A Narrative Study on Visual Cryptography Techniques for Robust and Secure Image Communication: A Review

For preserving the security of data there has been tremendous research areas evolved and explored since few years. Cryptography is seen to be the dominant strategy in the information security domain. To differentiate security of multimediadata, visual cryptography is seen as the prominent way for data confidentiality and secrecy of information being distributed. The mechanism of visual cryptography is widely used approach which encrypts the secrete image into the many meaningless share images and decodes by stacking some or all shares by human visual system. There are many methods presented for visual cryptography with their own advantages and disadvantages.. Over the years , in visual cryptography the scope of research mainly focused on developing techniques on grayscale , halftone , color visual cryptography, region incrementing visual cryptography, minimization of pixel expansion , multiple secret sharing and cheating prevention in visual cryptography. Recently new cheating–preventing scheme has been found whichis advantageous over a combined approach of two general VC codebooks. This method resulted into number of advantages such as computation cost is low; multi factor cheating detection is involved etc. However, we identified two research problems such as 1) there is no efficient generic method of generating (k,n) codebooks with minimizing the pixel expansion, 2) it is impractical and time-consuming to stack three or four shares. Therefore in this project our aim is to extend this hybrid codebook based method with goal of overcoming above two listed limitations. We are presenting the efficient approach for codebooks generation with less timing consuming while decryption. Keywords—Contrast,Share,Stacking,Pixel expansion.

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) is a method of encrypting a secret image into shares such that stacking a sufficient number of shares reveals the secret image. Shares are usually presented in transparencies. Each participant holds a transparency. Most of the previous research work on VC focuses on improving two parameters: pixel expansion and contrast. In this paper, we studied the cheating problem in VC and extended VC. We considered the attacks of malicious adversaries who may deviate from the scheme in any way. We presented three cheating methods and applied them on attacking existent VC or extended VC schemes. We improved one cheat-preventing scheme. We proposed a generic method that converts a VCS to another VCS that has the property of cheating prevention. The overhead of the conversion is near optimal in both contrast degression and pixel expansion.

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.

The world has become very much dependent on electronic devices and internet with the advancement of new technologies. So, security is also becoming a very vital issue as we share all our details through different electronic mediums to internet. Cryptography is a well known technique of hiding secret data. Visual Cryptography (VC) is a special type of cryptography where we can securely transmit secret data over different transmission mediums. Various visual cryptography schemes have been formulated to carry out the secure transmission of images efficiently. Visual Cryptography provides techniques to share an image efficiently over various internet services. In visual cryptography an image is broken into a number of share images which are later stacked upon to generate the original image. Out of various schemes some have shown very promising results with or without a small increase in the final image dimension which is also referred as pixel expansion. The proper alignment of the distributed shares reveals the original secret image. In this paper we provide a state-of-the-art review and analysis of the several existing schemes of Visual Cryptography.

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.

Region Incrementing Visual Cryptography (RIVC) was first introduced by R Z Wang in 2009. (2, n) region incrementing visual cryptographic scheme gradually reconstructs the secrets in a single image with multiple security levels. But Wang's scheme suffers from color reversal and pixel expansion. Later, in 2012, k out of n region incrementing scheme and Efficient Construction for Region Incrementing Visual Cryptography using linear programming are also introduced. But all of these have a large pixel expansion problem and some of the methods suffer from colour reversal also. In this paper, efficient construction method of (2, 3) RIVCS is introduced without any pixel expansion and increased contrast. The following are the important features of the proposed system. a) It has no pixel expansion b) Increased contrast c) The color reversal problem is completely eliminated.

In order to share a secret information among a group of participants, the method of secret sharing is used. The secret sharing method that is used to share or encrypt images is called Visual Cryptography. The main problems that subsist in Visual Cryptography are pixel expansion and poor image quality. Research are being conducted to solve the above mentioned problems. In this research, effective technique of share generation based on XOR-based visual cryptography for General Access Structures is introduced. Perfect restoration of the secret, no pixel expansion and no code book requirement are the advantages that the algorithm is expected to have. The generated shares are then covered in an image using steganography which provides additional security.

Visual cryptography (VC) is an emerging area used for data hiding, authentication, multimedia security and transmission of data. Parameters mainly focused in VC are pixel expansion, number of frames, type of images and number of undisclosed message images. Recent research shows many applications uses visual cryptography concept in authentication, secure transaction, secret sharing of information. But visual cryptography shows limited security for VC shares results in lack of security measure. In this paper work different VC (K, N) secret sharing techniques discussed and following analysis shows hybrid approach algorithms used in recent years that can be used for various applications in further implementation with high confidential secret sharing of data.

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.

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.

Conventional visual cryptography (VC) suffers from a pixel-expansion problem, or an uncontrollable display quality problem for recovered images, and lacks a general approach to construct visual secret sharing schemes for general access structures. We propose a general and systematic approach to address these issues without sophisticated codebook design. This approach can be used for binary secret images in non-computer-aided decryption environments. To avoid pixel expansion, we design a set of column vectors to encrypt secret pixels rather than using the conventional VC-based approach. We begin by formulating a mathematic model for the VC construction problem to find the column vectors for the optimal VC construction, after which we develop a simulated-annealing-based algorithm to solve the problem. The experimental results show that the display quality of the recovered image is superior to that of previous papers.

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

This paper proposes a (k,n) visual cryptography based on Shamir's secret sharing (VCSSS). Using Shamir's secret sharing, a binary secret image can be shared into n meaningless shares, in order to make the generated shares more like noise images, adding the randomness within the process of sharing. Picking any k shares from n meaningless shares, the secret image can be revealed by using Lagrange interpolation. The main contribution of this paper is that applying Shamir's secret sharing to realize a (k,n) visual cryptography, and this method neither requires code book nor suffers from pixel expansion. Experimental results show VCSSS can realize a (k,n) visual cryptography, and correct decoding rate (CDR) of revealed secret image can be guaranteed.

The traditional cheating prevention is usually based on visual cryptography (VC), in which the constructed image is bigger than the secret image because of the pixel expansion. In this paper, we studied the cheating problems in visual secret sharing (VSS) by random grids (RG) which can prevent the cheating activities with no pixel expansion. We considered the attacks of collusive cheaters who may deviate from the scheme in any way. We presented the cheating method and applied it on attacking existent n-out-of-n VSS scheme based on RG. Then we proposed one cheat-preventing scheme that can prevent the cheating activity upon.