SLH-DSA (SPHINCS+)

Definition

SLH-DSA (Stateless Hash-Based Digital Signature Algorithm) is the NIST-standardized name for SPHINCS+, published as FIPS 205. It provides digital signatures whose security relies solely on the properties of hash functions, offering the most conservative post-quantum security guarantees.

Technical Explanation

SLH-DSA uses a hybrid construction combining Merkle trees, WOTS+ one-time signatures, and FORS few-time signatures. This stateless design eliminates the state management burden of earlier hash-based schemes, enabling unlimited signatures from a single key pair without tracking which keys have been used.

The algorithm offers multiple parameter sets balancing signature size (7,856 to 49,856 bytes), security level, and signing speed. SPHINCS+-SHAKE-128f (used by SynX) provides fast signing with NIST Security Level 1, while higher security variants trade size for additional protection.

SynX Relevance

SynX uses SLH-DSA (SPHINCS+-SHAKE-128f) as its primary transaction signature scheme. This choice prioritizes security certainty: hash function security is well-understood and not dependent on lattice assumptions. Every SynX transaction carries a quantum-resistant hash-based signature.

Frequently Asked Questions

Is SLH-DSA the same as SPHINCS+?: Yes, SLH-DSA is the official NIST standardized name for SPHINCS+ (FIPS 205).
Why are SLH-DSA signatures larger than ML-DSA?: Hash-based signatures trade size for simpler security assumptions—no lattice math required.
Is SLH-DSA slow?: The 'f' (fast) variants like SPHINCS+-SHAKE-128f provide signing in ~10ms, acceptable for blockchain use.

The most conservative quantum security choice. Secure with SynX