Visual Secret Sharing Scheme Research Articles

Cheating Prevention Method in Visual Cryptography by Using Random Grids

The traditional cheating prevention is usually based on visual cryptography (VC), in which the constructed image is bigger than the secret image because of the pixel expansion. In this paper, we studied the cheating problems in visual secret sharing (VSS) by random grids (RG) which can prevent the cheating activities with no pixel expansion. We considered the attacks of collusive cheaters who may deviate from the scheme in any way. We presented the cheating method and applied it on attacking existent n-out-of-n VSS scheme based on RG. Then we proposed one cheat-preventing scheme that can prevent the cheating activity upon.

Improving the visual quality of random grid-based visual secret sharing via error diffusion

Random grid (RG) is an approach to implement visual secret sharing (VSS) without pixel expansion. However, visual quality of the recovered secret image in RG-based VSS is not satisfactory. In this paper, two methodologies are introduced for improving image quality. Firstly, a random noise balanced error diffusion (RNBED) algorithm is proposed for generating RGs whose black pixels are distributed homogeneously. By combining the proposed RNBED algorithm and existing RG-based VSS schemes, two approaches for enhancing the recovered image quality are presented. Experimental results are provided, illustrating that competitive visual quality is achieved.

Quality‐improved threshold visual secret sharing scheme by random grids

Random grids (RGs)-based visual secret sharing (VSS) has gained much attention in academia than before to avoid the potential drawbacks in visual cryptography-based VSS. With its still being in infancy, a growing number of researches to RG-based VSS demonstrate a great potential. Although there are some RG-based schemes proposed in the past years for different applications, most of them can still be improved to achieve a better performance. This study proposes a new threshold RG-based VSS scheme with better performance compared with the previous threshold RG-based VSS scheme. The experimental results illustrate the feasibility; the better performance is theoretically analysed.

A Cheat-Prevention Visual Secret Sharing Scheme with Efficient Pixel Expansion

A visual secret sharing (VSS) scheme with minimum pixel expansion is proposed to prevent malicious participants from deceiving an honest participant. A VSS scheme encrypts a secret image into pieces referred to as shares where each participant keeps a share so that stacking sufficient number of shares recovers the secret image. A cheat prevention VSS scheme provides another piece for each participant for verifying whether the shares presented by other participants are genuine. The proposed scheme improves the contrast of the recovered image and cheat-prevention functionality by introducing randomness in producing pieces for verification. Experimental results show the effectiveness of the proposed scheme.

Random grid-based visual secret sharing with abilities of OR and XOR decryptions

Random grid (RG) is a methodology to construct visual secret sharing (VSS) scheme without pixel expansion. In some reported RG-based VSS schemes, a secret image can be visually reconstructed only by stacking operation, even thought some light-weight computational devices are available. In this paper, a novel RG-based VSS is developed, where the secret image can be recovered in two situations: (1) when computational devices are not available, the secret image can be reconstructed by stacking the shares directly, and (2) when some light-weight computational devices are available, the secret image can be decrypted by XOR operation. Further, the decrypted secret image quality by stacking operation is approximately the same as that of conventional RG-based VSS. But better visual quality is obtained by XOR operation.

A Study on Visual Secret Sharing Schemes Using Biometric Authentication Techniques

Visual Secret sharing schemes (VSSS) and biometrics have been identified as the two most important aspects of digital security. VSSS uses the human visual system to perform the decryption. A VSSS allows confidential messages to be encrypted into k-out-of-n secret sharing schemes. Whenever the number of participants from the group (n) is greater than or equal to the threshold value (k), the confidential message can be obtained by these participants. VSSS is interesting because decryption can be done with no prior knowledge of cryptography and can be performed without any complex cryptographic Algorithms. Based on this study, a new approach to analyze VSSS that uses biometric approach is given in this paper.

A Weak Security Notion for Visual Secret Sharing Schemes

We propose a weak security notion for visual secret sharing (VSS) schemes. Under such a weak security notion, VSS schemes are designed to be secure against attackers' eyesight, but are not unconditionally secure, in general. In this paper, we theoretically discuss the relation between unconditionally secure (US) and weakly secure (WS) VSS schemes and present two constructions of WS-VSS schemes for color images. We show that WS-VSS schemes can achieve clearer color reproduced images with a smaller pixel expansion compared to those using US-VSS schemes, while we clarify that the basis matrices in both types of VSS schemes for black-white binary images are the same. These results suggest that the proposed VSS schemes can be regarded as ramp (or nonperfect) VSS schemes for color secret images.

A Survey on Various Visual Secret Sharing Schemes with an Application

This paper focuses mainly on the different kinds of Visual Secret sharing techniques that are existing, and framing all the techniques together as a literature survey. Aim an extensive experimental study of implementations of various available VSS techniques. Also focuses on the encryption techniques that are used in each schemes with their performance parameter, concentrates on to the security issues. This study extends to an application of the visual secret sharing scheme that embeds an extra confidential image with pair key structure with no pixel expansion. General Terms Image Encryption, Information Encryption, Double Encryption, Chaotic Encryption.

