A Note on Efficient Color Visual Encryption

A new type of secret sharing scheme [2] called VSS scheme, was first introduced by Naor and Shamir in 1994. The key features of the VSS scheme are that encodes a secret image is encoded into shadow images (called shares) and the decoder does not need knowledge of cryptography or cryptographic computations, but only the “eyes” of a human being. To decrypt the secret image, the reader should copy each share onto a separate transparency and then recover the secret image by stacking some of transparencies with the help of an overhead projector. Some authors [1, 3-4] have proposed colored VSS schemes, where users can share a colored secret image. In [1], it was shown that the 2-out-of-2 colored VSS scheme only needs m sub pixels to represent m! colors. However, the number of possible colors does not really reach m!. Herein, a correction for the Rijmen-Preneel scheme is given. This note is organized as follows. In Section 2, we will give a brief review of the Rijmen-Preneel colored VSS scheme. Section 3 will show the correction.