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Reliability assessment of patched SCADA EMS/DMS servers through similarity matching

From a national cybersecurity standpoint, patching of software and operating system vulnerabilities is a critical need. However, since patching may render a system unreliable, utility companies in the energy sector are reluctant to carry out patching on their substation SCADA control servers. In this paper, we present a similarity matching algorithm for assessing the reliability of software after patch application. Our methodology makes use of a backup control center in order to test the patched software. By running the test on input from field remote terminal units streamed from the same input source as that presented to the main control system, our algorithm is able to examine the degree of similarity of logged outputs, and highlight possible departures from expected behaviour. A metric called the fidelity score for the degree of similarity is presented along with initial results from a laboratory testbed. Initial results show that when patches are acceptable the algorithm consistently produces fidelity scores above 95%.