Three Branches of Accountability

Security protocols usually describe how honest agents behave, and one proves some security goals to hold even in the presence of an intruder who just does whatever he is capable of where cryptography alone does not provide sufficient protection, accountability can help as a deterrent for the intruder, because his actions may be detected and he could be punished. The novelty of this work is to model actually all three branches of government that are relevant here. First, instead of protocols we have a legal system that defines which actions are legal. Second, we have the police that may detect some crimes and collect evidence. Third, we have a justice system that evaluates evidence, can subpoena participants, and finally may convict players. The broad definition of a legal system allows us to avoid defining all protocols that honest participants may engage in. Rather we describe players (no matter if honest or dishonest) who may do anything that is legal and who can do anything except breaking the cryptography.