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Abstract: Event monitoring is a common application in wireless sensor networks. For event monitoring, a number of sensor nodes are deployed to monitor certain phenomenon. When an event is detected, the sensor nodes report it to a base station (BS), where a network operator can take appropriate action based on the event report. In this paper, we are interested in scenarios where the event must be reported within a time bound to the BS possibly over multiple hops. However, such event reports can be hampered by compromised nodes in the middle that drop, modify, or delay the event report. To defend against such an attack, we propose Sem, a Secure Event Monitoring protocol against arbitrary malicious attacks by Byzantine adversary nodes. Sem provides the following provable security guarantees. As long as the compromised nodes want to stay undetected, a legitimate sensor node can report an event to the BS within a bounded time. If the compromised nodes prevent the event from being reported to the BS within the bounded time, the BS can identify a pair of nodes that is guaranteSchool of Electrical and Computer Engineeringed to contain at least one compromised node. To the best of our knowledge, no prior work in the literature can provide such guarantees. Sem is designed to use the minimum level of asymmetric cryptography during normal operation when there is no attack, and use cryptographic primitives more liberally when an attack is detected. This design has the advantage that the overall Sem protocol is lightweight in terms of the computational resources and the network traffic required by the cryptographic operations. We also show an operational example of Sem using TOSSIM simulations. [Copyright &y& Elsevier]

Abstract: This paper studies an optimal monitoring problem for behavior-based detection in multi-channel multi-radio wireless mesh networks. In behavior-based detection, nodes overhear communications in their neighborhood to determine if the behaviors of their neighbors are legitimate. The objective of this work is to maximize the number of nodes being monitored by judiciously choosing a set of monitoring nodes and also channels for the chosen monitoring nodes. This problem is NP-hard, growing exponentially with the number of monitoring nodes. We develop three approximation algorithms, each of which achieves at least a constant factor of the optimum. Furthermore, one of our algorithms achieves the best possible approximation ratio among all polynomial-time algorithms, unless P = NP. We conduct simulations in random networks and scale-free networks to evaluate the coverage and the execution time of the three algorithms. [Copyright &y& Elsevier]

Abstract: Sensor networks enable a wide range of applications in both military and civilian domains. However, the deployment scenarios, the functionality requirements, and the limited capabilities of these networks expose them to a wide range of attacks against control traffic (such as wormholes, rushing, Sybil attacks, etc.) and data traffic (such as selective forwarding). In this paper we propose a framework called UnMask that mitigates such attacks by detecting, diagnosing, and isolating the malicious nodes. UnMask uses as a fundamental building block the ability of a node to oversee its neighboring nodes’ communication. On top of UnMask, we build a secure routing protocol, Lsr, that provides additional protection against malicious nodes by supporting multiple node-disjoint paths. We analyze the security guarantees of UnMask and use ns-2 simulations to show its effectiveness against representative control and data attacks. The overhead analysis we present shows that UnMask is a lightweight protocol appropriate for securing resource constrained sensor networks. [Copyright &y& Elsevier]

Abstract: Wireless reprogramming of a sensor network is useful for uploading new code or for changing the functionality of existing code. Reprogramming may be done multiple times during a node’s lifetime and therefore a node has to remain receptive to future code updates. Existing reprogramming protocols, including Deluge, achieve this by bundling the reprogramming protocol and the application as one code image which is transferred through the network. The reprogramming protocol being complex, the overall size of the program image that needs to be transferred over the wireless medium increases, thereby increasing the time and energy required for reprogramming a network. We present a protocol called Stream that significantly reduces this bloat by using the facility of having multiple code images on the node. It pre-installs the reprogramming protocol as one image and equips the application program with the ability to listen to new code updates and switch to this image. For a sample application, the increase in size of the application image is 1 page (48 packets of 36bytes each) for Stream and 11 pages for Deluge. Additionally, we design an opportunistic sleeping scheme whereby nodes can sleep during the period when reprogramming has been initiated but has not yet reached the neighborhood of the node. The savings become significant for large networks and for frequent reprogramming. We implement Stream on Mica2 motes and conduct testbed and simulation experiments to compare delay and energy consumption for different network sizes with respect to the state-of-the-art Deluge protocol. [Copyright &y& Elsevier]

Abstract: In multihop wireless systems, the need for cooperation among nodes to relay each other’s packets exposes them to a wide range of security attacks. A particularly devastating attack is the wormhole attack, where a malicious node records control traffic at one location and tunnels it to a colluding node, possibly far away, which replays it locally. This can have an adverse effect on route establishment by preventing nodes from discovering legitimate routes that are more than two hops away. Previous works on tolerating wormhole attacks have focused only on detection and used specialized hardware, such as directional antennas or extremely accurate clocks. More recent work has addressed the problem of locally isolating the malicious nodes. However, all of this work has been done in the context of static networks due to the difficulty of secure neighbor discovery with mobile nodes. The existing work on secure neighbor discovery has limitations in accuracy, resource requirements, and applicability to ad hoc and sensor networks. In this paper, we present a countermeasure for the wormhole attack, called MobiWorp, which alleviates these drawbacks and efficiently mitigates the wormhole attack in mobile networks. MobiWorp uses a secure central authority (CA) for global tracking of node positions. Local monitoring is used to detect and isolate malicious nodes locally. Additionally, when sufficient suspicion builds up at the CA, it enforces a global isolation of the malicious node from the whole network. The effect of MobiWorp on the data traffic and the fidelity of detection is brought out through extensive simulation using ns-2. The results show that as time progresses, the data packet drop ratio goes to zero with MobiWorp due the capability of MobiWorp to detect, diagnose and isolate malicious nodes. With an appropriate choice of design parameters, MobiWorp is shown to completely eliminate framing of a legitimate node by malicious nodes, at the cost of a slight increase in the drop ratio. The results also show that increasing mobility of the nodes degrades the performance of MobiWorp. [Copyright &y& Elsevier]

Abstract: Wireless sensor networks are increasingly being used in applications where the communication between nodes needs to be protected from eavesdropping and tampering. Such protection is typically provided using techniques from symmetric key cryptography. The protocols in this domain suffer from one or more of the following problems—weak security guarantees if some nodes are compromised, lack of scalability, high energy overhead for key management, and increased end-to-end data latency. In this paper, we propose a protocol called Secos that mitigates these problems in static sensor networks. Secos divides the sensor field into control groups each with a control node. Data exchange between nodes within a control group happens through the mediation of the control head which provides the common key. The keys are refreshed periodically and the control nodes are changed periodically to enhance security. Secos enhances the survivability of the network by handling compromise and failures of control nodes. It provides the guarantee that the communication between any two sensor nodes remains secure despite the compromise of any number of other nodes in the network. The experiments based on a simulation model show a seven time reduction in energy overhead and a 50% reduction in latency compared to SPINS, which is one of the state-of-the-art protocols for key management in sensor networks. [Copyright &y& Elsevier]