The main objective of this project is constructing a secure data storage system that with Public auditability: to allow TPA to verify the correctness of the cloud data on demand without retrieving a copy of the whole data or introducing additional online burden to the cloud users. Storage correctness: to ensure that there exists no cheating cloud server that can pass the TPA’s audit without indeed storing users data intact. Privacy-preserving: to ensure that the TPA cannot derive users data content from the information collected during the auditing process. Batch auditing: TPA should have the capability to examine the auditing delegations and also multiple Files simultaneously. Lightweight: to allow TPA to perform auditing with minimum communication and computation overhead.