The cryptography protecting your data today — keys, HTTPS, signatures — rests on mathematical problems that current computers cannot solve in any reasonable time. A large enough quantum computer could solve some of them. That is what post-quantum cryptography is: algorithms designed to resist both classical and quantum computers.
The threat is not only in the future
You might think: "no quantum computer can break my encryption yet, so I can wait." The problem is an attack called harvest now, decrypt later:
An adversary captures your encrypted traffic today and stores it. Once quantum capability exists years from now, they decrypt it.
If your data must stay secret ten years from now — medical records, trade secrets, personal data — the threat is present, not future. What you encrypt today with classical cryptography could be read tomorrow.
The new NIST standards
NIST, the US standards body, finalised the first post-quantum algorithms in 2024 after years of public analysis:
- ML-KEM (formerly CRYSTALS-Kyber): for key exchange — how two parties agree on a shared secret securely.
- ML-DSA (formerly CRYSTALS-Dilithium): for digital signatures — how to verify a message is authentic and unaltered.
These are no longer academic experiments. They are standards that governments and large companies are starting to require.
Hybrid encryption: the prudent approach
Post-quantum algorithms are new, and "new" in cryptography means "less battle-tested". That is why current best practice is hybrid: combine a well-established classical algorithm with a post-quantum one. The result only breaks if both fall at once. You gain post-quantum protection without giving up decades of confidence in classical cryptography.
Where to start
- Inventory where you use cryptography and which data must last years.
- Prioritise long-lived data at rest — the most exposed to "harvest now".
- Adopt hybrid encryption rather than wholesale replacement.
- Use libraries that compose verified primitives, not home-made cryptography.
That last point is the key one, and it is the philosophy behind Quipu, a free hybrid post-quantum encryption library for data at rest.
The code is at github.com/isazajuancarlos/quipu. It is AGPL-3.0, and the composition has not yet passed an independent cryptographic audit — which is worth saying out loud.
