Digital transformation has dramatically changed the world of industrial control systems (ICS) and operational technology (OT) all the way up to today, when they have joined the online world with direct factory-floor connections to the Internet.

Production floors are exposed to an entire spectrum of nonstop cyber threats — even hostile code from the 1990s — that we in the manufacturing community see continually.

Attacks are constant, they can come at any time from anywhere in the world, and our governments and regulators cannot protect us. When planning our tactical approach to risk mitigation at our company, we sometimes liken our situation to that of an independent city-state in medieval times. Enemies are everywhere, no one can be trusted, and we are on our own.

This metaphorical model can be extended to aptly describe the state-of-the-art cybersecurity we deployed that provides us with defense in depth across our entire OT infrastructure, one that previously was unprotected in almost every layer.

To better understand how to combat current cyber threats, let's explore tried-and-true lessons from these age-old medieval tactics.

Advanced Walls, Layered Fortifications, and Lockdowns
Castles of old layered their defenses, too, using moats, multiple perimeters, and even keeps for last-ditch protection. Gates tightly controlled who came in and who got out.

Similarly, each production system in our OT world must be separated from the rest of the world by multilayer virtual walls and air gaps, with entrances and exits via approved gates only. Elements in the IT security stack that help achieve this include next-gen firewalls and network access control (NAC); however, these generally do not natively protect ICS components.

It is necessary to integrate them with an ICS cybersecurity solution that discovers and monitors Industrial Internet of Things (IIoT) and ICS/OT devices and speaks their languages, such as Modbus and DNP3, and recognizes specialized ICS devices, such as programmable logic controllers and human-machine interfaces.

The gate for today's networks is the NAC. All communications, whether incoming or outgoing, must undergo checks to ensure the communication is legitimate and not hostile. Source and destination addresses are checked and behavior patterns analyzed. Anomalies and suspicious data exfiltration can be blocked.

Installing walls and gates is critical to protecting the vulnerable production system. But we know that no walls are 100% foolproof and hostile code may still break in. The ability to lock down and isolate a city and place it under quarantine at a moment's notice, so nothing goes in or out, will be carried out by the same walls that are supposed to protect, thereby mitigating the harm to the entire country/society.

Spy Network, Hunting, and Assassins
Sometimes information brought by spies has great value and can determine the outcome of a campaign. In the past, the internal and external espionage networks created an extensive intelligence infrastructure, and thus the kingdom was defended.

The parallel today is that listening to OT production networks is critical. The ability to understand their languages — different from those used in IT systems — and simultaneously hunt for any unusual activity requires the use of a purpose-built platform designed for the unique protocols, devices, and behaviors of OT networks.

Unusual activity, or anomalies, must generate alerts in a control center or even real-time mitigation through integration with a system information and event management system, NAC, or firewall.

Citizens' Awareness
Clever people have long used deception and others' gullibility in warfare. During the Crusades, for example, medieval knights handed over a well-fortified Syrian castle when they were presented with a forged letter purportedly from the Hospitallers' Grand Master ordering them to surrender. Similarly, today's cyber enemies use human nature as vulnerabilities to bypass sophisticated cyber mechanisms. Constant training is essential to ensure awareness and alertness of the employees. Addressing this weakness requires a unique awareness program for everyone, and the availability of a hotline around the clock for when suspicion arises on the production floor.

The Royal Court
In the past, threats to the city-state were always met with a keen sense of urgency. Information was passed to the ruler and his or her insiders in the king's court. Decisions were taken and commends for action meted out.

Of course, that all pales in comparison to the volume of information, complexity, and real-time scale of today's cybersecurity decision-making support systems.

What hasn't changed is the need to deliver all the information and alerts coming from the countermeasures and monitoring systems above into a nerve center where the information from the production floor will be processed in seconds, analyzed, and deemed normal or abnormal activity.

The decision-makers in these situations must have clear protocols on how to address various scenarios, and must be armed with the tools to take action.

Think Layered Fortifications
In all layers of this defense-in-depth discussion, presented using the medieval city-state as a metaphor, the unique needs of the IIoT/ICS environment must be addressed. A comprehensive approach incorporating layered fortifications, ICS-aware continuous monitoring, and employee awareness is essential for strategic risk mitigation, and to ensure safe and continuous operation of production facilities. 

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