Xi Jun Lin

Colour visual cryptography schemes

Visual cryptography scheme (VCS) is a kind of secret-sharing scheme which allows the encryption of a secret image into n shares that are distributed to n participants. The beauty of such a scheme is that, the decryption of the secret image requires neither the knowledge of cryptography nor complex computation. Colour visual cryptography becomes an interesting research topic after the formal introduction of visual cryptography by Naor and Shamir in 1995. The authors propose a colour (k, n)-VCS under the visual cryptography model of Naor and Shamir with no pixel expansion, and a colour (k, n)-extended visual cryptography scheme ((k, n)-EVCS) under the visual cryptography model of Naor and Shamir with pixel expansion the same as that of its corresponding black and white (k, n)-EVCS. Furthermore, the authors propose a black and white (k, n)-VCS and a black and white (k, n)-EVCS under the visual cryptography model of Tuyls. Based on the black and white schemes, the authors propose a colour (k, n)-VCS and a colour (k, n)-EVCS under the same visual cryptography model, of which the pixel expansions are the same as that of their corresponding black and white (k, n)-VCS and (k, n)-EVCS, respectively. The authors also give the experimental results of the proposed schemes, and compare the proposed scheme with known schemes in the literature.

Step Construction of Visual Cryptography Schemes

Two common drawbacks of the visual cryptography scheme (VCS) are the large pixel expansion of each share image and the small contrast of the recovered secret image. In this paper, we propose a step construction to construct VCSOR and VCSXOR for general access structure by applying (2,2)-VCS recursively, where a participant may receive multiple share images. The proposed step construction generates VCSOR and VCSXOR which have optimal pixel expansion and contrast for each qualified set in the general access structure in most cases. Our scheme applies a technique to simplify the access structure, which can reduce the average pixel expansion (APE) in most cases compared with many of the results in the literature. Finally, we give some experimental results and comparisons to show the effectiveness of the proposed scheme.

Cheating immune visual cryptography scheme

Most cheating immune visual cryptography schemes (CIVCS) are based on a traditional visual cryptography scheme (VCS) and are designed to avoid cheating when the secret image of the original VCS is to be recovered. However, all the known CIVCS have some drawbacks. Most usual drawbacks include the following: the scheme needs an online trusted authority, or it requires additional shares for the purpose of verification, or it has to sacrifice the properties by means of pixel expansion and contrast reduction of the original VCS or it can only be based on such VCS with specific access structures. In this study, the authors propose a new CIVCS that can be based on any VCS, including those with a general access structure, and show that their CIVCS can avoid all the above drawbacks. Moreover, their CIVCS does not care about whether the underlying operation is OR or XOR.

A new definition of the contrast of visual cryptography scheme

In this paper, some of the known definitions of the contrast of the Visual Cryptography Scheme (VCS) are shown to be inappropriate, and a new definition of the contrast based on our observations is proposed. It is also shown how our new definition of the contrast agreed with our observations.

Some Extensions on Threshold Visual Cryptography Schemes

Droste [CRYPTO’96] proposed a construction of threshold visual cryptography scheme (TVCS) under the visual cryptography model of Naor and Shamir, i.e. the visual cryptography model with the underlying operation OR. In this article, we give three extensions of TVCS. First, we prove that the TVCS proposed by Droste which was based on the OR operation is still a valid TVCS under the XOR operation, and then we propose a method to further reduce its pixel expansion. We then propose an interesting construction of TVCS with all shares being concolorous. Finally, we give a construction of threshold extended visual cryptography scheme (TEVCS) with the underlying operation OR or XOR. All of our schemes can be applied to the visual cryptography model introduced by Tuyls et al. (First Int. Conf. Security in Pervasive Computing 2004, International Patent with Application No.: PCT/IB2003/000261).

An efficient RSA-based certificateless public key encryption scheme

Abstract In order to resolve the key escrow in identity-based scheme and the significant cost of using a PKI system in traditional public key scheme, the notion of certificateless public key cryptography (CL-PKC) was introduced. The first certificateless public key encryption scheme (CL-PKE) was proposed by Al-Riyami and Paterson, and then further schemes were developed. However, most of them are constructed from the bilinear pairing which is a time costing operation. In this paper, we construct an efficient CL-PKE scheme from RSA since RSA is the de facto Internet standard and is widely used in many applications. The security is based on Kilian–Petrank’s RSA assumption which is a variant of RSA.

Certificateless public key encryption with equality test

Abstract In this paper, we present the concept of certificateless public key encryption with equality test (CL-PKEET), which integrates certificateless public key cryptography (CL-PKC) into public key encryption with equality test (PKEET) to solve the key escrow problem of identity-based encryption with equality test (IBEET). In the CL-PKEET scheme, the receiver first computes his private key with the receiver’s secret value and the partial private key generated by the key generation center (KGC). The trapdoor is generated with this private key. Then, using the trapdoor, the receiver authorizes the cloud server to test the equivalence between his ciphertexts and others’ ciphertexts. We formalize the system model and definition of CL-PKEET, propose the security models by considering four types of adversaries, and then present a concrete CL-PKEET scheme. Our proposal achieves the IND-CCA security against adversaries without trapdoor, and the OW-CCA security against adversaries with trapdoor. Furthermore, compared with IBEET and PKEET, our proposal which has the features of CL-PKC solves certificate management and key escrow problems simultaneously.