Visual cryptography

About: Visual cryptography is a research topic. Over the lifetime, 1724 publications have been published within this topic receiving 25300 citations.

Lower Bound for Visual Cryptography Schemes

Abstract: A visual cryptography scheme is a method to secretly share an image among a given group of participants. In this paper, we investigate the best pixel expansion of different models of visual cryptography schemes. In this regard, we consider visual cryptography schemes satisfying the model introduced by Tzeng and Hu [13]. In such a model the recovered secret image can be darker or lighter than the background. Blundo et al. [4] introduced a lower bound for the best pixel expansion of this scheme in terms of minimal qualified subsets. We present another lower bound for the best pixel expansion of the scheme. As a corollary, we introduce a lower bound based on an induced matching of hypergraph of qualified sets. Finally, we study access structures based on graphs and we present an upper bound for the smallest pixel expansion in terms of strong chromatic index.

Dynamic visual cryptography scheme on the surface of a vibrating structure

Abstract: Dynamic visual cryptography scheme based on time-averaged fringes generated by Ronchi-type geometric moire gratings on finite element grids is proposed in this paper. A single cover image is used to encode the secret image and is formed on the surface of a deformable structure. Time-averaged moire fringes leak the secret when the structure is oscillated according to a predefined Eigen-shape. The envelope functions determining the motion induced blur of the Ronchi-type moire grating depend on the characteristic features of the motion. And though harmonic oscillations do not result into a completely uniform time-averaged image of the Ronchi-moire grating, initial phase scrambling and phase normalization algorithms are used to encode the secret in the cover image. Theoretical relationships between the amplitude of the Eigen-shape, the order of the not completely developed time-averaged fringe and the pitch of the deformable one-dimensional Ronchi-type moire grating are derived.

A Probabilistic Model of Visual Cryptography Using Halftoned Technique for Color Image

Abstract: Visual Cryptography is a special type of encryption technique which is used to hide the information and data in images. In this technique the decryption process is done without any complex cryptographic computation. The encrypted data is decrypted using Human Visual System (HVS). This is the benefit of the visual secret sharing scheme. The encryption technique requires a cryptographic computation to divide the image into a number of parts or we can call it shares. We divide the image into n number of shares. In this paper we proposed a new secret sharing VC scheme for taking two images one is black and white image with size of 127x261 and other is color image with size of 196x92.In contrast with the previous color visual cryptography schemes, the proposed one enables to share images without pixel expansion and to detect a forgery as the color of the message is kept secret. In order to correctly print the colors on the media and to increase the security of the scheme, we use spectral models developed for color reproduction describing printed colors from an optical point of view.

Using Color Visual Cryptography Schemes and Watermarking for Sharing Black and White Secret Images

Abstract: Visual cryptography is a new secure technology that distributes a secret image by separating it into a number of shares using different visual cryptography schemes (VCS). Early VCS schemes mainly focused on black-and-white secret images. Using a black & white VCS normally degrade the image quality and also suffered from a major drawback of pixel expansion, which means that the size of each secret share is several times larger than that of the original image. The black & white VCS were extended to the colour VCS. The main problem with the colour VCS is larger pixel expansion when number of colours increases. So in order to avoid these drawbacks a scheme called Black&White-Colour Visual Cryptography Scheme (B&W-C VCS) is used here. This scheme exploits the colour model to split a b & w image into coloured shares using a smaller pixel expansion and improved contrast. For any of the VCS, the main issue to be considered is authentication, i.e., there are no means by which one can ensure that the secret recovered is genuine. It would be advantageous to check the fidelity of the shares before they are used to reconstruct the secret. For this purpose, this paper proposes a watermark method to authenticate coloured shares thereby ensuring a successful secret recovery. Unlike other watermarking techniques, the pattern is not directly embedded into the share, but an authentication matrix is generated which checks the authenticity of the shares before they are used for secret recovery.

An Ethnography Survey on Visual Cryptography Schemes

Abstract: Visual Cryptography Scheme (VCS) is an encryption method that uses combinatorial techniques to encode secret written materials. The idea is to convert the written material into an image and encode this image into n shadow images. The decoding only requires only selecting some subset of these n images, making transparencies of them, and stacking them on top of each other. In this survey paper, we will provide the readers an overview of the basic VCS constructions, as well as several extended work in the area. In addition, we also review several state-of-art applications that take full advantage of such simple yet secure scheme..