Wireless sensor network is a kind of ad-hoc network which consists of distributed sensors to monitor physical and environmental conditions which are of autonomous type. WSN is not yet implemented widely for such applications due to its energy consumption, challenges in environmental conditions etc. Security in Wireless Sensor Networks (WSNs) is an upcoming research field which is quite different from traditional network security mechanisms. In this paper, the authors propose an efficient PKC based security architecture. Key management plays an essential role in achieving security in WSNs.