Visual cryptography

About: Visual cryptography is a research topic. Over the lifetime, 1724 publications have been published within this topic receiving 25300 citations.

Halftone Visual Cryptography Via Error Diffusion

Abstract: Halftone visual cryptography (HVC) enlarges the area of visual cryptography by the addition of digital halftoning techniques. In particular, in visual secret sharing schemes, a secret image can be encoded into halftone shares taking meaningful visual information. In this paper, HVC construction methods based on error diffusion are proposed. The secret image is concurrently embedded into binary valued shares while these shares are halftoned by error diffusion-the workhorse standard of halftoning algorithms. Error diffusion has low complexity and provides halftone shares with good image quality. A reconstructed secret image, obtained by stacking qualified shares together, does not suffer from cross interference of share images. Factors affecting the share image quality and the contrast of the reconstructed image are discussed. Simulation results show several illustrative examples.

Visual authentication and identification

Abstract: The problems of authentication and identification have received wide interest in cryptographic research. However, there has been no satisfactory solution for the problem of authentication by a human recipient who does not use any trusted computational device, which arises for example in the context of smartcard-human interaction, in particular in the context of electronic wallets. The problem of identification is ubiquitous in communication over insecure networks. This paper introduces visual authentication and visual identification methods, which are authentication and identification methods for human users based on visual cryptography. These methods are very natural and easy to use, and can be implemented using very common low tech technology. The methods we suggest are efficient in the sense that a single transparency can be used for several authentications or for several identifications. The security of these methods is rigorously analyzed.

New Results on Visual Cryptography

Abstract: Naor and Shamir ([1]) defined the basic problem of visual cryptography by a visual variant of the k out, of n secret sharing problem: how can an original picture be encoded by n transparencies so that less than k of them give no information about the original, but by stacking k of them the original can be seen? They described a solution to this problem by a structure called k out of n secret sharing scheme whose parameters directly correspond to quality and usability of the solution. In this paper a new principle of construction for such schemes is presented which is easy to apply and in most cases gives much better results than the former principlcs. New bounds on relevant parameters of k out of n schemes are developed, too. Furthermore, an extension of the basic problem is introduced a.nd solved in which every combination of the transparencies can contain independent information.

On the Contrast in Visual Cryptography Schemes.

Abstract: A visual cryptography scheme is a method to encode a secret image SI into shadow images called shares such that certain qualified subsets of shares enable the ``visual'' recovery of the secret image. The ``visual'' recovery consists of xeroxing the shares onto transparencies, and then stacking them. The shares of a qualified set will reveal the secret image without any cryptographic computation. In this paper we analyze the contrast of the reconstructed image in k out of n visual cryptography schemes. (In such a scheme any k shares will reveal the image, but no set of k-1 shares gives any information about the image.) In the case of 2 out of n threshold schemes we give a complete characterization of schemes having optimal contrast and minimum pixel expansion in terms of certain balanced incomplete block designs. In the case of k out of n threshold schemes with $k\geq 3$ we obtain upper and lower bounds on the optimal contrast.