Visual cryptography

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

Visual document authentication using human-recognizable watermarks

Abstract: Digital signatures and message authentication codes are well known methods for ensuring message integrity. However, they rely on computations which are too hard to be performed by humans and are instead done on computers. Trusting a digital signature implies trusting the computer which produced/checked it. Often, this trust cannot be taken for granted. This paper presents a method for visual authentication of large messages which relies on embedding a human-recognizable watermark and needs practically no computational power on the receiver side. Also, using a simple challenge-response mechanism is proposed to prevent attackers from obtaining signatures without author's knowledge.

Magic sheets: Visual cryptography with common shares

Abstract: Visual cryptography (VC) is an encryption technique for hiding a secret image in distributed and shared images (referred to as shares). VC schemes are employed to encrypt multiple images as meaningless, noisy patterns or meaningful images. However, decrypting multiple secret images using a unique share is difficult with traditional VC. We propose an approach to hide multiple images in meaningful shares. We can decrypt multiple images simultaneously using a common share, which we refer to as a magic sheet. The magic sheet decrypts multiple secret images depending on a given share. The shares are printed on transparencies, and decryption is performed by physically superimposing the transparencies. We evaluate the proposed method using binary, grayscale, and color images.

Evaluation Criteria for Visual Cryptography Schemes via Neural Networks

Abstract: Visual cryptography schemes are developed for image security, where encryption is realized by distributing a secret image into shares and decryption is done only by stacking the shares. Human eyesight is usually used to evaluate the security and performance of visual cryptography schemes. However, objective criteria for visual cryptography schemes are not yet established. In this paper, by the aid of neural networks, we propose two criteria called encryption-inconsistency and decryption-consistency for evaluating the shares and the recovered images, respectively. We also implemented the experiments for two representatives of visual cryptography schemes by applying three popular convolutional neural networks (CNN) to adopt our proposed criteria.

Block Based Symmetry Key Visual Cryptography

Abstract: Visual cryptography is a method for protecting image-based secrets that has a computation- free decoding process. In this technique, numbers of shares have been generated from one image. The shares are sent through any channel to the receiver and the receiver can again produce original image by stacking all the shares in proper order. But, this method wastes a lot of bandwidth of the network. The techniques of generating shares have been used in several existing methods which are not unique. The different methods have been used in different types of images like binary, gray and color images. In this paper, a block based symmetry key visual cryptography algorithm has been proposed to convert image in encrypted form and decrypt the encrypted image into original form. The symmetric key has been generated from a real number. The encryption and decryption algorithm have been designed based on symmetry key. The algorithm with key has been used to encrypt image into single share and decrypt the single share into original image. The real number has been used to form the key may be predefined or may be sent by secure channel to the receiver. The proposed algorithm can be applied to any type images i.e. binary, gray scale and color images. A comparison has been made of the proposed algorithm with different existing algorithms like Ceaser cipher, transpose of matrix, bit comp, and transposition cipher based on the performance. The pixels distributed in original and share images have also been tested. Finally, it has shown that breaking of security level of proposed algorithm i.e. to guess the real number is huge time consuming.

A novel cryptographic technique that emphasis visual quality and efficieny by floyd steinberg error diffusion method

Abstract: Visual cryptography is a cryptographic technique which allows visual information to be encrypted in such a way that decryption becomes a mechanical operation that does not require a computer. The original image can be split into shares, where unauthorized person cannot get the data which we hide within that share images. By stacking the two shares, the secret data can be revealed. The highlighted issue in VC is, the size and quality of the reconstructed image should be same as the original image. In this paper, a novel k out of k extended visual cryptography scheme (EVCS) is used, to improve security and to produce meaningful shares. Halftone visual cryptography (VC) encodes a secret image into k halftone meaningful image shares through Floyd Steinberg error diffusion algorithm. The algorithm achieves dithering using error diffusion, meaning it pushes (adds) the residual quantization error of a pixel onto its neighboring pixels, to be dealt with later. This algorithm takes a substantial time for encryption and decryption in a considerably calmer manner. Comparisons with previous approaches show the superior performance of the new method.