RG-based Visual Secret Sharing Research Articles

Improved schemes for visual secret sharing based on random grids

Random grid (RG) is an alternative approach to realize a visual secret sharing (VSS) scheme. RG-based VSS has merits such as no pixel expansion and no tailor-made matrix requirement. Recently, many investigations on RG-based VSS are made. However, they need further improvements. In this paper, we obtain some improvements on RG-based VSS. Actually, two improved schemes are proposed, namely RG-based VSS for general access structure (GAS) with improved contrast and extended RG-based VSS with improved access structure. The first scheme can achieve better contrast than previous schemes. The second scheme reduces the chance of suspicion on secret image encryption by generating meaningful shares instead of noise-like shares in the first scheme, and improves the access structure from (k, k) to GAS while maintaining the property that the contrast of the recovered image is traded with that of share images by setting a certain parameter from small to large. Finally, theoretical analyses and experimental results are provided to demonstrate the effectiveness and advantages of the proposed schemes.

On the security of threshold random grid-based visual secret sharing

Visual secret sharing (VSS) technology encodes a secret image into some share images for sharing some classified information. Only when the participants gather and stack their share pictures the secret image would be reconstructed and recognizable by the human visual system. Two well-known encoding ways of VSS, visual cryptography (VC) and random grid (RG), have been developed in recent years. As both VC and RG have been considered as a secure way for communicating with high security, they have been pointed out with cheating problems. In this paper, we propose two RG-based VSS schemes with fraud prevention for the cases of (2,n) and (k,n). The experimental results and the analysis of security and contrast show that the proposed method is efficient and practical.

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

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.

Contrast-improved visual secret sharing based on random grid for general access structure

Random grid (RG)-based visual secret sharing (VSS) owns the advantages of no pixel expansion and codebook design. VSS for general access structure (GAS) possesses wider applications than VSS for (k,n) threshold. Previous RG-based VSS studies for GAS had the drawbacks of “all-or-nothing” or low visual quality. In this paper, we will develop a progressive VSS (PVSS) algorithm for GAS with improved visual quality based on RG. We employ different regions of the secret image and their generated corresponding random bits to improve the visual quality of the revealed secret image as well as to gain GAS with progressive feature, where the random bits are divided into three parts. In addition, our scheme has neither pixel expansion nor codebook design due to RG. We show the effectiveness of our proposed scheme in terms of experiments and analyses.

On the difficulty of aligning VSS random grids

Visual secret sharing (VSS) schemes are classified into two categories—visual cryptography-based (VC) and random grid-based (RG)—with the purpose of encoding a secret into several meaningless shared images that can be superimposed to reveal the secret again. VC-based VSS suffers from the problems of pixel expansion and difficulty in alignment. Although the first problem has been solved by RG-based VSS, the latter remains. This paper proposes a new deviation-tolerant RG-based VSS method without pixel expansion. To demonstrate its feasibility, experiments are conducted to show that the reconstructed secret image is still recognizable visually when one shared image shifts by one or more pixels. Compared with related works, the proposed scheme not only has higher misalignment tolerance but also avoids the significant drawbacks in the related work.

An enhanced threshold visual secret sharing based on random grids

Random grids (RG)-based visual secret sharing (VSS) scheme can easily avoid the pixel expansion problem as well as requires no codebook design. However, previous scheme still suffers from low visual quality. In this paper, a new threshold RG-based VSS scheme aiming at improving the visual quality of the previewed image is presented. Compared with previous schemes, our scheme can gain better visual quality in the reconstructed images as well as (k, n) threshold. In addition, the factor affecting the visual quality is analyzed and the differences between related approaches are discussed.

Visual multiple-secret sharing for flexible general access structure by random grids

For visual secret sharing (VSS), general access structure (GAS), which can freely define the qualified set and the forbidden set, provides dealers the ability to share secret information with the qualified set but not the forbidden set. In previous studies, the proposed GAS schemes have focused on strong GAS, but it has retained restrictions and inconvenience in some secret-sharing scenarios. Recently, the random-grid-based VSS (RG-based VSS) technique has aimed to overcome the problem of pixel expansion from which the visual-cryptography-based VSS (VC-based VSS) techniques usually suffer. This paper presents a flexible GAS VSS scheme by RG that is appropriate for wide use and that serves special cases like (2, n), (n, n), and (k, n). The paper also outlines how the scheme can be extended for multiple secrets. The performance and the security of the scheme are theoretically analyzed.

Friendly progressive random-grid-based visual secret sharing with adaptive contrast

Visual secret sharing (VSS) schemes providing secret communication services are classified into two categories depending on the method of encoding the secret: visual cryptography (VC)-based and random grid (RG)-based schemes. A friendly progressive version of the VC-based VSS scheme was presented in 2008; however, it is marred by pixel expansion, which is the innate deficiency of conventional VC-based VSS schemes. This paper proposes a suitable user-friendly RG-based VSS scheme with progressive secret reconstruction and without pixel expansion. The experimental results of the developed scheme validated its feasibility, and a theoretical analysis demonstrated its visual quality and security.

