Chair Professor Chin-Chen Chang (???)

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• Chair Professor Chin-Chen Chang (???)
• National Tsing Hua University (????)
• National Chung Cheng University (????)
• Feng Chia University (????)
• http//msn.iecs.fcu.edu.tw/ccc

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Outlines

• Concept of Secret Sharing
• Concept of visual cryptography
• Visual cryptography for binary images
• Visual cryptography for grayscale images
• Meaningful visual cryptography for grayscale
  images
• Meaningful and progressive visual cryptography
• Visual cryptography for color images
• Authenticatable VSS Scheme

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• Traditional (t, n)-secret sharing
• (Shamirs Method 1979)

secret message
(2, 3)-secret sharing
Alice
Ken
Bob
shadows
secret retrieval
Shamir, A. (1979) How to Share a Secret, CACM,
Vol. 22, Nov. 1979, pp. 612-613.
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How to Share a Secret (t, n)-threshold Scheme

• Ex (2, 3)-threshold Scheme (The secret k7)

3 shadows (1, 9), (2, 0), (3, 2)
y
(3, 2)
(2, 0)
(1, 9)
x
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How to Share a Secret (t, n)-threshold Scheme

• Ex (3, 5)-threshold Scheme (t3,
  n5, k13, p17)

Alice
Ken
Bob
Jesse
Eva
ID11
ID22
ID33
ID44
ID55
(1, 8)
(3, 10)
(5, 11)
Lagrange Interpolation
k
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Concept of Visual Cryptography

• Cryptography
• Traditional Cryptography
• Symmetric DES, AES
• Asymmetric RSA
• The encryption and decryption processes need high
  computation costs
• Need secret key for decoding
• Visual Cryptography
• low computation
• Fast decoding
• Without the secret key

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The Secret Image Airplane
Hidden in
Hidden in
The Counterfeit Image Minnie
The Basis Image Mickey
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The Basis Image Mickey
The Counterfeit Image Minnie
The Expanded Counterfeit Image Minnie-3X3
The Expanded Basis Image Mickey-3X3
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Mickey-3X3
Minnie-3X3
Airplane
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Visual Cryptography for Binary Image

• Naor and Shamir (1994) proposed a (k, k)VSS
  scheme
• Extend a secret pixel into a block of 2?2
  sub-pixels
• Contain two white pixels and two black pixels for
  each block
• White pixel transparent
• Black pixel black

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Share 1

Secret image
stacked result
Share 2
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(No Transcript)
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Visual Cryptography for Grayscale Image

• Transfer the grayscale image to the halftone
  image
• Utilize the density of black dots to simulate the
  content of grayscale image
• White area low density of black dots
• Black area high density of black dots

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Share 1
Share 2
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Meaningful Visual Cryptography for Grayscale Image
secret image
shadow 1
shadow 2
camouflage
stego image1
stego image2
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shadow1
shadow1
0 1
1 0
0 1
1 0








167
97

140
150
shadow2
stego image1
shadow2




0 1
1 0
1 0
0 1


167
170
83
140
stego image2
152 167
140 137
170 97
150 83
cover image
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stego image1
stacked result
stego image2
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Experimental Results
shadow1
cover image1
stego image1
cover image2
stego image2
shadow2
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stego image1
stego image2
stacked result
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shadow1
cover image1
stego image1
cover image2
stego image2
shadow2
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stego image1
stego image2
stacked result
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Meaningful and Progressive Visual Cryptography

• Meaningful shares friendly content
• Progressive visual cryptography
• Improve the stacked result progressively

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Progressive Visual Cryptography (t, 6)
(2, 6)
(3, 6)
(4, 6)
(5, 6)
(6, 6)
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Progressive Meaningful Visual Cryptography

• Meaningful shares friendly content

shadow 1
shadow n
secret image
camouflage

stego image1
stego image n
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extended secret image
secret image
cover image
shadow image
secret image
cover image
shadow image 1
shadow image 2
shadow image 3
shadow image 4
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secret image








cover image


t 2
t 3
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Experimental Results
(2, 6)
(3, 6)
(4, 6)
(5, 6)
(6, 6)
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Visual Cryptography for Color Image
RGB TVs and Monitors CMY
Color Printing Press
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(No Transcript)
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(No Transcript)
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Experimental Results
shadow image 1
shadow image 2
stacked image 2
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Authentication
Participant 1
Share 1
Recovered secret image
Participant 2
Share 2
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Authentication
Share 1
Share 2
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Authentication
Tampered share 1
Share 2
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Authenticatable VSS Scheme for Binary Secret
Grayscale image Lena
Grayscale image Baboon
Binary main secret
Halftone image of Lena
Halftone image of Baboon
Binary extra confidential image
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Authenticatable VSS Scheme for Binary Secret
Share image A
Share image B
Stacking result
Revealed extra confidential image
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Authenticatable VSS Scheme for Color Secret
Color image Lena
Color image Baboon
Color main secret
Color halftone extra confidential image
Color halftone image of Lena
Color halftone image of Baboon
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Authenticatable VSS Scheme for Color Secret
Share image A
Share image B
Stacking result
Revealed extra confidential image
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Visual cryptography (Cont.)
Rotating 40o
Stacking
Stacking
Share 2
Share 1
Secret 1 VISUAL
Secret 2 SECRET
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Steganography (Cont.)

• Text
• ???? ???
• ????? ????
• ???? ???
• ????? ????
• ?????? ?????
• ????? ????
• ????? ????
• Video
• Sound

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Conclusions

• An alternative for hiding visual secret
• Less secret
• Low computation cost

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Thanks for your listening