区块链原理及其核心技术

随着第一个去中心化加密货币系统——比特币系统自2009年上线成功运行至今,其背后的区块链技术也受到广泛关注.区块链技术独有的去中心化、去信任的特性,为构建价值互联平台提供了可能.在比特币白皮书中,区块链的概念十分模糊,而现有的一些介绍区块链的文章中,也多从抽象层次进行介绍,对于更深入的后续研究提供的帮助十分有限.本文首先将区块链技术从具体应用场景中抽象出来,提取出其五层核心架构,并就其中数据、网络、共识三层基础架构作详细说明.这三层架构包含了区块链系统中的三大核心技术:密码学、共识算法、网络.文中介绍这三种技术的研究现状,能够使读者迅速了解区块链技术的发展状况,并能根据自己的需要进行深入阅读.最后,介绍了区块链目前的应用现状和技术展望.

The Principle and Core Technology of Blockchain

While the first decentralized cryptocurrency system,Bitcoin,has run successfully since it was launched in 2009,the underlying technology,blockchain,now draws increasing attention.Based on the unique decentralization and trusted features of blockchain,it is possible to build a value-connected platform.However,the Bitcoin white paper does not provide a rigorous definition of blockchain.Meanwhile,prior related work mainly introduces high level concepts in blockchain,ignoring the important technique details.To provide an in-depth introduction of blockchain,this survey first extracts the blockchain technology from specific application scenarios,breaks the blockchain architecture into five core layers,and elaborates on the data,network,and consensus layers.More specifically,we introduce state-of-the-art techniques of three main components of a blockchain system:cryptography,consensus algorithm,and network in detail.We firstly introduce basic cryptographic tools involved in blockchain systems,such as hash calculation,Merkle tree,digital signature,elliptic curve digital signature algorithm(ECDSA),ring signature algorithm,zero-knowledge proof,and anti-quantum cryptographic algorithm.We then summarize the mainstream consensus processes involved in the existing systems and refine the consensus framework.Users can choose different consensus components to build their own consensus models according to the characteristics of the application scenarios.The end of the consensus section introduces the methods for modeling consensus algorithms abstractly and the two approaches used to formally prove and analyze the essential features of consensus models.Further,we introduce the network topologies and common network protocols adopted in blockchain systems.In addition,we introduce three hot issues related to blockchain,which are privacy protection,common attack schemes and capacity expansion.The paper analyzes the existing research results on the anonymity of Bitcoin,and then introduces three options to enhance its privacy:mixed currency,ring signature and zero knowledge proof.The existing attack schemes are divided into two categories in the paper,one based on the consensus model adopted by the system,and the other based on the network.We summarize the existing blockchain expansion schemes as single-chain extensions and cross-chain extensions,and analyze the two types in detail.At last,the current application situation and technical prospects of blockchain are introduced.We introduce three phases of the development of blockchain application,namely the digital currency,smart contract and new extensions in other areas.We compared different digital currencies in terms of purpose,distribution method,consensus algorithm and other aspects.We select three typical systems,Ethereum,Hyperledger and Enterprise Operation System(EOS),as the examples to show how to build smart contracts.Blockchain has made significant impact on the innovation and evolution of various fields,especially in the areas of Internet of Things,medical and public key infrastructure.Compared with other blockchain surveys,this survey summarizes and refines the papers in the blockchain field rather than a simple combination of prior work.For example,in the introduction to the consensus module,we extract a general framework from many existing consensus models.We split the consensus instances in different systems according to the hierarchy of the framework,and extract the components that are necessary for building a consensus model.Based on this survey,readers are able to understand the development of blockchain quickly and can explore in depth according to their respective needs.