The idea of big data has gained extensive attention from governments and academia all over the world. It is especially relevant for the establishment of a smart city environment combining complex heterogeneous data with data analytics and artificial intelligence (AI) technology. Big data is generated from many facilities and sensor networks in smart cities and often streamed and stored in the cloud storage platform. Ensuring the integrity and subsequent auditability of such big data is essential for the performance of AI-driven data analysis. Recent years has witnessed the emergence of many big data auditing schemes that are often characterized by third party auditors (TPAs). However, the TPA is a centralized entity, which is vulnerable to many security threats from both inside and outside the cloud. To avoid this centralized dependency, we propose a decentralized big data auditing scheme for smart city environments featuring blockchain capabilities supporting improved reliability and stability without the need for a centralized TPA in auditing schemes. To support this, we have designed an optimized blockchain instantiation and conducted a comprehensive comparison between the existing schemes and the proposed scheme through both theoretical analysis and experimental evaluation. The comparison shows that lower communication and computation costs are incurred with our scheme than with existing schemes. INDEX TERMS Big data, smart city, data auditing, blockchain.

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Nowdays, cloud storage technology has become a hot topic, and an increasing number of users are concerned with the security of their data in the cloud. Many auditing schemes on the cloud are proposed and the introduction of a third‐party auditor to assist users in verifying the integrity of cloud data. As a centralized node, the third‐party auditor has to communicate with all cloud users and cloud service providers, which becomes the bottleneck of the whole scheme. To solve this problem, we design a blockchain‐based flexible cloud data auditing scheme. In our scheme, a decentralized auditing framework is proposed to eliminate the dependency on the third‐party auditor, which increases the stability, security and performance of the whole scheme. Since the cloud service provider can automatically generates auditing proofs, our scheme can relieve the communication burdens of the cloud service provider. The proposed scheme also adapts the Merkle Hash tree to improve the verification performance. Security analysis and experiments show that the proposed scheme is secure and has better stability and verification efficiency.

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