Pixel Expansion Research Articles

A distortion free multi-secret image sharing with efficient shadow communication overhead

Traditional secret image sharing deals with encoding one secret image into two shares. Natural extension of traditional secret image sharing is multiple secret encoding into the same number of shares which reduces the communication and storage overhead. This paper proposes a multiple secret image sharing technique with minimum pixel expansion and share size. In (2, 2) secret image sharing generally two shares of equal size are required to be stored. While in the proposed scheme, one of the shares is replaced with a key which is taking the size of only one row of the share. However minimum bits are required to be 100 for the security reason, so if the bits in key is less than this value, it is made up to this size by padding extra random bits. So now in total, only one share with almost one extra row is needed to be stored resulting in the reduction of communication and storage overhead to almost half. The size of the shares and original secret image is approximately same so the reconstructed secret image will be distortion free. The advantages and its applicability of the propose scheme has been demonstrated by experimental results.

Contrast-improved visual secret sharing based on random grid for general access structure

Random grid (RG)-based visual secret sharing (VSS) owns the advantages of no pixel expansion and codebook design. VSS for general access structure (GAS) possesses wider applications than VSS for (k,n) threshold. Previous RG-based VSS studies for GAS had the drawbacks of “all-or-nothing” or low visual quality. In this paper, we will develop a progressive VSS (PVSS) algorithm for GAS with improved visual quality based on RG. We employ different regions of the secret image and their generated corresponding random bits to improve the visual quality of the revealed secret image as well as to gain GAS with progressive feature, where the random bits are divided into three parts. In addition, our scheme has neither pixel expansion nor codebook design due to RG. We show the effectiveness of our proposed scheme in terms of experiments and analyses.

Combination of Sharing Matrix and Image Encryption for Lossless $(k,n)$ -Secret Image Sharing.

This paper first introduces a (k,n) -sharing matrix S(k, n) and its generation algorithm. Mathematical analysis is provided to show its potential for secret image sharing. Combining sharing matrix with image encryption, we further propose a lossless (k,n) -secret image sharing scheme (SMIE-SIS). Only with no less than k shares, all the ciphertext information and security key can be reconstructed, which results in a lossless recovery of original information. This can be proved by the correctness and security analysis. Performance evaluation and security analysis demonstrate that the proposed SMIE-SIS with arbitrary settings of k and n has at least five advantages: 1) it is able to fully recover the original image without any distortion; 2) it has much lower pixel expansion than many existing methods; 3) its computation cost is much lower than the polynomial-based secret image sharing methods; 4) it is able to verify and detect a fake share; and 5) even using the same original image with the same initial settings of parameters, every execution of SMIE-SIS is able to generate completely different secret shares that are unpredictable and non-repetitive. This property offers SMIE-SIS a high level of security to withstand many different attacks.

A Study on Visual Cryptography for Colour Images

The intent of this paper is to present some of the major things about visual cryptography for colour images. The idea behind this technique is quite simple and powerful. Visual cryptography deals with visual information like picture, printed text and written notes etc. Visual cryptography also called secret sharing. As the name implies visual cryptography which has a single secret image and more than one shadow images and provided for numerous users. Visual cryptography process depends on various measures such as accuracy, computational complexity, pixel expansion, contrast whether generated it is meaningless or meaningful. Encryption performed by image processing techniques and the decryption carried out by human visual system with the stacking images. Visual cryptography need not require any complicated cryptographic proficiency. So, the intruders or hackers get hard to hack the details programmatically. However, this papers deals with visual cryptography for colour images.

