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starkware-libs/stwo

A Rust implementation of Circle STARK proving and verification over the M31 field, with a no_std verifier and SIMD prover backend.

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What is it?

Stwo is a Circle STARK prover and verifier written in Rust. It runs the proof system over the Mersenne prime field M31 (2^31 − 1), which allows 32-bit modular arithmetic that maps onto SIMD lanes such as AVX2, AVX-512, NEON and WebAssembly SIMD. The library includes the M31, CM31 and QM31 field tower, circle FFT, a FRI variant for the circle domain, lifted Merkle commitments, and several Fiat-Shamir channels including Blake2s, Blake3, Poseidon252 and Keccak256.

The repository is split into crates. The core crate separates a no_std verifier from the prover, which is enabled by the `prover` feature. Constraint-framework, air-utils and reference examples (Fibonacci, Poseidon2, Blake, PLONK-style and a state machine) sit alongside it. GKR and LogUp lookup arguments are included for memory and table checks.

Stwo is the foundation of StarkWare's SHARP prover and the stwo-cairo prover for the Cairo VM. Application-specific provers are developed in separate repositories. Development is moving to starkware-libs/proving from the end of July 2026.

Key features

  • 01Circle STARK prover and verifier over the M31 field.
  • 02A no_std verifier that can be built without the prover code.
  • 03SIMD backend for AVX2, AVX-512, NEON and WebAssembly, plus a CPU reference backend.
  • 04Multiple Fiat-Shamir channels: Blake2s, Blake3, Poseidon252 and Keccak256.
  • 05GKR and LogUp lookup arguments for memory and table checks.
  • 06Optional Rayon-based parallel proving behind the `parallel` feature.

Use cases

  • Building a zkVM or verifiable computation system on a STARK backend.
  • Embedding a small STARK verifier in on-chain environments such as Solidity or Cairo contracts.
  • Experimenting with Circle STARK constructions and FRI over circle domains.
  • Studying reference circuits such as Poseidon2 and Blake for STARK-based proving.

Quick start

  1. 1

    Add stwo as a Rust dependency (verifier only or with prover feature)

  2. 2

    Build the full prover in release mode

    cargo build --release --features prover
  3. 3

    Run the standard test suite

    cargo test --features prover

Things to know

  • Requires Rust nightly, pinned in rust-toolchain.toml.
  • Full prover performance needs AVX2, AVX-512, or NEON CPU support.
  • Development is moving to a new repository starting July 2026.

Topics

#zero-knowledge#stark#rust#zkvm#cryptography#simd#formal-verification

FAQ

What is stwo?
A Rust implementation of Circle STARK proving and verification over the M31 field, with a no_std verifier and SIMD prover backend. Stwo is a Circle STARK prover and verifier written in Rust. It runs the proof system over the Mersenne prime field M31 (2^31 − 1), which allows 32-bit modular arithmetic that maps onto SIMD lanes such as AVX2, AVX-512, NEON and WebAssembly SIMD. The library includes the M31, CM31 and QM31 field tower, circle FFT, a FRI variant for the circle domain, lifted Merkle commitments, and several Fiat-Shamir channels including Blake2s, Blake3, Poseidon252 and Keccak256.
Is stwo free to use? What license does it have?
stwo is open source under the Apache-2.0 license. Check the license terms before using it in commercial products.
Is stwo still maintained?
Actively maintained. The last commit to stwo was on Nov 5, 2026.
What can I use stwo for?
Building a zkVM or verifiable computation system on a STARK backend. Embedding a small STARK verifier in on-chain environments such as Solidity or Cairo contracts. Experimenting with Circle STARK constructions and FRI over circle domains. Studying reference circuits such as Poseidon2 and Blake for STARK-based proving.
How do I install stwo?
Add stwo as a Rust dependency (verifier only or with prover feature) Build the full prover in release mode: cargo build --release --features prover Run the standard test suite: cargo test --features prover
Where can I get stwo?
The source code and installation instructions are on GitHub: https://github.com/starkware-libs/stwo

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