A Secured Visual Cryptography Mechanism

To prevent the confidential information from being disclosed, one needs to apply some techniques to protect it. Visual cryptography scheme is a secret sharing technique used for encrypting binary images. It splits a binary image into n shares, and gathering more than k shares can recover the secret. The remarkable feature of a visual cryptography scheme is that the decoding process is done by human eyes. A conventional visual cryptography scheme encodes a pixel on the secret image into m subpixels. This gives a study of the cheating problem in visual cryptography and extended visual cryptography schemes. This dissertation reviews the attacks of malicious adversaries who may deviate from the scheme in any way and presents three cheating methods and applied them on attacking existent visual cryptography or extended visual cryptography schemes. This dissertation proposed a generic method that converts a visual cryptography scheme to another visual cryptography scheme that has the property of cheating prevention. The overhead of the conversion is near optimal in both contrast degression and pixel expansion.