An Improved Visual Cryptography with Cheating Prevention

Visual cryptography (VC), proposed by Naor and Shamir, has numerous applications, including visual authentication and identification, steganography, and image encryption. In 2006, Horng showed that cheating is possible in VC, where some participants can deceive the remaining participants by forged transparencies. Since then, designing cheating-prevention visual secret-sharing (CPVSS) schemes has been studied by many researchers. In this paper, we cryptanalyze the Hu-Tzeng CPVSS scheme and show that it is not cheating immune. We also outline an improvement that helps to overcome the problem.

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.

The reconstructed image of the size-invariant visual cryptography (VC) is inevitably accompanied by the loss of secret image information and the degradation of perceptual quality. Here, the halftone technique comes to the forefront since it can realistically simulate the grayscale image from a discrete binary image. Thus, by combining VC sharing with grayscale image halftone technique, this paper proposes a size-invariant VC scheme for grayscale image underpinned by the efficient direct binary search (EDBS) algorithm, in which the multi-pixel encryption VC sharing is adopted into the EDBS halftone process. Through local optimizations and global iterations, the optimal reconstructed image is obtained. To further enhance the contrast of the reconstructed image with limited computational power, the image information is probabilistically extracted according to the inverse mapping in the codebook. It is theoretically proved that the proposed scheme is as secure as the traditional VC, while its effectiveness is validated through experiments and comparative analyses.

In the past decade, the researchers paid more attention to the cheating problem in visual cryptography (VC) so that many cheating prevention visual cryptography schemes (CPVCS) have been proposed. In this paper, the authors propose a novel method, which first makes use of Latin square to prevent cheating in VC. Latin squares are utilised to guide the choosing of authentication regions in different rows and columns of each divided block of the shares, which ensures that the choosing of authentication regions is both random and uniform. Without pixel expansion, the new method provides random regions authentication in each divided block of all shares. What is important is that the proposed method is applicable to both ( k , n )‐deterministic visual cryptography scheme (( k , n )‐DVCS) and ( k , n )‐probabilistic visual cryptography scheme (( k , n )‐PVCS). Experimental results and properties analysis are given to show the effectiveness of the proposed method.

The reconstructed image of probabilistic visual cryptography (VC) is inevitably accompanied by the loss of secret image information and degradation of visual quality. Since halftone technique can realistically simulate grayscale continuous tone image with a binary image, in this paper, by combining VC sharing with grayscale image halftone technique, we propose a probabilistic VC scheme for grayscale image using EDBS (Efficient Direct Binary Search) to improve the quality of the reconstructed image. The probabilistic VC sharing is adopted into the EDBS halftone process, and the reconstructed image is taken as the optimization object. Through local optimizations and global iterations, the optimal reconstructed image is finally achieved under the established optimization strategy. Theoretically the proposed scheme possesses the same security strength as the traditional VC and experimentally the comparative analysis verifies the effectiveness of this scheme.

Security has gained a lot of importance with the rapid development of communication/storage technology. Protecting the data has become an important issue. In this paper a transmission system with enhanced security is proposed for the image information. Here, the secret image is encrypted and transmitted by using a combined technique that make use of Discrete Wavelet Transform (DWT), Visual Cryptography (VC) and Water marking. DWT is first used for the compression of the secret image. Visual cryptography encodes the compressed image into noise like shadow images known as shares. Shares are made invisible by digital watermarking, which provides additional security. By stacking the shares together, the secret image can be visually decoded. Different image types are used to evaluate the performance of the proposed scheme. Comparison with different values of scaling parameter M, which is used to decrease the size of image in the VC is also done. The results clearly indicate that the proposed scheme can send more data with less bandwidth more secretly.

Visual cryptography is a powerful method for securely sharing and protecting visual data by splitting an image into multiple shares. Individual shares do not reveal any information, but when combined, they allow for the reconstruction of the original image. The survey categorizes different approaches based on pixel expansion, complexity, and the quality of the reconstructed image. It focuses specifically on color image encryption, an emerging field of interest because of its use in secure communication, digital media, and medical imaging. The paper provides a comprehensive review of recent advances in color visual cryptography, discussing the latest techniques and challenges in the field. his paper is a systematic review of color visual cryptography techniques. The contribution is threefold: (i) categorizing schemes by pixel expansion, complexity, and reconstruction quality, (ii) critically analyzing limitations and trade-offs, and (iii) identifying open research gaps and future directions.

