SPHINCS+ (SLH-DSA)

Definition

SPHINCS+ is a stateless hash-based digital signature algorithm selected by NIST as a post-quantum standard. Officially designated SLH-DSA (Stateless Hash-Based Digital Signature Algorithm) in FIPS 205, SPHINCS+ provides transaction authorization that remains secure against quantum computer attacks.

Technical Explanation

SPHINCS+ security relies solely on the properties of cryptographic hash functions, making it among the most conservative post-quantum choices. The algorithm constructs signatures using Merkle trees, WOTS+ (Winternitz One-Time Signature) chains, and FORS (Forest of Random Subsets) components.

Parameter sets include SPHINCS+-128, SPHINCS+-192, and SPHINCS+-256, with "f" (fast) and "s" (small) variants trading signature size for signing speed. Signatures range from 7 KB to 49 KB. Verification is fast; signing is slower than lattice alternatives but acceptable for transaction workloads.

SynX Relevance

SynX uses SPHINCS+ for all transaction signatures, ensuring maximum long-term security confidence. Every SynX transaction carries a SPHINCS+ signature proving authorization from the private key holder. This hash-based approach provides security even if lattice problems were somehow compromised.

Frequently Asked Questions

Why are SPHINCS+ signatures larger than ECDSA?: Hash-based constructions require more data to achieve security without relying on algebraic structures vulnerable to quantum attacks.
Is SPHINCS+ slow?: Signing takes milliseconds—imperceptible for wallet users, though slower than Dilithium for high-volume applications.
What if SHA-256 is broken?: SPHINCS+ supports multiple hash functions including SHAKE256, providing algorithm agility.

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