Paper 2023/907

Efficient Zero Knowledge for Regular Language

Abstract

A succinct zero knowledge proof for regular language mem- bership, i.e., to prove a secret string behind an encryption (hash) belongs to a regular language is useful, e.g., for asserting that an encrypted email is free of malware. The great challenge in practice is that the regular language used is often huge. We present zkreg, a distributed commit- and-prove system that handles such complexity. In zkreg, cryptographic operations are encoded using arithmetic circuits, and input acceptance is modeled as a zero knowledge subset problem using Σ-protocols. We in- troduce a Feedback Commit-and-Prove (FB-CP) scheme, which connects Σ-protocols and the Groth16 system with O(1) proof size and verifier cost. We present a close-to-optimal univariate instantiation of zk-VPD, a zero knowledge variation of the KZG polynomial commitment scheme, based on which an efficient zk-subset protocol is developed. We develop a 2-phase proof scheme to further exploit the locality of Aho-Corasick automata. To demonstrate the performance and scalability of zkreg, we prove that all ELF files (encrypted and hashed) in a Linux CentOS 7 are malware free. Applying inner pairing product argument, we obtain an aggregated proof of 1.96 MB which can be verified in 6.5 seconds.