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Interview question · Cryptography, PKI & TLS

Walk through a TLS 1.2 handshake message by message, then explain exactly what TLS 1.3 changed and why each change matters for security.

Most candidates can recite TLS 1.3. Interviewers ask for 1.2 because it is still everywhere, and because every change in 1.3 is the fix for an attack on 1.2.

mediumEssentialNewPreparation tags: Google, Microsoft, AmazonUpdated Nov 2026

Most candidates can recite TLS 1.3. Interviewers ask for 1.2 because it is still everywhere, and because every change in 1.3 is the fix for an attack on 1.2.

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

Your load balancer still allows TLS 1.2 for some legacy clients, and a reviewer asks what you lose compared with TLS 1.3.

  1. How does a TLS 1.2 ECDHE handshake work?
  2. What does TLS 1.3 change?
  3. What risks come with TLS 1.2 specifically?
  4. What about downgrade?
  5. What would you do about the legacy clients?
  6. What would you tell the reviewer?

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 trackTake a TLS certificate apart field by field. Which fields and extensions do validators actually check, and which mistakes do they catch?Next in this trackWho decides which root CAs your devices trust? Explain root programs, trust stores per runtime, distrust events and root expiry.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?
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