A Watermarking-based Visual Cryptography Scheme with Meaningful Shares

Traditional visual secret sharing (VSS) schemes that encrypt secret images into noise-like images have been extended to multiple secret sharing (MSS) schemes to share multiple secret images using meaningful shares. Due to poor visual quality, such schemes are vulnerable to attacks from intruders. In this paper, we propose an efficient (n, n) MSS scheme for sharing n secret images, where n cover images are embedded in n meaningful shares. The proposed scheme provides improved visual quality with higher sharing capacity. Security is enhanced by meaningful share images. Thus, the proposed scheme offers enhanced quality and efficiency while satisfying security criteria.

A (k, n)-conventional visual cryptography (VC) scheme is designed to share one secret and each participant takes one share. When some common participants are involved in multiple VC schemes for multiple secrets, each needs to take multiple shares. This procedure needs more shares, which is inconvenient. It is desirable that the collaboration between the VC schemes can allow each common participant to keep only one share. Simply merging or gluing together two traditional (k(1), n(1))- and (k(2), n(2))-VC schemes, after making their pixel expansions the same, might be able to facilitate the collaboration and allow each common participant to keep only one share. But there is a security risk that when a subset of k(1) participants are from the collection of noncommon participants, some from scheme 1 and some from scheme 2, they can reconstruct secret 1, which is inconsistent with the intention of the original scheme. Similarly, k(2) noncommon participants could reconstruct secret 2. This shortcoming is inherited from the brute-force combination of traditional schemes. Therefore, a more sophisticated mechanism is required; this is the main task of this paper. In this paper, we first transform collaborative VC (CVC) schemes into the multiple secrets VC scheme with a general access structure. The construction of the basis matrices in CVC scheme between two VC schemes is formulated into an integer linear programming problem that minimizes the pixel expansion under the corresponding security and contrast constraints. Also the collaboration among more VC schemes is constructed. Finally, the experimental results illustrate the construction procedure of the CVC scheme and demonstrate the effectiveness of the CVC scheme.

Visual cryptography (VC) schemes provide a distinguished image encryption technique to protect image security since it can visually decrypt the secret image by superimposing the encrypted shadows. VC schemes for both threshold access structures and general access structures are generally constructed based on the OR operation to minimize the pixel expansion. However, VC schemes with optimal pixel expansion typically have low contrast. Stacking operation OR frequently produces recovered images with poor visual quality and are never able to deliver flawless recovery for secret images. Therefore, we studied XOR-based VC (XVC) schemes that employ linear programming to maximize their contrast. Three schemes for general access structures and three schemes for threshold access structures are designed to maximize their contrast. The proposed schemes’ construction is reduced to a linear programming to maximize the contrast by determining the ideal combinations of basis matrices in terms of primary column matrices and unit matrices, respectively. The comparison study and experimental results demonstrate that the contrast of the previous VC and XVC schemes can be further improved.

This letter presents a method for implementing visual cryptography (VC) in which an additional tag is attached to each generated share. The proposed (t, n), 2 ≤ t ≤ n tagged visual cryptography (TVC) scheme works like a traditional VC scheme does, where the original image is encoded in n shares in such a way that the secret can be revealed by superimposing any t or more shares, but knowledge of less than t shares gets no secret information. A notable characteristic of TVC is that an extra tag can be revealed by folding up each share, which provides users with supplementary information such as augmented message or distinguishable patterns to identify the shares. The tagging property can easily be applied to any reported VC scheme to endow the generated shares with more capabilities. Construction methods and simulation results of the proposed (t , n) TVC based on conventional matrix-based VC and probabilistic-VC are illustrated in the letter.

