[Resource Topic] 2019/252: Reversible Proofs of Sequential Work

Welcome to the resource topic for 2019/252

Title:
Reversible Proofs of Sequential Work

Authors: Hamza Abusalah, Chethan Kamath, Karen Klein, Krzysztof Pietrzak, Michael Walter

Abstract:

Proofs of sequential work (PoSW) are proof systems where a prover, upon receiving a statement \chi and a time parameter T computes a proof \phi(\chi,T) which is efficiently and publicly verifiable. The proof can be computed in T sequential steps, but not much less, even by a malicious party having large parallelism. A PoSW thus serves as a proof that T units of time have passed since \chi was received. PoSW were introduced by Mahmoody, Moran and Vadhan [MMV11], a simple and practical construction was only recently proposed by Cohen and Pietrzak [CP18]. In this work we construct a new simple PoSW in the random permutation model which is almost as simple and efficient as [CP18] but conceptually very different. Whereas the structure underlying [CP18] is a hash tree, our construction is based on skip lists and has the interesting property that computing the PoSW is a reversible computation. The fact that the construction is reversible can potentially be used for new applications like constructing \emph{proofs of replication}. We also show how to embed" the sloth function of Lenstra and Weselowski [LW17] into our PoSW to get a PoSW where one additionally can verify correctness of the output much more efficiently than recomputing it (though recent constructions of verifiable delay functions" subsume most of the applications this construction was aiming at).

ePrint: https://eprint.iacr.org/2019/252

Talk: https://www.youtube.com/watch?v=fgTAmyGC89Y

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