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Interview question · Software, Data & Model Supply Chain

Why does a code signature need a trusted timestamp, and what happens when the signing certificate expires or is revoked?

Signed software outlives the certificate that signed it. The scored answer explains how a timestamp proves the signature was made while the certificate was valid, and how revocation dates interact with it.

hardNewPreparation tags: Microsoft, Apple, GoogleUpdated Nov 2026

Signed software outlives the certificate that signed it. The scored answer explains how a timestamp proves the signature was made while the certificate was valid, and how revocation dates interact with it.

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

A code-signing certificate expires next month, and thousands of installed copies of your software were signed with it.

  1. What happens to signatures when a certificate expires?
  2. How does a trusted timestamp help?
  3. What if the key was compromised from a certain date?
  4. What if the timestamp authority itself is compromised?
  5. How does Sigstore use this idea?
  6. What would you tell the release team?

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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