With fast growth in Internet and digital imaging knowledge, there are progressive customs to simply generate, distribute and allocate the images. Measured the association among digital imaging and privacy fortification, Visual Cryptography and Secret Image Sharing is an inclusive preamble to original security methods. The secret sharing control system is used to guard unauthorized data access and to secure distribution of responsive information. An efficient color image visual cryptic filtering scheme is to improve the image quality on restored original image from visual cryptic shares. The color image visual cryptic filtering scheme presents a deblurring effect on the non-uniform distribution of visual cryptic share pixels. Fourier transformation and texture overlapping is applied to normalize the unevenly transformed share pixels on the original restored image. This in turn improves the quality of restored visual cryptographic image to its optimality. The privacy preservation in visual cryptography plays a major role to provide an efficient secure communication for the users. To address data sharing issues more sensitively, a privacy preservation achieved by using cache-cache mechanism. The cache-cache mechanism maintains a cache inside a cache to preserve the details about the users who shared the secret parts of digital document, which has been splitted in a scheme of visual cryptography. In this work, the binary spanning trees are used to enhance the progress of secure distributed file sharing in visual cryptography. Privacy of file sharing is done with file block id relating to the participant id using binary trees. Group dynamics is handled effectively with distributed key exchange model, based on the principal operation of minimum spanning tree variants. Experimentation carried out with bench mark data sets of real and synthetically generated data sets to estimate the performance of the proposed controlled adaptable distributed file sharing with multiple participants in visual cryptography in terms of group dynamic rate, tree spanning length and privacy overhead.

In 1994, Naor and Shamir introduced an unconditionally secure method for encoding black and white images. This method, known as a threshold visual cryptography scheme (VCS), has the benefit of requiring no cryptographic computation on the part of the decoders. In a (k, n)-VCS, a share, in the form of a transparency, is given to n users. Any k users can recover the secret simply by stacking transparencies, but k-1 users can gain no information about the secret whatsoever. In this paper, we first explore the issue of contrast, by demonstrating that the current definitions are inadequate, and by providing an alternative definition. This new definition motivates an examination of minimizing pixel expansion subject to fixing the VCS parameters h and l. New bounds on pixel expansion are introduced, and connections between these bounds are examined. The best bound presented is tighter than any previous bound. An analysis of connections between (2, n) schemes and designs such as BIBD's, PBD's, and (r, λ)-designs is performed. Also, an integer linear program is provided whose solution exactly determines the minimum pixel expansion of a (2, n)-VCS with specified h and l.

For visual cryptography scheme (VCS), normally, the size of the recovered secret image will be expanded by m( ≥ 1) times of the original secret image. In most cases, m is not a square number, hence the recovered secret image will be distorted. Sometimes, m is too large that will bring much inconvenience to the participants to carry the share images. In this paper, we propose two visual cryptography schemes which simulated the principle of fountains. The proposed schemes have two advantages: non-distortion and flexible (with respect to the pixel expansion). Furthermore, the proposed schemes can be applied to any VCS that is under the pixel by pixel encryption model, such as VCS for general access structure, color VCS and extended VCS, and our VCS does not restrict to any specific underlying operation. Compared with other non-distortion schemes, the proposed schemes are more general and simpler, real flexible and has competitive visual quality for the recovered secret image.

In Visual Cryptography Schemes (VCSs), for message n transparencies are generated, such that the original message is visible if any k of them are stacked. VCS especially for large values of k and n, the pixel expansion’s reduction and enhancement of the recovered images’ display quality continue to be critical issues. In addition to this, it is challenging to develop a practical and systematic approach to threshold VCSs. An optimization-based pixel-expansion-free threshold VCSs approach has been proposed for binary secret images’ encryption. Along with contrast, blackness is also treated as a performance metric for assessing the recovered images’ display quality. An ideally secure technique for a secret image’s protection through its partition into shadow images (known as shadows) is the Visual Secret Sharing (VSS) scheme. Acquirement of a smaller shadow size or a higher contrast is the VSS schemes’ latest focus. The white pixels’ frequency has been utilized to demonstrate the recovered image’s contrast in this work. While the Probabilistic VSS (ProbVSS) scheme is non-expansible, it can also be readily deployed depending upon the traditional VSS scheme. Initially, this work has defined the problem as a mathematical optimization model such that, while contingent on blackness and density-balance constraints, there is the maximization of the recovered images’ contrast. Afterward, an algorithm dependent on the Tabu Search (TS) is devised in this work for this problem’s resolution. Multiple complicated combinatorial problems have been successfully resolved with the powerful TS algorithm. Moreover, this work has attempted to bolster the contrast through the density-balance constraint’s slight relaxation. Compared to the older techniques, the proposed optimization-based approach is superior regarding the recovered images’ display quality and the pixel expansion factor from the experimental outcomes.