A (n, n) threshold non-expansible XOR based visual cryptography with unique meaningful shares

Cloud-based multimedia systems are attracting end users with high end infrastructure resources and enormous storage facilities. However, there persists a high chance of leakage of sensitive information if outsourced to the remote cloud servers without encryption. In this article, a secure way of obscuring the information based on XOR based Visual Cryptography (VC) has been proposed. It obscures the secret information into multiple meaningful shares prior to outsourcing which reduces the vulnerability of random looking shares to cryptanalysis. The scheme also overcomes the problems existing in the traditional VC schemes like pixel expansion, share alignment problem, contrast loss, explicit codebook requirement, limitation on number of participants and lossy recovery of the secret. Proposed scheme ensures perfect recovery of the secret with high boost in contrast at the authentic entity end. Three novel algorithms have been proposed for generation of basis matrices, generation of random shares and conversion of random shares to meaningful shares to achieve this objective. The visual quality of the meaningful shares and the recovered secret image is quite good as evaluated by various objective error metrics. Comparative results based on various aspects of visual cryptography prove the efficiancy of the proposed approach over existing state-of-the-art approaches.

Boolean operations-based visual secret sharing for general access structures

Compared to conventional visual secret sharing (VSS), Boolean operations-based VSS solves the problems of the large pixel expansion (pe) and the complex computation involved in the decryption process. However, the existing VSS schemes based on Boolean operations are limited only to (2, n), (n, n) and (k, n). In this paper, we propose a Boolean operations-based VSS scheme for general access structures. The proposed scheme encodes the secret image into several shares such that the secret image can be reconstructed only by any qualified subset of the shares. The proposed scheme has lossless secret reconstruction with an acceptable pixel expansion (0 < pe < 1.5) and fast decoding process. The correctness of the proposed scheme is validated by formal security analysis and the experimental results.

A Novel Pixel Merging-Based Lossless Recovery Algorithm for Basic Matrix VSS

Lossless recovery in visual secret share (VSS) is very meaningful. In this paper, a novel lossless recovery algorithm for the basic matrix VSS is proposed. The secret image is reconstructed losslessly by using simple exclusive XOR operation and merging pixel. The algorithm not only can apply to the VSS without pixel expansion but also can apply to VSS with pixel expansion. The condition of lossless recovery of a VSS is given by analyzing the XOR all columns of basic matrixes. Simulations are conducted to evaluate the efficiency of the proposed scheme.

Cheating prevention visual cryptography scheme using Latin square

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.

Visual cryptograms of random grids via linear algebra

Two visual models of image secret sharing have been studied: visual cryptography schemes (VCS), introduced by Naor and Shamir, and visual cryptograms of random grids (VCRG), introduced by Kafri and Keren. VCRG has gained much attention in academia than before to avoid the pixel expansion of VCS. Although there is a strict relation between VCRG and VCS, VCRG can still be improved to achieve a better result. In this paper, based on new insight into linear algebraic technique to construct VCS, where we are able to construct VCS by solving a linear system of more equations at a time, we put forward a new construction of VCRG for general access structures. The effectiveness and advantage of the proposed construction are formally analyzed and experimentally demonstrated. With theoretical and practical interests, our construction exposes new possibilities to the researches of visual models of image secret sharing.

XOR-based progressive visual secret sharing using generalized random grids

This paper proposes an exclusive or (XOR)-based progressive visual secret sharing scheme that uses generalized random grids. This scheme differs from conventional visual secret sharing schemes. In addition to progressive recovery of secret messages, decrypting with an XOR operator produces reconstructed secret images with high visual quality when more shares are collected. Furthermore, the proposed scheme does not require a codebook to generate shares. In addition, there is no pixel expansion of the shares; thus, storing the shares does not result in additional burden. Experimental results reveal that the proposed scheme is superior to existing approaches with respect to performance and practicability.

Generating random grid-based visual secret sharing with multi-level encoding

Most visual secret sharing (VSS) schemes are employed for the secret sharing of binary secret images. In these schemes, the share appears as a noise-like image, such that no information about the secret image can be obtained from an individual share. The recovered secret message can only be decrypted by the human eye following rendering using two different light transmissions. However, these schemes do not apply well to gray-level secret images because the halftone region of gray-level secret images cannot be adequately recovered. In this paper, we propose a VSS scheme with multi-level encoding based on a generalized random grid, which can retrieve the secret in a multi-level secret image with a high visual quality using the XOR operant during decryption. The proposed method produces a share of the same size as the original secret image without pixel expansion and does not require a codebook in the encoding process.

