摘要:区块链是一种结合分布式共识、加密、时间戳等方法,在不依赖任何第三方中心化机构的情况下,实现点 对点交易、协调以及协作的技术.近几年,区块链技术的不断发展引起了产业界和学术界的极大兴趣.但是,区块链的 存储可扩展性问题,提高了区块链设备的门槛,成为了区块链应用落地的瓶颈.介绍了区块链的基本原理和存储模 型,分析了当前区块链所面临的存储问题;然后,针对区块链存储可扩展性问题,从链下存储和链上存储这两条技术 路线出发,论述了主要的解决方案的原理与思路;最后,总结了提高区块链存储可扩展性的技术研究进展,指出了当 前解决方案所面临的问题,为未来的研究工作提供了方向.

摘要:Modern cryptocurrency systems, such as Ethereum, permit complex financial transactions through scripts called smart contracts. These smart contracts are executed many, many times, always without real concurrency. First, all smart contracts are serially executed by miners before appending them to the blockchain. Later, those contracts are serially re-executed by validators to verify that the smart contracts were executed correctly by miners. Serial execution limits system throughput and fails to exploit to- day’s concurrent multicore and cluster architectures. Nevertheless, serial execution appears to be required: contracts share state, and contract programming languages have a serial semantics. This paper presents a novel way to permit miners and validators to execute smart contracts in parallel, based on techniques adapted from software transactional memory. Miners execute smart con- tracts speculatively in parallel, allowing non-conflicting contracts to proceed concurrently, and “discovering” a serializable concurrent schedule for a block’s transactions, This schedule is captured and encoded as a deterministic fork-join program used by validators to re-execute the miner’s parallel schedule deterministically but concurrently. Smart contract benchmarks run on a JVM with ScalaSTM show that a speedup of 1.33x can be obtained for miners and 1.69x for validators with just three concurrent threads.

摘要:本文从区块链可扩展性、安全与隐私保护、区块链监管审计及智能合约开发与保障四个 方面分析总结了区块链当前存在的问题，阐述了解决相关问题需要研究的基础理论和关键技术；进 一步探讨了区块链技术的发展趋势和影响；最后给出了对策建议。

摘要:摘要:现有区块链主要分为公链和联盟链，公链是区块链思想的本源，然而现有公链体系存在匿名 账户难以与现实世界对应，以及系统执行效率低两大缺陷，同时，联盟链较差的隐私性和信息安全性又备 受诟病，鉴于此，提出许可公链(permissionedpublicblockchain,PPC)的概念和实现方案.许可公链通过链 ，上分布式密码学注册方案，实现公共许可机制;通过可订阅二层合约、区块快速转发和结构化广播3个技 术提高大规模区块链的交易速度，因此，许可公链融合联盟链的许可机制与公链技术，是面向公众用户的、 可监管的创新公链方案、所提出许可公链系统不仅建立个人和账户的安全隐私对应关系，而且新架构灵活 高效，可支持复杂的实际应用，尤其适用于金融业务与智能金融监管。

摘要:以上海证券交易所“去中心化的主板核心交易系统”作为业务场景,旨在研究高性能联盟区块链的优化算 法.在联盟链关键技术研究的基础上,结合现有主板证券竞价交易系统的业务,提出了系统架构以及关键技术的实 现.对业务逻辑与共识分离、存储优化和数字签名验证优化(包括合并验签和 GPU 加速)等可提高联盟链性能的优 化策略进行了详细的介绍和分析.最后,通过一系列对比实验来验证优化策略的有效性.实验结果表明,这些优化手 段极大地提高了去中心化的主板核心交易系统的性能.

摘要:Blockchain-based platforms, such as Ethereum, allow trans- actions in blocks to call user-defined scripts named smart contracts. In the blockchain network, after being generated by a miner, a block will be validated many times by the peers who accept it. Hence by enabling concurrency on smart contracts, especially validation, we can improve the efficiency and the throughput of those platforms. By introducing multiversion transaction ordering, this paper presents a concurrent scheme called MVTO to run smart contracts concurrently. First, the miners are able to use any concurrency control technique to discover a conflict-serializable schedule. Then, validators use MVTO to verify the block by replaying this schedule concurrently and deterministi- cally. The evaluation shows that this mechanism achieves approximately 2.5x speedup in the block validation using a thread pool with 3 threads.

摘要:In this paper, we explore remarkable similarities between multi-transactional behaviors of smart contracts in cryptocurrencies such as Ethereum and classical problems of shared-memory concurrency. We examine two real-world examples from the Ethereum blockchain and an- alyzing how they are vulnerable to bugs that are closely reminiscent to those that often occur in traditional concurrent programs. We then elaborate on the relation between observable contract behaviors and well-studied concurrency topics, such as atomicity, interference, synchro- nization, and resource ownership. The described contracts-as-concurrent- objects analogy provides deeper understanding of potential threats for smart contracts, indicate better engineering practices, and enable appli- cations of existing state-of-the-art formal verification techniques.

