Towards Measuring Anonymity

This paper introduces an information theoretic model that allows to quantify the degree of anonymity provided by schemes for anonymous connections It considers attackers that obtain probabilis - tic information about users The degree is based on the probabilities an attacker, after observing the system, assigns to the di?erent users of the system as being the originators of a message As a proof of concept, the model is applied to some existing systems The model is shown to be very useful for evaluating the level of privacy a system provides under various attack scenarios, for measuring the amount of information an at - tacker gets with a particular attack and for comparing di?erent systems amongst each other