Cryptographic Key Management Technique in Hierarchical Wireless Sensor Networks

A wireless sensor network can be defined as a network of possibly low-size and low-complex devices denoted as sensor nodes that can sense the environment and communicate the information gathered from the monitored field through wireless links. The sensor nodes are battery powered or the energy is scavenged from the environment. Also they are limited in memory, bandwidth, computation power and energy. The wireless sensor networks are usually deployed in hostile environments so security becomes a serious concern. Nodes deployed are susceptible to both internal and external attacks. And such attacks are difficult to detect since the sensor nodes doesnt communicate in a regular manner. So the communication between the nodes must be protected using encryption techniques. For that encryption keys must be provided. Key Management is the management of cryptographic keys in the cryptosystem. Here an inter-cluster key management scheme for hierarchical WSNs is proposed. The Group-based Deployment Model is employed in this scheme. Before network deployment, nodes are divided into different deployment groups. There are different types of sensor nodes, based on the levels of implementation as member sensor nodes, cluster heads and super cluster heads. This scheme is based on the congruence property of modular arithmetic. Each Super Cluster head is pre-distributed with private and public keys. The Cluster Head will store a key seed send by the super cluster head. This seed is used to compute a unique shared key with its super cluster head and a group key shared with other nodes in the same cluster. Thus it requires minimum key storage space only. Also the failure of the cluster head due to energy drain and frequent packet drop (a malicious behavior) is addressed.