Robust Cheat-prevention for Random Grids Based Visual Secret Sharing Scheme

In conventional visual secret sharing (VSS), a secret image is encrypted into noise-like random-looking shares, a subset of which when stacked together reveal the secret. Random grids (RG) eliminate pixel expansion and extensive codebook designs of conventional VSS. However, like conventional VSS, RG-based VSS are prone to collusion attacks. Existing cheat-prevention algorithms reduce the probability of collusion attacks, but these do not consider issues arising due to noise-like nature of the shares. We introduce two issues that may lead to false accusations and we devise a robust cheat-prevention algorithm to tackle these. Experimental results validate the efficacy of the algorithm.

Visual multi secret sharing by cylindrical random grid

Visual secret sharing (VSS) is the process of encoding a secret image into several share images in which the original secret image can be reconstructed and recognized by stacking all of the share images together. VSS has two categories: visual cryptography (VC) and Random Grid (RG). The VC is affected by various drawbacks such as: enlarging the size of original image, need for a codebook and the limitation to encode only one secret image at a time. RG solves the first two drawbacks of VC. To solve the third drawback and provide a solution to optimize recent algorithms, we propose a novel RG-based VSS scheme which encodes several secret images at a time. Instead of using only (2, 2) visual secret sharing, (2, n) and (n, n) is employed. This scheme has the ability to encode one or multiple secret images into multiple shares in place of two shares. In our proposed scheme, instead of Circular Random Grid, a new algorithm named Cylindrical Random Grid is used. It encrypts multiple secret images into two or more shares. To decrypt the first secret image, shares are stacked together. For decrypting of other secret images, one of the stacked shares is rotated in a fixed size over other shares based on the number of secret images which are encrypted. This algorithm is simple to implement and less time consuming.

A random grid-based cyclic access structure VSS scheme for multiple secret images

Visual secret sharing (VSS) schemes based on visual cryptography (VC) or random grids (RGs) have been proposed in the past decade with the advantages of easy implementation, efficiency secret recovering and perfect security. As the concept of multiple secret images has gained more and more attention in academia, the novel concept of VC-based VSS with cyclic access structure has been discussed recently, which is a special case of multiple VSS, allowing participants to reconstruct the secret with the one next or last to him/her in a cyclic order. To obtain the benefit of RG-based VSS compared with VC-based VSS, this paper proposes the new VSS scheme with cyclic access structure for multiple secret images by random grids. The experimental results and theoretical security analysis demonstrate the feasibility.

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.

Visual secret sharing for general access structures by random grids

Visual secret sharing (VSS) is a way to protect a secret image among a group of participants by using the notions of perfect ciphers and secret sharing. However, each share generated by conventional VSS is m times as big as the original secret image, where m is called pixel expansion. Random grid (RG) is an alternative approach to implement VSS without pixel expansion. However, reported RG-based VSS methods are threshold schemes. In this study, RG-based VSS for general access structures is presented. Secret image is encoded into n RGs while qualified sets can recover the secret visually and forbidden sets cannot. The proposed scheme is a generalisation of the threshold methods, where those reported RG-based schemes can be considered as the special cases of the proposed scheme. Experimental results are provided, demonstrating the effectiveness and advantages of the proposed scheme.

Improving the visual quality of random grid-based visual secret sharing

Pixel expansion and visual quality of the revealed secret image are two major concerns in visual secret sharing (VSS). Random grid (RG) is an alternative approach to solve the pixel expansion problem by making the share as big as the original secret image, at the expense of sacrificing the visual quality of the reconstructed secret image. In this paper, two algorithms, including a contrast-enhanced RG-based VSS and a void-and-cluster-based (VAC-based) post-processing, are introduced to improve the reconstructed image quality. Experimental results and theoretical analysis are provided, illustrating that competitive visual quality is obtained by combined use of the two proposed methods.

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.

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.

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.

Insight into collusion attacks in random-grid-based visual secret sharing

Visual secret sharing (VSS), either visual-cryptography-based (VC-based) VSS or random-grid-based (RG-based) VSS, is a well-known technology of secret communication for sensitive security applications. Horng et al. (2006) kindled the interest in the cheating problem existing in threshold VC-based VSS. The cheating problem happened when dishonest participants collude to cheat honest ones by enabling the latter to accept the wrong secret information generated by the former. As RG-based VSS (RGVSS) has gained significant attention in academia in the past years, it is concerned that RG-based VSS may also suffer cheating attacks. The authors of the present study demonstrate that the security risk does exist in RG-based VSS. To prove the feasibility of cheating, the experimental results and formal analysis illustrate that the proposed collusion attacks do work.