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Paper: On the Contrast in Visual Cryptography Schemes

Authors:
Carlo Blundo
Alfredo De Santis
Douglas R. Stinson
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URL: http://eprint.iacr.org/1996/013
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Abstract: A visual cryptography scheme is a method to encode a secret image SI into shadow images called shares such that certain qualified subsets of shares enable the ``visual'' recovery of the secret image. The ``visual'' recovery consists of xeroxing the shares onto transparencies, and then stacking them. The shares of a qualified set will reveal the secret image without any cryptographic computation. In this paper we analyze the contrast of the reconstructed image in k out of n visual cryptography schemes. (In such a scheme any k shares will reveal the image, but no set of k-1 shares gives any information about the image.) In the case of 2 out of n threshold schemes we give a complete characterization of schemes having optimal contrast and minimum pixel expansion in terms of certain balanced incomplete block designs. In the case of k out of n threshold schemes with k>2 we obtain upper and lower bounds on the optimal contrast.
BibTeX
@misc{eprint-1996-11279,
  title={On the Contrast in Visual Cryptography Schemes},
  booktitle={IACR Eprint archive},
  keywords={},
  url={http://eprint.iacr.org/1996/013},
  note={Appeared in the THEORY OF CRYPTOGRAPHY LIBRARY and has been included in the ePrint Archive. carblu@udsab.dia.unisa.it 10500 received September 25, 1996.},
  author={Carlo Blundo and Alfredo De Santis and Douglas R. Stinson},
  year=1996
}