Abstract
In this paper we provide a formal treatment of proof of replicated storage, a novel cryptographic primitive recently proposed in the context of a novel cryptocurrency, namely Filecoin.
In a nutshell, proofs of replicated storage is a solution to the following problem: A user stores a file m on n different servers to ensure that the file will be available even if some of the servers fail. Using proof of retrievability, the user could check that every server is indeed storing the file. However, what if the servers collude and, in order to save on resources, decide to only store one copy of the file? A proof of replicated storage guarantees that, unless the (potentially colluding) servers are indeed reserving the space necessary to store n copies of the file, the user will not accept the proofs. While some candidate proofs of replicated storage have already been proposed, their soundness relies on timing assumptions i.e., the user must reject the proof if the prover does not reply within a certain time-bound.
In this paper we provide the first construction of a proof of replication which does not rely on any timing assumptions.
This work was supported by the: Protocol Labs RFP Program; Danish Independent Research Council under Grant-ID DFF-6108-00169 (FoCC); European Research Council (ERC) under the European Unions’s Horizon 2020 research and innovation program under grant agreement No. 669255 (MPCPRO) and No. 803096 (SPEC); Concordium Blockchain Research Center, Aarhus University, Denmark.
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Notes
- 1.
Other related notions in the context of data replication have been studied earlier in the cryptographic literature; we discuss the connection and differences in the related work section.
- 2.
Of course, if a single server would store all replicas, we can optimize the communication needed, this is also easy to see for our protocol, but this hardly seems like an interesting use case.
- 3.
It is hard to compare our analysis with that of Hourglass since in [VDJO+12] only an informal security argument of incompressibility is given.
- 4.
One can think of the random permutation T as a random oracle which can be invoked in both directions.
- 5.
For instance, an honest server does not need to communicate with the other servers, nor know that they exist.
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Damgård, I., Ganesh, C., Orlandi, C. (2019). Proofs of Replicated Storage Without Timing Assumptions. In: Boldyreva, A., Micciancio, D. (eds) Advances in Cryptology – CRYPTO 2019. CRYPTO 2019. Lecture Notes in Computer Science(), vol 11692. Springer, Cham. https://doi.org/10.1007/978-3-030-26948-7_13
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