## Cryptology ePrint Archive: Report 2019/252

Reversible Proofs of Sequential Work

Hamza Abusalah and Chethan Kamath and Karen Klein and Krzysztof Pietrzak and 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).

Category / Keywords: Proof of work, Proof of sequential work

Original Publication (in the same form): IACR-EUROCRYPT-2019

Date: received 28 Feb 2019

Contact author: hamzaabusalah at gmail com,ckamath@ist ac at,karen klein@ist ac at,krzpie@gmail com,michael walter@ist ac at

Available format(s): PDF | BibTeX Citation

Short URL: ia.cr/2019/252

[ Cryptology ePrint archive ]