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 principles. New bounds on relevant parameters of k out of n schemes are developed, too. Furthermore, an extension of the basic problem is introduced and solved in which every combination of the transparencies can contain independent information.