What Is The Purdue Model for ICS Security? Explained 101

You can’t imagine a world without power grids, water treatment plants, and manufacturing facilities. And it’s important they operate at optimal efficiency. Being the backbone of the society these systems are known as Industrial Control Systems (ICS).

Imagine a hacker breaking into a power grid's control system which can cause massive blackouts. It’s a real risk to our economy and public safety, so it’s important that preventive measures are taken.

As technology grows, these systems are facing cyberattacks. These attacks can disrupt vital services, creating chaos. That’s where the Purdue Model comes in to help.

Created at Purdue University, the Purdue Model is a structured plan to protect industrial control systems. It breaks down the layers of these systems and offers a clear path to defend them from cyber threats.

Let’s explore how ICS security works, guided by Purdue’s approach, and learn how we can better protect our essential infrastructure for a safer future.

What Do You Understand By Industrial Control Systems (ICS)?

What are industrial control systems?

It helps to keep everything together to achieve the desired output. ICS includes hardware, software, and networks that monitor and control machines and industrial processes. ICS are used in many industries like energy, manufacturing, water treatment, and transportation. For example, a power plant can adjust how much electricity it produces based on demand, or a factory can produce cars with precision, all thanks to ICS.

Why is ICS Important for Critical Infrastructure?

ICS are the hidden systems that keep important parts of our society running smoothly. They control essential services like the water from your tap, the lights in your home, and the fuel for your car. These systems ensure that these services are reliable, efficient, and safe.

Now, let’s look at the Purdue Model, which helps protect these vital systems from cyber threats.

Overview of the Purdue Model

In the world of ICS, where accuracy is key, the Purdue Model is like a guide for defending against cyberattacks. Created at Purdue University, this model provides a clear, step-by-step plan to secure important infrastructure, like a blueprint for building a strong defense.

The Beginning of the Purdue Model

The Purdue Model was created at Purdue University. The engineers and experts at the university saw the need for a clear framework to secure Industrial Control Systems (ICS). They wanted to design a simple, structured system to map out the different parts of ICS architecture. This model has since become a key tool for protecting these important systems.

Understanding the Purdue Model

It has multiple layers with each layer representing a different part of the ICS. It breaks down the complex system into clear, manageable pieces. While it has evolved over time, its main principles remain the same, making it a reliable tool for ICS security.

Why Is the Purdue Model Important?

The Purdue Model is like a guide, helping organizations secure their ICS. By understanding its different layers, companies can better protect their critical infrastructure. The model helps them find weaknesses, put security measures in place, and respond quickly to potential threats.

Layers of the Purdue Model

The Purdue Model has several layers, each with a specific role in securing ICS. These layers provide a clear way to categorize the different parts and functions of an ICS environment.

Layer	SCADA/ICS Description	Risk/Material Profile	Functional Layer	Standards
Overall section where network segments reside within a company’s overall enterprise network.	General description of assets within each layer.	Risk rating and material impact assessment for each layer.	Explanation of how industrial control and business systems are coordinated and deployed within each layer.	Identification of common standards that facilitate governance within each layer.

The Purdue Model: Five Layers Explained

The Purdue Model is a framework that helps understand the structure of ICS. It consists of five layers, each representing a specific part of the ICS architecture.

Have a look:

Level 0: Field Devices and Processes

• Description: It sets the base for the Purdue model. It has physical equipment like sensors, pumps, and valves. They interact with real-world processes.
• Function: Devices at this level gather data such as temperature, pressure, and flow rates. They also execute commands to control processes.
• Significance: Level 0 is where the actual control and monitoring happen. Data collected here is sent to higher levels for analysis and decision-making.

Level 1: Process Control

• Description: This layer builds on Level 0 and controls specific processes. It receives data from Level 0 and sends commands back to control the processes.
• Function: Control systems at this level process data and make decisions to keep operations stable and efficient.
• Significance: Level 1 ensures that individual processes run as they should, maintaining safety, quality, and efficiency.

