Biblio

In this paper, we provide a secure and efficient outsourcing scheme for multi-owner data sharing on the cloud. More in detail we consider the scenario where multiple data owners outsource their data to an untrusted cloud provider, and allow authorized users to query the resulting database, composed of the encrypted data contributed by the different owners. The scheme relies on a proxy re-encryption technique that is implemented using an El-Gamal Elliptic Curve(ECC) crypto-system. We experimentally assess the efficiency of the implementation in terms of computation time, including the key translation process, data encryption and re-encryption modules, and show that it improves over previous proposals.

Together with its great advantages, cloud storage brought many interesting security issues to our attention. Since 2007, with the first efficient storage integrity protocols Proofs of Retrievability (PoR) of Juels and Kaliski, and Provable Data Possession (PDP) of Ateniese et al., many researchers worked on such protocols.

The difference among PDP and PoR models were greatly debated. The first DPDP scheme was shown by Erway et al. in 2009, while the first DPoR scheme was created by Cash et al. in 2013. We show how to obtain DPoR from DPDP, PDP, and erasure codes, making us realize that even though we did not know it, we could have had a DPoR solution in 2009.

We propose a general framework for constructing DPoR schemes that encapsulates known DPoR schemes as its special cases. We show practical and interesting optimizations enabling better performance than Chandran et al. and Shi et al. constructions. For the first time, we show how to obtain constant audit bandwidth for DPoR, independent of the data size, and how the client can greatly speed up updates with O(λ√n) local storage (where n is the number of blocks, and λ is the security parameter), which corresponds to ~ 3MB for 10GB outsourced data, and can easily be obtained in today's smart phones, let alone computers.