FIPS 205 (SLH-DSA)

Definition

FIPS 205 is the NIST standard for SLH-DSA (Stateless Hash-Based Digital Signature Algorithm), previously known as SPHINCS+. Published in August 2024, FIPS 205 provides the most conservative post-quantum signature scheme, relying only on hash function security.

Technical Explanation

FIPS 205 specifies twelve parameter sets across three security levels and two variants (fast "f" and small "s"). Signatures range from 7 KB to 49 KB. Security requires only hash function properties—the simplest and most verifiable cryptographic assumptions.

The stateless design eliminates state management concerns that plagued earlier hash-based schemes. Hypertree structures enable unlimited signings from one key pair. Performance is slower than lattice alternatives but acceptable for transaction workloads.

SynX Relevance

SynX implements SLH-DSA per FIPS 205 as its primary signature algorithm. This choice prioritizes long-term security confidence—if hash functions remain secure, so do SynX signatures. Every transaction carries FIPS 205 compliant quantum-resistant authorization.

Frequently Asked Questions

Why is SLH-DSA more conservative than ML-DSA?: SLH-DSA relies only on hash security, studied for decades. ML-DSA assumes lattice hardness, newer but well-analyzed.
Are 49 KB signatures practical?: For transactions, yes—modern networks handle this easily. Smaller parameter sets reduce size.
Is FIPS 205 the safest option?: It has the simplest security assumptions, making it the most conservative choice available.

Maximum conservatism per FIPS 205. Safest signatures with SynX