Level 2: Area Supervisory Control

• Description: Level 2 oversees multiple process control units in a specific area of a facility. It focuses on coordinating activities from Level 1.
• Function: This layer collects data from Level 1, monitors processes, and implements higher-level control strategies to optimize performance.
• Significance: It improves coordination and efficiency within a specific area, ensuring everything works together smoothly.

Level 3: Site Supervisory Control

• Description: Level 3 manages the entire industrial site, coordinating operations across all areas and processes.
• Function: At this level, decisions are made about resource allocation, energy usage, and overall efficiency across the site.
• Significance: Level 3 optimizes the entire facility's performance, ensuring all processes and areas work together to meet business goals.

Level 4: Enterprise Business Planning

• Description: This is the highest layer in the Purdue Model, connecting ICS to business systems like Enterprise Resource Planning (ERP).
• Function: It focuses on long-term planning, strategic decisions, and aligning ICS operations with business objectives like scheduling and resource management.
• Significance: Level 4 links ICS operations with broader business goals, ensuring day-to-day decisions support the company’s overall strategy.

Here's a tabular representation of the Purdue Model, detailing each of its five layers:

Purdue Model Layer	Description	Function	Significance
Level 0: Field Devices and Processes	Represents physical processes and equipment.	Gather data from field devices and control processes.	Foundation for control and monitoring of processes.
Level 1: Process Control	Controls specific processes or units.	Processes data from Level 0 and maintains stability.	Ensures the stability and efficiency of individual processes.
Level 2: Area Supervisory Control	Oversees multiple units within an area.	Coordinates Level 1 controllers and optimizes units.	Enhances coordination and efficiency within areas.
Level 3: Site Supervisory Control	Manages an entire industrial site.	Allocates resources and manages site-wide efficiency.	Optimizes performance across the entire site.
Level 4: Enterprise Business Planning	Connects ICS to enterprise-level systems.	It focuses on long-term planning and aligns with business.	Links ICS operations with a broader business strategy.

What Are the Security Challenges in ICS?

Some of the security challenges in ICS are:

1. Hackers can attack ICS systems because they control important services like electricity and water. If they get hands on the weak spots they can steal data or take control of the system.
2. Many ICS were built long ago, and they weren’t designed with modern security in mind. These old systems are hard to protect and update.
3. ICS systems can’t be turned off often for updates, so they might run with old, vulnerable software for a long time, which can make them easier to hack.
4. If the system doesn’t have strong security checks for who can access it, unauthorized people might get in and cause damage.
5. People working with ICS can accidentally make mistakes, like misconfiguring the system or falling for phishing attacks, which can lead to security problems.
6. ICS equipment often comes from many different suppliers. If one of these suppliers has weak security, it can put the whole system at risk.
7. Employees or contractors with access to ICS systems can sometimes intentionally or accidentally cause harm, like leaking data or damaging equipment.
8. If the ICS network isn’t properly divided into sections, a security threat can spread quickly through the whole system.
9. Some ICS professionals don’t have enough training in cybersecurity, making it harder for them to spot and stop security risks.
10. As ICS systems become more connected to enterprise networks and the internet, it’s easier for cyber threats to move between systems.
11. ICS operators must follow strict cybersecurity rules. Failing to follow these rules can result in legal trouble and fines.
12. Some companies don’t have enough money or staff to invest in strong ICS security measures.
13. Traditional security tools don’t always work well for ICS, making it hard to detect and respond to cyber threats in time.
14. Cyber threats are always changing, so ICS systems must constantly update and improve their defenses.

How to Apply The Purdue Model to ICS Security?

