[Resource Topic] 2024/1131: Jolt-b: recursion friendly Jolt with basefold commitment

Welcome to the resource topic for 2024/1131

Title:
Jolt-b: recursion friendly Jolt with basefold commitment

Authors: Hang Su, Qi Yang, Zhenfei Zhang

Abstract:

The authors of Jolt [AST24] pioneered a unique method for creating zero-knowledge virtual machines, known as the lookup singularity. This technique extensively uses lookup tables to create virtual machine circuits. Despite Jolt’s performance being twice as efficient as the previous state-of-the-art1 , there is potential for further enhancement.

The initial release of Jolt uses Spartan [Set20] and Hyrax [WTs+ 18] as their backend, leading to two constraints. First, Hyrax employs Pedersen commitment to build inner product arguments, which requires elliptic curve operations. Second, the verification of a Hyrax commitment takes square root time O(\sqrt{N}) relative to the circuit size N . This makes the recursive verification of a Jolt proof impractical, as the verification circuit would need to execute all the Hyrax verification logic in-circuit. A later version of Jolt includes Zeromorph [KT23] and HyperKZG as their commitment backend, making the system recursion-friendly, as now the recursive verifier only needs to perform O(\log N) operations, but at the
expense of a need for a trusted setup.

Our scheme, Jolt-b, addresses these issues by transitioning to the extension field of the Goldilocks and using the Basefold commitment scheme [ZCF23], which has an O(\log^2 N) verifier time. This scheme mirrors the modifications of Plonky2 over the original Plonk [GWC19]: it transitions from EC fields to the Goldilocks field; it replaces the EC-based commitment scheme with an encoding-based commitment scheme.

We implemented Jolt-b, along with an optimized version of the Basefold scheme. Our benchmarks show that at a cost of 2.47x slowdown for the prover, we achieve recursion friendliness for the original Jolt. In comparison with other recursion-friendly Jolt variants, our scheme is 1.24x and 1.52x faster in prover time than the Zeromorph and HyperKZG variants of Jolt, respectively.

ePrint: https://eprint.iacr.org/2024/1131

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