# AEF: Adaptive En-Route Filtering to Extend Network Lifetime in Wireless Sensor Networks
## 1 Introduction  
Wireless sensor networks (WSNs) have witnessed mushroom growth due to the recent advancement in microelectromechanical systems (MEMS) [1; 2]. WSNs are being adapted in numerous applications due to their low cost, small size, tether-lessness, and high density characteristics. Their widespread deployment requires countermeasures against security threats. One such threat is false report injection attacks, hereinafter referred to as attacks, resulting in draining energy of nodes on the path. An example of such an attack is shown in Figure 1. It is worth mentioning that, although our proposed scheme can also be effective against eavesdropping or modification attacks, this is out ofthe scope of our paper. A compromised node generates a false report about a nonexistent event and transmits it to the base station (BS), draining energy of the nodes on the path. It could also trigger false alarms about nonexistent events to the end user. En-route filtering schemes in general and dynamic en-route filtering (DEF) [3] and commutative cipher-based en-route filtering (CCEF) [4] in particular offer better security at the expense of network lifetimes. DEF uses the hill-climbing approach for key dissemination for early detection of false report attacks. A legitimate report is approved by several nodes using their keys and secret key from a global key poll. Verification nodes on path can drop reports which are not validated. Since, DEF uses many keys in a key chain method, it becomes complicated for large-size WSNs. On the other hand, CCEF is based on expansive public key infrastructure. In most en-route filtering schemes [3; 4; 5; 6; 7; 8], similar limitations are observed: (1) an underlying fixed path routing that does not consider network lifetime in the design and (2) fixed responses (i.e., detection capacity) to different number of attacks, among other limitations. An example of shortest path or greedy routing, which results in fixed path routing, is greedy perimeter-based stateless routing (GPSR) [9]. In this paper, the first limitation is countered by the proposed energy-aware dynamic routing and the other is catered by pre-deterministic key distribution. These methods equip our proposed scheme to dynamically respond to network conditions and attack intensity. Dynamic path routing not only serves our purpose of avoiding the energy-hole problem but also can grant multiple paths and load balancing. Sensor networks suffers from the energy-hole problem as the rate of energy consumption on critical paths and around the base station is significantly higher compared to the distant nodes. It results in network partition--communication between different parts of the network is broken. This is such a state at which disconnected parts of network cannot be reached. Therefore, the energy-hole problem resulting in network partitioning can be avoided using dynamic path routing. In this paper, we prefer dynamic path routing over other strategies which may alleviate energy-hole problems such as dynamic clustering and sink mobility. Compared to the aforementioned techniques, the dynamic routing strategy grants additional multiple paths with different number of keys in each path along with a distinct level of security. As a result, our scheme can  
Figure 1: False report injection attack in wireless sensor networks. respond dynamically with changes in attack intensity and load balancing while avoiding the energy-hole problem. In addition to countering attacks, the proposed scheme can also be effective against eavesdropping or modification attacks [10]. Since, event reports are not transmitted through a single path, an adversary cannot interpret the entire message. As events report are routed through multiple paths, AEF can be more robust and reliable against these attacks. Various assumptions about radio characteristics might be beneficial to different protocols such as energy dissipated in transmitters and receivers. Here, we assume a simple and most commonly used radio model [11] to achieve an acceptable \(E_{b}/N_{0}\)[12].