Ran-Zan Wang

Sharing multiple secrets in visual cryptography

The secret sharing schemes in conventional visual cryptography are characterized by encoding one shared secret into a set of random transparencies which reveal the secret to the human visual system when they are superimposed. In this paper, we propose a visual secret sharing scheme that encodes a set of x≥2 secrets into two circle shares such that none of any single share leaks the secrets and the x secrets can be obtained one by one by stacking the first share and the rotated second shares with x different rotation angles. This is the first true result that discusses the sharing ability in visual cryptography up to any general number of multiple secrets in two circle shares.

Scalable secret image sharing

In this paper, we propose an innovative scheme, namely the scalable secret image sharing scheme, for sharing an image O among n participants such that the clarity of the reconstructed image (i.e., the amount of information therein) scales with proportion with the number of the participants. The proposed scheme encodes O into n shadow images that exhibit the following features: (a) each shadow image reveals no information about O, (b) each shadow image is only half the size of O, (c) any k (2=

An image-hiding method with high hiding capacity based on best-block matching and k-means clustering

This paper presents a novel image-hiding method that exhibits a high hiding capacity that allows the embedded important image to be larger than the cover image, a facility that is seldom described in the literature. In the proposed method, the entire important image is divided into many nonoverlapping blocks. For each block of the important image, a block-matching procedure is used to search for the best similar block from a series of numbered candidate blocks. The obtained indices of the best-matching blocks are encoded using Huffman coding scheme, and then recorded in the least-significant-bit planes of the cover image through a monoalphabetic transposition cipher. The proposed method exhibits the following advantages over existing methods: (1) a high hiding capacity such that the embedded important image can be larger than the cover image; (2) a stego-image with a high quality, which improves the secrecy of the hidden image; and (3) a small error between the extracted important image and the original important image indicating that the extracted important image is of acceptable quality.

An Advanced Least-Significant-Bit Embedding Scheme for Steganographic Encoding

The advantages of Least-Significant-Bit (LSB) steganographic data embedding are that it is simple to understand, easy to implement, and it results in stego-images that contain hidden data yet appear to be of high visual fidelity. However, it can be shown that under certain conditions, LSB embedding is not secure at all. The fatal drawback of LSB embedding is the existence of detectable artifacts in the form of pairs of values (PoVs). The goals of this paper are to present a theoretic analysis of PoVs and to propose an advanced LSB embedding scheme that possesses the advantages of LSB embedding suggested above, but which also provides an additional level of communication security. The proposed scheme breaks the regular pattern of PoVs in the histogram domain, increasing the difficulty of steganalysis and thereby raising the level of security. The experimental results show that both the Chi-square index and RS index are less than 0.1, i.e., the hidden message is undetectable by the well-known Chi-square and RS steganalysis attacks.

Prevention of cheating in visual cryptography by using coherent patterns

A new VC scheme with cheating-prevention ability is proposed.It reveals solid pattern with moderate-scale on partial-superimposed image.The proposed method verifies shares without any additional authentication shares.The proposed method endows conventional VC with cheating-prevention ability. This paper proposes a simple method for establishing a visual cryptographic (VC) scheme with the ability to prevent cheating. Given the n base-shares generated in a conventional (t,n), 2≤t≤n, VC scheme, an authentication pattern stamping process was designed to encode the n base-shares to get n verifiable shares that exhibit the following properties: (1) knowledge of less than t verifiable-shares gets no secret information, (2) the secret can be revealed by completely superimposing t or more verifiable-shares, and (3) the authentication pattern can be revealed by partially superimposing any pair of verifiable-shares. Theoretical proof and computer simulation for the proposed method are provided. The proposed method has smaller pixel expansion than previous cheating prevention VC schemes, and the verification process is fulfilled without resorting to any additional dedicated verification share. It can be attached easily to any reported VC scheme to endow legitimate users with the capability of detecting faked shares provided by malicious participants.

A Vision-Based Augmented-Reality System For Multiuser Collaborative Environments

This work presented a novel vision-based augmented-reality system for applications in multiuser collaborative environments. The kernel technology of this vision-based system locates the cameras that are utilized to point and simulate the positions of multiple viewers. Camera calibration based on computer vision is employed during the cameras locating process. The applications in multiuser collaborative environments allow the viewers to view various positions and in numerous directions. However, traditional calibration approaches are not suitable for these cases sufficiently. A novel calibration pattern based on pseudo-random arrays is designed for multiuser collaborative applications. The pattern has a simple and regular structure, easily extracts features, achieves robust recognition using local information, and does not limit viewer positions and directions. Experimental results indicate that the proposed system provides a effective platform for applications in multiuser collaborative environments.

High-Payload Image Hiding Scheme Using k-Way Block Matching

This paper proposes a high-payload image hiding scheme using k-way block matching. The method divides the important image into multiple non-overlapping blocks. For each block, a k-way block matching procedure is designed to search for the most similar block from k (k_ 2) sets of 2n candidate blocks. By carefully applying a k-base modulus operation to evaluate k [base, difference] mappings for a block, the proposed scheme enlarges the searching space of an n-bit index to k_2n candidate blocks, which reduces the quantity of data should be recorded, hence increases the quality of the embedding results. Experimental results show that the qualities of the obtained stego-image and the extracted image are better than those reported in previous block-matching-based image steganography schemes.

Verifiable Visual Cryptography

The paper presents a verifiable visual cryptography (VC) scheme for checking the validness to the shares engaged in a VC decoding instance. The idea is to stamp a continuous pattern on the shares belonging to the same secret image, and a part of the pattern can be revealed through aligning and stacking half of two shares together. The visual coherent among the revealed patterns of all pair of shares provides evidence to the genuine of the shares engaged in the decoding process. Compare to the reported cheating prevention VC schemes, the proposed scheme maintains the original pixel expansion in VC scheme without cheating prevention ability, and the share verification process is done without resorting to any additional verification image. Besides, the proposed verification mechanism can easily be attached to any VC schemes in the literature to endow legitimate user with the ability to prevent cheating from malicious participants.

Improved Invertible Secret Image Sharing with Steganography

In 2010, Lin and Chan proposed an invertible secret image sharing with steganography scheme, in which each generated shadow image has natural appearance that conceals the track of the shared secret image elaborately. The method not only can reconstruct the secret image loss less but also can change the distorted cover image back to its origin version. It is practical for fulfilling image sharing with steganography scheme where the cover image is sensitive to alterations. However, the scheme suffers from an overflow problem in the case of embedding data in pixels with value greater than or equal to floor(2^k/p)¡Ñp in a k-bit cover image, where p is a prime number set in the sharing function, and some secret patterns were leaked from a single shadow image. In this paper an improved method of Lin and Chan¡¦s invertible secret image sharing scheme is proposed. The scheme divides the input secret image into multiple sections with each section fits in an alpha-bit space, the sharing function is carefully designed to conceal the statistical property of the secret image properly, and all arithmetic operations are performed in power-of-two Galois Field GF(2^alpha). Experimental results show that the proposed scheme obtains better quality of shadow images, and the security property to the secret image is improved.

Rendering 3D Solid Model

A method of filling 3D model using generated solid textures is proposed. Using 3D texture synthesis, a 2D exemplar texture is synthesized to be a solid texture. The synthesized solid texture can be the stuffed material of 3D Solid model or the solid material of surficial mesh. The proposed method designs two algorithms to cutting the model. After cutting, we will repair the cross section. It makes the surface model look like the solid model. And it is real time display when cutting. Because, we can preview the 3D model and it internal cross section before printing, the application can also be combined with 3D printing.