The backdrop: visual cryptography represents a contemporary encryption technology valued for its ease of implementation and comprehensibility, eliminating the need for a secure channel for key transmission and similar requirements. This paper aims: delve into the diverse methods employed in optical encryption, exploring their advantages and drawbacks, with a particular focus on image encryption techniques and the outcomes documented in various research studies. The objective is to identify the strengths and weaknesses inherent in these methodologies, paving the way for potential solutions in the future of optical encryption research. Notably, challenges persist in effectively handling color images and utilizing multiple shares (n, n), impacting both the security and the restoration aspects. The time computation aspects, encompassing creation, encryption, and restoration of these shares, also present challenges. Consequently, ongoing improvements are necessary to address these intricacies and enhance the robustness and applicability of visual cryptography technologies in diverse contexts

Steganography is the art of hiding secret data in a medium whereas visual-cryptography is a cryptographic technique where a full image is encrypted. The security of image steganography depends on the secret key set which is used for embedding the secret image. If the secret key is exposed, the secret image can be retrieved. To solve this security issue we propose a new type of steganography method using visual cryptography. In this method, text and image are used as a secret message and image for the cover object. 24-bit RGB color images are used as both secret and cover images. In this method, we use a new image namely share1 which converts a secret image to a totally different image called share2 image. Typically, knowing the extraction method, people can retrieve the secret message easily. A pseudorandomly generated image is used as a key for visual encryption and this ensures the extra layer of security. By this proposed method, we ensure more secured image steganography.

With visual cryptography in mind, the security property of a new scheme is always one of main concerns. However, the ideal security is not taken into account in some visual cryptography schemes sharing multiple secrets. In this paper, the security of a multi-secret visual cryptography scheme proposed by Feng et al. is analyzed. We show that the security of their scheme is not ideal. Precisely, it is insecure since some information of the secret images can be inferred by block attacking the second share alone. In order to realize the ideal security, we redesign the visual patterns and the rule of random permutation. Moreover, the proposed ideal secure scheme has better pixel expansion and relative difference. Finally, we give some experimental results and comparisons to show the effectiveness of the proposed scheme.

Chapter 11 - Badge Surveillance

This paper proposes a scheme to hide some extra confidential data in transparencies during secret image encryption in visual cryptography. The secret image is multitoned into several levels first. An extended non-expansion visual secret sharing model is employed, i.e. size of transparencies is equal to that of the secret image. Thus less time and space are needed for transparencies transmission and storage.

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.

Recently, Hou et al. Introduced a (2, n) block-based progressive visual cryptographic scheme (BPVCS), which the image blocks can be gradually recovered step by step. In Hou et al.’s (2, n)-BPVCS, a secret image is subdivided into n non-overlapped image blocks. When stacking any t (2 ≤ t ≤ n) shadows, the image blocks associated with these t participants will be recovered. Unfortunately, Hou et al.’s (2, n)-BVCPS suffers from the cheating problem, which any two dishonest participants might collude together to tamper their image blocks shared with other honest participants. Also, they can impersonate an honest participant to force other honest participants to reconstruct the wrong secret. In this paper, we solve the cheating problem and propose a cheating immune (2, n)-BPVCS.

The fifth-generation (5G) and beyond cellular networks are expected to support a huge number of mobile devices, roaming seamlessly across very small cells. Consequently, the handover rate for these extremely dense networks is expected to be very high. To reduce the burden caused by rapid handover requests, and to support a massive number of highly mobile devices in 5G and beyond networks, this study suggests using proximity-based clusters as nomadic cells integrated with Aerial Access Networks (AANs). These nomadic cells are formed by two-levels hierarchical partitioning of the mobile devices into proximity-based clusters. Previous distributed mobility management schemes are not sufficiently efficient to support the handover rate expected for 5G and beyond networks. Due to their high computational complexity, previous group-based methods are not applicable for real-time services. In contrast to these schemes, the proposed scheme is scalable with the number of devices. Moreover, the creation of a mobility group raises practical as well as security and privacy issues that were overlooked by previous schemes. These issues are addressed in this study.