Process Control Systems monitor and control processes that manage critical infrastructure systems. To enable these systems to continue working uninterrupted, situational awareness is imperative. Communication systems that provide situational awareness pose challenges such as low latency, high availability and security. Being a modern life supporting system, critical infrastructures such as electric power grids have very high risk and may potentially result in enormous economic and social impact if attacked. Authentication is the fundamental step towards security. The goals of other security services can be attained only if they are based on successful authentication. This thesis presents an authentication framework that authenticates nodes to ensure that they are genuine. A set of authentication protocols that employ authentication modules that can be changed at runtime to support long-lived systems such as Process Control Systems are introduced in this work. The protocols use a pre-loaded key set as identification material. The pre-loaded key set is used minimally and only for authentication purposes. Keys for encryption are generated and exchanged between authenticated nodes thus enabling the security architecture to function longer. GridStat, a publish/subscribe middleware system offers mechanisms that enable low latency and high availability for operational data delivery. GridStat has been designed specifically to improve situational awareness in the electric power grid. GridStat Security Management System protects the data exchanged using GridStat with confidentiality, integrity and availability. These capabilities would be able to serve their purpose only if authentic GridStat entities are exchanging the information being protected. This thesis presents the authentication framework and protocols in the context of GridStat
