Perfect secrecy

Forward secrecy is a feature of key-agreement protocols that ensures session keys will not be compromised even if long-term secrets used in the session key exchange are compromised. It protects past sessions against future compromises of keys or passwords by generating unique session keys for each session. It also reduces the motivation for attackers to compromise keys, as any information leaked in a forward secure system is limited. However, it is limited by the assumption that an adversary will only passively collect traffic and not actively use a man-in-the-middle attack.