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Issuing vouchers is a means of implementing social welfare. There are some security concerns about paper-based vouchers, such as counterfeiting, reproducing, their low operating efficiency and so on. This study explores how to apply blockchain technology and cryptography to build a secure e-voucher system in order to solve various shortcomings of paper vouchers. A feasible application model is proposed that integrates blockchain technology in the context of vouchers to support the field of social welfare. In this study, we conducted an analysis to prove that the security requirements of the e-voucher system are met when applying this model. Subsequently, we used the Hyperledger Fabric blockchain platform and Kafka ordering services to implement the campus welfare meal voucher system. A large number of experimental data were obtained to show that the system has a satisfactory performance. In the conclusion section, we discussed the theoretical and management implications of this study, and how this study meets UN Sustainable Development Goals.Sustainability 2020, 12, 3362 2 of 22 stores then ask the government or non-profit organizations for money with the voucher received. Government or non-profit organizations may use cash vouchers to reach consumption incentives or public welfare. In Zambia, poverty is a challenge that this country has always faced. Since agriculture is the main economic body, the Zambian government launched the Farmer Input Support Program (FISP) to subsidize farmers' crop losses due to natural disasters. The government issued a physical pre-paid voucher card to the farmer, and the farmer can use the card to redeem agricultural input supply. Zambia expects farmers who have been subsidized for two years to leave the plan, but the government has no way to track who has reached the subsidy deadline, thus the cost of FISP has exploded. Later, Zambia decided to build an electronic voucher system to try to solve some problems [8,9]. However, the Zambian government still faced some problems, which we will discuss later in the next section.Since a voucher is equivalent to proof of cash value and is not redeemable for cash, the anti-counterfeiting of vouchers is a very important issue. Because vouchers have a welfare purpose, only eligible individuals can receive and use vouchers. Therefore, preventing the transfer of vouchers is also a very important issue. Moreover, the relevant parties involved in the e-voucher system are more diverse than those involved in the general admission system, so mutual trust between groups is a key factor in the success of the e-voucher system. Recently, an emerging technology, called blockchain, has brought many new opportunities to the industry. Blockchain technology achieves trust among parties and fault tolerance through cryptography and decentralized architecture. The blockchain has evolved over several stages since its introduction. Virtual currency is the earliest application of blockchain technology. Gradually, it has been found that the special features of blockc...

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Abstract. Visual cryptography schemes encrypt a secret image into n shares so that any qualified set of shares enables one to visually decrypt the hidden secret; whereas any forbidden set of shares cannot leak out any secret information. In the study of visual cryptography, pixel expansion and contrast are two important issues. Since pixel-expansion based methods encode a pixel to many pixels on each share, the size of the share is larger than that of the secret image. Therefore, they result in distortion of shares and consume more storage space. In this paper, we propose a method to reach better contrast without pixel expansion. The concept of probability is used to construct an optimization model for general access structures, and the solution space is searched by genetic algorithms. Experimental result shows that the proposed method can reach better contrast and blackness of black pixels in comparison with Ateniese et al.'s.

This article presents a novel watermarking scheme for digital images based on Block Truncation Coding (BTC). Unlike other watermarking schemes, the proposed method does not alter the original image during the process of watermark casting. Instead, an ownership share is constructed as a key to reveal the watermark without resorting to the original image. Moreover, it is possible to register multiple watermarks for a single host image in the proposed scheme. During watermark casting, the feature of the host image, which is extracted by means of BTC, is combined with the watermark to generate an ownership share. When revealing the watermark, the author can address his/her ownership share to extract the watermark. Even though the host image has been attacked, the extracted watermark is still perceivable. Altogether, the method has many other applications besides copyright protection. For example, it can be used to cover the transmission of confidential images. The experimental results of this study show the robustness of the novel scheme against several common attacks.