SLH-DSA
FIPS 205, formerly SPHINCS+
A stateless hash-based post-quantum signature scheme whose security depends only on the strength of its underlying hash function. Signatures are large and slow, but the security assumptions are the most conservative of the NIST signature standards.
In practice
Chosen for firmware signing and long-life roots of trust, where diversification away from lattice assumptions matters more than signature size.
Related terms
The NIST-standardised lattice-based digital signature algorithm, intended as the general-purpose post-quantum replacement for RSA-PSS and ECDSA. Signatures are larger than ECDSA but performance is practical for most uses.
A signature scheme built only from hash functions, with no number-theoretic or lattice assumptions. Security reduces to the collision and preimage resistance of the hash, which is unusually well understood.
The ability to change cryptographic algorithms, parameters or libraries without redesigning the systems that depend on them. Agility is what turns the next migration from a rewrite into a configuration change.