PFS stands for Perfect Forward Secrecy, which is a property of some cryptographic protocols that ensures that the compromise of a long-term key does not affect the security of past or future sessions. PFS provides the highest level of protection against brute-force attacks, because even if an attacker manages to break the long-term key, they cannot decrypt the previous or subsequent communications that use different session keys. PFS is achieved by using ephemeral or temporary keys that are derived from a Diffie-Hellman key exchange, and are not based on the long-term key. Therefore, each session has a unique and independent key that is not stored or reused. PFS is supported by some protocols such as TLS, SSH, and IPsec123. References := 1: Implementing and Operating Cisco Security Core Technologies (SCOR) v1.0, Module 4: Securing Networks with Cisco Firepower Next Generation IPS, Lesson 4.1: Deploying Cisco Firepower Next-Generation IPS, Topic 4.1.2: Cisco Firepower NGIPS Device Management 2: What is Perfect Forward Secrecy? | Baeldung on Computer Science4 3: Perfect Forward Secrecy - an overview | ScienceDirect Topics5