Multi secret sharing with unexpanded meaningful shares

Abstract

Traditional Visual Cryptography (VC) facilitates a technique to protect only one secret image using single set of shares. Recent researches enhance the capabilities of traditional VC by providing the feature of Multi Secret Sharing (MSS), where more than one secret image can be protected at a time. In MSS different secret images are revealed by the stacking of same set of shares at different angles. Most of the existing state of art researches on MSS have common problem of pixel expansion and random pattern of the shares. Due to pixel expansion, there is wastage of the storage space and transmission time, moreover random pattern of the shares increases the vulnerability for cryptanalysis. In this paper a novel Multi Secret Sharing scheme with unexpanded as well as meaningful shares has been proposed to protect two secret images at a time. In the proposed approach the recovery probability of black pixels of the secret images in the decoded images is always 1 while that of white pixels, it is 0.25. Therefore the contrast of the decoded images is obtained as 25 % which is same as in most of the earlier researches with pixel expansion & random shares. Experiments confirm that all meaningful shares fulfill the contrast and security conditions. Secret images can be easily decoded by only human visual system without any computation at receiver end.