Cloud Computing is current trend which is considered as the next generation information technology enterprise architecture. It manages all form of software starting from databases to the application software. Cloud Storage, can remotely store data and provide the on-demand high quality applications and services from a shared pool of configurable computing resources, without the burden of local data storage and maintenance. This work helps us to have a third party auditor with integrity algorithm to protect the cloud. This enables public audit ability for cloud storage, a third party auditor (TPA) to check the integrity of outsourced data and relaxed that data is secure. In this paper, we propose a secure cloud storage system supporting privacy-preserving public auditing. We further extend this to enable the TPA to perform audits for no of users simultaneously with efficiency. Extensive security and performance analysis show the proposed schemes are provably secure and highly efficient.