Study On Trust Models For Pervasive Computing Environments And Relative Applications

The network environment for pervasive computing has the characters of dynamic and unpredictable, interactions could be launched between familiar entities or totally unknown entities. As the security and trust problem existed in human society, these problems also exist in the development of pervasive computing technology, however, traditional static security mechanisms like PKI and CA are not appropriate for such open and dynamic environments. Pervasive computing can not be realized without the quarantee of efficient security and trust mechanism. A hot spot research in recent years is how to design an effective dynamic trust mechanism to deal with the dynamic and unpredictable pervasive environments. However, most trust models proposed for pervasive environments is not yet perfect, some disadvantages are. existed as described following:1:Most trust models lack of the ability of context awareness and adaptiveness, contexts like time,location and interaction service can not be awared and distinguished by trust models.2:The semantic relations between different trust categories and between different interact entities are not considered in these trust models, while it may lead to low efficiency and low accuracy.3:Most existed trust models are too complicated, and are not appropriate for resource constrained environments. These above problems are deeply studied and partly solved by new trust models proposed in this paper, based on this, we also list some research work on applying trust models under the pervasive environments. The applications of trust models for pervasive environments are concentrated on two aspects. The first research aspect is to take use of trust model to enhance trust levels between entities and increase the cooperation level between entities, related to this, two methods are studied in chapter5and chapter6to increase the cooperation level under different networks in pervasive environments. The second research aspect is to afford security guarantees for the applications in pervasive environments, related to this, a routing algorithm based on trust routing tree for WSN is proposed in chapter7. The main work and contributions are presented in the following aspects:(1) A Context-Aware and Self-Adaptive Trust Model(CASATM) for pervasive environments is proposed, our trust model provide security protection based on service content adaptively at various level, and be sensitive to contexts such as time, location and service content. A simple and efficient risk evaluation model was presented to initialize trust value to unknown entities which is a common phenomenon in pervasive environments. Simulation results testify to the contexts Awareness of our model, as well as resistance of periodically cheating behaviour from malicious entity.(2) A semantic distance based trust model is proposed in this paper. The semantic distance between entities and between trust categories is borrowed to calculate trustworthiness more precisely. In our model, the behavior trust and capability trust is distinguished, all entities in pervasive environments make independent decisions which can maximize their own profit with our trust model. The simulation experiment results proved the effectiveness of our model in increasing the interaction success ratio between entities as well as the interaction efficiency.(3) The application of distributed trust model in cooperation evolution under pervasive environments is researched. Game theory is borrowed and integrated in trust models to stimulate nodes’cooperation behavior. A distributed trust model based on a non-cooperative game that uses a genetic algorithm to let the nodes quickly learn the appropriate cooperation behavior is proposed in this paper, unlike traditional distributed model, a good behavior strategy with high fitness owns a higher transmitting efficiency to accelerate the convergence process. Further more, to prolong the network life, we expand the payoff table to encourage node’s selfish behavior in case of low energy level.(4) The application of trust model in cooperation evolution under multi-agents system of P2P networks is studied. An interest-trust based cooperation model is proposed, the interest-trustworthiness of agents is evaluated in different interest fields by utilizing Bayesian method. By updating the interest-trust based connection between agents, a robust multi-agent cooperative system is formed. Simulation results prove that the proposed interest-trust based cooperation model can not only increase the ratio of successful execution of tasks, but also improve network topology to cluster nodes around the trustworthy nodes in different interest fields. The advantage of our model include following features:a kind of interest-trust based clustering is formed, network assimilation is avoided and agent’s personality is embodied.(5) The application of trust model in the data packets routing under WSN networks is studied in chapter7. A novel routing algorithm base on trustworthy core tree (TCTR) is proposed aims to prolong network lifetime as well as increase network security in a hierarchical-cluster sensornet. Cluster heads with higher residual energy and trust level are elected from underlying sensor nodes. A minimum pathloss tree algorithm is borrowed to organize all cluster heads as a trustworthy core tree with sink node as tree root. Expand the Trustworthy core tree to cover all nodes so that each node report to sink node with a certain route. A trust model is integrated in TCTR to evaluate node’s trust level and detect evil nodes. Simulation results testify to the effectiveness of the algorithm in producing a longer network lifetime and a safer network.