Visual cryptography

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

Visual Cryptography and Random Grids Schemes

Abstract: Visual Cryptography (VC) and Random Grids (RG) are both visual secret sharing (VSS) techniques, which decode the secret by stacking some authorized shares. It is claimed that RG scheme benefits more than VC scheme in terms of removing the problems of pixel expansion, tailor-made codebook design, and aspect ratio change. However, we find that the encryption rules of RGS are actually the matrices sets of probabilistic VCS. The transformation from RGS to PVCS is proved and shown by means of giving theoretical analysis and conducting some specific schemes. The relationship between codebook and computational complexity are analyzed for PVCS and RGS. Furthermore, the contrast of PVCS is no less than the one of RGS under the same access structure, which is shown by experimental results.

Efficient Construction for Region Incrementing Visual Cryptography

Abstract: A region incrementing visual cryptography scheme (RIVCS) deals with the sharing of an image consisting of multiple regions with different secrecy levels, which can be incrementally revealed as the number of shares increases. The encoding basis matrices of RIVCS for an image containing three to five regions have been reported in the literature, but no construction method has ever been studied. We develop a novel and efficient construction for RIVCS using linear programming in this paper. The proposed integer linear program aims at the minimization of the pixel expansion under the constraints for being a RIVCS. Experimental results demonstrate the feasibility, applicability, and flexibility of our construction. The pixel expansions and contrasts derived from our scheme are also better than the previous results.

Progressive (k,n) secret image sharing schemes based on Boolean operations and covering codes

Abstract: ( k , n ) progressive secret image sharing (PSIS) schemes were discussed frequently in recent years. A ( k , n ) PSIS scheme consists of sharing phase and reconstruction phase. During sharing phase, a secret image is encrypted into n image-shadows; while during reconstruction phase, k to n image-shadows can progressively recover the image; fewer than k image-shadows get no information on the image. Most previous PSIS schemes can be divided into two categories, polynomial based PSIS schemes and visual cryptography based PSIS schemes. Polynomial based schemes can recover high quality image with complicated cryptographic computations; visual cryptography based PSIS schemes can reconstruct image using human visual system without any cryptographic computation, however, the size of image shadow expands largely from the image and the recovered image is quality-distortion. The motivation of this work is to solving the problems in existing PSIS schemes. Thus, in this paper, we adopt three Boolean operations: bit-level XOR, C O V ( 1 , 7 , 3 ) from ( 7 , 4 ) Hamming code and C O V ( 2 , 8 , 4 ) from ( 8 , 4 ) shortened Hamming code to propose three ( k , n ) PSIS schemes. In our schemes, k to n image-shadows can decrypt randomly partial pixels on entire image, and reconstruct image progressively. Comparing with previous PSIS schemes, our schemes has smaller image-shadow size and higher quality of recovered image than visual cryptography based PSIS schemes. On the other hand, our schemes has much more efficient operations in sharing procedure and image reconstruction procedure than polynomial based PSIS schemes.

Recursive Visual Cryptography Using Random Basis Column Pixel Expansion

Abstract: In this paper we present a new method for a visual cryptography scheme that uses random basis column pixel expansion technique. This method encoded the secret image into 'n' share images in a recursive manner, which have dimensions identical to the secret image. In this scheme, the encoded n shares further encoded into number of subshares recursively. It will increase the level of security of the encrypted message.

Secure and Efficient Medical Image Transmission by New Tailored Visual Cryptography Scheme with LS Compressions

Abstract: Exchanging a medical image via network from one place to another place or storing a medical image in a particular place in a secure manner has become a challenge. To overwhelm this, secure medical image Lossless Compression LC schemes have been proposed. The original input grayscale medical images are encrypted by Tailored Visual Cryptography Encryption Process TVCE which is a proposed encryption system. To generate these encrypted images, four types of processes are adopted which play a vital role. These processes are Splitting Process, Converting Process, Pixel Process and Merging process. The encrypted medical image is compressed by proposed compression algorithms, i.e Pixel Block Short algorithm PBSA and one conventional Lossless Compression LC algorithm has been adopted JPEG 2000LS. The above two compression methods are used to separate compression for encrypted medical images. And also, decompressions have been done in a separate manner. The encrypted output image which is generated from decompression of the proposed compression algorithm, JPEG 2000LS are decrypted by the Tailored Visual Cryptography Decryption Process TVCD. To decrypt the encrypted grayscale medical images, four types of processes are involved. These processes are Segregation Process, Inverse Pixel Process, 8-Bit into Decimal Conversion Process and Amalgamate Process. However, this paper is focused on the proposed visual cryptography only. From these processes, two original images have been reconstructed which are given by two compression algorithms. Ultimately, two combinations are compared with each other based on the various parameters. These techniques can be implemented in the field for storing and transmitting medical images in a secure manner. The Confidentiality, Integrity and Availability CIA property of a medical image have also been proved by the experimental results. In this paper we have focused on only proposed visual cryptography scheme.