MacPherson, Lesley2006-08-222006-08-2220022002http://hdl.handle.net/10012/1126Visual cryptography, first introduced by Naor and Shamir, allows a secret (black and white) image to be encoded and distributed to a set of participants such that certain predefined sets of participants may reconstruct the image without any computation. In 2000, Blundo, De Santis, and Naor introduced a model for grey-level visual cryptography which is a generalization of visual cryptography for general access structures. Grey-level visual cryptography extends this model to include grey-scale images. Decoding is done by the human visual system. In this thesis we survey known results of grey-level visual cryptography and visual cryptography for general access structures. We extend several visual cryptography constructions to grey-level visual cryptography, and derive new results on the minimum possible pixel expansion for all possible access structures on at most four participants.application/pdf283228 bytesapplication/pdfenCopyright: 2002, MacPherson, Lesley. All rights reserved.Computer Sciencevisual cryptographysecret sharingcryptographyMaster Thesis