Using cloud storage, users can remotely store their data and enjoy high quality applications and services from a shared pool of resources. However, users, when they don't have the physical possession of the data, chances of raising data integrity issue are possible. Thus, verification of data integrity is the at most important for a user, who has outsourced data to the cloud. To make the integrity check, a public auditing must be made possible. For it, the authors resort to a Third Party Auditor (TPA).