Comment on “Cheating Prevention in Visual Cryptography”

Visual cryptography was firstly proposed by Naor and Shamir in 1994, which has been extended into many applications, including image encryption, information hiding, visual authentication, and visual identification. One important security issue in visual cryptography is the cheating prevention. However, in 2006, Horng et al. introduced the cheating problem in visual cryptography, where some dishonest participants, cheaters, can deceive other participants, victims, using forged transparencies. Since that, many cheating prevention works have been done in this area. In this paper, we introduce a new cheating prevention scheme which is secure and more efficient than previous schemes.

This paper shows that the largest possible contrast $C_{k,n}$ in a $k$-out-of-$n$ secret sharing scheme is approximately $4^{-(k-1)}$. More precisely, we show that $4^{-(k-1)} \leq C_{k,n} \leq 4^{-(k-1)}n^k/(n(n-1)\cdots(n-(k-1)))$. This implies that the largest possible contrast equals $4^{-(k-1)}$ in the limit when $n$ approaches infinity. For large $n$, the above bounds leave almost no gap. For values of $n$ that come close to $k$, we will present alternative bounds (being tight for $n=k$). The proofs of our results proceed by finding a relationship between the largest possible contrast in a secret sharing scheme and the smallest possible approximation error in problems occurring in approximation theory.

Traditional k out of n visual cryptography scheme has been proposed to encrypt single secret image into n shares where only k or more shares can decode the secret image. Many existing schemes on visual cryptography are restricted to consider only binary images as secret which are not appropriate for many important applications. Store-and-Forward telemedicine is one such application where medical images are transmitted from one site to another via electronic medium to analyze the patient's clinical health status. The main objective of Store-and-Forward telemedicine is to provide remote clinical services via two-way communication between the patient and the healthcare provider using electronic medical image, audio and video means. In this paper, a new XOR based Continuous-tone Multi Secret Sharing scheme suitable for store-and-forward telemedicine is proposed to securely transmit the medical images. It also eliminates basic security constraints of VC like pixel expansion in shares/recovered secret images, random pattern of shares, explicit codebook requirement, lossy recovery of secret and limitation on number of secret and shares. Proposed approach is n out of n multi secret sharing scheme which is able to transmit n secret images simultaneously. All secrets could be revealed only after some computations with all n shares and one master share. Master share has been created with the secret key at encoding phase and it can be regenerated at the time of decoding using same secret key. Here all shares are meaningful in continuous-tone which may provide confidentiality to medical images during transmission. Proposed approach not only preserves all basic characteristics of traditional VC but also increases the capacity of secret image sharing. From the experiments we found that irrespective of visible contents of the shares, the probability of getting back the pixel values of respective original secret images at the receiver end is very high.

In recent years, there has been a rapid development in the digital world of image communication over unsecured networks. Many domains, including military, medical, government, and education, require transmitting sensitive data through images. Hence, it raises the primary concern of its secrecy with the advancement of technologies. Traditional methods such as Advanced Encryption Standard (AES) and Data Encryption Standard (DES) have been widely used for image security. However, key management is the main concern in protecting image data. This work uses Visual Secret Sharing Scheme (VSS) or Visual Cryptography (VC) to handle the above mentioned issue. Modulo encryption-based VSS scheme (MEVSS) is proposed to encrypt the secret image shared among n number of users. The secret image is recovered loss-less by XORing n shares followed by modulo decryption. Experimental results show that the proposed technique outperforms the exiting techniques Binary tree-based Secret Sharing Scheme and RSA-based VSS in Unified average changing intensity (UACI) and Number of Pixel Change Rate (NPCR), While, the proposed model outperforms the existing techniques in term of Pixel to Signal Noise Ratio (PSNR). Moreover, it is faster than traditional techniques as it works directly on color image without converting it into another form like binary or grayscale.

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.

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

Visual cryptography is a cryptographic method that encrypts visual facts and the information decrypted appears as an original visual image. Here, the confidential data is shared by dividing the visual details into multiple shares such that the encryption and the decryption are performed for reconstructing the original image back by stacking the splitted shares. However, the data sharing process lacks adequate security protection. To overcome the issues, this paper presents a robust visual cryptography-based data sharing scheme, named Competitive Swarm Improved Invasive Weed Optimization (CSIIWO) for sharing multiple data. Initially, the grayscale input image is shared between several parties, such that the shared image is encrypted and decrypted for retrieving the original image back. However, the cryptographic key generation is done using the devised CSIIWO algorithm such that the cryptographic keys are generated for the data sharing process to maintain confidentiality among multiple parties. Moreover, the devised method achieved the maximum Peak signal-to-noise ratio (PSNR) of 40.749 dB, minimum conditional privacy loss of 0.508, and maximum entropy of 7.987, respectively using Lena image. Furthermore, the proposed scheme can protect the multiple data sharing information and has numerous advantages compared with the previous mechanisms.

