Which key exchange mechanism in TLS 1.3 provides forward secrecy by generating ephemeral session keys?

• A. Ephemeral Diffie-Hellman (ECDHE)
• B. RSA static key exchange
• C. Diffie-Hellman with static keys
• D. RSA with PKCS#1 v1.5

Answer: (A)

Forward secrecy is achieved when session keys are created from ephemeral, per-session key material, so a future compromise of the server’s private key cannot reveal past conversations. Ephemeral Diffie-Hellman (ECDHE) does exactly this: for each TLS session, a fresh ephemeral key pair is generated and used in the Diffie-Hellman exchange to derive a unique shared secret that becomes the session keys. Since these keys are derived from ephemeral values and not from a long-term private key, even if the server’s private key is later compromised, past session keys stay secure.

Other methods rely on the server’s long-term private key during the handshake, so they do not provide forward secrecy in the same way. For example, static private-key exchanges use a fixed private key, and RSA-based exchanges in older TLS versions encrypt the pre-master secret with a long-term key, meaning past sessions could be compromised if that key is ever exposed. In TLS 1.3, the standard approach is to use ephemeral key exchange, specifically ECDHE.