摘要:Ethereum smart contract makes developers can deploy decentralized applications to inherit features from blockchain, such as decentralization and openness. Although Ethereum provided a decentralized platform, Ethereum Virtual Machine for smart contracts, it lacks of ability to fetch off-chain data. The general solution is Oracle data carrier. However, Oracle results in rising deployment costs. It requires Ethereum smart contract developers to follow format in programing contract, this constraint decreases the readability of smart contract. This paper proposes an off-chain data fetching architecture which is cost-effective and highly elastic for smart contract. It also compatible with exited contract, which makes Ethereum smart contract owner able to automate the reply process.

摘要:Smart contract, which could help developer deploy decentralized and secure blockchain application, is one of the most promising technologies for modern Internet of things (IoT) ecosystem today. However, Ethereum smart contract lacks of ability to communicate with outside IoT environment. To enable smart contracts to fetch off-chain data, this paper proposes a data carrier architecture that is cost-effective and elastic for blockchain-enabled IoT environment. Three components, namely Mission Manager, Task Publisher and Worker, are presented in the data carrier architecture to interact with contract developer, smart contract, Ethereum node and off-chain data sources. Selective solutions are also proposed for filtering smart contract event and decoding event log to fit different requirements. The evaluation results and discussions show the proposed system will decrease about 20USD deployment cost in average for every smart contract, and it is more efficient and elastic compared with Oraclize Oracle data carrier service.

摘要:Public key infrastructure (PKI) is the foundation and core of network security construction. Blockchain (Be) has many technical characteristics, such as decentralization, impossibility of being tampered with and forged, which makes it have incomparable advantages in ensuring information credibility, security, traceability and other aspects of traditional technology. In this paper, a method of constructing PKI certificate system based on permissioned BC is proposed. The problems of multiCA mutual trust, poor certificate configuration efficiency and single point failure in digital certificate system are solved by using the characteristics of BC distribution and non-tampering. At the same time, in order to solve the problem of identity privacy on BC, this paper proposes a privacy-aware PKI system based on permissioned BCs. This system is an anonymous digital certificate publishing scheme, which achieves the separation of user registration and authorization, and has the characteristics of anonymity and conditional traceability, so as to realize to protect user's identity privacy. The system meets the requirements of certificate security and anonymity, reduces the cost of CA construction, operation and maintenance in traditional PKI technology, and improves the efficiency of certificate application and configuration.

摘要:The public blockchain was originally conceived to process monetary transactions in a peer-to-peer network while preventing double-spending. It has since been extended to numerous other applications including execution of programs that exist on the blockchain called “smart contracts.” Smart contracts have a major limitation, namely they only operate on data that is on the blockchain. Trusted entities called oracles attest to external data in order to bring it onto the blockchain but they do so without the robust security guarantees that blockchains generally provide. This has the potential to turn oracles into centralized points-of-failure. To address this concern, this paper introduces ASTRAEA, a decentralized oracle based on a voting game that decides the truth or falsity of propositions. Players fall into two roles: voters and certifiers. Voters play a low-risk/low-reward role that is resistant to adversarial manipulation while certifiers play a high-risk/high-reward role so they are required to play with a high degree of accuracy. This paper also presents a formal analysis of the parameters behind the system to measure the probability of an adversary with bounded funds being able to successfully manipulate the oracle’s decision, that shows that the same parameters can be set to make manipulation arbitrarily difficult—a desirable feature for the system. Further, this analysis demonstrates that under those conditions a Nash equilibrium exists where all rational players are forced to behave honestly

摘要:Fog computing is a new computing paradigm that can provide flexible resources and services at the edge of network. It is an extension of cloud computing and usually cooperated with cloud computing. Therefore, end users, fog nodes, and cloud servers can form a three-layer service model in practical application. In this model, they should have an agreement on a service contract,which contains every party's rights and obligations before the beginning of the service.However, due to lack of trust, it will suffer from some fairness problems during signing a service contract.Contract signing protocol allows two or more mutual distrust entities to sign a predefined digital contract in a fair and effective way. In this paper, we propose a fair three-party contract signing protocol based on the primitive of blockchain, which can be applied to the scenario of fog computing. Our proposed construction allows the participants to sign a contract in a fairway without the involvementof an arbitrator.Moreover, the privacy of the contract content can be preserved on the public chain. Finally, we realize the proposed protocol through the private blockchain and provide the experimental simulation that analyzes the efficiency and effectiveness.

