SLH-DSA-256 (FIPS 205 Level 5) Parameter Tier
Parameter-tier sub-spec for SLH-DSA-256 (NIST FIPS 205 security level 5), the maximum-security hash-based signature variant. Algorithm definition deferred to LP-4500.
Implementation status (code-audited 2026-07-03): SHIPPED Parameters confirmed against luxfi/crypto/slhdsa (circl v1.6.3).
Abstract
SLH-DSA-256 is the NIST FIPS 205 security-level-5 parameter family of the Stateless Hash-based Digital Signature Algorithm. This LP pins the tier identifier, covers both the "s" (small, ~29 KB sig) and "f" (fast, ~49 KB sig) sub-variants, and points at the algorithm spec in LP-4500. Sizes: public key 64 B, secret key 128 B. Use SLH-DSA-256 for 50+ year archival signing where both lattice and hash-collision security margins must be at maximum — long-term treasury controls, regulatory archival of ATS records, sovereign key escrow. For network defaults use SLH-DSA-192 (LP-4520).
Reference implementation
- Primitive:
luxfi/crypto/slhdsa/slhdsa256 - Hash backend: SHA2-512 or SHAKE256
- Test vectors: NIST KAT vectors (FIPS 205 Appendix B)
Provenance
Originally LP-4430, renumbered 2026-05-18 to consolidate all cryptographic primitives into the 4xxx range with family sub-ranges (PQ hash signatures 4500-4599). The 4430 slot is retained as a permanent pointer to this LP.
Copyright
Copyright and related rights waived via CC0.