Data Integrity and Availability in Power System Communication Infrastructures

Sammanfattning: Society is increasingly dependent on the proper functioning of electric power systems. Today's electric power systems rely heavily on information and networking technology in order to achieve efficient and secure operation. Recent initiatives to upgrade power systems into smart grids target an even tighter integration with information and communication technologies in order to enable the integration of renewable energy sources, local and bulk generation and demand response. Therefore for a proper functioning of smart grids, it is essential that the communication network is secure and reliable both in the face of network failures and in the face of attacks. This thesis contributes to improving the security of power system applications against attacks on the communication infrastructure. The contributions lie in two areas. The first area is the interaction of network and transport layer protocols with power system application layer security. We consider single and multi-area power system state estimation based on redundant telemetry measurements. The state estimation is a basis for a set of applications used for information support in the control center, and therefore its security is an important concern. For the case of single-area state estimation, we look at the security of measurement aggregation over a wide area communication network. Due to the size and complexity of power systems, it can be prohibitively expensive to introduce cryptographic security in every component of the communication infrastructure. Therefore, we investigate how the application layer logic can be leveraged to optimize the deployment of network, transport and application layer security solutions. We deffine security metrics that quantify the importance of particular components of the network infrastructure. We provide efficient algorithms to calculate the metrics, and that allow identication of the weakest points in the infrastructure that have to be secured. For the case of multi-area state estimation, we look at the security of data exchange between the control centers of neighboring areas. Although the data exchange is typically cryptographically secure, the communication infrastructure of a control center may get compromised by a targeted trojan that could attack the data before the cryptographic protection is applied or after it is removed. We deffine multiple attack strategies for which we show that they can signicantly disturb the state estimation. We also show a possible way to detect and to mitigate the attack.The second area is a study of the communication availability at the application layer. Communication availability in power systems has to be achieved in the case of network failures as well as in the case of attacks. Availability is not necessarily achieved by cryptography, since traffic analysis attacks combined with targeted denial-of-service attacks could signicantly disturb the communication. Therefore, we study how anonymity networks can be used to improve availability, which comes at the price of increased communication overhead and delay. Because of the way anonymity networks operate, one would expect that availability would be improved with more overhead and delay. We show that surprisingly this is not always the case. Moreover, we show that it is better to overestimate than to underestimate the attacker's capabilities when conguring anonymity networks.