摘要:In blockchain ecosystems, an Oracle is a service tool which provides real-world data for smart contracts and other blockchain applications. At present, there are several Oracle implementation schemes, e.g. centralized Oracles, decentralized Oracles, and hardware Oracles. However, these schemes typically suffer from single source of data and low scalability. Application Specific Knowledge Engine (ASKE) is an integrated topic/application-centered knowledge portal that supports effective information retrieval and analysis. Inspired by ASKE, in this paper, we propose a novel Oracle implementation scheme. The proposed scheme can realize multi-source data extraction and analysis, then working prototypes are demonstrated to show the validity of the scheme.

摘要:Smartphones have become an indispensable item for people and are carried with people throughout the day. They are often embedded with various sensors such as accelerometers, magnetometers, barometers, microphone, humidity, light sensors, cameras, along with GPS.

摘要:Thanks to its decentralized structure and immutability, blockchain technology has the potential to address relevant security and privacy challenges in the Internet of Things (IoT). In particular, by hosting and executing smart contracts, blockchain allows secure, flexible, and traceable message communication between IoT devices. The unique characteristics of IoT systems, such as heterogeneity and pervasiveness, however, pose challenges in designing smart contracts for such systems. In this paper, we study these challenges and propose a design approach for smart contracts used in IoT systems. The main goal of our design model is to enhance the development of IoT smart contracts based on the inherent pervasive attributes of IoT systems. In particular, the design model allows the smart contracts to encapsulate functionalities such as contractlevel communication between IoT devices, access to data-sources within contracts, and interoperability of heterogeneous IoT smart contracts. The essence of our approach is structuring the design of IoT smart contracts as self-contained software services, inspired by the microservice architecture model. The flexibility, scalability and modularity of this model make it an efficient approach for developing pervasive IoT smart contracts.

摘要:With the rapid development of cryptocurrency and its underlying blockchain technologies, platforms such as Ethereum and Hyperledger began to support various types of smart contracts. Smart contracts are computer protocols intended to digitally facilitate, verify, or enforce the negotiation or performance of a contract. Smart contracts have broad range of applications, such as financial services, prediction markets and Internet of Things (IoT), etc. However, there are still many challenges such as security issues and privacy disclosure that await future research. In this paper, we present a comprehensive overview on blockchain powered smart contracts. First, we give a systematic introduction for smart contracts, including the basic framework, operating mechanisms, platforms and programming languages. Second, application scenarios and existing challenges are discussed. Finally, we describe the recent advances of smart contract and present its future development trends, e.g., parallel blockchain. This paper is aimed at providing helpful guidance and reference for future research efforts.

摘要:Smart cities aim to provide smart governance with the emphasis on gaining high transparency and trust in public services and enabling citizen participation in decision making processes. This means on the one hand data generated from urban transactions need to be open and trustworthy. On the other hand, security and privacy of public data needs to be handled at different administrative and geographical levels. In this paper, we investigate the pivotal role of blockchain in providing privacy, self-verification, authentication, and authorization of participatory transactions in open governance. We also investigate up to what extent edge computing can contribute towardmanagement of permissioned sharing at specific administrative levels and enhance privacy and provide an economic approach for resource utilization in a distributed environment. We introduce a novel architecture that is based on distributed hybrid ledger and edge computing model. The architecture provides refined and secure management of data generated and processed in different geographical and administrative units of a city. We implemented a proof of concept of the architecture and applied it on a carefully designed use case, ie, citizen participation in administrative decisions through consensus. This use case highlights the need to keep and process citizen participation data at local level by deploying district chaincodes and only share consensus results through permissioned chaincodes. The results reveal that proposed architecture is scalable and provide secure and privacy protected environment for citizen participatory applications. Our performance test results are promising and show that under control conditions, the average registration time for a citizen transaction is about 42ms, whilst the validation and result compilation of 100 concurrent citizens' transactions took about 2.4 seconds.

