Massoud Hadian Dehkordi - Department of Mathematics Iran University of Since & Technology, Tehran, Iran
Abbas Cheraghi - Department of Mathematics Iran University of Since & Technology, Tehran, Iran

A visual cryptography scheme for a set P of n participants is a method to encode a secret image SI into n shadow image called shares, where each participant in P receives one share. In this paper, access structures based on graphs is studied. We consider graph-based access structure, i.e., access structures in which any qualified set of participants contains at least an edge of a given graph whose vertices represent the participants of the scheme and use one technique to compute lower bound on the pixel expansion of matching access structures.

Visual Cryptography, Secret Sharing, Pixel Expansion, Graph-based Access Structure