Using Variance to Analyze Visual Cryptography Schemes

A visual cryptography scheme (VCS) is a secret sharing method, for which the secret can be decoded by human eyes without needing any cryptography knowledge nor any computation. Variance is first introduced by Hou et al. in 2005 and then thoroughly verified by Liu et al. in 2012 to evaluate the visual quality of size invariant VCS. In this paper, we introduce the idea of using variance as an error-detection measurement, by which we find the security defect of Hou et al.’s multi-pixel encoding method. On the other hand, we find that variance not only effects the visual quality of size invariant VCS, but also effects the visual quality of VCS. At last, average contrast associated with variance is used as a new criterion to evaluate the visual quality of VCS.