Visual cryptography is an encryption technique that decomposes secret images into multiple shares. These shares are digitally or physically overlapped to recover the original image, negating the need for complex mathematical operations or additional hardware. There have been many variations of visual cryptography proposed over the years, each addressing different problems or to fulfill different security requirements. Existing review papers on the area only cover certain types of visual cryptography or lack comparisons between the various schemes. To address this gap, this paper provides broad overview of the area to aid new researchers in identifying research problems or to select suitable visual cryptography methods for their desired applications. For more veteran researchers in the area, our paper provides the most up-to-date coverage of the state-of-the-art. We first provide an introduction to the various categories of visual cryptography techniques, including a discussion on recently proposed schemes. These schemes are then compared in terms of their features, performance metrics, advantages and disadvantages. Compared to prior work, we extend the number of comparison metrics to include signal-to-noise ratio and the type of shares. Over 40 visual cryptography schemes that have been proposed in the past two decades were analyzed and compared. Our findings indicate that existing problems such as pixel expansion, poor quality of recovered image quality, computational and memory complexities still exist, and a optimizing the trade-off between these requirements still requires further investigation. We conclude the paper with a discussion of these open problems and future research directions.

An overview of visual cryptography techniques

For preserving the security of data there has been tremendous research areas evolved and explored since few years. Cryptography is seen to be the dominant strategy in the information security domain. To differentiate security of multimediadata, visual cryptography is seen as the prominent way for data confidentiality and secrecy of information being distributed. The mechanism of visual cryptography is widely used approach which encrypts the secrete image into the many meaningless share images and decodes by stacking some or all shares by human visual system. There are many methods presented for visual cryptography with their own advantages and disadvantages.. Over the years , in visual cryptography the scope of research mainly focused on developing techniques on grayscale , halftone , color visual cryptography, region incrementing visual cryptography, minimization of pixel expansion , multiple secret sharing and cheating prevention in visual cryptography. Recently new cheating–preventing scheme has been found whichis advantageous over a combined approach of two general VC codebooks. This method resulted into number of advantages such as computation cost is low; multi factor cheating detection is involved etc. However, we identified two research problems such as 1) there is no efficient generic method of generating (k,n) codebooks with minimizing the pixel expansion, 2) it is impractical and time-consuming to stack three or four shares. Therefore in this project our aim is to extend this hybrid codebook based method with goal of overcoming above two listed limitations. We are presenting the efficient approach for codebooks generation with less timing consuming while decryption. Keywords—Contrast,Share,Stacking,Pixel expansion.

Cheating Prevention in Visual Cryptography : A survey

Cryptographic technique has become an important field of study in modern cryptography. Visual cryptography (VC) has quite a few applications and some of them are authentication and identification, steganography, and image encryption. As the era demands the need of security and Visual Secret Sharing to resist cheating scenario is a Visual Cryptographic technique. VSS is simple as it is easily detectable by human visual system. A secret image sharing scheme is used for identifying the existence of cheater. The use of verifiable scheme leads helps find the presence of a cheater. The problem of cheating prevention exists and researchers have proposed scheme like Cheating-prevention visual secret-sharing (CPVSS) schemes. This paper is based on the study of the cheating prevention happening in Visual Cryptography.

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A Survey on Cheating Prevention with Verifiable Scheme

In this paper, we propose an (n, n) threshold visual cryptography scheme for cheating prevention to improve the generic transformation for cheating prevention scheme (GTCP). We analysis the cheating problem in the GTCP, and present the cheating method applied it to attack on the GTCP. Then we construct the matrices for cheating prevention with following features: (a) each participant can't gain any useful information from his shares, (b) each pixel has the same number of black and white subpixels in the secret share and in the verification share, (c) one's verification image will be recovered by stacking of his verification share and the secret share, (d) the secret image can be revealed by stacking all the secret shares. The analysis showed that our scheme can avoid cheating.

Wen-Fang Peng

Papers

An (n, n) threshold visual cryptography scheme for cheating prevention