Abstract: People prefer to use cloud storage due to its advantages of high scalability and low cost,but ensuring the integrity of cloud data has become a security challenge that needs to be solved immediately.While blockchain's characteristics of de-centralization and tamper resistance can greatly solve the problems such as single-point failures and security threats existing in cloud auditing schemes based on third party auditor(TPA),some scholars propose blockchain-based cloud auditing schemes.But these schemes need data owner(DO) or a delegated DO to validate the auditing proof,which not only requires DO to keep online,but increases its auditing burden.Moreover,most of them are only implemented in a simulated blockchain environment.Therefore,this paper proposes a cloud auditing scheme with Ethereum smart contracts－CASESC.CASESC uses solidity language to write Ethereum smart contract code which can send auditing requests and validate the auditing proof returned from cloud server provi-der(CSP) and stores auditing results and related information in the Ethereum that can be referred to by DO.Without delegating others or keeping online status,CASESC can replace DO to work and reduces its auditing overhead.Besides,CASESC conducts experiments in Ethereum public blockchain called Goerli and private blockchain constructed by Ganache in order to prove its availability.Theoretical analysis and experimental evaluation show that CASESC can significantly reduce the auditing overhead of DO without increasing overall auditing overhead.

Key words: Cloud auditing, Blockchain, Ethereum, Smart contract