Algorithm

SPHINCS+C

Family: hash-based.

SPHINCS+C is a variant of SPHINCS+ that makes signatures smaller. The signer tries different random values until the hash of the message has a required form. For such hashes, part of the signature is not needed, so the signer omits it and the verifier never uses it. The search adds a small amount of signing work, and verification gets faster. The scheme stays stateless and uses hash functions only.

Safety: High

Why this rating

Security rests only on the properties of the hash function, and the scheme is stateless. It is newer and less widely reviewed than SPHINCS+ and SLH-DSA, and it is not a NIST standard. The signer's extra search adds signing time, and implementations need review.

Standard

https://eprint.iacr.org/2022/778

Research

• SPHINCS+C: Compressing SPHINCS+ With (Almost) No Cost (2022)

Implemented by

• hashsigs