Date Added: Sep 2010
Several credential systems have been proposed in which users can authenticate to service providers anonymously. Since anonymity can give users the license to misbehave, some variants allow the selective deanonymization (or linking) of misbehaving users upon a complaint to a Trusted Third Party (TTP). The ability of the TTP to revoke a user's privacy at any time, however, is too strong a punishment for misbehavior. To limit the scope of deanonymization, some systems have been proposed in which users can be deanonymized only if they authenticate "Too many times," such as "Double spending" with electronic cash. While useful in some applications, such techniques cannot be generalized to more subjective definitions of misbehavior, e.g., using such schemes it is not possible to block anonymous users who "Deface too many webpages" on a website.