Wireless sensor networks (WSNs) are formed by sensor nodes that have the ability to sense the environment, process the sensed information, and communicate via radio without any additional prior backbone infrastructure. WSNs cover a wide range of applications such as military applications, event detection, telemedicine, home security, etc. Sensor nodes have limited resources in terms of power, computation and communication. Also, unlike other wireless networks, it is dicult (or infeasible) to replace/recharge exhausted batteries attached to sensor nodes.

In WSNs, communication with other nodes is the most energy consuming task. Hence, the primary objective in designing protocols for WSNs is to minimize communication over- head. This is often achieved using in-network data aggregation.

As WSNs are often deployed in open environments, they are vulnerable to security attacks. Many applications of WSNs collect sensitive information, thus the security of collected information has become an important issue. Due to resource constraints in the sensor nodes, traditional security mechanisms with large overhead of computation and communication are infeasible in WSNs.

This thesis contributes toward the design of energy ecient secure and privacy pre- serving data aggregation protocol for WSNs. First, we classify the main existing secure and privacy-preserving data aggregation protocols for WSNs in the literature. Most of the existing protocols suer from high communication overhead (and thus high energy consumption) and do not address node failure. Through the study on the state-of-the-art protocols, we highlight the limitations of existing protocols for WSNs.

We then propose an energy-ecient secure and privacy-preserving data aggregation (ESP P A) scheme for WSNs. ESP P A scheme is tree-based and achieves data confiden- tiality and data privacy based on shuing technique. We propose a secure tree construction (ST) and tree-reconstruction scheme which takes into account node failure and maintain connectivity. Simulation results show that ESPPA scheme eectively preserve data pri- vacy, data confidentiality, and has less communication overhead than SMART (the most studied scheme).

Finally we propose an extension of ST scheme, called secure coverage tree (SCT) construction scheme. SCT applies sleep scheduling, identify sensor nodes which give re- dundant sensing coverage and put them into sleep to conserve energy without aecting network coverage. Nodes in sleep mode can be used later to replace failed nodes. Through simulations, we show the ecacy and eciency of the SCT scheme.

Beside the work on secure and privacy preserving data aggregation, during my research period, we have also worked on another interesting topic (i.e., composite event detection for WSNs). Appendix B presents a complementary work on composite event detection for WSNs.