Gwoboa Horng

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 publicly verifiable copyright-proving scheme resistant to malicious attacks

A wavelet-based copyright-proving scheme that does not require the original image for logo verification is proposed in this paper. The scheme is strong enough to resist malicious manipulations of an image including blurring, JPEG compression, noising, sharpening, scaling, rotation, cropping, scaling-cropping, and print-photocopy-scan attacks. The proposed scheme is also resistant to StirMark and unZign attacks and it is not only a robust method but also a lossless one. Experiments are conducted to show the robustness of this method. Moreover, cryptographic tools, such as digital signature and timestamp, are introduced to make copyright proving publicly verifiable.

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.

Encrypted signal-based reversible data hiding with public key cryptosystem

Abstract Encrypted image-based reversible data hiding (EIRDH) is a well-known method allowing that (1) the image provider gives the data hider an encrypted image, (2) the data hider embeds the secret message into it to generate the encrypted image with the embedded secret message to the receiver, and (3) finally the receiver can extract the message and recover the original image without encryption. In the literature, the data hider and image provider must be specific parties who know the shared key with the receiver in traditional encrypted image-based reversible data hiding. In this paper, we propose an encrypted signal-based reversible data hiding (ESRDH) with public key cryptosystem, not only for images. The proposed scheme is secure based on Paillier homomorphic encryption. Finally, the experimental results show that the proposed scheme has much payload and high signal quality.

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.

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.

Research note: Key authentication scheme for cryptosystems based on discrete logarithms

Protecting public keys against intruders is very important in public key cryptosystems. Most key authentication schemes require one or more authorities to authenticate keys. In this paper, we propose a new scheme for cryptosystems based on discrete logarithms. It is similar to the conventional certificate-based schemes, yet it requires no authorities. The certificate of the public key of a user is a combination of his password and private key. Our scheme is highly secure and the authentication process is very simple.

Password authentication without using a password table

Password authentication is the most widely used mechanism for authenticating legal users in multiuser computing systems. Most password authentication schemes keep a password table for verification. However, it is vulnerable to keep such a table. In this paper, we propose a password authentication scheme where the system keeps polynomials instead of a table.