Basic visual cryptography algorithms

© Springer Nature Singapore Pte Ltd. 2020. This chapter aims to help the readers to get familiar with the classical VC algorithms. These algorithms are also stepstones for developing more complicated algorithms in later chapters. First, we introduce the general framework of VC, such as access structure and general requirements (security and contrast). Then, we introduce the classical deterministic VC with pixel expansion as developed in Naor and Shamir’s seminal work. Next, the size-invariant algorithms are summarized, including the probabilistic VC and random grid VC. Some examples will be discussed for the readers that are new to this topic. Finally, various security levels in visual cryptography will be discussed, including strong security and several weak securities.