PFS, Perfect Forward Secrecy

Perfect forward secrecy is relevant in many authenticated key-agreement protocols that use Public-key cryptography. Forward secrecy is commonly used as a synonym of perfect forward secrecy even though the term “perfect” isn’t well represented in this context. Another reference distinguishes the two terms, defining perfect forward secrecy as a property in which an agreed key will not be compromised even if an agreeable set derived from the same long-term keying materials of a subsequent secret are compromised. PFS was originally developed and used to detail a property of STS (Station-to-Station), a protocol in which long-term secrets are represented by private keys. It’s current use requires the aid of Public-key cryptography where a public and private key is used. PFS cannot be achieved with symmetric cryptography alone. PFS has also been used to represent the analogous property of various password-authenticated protocols in which a long-term secret is a shared password.