Server Re-Tag Provable Data Possession in Public Cloud

Integrity checking becomes imperative to secure data in a cloud environment. Especially in mobile cloud storage, clients can easily modify and share data as a group, which easily result in the stored data is neither compromised nor corrupted. To ensure data integrity can be audited publicly, clients need to compute signatures on all the blocks in shared data .In mobile cloud storage environment, the clients frequently join or leave groups. Once the client leaves the group, the blocks, which were previously signed, must be re-signed by an existing client. One method to allow other client to download the shared data and re-sign it, but it is inefficient due to the large size of shared data in the cloud. In this paper, we propose server re-tag provable data possession (SRT-PDP). By utilizing proxy re-signatures, we allow the cloud severs as the group manager to re-sign blocks after the client sign the shared data, so that existing clients do not have to do anything even if some clients leave the group. In addition, a public verifier is always able to audit the integrity of shared data without retrieving the entire data from the cloud servers. SRT-PDP enable the cloud server takes the most of the work, and reduce the burden of client, which is suit for mobile device.