The Purdue Model provides a clear structure for understanding and securing Industrial Control Systems (ICS). It helps organizations design security measures that fit the different layers of ICS. Here’s how the Purdue Model can be used to improve ICS security:

1. The first step is to identify important components and processes in each layer of the Purdue Model. This includes finding the key sensors, controllers, and networks that need protection.
2. Once critical assets are identified, conduct a risk assessment for each layer. This involves looking for potential threats, weaknesses, and the impact of security incidents. Risk assessments help prioritize where to focus security efforts.
3. Strong access control should be applied at every layer. Only authorized personnel should have access. Use authentication and authorization tools to prevent unauthorized access to important systems.
4. Network segmentation is essential to keep different layers separate. This prevents security breaches from spreading across layers and limits the damage caused by an attack. Isolating critical assets helps contain threats.
5. Each layer has its own security needs. For example, Level 0 (field devices) may need physical security, while Level 3 (site supervisory control) could benefit from intrusion detection systems.
6. Create a strategy for patching systems at each layer. Even though ICS systems require minimal downtime, it’s important to schedule and apply security patches quickly to fix vulnerabilities.
7. Set up monitoring and logging tools at each layer to detect any unusual activity. Analyzing logs can provide early warnings about potential security threats.
8. Develop incident response plans for each layer. Clearly define who is responsible for responding to security issues and make sure the team is trained to act quickly in case of an incident.
9. Train employees and operators at all levels about cybersecurity best practices. Human errors are a common cause of security problems, so raising awareness is a key defense.
10. Ensure that security measures comply with industry standards and regulations, such as NIST or ISA/IEC 62443. This is important for staying up to date with the latest security practices.
11. Periodically conduct vulnerability assessments, penetration testing, and security audits for each layer. This helps identify weaknesses and ensures security measures are effective.
12. ICS security is an ongoing effort. Regularly review and update security measures to adapt to new threats and changes in technology.

Tools and Technologies for Securing ICS with the Purdue Model

To secure ICS using the Purdue Model, organizations need a variety of tools and technologies. These tools help implement, monitor, and maintain security across the different layers of the model. Below are the essential tools and technologies for each area of security:

Network Security Tools

• Firewalls: Firewalls are used at network boundaries to filter traffic, enforce access controls, and prevent unauthorized access.
• Intrusion Detection Systems (IDS) & Intrusion Prevention Systems (IPS): IDS and IPS monitor network traffic for suspicious activity, issuing alerts or blocking potential threats.
• Virtual Private Networks (VPNs): VPNs provide secure communication channels for remote access and data exchange between layers of the Purdue Model.

Endpoint Security Tools

• Antivirus and Anti-Malware: These tools protect devices like workstations and servers from malicious software.
• Host-Based Intrusion Detection Systems (HIDS): HIDS monitors activities on individual endpoints, detecting and alerting administrators to potential security threats.

Security Information and Event Management (SIEM) Systems

• SIEM Solutions: SIEM systems collect and analyze security data from multiple sources, enabling real-time monitoring, incident detection, and forensic investigation.

Access Control and Authentication Solutions

• Multi-Factor Authentication (MFA): MFA adds an extra layer of security by requiring users to provide more than one form of identification before accessing the system.
• Role-Based Access Control (RBAC): RBAC ensures that users only have access to the systems and resources needed for their specific job roles.

Patch Management Tools

• These tools help apply security updates and patches to ICS components while minimizing system downtime, ensuring vulnerabilities are fixed quickly.

Network Segmentation Solutions

• VLANs and Software-Defined Networking (SDN): These technologies help create isolated segments within the network to prevent the spread of threats between layers of the Purdue Model.

Security Awareness Training Platforms

• These platforms provide ongoing training to employees and ICS operators, improving their understanding of cybersecurity best practices.

Encryption Technologies

• Encryption secures data both in transit and at rest, ensuring that information remains confidential and intact.

Incident Response and Forensic Tools

• These tools assist in investigating and analyzing security incidents, helping organizations understand and respond to security breaches effectively.

Compliance and Governance Solutions

• These tools help manage compliance with industry regulations, ensuring that security measures align with standards like NIST or ISA/IEC 62443.

Continuous Monitoring and Threat Intelligence Platforms

• Real-time monitoring solutions integrate threat intelligence, allowing for proactive detection and response to emerging security threats in ICS environments.

Customized ICS Security Solutions

• Many organizations develop or adapt security tools to fit their specific ICS environment, addressing the unique requirements of each layer in the Purdue Model.