摘要:ABSTRACT PBFT (Practical Byzantine Fault Tolerance) is one of the most popular consensus protocols of blockchain. However, in the PBFT, the enthusiasm of reliable nodes cannot be stimulated effectively, and a large amount of communication resources are used for data consistency. Therefore, a new consensus protocol — CDBFT (Credit-Delegated Byzantine Fault Tolerance) is proposed in this paper. CDBFT works as following: (1) a VRP(Voting Rewards and Punishments) scheme and its corresponding credit evaluation scheme are proposed not only to stimulate enthusiasm of reliable nodes but also to reduce the participation of abnormal nodes in the consensus process, and the virtuous circle of the system can be founded; (2) consistency and checkpoint protocols based on PBFT are proposed to improve the efficiency and flexibility of system. From the simulation results, a conclusion can be drawn, the participation probability of abnormal nodes in the consensus process can be reduced to 5%, and the efficiency and stability of the system are improved greatly in long-time running.

摘要:HoneyBadgerBFT, proposed by Miller et al. [35] as the first practical asyn- chronous atomic broadcast protocol, demonstrated impressive performance. The core of HoneyBadgerBFT (HB-BFT) is to achieve batching consensus using asynchronous common subset protocol (ACS) of Ben-Or et al., constituted with n reliable broadcast protocol (RBC) to have each node propose its input, followed by n asynchronous binary agreement protocol (ABA) to make a decision for each proposed value (n is the total number of nodes). In this paper, we propose two new atomic broadcast protocols (called Dumbo1, Dumbo2) both of which have asymptotically and practically better efficiency. In particular, the ACS of Dumbo1 only runs a small κ (independent of n) instances of ABA, while that of Dumbo2 further reduces it to constant! At the core of our techniques are two major observations: (1) reducing the number of ABA instances significantly improves efficiency; and (2) using multi-valued validated Byzantine agreement (MVBA) which was considered sub-optimal for ACS in [35] in a more careful way could actually lead to a much more efficient ACS. We implement both Dumbo1, Dumbo2 and deploy them as well as HB-BFT on 100 Amazon EC2 t2.medium instances uniformly distributed throughout 10 different regions across the globe, and run extensive experiments in the same environments. The experimental results show that our protocols achieve multi-fold improvements over HoneyBadgerBFT on both latency and throughput, especially when the system scale becomes moderately large.

摘要:Data,akeyassetinourdata-driveneconomy,hasfueled the emergence of a new data trading industry. However, there are a number of limitations in conventional data trading platforms due to the existence of dishonest buyer/data broker. To mitigate these limitations,weposittheimportanceofadataprocessing-as-a-service model,whichcomplementsconventionaldatahosting/exchange-as-aservice model. Specifically, in this paper, we introduce a secure data trading ecosystem and present a new blockchain-based data trading ecosystem (hereafter referred to as SDTE). In the ecosystem, both data broker and buyer are not able to obtain access to the seller’s raw data, as they are only getting access to the analysis findings that they require. In other words, we reduce the challenge of securing the dataset to the challenge to secure the data processing. We also build a security model to analyze the data trading market, and describe a new set of trading protocols for the entire data trading market. To demonstrate utility, we implement our proposed secure data trading platform (SDTP) on Ethereum & Intels Software Guard Extensions (SGX) and perform an in-depth analysis.

摘要:The surprising success of cryptocurrencies has led to a surge of interest in deploying large scale, highly robust, Byzantine fault tolerant (BFT) protocols for mission-critical applications, such as financial transactions. Although the conventional wisdom is to build atop a (weakly) synchronous protocol such as PBFT (or a variation thereof), such protocols rely critically on network timing assumptions, and only guarantee liveness when the network behaves as expected. We argue these protocols are ill-suited for this deployment scenario. We present an alternative, HoneyBadgerBFT, the first practical asynchronous BFT protocol, which guarantees liveness without making any timing assumptions. We base our solution on a novel atomic broadcast protocol that achieves optimal asymptotic efficiency. We present an implementation and experimental results to show our system can achieve throughput of tens of thousands of transactions per second, and scales to over a hundred nodes on a wide area network. We even conduct BFT experiments over Tor, without needing to tune any parameters. Unlike the alternatives, HoneyBadgerBFT simply does not care about the underlying network.

摘要:Reliablecomputersystems musthandlemalfunctioningcomponentsthat giveconflictinginformation to different parts of the system. This situation can be expressed abstractly in terms of a group of generals of the Byzantine army camped with their troops around an enemy city. Communicatingonly by messenger, the generals must agree upon a common battle plan. However, one or more of them may be traitors who will try to confuse the others. The problem is to find an algorithm to ensure that the loyal generals will reach agreement. It is shown that, using only oral messages, this problem is solvable if and only if more than two-thirds of the generals are loyal; so a single traitor can confound two loyal generals. With unforgeable written messages, the problem is solvable for any number of generals and possible traitors. Applications of the solutions to reliable computer systems are then discussed.