What happens during an HTTPS TLS handshake?
Reported in Google DeepMind European engineering loops. Security and networking question covering encryption, certificates, and performance.
Interview scenario
Often asked in Google DeepMind loops at European offices (London, Berlin, Amsterdam, Paris, Stockholm, Dublin, and remote EU). Prepare a clear spoken answer plus key trade-offs.
Model answer
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Cover trade-offs, structure, and a concrete example before revealing the baseline response.
How to frame this at Google DeepMind: Connect your answer to measurable impact, clarity of thought, and trade-offs the team cares about. Below is a strong baseline response you can adapt with your own project examples.
HTTPS wraps HTTP in TLS. Simplified 1.3 handshake: client sends ClientHello (supported ciphers, key shares); server responds ServerHello, certificate chain, and key share; both derive session keys; encrypted application data follows.
Server proves identity via X.509 certificate signed by trusted CA—browser validates chain and hostname. Mutual TLS (mTLS) also requires client certificate for service-to-service auth.
Performance: TLS 1.3 reduces round trips vs 1.2; session resumption (tickets) avoids full handshake on repeat visits; HTTP/2 multiplexing over one connection.
Engineering relevance: terminate TLS at load balancer vs app; HSTS header; certificate rotation automation (Let's Encrypt); and debugging with openssl s_client.
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