Exploring Visual Cryptography Techniques: A Comprehensive Review

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.

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 this paper, we use an authentication system that combines Biometrics, Visual cryptography and One-Time password (OTP). We propose a basis matrix construction method for generating shares in visual cryptography technique. Generated shares are in mutually orthogonal groups so that only shares from the same group can reveal the original image. The system provides the user a share of the biometric data and keeps the other share in the server itself. The security of our scheme is based on biometric verification using visual cryptography and hash of a OTP. Therefore, the scheme is appropriate to be used in applications such as smart card and device authentication systems.

Security in internet of things is very critical. The computer systems that use image acquisition and processing from onboard or remote systems need to secure image data over the internet. Security of multimedia image data transmitted over secured and unsecured communications channel in today’s cyberspace is of paramount consideration due to malicious activities over these channels and there has been a high demand especially for end to end security applications for mobile devices. This is to ensure safety and security as well as privacy to transmitted data and stored data in the clouds. In this paper, we proposed a hybrid approach for securing digital images for devices by engaging lossy compression using 2-D discrete cosine transform and Visual Cryptographic Technique. The DCT was used for the lossy compression process and the visual cryptography was used to encrypt the image for confidentiality. The results showed to be very effective and the implementation was done using MATLAB.

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.

By splitting a picture into many parts, which, when reassembled, disclose the original image without requiring complicated math, visual cryptography is a strong method for protecting visual information. Problems with pixel enlargement, decreased picture quality, and restricted access structures are common with traditional visual cryptography techniques. Our proposed improved visual cryptography approach incorporates pixel-wise operations and critical access structures to solve these challenges and increase flexibility, picture quality, and security. To reconstruct a picture, our technique calls for building visual cryptographic shares based on critical access structures that specify the exact combinations of shares needed. In order to maintain the image's resolution and reduce pixel expansion, we use pixel-wise processes. By improving the peak signal-to-noise ratio (PSNR) by up to 20% compared to conventional approaches, experimental data show that our strategy greatly improves picture quality. In addition, the suggested approach guarantees that individual shares do not disclose any information on the original picture, thereby maintaining high security requirements. Finally, it is clear that the enhanced visual cryptographic system is well-suited for a wide range of uses in safe communications and data security due to its strong solution for secure picture sharing, increased picture quality, and adjustable access control.

The conventional power information field level sharing permission security control technology DPT (Dynamic proxy technology) mainly uses the dynamic proxy method to output permission control logic, which is vulnerable to the impact of access mode defects, resulting in sharing access failure. Therefore, a power information field level sharing permission security control technology based on visual cryptography is proposed. That is to build the security control system of power information field level sharing authority, and use the visual password to become the security authentication scheme of SIP power information field level sharing authority, thus realizing the security control technology of power information field level sharing authority. The experimental results show that the power information field level sharing permission security control technology based on visual cryptography can successfully share access under different name fields, and the user credibility is high, which has certain application value, and has made certain contributions to improving the operation reliability of the power information system.

The rapid deployment of modern technologies such as iPhone, laptops, digital watch, social network, internet are resulted in handling of enormous amount of data in our day-to-day life. Since the data storage is increased abundantly and techniques to retrieve the relevant information and protection of data related issues to be focused efficiently to protect this big data. However various organisations and IT industries dealing with big data are faced with many security risks in storage and processing of data. Hence the protecting the big data is challenging task for the researchers. MapReduce is an efficient tool for processing large volume of data in a distributed environment. Security and secrecy of data are vital concerns while processing data carried out in MapReduce. In this article, the proposed secure data processing on big data using visual cryptography (SDPBDVC) technique ensures the protection of sensitive information by applying the visual cryptography technique and the processing done only by authorised entities.

A highly robust and secure image watermarking based on classification and visual cryptography

Visual cryptography (VC) technique encodes an image into two or more shares that appear random in human eyes. In the decryption section, the pixels in the shared images are combined to obtain the information contained in the original image. This study applies visual cryptographic techniques to graysle and color images for user authentication in online transactions using the VC2,2 scheme. The server computer encodes the CAPTCHA image into two shared images that are sent to the user through different channels or applications. To authenticate himself, the user performs an XOR operation on both share images, identifies the information contained in the CAPTCHA and sends it to the server. In encryption test, histogram of the share image has a different pattern from the original image. The description test shows the decrypted image in this study visually has a better quality than the binary image has better quality than binary images.

