Visual cryptography and its applications

" In this thesis, a number of new schemes are presented which address current problems and shortcomings within the area of visual cryptography. Visual cryptography provides a very powerful means by which a secret, in the form of a digital image, can be distributed (encoded) into two or more pieces known as shares. When these shares are xeroxed onto transparencies and superimposed exactly together, the original secret can be recovered (decoded) without the necessity for computation. Traditionally, visual cryptography allows effective and efficient sharing of a single secret between a number of trusted parties. One aspect of the research within this thesis specifically addresses the issues of embedding more than two secrets within a set of two shares. Alignment poses a further problem. The placement of the shares must be specific. In order to ease ali~ent, the techniques developed within this thesis for sharing multiple secrets relaxes this restriction. The result is a scheme in which the shares can be superimposed upon one another in a multitude of positions and alignment styles which enables multiple secret recovery. Applications of visual cryptography are also examined and presented. This is an area within visual cryptography that has had very little attention in terms of research. The primary focus of the work presented within this thesis concentrates on applications of visual cryptography in real world scenarios. For such a simple and effective method of sharing secrets, practical applications are as yet, limited. A number of novel uses for visual cryptography are presented that use theoretical techniques in a practical way.