What are ML-DSA and SLH-DSA?
They are the two post-quantum signature standards: ML-DSA (FIPS 204, from CRYSTALS-Dilithium) and SLH-DSA (FIPS 205, from SPHINCS+). A digital signature proves who produced a piece of data and that nobody changed it; it protects certificates, software updates, firmware, documents and code. ML-DSA is the general-purpose choice: fast, with signatures of a few kilobytes instead of the 64 bytes a typical ECDSA signature takes. SLH-DSA relies only on the security of hash functions, which makes it very conservative, at the cost of larger signatures and slower signing; it suits long-lived roots of trust and firmware signing. Signatures matter less for harvest now, decrypt later, because a forged signature only helps an attacker once a quantum computer exists. That is why most organisations change key exchange first and signatures later. The certificate ecosystem for post-quantum signatures is still being built, so ask your suppliers for their plans rather than expecting post-quantum certificates today.
This answer is part of the guide: Post-quantum readiness: where to start