摘要:Smart contract technology is reshaping conventional industry and business processes. Being embedded in blockchains, smart contracts enable the contractual terms of an agreement to be enforced automatically without the intervention of a trusted third party. As a result, smart contracts can cut down administration and save services costs, improve the efficiency of business processes and reduce the risks. Although smart contracts are promising to drive the new wave of innovation in business processes, there are a number of challenges to be tackled. This paper presents a survey on smart contracts. We first introduce blockchains and smart contracts. We then present the challenges in smart contracts as well as recent technical advances. We also compare typical smart contract platforms and give a categorization of smart contract applications along with some representative examples.

摘要:智 能合 约是 一种 无需 中 介 、 自 我验证 、 自 动执行合约条款 的计算机交易 协议 ， 近年来 随着 区块链技术 的 日 益普及而 备 受关 注 区 块链上 的智 能合 约具有去 中 心化 、 去信 任 、 可编程 、 不可篡 改等特 性 ， 可灵活嵌入各种数据 和 资产， 帮 助实现安全 高效 的信息交 换、 价值转移和 资产管理， 最 终 有望深入变革传统商业模 式和 社 会生产 关 系 ， 为构建可编程 资产 、 系 统和 社会奠 定基础 本文致力于 以 区块链智 能合约为研究对象 ， 对 已 有的 研究成果进行全面梳理和 系 统概述 ， 提 出 了 智 能合约 的基础架构 模 型并以 此为研究框架 阐 述了 智 能合约 的 运行 机制 与基 础架构， 总结 了 智 能 合约的 研究挑 战 与进展， 介绍 了 智 能合 约 的技术 优势与典型应用 领域 ， 讨 论了 智能 合约的 发展 趋势， 以期 为智能 合约 的后续研究提供参考

摘要:Smart Health is a real-time, intelligent, ubiquitous healthcare service based on the IoT aware network and sensing infrastructure. Thanks to the rapid development of related technologies such as cloud computing, fog computing and IoT, research on smart health is gradually on the right track. This paper analyzes research on smart health in recent years and then discusses the development of smart health from both cloud and edge, including cloud computing, fog computing, IoT sensors, blockchain, and privacy and security. At present, in the research of cloud and smart health, the focus is on how to use the cloud to complete the challenges of massive health data and improve service performance, including related issues such as storage, retrieval and calculation of health big data in the cloud. At the edge, research focuses on the collection, transmission, and computation of health data, including sensors and wearable devices for collecting health data, various sensor networks, and how to process health data and improve service performance at the edge. As an emerging technology, blockchain has a wide range of applications in smart health. We discuss typical smart health application, blockchain in smart health and privacy and security issues related to smart health. Finally, we present challenges and opportunities for smart health in the edge computing era.

摘要:智能合约是区块链系统的核心组件,在现实中广泛应用.然而,目前没有关于智能合约的统一定义,在不同 的区块链平台上,智能合约的实现也相差甚远.这样将影响公众对智能合约的认知,也对产业的发展造成障碍.回顾 了智能合约的发展历史,梳理其概念的变化过程.归纳智能合约的本质,对现有智能合约的实现进行了分析和对比. 给出了面向合同的智能合约的形式化定义,为智能合约的标准化奠定基础.提出了独立于区块链平台的、通用的智 能合约实现方法.在目前广泛应用的联盟链区块链平台 Hyperledger Fabric 上面进行了具体实现.最后对未来工作进 行了展望.

摘要:随着以比特币为代表的区块链技术的蓬勃发展，区块链技术已经开始逐步超越可编程货币时代 而进入智能合约时代．智能合约（ｓｍａｒｔｃｏｎｔｒａｃｔ）是一种由事件驱动的、具有状态的代码合约和算法合 同，随着区块链技术的深入发展而受到广泛关注和研究．智能合约利用协议和用户接口完成合约过程的 所有步骤，允许用户在区块链上实现个性化的代码逻辑．基于区块链的智能合约技术具有去中心化、自治化、可观察、可验证、可信息共享等特点，可以有效构建可编程金融和可编程社会，广泛应用于数字 支付、金融资产处置、多重签名合约、云计算、物联网、共享经济等多个领域．首先阐述了智能合约技术的 基本概念、全生命周期、基本分类、基本架构、关键技术、发展现状以及智能合约的主要技术平台；然后探 讨了智能合约技术的应用场景以及发展中所存在的问题；最后，基于智能合约的理论知识，搭建了以太 坊实验环境并开发了一个众筹智能合约系统，旨在为基于区块链的智能合约技术的研究与发展提供参 考与借鉴．