(t, k, n) XOR-based visual cryptography scheme with essential shadows

Visual cryptography is an encryption technique that decomposes secret images into multiple shares. These shares are digitally or physically overlapped to recover the original image, negating the need for complex mathematical operations or additional hardware. There have been many variations of visual cryptography proposed over the years, each addressing different problems or to fulfill different security requirements. Existing review papers on the area only cover certain types of visual cryptography or lack comparisons between the various schemes. To address this gap, this paper provides broad overview of the area to aid new researchers in identifying research problems or to select suitable visual cryptography methods for their desired applications. For more veteran researchers in the area, our paper provides the most up-to-date coverage of the state-of-the-art. We first provide an introduction to the various categories of visual cryptography techniques, including a discussion on recently proposed schemes. These schemes are then compared in terms of their features, performance metrics, advantages and disadvantages. Compared to prior work, we extend the number of comparison metrics to include signal-to-noise ratio and the type of shares. Over 40 visual cryptography schemes that have been proposed in the past two decades were analyzed and compared. Our findings indicate that existing problems such as pixel expansion, poor quality of recovered image quality, computational and memory complexities still exist, and a optimizing the trade-off between these requirements still requires further investigation. We conclude the paper with a discussion of these open problems and future research directions.

An overview of visual cryptography techniques

A visual cryptography scheme (VCS) is a kind of secret sharing scheme which allows the encoding of a secret image into n shares distributed to n participants. The beauty of such a scheme is that a set of qualified participants is able to recover the secret image without any cryptographic knowledge and computation devices. An extended visual cryptography scheme (EVCS) is a kind of VCS which consists of meaningful shares (compared to the random shares of traditional VCS). In this paper, we propose a construction of EVCS which is realized by embedding random shares into meaningful covering shares, and we call it the embedded EVCS. Experimental results compare some of the well-known EVCSs proposed in recent years systematically, and show that the proposed embedded EVCS has competitive visual quality compared with many of the well-known EVCSs in the literature. In addition, it has many specific advantages against these well-known EVCSs, respectively.

Embedded Extended Visual Cryptography Schemes.

Extended XOR-based Visual Cryptography Schemes by Integer Linear Program

Hou et al. introduced a (2, n) block-based progressive visual cryptographic scheme (BPVCS). In (2, n)-BPVCS, a secret image is subdivided into n non-overlapped image blocks. When t (2 ≤ t ≤ n) participants stack their shadow images, the image blocks belonged to these t participants will be recovered. Unfortunately, Hou et al.’s (2, n)-BPVCS suffers from the cheating problem. Additionally, Hou et al.’s scheme is only suitable for 2-out-of-n case, i.e., (k, n)-BPVCS where k = 2. In this paper, we propose a cheating immune (k, n)-BPVCS for k>2. The main contribution of our paper is that the proposed (k, n)-BPVCS is not only cheating immune, but also suitable for general k-out-of-n threshold, where k and n are integers with 2 ≤ k ≤ n. Theoretical analysis demonstrates that our scheme still holds progressive recovery and security, and meantime has cheating immune capability.

Cheating immune k-out-of-n block-based progressive visual cryptography

Visual cryptography scheme (VCS) shares a binary secret image into multiple shadows, stacking qualified set of shadows will decode the secret image without computer resources. In this paper, we propose a (2, 3)-VCS, which can share one or two secret images into 3 shadows, stacking any two shadows will reveal the secret image. The shadow size is 3/2 times of the secret image. The contrasts of the revealed image are 1/3 and 1/2 when we share one and two secret images, respectively. We can also reveal the secret image by XOR decoding operation, and the visual quality of the revealed image can be further improved. By XOR decoding operation, the contrasts of the revealed image will be 2/3 and 1 when we share one or two secret images, respectively. In the case of sharing two secret images, the revealed two secret images have no distortion. Theoretic analysis and experimental results demonstrate the feasibility and advantages of the proposed (2, 3)-VCS.

/pdf/a-construction-method-of-2-3-visual-cryptography-scheme-3ak68sog9l.pdf

Quan Ma

Papers

(t, k, n) XOR-based visual cryptography scheme with essential shadows

A Construction Method of (2, 3) Visual Cryptography Scheme