区块链技术和比特币在2008年相伴而生，但随着各界对其研究与应用不断深入，区块链技术已经开始独立于加密数字货币，发展成为一个新的研究领域。区块链技术利用密码学原理、分布式数据存储技术、点对点网络及共识机制构建的分布式账本为解决多方合作过程中的信任、隐私、数据差异等问题带来了契机。诸多产业领域如金融、政务、医疗、城市建设等均开始应用区块链技术。当前，随着区块链技术的应用与推广，区块链技术也遇到了诸如扩展性、安全性、监管难等方面的挑战，催生了各界围绕区块链技术的各个方面及相关的密码学技术不断进行创新研究或引入新技术进行补充。本文结合当前学界及产业界的研究及应用情况，总结了区块链技术的五层基础体系架构，即数据层、网络层、共识层、合约层及应用层，并综述了该架构中各个层次的原理与技术。在此基础上，进一步介绍了针对区块链与传统网络结合、区块链技术自身以及相关密码学技术的各种典型的扩展技术，并讨论这些技术对区块链技术带来的影响。最后，结合区块链技术当前的发展现状，分析了其在研究应用中面临的挑战及其未来的发展方向，以期为未来的研究工作带来启发与借鉴。

Blockchain (or distributed ledger) technology was introduced in 2008, when the famous Bitcoin cryptocurrency was initiated. Blockchain has been undergoing rapid growth in both academia and industry. Today, it is no exaggeration to say that blockchain has become a new, independent research topic—not a subtopic subsumed within cryptocurrencies. From a technical perspective, blockchain technology is based on various fundamental computing technologies, such as advanced cryptography, distributed data storage, peer-to-peer networking, and distributed consensus protocols. Generally, blockchain technology involves creating a shared, distributed ledger: that ledger can offer great flexibility and potential in resolving many important challenges in a complex computing context that involves multiple parties. Examples of such challenges include achieving mutual trust, privacy protection, and data consistency in large-scale business scenarios. Many business applications have already covered a broad range of industrial services, such as those related to finance, governance, medicine, and city construction. Blockchain technology is becoming increasingly adopted and applied; however, the current design of blockchain is practically far from sufficient—especially when dealing with critical domain challenges. Specifically, the key limitations of blockchain mainly derive from poor system scalability, weak resilience to external security attacks, and lack of computing interfaces for regulatory processes. Conversely, it is the very shortcomings of blockchain technology that motivate research efforts into many related technologies. Based on conventional blockchain design, new functional extensions and cryptography technical optimizations have been continuously proposed by researchers and practitioners: the aim is to make blockchain technology more practically applicable and meet various demands of different business users. In this overview paper, using the latest findings from both academic and industrial research, we systematically present the general architecture of blockchain technology with its five functional layers. The five-layered architecture comprises the following: a data layer; a network layer; a distributed consensus layer; a smart contract layer; and an application layer. We also provide a technical description of key theories and important techniques related to each functional layer. From the proposed general architecture of blockchain technology, we offer an in-depth explanation of its core technical extensions with respect to the following: blockchain integration with existing computer network techniques; the blockchain framework itself and important modules; and underlying critical cryptography techniques. Further, we discuss potential contributions that these promising technical extensions could provide with respect to reshaping and optimizing blockchain technology. Finally, following current developments with blockchain technology and its existing mainstream applications, the general views about future challenges and important directions for this technology is to facilitate future follow-up research.