Cyber Physical Security for Power Grid Protection
Security of cyber-physical systems (CPSs), such as power systems, is becoming increasingly important due to the fact that these systems are accessible from the Internet, and therefore, are subject to a variety of threats that could have severe impact on their stability and performance. Network intrusion detection systems (NIDSs) are widely used to safeguard CPSs within a network perimeter from external threats by continuously monitoring and analyzing network traffic. This is a step up from the protection provided by traditional firewalls, since NIDS can sometimes go further than simple packet filters by performing more advanced types of deep packet inspection.
This thesis focuses on a novel use of NIDS that we call hybrid control NIDS (HC-NIDS). The HC-NIDS is tailored to detect attacks on networks that support hybrid controllers with power grid protection schemes. The security policies, derived form the hybrid automaton that designates the expected operation of the system, combine knowledge of desired communication rules as well as physical laws and limits that the system should obey in order to characterize network traffic as “safe” or “unsafe”.
We apply HC-NIDS to two well-known protection mechanisms of power systems: the fault location, isolation and service restoration (FLISR) process in automated distribution systems (ADSs), and the power transformer’s overcurrent protection scheme in transmission lines. For each case, we implement a set of specification-based intrusion detection rules based on the hybrid automaton that models the desired behavior of the system. Then, we create several attack scenarios to demonstrate our approach. As part of this evaluation, we developed an experimental framework that consists of a simulation of a physical system, and an emulation of the master controller, which implements the protection mechanism in the power grid, and allows communication via the Modbus TCP industrial control protocol.
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