Q-Day and quantum risk planning

What Q-Day means

Q-Day is shorthand for the point at which a quantum computer could practically defeat important deployed public-key cryptography. A cryptographically relevant quantum computer (CRQC) is defined by that capability, not simply by a headline qubit count.

Which dependencies matter

RSA and elliptic-curve systems support key establishment and digital signatures across many services. A sufficiently capable quantum computer would affect the mathematical problems on which those systems rely. Symmetric encryption and hash functions face different considerations; not all cryptography fails in the same way.

Do not build a plan around a forecast

There is no verified calendar date for Q-Day. Hardware progress, error correction, algorithmic improvements and engineering requirements make forecasts uncertain. A migration deadline is a planning target, not evidence that a cryptographic break will occur in that year.

Make the decision useful now

Catalogue dependencies, identify long-lived confidential information and ask suppliers about supported transition routes. Use lead times and service criticality to prioritise work.

Boards can ask for evidence of ownership, inventory coverage, supplier engagement and tested change capability. Those measures reveal progress without requiring a claim about when a quantum computer will become capable.

Continue exploring

• PQCEMM: enterprise post-quantum maturity
• Harvest now, decrypt later: the business risk
• The NCSC post-quantum migration timeline

Primary sources

• NIST PQC project
• NCSC migration timelines