Why it matters

All modern web traffic uses TLS. Understanding it enables debugging cert issues, optimizing handshake latency, and reasoning about security.

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The architecture

Handshake: client hello (supported ciphers), server hello + certificate, key exchange, verify certificate, derive session keys.

Data: symmetric encryption of data using session keys. AES-GCM typical.

TLS sessionHandshakecert + key exchangeEncrypted streamAES-GCM typicalSession ticketsresume without re-handshakeTLS 1.3 does handshake in 1-RTT (0-RTT with resumption); much faster than 1.2
TLS lifecycle.
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How it works end to end

Certificate: X.509. Signed by CA. Contains public key + identity.

Cert chain: server → intermediate CA → root CA. Client verifies chain to trusted root.

SNI: Server Name Indication. Sent unencrypted in handshake; enables multi-cert servers.

TLS 1.3: 1-RTT handshake, removed insecure ciphers, mandatory perfect forward secrecy.