A remarkable interest in the Internet of Things (IoT)-based smart cities from both academia and industry has been observed in recent years. Smart cities can offer various smart applications such as intelligent transportation, industry 4.0, smart banking, among others, for boosting the life quality of citizens. Security is one of the key challenges of a smart city. One can enable smart cities with a blockchain to offer enhanced security via storing transactions in a secure, transparent, decentralized, and immutable ledger. However, both blockchain and smart cities are in their infancy and significant research efforts are needed to integrate them. In this paper, we comprehensively review the role of blockchain in enabling IoT-based smart cities. First, we present the evolution of blockchain technology in terms of constituent technologies, consensus algorithms, and blockchain platforms. Second, we discuss and critically evaluate various smart applications enabled by blockchain. Third, we present real-world blockchain implementation in smart cities as case studies. Fourth, we present the key requirements to integrate blockchain with smart cities. Finally, we present open research challenges along with their key causes and possible solutions.

近年来，学术界和工业界都对基于物联网（IoT）的智慧城市表现出了极大的兴趣。智慧城市可以提供各种智能应用程序，例如智能交通，工业4.0，智能银行等，以提高市民的生活质量。安全是智慧城市的主要挑战之一。通过将交易存储在安全，透明，分散和不变的分类帐中，可以使具有区块链的智慧城市提供增强的安全性。但是，区块链和智慧城市都处于起步阶段，需要进行大量研究才能整合它们。在本文中，我们全面回顾了区块链在启用基于IoT的智慧城市中的作用。首先，我们从构成技术的角度介绍了区块链技术的发展，共识算法和区块链平台。其次，我们讨论并严格评估由区块链支持的各种智能应用程序。第三，我们以案例研究的形式介绍了智慧城市中的现实世界中的区块链实施。第四，我们提出了将区块链与智慧城市整合的关键要求。最后，我们提出了开放的研究挑战以及它们的关键原因和可能的解决方案。