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

1Department of Applied Informatics and Multimedia, Asia University, Lioufeng Rd., Wufeng, Taichung, Taiwan, Republic of China 2Department of Medical Research , China Medical University Hospital , China Medical University Taichung, Taiwan, Republic of China 3Department of Industrial Education and Technology, National Changhua University of Education, No.1, Jin-De Road, Changhua City, Taiwan, Republic of China 4Department of Information and Communication Engineering, Chaoyang University of Technology, Jifeng E. Rd., Wufeng District, Taichung, Taiwan, Republic of China ∗Corresponding author: tychang@cc.ncue.edu.tw

Meaningful Share Generation for (2, 2)-Multiple Visual Secret Sharing Scheme Without Pixel Expansion

1 PG Student, 2 HOD & Asst. Professor, 3 Asst. Professor Dept. of CSE, Priyadarshini Bhagwati College of Engineering, Nagpur, India megha.bgoel@gmail.com, manojchaudhary2@gmail.com , shweta_amt80@rediffmail.com ________________________________________________________________________________________________________ Abstract— Steganography is the art & science of hiding data in the images. From thousands of year, our ancestors have invented various ways to pass information in hidden form from one place to another place. For eg. Papyrus scroll, cryptex, invisible ink, tattooing, pencil marks on handwritten characters etc. Cryptography is a technique which converts the data or simple text into an unreadable form. Visual cryptography schemes hide the secret image into two or more images which are called shares. It is different from the traditional cryptography, because for decrypting the secret image, it does not need any complex computation. The secret image can be decrypted or recovered when all the shares are stacked together. The advantage of visual cryptography is that if any one captures a share then single share would not reveal anything about the data. In this paper, we discuss about various visual cryptographic schemes based on share generated is meaningful or meaningless, type of secret images (either binary or color) and number of secret images (either single or multiple) encrypted by the various visual cryptography scheme. Also this paper proposed a new way for hiding data in images by combining steganography & visual cryptography.

A Review on Data Hididng using Steganography & Visual Cryptography

A description and comparison of three visual extended cryptography algorithms is presented. Currently these methods are often used as a basis for developing more complex schemes. Results related to overlapping shades, pixel expansion, quality of images and shades, and the number of coded images are obtained. In conventional visual cryptography a secret image is encrypted into a set of images that look like random-noise and are distributed to each participant of the scheme. To obtain the secret image the images received must be super-imposed. .In the extended visual cryptography the shades are visually recognizable images. It is concluded that the three methods present particular advantages depending on the application.

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Comparación entre Varios Esquemas de Criptografía Visual Extendida

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

In the traditional visual cryptography schemes, only one piece of image was encoded during encryption. And each of the shares that are generated was shown as a disorganized image. Due to the capacity of encrypted information, these schemes have few applications and because of the disorganized image share, they are easily suspected by hacker. In order to solve these problems, an Extended Visual Cryptography Scheme with multiple secrets hidden is proposed. Meaningful shares are generated by utilizing the principle of contrast and multiple secret images may be hidden by changing the overlapping angle of the shares. The scheme may also apply to color image which has been processed by halftone technology. The scheme is easy and effective and the shares also have sufficient security level.

An Extended Color Visual Cryptography Scheme with Multiple Secrets Hidden

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.

Qin Chen

Papers

An Extended Color Visual Cryptography Scheme with Multiple Secrets Hidden

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