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.

In the realm of visual cryptography, secret sharing is the predominant method of transmission and reception of secure data. Most of the (n, n) secret sharing schemes suffer from one common flaw — locking of information when the all- n number of receivers are not available for some reason. This paper proposes a new method of compartmented secret sharing scheme where some threshold number of equally privileged from each compartment can retrieve data. This scheme rules out regeneration of secret image at the single compartment thereby eliminating the danger of misusing secret image. The key features of this scheme are: better visual quality of the recovered image with no pixel expansion; non-requirement of half toning of color images; less computational complexity by reconstructing secret through XORing and simple addition of all share images. This scheme is highly beneficial in applications where data has to be stored securely in a database and in cloud computing to synchronize information passed to different groups or clusters from a single host.

The exponential growth of data and our dependence on it has increased security concerns over the protection of data. Various methodologies have been suggested to meet the security services namely; confidentiality, authentication and authorization. The (k:n) secret sharing scheme was recommended to isolate the dependence on a single entity for the safety of data. Random Grids Visual Secret Sharing (RGVSS), a category of a Visual Cryptography Secret Sharing scheme aims at encrypting a secret image into several shares using a simple algorithm. The encrypted information can be revealed by stacking the shares which can be recognized by the Human Visual System (HVS). The proposed VSS scheme exploits the geometrical configuration of the cube without distorting any of the secret information embedded on the shares. The rest of the secrets are decrypted by stacking the cubes and changing the orientation of one of the cube over the fixed one. Each side of the cube encrypts up to four secrets, the first secret can be decrypted by stacking the two cubical shares and rotating the stacked face of the cube at 90 degrees, 180 degrees and 270 degrees, reveals the other three shares respectively The proposed scheme increases the capacity of secret communication avoiding the pixel expansion problem which in turn reduces the overhead of storage and communication significantly without compromising on security and authenticity of the secret information.

Data Security is the most challenging area in Internet communication, where most of the secret sharing schemes are proposed for binary images.But still it lacks in providing security for data communication, especially in image transmission.Traditional visual cryptography scheme generate meaningless diwies and the reconstruction phase leads to quality degradation over the secret image.In this work, an intelligent two dimensional secret share construction scheme is proposed.A secret image is expanded into n diwies with the choice of scheme selection.By Stacking all the qualified diwies to revert the secret image without content loss and less than s* -1 shares could not reveal any information about the secret image.The experimental results emphasize that the proposed secret share scheme is highly secured for image transmission.

Image security in visual data is growing in importance due to the increasing use of digital images in many applications. This paper describes a novel image encrypting system using deep generative models with a self-attention mechanism to improve encrypting speed, decrypting speed, or both. Based on the CycleGAN models, the encrypting generator encrypts images while a dedicated decryption network decrypts them properly. The self-attention module improves the dispersibility of visual data to capture global dependencies among images at variable scales to achieve a highly secure image transformation with high reconstruction accuracy. Performance analysis has been done using two color image sets, brain MRI images to detect brain tumors, and images to detect skin cancer. Analysis indicates high security (Entropy = 7.9996, NPCR ≈ 99.99%), high reconstruction accuracy (SSIM ≈ 0.99, PSNR > 40 dB), and high resistance to differential (UACI ≈ 33.46) and occlusion attacks to images. This paper opens up novel avenues in applying deep models to visual cryptography schemes.

Chalcogenide material Ge2Sb2Te5 (GST) has bistable phases, the so‐called amorphous and crystalline phases that exhibit large refractive index contrast. It can be reversibly switched within a nanosecond time scale through applying thermal bias, especially optical or electrical pulse signals. Recently, GST has been exploited as an ingredient of all‐optical dynamic metasurfaces, thanks to its ultrafast and efficient switching functionality. However, most of these devices provide only two‐level switching functionality and this limitation hinders their application to diverse all‐optical systems. In this paper, the method to expand switching functionality of GST metasurfaces to three level through engineering thermo‐optically creatable hybrid state that is co‐existing state of amorphous and crystalline GST‐based meta‐atoms is proposed. Furthermore, the novel hologram technique is introduced for providing the visual information that is only recognizable in the hybrid state GST metasurface. Thanks to thermo‐optical complexity to make the hybrid state, the metasurface allows the realization of highly secured visual cryptography architecture without the complex optical setup. The phase‐change metasurface based on multi‐physical design has significant potential for applications such as all‐optical image encryption, security, and anti‐counterfeiting.