Visual cryptography
The book is about an interesting branch of cryptography, introduced in 1994 by Moni Naor and Adi Shamir. The original idea of a secret sharing scheme in which an image can be reconstructed ``visually'' by superimposing two shares -- transparencies made up of black and transparent pixels is described and further elaborated there in 7 chapters. The first chapter provides an introduction into the idea of visual cryptography as well as some very basic introduction to cryptography. The second chapter is devoted to the theory of cryptosystem in the Shannon (information-theoretic) sense. Some basic considerations concerning attack and defense are then presented in chapter 3. Chapter 4 shows that visual cryptography may use more than two transparencies (shares) and describes various approaches to construct \(2\)-out-of-\(n\) visual secret sharing schemes. The next chapter deals with combinations of visual cryptography and steganography and chapter 6 discusses the problem of cheating in visual secret sharing schemes. While in all these cases only black and white images are considered, the last chapter provides a glimpse into colour visual cryptography. The book comprises a useful overview for those interested in various facets of visual cryptography.
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