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Hierarchical Trust and Fault-Tolerant Group Key Agreement for MANETs
Mustapha Sadi, Mourad Amad and Nadjib Badache

Scalability and robustness are two basic factors that determine the efficiency of any group key management protocol. Designing such protocols for Mobile Ad-Hoc Networks (MANETs) becomes more complex because of their frequent node and link failures, high dynamic topology and limited energy autonomy. Group key in MANETs is generally obtained in a contributory manner using Group Key Agreement (GKA) scheme. Efficiency of each solution is measured by the computation and communication cost of the key generation and re-keying operations. Scalability is the main drawback of known basic GKA protocols. Providing large-scale systems using hierarchical solutions is a challenge. Thus, members of the whole group are broken into subgroups by adopting various clustering schemes. Trust oriented clustering scheme is the most adequate to secure group communication. Whereas the scalability is sufficiently considered in existing hierarchical GKA protocols, they assume that group members are not faulty so they were not interested to their robustness. In distributed systems, unreliable failure detectors are classical mechanisms that provide information about processes failures and can help systems to cope with the high dynamism of the networks. In this paper, we propose a new model that determines the degree of fault tolerance by considering both failure detections and trust that can have every member on the others. Our solution allows to evict malicious members or the ones that fails to be chosen as cluster-head and be a participating member in group key management. The proposed GKA scheme is both efficient, scalable and robust.

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