An identity-based online/offline secure cloud storage auditing scheme

Cloud storage has significantly reduced data management costs for data owners. However, loss of physical control over the data after outsourcing, triggers some security concerns such as data integrity. Provable Data Possession (PDP) protocols, enable data owners to audit the integrity of their outsourced data without the need to retrieve the file from cloud server. However, most existing PDP schemes require resource-constrained users to perform costly operations for generating metadata on file blocks. In online/offline PDP mechanisms introduced most recently, the user's computation is divided into online/offline phases, where the costly operations are allowed to be carried out in the offline phase. The users only require to perform lightweight operations in the real-time online phase. In this paper, we propose an identity-based (ID-based) online/offline PDP protocol which not only has lightweight computations at the users side, but also removes the complex certificate management/verification costs caused by expensive Public Key Infrastructure. The proposed scheme is based on an ID-based online/offline signature designed in this paper. The protocol is proven to be secure against a malicious cloud server in the random oracle model. We also prove the privacy preserving property of the protocol in the sense that it leaks no information of the outsourced data to the public verifier during the protocol execution. Moreover, our mechanism supports batch verification of multiple auditing tasks and fully dynamic data operations, efficiently. Experimental results demonstrate fine efficiency of our scheme in comparison to the recent proposals.