On general construction for extended visual cryptography schemes

Multi-pixel encoding is an emerging method in visual cryptography for that it can encode more than one pixel for each encoding run. Nevertheless, in fact its encoding efficiency is still low because of that the encoding length is invariable and very small for each run. This paper presents a novel multi-pixel encoding called pixel-block aware encoding. It scans the secret image by zigzag and perceives a pixel block with as many pixels as possible to encode for each run. A pixel-block consists of consecutive pixels of same type during the scanning. The proposed scheme has advantage in encoding efficiency over singlepixel encoding and other known multi-pixel encoding methods. Furthermore, this scheme can work well for both threshold access structure and general access structure and well for both gray-scale and chromatic images without pixel expansion. The experimental results also show that it can achieve good quality for overlapped images.

Visual Cryptography for General Access Structure Using Pixel-block Aware Encoding

In this paper, we consider a new visual cryptography scheme that allows for sharing of multiple secret images on graphs: we are given an arbitrary graph (V,E) where every node and every edge are assigned an arbitrary image. Images on the vertices are "public" and images on the edges are "secret". The problem that we are considering is how to make a construction such that when the encoded images of two adjacent vertices are printed on transparencies and overlapped, the secret image corresponding to the edge is revealed. We define the most stringent security guarantees for this problem (perfect secrecy) and show a general construction for all graphs where the cost (in terms of pixel expansion and contrast of the images) is proportional to the chromatic number of the cube of the underlying graph. For the case of bounded degree graphs, this gives us constant-factor pixel expansion and contrast. This compares favorably to previous works, where pixel expansion and contrast are proportional to the number of images.

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Visual cryptography on graphs

Multi-pixel encoding is an emerging method in visual cryptography for that it can encode more than one pixel for each run. However, in fact its encoding efficiency is still low. This paper presents a novel multi-pixel encoding which can encode variable number of pixels for each run. The length of encoding at one run is equal to the number of the consecutive same pixels met during scanning the secret image. The proposed scheme can work well for general access structure and chromatic images without pixel expansion. The experimental results also show that it can achieve high efficiency for encoding and good quality for overlapped images.

Visual Cryptography for General Access Structure by Multi-pixel Encoding with Variable Block Size

A visual cryptography scheme (VCS) for general access structures is a method to encode a secret image into n shares for n participants. Only qualified subsets of participants can recover the secret image. The yet known schemes omitted the deference between primary information and secondary one in secret image, and its best known upper bound on the share size is exponential. Besides its information communication rate is high. This paper proposes a new VCS for general access structures using pi-sigma neural networks (VCSPSN). A pi-sigma neural network (PSN) is a class of two-layer feedforward net-work. Compared to other high-order networks, a PSN has a highly regular structure, needs a much smaller number of weights and less training time. Using PSN's capability of large-scale parallel classification, VCSPSN reduces the information communication rate greatly, makes best known upper bound polynomial, and distinguishes the deferent information in secret image. This paper firstly introduces the structure of PSN, and then constructs the VCSPSN and analysis its security and capability.

Visual Cryptography Scheme Using Pi-sigma Neural Networks

In the proposed visual cryptography schemes for general access structures, the single secret image black-and-white visual cryptography schemes with meaningful shares have been constructed, in which the shares are innocent looking images. The meaningful shares have not been realized in single secret image color schemes; neither have the multi secret images color schemes. In this paper, the multi secret images color visual cryptography schemes for general access structures with meaningful shares are constructed by the method of matrix concatenation, the pixel expansion is obtained, and the validity of the scheme is proven. In our scheme, the different combination of meaningful color shares can be used to recover distinct color secret images. The multi secret images black-and-white visual cryptography scheme is a special case of our color scheme. *Supported by National Natural Science Foundation of China (Grant No. 90304014) and the Major State Basic Research Development Program of China (Grant No. ...

Multi secret image color visual cryptography schemes for general access structures

Visual secret sharing scheme (VSSS) is a secret sharing method which decodes the secret by using the contrast ability of the human visual system. Autostereogram is a single two dimensional (2D) image which becomes a virtual three dimensional (3D) image when viewed with proper eye convergence or divergence. Combing the two technologies via human vision, this paper presents a new visual secret sharing scheme called (k, n)-VSSS with autostereogram. In the scheme, each of the shares is an autostereogram. Stacking any k shares, the secret image is recovered visually without any equipment, but no secret information is obtained with less than k shares.

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Feng Yi

Papers

Multi secret image color visual cryptography schemes for general access structures

Visual secret sharing scheme with autostereogram.