<p>Cloud storage provides convenience in managing data for users. Data integrity becomes important because data owner (DO) loses control of their data once it is uploaded to the cloud server (CS). Public auditing is used to check data integrity in cloud storage. Traditional public auditing schemes introduce a third-party auditor (TPA) to help users check their data. However, TPA is assumed to be trusted in these schemes, which may not be practical. A dishonest TPA may provide a good report to DO without executing the auditing task timely. If the data loss could not be detected timely, it may cause a great loss to DO. In this paper we aim to solve these problems using blockchain technique. In our scheme DO, TPA and CS interact with blockchain via smart contracts. We utilize a time-locked deposit smart contract to incentive TPA and CS for their fulfillment in the auditing task honestly. Otherwise, they would be amerced. We use storage smart contracts to ensure the auditing process transparency, and utilize zero-knowledge proof to protect DO&rsquo;s privacy. The scheme is extended to support batch auditing to reduce the user&rsquo;s cost. Experimental results show that our scheme is efficient and practical.</p> <p>&nbsp;</p>