Visual Cryptography is a secret sharing scheme which owns the technique of sharing the visual information like pictures, text etc. It encrypts a secret into n visual shares printed in transparencies and shared among n participants. Qualified subsets of participants superimpose their transparencies to reconstruct the actual visual secret. The decryption of the visual secret demands no complex computation as the image can be retrieved by the human visual system after superimposing. This paper proposes a tagged visual cryptography for color images, where the secret image is splitted into two base shares based on the traditional visual cryptography scheme. The generated base shares are stamped with the tag pattern using the probabilistic visual cryptography scheme to obtain the tagged shares. One of the main advantage of using tag patterns is providing the participants with augmented information to identify the relevant shares among the numerous shares. During reconstruction the tag patterns are obtained by folding up the individual tagged shares. Superimposing the shares results in the secret color image which retains its original size thus ensuring no pixel expansion.

Visual Cryptography is an image encryption technique which reconstructs the image using human visual system. Presently used size invariant visual cryptography schemes (VCS) does not preserves both security and contrast conditions. In this paper we proposed a new method for size invariant block wise encoding VCS based on perfect reconstruction of white pixels which provides perfect security and retains the contrast. Here we have discussed an outline of size invariant VCS based on random basis column pixel expansion, block wise encoding and random basis VCS with perfect reconstruction of white pixels (PRWP) which have been demonstrated based on various research studies. We have also discussed the demerits of the existing models and made an experimental analysis between previous models and the proposed model. From the analysis we proved that the proposed method enhances the security and maintain the contrast.

Visual Cryptography for General Access Structures

Since visual cryptography scheme (VCS) was introduced by Naor and Shamir, contrast has been always regarded as an evaluation standard of visual quality of the revealed secret image. However, its original definition only reflects the relative difference between white area and black area of the revealed secret image so that it is incapable to access actual visual quality. Although other definitions of contrast were also proposed, researchers have not reached consensus on the definition of contrast until now. In this paper, a novel method is proposed to obtain recognition result of the revealed character secret image through simulating the recognition procedure of our human eyes. Recognition rate is adopted to evaluate the clearness of the revealed secret image. Experimental results and comparisons demonstrate that recognition rate can be regarded as a new visual evaluation criterion of VCS for character secret image. Finally, a construction of VCS with optimized overall pixel expansion is provided, in which the pixel expansion is thoroughly determined by recognition rate, rather than contrast.

In visual cryptography schemes (VCS), we often denote the set of all parties by \(P=\{1,2,\cdots ,n\}\). Arumugam et al. proposed a \((k,n)\)-VCS with one essential party recently, in which only subset \(S\) of parties satisfying \(S\subseteq P\) and \(|S|\ge k\) and \(1\in S\) can recover the secret. In this paper, we extend Arumugam et al.’s idea and propose a \((k,n)\)-VCS with \(t\) essential parties, say \((k,n,t)\)-VCS for brevity, in which only subset \(S\) of parties satisfying \(S\subseteq P\) and \(|S|\ge k\) and \(\{1,2,\ldots ,t\}\in S\) can recover the secret. Furthermore, some bounds for the optimal pixel expansion and optimal relative contrast of \((k,n,t)\)-VCS are derived.KeywordsVisual cryptographyEssential partiesPixel expansionRelative contrast

In this paper, we propose a security-enhanced method for the visual cryptography schemes using recursion. Visual cryptography is interesting because decryption can be done with no prior knowledge of cryptography and can be performed without any cryptographic computations. The proposed method, the secret image is encoded into shares and subshares in a recursive way. By using recursion for the visual cryptography schemes, the security and reliability of the secret image can be improved than in the case of existing visual cryptography schemes.

Image secret sharing method with two-decoding-options: Lossless recovery and previewing capability