Efficient Group-Key Management for Low-bandwidth Smart Grid Networks

As Smart Grid comes with new smart devices and additional data collection for improved control decisions, this puts a lot of burden on the underlying legacy communication infrastructures that may be severely limited in bandwidth. Therefore, an alternative is to consider publish-subscribe architectures for not only enabling flexible communication options but also exploiting multicasting capabilities to reduce the number of data messages transmitted. However, this capability needs to be complemented by a communication-efficient group key management scheme that will ensure security of multicast messages in terms of confidentiality, integrity and authentication. In this paper, we propose a group-key generation and renewal mechanism that minimizes the number of messages while still following the Diffie-Hellman (DH) Key exchange. Specifically, the Control Center (CC) utilizes Shamir's secret key sharing scheme to compute points for each device using random pairs sent by group members. Such points are then utilized to derive the group key based on Lagrange interpolation. The hash-chain concept is employed to renew the group key without requiring further message exchanges, essentially achieving key renewal in a single message. We evaluated our protocol by creating an MQTT-based testbed supporting multicasting. The results show that number of messages are decreased significantly compared to alternative approaches.