zkSaaS: Zero-Knowledge SNARKs as a Service

A decade of active research has led to practical constructions of zero-knowledge succinct non-interactive arguments of knowledge (zk-SNARKs) that are now being used in a wide variety of applications. Despite this astonishing progress, overheads in proof generation time remain significant. In this work, we envision a world where consumers with low computational resources can outsource the task of proof generation to a group of untrusted servers in a privacy-preserving manner. The main requirement is that these servers should be able to collectively generate proofs at a faster speed (than the consumer). Towards this goal, we introduce a framework called zk-SNARKs-as-a-service (zkSaaS) for faster computation of zk-SNARKs. Our framework allows for distributing proof computation across multiple servers such that each server is expected to run for a shorter duration than a single prover. Moreover, the privacy of the prover's witness is ensured against any minority of colluding servers. We design custom protocols in this framework that can be used to obtain faster runtimes for widely used zk-SNARKs, such as Groth16 [EUROCRYPT 2016], Marlin [EUROCRYPT 2020] and Plonk [EPRINT 2019]. We implement proof of concept zkSaaS for the Groth16 and Plonk provers. In comparison to generating these proofs on commodity hardware, we can not only generate proofs for a larger number of constraints (without memory exhaustion), but can also get approximate to 22x speedup when run with 128 parties for 2(25) constraints with Groth16 and 2(21) gates with Plonk.