Yet another multiple-image encryption by rotating random grids

A visual secret sharing (VSS) technique constructed by random grids (RG) aims at encrypting a secret image into several shared ones and, later, reconstructing the secret by stacking the shared images to be recognized by the human visual system. The main advantages of VSS by adopting random grids, not Visual Cryptography (VC), include no pixel expansion, or cost of sophisticated codebook design. The authors of this paper present a new RG-based VSS scheme, which encrypts up to four secret images into two random grids without any pixel expansion and, later, decrypts one secret image by directly stacking two random grids and the other three in an additional way of rotating one RG at 90, 180, or 270 degrees, respectively. The proposed scheme not only raises the capacity of secret communication but also avoids the pixel expansion problem so that the overhead of storage and communication can be significantly reduced.

Identity Document Authentication Based on VSS and QR Codes

In this paper, an identification document authentication system is proposed, taking advantage of the perfect secrecy of the Visual Secret Sharing (VSS) scheme and the powerful and practical Quick Response (QR) code. In the proposed scheme, a binary secret image is encrypted into two shares, which are generated under a (2,2)-threshold VSS, and encoded into two QR codes. The first code is printed onto an ID-card, while the other is kept in a database. When the ID-card authentication is required, using a mobile phone the printed QR code is read and the share is extracted from it. Next the share kept in database is read and stacked with the extracted share from ID-card. Finally the stacking result of both shares determines the authenticity of the ID-card.

Random grid-based visual secret sharing for general access structures with cheat-preventing ability

Conventional visual secret sharing (VSS) encodes a secret image into shares which are m times as big as the secrets. m is called pixel expansion. Random grid (RG) is an approach to solve pixel expansion problem. However, the existing VSS methods using RGs are confined to (2,n),(n,n) and (k,n). In this paper, RG-based VSS schemes for general access structures are proposed. The proposed algorithms can encode one secret image into n random grids while qualified sets can recover the secret visually. Furthermore, a cheating immune method is also presented to provided extra ability of cheat-preventing for RG-based VSS. Experimental results demonstrate that both the RG-based VSS for general access structures and cheating immune method are effective. More complicated sharing strategies can be implemented.

Multi-image encryption by circular random grids

Visual secret sharing (VSS) can encode a secret image into several share images where the original secret can be reconstructed and recognized by sight by stacking all share images. There are two categories of VSS schemes: visual cryptography (VC) and random grids (RG). VC has three main drawbacks: the large size, the need for the codebook to be redesigned for specific applications, and the ability to encode only one secret image at a time. RG removes the first two drawbacks. This paper proposes a novel RG-based VSS scheme that encodes multiple secret images at a time. The scheme encrypts multiple secret images into two circular cipher-grids and decrypts the images by stacking two circular cipher-grids to obtain the first secret and gradually rotating one circular cipher-grid at a fixed degree (based on the quantity of the secret images encrypted) to disclose other secrets. Compared with conventional VC-based VSS, the proposed scheme has no pixel expansion, a higher capacity for secret sharing, and no need for a complex VC codebook to be redesigned. Theoretical analysis of visual quality and security is demonstrated.

Towards Shift Tolerant Visual Secret Sharing Schemes

In a (k, n) visual secret sharing (VSS) scheme, the alignment of the transparencies is important to the visual quality of the reconstructed secret image. Each pixel of the original secret image is expanded to m subpixels in a share image. If a share image is printed on a paper with the same size as the original secret image, the alignment or the registration of the subpixels, which is only m times smaller than that of the original secret image, could be troublesome. In this paper, we propose a (2, n)-VSS scheme that allows a relative shift between the shares in the horizontal direction and vertical direction. When the shares are perfectly aligned, the contrast of the reconstructed image is equal to that of the traditional VSS scheme. When there is a shift, the average contrast of the reconstructed image is higher than that of the traditional VSS scheme, and the scheme can still work in cases where very little shape redundancy is present in the image. The trade-off is that our method involves a larger pixel expansion. The basic building block of our scheme is duplication and concatenation of certain rows or columns of the basic matrices. This seemingly simple but very powerful construction principle can be easily used to create more general (k, n) schemes.

Threshold visual secret sharing by random grids

A new visual secret sharing (VSS) approach by random grids (RG-based VSS), proposed by Kafri and Keren (1987), has drawn close attention recently. With almost all advantages of visual cryptography-based VSS, RG-based VSS benefits more from keeping the same size of secret images without the problem of pixel expansion from which VC-based VSS suffer. In this paper, a threshold RG-based VSS scheme aiming at providing the wide-use version is presented. This is the first effort to develop the technique. The experimental results and theoretically analysis in visual quality and security show that the proposed scheme performs well.

