What is post-quantum cryptography, and why migrate now?

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

1. Inventory where you use cryptography and which data must last years.
2. Prioritise long-lived data at rest — the most exposed to "harvest now".
3. Adopt hybrid encryption rather than wholesale replacement.
4. 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.