# Hash-based signatures

Hash-based signatures, including SLH-DSA (FIPS 205), LMS, and HSS, derive their security purely from hash functions, the most conservative post-quantum assumption available. Selected by several blockchain ecosystems for quantum resistance, they are mathematically incompatible with MPC, which requires algebraic structure hash functions lack.

## The scheme MPC architectures cannot sign

Because hash functions have no algebraic structure, no threshold protocol can split a hash-based signing key among parties, so MPC-only custody cannot support these schemes at all. HSMs sign them within the hardware boundary today, natively or through functionality modules.

This asymmetry is central to custody due diligence: Taurus custody, HSM-rooted with no MPC dependency, supports every post-quantum signature family, including the hash-based schemes chosen by ecosystems such as Circle and Aptos and considered by Ethereum.

FAQ:

- Why would a blockchain choose hash-based signatures? Maximum assurance: security reduces to the hash function alone, with decades of analysis behind it. Ecosystems planning for the long term value that conservatism despite larger signatures.

Related: https://www.taurushq.com/security/post-quantum-ready/ https://www.taurushq.com/glossary/multi-party-computation-mpc/ https://www.taurushq.com/glossary/ml-dsa/

Learn more: https://www.taurushq.com/glossary/hash-based-signatures/