Probabilistic visual secret sharing schemes for grey-scale images and color images

Visual secret sharing (VSS) scheme is an encryption technique that utilizes the human visual system in recovering the secret image and does not require any cryptographic computation. Pixel expansion has been a major issue of VSS schemes. A number of probabilistic VSS schemes with minimum pixel expansion have been proposed for binary secret images. This paper presents a general probabilistic ( k, n)-VSS scheme for grey-scale images and another scheme for color images. With our schemes, the pixel expansion can be set to a user-defined value. When this value is 1, there is no pixel expansion at all. The quality of reconstructed secret images, measured by average contrast (or average relative difference), is equivalent to the contrast of existing deterministic VSS schemes. Previous probabilistic VSS schemes for black-and-white images can be viewed as special cases in the schemes proposed here.

A Novel Non-Expansion Visual Secret Sharing Scheme For Binary Image

A Novel Non-Expansion Visual Secret Sharing Scheme For Binary Image

On Converting Secret Sharing Scheme to Visual Secret Sharing Scheme

Traditional Secret Sharing (SS) schemes reconstruct secret exactly the same as the original one but involve complex computation. Visual Secret Sharing (VSS) schemes decode the secret without computation, but each share is m times as big as the original and the quality of the reconstructed secret image is reduced. Probabilistic visual secret sharing (Prob.VSS) schemes for a binary image use only one subpixel to share the secret image; however the probability of white pixels in a white area is higher than that in a black area in the reconstructed secret image. SS schemes, VSS schemes, and Prob. VSS schemes have various construction methods and advantages. This paper first presents an approach to convert (transform) a (k, k)-SS scheme to a (k, k)-VSS scheme for greyscale images. The generation of the shadow images (shares) is based on Boolean XOR operation. The secret image can be reconstructed directly by performing Boolean OR operation, as in most conventional VSS schemes. Its pixel expansion is significantly smaller than that of VSS schemes. The quality of the reconstructed images, measured by average contrast, is the same as VSS schemes. Then a novel matrix-concatenation approach is used to extend the greyscale (k, k)-SS scheme to a more general case of greyscale (k, n)-VSS scheme.

A novel visual secret sharing scheme for multiple secrets without pixel expansion

The main concept of the original visual secret sharing (VSS) scheme is to encrypt a secret image into n meaningless share images. It cannot leak any information of the shared secret by any combination of the n share images except for all of images. The shared secret image can be revealed by printing the share images on transparencies and stacking the transparencies directly, so that the human visual system can recognize the shared secret image without using any devices. The visual secrets sharing scheme for multiple secrets (called VSSM scheme) is intended to encrypt more than one secret image into the same quantity of share images to increase the encryption capacity compared with the original VSS scheme. However, all presented VSSM schemes utilize a pre-defined pattern book with pixel expansion to encrypt secret images into share images. In general, it leads to at least 2× times pixel expansion on the share images by any one of the VSSM schemes. Thus, the pixel expansion problem becomes more serious for sharing multiple secrets. This is neither a practical nor the best solution for increasing the number of secret sharing images. In this paper, we propose a novel VSSM scheme that can share two binary secret images on two rectangular share images with no pixel expansion. The experimental results show that the proposed approach not only has no pixel expansion, but also has an excellent recovery quality for the secret images. As our best knowledge, this is the first approach that can share multiple visual secret images without pixel expansion.

A Novel Ideal Contrast Visual Secret Sharing Scheme with Reversing

In visual secret sharing (VSS) schemes, a secret image can be visually revealed from overlapping shadow images without additional computations. However, the contrast of reconstructed image is much lost. Employing reversing operation to reverse black and white pixels as well as increasing encoding runs is an effective way to improve the contrast. A novel VSS scheme with reversing is presented in this paper. It achieves really ideal contrast within only [m/h] encoding runs (where m and h are the number of the total columns and the number of the wholewhite columns in the basis matrix to encode white pixels, respectively) and no pixel expansion occurs. It encodes the secret image block by block. A block consists of m pixels, which means that m pixels together join into each encoding step. It is suitable for all access structures and can be applied to encrypt black-white, gray-scale and chromatic images. The experimental results, analyses and comparisons show that the proposed scheme is optimal among those schemes with reversing in encoding runs, pixel expansion, complexity, system capacity and encoding efficiency.

MTVSS: (M)isalignment (T)olerant (V)isual (S)ecret (S)haring on resolving alignment difficulty

A ( k, n)-threshold visual secret sharing (VSS) scheme has the distinctive property of easy decryption by manually printing out shadow images on transparencies and stack them to visually reveal the secret image. However, the decoding is highly dependent on the precise alignment of transparencies by hand. The misalignment makes the secret in reconstructed image invisible, and this is referred to as the misalignment problem. In this paper, we consider the misalignment problem in VSS scheme. We design a misalignment tolerant VSS (MTVSS) scheme based on the trade-off between the usage of big and small blocks to address this misalignment problem. Our MTVSS scheme allows people visually reveal the original secret image, and it is not necessary to align the transparencies precisely.