SPARKs: Succinct Parallelizable Arguments of Knowledge

Naomi Ephraim; Cody Freitag; Ilan Komargodski; Rafael Pass

Paper 2020/994

SPARKs: Succinct Parallelizable Arguments of Knowledge

Naomi Ephraim, Cody Freitag, Ilan Komargodski, and Rafael Pass

Abstract

We introduce the notion of a Succinct Parallelizable Argument of Knowledge (SPARK). This is an argument of knowledge with the following three efficiency properties for computing and proving a (non-deterministic, polynomial time) parallel RAM computation that can be computed in parallel time T with at most p processors: (1) The prover’s (parallel) running time is T + polylog(T * p). (In other words, the prover’s running time is essentially T for large computation times!) (2) The prover uses at most p * polylog(T * p) processors, and (3) the communication and verifier complexity are both polylog(T * p). The combination of all three is desirable as it gives a way to leverage a moderate increase in parallelism in favor of near-optimal running time. We emphasize that even a factor two overhead in the prover’s parallel running time is not allowed. Our main contribution is a generic construction of SPARKs from any succinct argument of knowledge where the prover’s parallel running time is T * polylog(T * p) when using p processors, assuming collision-resistant hash functions. When suitably instantiating our construction, we achieve a four-round SPARK for any parallel RAM computation assuming only collision resistance. Additionally assuming the existence of a succinct non-interactive argument of knowledge (SNARK), we construct a non-interactive SPARK that also preserves the space complexity of the underlying computation up to polylog(T * p) factors. We also show the following applications of non-interactive SPARKs. First, they immediately imply delegation protocols with near optimal prover (parallel) running time. This, in turn, gives a way to construct verifiable delay functions (VDFs) from any sequential function. When the sequential function is also memory-hard, this yields the first construction of a memory-hard VDF.

Note: This version includes constructions of SPARKs for parallel RAM computations.

Metadata

Available format(s): PDF
Category: Foundations
Publication info: Published elsewhere. Major revision. EUROCRYPT 2020
Keywords: Succinct arguments SNARK verifiable computation interactive proofs
Contact author(s): nephraim @ cs cornell edu
cfreitag @ cs cornell edu
History: 2020-08-18: received
Short URL: https://ia.cr/2020/994
License: CC BY

BibTeX

@misc{cryptoeprint:2020/994,
      author = {Naomi Ephraim and Cody Freitag and Ilan Komargodski and Rafael Pass},
      title = {{SPARKs}: Succinct Parallelizable Arguments of Knowledge},
      howpublished = {Cryptology {ePrint} Archive, Paper 2020/994},
      year = {2020},
      url = {https://eprint.iacr.org/2020/994}
}