Cloud computing is a network model of on-demand access for sharing configurable computing resource pools. Compared with conventional service architectures, cloud computing introduces new security challenges in secure service management and control, privacy protection, data integrity protection in distributed databases, data backup, and synchronization. Blockchain can be leveraged to address these challenges, partly due to the underlying characteristics such as transparency, traceability, decentralization, security, immutability, and automation. We present a comprehensive survey of how blockchain is applied to provide security services in the cloud computing model and we analyze the research trends of blockchain-related techniques in current cloud computing models. During the reviewing, we also briefly investigate how cloud computing can affect blockchain, especially about the performance improvements that cloud computing can provide for the blockchain. Our contributions include the following: (i) summarizing the possible architectures and models of the integration of blockchain and cloud computing and the roles of cloud computing in blockchain; (ii) classifying and discussing recent, relevant works based on different blockchain-based security services in the cloud computing model; (iii) simply investigating what improvements cloud computing can provide for the blockchain; (iv) introducing the current development status of the industry/major cloud providers in the direction of combining cloud and blockchain; (v) analyzing the main barriers and challenges of integrated blockchain and cloud computing systems; and (vi) providing recommendations for future research and improvement on the integration of blockchain and cloud systems.

中文翻译：

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集成区块链和云计算系统：系统调查、解决方案和挑战

云计算是一种按需访问的网络模型，用于共享可配置的计算资源池。与传统的服务架构相比，云计算在安全的服务管控、隐私保护、分布式数据库中的数据完整性保护、数据备份与同步等方面带来了新的安全挑战。可以利用区块链来应对这些挑战，部分原因在于透明度、可追溯性、去中心化、安全性、不变性和自动化等基本特征。我们对区块链如何在云计算模型中提供安全服务进行了全面的调查，并分析了当前云计算模型中区块链相关技术的研究趋势。在审核过程中，我们还简要研究了云计算如何影响区块链，特别是关于云计算可以为区块链提供的性能改进。我们的贡献包括：（i）总结了区块链和云计算融合的可能架构和模型以及云计算在区块链中的作用；(ii) 根据云计算模型中不同的基于区块链的安全服务，对近期相关工作进行分类和讨论；(iii) 简单地研究云计算可以为区块链提供哪些改进；(iv) 介绍行业/主要云提供商在云和区块链结合方向上的发展现状；(v) 分析集成区块链和云计算系统的主要障碍和挑战；