In August 2024 NIST published its first three post-quantum cryptography standards: FIPS 203 (ML-KEM) for key establishment, and FIPS 204 (ML-DSA) and FIPS 205 (SLH-DSA) for digital signatures. For most organisations, the immediate question is not which algorithm to choose but where to begin.

The threat is already in motion

A cryptographically relevant quantum computer would break the public-key algorithms that protect most key exchange today, including RSA and elliptic-curve Diffie-Hellman. An adversary does not need that computer today to cause harm. Encrypted traffic and data captured now can be stored and decrypted later.

This harvest-now, decrypt-later risk means that the urgency of migration depends on how long your data must remain confidential, not on when a quantum computer arrives.

Start with a cryptographic inventory

You cannot migrate what you cannot find. Cryptography is embedded in application code, libraries, TLS terminators, VPNs, HSMs, databases, identity providers, mobile apps and third-party products. A useful inventory records, for each use:

  • the algorithm and key size
  • the protocol or library providing it
  • the data or transaction it protects
  • how long that data must stay confidential
  • who owns the system and whether a vendor controls the implementation

Prioritise by data lifetime and exposure

Not every system needs to migrate first. Prioritise systems that protect long-lived sensitive data, are exposed to networks an adversary could observe, and depend on public-key key exchange. Internal systems protecting short-lived data can follow later.

Plan for hybrid, and for agility

Most current guidance favours hybrid key exchange during the transition, combining a classical algorithm with ML-KEM so that security holds if either is later weakened. More importantly, treat this migration as an opportunity to build crypto-agility: centralised policy and abstraction that make the next algorithm change routine rather than another multi-year programme.

The organisations that will migrate smoothly are the ones that start their inventory now.