Constructions Of Visual Cryptography Schemes With The Applications

Visual cryptography schemes are considered in this paper. A (k,n) visual cryptog-raphy scheme is a method in which a secret image can be divided into n shadow images (called shares), where the image will be revealed by stacking any k shares, and any k - 1 or fewer of them give no information about the image.This paper consists of four chapters, and is organized as follows:In the first chapter a brief survey of visual cryptography schemes is given. In the second chapter, we study black and white schemes. Firstly, a new construction of 2 out of n visual cryptography schemes is given, which is the extension of the result in [8]. Secondly, a construction of (2,n) visual cryptography scheme from a (2,ni) visual cryptography scheme and a (2, n2) visual cryptography scheme where n=n1+n2 are also obtained, this scheme can be used in company merger. Finally, a (k, n) visual cryptography scheme is proposed based on t-designs. In the third chapter colored schemes are investigated. By extending colored (k, k) visual cryptography scheme[11] with optimal pixel expansion, a colored (k,n) visual cryptography scheme is obtained which has better pixel expansion. In the fourth chapter a cheating prevention scheme is given.