International Association for Cryptologic Research

International Association
for Cryptologic Research


Arasu Arun


Jolt: SNARKs for Virtual Machines via Lookups
Succinct Non-interactive Arguments of Knowledge (SNARKs) allow an untrusted prover to establish that it correctly ran some “witness-checking procedure” on a witness. A zkVM (short for zero-knowledge Virtual Machine) is a SNARK that allows the witness-checking procedure to be specified as a computer program written in the assembly language of a specific instruction set architecture (ISA). A front-end converts computer programs into a lower-level representation such as an arithmetic circuit or generalization thereof. A SNARK for circuit- satisfiability can then be applied to the resulting circuit. We describe a new front-end technique called Jolt that applies to a variety of ISAs. Jolt arguably realizes a vision called the lookup singularity, which seeks to produce circuits that only perform lookups into pre-determined lookup tables. The circuits output by Jolt primarily perform lookups into a gigantic lookup table, of size more than 2^128, which depends only on the ISA. The validity of the lookups are proved via a new lookup argument described in a companion work called Lasso. Although size 2^128 tables are vastly too large to materialize in full, the tables arising in Jolt are structured, avoiding costs that grow linearly with the table size. We describe performance and auditability benefits of Jolt compared to prior zkVMs, focusing on the popular RISC-V ISA as a concrete example. The dominant cost for the Jolt prover applied to this ISA (on 64-bit data types) is cryptographically committing to about six 256-bit field elements per step of the RISC-V CPU. This compares favorably to prior zkVM provers, even those focused on far simpler VMs.
Dew: A Transparent Constant-sized Polynomial Commitment Scheme
We construct a polynomial commitment scheme with constant (i.e., independent of the degree) sized evaluation proofs and logarithmic (in the degree) verification time in the transparent setting. To the best of our knowledge, this is the first result achieving this combination of properties. We build our scheme from an inner product commitment scheme with constant-sized proofs but with linear verification time. To improve the verification time to logarithmic for polynomial commitments, we prove a new extremal combinatorial bound. Our constructions rely on groups of unknown order instantiated by class groups. We prove security of our constructions in the Generic Group Model. Compiling known information-theoretic proof systems using our polynomial commitment scheme yields transparent and constant-sized zkSNARKs (Zero-knowledge Succinct Non-interactive ARguments of Knowledge) with logarithmic verification.
Short-lived zero-knowledge proofs and signatures 📺
We introduce the short-lived proof, a non-interactive proof of knowledge with a novel feature: after a specified period of time, the proof is no longer convincing. This time-delayed loss of soundness happens "naturally" without further involvement from the prover or any third party. We propose definitions for short-lived proofs as well as the special case of short-lived signatures. We show several practical constructions built using verifiable delay functions (VDFs). The key idea in our approach is to allow any party to forge any proof by executing a large sequential computation. Some constructions achieve a stronger property called reusable forgeability in which one sequential computation allows forging an arbitrary number of proofs of different statements. We also introduces two novel types of VDFs, re-randomizable VDFs and zero-knowledge VDFs, which may be of independent interest. Our constructions for short-lived Sigma-protocols and signatures are practically efficient for provers and verifiers, adding a few hundred bytes of overhead and tens to hundreds of milliseconds of proving/verification time.