Lesson 4.39: Post-quantum migration as a multi-year programme
A large enough quantum computer would break the public-key cryptography almost everything uses today (RSA and elliptic curves), while symmetric ciphers such as AES-256 stay strong. Nobody knows when such a machine will exist, but two things are certain: data recorded today can be decrypted later ('harvest now, decrypt later'), and replacing cryptography across a company takes years. In August 2024 NIST published the first post-quantum standards, FIPS 203 (ML-KEM), 204 (ML-DSA) and 205 (SLH-DSA). In the lab you turn Northwind's cryptography inventory into a prioritised, multi-year migration plan.
20 min
You will learn to
- Explain which cryptography quantum computers threaten
- Explain harvest-now-decrypt-later
- Apply Mosca's inequality with planning assumptions
- Prioritise long-lived data and long-lived signatures
- Plan around vendor readiness
Key terms
- Post-quantum cryptography (PQC)
- Public-key algorithms designed to resist attacks by quantum computers.
- FIPS 203 / 204 / 205
- NIST standards published in August 2024: ML-KEM (key encapsulation), ML-DSA and SLH-DSA (signatures).
- Harvest now, decrypt later
- Recording encrypted traffic today to decrypt it once quantum computers can.
- Mosca's inequality
- If data shelf life (x) plus migration time (y) exceeds time until a quantum threat (z), act now.
- Hybrid key exchange
- Combining a classical and a post-quantum algorithm so both must be broken.
- Crypto-agility
- Designing systems so algorithms can be replaced without rebuilding them.
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