Study Of Communication Trustworthiness In Ad Hoc Networks

Security is one of the key factors for the ad hoc network in determining whether its potential capability can be developed or not, especially during its application in military and business. Compared with traditional wired networks, ad hoc network is vulnerable for attacks and threats, such as Bad-mouthing attack, On-off attack and Conflicting behavior attack. Present security technology mainly focuses on encryption algorithms and protocols, and lack flexibility in the peer to peer network environment without any third-party. Dynamic trust model could accurately capture the behavior information between nodes and then obtain their mutual trust values. The trust management mechanism could furtherly be introduced into the network, which could consequently implement the forecast and control of node's behavior and increase the reliability of the network.In this thesis, the existing security problems in ad hoc networks are firstly analyzed. In view of the problems and deficiencies of the proposed techniques and standards, such as encryption and the PKI, the concept of trust and the framework of dynamic distributed security mechnasim are proposed to resolve the communication problem in ad hoc networks. The trust chain theory based on node's depth-expurgation rules in direct acyclic graph is introduced, which could calculate the trust scale between two indirect interaction nodes. Compared with related research results, the algorithm could reduce the difference rate to [-1%, 1%] as shown in the experiment. Meanwhile, the algorithm shows obvious superiority at mitigating malicious coordinated attacks.Based on the trust evaluation model, the trusted routing algorithms and protocols in the routing layer are studied in this thesis. In view of the fuzzy network environment and dynamic characteristics of networks, combined with Fuzzy Dynamic Programming (FDP) theory, trusted routing algorithms which are distributed and local decision are adopted. Improved model and the corresponding algorithm based on FDP finite horizon decision model, are constructed for ad hoc network to solve the trusted routing decision problem. Moreover, based on the traditional Dynamic Source Routing (DSR) protocol, the Fuzzy Trust Dynamic Source Routing (FTDSR) protocol is obtained. According to the simulation implementd on OPNET simulation platform, the algorithm could identify and purge the malicious nodes efficiently and increase the network performance consequently. In addition, the algorithm has the feature of distributed parallel computing which can distribute the routing computation and route storage requirement to each device, so that it can balance the workload between all the devices without increasing the workload of a single one and complete the routing calculations effectively in real-time.Finally, some research and practice are done in the implement level of the trusted routing protocol in this thesis. In the data packets routing process, malicious nodes always drop packets deliberately, send redundant packets arbitrarily as well as modify packets illegally. Through the analysis of these malicious behaviors, a trust evaluation model based on Linux Net-filter frame is proposed, which could monitor the illegal operations and evaluate the trust value of nodes, the Trust Dynamic Source Route (TDSR) protocol is implemented finally by this approach, which could improve the performance of the network, and the flow chart as well as the trust routing optimization stratigy is also given.