Novel basis matrix creation and preprocessing algorithms for friendly progressive visual secret sharing with space-efficient shares

Abstract

The traditional k out of n Visual Secret Sharing (VSS) scheme encodes a secret binary image into n shares of random pattern. If the shares are printed onto transparencies, the secret image can be visually revealed only when a subset of k or more transparencies are stacked together otherwise nothing will be revealed. Progressive Visual Secret Sharing (PVSS) also allows the decryption of secret image by stacking of physical transparencies but clarity and contrast of the decoded secret image will be increased progressively with the number of stacked shares. Most of the existing researches on PVSS suffer with the common problems like space-inefficiency(pixel expansion) and noise-like shares. This paper proposes a novel PVSS scheme with four or more number of space-efficient as well as meaningful shares. To achieve this, an efficient preprocessing approach and a basis matrix creation algorithm have also been proposed. This paper also addresses many avoidable encryption limitations like explicit requirement of codebook, restriction on number of shares etc. Experiments show that the contrast of reconstructed secret image is 50% and can be easily decrypted by only human visual system without any cryptographic computation.