Toward Safe Integration of Legacy SCADA Systems in the Smart Grid

A SCADA system is a distributed network of cyber-physical devices used for instrumentation and control of critical infrastructures such as a electric power grid. With the emergence of the smart grid, SCADA systems are increasingly required to be connected to more open systems and security becomes crucial. However, many of these SCADA systems have been deployed for decades and were initially not designed with security in mind. In particular, the field devices in these systems are vulnerable to false command injection from an intruding or compromised device. But implementing cryptographic defence on these old-generation devices is challenging due to computation constraints. Consequently, solutions to protect legacy SCADA systems have to be an add-on. This paper discusses two add-on defence strategies for legacy SCADA systems -- the data diode and detect-and-respond approaches -- and compares their security and application scenarios. A generic architectural framework is also proposed to implement the detect-and-respond strategy, with an instantiation to demonstrate its practicality.