New Approaches for Constructing Efficient Visual Cryptographic Schemes

Abstract

Visual Cryptographic scheme (VCS) is a variant form of secret sharing method to newlineencode a secret image into n distinct shares. The dealer distributes each of the newlinen shares to the corresponding participants in such a way that, certain qualified newlinesubsets of participants can visually recover the secret, but forbidden subsets of newlineparticipants have no information on the secret. Such a system is called general newlineaccess structure VCS. In a variant of this, called the essential access structure newlineVCS, certain special participants out of the n participants will be there in all the newlinequalified subsets. A secure scheme with small pixel expansion and high contrast newlineis a good VCS. In VCS, the pixel-wise Boolean operations such as OR, AND, newlineNOT and XOR can be used alone or in combinations for reconstructing the secret newlineimage. Many deterministic/ probabilistic VCS were proposed in the literature newlinewhich can be used to share binary/ grey/ color images with a goal to provide newlineideal/ optimal contrast for the reconstructed image. New VCS constructions (PC newline1 to 15) discussed in this thesis are applicable to general/ essential strong access structures for sharing a single binary/ grey image, make use of novel combina newlinetions of Boolean operations during reconstruction, which either reduce the pixel newlineexpansion or increases the contrast of the reconstructed image when compared newlinewith the existing results in the literature. One of the drawbacks in VCS is cheating attacks, where the malicious adversaries can cheat the honest participant by newlinesubmitting fake shares during reconstruction phase. Share/ Blind authentication newlinebased cheating immune schemes are used for mitigating cheating attacks in visual newlinecryptography. We demonstrated a collusive attack on the XOR operation based newlineideal contrast step construction for general access structure VCS proposed by Liu newlineet al. [39] in 2010. We constructed a blind authentication based cheating immune newlinescheme for mitigating collusive attacks on XOR operation based ideal contrast newlinestep construction by Liu et al.