Multiple-Image Encryption by Rotating Random Grids

It is the well-known visual secret sharing (VSS) technique that encrypts a secret image into several share images and, later, decrypts the secret by stacking the share images and recognizing by the human visual system. Due to the perfect secrecy, VSS is one of well-candidate for achieving secure e-commerce. Furthermore, the other visual secret sharing technique is constructed by random grids. The main advantages of VSS by adopting random grids compared with VC include no pixel expansion, and no cost of sophisticated codebook design. In this paper, the authors present the new scheme which encrypts two secret images into two random grids without any pixel expansion and, later, decrypts the original secrets by directly stacking two random grids in an additional way of rotating one random grid at 90, 180 or 270 degrees. The proposed scheme not only has no pixel expansion so that the overhead of storage and communication can be reduced but also raises the capacity of secret communication.