In this paper, we study multiple server PoR systems. Our contribution in multiple-server $\por$ systems is as follows.
1. We formalize security definitions for two possible scenarios: (i) when a threshold of servers succeed with high enough probability (worst-case) and (ii) when the average of the success probability of all the servers is above a threshold (average-case). We also motivate the study of confidentiality of the outsourced message.
2. We give M-PoR schemes which are secure under both these security definitions and provide reasonable confidentiality guarantees even when there is no restriction on the computational power of the servers. We also show how classical statistical techniques used by Paterson, Stinson and Upadhyay (Journal of Mathematical Cryptology: 7(3)) can be extended to evaluate whether the responses of the provers are accurate enough to permit successful extraction.
3. We also look at one specific instantiation of our construction when instantiated with the unconditionally secure version of the Shacham-Waters scheme (Asiacrypt, 2008). This scheme gives reasonable security and privacy guarantee. We show that, in the multi-server setting with computationally unbounded provers, one can overcome the limitation that the verifier needs to store as much secret information as the provers.Category / Keywords: Proof-of-Retrievability, Unconditional Security Date: received 8 Mar 2016, last revised 8 Mar 2016 Contact author: m paterson at bbk ac uk, dstinson@math uwaterloo ca, jalaj@psu edu Available format(s): PDF | BibTeX Citation Version: 20160308:210313 (All versions of this report) Short URL: ia.cr/2016/265 Discussion forum: Show discussion | Start new discussion