The paradigm of Internet of Things (IoT) is paving the way for a world, where many of our daily objects will be interconnected and will interact with their environment in order to collect information and automate certain tasks. Such a vision requires, among other things, seamless authentication, data privacy, security, robustness against attacks, easy deployment, and self-maintenance. Such features can be brought by blockchain, a technology born with a cryptocurrency called Bitcoin. In this paper, a thorough review on how to adapt blockchain to the specific needs of IoT in order to develop Blockchain-based IoT (BIoT) applications is presented. After describing the basics of blockchain, the most relevant BIoT applications are described with the objective of emphasizing how blockchain can impact traditional cloud-centered IoT applications. Then, the current challenges and possible optimizations are detailed regarding many aspects that affect the design, development, and deployment of a BIoT application. Finally, some recommendations are enumerated with the aim of guiding future BIoT researchers and developers on some of the issues that will have to be tackled before deploying the next generation of BIoT applications.

翻译：物联网（IoT）范式正推动世界迈向新阶段——我们的日常物品将相互连接，并与环境交互以收集信息和自动化特定任务。这一愿景需要实现无缝认证、数据隐私、安全性、抗攻击能力、易部署性和自我维护等特性。区块链技术（最初源于加密货币比特币）能够提供这些功能。本文全面综述了如何将区块链适配到物联网的特定需求中，以开发基于区块链的物联网（BIoT）应用。在阐述区块链基本原理后，介绍了最相关的BIoT应用，重点强调了区块链如何影响传统以云为中心的物联网应用。随后，从影响BIoT应用设计、开发和部署的多个维度，详细探讨了当前面临的挑战及可能的优化方案。最后，列举了若干建议，旨在指导未来BIoT研究人员和开发者解决部署下一代BIoT应用前必须应对的诸多问题。