Public Auditing for Shared Data with user Repealability in the Cloud

Now a days, cloud is frequently expanding its storage and data sharing services. Users can easily modify and share data as a group. But in technical organizations, data integrity needs to be verified publicly. The existing method, allows the user to download the corresponding part of shared data and re-sign it during user revocation, is inefficient due to the large size of shared data in the cloud. In this approach, we propose a public auditing system with extended features for the integrity of shared data with efficient user revocation. By utilizing the concept of proxy re-signatures, we allow the cloud to resign blocks on behalf of current users during user revocation, so that existing users do not need to download and re-sign blocks .The public verifier is always able to audit the integrity of shared data correctly without retrieving the entire data from the cloud, even if some part of that data has been already re-signed by the cloud.