TLS Session Resumption

Mechanisms that allow a client to skip the full TLS handshake when reconnecting to a server it has previously established a session with. TLS 1.2 supports two methods: session IDs (server stores session state) and session tickets (server encrypts state and gives it to the client). TLS 1.3 replaces both with PSK (Pre-Shared Key) resumption via session tickets, combined with optional 0-RTT data in the first flight. Resumption reduces handshake latency from 1-RTT to 0-RTT at the cost of a replay risk for 0-RTT data.