Two novel visual cryptography (VC) schemes are proposed by combining VC with single-pixel imaging (SPI) for the first time. It is pointed out that the overlapping of visual key images in VC is similar to the superposition of pixel intensities by a single-pixel detector in SPI. In the first scheme, QR-code VC is designed by using opaque sheets instead of transparent sheets. The secret image can be recovered when identical illumination patterns are projected onto multiple visual key images and a single detector is used to record the total light intensities. In the second scheme, the secret image is shared by multiple illumination pattern sequences and it can be recovered when the visual key patterns are projected onto identical items. The application of VC can be extended to more diversified scenarios by our proposed schemes.

Visual cryptography in single-pixel imaging.

Quick response (QR) codes have been widely used in applications, such as data storage and high-speed machine reading. Anyone can gain access to the information stored in QR codes; therefore, they are unsuitable for encoding secret information without the addition of cryptography or other protection. In this paper, we propose a visual secret sharing scheme to encode a secret QR code into several shares. In contrast with other techniques, the shares in our scheme are valid QR codes that can be decoded with some specific meaning by a standard QR code reader, thereby avoiding raising suspicion in potential attackers. Moreover, the secret message is recovered by XOR-ing the qualified shares, an operation that can easily be performed using smartphones or other QR scanning devices. Experimental results show that the proposed scheme is both feasible and reasonably secure. Our scheme’s high sharing efficiency is also highlighted in this paper.

Improved Visual Secret Sharing Scheme for QR Code Applications

In reversible image secret sharing (RISS), the cover image can be recovered to some degree, and a share can be comprehensible rather than noise-like. Reversible cover images play an important role in law enforcement and medical diagnosis. The comprehensible share can not only reduce the suspicion of attackers but also improve the management efficiency of shares. In this paper, we first provide a formal definition of RISS. Then, we propose an RISS algorithm for a $(k,n)$ -threshold based on the principle of the Chinese remainder theorem-based ISS (CRTISS). In the proposed RISS, the secret image is losslessly decoded by a modular operation, and the original cover image is recovered by a binarization operation, both of which are just simple operations. Theoretical analyses and experiments are provided to validate the proposed definition and algorithm.

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Reversible Image Secret Sharing

In this paper, a novel visual secret sharing (VSS) scheme based on QR code (VSSQR) with (k, n) threshold is investigated. Our VSSQR exploits the error correction mechanism in the QR code structure, to generate the bits corresponding to shares (shadow images) by VSS from a secret bit in the processing of encoding QR. Each output share is a valid QR code that can be scanned and decoded utilizing a QR code reader, which may reduce the likelihood of attracting the attention of potential attackers. Due to different application scenarios, two different recovered ways of the secret image are given. The proposed VSS scheme based on QR code can visually reveal secret image with the abilities of stacking and XOR decryptions as well as scan every shadow image, i.e., a QR code, by a QR code reader. The secret image could be revealed by human visual system without any computation based on stacking when no lightweight computation device. On the other hand, if the lightweight computation device is available, the secret image can be revealed with better visual quality based on XOR operation and could be lossless revealed when sufficient shares are collected. In addition, it can assist alignment for VSS recovery. The experiment results show the effectiveness of our scheme.

Visual secret sharing scheme for (k, n) threshold based on QR code 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.

Progressive Visual Secret Sharing for General Access Structure with Multiple Decryptions

In comparison with Shamir’s original polynomial-based secret image sharing (SIS), Chinese remainder theorem-based SIS (CRTSIS) overall has the advantages of lossless recovery, low recovery computation complexity and no auxiliary encryption. Traditional CRTSIS methods generally suffer from no (k, n) threshold, lossy recovery, ignoring the image characteristics and auxiliary encryption. Based on the analysis of image characteristics and SIS, in this paper we propose a CRTSIS method for (k, n) threshold, through dividing the gray image pixel values into two intervals corresponding to two available mapping intervals. Our method realizes (k, n) threshold and lossless recovery for gray image without auxiliary encryption. Analysis and experiments are provided to indicate the effectiveness of the proposed method.

Chinese Remainder Theorem-Based Secret Image Sharing for ( k , n ) Threshold

In this paper, homomorphic visual cryptographic scheme HVCS is proposed. The proposed HVCS inherits the good features of traditional VCS, such as, loss-tolerant e.g., k, n threshold and simply reconstructed method, where simply reconstructed method means that the decryption of the secret image is based on human visual system HVS without any cryptographic computation. In addition, the proposed HVCS can support signal processing in the encrypted domain SPED, e.g., homomorphic operations and authentication, which can protect the user's privacy as well as improve the security in some applications, such as, cloud computing and so on. Both the theoretical analysis and simulation results demonstrate the effectiveness and security of the proposed HVCS.

Exploiting the Homomorphic Property of Visual Cryptography

The visual quality of the recovered secret image is usually evaluated by contrast in visual cryptography (VC). Precisely, the reconstructed secret image can be recognized as the original secret image when contrast is greater than zero. It is important for the user to know the clarity of the revealed secret image corresponding to different contrast values. In this paper, the clarity corresponding to contrast is investigated through conducting subjective evaluation scores and objective evaluation indexes, which can be extended to general applications.

Song Wan

Papers

Visual secret sharing scheme for (k, n) threshold based on QR code with multiple decryptions

Progressive Visual Secret Sharing for General Access Structure with Multiple Decryptions

Chinese Remainder Theorem-Based Secret Image Sharing for ( k , n ) Threshold

Exploiting the Homomorphic Property of Visual Cryptography

Clarity Corresponding to Contrast in Visual Cryptography