ABSTRACT
Visual cryptography (VC), proposed by Naor and Shamir in [19], is a paradigm for cryptographic schemes that allows the decoding of concealed images without any cryptographic computation. Particularly in a k-out-of-n visual secret sharing scheme (VSS), a secret image is cryptographically encoded into n shares. Each share resembles a random binary pattern. The n shares are then xeroxed onto transparencies respectively and distributed among n participants. The secret images can be visually revealed by stacking together any k or more transparencies of the shares and no cryptographic computation is needed. However, by inspecting less than k shares, one cannot gain any information about the secret image, even if infinite computational power is available. Aside from the obvious applications to information hiding, VC can be applied to access control, copyright protection [10], watermarking [8], visual authentication, and identification [18].