Chapter 2 - Information Visualization: Scope, Techniques and Opportunities for Geovisualization

In recent years, encryption technology has been developed quickly and many image encryption methods have been put forward. Chaos based image encryption technique is a new encryption technique for images. It utilizes chaos random sequence to encrypt image, which is an efficient way to deal with the intractable problem of fast and highly secure image encryption. However, the Chaos based image encryption technique has some deficiencies, such as the limited accuracy problem. This paper researches on the chaotic encryption, DES encryption and a combination of image encryption algorithm, and simulate these algorithms, through analysis of the algorithm to find the gaps. And on this basis, the algorithm has been improved. The new encryption scheme realizes the digital image encryption through the chaos and improving DES. Firstly, new encryption scheme uses the Logistic chaos sequencer to make the pseudo-random sequence, carries on the RGB with this sequence to the image chaotically, then makes double time encryptions with improvement DES, displays they respective merit. Theoretical analysis and the simulation indicate that this plan has the high starting value sensitivity, and enjoys high security and the encryption speed. In addition it also keeps the neighboring RGB relevance close to zero. The algorithm can be used in the actual image encryption.

With the rapid development of computer network technology, information security has attracted increasing attention. Due to the characteristics of multi-dimensional operation and parallel processing capability, optical image encryption techniques have been receiving more and more attention. Since the well-known double random phase encoding technique was proposed, many other methods based on optical information processing means such as the use of optical transform, interference, and polarized light encoding, have been proposed for optical image encryption. However, recent researches have demonstrated that traditional optical encryption techniques are symmetric cryptosystems, in which decryption keys are identical to encryption keys and they have been found to be vulnerable to different types of attacks, such as known plaintext and chosen plaintext attacks. To overcome this shortcoming, asymmetric cryptosystems based on nonlinear phase-truncation techniques and phase retrieval algorithm have been proposed. Asymmetric cryptosystem is a cryptographic system in which encryption keys are different from decryption keys. The encryption keys are used as public keys which are disseminated widely, and the decryption keys are used as private keys which are known only to the authorized users. So, asymmetric cryptosystem can offer a higher-level security than symmetric cryptosystem. However, asymmetric cryptosystems based on phase retrieval algorithms require a lot of computational time, and asymmetric cryptosystems based on phase-truncated Fourier transforms have been found to be vulnerable to special attack. Therefore, in this paper, a novel asymmetric image encryption method is proposed by using the gyrator transform and vector operation. The original image is encrypted into two phase masks with vector operation. One is a random phase mask and the other is a phase mask related to the original image. In the encryption process, the random phase mask is used as a phase key and the other phase mask is transformed by gyrator transform. The transform result is performed by Fourier transform after being modulated by a phase distribution. The ciphertext is the amplitude of the above result. Compared with previous encryption schemes, the suggested method has two advantages. Firstly, we have proposed a new asymmetric encryption method based on the gyrator transform and vector operation. The decryption process is different from the encryption process. The gyrator transform and Fourier transform are used in the encryption process, while only the inverse operation of Fourier transform is employed in the decryption process. In addition, the decryption keys produced in the encryption process are different from the encryption keys. Therefore, the proposed scheme has high resistance against the conventional attacks. Secondly, the encrypted result is real-valued, which is convenient for display, transmission and storage.Numerical simulations illustrate the feasibility and effectiveness of the proposed encryption scheme.

In this paper, a virtual optical encryption open source software system for image security is proposed. Our system makes it possible to encrypt and decrypt images based on the optical theorem, which includes the virtual optical image encryption technique (VOIET), the data hiding technique (DHT), the data extraction technique (DET), and the virtual optical image decryption technique (VOIDT). The optical theorem is based the digitized double-random-phase algorithm, which is called the virtual optical theorem. In the system, secret data can be embedded into the encrypted image data without distortion. The comparison of data hiding capacity and reconstructed image quality is performed in the experiment. Our system is designed and implemented by the open source software, which is called the Virtual Optical Image Encryption System (VOIES) and released on the Open Source Software Foundry (OSSF).

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