Cryptography Reference
In-Depth Information
10
Cheating P
revention in Visual Cryptography
Yu-Chi Chen
National Chung Hsing University, Taiwan
Gwoboa Horng
National Chung Hsing University, Taiwan
Du-Shiau Tsai
Hsiuping Institute of Technology, Taiwan
CONTENTS
10.1
Introduction :::::::::::::::::::::::::::::::::::::::::::::::::::::: 281
10.2
Preliminaries ::::::::::::::::::::::::::::::::::::::::::::::::::::: 282
10.2.1
Visual Cryptography :::::::::::::::::::::::::::::::::::: 282
10.2.2
Cheating in VC :::::::::::::::::::::::::::::::::::::::::: 285
10.3
Cheating Prevention Schemes :::::::::::::::::::::::::::::::::::: 287
10.3.1
HCT1 and HCT2 :::::::::::::::::::::::::::::::::::::::: 287
10.3.2
HT ::::::::::::::::::::::::::::::::::::::::::::::::::::::: 289
10.3.3
TCH ::::::::::::::::::::::::::::::::::::::::::::::::::::: 290
10.3.4
PS1 and PS2 ::::::::::::::::::::::::::::::::::::::::::::: 292
10.4
Analysis of Cheating Prevention Schemes ::::::::::::::::::::::: 294
10.5
Conclusions ::::::::::::::::::::::::::::::::::::::::::::::::::::::: 295
10.1 Introduction
In 1994, Naor and Shamir proposed a variant of secret sharing called Visual
Cryptography (VC) [9], where the shares given to participants are xeroxed
onto transparencies. If X is an authorized subset, then the participants in X
can visually recover the secret image by stacking their transparencies together
without performing any computation. One special property distinguishes VC
from conventional secret sharing scheme [16, 17] is that the security of VC is
achieved by losing the contrast and the resolution of the secret image. In other
words, the quality of the reconstructed secret image is inferior to that of the
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