Paper 2021/1038

Reinforced Concrete: Fast Hash Function for Zero Knowledge Proofs and Verifiable Computation

Mario Barbara and Lorenzo Grassi and Dmitry Khovratovich and Reinhard Lueftenegger and Christian Rechberger and Markus Schofnegger and Roman Walch

Abstract

We propose a new hash function Reinforced Concrete for the proof systems that support lookup tables, concretely Plookup based on KZG commitments or FRI. It has two solid advantages over predecessors: (a) Table lookups instead of (big) modular reductions are much faster both in ZK and plain computations thus making verifiable computation protocols based on recursive proofs (current trend) much more efficient; (b) the security is no longer solely based on (high) algebraic degree but rather on more traditional AES-like components inheriting decades of public scrutiny. Our design also employs a novel and fast field-to-tables conversion, which is of independent interest and can be used in other Plookup-friendly constructions. The new hash function is suitable for a wide range of applications like privacy-preserving cryptocurrencies, verifiable encryption, protocols with state membership proofs, or verifiable computation. It may serve as a drop-in replacement for various prime-field hashes such as variants of MiMC, Poseidon, Pedersen hash, and others.