What is the difference between Perfect Forward Secrecy (PFS) and standard key exchange in TLS?

Question

Cybersecurity Fundamentals — Hard

What is the difference between Perfect Forward Secrecy (PFS) and standard key exchange in TLS?

Accepted Answer

Perfect Forward Secrecy (PFS) generates unique session keys for each session, protecting past sessions if the server's long-term private key is compromised. In contrast, standard key exchange in TLS derives session keys directly from the server's long-term key, making past sessions vulnerable.