key exchange
termcryptography
How two parties agree on the session's secret key - the part of a cipher suite that decides whether recorded traffic stays sealed.
Ephemeral Diffie-Hellman (ECDHE on X25519 or P-256) generates fresh keys per connection, giving forward secrecy; static-RSA key transport does not, which is why TLS 1.3 removed it and made ephemeral exchange structural. The post-quantum transition happens here too: hybrid X25519+ML-KEM runs both worlds side by side.
Also known as: key exchange, key agreement, kex, kx