Cryptology ePrint Archive: Report 1996/007
Visual Cryptography II: Improving the Contrast Via the Cover Base
Moni Naor and Adi Shamir
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.
Category / Keywords:
Publication Info: Appeared in the THEORY OF CRYPTOGRAPHY LIBRARY and has been included in the ePrint Archive.
Date: received June 14th, 1996.
Contact author: naor at narkis wisdom weizmann ac il
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