What is FN-DSA?
FN-DSA is a post-quantum digital signature algorithm that NIST is standardising as FIPS 206, based on an algorithm called Falcon. Its appeal is size: its signatures are much smaller than those of ML-DSA, which matters wherever every byte counts. Its drawback is that it's harder to implement safely. Unlike ML-DSA and SLH-DSA, it isn't a final standard yet, so check NIST's post-quantum project page for its current status before planning around it.
What the name means
FN refers to FFT over NTRU lattices: the mathematics it uses (NTRU lattices) and a technique it relies on (the fast Fourier transform). DSA stands for digital signature algorithm. NIST selected Falcon for standardisation in 2022, alongside the algorithms that became ML-DSA and SLH-DSA.
Why it's attractive
| ML-DSA-65 | Falcon-512 | |
|---|---|---|
| Public key size | 1,952 bytes | 897 bytes |
| Signature size | 3,309 bytes | About 666 bytes |
| Implementation difficulty | Moderate | High |
Smaller signatures help most where many signatures travel together, such as a chain of certificates in every secure connection, and in constrained devices and tight message formats.
Why it's harder
Signing with Falcon needs careful floating-point arithmetic and sampling from precise distributions. Done carelessly, it can leak information about the private key through timing or power use. That makes good implementations harder to write and to certify, which is a large part of why its standard has taken longer.
For most organisations, FN-DSA is something to track rather than plan around today. The practical step is to make sure systems could adopt it later without being rebuilt.
Common confusions
- "It's already a standard." Not as a final FIPS yet. ML-DSA and SLH-DSA are.
- "Smaller means weaker." No. The size comes from different mathematics, not lower ambition.
- "It's part of the new signature competition." No. NIST is separately running an additional signatures process, which advanced nine candidates to a third round in May 2026. FN-DSA was selected earlier.
Sources and further reading
Tags show what kind of source each one is (how sources are used). Checked against these sources on 12 October 2026. Spotted an error? Email hello@plainquantum.com and it will be corrected, with a note.
- StandardPost-Quantum Cryptography project (status of FN-DSA and other work)NIST Computer Security Resource Center
- StandardPost-Quantum Cryptography project news (FIPS 206 progress, additional signatures, SP 800-227)NIST Computer Security Resource Center
- StandardFIPS 204: Module-Lattice-Based Digital Signature Standard (ML-DSA)NIST, 2024