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Interview question · Cryptography, PKI & TLS

Who decides which root CAs your devices trust? Explain root programs, trust stores per runtime, distrust events and root expiry.

There is no single list of trusted roots. Browsers, operating systems, language runtimes and container images each carry their own, updated on their own schedules, and production outages follow from the differences.

hardEssentialNewPreparation tags: Google, Apple, MicrosoftUpdated Nov 2026

There is no single list of trusted roots. Browsers, operating systems, language runtimes and container images each carry their own, updated on their own schedules, and production outages follow from the differences.

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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

A CA your company uses is announced as distrusted by a major browser for certificates issued after a cut-off date.

  1. Who decides which CAs are trusted?
  2. Which trust store does each client use?
  3. What does a distrust with a cut-off date mean?
  4. What should the company do?
  5. What about internal clients and pinning?
  6. What would your response plan be?

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
Next in this trackHow does a CA verify you control a domain before issuing a certificate (ACME, HTTP-01, DNS-01, TLS-ALPN-01), and how is that subverted?Next in this trackWhere should mutual TLS terminate (app, load balancer, sidecar), and how does the client's identity reach the application safely?Next in this trackHow does an HSM actually protect keys: non-extractable attributes, PKCS#11 sessions, FIPS 140-3 levels, key ceremonies and backup?
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