A three-party signing protocol uses a Trusted Third Party (denoted T) to simulate a two-party protocol in which a sender, designated party A, anonymously signs data intended for a particular receiver, designated party B, such that B can verify the signature on the data without learning A's true identity,...http://www.google.co.uk/patents/US20030190046?utm_source=gb-gplus-sharePatent US20030190046 - Three party signing protocol providing non-linkability
