Cloud computing is the long dreamed vision of computing as a utility, where users can remotely store their data into the cloud so as to enjoy the on-demand high quality applications and services from a shared pool of configurable computing resources. By data outsourcing, users can be relieved from the burden of local data storage and maintenance. It also eliminates their physical control of storage dependability and security, which traditionally has been expected by both enterprises and individuals. This unique paradigm brings about many new security challenges, which need to be clearly understood and resolved. This work studies the problem of ensuring the integrity of data storage in Cloud Computing. To ensure the correctness of data, we consider the task of allowing a third party auditor (TPA), on behalf of the cloud consumer, to verify the integrity of the data stored in the cloud. This scheme ensures that the storage at the client side is minimal which will be beneficial for thin clients.