Forward anonymity

Forward anonymity, analogous to forward secrecy, in computer security and cryptography is the property which prevents an attacker who has recorded past communications from discovering the identities of the participants, even after the fact.

When speaking of forward secrecy, system designers attempt to prevent an attacker who has recorded past communications from discovering the contents of said communications later on. One example of a system which satisfies the perfect forward secrecy property is one in which a compromise of one key by an attacker (and consequent decryption of messages encrypted with that key) does not undermine the security of previously used keys.

When speaking of forward anonymity, system designers attempt to prevent an attacker who has recorded past communications from discovering the identities of the participants, even after the fact. This property is not to be confused with sender (or receiver) anonymity, in which the identity of the sender (or receiver) remains unknown to all entities in the system.