Andreas Hülsing
German cryptographer who made hash-based signatures practical – first XMSS, then SPHINCS+, which became the US standard SLH-DSA in 2024.
Hash-based signatures go back to Lamport and Merkle in the 1970s and have an unusual property: their security rests only on the hash function holding up, with no number-theoretic assumptions at all. The catch was state. Sign twice with the same one-time key and you are finished, so the signer has to remember every key it has ever used.
Hülsing did his PhD under Johannes Buchmann in Darmstadt and co-developed XMSS (2011), standardised as RFC 8391. He was then one of the principal authors of SPHINCS (2015) and SPHINCS+, which drop the state at the cost of bigger signatures. NIST published SPHINCS+ as FIPS 205, SLH-DSA, in August 2024 – the fallback in case lattice-based ML-DSA ever breaks. He is based at TU Eindhoven.