Joint Multiple Watermarking and Non-Expansion Visual Cryptography

1
Joint Multiple Watermarking and Non-Expansion
Visual Cryptography

• Hao Luo, Zhenfei Zhao, Jeng-Shyang Pan, Zhe-Ming
  Lu
• Signal Design and Its Applications in
  Communications, 2007. IWSDA 2007. 3rd
  International Workshop on

2
Outline

• Introduction
• Conventional 2,2 VSS
• Proposed scheme
• Experimental results
• Conclusions

3
Introduction(1/3)

• Visual cryptography a technique of encrypting a
  two-tone secret image into a set of binary
  transparency images which look like random noise.
• Visual secret sharing scheme based on a
  ?k,n?-threshold framework.
• A secret image is encrypted into n transparencies
  distributed to n participants.
• Only when k or more than k transparencies are
  stacked, content of the secret image is visible.

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Introduction(2/3)

• Fang et als scheme has following properties
• As the input secret image is a halftone image, it
  can not be directly used for gray level images.
• Only one watermark is embedded in two
  transparencies.
• The secret sharing model used is the conventional
  ?2,2?-threshold VSS.
• It will greatly places heavy loading for the
  limited network bandwidth and the storage space.

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Introduction(3/3)

• To improve the inefficiencies of Fang et als
  method
• The input secret image is a gray level image
  instead of a halftone image.
• There are two watermarks instead of one are
  embedded and thus the hidden data capacity is
  enhanced.
• A non-expansion visual secret sharing model
  instead of the conventional ?2,2?VSS model is
  used, and the size of shares is equal to that of
  the secret image.

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Conventional?2,2?VSS(1/2)
Fig. 1. Codewords of ?2,2?VSS
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Conventional?2,2?VSS(2/2)
(b) the first transparency 512x512
(a) secret image 256x256
(c) the second transparency 512x512
(d) stacking result 512x512
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Proposed Scheme(1/10)
Secret image
Error diffusion Half-toning
Watermark W1
Visual secret sharing
Watermark W2
Watermarked Share image S1
Watermarked Share image S2
Watermark embedding and secret image encryption
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Proposed Scheme(2/10)
Watermarked Share image S1
Watermarked Share image S2
Watermark W2
XOR operation
Watermark W1
Watermarked halftone image
Watermark extraction and secret image decryption
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Proposed Scheme(3/10)

• Watermark embedding in half-toning
• The secret image S is scaled into a half sized
  image k1k2/2 HS.

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Proposed Scheme(4/10)

• HS is used as the input image of error diffusion
  half-toning.

W1
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Proposed Scheme(5/10)
w
b(i,j)0 or 255
u(i,j) x(i,j)-x(i,j)
Threshold t(i,j)128
?

x(i,j)
-
x(i,j)
-
?

Kernel K
ei,j bi,j- ui,j
Watermark (W1) embedding in halftoning
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Proposed Scheme(6/10)

• Watermark embedding in encryption

Encryption and decryption strategy
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Proposed Scheme(7/10)
c1
c2
Codewords of non-expansion VSS
W2
B11
B12
B22
B21
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Proposed Scheme(8/10)
Watermark 0 1 1 0
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Proposed Scheme(9/10)

• W2 extraction XOR(B11,B22)

1 1 0 W2
XOR
0
XOR
XOR
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Proposed Scheme(10/10)

• W1 extraction
• Based on the perfectly reconstructed watermarked
  halftone image.
• To find the selected pixels positions using the
  pseudo random number generator with the same key.
  
• Retrieve the pixel values in these positions and
  rearrange it into a binary sequence.

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Experimental results(1/3)
W1 32x32 ( binary image )
W2 256x512 ( binary image )
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Experimental results(2/3)
Secret image 512x512 ( Gray level image )
The halftone Lena with watermark KUAS embedded
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Experimental results(3/3)
Transparency images T1,T2( 512x512 )
Stacking result
Extracted watermarks
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Conclusions

• Proposes a scheme to hide two watermarks in
  transparencies of visual cryptography.
• Watermark extraction is simple for only XOR
  computations of two transparencies are needed.

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References(1/2)

• 1 M. Naor and A. Shamir, Visual cryptography,
  Eurocrypt94, Lecture Notes in Computer Scienece,
  Vol. 950, pp. 1-12, 1995.
• 2 C.C. Lin, W. H. Tsai, Visual cryptography
  for gray-level images by dithering techniques,
  Pattern Recognition Letters, vol. 24, pp.
  349-358, 2003.
• 3 C. Blundo, Santis A De. and M. Naor, Visual
  cryptography for grey level images, Information
  Processing Letters. vol. 75(6), pp. 255-259,
  2000.
• 4 D. Jin, W.Q. Yan and M.S. Kankanhalli,
  Progressive Color Visual Cryptography, Journal
  of Electronic Imaging, vol. 14(3), 2005.

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References(2/2)

• 5 J. S. Pan, H.C. Huang, and L.C. Jain,
  Intelligent Watermarking Techniques, World
  Scientific Publishing Company, Singapore, 2004.
• 6 W. P. Fang and J.C. Lin, Visual Cryptography
  with Extra Ability of Hiding Confidential Data,
  Journal of Electronic Imaging, vol. 15(2), 2006.