Blockchain and the Internet of things (IoT) systems are attracting more and more research efforts from both academia and industry. Blockchain is rapidly evolving to be a new infrastructure for building robust distributed applications. Similarly, Internet of things is getting increasing deployment in the context of smart city, smart home, smart healthcare, etc. On the intersection of the two emerging areas, researchers are proposing to use blockchain to build more dependable IoT systems. This paper reviews the most recent research advances in this direction during the past four years. Specifically, we review, summarize, and categorize existing research works. We divide the research works into four groups according to the roles that the blockchain plays in IoT systems, i.e., access control platform, data security platform, trusted third party, and automatic payment platform. For each group, we also discuss future research challenges. From the review, we further summarize the usage paradigms and open issues on using blockchain to build dependable IoT systems. We hope this work serves as a reference of existing models for both researchers and engineers that are interested to leverage blockchain to build future IoT systems.

区块链和物联网（IoT）系统吸引了学术界和工业界越来越多的研究工作。区块链正在迅速发展成为构建健壮的分布式应用程序的新基础架构。同样，物联网正在智能城市，智能家居，智能医疗等领域得到越来越多的部署。在两个新兴领域的交汇处，研究人员提议使用区块链来构建更可靠的物联网系统。本文回顾了过去四年中在这一方向上的最新研究进展。具体来说，我们对现有研究工作进行回顾，总结和归类。根据区块链在物联网系统中所扮演的角色，我们将研究工作分为四类，即访问控制平台，数据安全平台，受信任的第三方，和自动付款平台。对于每个小组，我们还将讨论未来的研究挑战。通过审查，我们进一步总结了使用区块链构建可靠的IoT系统的使用范例和未解决的问题。我们希望这项工作可以为有兴趣利用区块链构建未来物联网系统的研究人员和工程师提供现有模型的参考。