Lossless Compression of VC Shares in RGB Color Space

Visual Cryptography is a special encryption technique to hide information in images in such a way that it can be decrypted by the human vision if the correct key image is used. In Visual Cryptography the reconstructed image after decryption process encounters a major problem of Pixel expansion. This is overcome in this proposed method by minimizing the memory size using lossless image compression techniques. Image compression is minimizing the size in bytes of a graphics file without degrading the quality of the image to an unacceptable level. The reduction in file size allows more images to be stored in a given amount of disk or memory space. It also reduces the time required for images to be sent over the Internet or downloaded from Web pages. Hybrid techniques are used in this proposed method as it can exploit multiple kinds of redundant information Keywords: Visual Cryptography; HVS; Image Compression; Vector Quantization; Run Length Encoding; Huffman Coding

On the design of a two-decoding-option image secret sharing scheme

In an image secret sharing scheme (ISSS), two main categories are discussed. One is the polynomial-style image secret sharing scheme (PISSS), and the other is the visual secret sharing (VSS). It is interesting to combine the main properties of these two schemes. When the encoded secret images are received, we can decode them by combining these two schemes’ properties, utilizing the VSS property to seek the secret immediately by human visual system (HVS) and the PISSS property to recover the secret perfectly with a decoding machine. This paper combines PISSS and random grids-based VSS to remove all the drawbacks existing in the previous works including 1) distortion by compressing a secret image, 2) non-perfect reconstructed image, 3) distortion of pixel expansion, and 4) size-reduced halftone image. The experimental results demonstrate the proposed scheme does work well.

On the Pixel Expansion of Visual Cryptography Scheme

In this paper, we first follow Ateniese et al.'s work that provides upper bounds of the pixel expansion of visual cryptography schemes(VCSs) for more kinds of graph access structures, in which we require that a subset of parties can determine the secret if they contain an edge of the graph G. The constructive upper bounds are derived by the graph decomposition technique. Then we generalize Ateniese et al.'s method of comparing the optimal pixel expansion of VCSs with two different access structures.

Multi secret sharing with unexpanded meaningful shares

Traditional Visual Cryptography (VC) facilitates a technique to protect only one secret image using single set of shares. Recent researches enhance the capabilities of traditional VC by providing the feature of Multi Secret Sharing (MSS), where more than one secret image can be protected at a time. In MSS different secret images are revealed by the stacking of same set of shares at different angles. Most of the existing state of art researches on MSS have common problem of pixel expansion and random pattern of the shares. Due to pixel expansion, there is wastage of the storage space and transmission time, moreover random pattern of the shares increases the vulnerability for cryptanalysis. In this paper a novel Multi Secret Sharing scheme with unexpanded as well as meaningful shares has been proposed to protect two secret images at a time. In the proposed approach the recovery probability of black pixels of the secret images in the decoded images is always 1 while that of white pixels, it is 0.25. Therefore the contrast of the decoded images is obtained as 25 % which is same as in most of the earlier researches with pixel expansion & random shares. Experiments confirm that all meaningful shares fulfill the contrast and security conditions. Secret images can be easily decoded by only human visual system without any computation at receiver end.

