I. Introduction
Wireless sensor networks (WSN) are ideal candidates to monitor the environment in various applications such as military surveillance, habitat monitoring and health care [1]. For this network, large amount of sensor nodes with limited resources are deployed in a hostile environment. Once a node is compromised, all the keys stored in it will be disclosed by the attacker, and the attacker can easily launch false data injection attacks, i.e., attackers can abuses the keys to inject bogus data reports into sensor networks [2]. This attack may cause not only false alarms but also the depletion of the limited resources of the network.