Advances in technology introduce new application areas for wireless sensor networks (WSNs). Foreseeable wide deployment of mission critical sensor networks creates concerns on security issues because they are more vulnerable to attacks due to broadcast nature of transmission medium, resource limitation on sensor nodes and uncontrolled environments where they are left unattended. The most critical security requirements in WSNs include authentication and confidentiality .These security requirements can be provided by a key management but it is difficult due to the adhoc nature, intermittent connectivity, and resource limitations of the sensor networks .In this paper we proposed a key management scheme for clustered wireless sensor networks based on the random key distribution. Our analysis of this scheme shows that it is more resilient to node capture as compared to other random key distribution schemes. It also provide global and continuous authentication of each entity in the network and multiple level of encryption.