International Association for Cryptologic Research

International Association
for Cryptologic Research


Paper: Visual Cryptography II: Improving the Contrast Via the Cover Base

Moni Naor
Adi Shamir
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Abstract: In Eurocrypt'94 we proposed a a new type of cryptographic scheme, which can decode concealed images without any cryptographic computations, by placing two transparencies on top of each other and using the decoder's (human) visual systems. One of the drawback of that proposal was a loss in contrast: a black pixel is translated in the reconstruction into a black region, but a white pixel is translated into a grey region (half black and half white). In this paper we propose am alternative model for reconstruction with a different set of operation (which we call the ``Cover" semi-group) is proposed. In this model we are able to obtain a better contrast than is possible in the previous one. We prove tight bounds on the contrast as a function of the complexity of the scheme. We also show that for constructing k-out-n secret sharing schemes when n and k are greater than 2 the new method is not applicable.
  title={Visual Cryptography II: Improving the Contrast Via the Cover Base},
  booktitle={IACR Eprint archive},
  note={Appeared in the THEORY OF CRYPTOGRAPHY LIBRARY and has been included in the ePrint Archive. 10500 received June 14th, 1996.},
  author={Moni Naor and Adi Shamir},