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Interview question · Cryptography, PKI & TLS

What is 'harvest now, decrypt later', and how would you plan a post-quantum migration?

Data encrypted today can be recorded and decrypted when a capable quantum computer exists. The scored answer prioritises by how long data must stay secret, starts with key exchange, and builds crypto agility.

hardNewPreparation tags: Google, Microsoft, AppleUpdated Nov 2026

Data encrypted today can be recorded and decrypted when a capable quantum computer exists. The scored answer prioritises by how long data must stay secret, starts with key exchange, and builds crypto agility.

Make your first attempt

What would you say before reading the answer?

  1. 01 State the assumptions your answer depends on.
  2. 02 Explain the mechanism and choose a control.
  3. 03 Name a condition that would change your decision.

The worked answer includes an approach, scoring criteria and follow-up questions. Compare the reasoning with your own.

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What if · the follow-ups in this answer

The answer works through 6 follow-ups like an interviewer would

Leadership asks for a post-quantum cryptography migration plan for a company that stores health records and runs long-lived device fleets.

  1. What is the quantum threat?
  2. Why act before such a computer exists?
  3. What standards exist?
  4. Where would you start?
  5. What about devices and signatures?
  6. What plan would you present?

Each rung has a nudge, a model answer, the principle that carries over and the weak answer to avoid. Premium opens every answer and ladder.

UP NEXT ON YOUR JOURNEY
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