Delving into Network Segmentation-Based Reference Architecture – the Purdue Model

From introducing you to Industry 4.0, securing the OT/IoT infrastructure, the relevance of cybersecurity in the OT/IoT industry, and how to overcome some of the challenges present in OT/IoT, we’ll move straight on to addressing the architecture followed in the industry today. It is very important to get a clear picture of the architecture implemented by organizations and the networks connecting devices.

In this chapter, we will cover the following topics:

• Zero-trust architecture
• Network segmentation in the IoT/OT environment
• Understanding the layers of the Purdue model
• How layers disrupt security when not managed well

Zero-trust architecture

It goes without saying that understanding zero-trust implementation is important to ensure the hardware root of trust is not breached and to ensure device integrity when we start architecting an organization’s digital layout (including IT, OT, and IoT).

Zero-Trust Architecture (ZTA) is a strategy to gain the best possible security where nothing is trusted. It’s a method for developing and putting into practice the following set of security principles:

• Verify explicitly: Always use the most up-to-date data points to authenticate and authorize.
• Use least privilege: Use data protection, risk-based adaptive rules, and just-in-time and just enough access (JIT/JEA) to restrict user access.
• Assume a breach: Minimize an attack’s blast arc and divide the access area. Use analytics to drive threat detection, gain awareness, and strengthen defenses while verifying end-to-end encryption.

The zero-trust strategy helps organizations...

Network segmentation in the IoT/OT environment

Network segmentation is an old but sure way of minimizing threats and protecting data or environments. This can be achieved both physically and logically.

With the arrival of Industry 4.0, industries are fast seeing the convergence of IT and OT. The advantages of bringing enterprise and industrial segments of networks together are simply too great to ignore. However, organizations need to take the utmost precaution when bridging the two historically isolated segments of the business as they bring together new vulnerabilities that are introduced by direct or indirect (through an intermediate device) internet connectivity.

OT systems were designed for a specific purpose—to last a long time and tolerate extreme weather conditions, in wet or caustic environments, and communicate over a proprietary protocol. These control systems were isolated from corporate networks. Hence, very often, we find OT networks are flat networks in...

Understanding the layers of the Purdue model

You might have already obtained an idea of the Purdue model. Let’s delve a little deeper into the layers it has and how it contributes to Industry 4.0.

Figure 2.2 gives us a clear representation of the Purdue model:

Figure 2.2 – Layers of the Purdue model

Let us look at these layers in detail:

• Layer 0 – Bus Network: This involves physical components such as sensors, actuators, and motor pump valves at the end of the cycle to produce the final product. Think of smart manufacturing—smart factories assembling products—as an example. These are called intelligent devices.
• Layer 1 – Controllers: The logic used to send commands to the devices at Layer 0 is from systems at Layer 1. Examples include Programmable Logic Controllers (PLCs), Remote Terminal Units (RTUs), Supervisory Control and Data Acquisition (SCADA), and Distributed Control Systems (DCSs). Control systems...

How layers disrupt security when not managed well

Grouping similar systems together to ensure we balance both performance and security is the key goal of the Purdue model. We have learned so far that segmentation and isolation are critical in ensuring security.

We are also clear on the benefits the convergence of IT and OT has brought to the industry. However, it has brought along with it attacks once only aimed at enterprises or IT now aimed toward OT assets as well. Every device is deemed mission critical as an attack on a front-line device or workstation or engineering system can lead to an attack on OT systems. This not only affects the business, revenue, and reputation but also human life, depending on the type of OT infrastructure.

Here is a scenario about the reconnaissance activity happening for TCP port 502. These activities not only have increased in the recent past but also, if successful, can issue harmful commands to OT devices.

TCP port 502 is commonly used in...

Summary

In conclusion, we can say that ZTA is a long-term plan for many organizations following Industry 4.0. However, it should be started early with a vision to achieve the principles of ZTA in the long term. Doing so also ensures that network segmentation is achievable through the Purdue model or variations of it. Security at every network segment is critical as we have seen that a breach at any point can lead to lateral movement and compromise of the physical IT/OT/IoT assets, as explained in the kill chain. The security can further be enhanced by using data diodes and their one-way transfer functionality.

In the next chapter, we will learn more about attacks and threat vectors in the OT/IoT environment.