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Interview question · Cryptography, PKI & TLS

What does a MAC prove, what does a signature prove, and why can a MAC not give non-repudiation?

Both detect tampering. The difference is who else could have made the tag, and that decides webhooks, tokens and audit evidence.

mediumNewPreparation tags: Google, Amazon, StripeUpdated Nov 2026

Both detect tampering. The difference is who else could have made the tag, and that decides webhooks, tokens and audit evidence.

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 team must choose between HMAC and digital signatures for authenticating messages between their services and for receipts sent to customers.

  1. What does a MAC prove?
  2. What does a signature prove?
  3. Why can a MAC not give non-repudiation?
  4. Which fits service-to-service messages?
  5. Which fits customer receipts?
  6. What would you recommend?

Each rung has a nudge, a model answer, the principle that carries over and the weak answer to avoid. Sign in free to open it.

UP NEXT ON YOUR JOURNEY
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