On the Contrast in Visual Cryptography Schemes

Carlo Blundo; Alfredo De Santis; Douglas R.  Stinson

Paper 1996/013

On the Contrast in Visual Cryptography Schemes

Carlo Blundo, Alfredo De Santis, and Douglas R. Stinson

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.

Metadata

Available format(s): PS
Publication info: Published elsewhere. Appeared in the THEORY OF CRYPTOGRAPHY LIBRARY and has been included in the ePrint Archive.
Contact author(s): carblu @ udsab dia unisa it
History: 1996-09-25: received
Short URL: https://ia.cr/1996/013
License: CC BY

BibTeX

@misc{cryptoeprint:1996/013,
      author = {Carlo Blundo and Alfredo De Santis and Douglas R.  Stinson},
      title = {On the Contrast in Visual Cryptography Schemes},
      howpublished = {Cryptology ePrint Archive, Paper 1996/013},
      year = {1996},
      note = {\url{https://eprint.iacr.org/1996/013}},
      url = {https://eprint.iacr.org/1996/013}
}