Poseidon2b hash targets faster binary field zero knowledge proofs

Security math experts published Poseidon2b for zero know systems that prefer binary fields. The IACR ePrint 2025/058 release includes code tuned for the Binius prover stack.

The short version

Poseidon2b adapts the Poseidon2 hash design to GF(2^n) fields. It targets SNARKs built on binary towers such as Binius. Reference test suites report smaller proofs and fast verify times on mix step heavy workloads.

What the researchers did

Lorenzo Grassi, Dmitry Khovratovich, Katharina Koschatko, Christian Rechberger, Markus Schofnegger, and Verena Schroppel wrote Poseidon2b: A Binary Field Version of Poseidon2. IACR ePrint 2025/058 hosts the PDF.

Poseidon hashes are common inside zk circuits because they use fewer constraints than SHA256. Poseidon2b keeps a low degree power map with sparse constants for CPU speed.

The Poseidon Hash GitHub repo ships Sage parameter notebooks and Rust examples integrated with Binius circuits. Developers can run cargo examples with chosen field width and state size.

Photo: Anna Shvets / Pexels

What they found

Published test suite tables compare Poseidon2b mix steps against Keccak, SHA256, and other hashes inside Binius style proofs. One listed row for Poseidon2b with n thirty two and t sixteen reports about four hundred two KiB proof size for two to the fourteen mix steps.

Proving times in that table fall below one second in multi threaded mode for the same row. Verify times stay near five milliseconds in the published figures.

Multiple parameter sets cover n thirty two, sixty four, and one hundred twenty eight with varying state width. Sage notebooks emit concrete constants for each instance.

Photo: Karolina Grabowska / Pexels

Why it matters for you

Zk rollup teams choosing hash functions affect proof size, verifier cost, and audit surface. Binary field friendly hashes matter when the prover already lives in GF(2^n). Wallet and bridge engineers should track whether ecosystems standardize Poseidon2b instances or stick to prime field Poseidon2.

Auditors need parameter provenance docs when reviewing custom hash choices in new L2 designs.

What to keep in mind

IACR ePrint is not the same as journal peer review. Parameters must match the cited notebook outputs byte for byte.

Binius original repo archived in favor of Binius64. Integrators should confirm which prover line their stack ships.

Test suite rows use specific mix step counts. Do not extrapolate to your chain's transaction mix without re measuring.

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Teams that ship fast should still read the full PDF tables. Headline wins on clean test suites often fade once real data adds noise, broken tools, and slow networks.

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Key takeaways

• Poseidon2b is a binary field hash aimed at Binius style zk proofs.
• IACR ePrint 2025/058 documents design and test suite tables.
• Open Sage and Rust code generates parameters and sample circuits.
• Listed proofs stay near four hundred KiB for a high mix step test suite row.
• Protocol designers should compare hash choice against prime field alternatives.

Sources

• Primary — IACR ePrint, Poseidon2b: A Binary Field Version of Poseidon2 (2025). Defines instances and security discussion.
• Secondary — GitHub, Poseidon-Hash/Poseidon2b (2025). Sage notebooks, Binius circuit examples, and test suite scripts.