Wireless Sensor Networks (WSNs) consists of small nodes with constrained capabilities to sense, collect, and disseminate information in many types of applications. Wireless Sensor Networks (WSN) have attracted significant interests from the research community in a wide range of applications such as target tracking, environment monitoring, military sensing, distributed measurement of seismic activity, and so on. As sensor networks become wide-spread, security issues become a central concern. In this paper, the authors identify the Security requirements of key management in WSN. The secure management of the keys is one of the most critical elements when integrating cryptographic functions into a system.