Software Design

TLS 1.3 Handshake in a Single Round Trip

UML Sequence Diagrams · made in Skemio

Sequence diagram showing 1-RTT handshake between client browser and TLS 1.3 server with ClientHello, ServerHello, and encrypted app data.
Sequence diagram showing 1-RTT handshake between client browser and TLS 1.3 server with ClientHello, ServerHello, and encrypted app data.
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What it shows

  • Client sends cryptographic key shares inside ClientHello in round trip 1
  • Server selects cipher and sends ServerHello with immediate encryption
  • HTTP application traffic begins immediately after 1-RTT handshake completes

The takeaway

TLS 1.3 eliminates round trips by guessing the key exchange algorithm up front and encrypting handshake metadata.

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