An overview of an Industrial control system

From the traffic lights on your drive to work, or the collision avoidance system of the train or metro, to the delivery of electricity that powers the light you use to read this book, to the processing and packaging that went into creating the jug of milk in your fridge, to the coffee grinds for that cup of joe that fuels your day; what all these things have in common are the Industrial control systems driving the measurements, decisions, corrections, and actions that result in the end products and services that we take for granted each day. 

The following diagram shows the architecture of a properly designed, modern ICS. The intent of this book is to educate you on the methodologies and considerations that went into the design of an architecture, such as the one shown here:

Technically speaking, the Industrial control system lives in the area marked Industrial Zone of the preceding diagram. However, as we will discuss later in this book, because most ICSes interact with the Enterprise Zone, in order to effectively secure the system as a whole, consideration must also be given to the systems in the Enterprise Zone.

An ICS is a variety of control systems and associated instrumentation used in industrial production technology to achieve a common goal, such as creating a product or delivering a service. From a high-level perspective, ICSes can be categorized by their function. They can have one or several of the functions discussed in the following sections.

The view function

The view function encompasses the ability to watch the current state of the automation system in real time. This data can be used by operators, supervisors, maintenance engineers, or other personnel to make business decisions or perform corrective actions. For example, when the operator sees that the temperature of cooker 1 is getting low, they might decide to increase the steam supply of the cooker to compensate this. The view process is passive in nature, merely providing the information or view for a human to react on:

From a security perspective, if an attacker can manipulate the operator's view of the status of the control system or, in other words, can change the values the operator bases their decisions on, the attacker effectively controls the reaction and, therefore, the complete process. For example, by manipulating the displayed value for the temperature of cooker 1, an attacker can make the operator think the temperature is too low or too high and have him or her act upon the manipulated data.

The monitor function

The monitor function is often part of a control loop, such as the automation behind keeping a steady level in a tank. The monitor function will keep an eye on a critical value, such as pressure, temperature, level, and so on, and compare the current value against predefined threshold values, and alarm or interact depending on the setup of the monitoring function. The key difference between the view function and the monitor function is in the determination of deviation. With monitoring functions, this determination is an automated process, whereas with a view function, this determination is made by a human looking at the values. The reaction of the monitor function can range from a pop-up alarm screen to a fully automated system shutdown procedure.

From a security perspective, if an attacker can control the value that the monitor function is looking at, the reaction of the function can be triggered or prevented; for example, a case where a monitoring system is looking at the temperature of cooker 1, preventing the temperature from exceeding 300 degrees Fahrenheit. If an attacker feeds a value of less than 300°F into the system, that system would be tricked into believing all is well, while in actuality, the system could be in meltdown.

The control function

The following diagram illustrates the control function:

The control function is where things are controlled, moved, activated, and initiated. The control system is what makes actuators engage, valves open, and motors run. The control actions can either be initiated by an operator pushing a button or changing a set point on an HMI screen, or it can be an automated response as part of the process control.

From a security perspective, if an attacker can manipulate the values (the input) the control system reacts to or if the attacker can change or manipulate the control function itself (the control program), the system can be tricked into doing things it wasn't designed to do or intended for.

Now I can hear you all say that manipulating values is all nice and dandy, but surely that cannot be done with modern switched networks and encrypted network protocols. That would be true if those technologies were implemented and used. The sad state of affairs is that on most, if not all, ICS networks, the confidentiality and integrity parts of the CIA security triage are of less importance than availability. Even worse, for most Industrial control systems, availability ends up being the only design consideration when architecting the system. Combine that with the fact that the ICS communication protocols that run on these networks were never designed with security in mind, and one can start to see the feasibility of the scenarios mentioned.

More about all this will be discussed in later chapters, when we dive deeper into the vulnerabilities mentioned and look at how they can be exploited.