TLS: how HTTPS gets secure in one round trip

What you take away

• TLS 1.3 needs one round trip on a new connection, and none when resuming a previous one (0-RTT).
• The certificate proves you are talking to the owner of that domain; the key exchange agrees a secret nobody listening can compute.
• The cost of HTTPS is round trips, not encryption: symmetric crypto runs at GB/s in hardware.
• Where TLS terminates decides what is plaintext: past the termination point, traffic is clear unless you re-encrypt.

How the class is laid out

1. The problem
2. The simple version
3. One round trip, in four moves
4. Where it terminates decides what is plaintext
5. Check your understanding