Abstract-To securely exchange data over public networks, such as the Internet, organizations often utilize Virtual Private Networks (VPNs). However, relying on these potentially large overlay networks makes them vital targets for Denial-ofService (DoS) attacks. Thus, recent approaches for VPN autoconfiguration address DoS resistance by employing distributed management algorithms. Nevertheless, there is no satisfying solution for time synchronization within VPNs that is designed for resistance against DoS as well as internal attacks. For example, Network Time Protocol (NTP) relies on hierarchical structures, and cannot comply with DoS resistance. Thus, in this article we present a novel, fully distributed and fault tolerant time synchronization approach, which is designed to be transparently integrated in VPN gateways. Combining diffusion-based roundtrip-synchronization with an internal attacker detection, the proposed mechanism is making a contribution to resilient VPN design. Simulation results reveal a robustness against rather powerful internal attackers.

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Large-scale data acquisition and distributed processing of video material requires smart camera devices to collaborate over arbitrary transport networks with no further centralized coordinating instances. Especially in the context of surveillance and security in public transportation networks, the knowledge of spatio-temporal traffic flows can support applications like anomaly detection, smart navigation, or prosecution. Therefore, the problem of autonomously estimating a logical camera topology with respect to scalability, agility and robustness must be solved by efficient communication about distributed detected events. Simple broadcasting or flooding of information does not scale well with the number of nodes and leads to strong requirements on bandwidth and processing power. Thus, a generic system model, describing the process of generating eventbased distributed knowledge without making use of flooding, broadcast or multicast, is introduced and evaluated. The results of a conducted simulation study reveal the potential of saving a significant amount of messages on the one hand, and being able to handle poor performance of object recognition algorithms on the other hand.