7. Conclusion

In this paper, we propose an efficient dynamic trust evaluation model for WSNs. It includes the direct trust module with multiple trust factors, the trusted recommendation trust module, the dynamic trust integration module, and the adjustable trust update module. In the course of the calculation of direct trust, we take the communication trust, data consistency, and energy trust into account; it can achieve accurate trust evaluation against routing attacks and data information attacks. The punishment factor and regulating function are introduced based on the character   "trust is hard to acquire and easy to lose". The calculation of indirect trust is invoked conditionally in order to enhance the accuracy of trust value, which can be against the trust model attacks such as bad-mouth attack. Moreover, in the process of the integrated trust quantitative calculation, we define a dynamic balance weight factor function to overcome the defect caused by allotting weights subjectively. Afterwards, we give the update mechanism based on IOWA to enhance flexibility. During this process, we can dynamically adapt the parameters to change the weight sequence to meet the actual needs of the network. The proposed dynamic trust model enables dynamic, accurate, and objective evaluation of trust between nodes based on the behavior of nodes.

We have performed several tests to validate the proposed trust model. Simulation results indicate that DTEM is an efficient dynamic and attack-resistant trust evaluation model. It can dynamically evaluate the reputation among nodes based on the communication behavior, data consistency, and energy consumption of nodes. And having compared RFSN, BTMS, and DTEM, DTEM is of great help in defending against routing attacks, data information attacks, and trust model attacks. It can effectively identify various malicious attacks.

The traditional security mechanisms (cryptography, authentication, etc.) are widely used to deal with external attacks. Trust model is a useful complement to the traditional security mechanism, which can solve insider or node misbehavior attacks. Hence, trust model is important to providing security service for upper layer network application in WSNs, such as secure routing and secure data fusion. In our future work, we would like to focus on the application of trust model in routing and data fusion for WSNs.