User-Friendly Random-Grid-based Visual Secret Sharing For General Access Structures

The range of digital images and the Internet are becoming more and more widely and the protection of images is becoming more and more important and getting more and more attention. Visual secret sharing(VSS), an application of the secret sharing scheme in the image field. And it is an effective way to protect a secret image during its storage, transmission and protection. It is such a technology that a secret image is transformed into multiple meaningless shares in the encryption stage, so that the secret image can be recovered with a certain set of shares in the recovery phase and we can not see the secret image with a uncertain set of shares. Therefore, it is an effective method to ensure the security of the secret image during storage or transmission, especially in the fields of military, commercial, financial, etc.In the field of visual secret sharing, there are some hot issues now. A conventional visual-cryptography-based visual secret sharing scheme has some drawbacks, such as the pixel expansion and the requirement of predetermined sophisticated codebooks. Besides, most of the existing publications about the VSS scheme only deal with the threshold access structures, but there is hardly any appropriate method to construct the RGVSS scheme for general access structures(GASs), and the low constraint ability of the share is one of the research focuses. While most of the shares of the existing publications are meaningless, the data management problem makes some troubles to participants. When a participant manages many shares of the different secret images, and the defect is more obvious and it is very difficult to distinguish every share. So design a novel method the about the user friendly RGVSS scheme for GASs is very important, in which the resulting shares can be any meaningful gray scale images.To above-mentioned problem, a novel method to construct a generalized RGVSS(GRGVSS) scheme for GASs is first proposed in our paper. The construction algorithm consists of two parts. In the first part, a more general(n, n)-threshold GRGVSS scheme is proposed; in addition, the visual quality of the reconstructed secret image for this GRGVSS scheme is formally proof and analyzed. In the second part, we utilize this(n, n)-GRGVSS to construct the GRGVSS scheme for GASs by treating the procedure as a nonlinear 0-1 programming model. In the experimental phase, by changing the givenpreconditions, we analyze the security of the proposed scheme and assess the visual quality of the recovered secret images for the proposed scheme under different situations. The simulation results proof that the proposed GRGVSS scheme for GASs is efficient and feasible.Another one of the innovation points of this paper, a novel method also was proposed to design the UFRGVSS scheme for GASs, in which the resulting shares can be any meaningful gray scale images. We use the histogram depth-equalization method and by properly transforming the dithering matrix generation method combining it with the patterning dithering halftone technique to handle the cover gray scale images, and make the shares of the gray scale image are meaningful. By combining with the proposed GASs scheme, we can achieve the final user friendly shares. Also the final shares and the reconstructed secret image have the high visual quality. Experimental results show the feasibility of the proposed method by assessing its performance under different situations. And our scheme maybe the first attempt to construct the UFRGVSS scheme for GASs.In conclusion, our paper mainly proposed a user-friendly random-grid-based visual secret sharing for general access structures scheme. The main advantages of the proposed scheme are improving the safety of shares and facilitate the management of the managers.