# Social Milieu Oriented Routing: A New Dimension to Enhance Network Security in WSNs
## 1 Introduction  
Wireless sensor networks (WSNs) [1] have prevailed in many areas, such as battlefield sensing, environmental monitoring, disaster handling, and traffic control, and have gained much attention from the world in recent years. In WSNs, sensor nodes with limited communication capabilities, less computation power, and less memory are deployed in the specific environment. Due to the constraints, conventional routing protocols are designed for resource-limited self-organized WSNs, which have been widely explored in recent years [2; 3; 4; 5; 6; 7; 8; 9]. Trust, an important social concept in all human interactions, has been proven to be a promising way to resolve the security issues raised by distributed collaborations. Recent progress in the area of social networks study shows that establishing trust in WSNs yields many benefits, such as giving nodes incentives to cooperate in packet forwarding, providing corresponding access control, and making the traditional security services more robust and reliable [10], and to the end, greatly enhance network performance in WSNs. However, few existing routing protocols take trust into consideration. On the one hand, trust establishment requires an evaluation of the trustworthiness of a trustee node along a certain trust path from a trustor node to the trustee node [11]. However, there are usually many trust paths between one trustor and trustee pair in large scale WSNs. On the other hand, mainstream trust research in wireless networks, including WSNs, mainly focuses on trust or reputation management without differentiating between trust between twonodes and recommendation from third party nodes. It has been proved that it would be better to regard trust and recommendation as two different independent Quality of Trust (QoT) attributes to reflect the real-world situation better [11]. Thus, a challenging problem is which the social trust path is the optimal one that can yield the most trustworthy evaluation result with two different independent end-to-end QoT constraints in large scale WSNs. This optimal social trust path (OSTP) selection problem subject to more than one end-to-end QoT constraint has been proved to be NP-complete [11]. Since there may be over thousands of paths between a pair of trustor and trustee nodes in large scale WSNs, evaluating the trustworthiness of the target trustee node along all these social trust paths requires a large amount of computation time [12]. To make this problem practically solvable, we propose an efficient and effective approximation algorithm, called the QA-based optimal social trust path (QA_OSTP) selection algorithm. Our main contributions are:  
1. For the first time, we map the aforementioned OSTP selection problem in large scale WSNs onto a transverse Ising spin glass (TISG) model. Then, we utilize configuration path-integral Monte Carlo (CPIMC) technology [13] with the aid of quantum-classical mapping and Jarzynski equality to perform the practical implementation of quantum annealing (QA) and solve the time-dependent Schrodinger equation in a very large and exponentially growing Hilbert space.
2. We carry out the performance evaluation of the newly constructed QA_OSTP and compare it with the referenced method based on extensive experiments. The experimental results demonstrate the effectiveness of QA_OSTP and prove that QA_OSTP has better performance in terms of the utility of the selected social trust path and execution time than its counterpart does.  
The rest of this paper is organized as follows. Section 2 summarizes related work in literature. In Section 3, the novel QA-based OSTP selection algorithm (QA_OSTP) is presented, and efficiency concerns are addressed. Section 4 contains experimental results and analysis, which show that QA_OSTP outperforms state-of-the-art heuristic algorithms significantly. Finally, we conclude this paper in Section 5 with a summary and future research direction.