Visual Cryptography Schemes with Reversing - Visual Cryptography and Secret Image Sharing - page 249

9

Visual Cryp tography Schemes with Reversing

Alfredo De Santis
Universita di Salerno, Italy

Anna Lisa Ferrara
Universita di Salerno, Italy

Barbara Masucci
Universita di Salerno, Italy

CONTENTS
9.1

Introduction :::::::::::::::::::::::::::::::::::::::::::::::::::::: 255

9.2 Visual Cryptography Schemes ::::::::::::::::::::::::::::::::::: 258

9.2.1 (k;k)-Threshold Visual Cryptography Schemes ::::::::: 259

9.2.2 Perfect Black Visual Cryptography Schemes :::::::::::: 260

9.3 Almost Ideal Contrast VCS with Reversing ::::::::::::::::::::: 262

9.4 Ideal Contrast VCS with Reversing :::::::::::::::::::::::::::::: 265

9.4.1 A Construction Using a Binary Secret Sharing Scheme 266

9.4.2 Constructions Using Perfect Black VCSs ::::::::::::::: 268

9.4.2.1

The Scheme by Cimato, De Santis, Ferrara,
and Masucci :::::::::::::::::::::::::::::::::: 269

9.4.2.2 The Scheme by Hu and Tzeng ::::::::::::::: 271

9.4.2.3 The Scheme by Yang, Wang, and Chen :::::: 274

9.4.2.4 Comparisons :::::::::::::::::::::::::::::::::: 276

9.4.3 A Construction Using a Nonperfect Black VCS :::::::: 276

9.5 Conclusions ::::::::::::::::::::::::::::::::::::::::::::::::::::::: 278

Bibliography :::::::::::::::::::::::::::::::::::::::::::::::::::::::: 278

9.1 Introduction
A visual cryptography scheme for a set of n participants is a method to en-
code a secret image, consisting of black and white pixels, into n shadow im-
ages called shares, one for each participant. Each share is a collection of black
and white subpixels, which are printed in close proximity to each other, so