Visual cryptographic schemes using combined Boolean operations

Visual Cryptographic scheme (VCS) is a variant form of secret sharing method to encode a secret image into n distinct shares. The dealer distributes shares to each participants in such a way that, while certain qualified subsets of participants can visually recover the secret, but other forbidden sets of participants have no information on the secret. Such a system is the general access structures in VCS. The essential access structure (k, n)* is a type of threshold scheme were one participant is the leader who holds the essential share and the remaining n-1 shares are given to n-1 participants. The secret image cannot be retrieved in the absence of leader and the leader needs the support of at least k-1 remaining participants to recover the secret image. Small pixel expansion and maximum contrast are the basic parameters for measuring the quality of the VCS. In the literature there are constructions for both deterministic and probabilistic (k, n)*-VCS. The following are the important contributions of this paper. (1) A deterministic (k, n)*-VCS with improved contrast. (2) A deterministic (k, n)- VCS for t essential participants with improved contrast and less pixel expansion. (3) An ideal contrast general access structure construction with AND operation for grey scale images. (4) An ideal contrast (k, n)*-VCS construction for both binary and grey scale images. (5) An ideal contrast (k, n)-VCS for t essential participants for both binary and grey scale images.

Progressive visual secret sharing for general access structure with multiple decryptions

Visual secret sharing (VSS) for general access structure (GAS) owns wider applications than (k, n) threshold VSS. VSS with multiple decryptions realizes the functionalities of both OR-based VSS (OVSS) and XOR-based VSS (XVSS), which can broaden the applications as well compared to one recovery method-based VSS. In this paper, we propose a progressive VSS (PVSS) scheme for GAS with the features of both OR and XOR decryptions based on random grid (RG). The different regions of the secret image and corresponding genearted random bits are employed to gain progressive property as well as GAS with OR and XOR decryptions. For the qualified sets, if we have a copy machine, we can reconstruct the secret by stacking. On the other hand, if a device with XOR operation is available, we can improve the visual quality of the recovered secret image as well as we can reconstruct the secret image losslessly when we collect all the n shares. In addition, our scheme has neither pixel expansion nor codebook design due to RG. The effectiveness of the proposed scheme are shown in terms of experimental results and analyses.

A Secure Visual Cryptography Scheme Using Private Key with Invariant Share Sizes

Visual cryptography (VC) is one of the best techniques used to secure information. It uses the human vision to decrypt the encrypted images without any cryptographic computations. The basic concept of visual cryptography is splitting the secret image into shares such that when the shares are stacked, the secret image is revealed. In this paper we proposed a method that is based on the concept of visual cryptography for color images and without any pixel expansion which requires less space. The proposed method is used to encrypt halftone color images by generating two shares, random and key shares which are the same size as the secret color image. The two shares are generated based on a private key. At the receiving side, the secret color image is revealed by stacking the two shares and exploiting the human vision system. In this paper, we produce an enhanced form of the proposed method by modifying the encryption technique used to generate the random and the key shares. Experimental results have shown that the proposed and the enhanced methods suggest an efficient way to encrypt a secret color image with better level of security, less storage space, less time of computation and with a better value of PSNR.

Hierarchical threshold secret sharing scheme for color images

The applications that use pattern recognition via secret sharing are seldom linear, straightforward and uncomplicated. The layers of complexity grows as the process turns more secretive. In applications, such as banking transactions, hierarchical secret sharing comes in as a handy tool. This paper analyses the use of disjunctive hierarchy of secret sharing without compromising security while saving time. This scheme simplifies the process when more hands are involved by using simple Boolean and arithmetic operations and thus reduces the computational complexity from O (nlog2n) to O (n). The other features are authentication of the participants using Lagrange Interpolation; non-requirement of half toning of color images; no pixel expansion without degradation in visual quality of the recovered secret image. This paper also provides solution for meaningful share images with the ability to detect the manipulation of share images. The main advantage of this scheme is that it gives the benefit in scenarios in which participants of different levels are involved.

Region splitting visual cryptography using random grids

Visual cryptography is encryption technique to hide secret image into noise–like images, called as shares. Shares are stacked together to decrypt secret image. This paper presents multiple secrets sharing scheme called region splitting visual cryptography (RSVC) using random grids. To share n secrets, n shares are utilized along with common universal share. Proposed method has following features:(1) universal share for all secret messages, (2) any number of shares cannot reveal any information of universal share and secret messages, (3) no pixel expansion of shares, (4) no codebook requirement, and (5) human visual system is employed to decrypt the secret messages where no computational device or cryptographic knowledge is required.