Authors: Tzung-Her Chen, Kai-Hsiang Tsao, and Kuo-Chen Wei Source: Proceedings of The 8th International Conference on Intelligent System Design and Applications (ISDA 2008)

學生：張若怡 P78011044 許伯誠 P76011242

Date: 2013/01/18

Multiple-Image Encryption by Rotating Random Grids

Outline

Introduction Motivation Related Work Research Methods• Encryption phase • Decryption phase

Research Results Conclusion

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Introduction – Visual Cryptography

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Traditional Cryptography- Encryption and Decryption by computer

Visual Cryptography (VC), also called Visual Secret Sharing (VSS)- Encrypted by computer, Decrypted by human vision

Introduction

Traditional VC and Random Grid Traditional VC and Random Grid

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• VSS Traditional VC-based VSS (Codebook)RG-based VSS (Random Grid)

• Traditional VC-based VSS has at least two drawbacks as follows :1. Codebook design2. Pixel expansion

Introduction

Pixel expansionPixel expansion

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Secret image

Share1

Share2

Share1 + Share2

Traditional VC-based VSS:

Introduction

Traditional VC and Random Grid Traditional VC and Random Grid

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• VSS Traditional VC-based VSS (Codebook)RG-based VSS (Random Grid)

• Traditional VC-based VSS has at least two drawbacks as follows :1. Codebook design2. Pixel expansion

Motivation

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SA G1 G2 SA’

G1 G2

SA

SB

SA’

SB’

Related Work

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b g1 g2 g1⊕ g2

0 0 0 0 1 1 1

1 0 1 1 1 0 1

SA G1

for(i=0 ; i<w ; i++) for(j=0 ; j<h ; j++)　　　　 if(B[i][j] == 0) G2[i][j] = G1[i][j];　　　　 else G2[i][j] = G1[i][j];Output(G1 , G2);

G2

Random Grid Algorithm1:

O. Kafri, and E. Keren, “Encryption of pictures and shapes by random grids,” Optics Letters, vol. 12, no. 6, 1987, pp. 377-379.

In 1987, Kafri and Keren propose three different algorithms to encrypt a binary secret image.

Research Methods

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Research Methods

Encryption phase:Step 1: SA(i, j) ← f RSP(SA).

Randomly select a pixel SA(i, j) from the first secret image SA, where the i-th row and the j-th column of the matrix SA are in the range of [0,m-1].

Step 2: G1(i, j)||G2(i, j) ← f RG(SA(i, j))

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Research Methods

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Research Methods

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Research Methods

Step 8: G1((m-1)-j, i) ← random(0,1)

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Research Methods

Decryption phase

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Research Results

Simulation 1: binary secrets, 90-degree rotation • Two secret images SA and SB with the size of 512×512

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Research Results

Simulation 2: Halftone secrets, 90-degree rotation • Two gray-level secret images SA and SB with the size of

512×512

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Research Results

Simulation 3: binary secrets, 180-degree rotation

Simulation 4: binary secrets, 270-degree rotation

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Conclusion

Property 1: No extra codebook redesigned Property 2: No extra pixel expansion introduced Property 3: Multiple secrets encoded Property 4: Bandwidth and storage saving Property 5: Wide image format

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