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Abstract.A passive attacker can compromise a generic anonymity protocol by applying the so called disclosure attack, i.e. a special traffic analysis attack. In this work we present a more efficient way to accomplish this goal, i.e. we need less observations by looking for unique minimal hitting sets. We call this the hitting set attack or just HS-attack. In general, solving the minimal hitting set problem is NP-hard. Therefore, we use frequency analysis to enhance the applicability of our attack. It is possible to apply highly efficient backtracking search algorithms. We call this approach the statistical hitting set attack or SHS-attack. However, the statistical hitting set attack is prone to wrong solutions with a given small probability. We use here duality checking algorithms to resolve this problem. We call this final exact attack the HS*-attack.

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Abstract-Network layer anonymization protects only some of the user's personal identification information, namely network addresses of the communicating parties. However, even if the lower layers of communication provide perfect protection for the user's profile, information leakage on the application layer destroys the whole effort. Currently, all widespread implementations of anonymizing networks do not use a holistic approach and therefore, neither filter nor actively warn users about information leakage from the upper layers, which may look innocent to the end user.We extend existing work on security of anonymizing networks to take into account additional information leakage from the application layer. Further we show, under which conditions and how this kind of information can be used not only to build an extensive user profile at "low costs", but also to speed up traditional attacks that are targeted at the network layer identification of users' peer partners.

Abstract. We propose a novel mechanism for authentication of queries in a sensor network in case these queries are flooded. In our protocol, the base station appends an authenticator to every query, such that each sensor can verify with certain probability that the query is sent by the base station. Implicit cooperation between sensor nodes during the flooding process ensures that legitimate queries propagate quickly in the network, whereas the propagation of illegitimate queries is limited to only a small part of the network.