Privacy-preserving cloud auditing with multiple uploaders
The provable data possession (PDP) allows the cloud server to prove that its client's data is securely stored, and allows the data uploader to check the integrity of the data (alternatively, a third party auditor (TPA) can perform the auditing on behalf of the uploader). Sharing data among multiple uploaders is another attracting advantage of cloud storage. However, privacy issues on multiple uploaders should be considered. During an auditing process, the TPA should not be able to learn the identity of the uploader. To address this problem, some privacy-preserving auditing schemes were found in the literature, utilizing ring signature or group signature techniques, which are not computationally efficient. How to improve efficiency in a cloud storage system with multiple uploaders is a challenge. In this paper, we propose an anonymous cloud auditing scheme with multiple uploaders (ACAMU). The authentication tag of a message consists of only one element. Therefore, the storage cost of the tags and the transmission and verification cost during the auditing process can be significantly reduced. We provide a full security proof for our scheme. Meanwhile, our scheme achieves unconditional anonymity for the uploaders, namely, the TPA cannot distinguish the identity of the uploader even though it holds all the uploaders' secret keys after performing the auditing operation.