constraint. This paper proposes a new secret image sharing scheme for true-color secret images. Through combination of neural networks and variant visual secret sharing, the quality of the reconstructed secret image and camouflage images are visually the same as the corresponding original images. Compared with other schemes, the proposed one alone supports true-color secret image with size constraint on shares. Experimental results and comparisons demonstrate the feasibility of this scheme.

Reversible data hiding scheme based on neighboring pixel differences

In this paper, we propose a reversible data hiding algorithm for grayscale images. Specifically, our algorithm is based on the histogram modification technique. The premise of this algorithm is that a histogram is constructed from the differences between each pixel and its neighbors. In the data embedding process, a modified histogram shifting scheme is used to embed a secret message into the pixels whose pixel difference is located at the peak value within the histogram. Experimental results show that our algorithm can achieve higher embedding capacity and imperceptible distortion. Performance comparisons with other existing algorithms are also provided to demonstrate the feasibility of our proposed algorithm in reversible data hiding.

Comment on “Cheating Prevention in Visual Cryptography”

Visual cryptography (VC), proposed by Naor and Shamir, has numerous applications, including visual authentication and identification, steganography, and image encryption. In 2006, Horng showed that cheating is possible in VC, where some participants can deceive the remaining participants by forged transparencies. Since then, designing cheating-prevention visual secret-sharing (CPVSS) schemes has been studied by many researchers. In this paper, we cryptanalyze the Hu-Tzeng CPVSS scheme and show that it is not cheating immune. We also outline an improvement that helps to overcome the problem.

Owner-customer right protection mechanism using a watermarking scheme and a watermarking protocol

Over the past few years, there have been more and more robust watermarking schemes proposed for copyright protection of digital documents. The authors combine cryptography with watermarking to simultaneously address the problems of protecting the owners copyright and the legal customers ownership. The authors propose a robust watermarking scheme based on visual cryptography and a watermarking protocol based on asymmetric cryptography. It is worthwhile to note that the proposed schemes are resistant to counterfeit, collusion, averaging, and copy attacks, while the large majority of robust watermarking schemes are not. Furthermore, the application of digital signature and timestamp makes public verification possible.

On generating meaningful shares in visual secret sharing scheme

Abstract In the k-out-of-n visual secret sharing scheme (VSSS) proposed by Naor and Shamir, a binary secret image is encoded into n shares called transparencies. Each share, consisting of black and white pixels, is in the form of noise and has size larger than that of the secret image. The binary secret image can be decoded by using the visual system through superimposing any k of n transparencies without performing any cryptographic computation. In practice, meaningless shares, however, might invite the adversarys attention and to manage numerous increasing transparencies belonging to different secrets is also a problem. In the present paper, a simple method to transform meaningless shares in VSSS into natural colourful images is proposed. Experiment results show that this method does provide a general solution to the k-out-of-n VSSS with few additional pixel expansions and low computational power as compared with others.

A new authentication based cheating prevention scheme in Naor-Shamir's visual cryptography

Visual cryptography (VC), first presented by Naor and Shamir, is a variant of secret sharing, thus it also called visual secret sharing. It can be widely used in many applications such as encrypting large data efficiently. In the literature, the problem of cheating is under consideration in secret sharing. Recently, Horng et al. pointed out that cheating is possible in k-out-of-n VC schemes, and presented two kinds of the cheating prevention schemes for protecting honest participants. One of them is the authentication based cheating prevention scheme. In this paper, we analyze the definition of cheating prevention and propose a new authentication based cheating prevention scheme. This scheme is constructed with Naor-Shamirs VC scheme. Finally, we give the security analysis to prove that the proposed scheme is immune to cheating.

Visual secret sharing with cheating prevention revisited

Visual secret sharing (VSS) is a variant form of secret sharing, and is efficient since secret decoding only depends on the human vision system. However, cheating in VSS, first showed by Horng et al., is a significant issue like a limelight. Since then, plenty of studies for cheating activities and cheating prevention visual secret sharing (CPVSS) schemes have been introduced. In this paper, we revisit some well-known cheating activities and CPVSS schemes, and then categorize cheating activities into meaningful cheating, non-meaningful cheating, and meaningful deterministic cheating. Moreover, we analyze the research challenges in CPVSS, and propose a new cheating prevention scheme which is better than the previous schemes in the aspects of some security requirements.

An anonymous buyer-reseller watermarking protocol

Abstract In (Memon and Wong, 2001), Memon and Wong first proposed a buyer‐seller watermarking protocol. Inspired by (Memon and Wong, 2001), Cheung and Curreem recently proposed a buyer‐reseller watermarking protocol to address the digital contents redistribution in the second‐hand markets over the Internet (Cheung and Curreem, 2002). In this paper, we show that their watermarking protocol is vulnerable to malicious attacks and propose a simple improvement. The main contribution is that we extend their schemes to enable anonymous transactions among a buyer, a reseller, and a seller in order to further protect the privacy of the buyers.