Visual cryptography

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

Random grid-based threshold visual secret sharing with improved visual quality and lossless recovery ability

Abstract: Visual secret sharing (VSS) by random grids (RG) has gained much attention since it avoids the pixel expansion problem as well as requires no basic matrixes design. However, most of the previous RG-based threshold VSS still suffer from low visual quality or worse reconstructed secrets when more shadows are stacked. In this paper, a new RG-based threshold VSS with improved visual quality and lossless recovery ability is proposed. The random bits are utilized to improve the visual quality as well as to decrease the darkness of the reconstructed secret image. And the secret image can be losslessly recovered in the proposed scheme if the computational device is available. Simulation results and analyzes show the effectiveness of the proposed scheme. In addition, this paper gave the preliminary definition and evaluation of progressive secret sharing (PSS) based on mathematical differential and expectations.

Enhanced password processing scheme based on visual cryptography and OCR

Abstract: Traditional password conversion scheme for user authentication is to transform the passwords into hash values. These hash-based password schemes are comparatively simple and fast because those are based on text and famed cryptography. However, those can be exposed to cyber-attacks utilizing password by cracking tool or hash-cracking online sites. Attackers can thoroughly figure out an original password from hash value when that is relatively simple and plain. As a result, many hacking accidents have been happened predominantly in systems adopting those hash-based schemes. In this work, we suggest enhanced password processing scheme based on image using visual cryptography (VC). Different from the traditional scheme based on hash and text, our scheme transforms a user ID of text type to two images encrypted by VC. The user should make two images consisted of subpixels by random function with SEED which includes personal information. The server only has user's ID and one of the images instead of password. When the user logs in and sends another image, the server can extract ID by utilizing OCR (Optical Character Recognition). As a result, it can authenticate user by comparing extracted ID with the saved one. Our proposal has lower computation, prevents cyber-attack aimed at hash-cracking, and supports authentication not to expose personal information such as ID to attackers.

General construction for XOR-based visual cryptography and its extended capability

Abstract: A visual cryptography scheme (VCS) can be realized by Boolean operations OR and XOR, respectively. The monotone property of OR operation reduces the visual quality of recovered image. To overcome this problem, some advanced XOR based VCSs (VCSXOR) were further designed to provide some favorable features such as high contrast and good resolution. However, they are all confined to non-strong access structures. In this paper, we focus on strong access structures and propose a general construction of VCSXOR, which provides flexible sharing strategies, perfect reconstruction of secret image. Furthermore, a new region incrementing VCS based on XOR (RIVCSXOR) is presented, which exploits the proposed VCSXOR. Experimental results show that our schemes further enrich the application scenarios and outperform previous schemes significantly.

Efficient Visual Cryptography

Abstract: Visual cryptography scheme (VCS) is a secret- sharing scheme which allows the encryption of a secret image into n shares that are distributed to n participants. The beauty of such a scheme is that, the decryption of the secret image requires neither the knowledge of cryptography nor complex computation. Colour visual cryptography becomes an interesting research topic after the formal introduction of visual cryptography by Naor and Shamir in 1995. It is a powerful technique which combines the notions of perfect ciphers and secret sharing in cryptography with that of raster graphics. A binary image can be divided into shares which can be stacked together to approximately recover the original image. Unfortunately, it has not been used much primarily because the decryption process entails a severe degradation in image quality in terms of loss of resolution and contrast. Its usage is also hampered by the lack of proper techniques for handling grayscale and color images. In this paper, I have developed a novel technique which enables visual cryptography of color as well as grayscale images. The physical transparency stacking type of decryption allows for the recovery of the traditional visual cryptography quality image. An enhanced stacking technique allows for the decryption into a halftone quality image. And finally, a computation based decryption scheme makes the perfect recovery of the original image possible. Based on this basic scheme, I have then established a progressive mechanism to share color images at multiple resolutions. I extracted shares from each resolution layer to construct a hierarchical structure; the images of different resolutions can then be restored by stacking the different shared images together. I have implemented our technique and present results.

An (3, 3)-Visual Secret Sharing Scheme for Hiding Three Secret Data

Abstract: Visual cryptography is one kind of image encrypting. It is different from traditional cryptography, because it does not need complex computation to decrypt. In current technology, most of visual cryptography are embedded a secret using two shares is limited. This paper proposes a new approach of (3, 3)visual secret sharing scheme to embed more information and have more secure than traditional visual cryptography.