A New Simple Non-Expansion Algorithm for (2,2) - Visual Secret Sharing Scheme

Abstract

Visual cryptography (VC) is a powerful encryption technique which combines perfect secrecy and secret sharing in cryptography with respect to images. VC takes a binary image (the secret) and divides it into two or more pieces known as shares (transparencies). When the shares are superimposed, the secret can be recovered. One of the distinguishing features of VC is that it needs no computational power for decryption. All what VC needs for decryption is the human visual system (the human eye). Two main factors affect the quality of a visual cryptography scheme; the pixel expansion and the contrast. In this papers we propose a new simple non-expansion algorithm for (2,2)-visual secret sharing scheme (VSS). The shares produced by this algorithm and the reconstructed image are not expanded in size, and all have the same size as the original (secret) image. It encodes the original (secret) image a 4-pixel blockwise to 4-pixel blocks in each share.