Commensurate Rigor: Building Confidence in Secure Engineering

When it comes to designing secure systems, confidence in your processes and outcomes isn't a luxury—it's a necessity. The principle of Commensurate Rigor, as outlined in NIST SP 800-160, Volume 1, emphasizes aligning the depth and thoroughness of engineering activities with the potential impact of adverse effects. For tech-savvy professionals tasked with securing critical systems, understanding and implementing this principle is vital to mitigating risks and ensuring trustworthiness.

In this blog, we’ll explore Commensurate Rigor, its applications, and how it supports risk-based decision-making, empowering engineers to meet today’s complex security challenges head-on.

What Is Commensurate Rigor?

At its core, Commensurate Rigor is about aligning the level of effort, depth, and detail of engineering activities with the significance of the adverse effects those activities aim to prevent or address. This principle ensures that rigorous methods are applied where stakes are high, delivering confidence in system performance while balancing cost, schedule, and other constraints.

Key Tenets of Commensurate Rigor:

1. Scope and Depth: The thoroughness of activities should correspond to the potential impact of system failures or threats.
2. Confidence Through Evidence: Rigor generates evidence-based assurance, reducing uncertainty and supporting risk-based decisions.
3. Trade-Off Consideration: Balancing rigor against cost, capability, and time is critical, especially in high-stakes environments like critical infrastructure.
   
   

Why Rigor Matters in Systems Engineering

Imagine an engineering process with minimal rigor: the lack of thoroughness could lead to unaddressed vulnerabilities, putting assets, data, or even lives at risk. Conversely, excessive rigor in a low-risk scenario could waste time and resources. Commensurate Rigor ensures a measured approach.

Benefits of Implementing Rigor:

• Increased Confidence: A rigorous process fosters trust in system reliability.
• Risk Mitigation: Reduces uncertainty and provides actionable insights to prevent or minimize losses.
• Adaptability: Graduated application of rigor allows for flexibility based on the criticality of assets.
  
  

The Role of Rigor in Critical Systems

Critical systems—such as those in healthcare, energy, and defense—require heightened rigor due to their potential impact. For example:

• Healthcare Systems: A flaw in electronic health records could jeopardize patient safety.
• Energy Infrastructure: Cyberattacks on power grids could disrupt millions of lives.
• Defense Applications: National security depends on flawless system operation.

In these scenarios, rigorous engineering processes ensure systems are robust against failures or attacks, minimizing the likelihood of catastrophic losses.

Measuring and Applying Rigor

One of the strengths of the Commensurate Rigor principle is its measurability. By generating evidence through engineering processes, teams can assess the adequacy of rigor applied.

Steps to Apply Commensurate Rigor:

1. Assess Risk: Identify the criticality of assets and the potential impact of system failures.
2. Determine Rigor Levels: Match the engineering activities' scope and depth with the severity of possible adverse effects.
3. Generate Evidence: Use tools, methods, and testing to document confidence in outcomes.
4. Evaluate Trade-Offs: Balance the need for rigor against constraints like cost and schedule.

Graduated vs. Substantial Rigor

Rigor isn't a one-size-fits-all solution. Depending on the scenario, it can range from minimal to substantial.

• Graduated Rigor: Ideal for systems with lower risk profiles or where the potential for loss is less severe.
• Substantial Rigor: Necessary for critical systems where failure isn’t an option.

For example, securing a public-facing website might require graduated rigor, whereas a nuclear power plant's control systems demand substantial rigor to address the highest stakes.

Challenges in Implementing Commensurate Rigor

While the benefits are clear, implementing Commensurate Rigor isn’t without challenges.

Common Obstacles:

• Resource Allocation: Increased rigor often requires higher costs and longer timelines.
• Complexity: Determining the appropriate level of rigor for a given scenario can be challenging.
• Stakeholder Buy-In: Convincing stakeholders to invest in rigorous processes can be difficult when immediate risks aren’t evident.
  
  

Overcoming Challenges:

• Leverage Tools and Frameworks: Use established methodologies to streamline rigorous processes.
• Engage Stakeholders: Communicate the long-term benefits of rigor to secure support.
• Iterative Refinement: Continuously evaluate and adjust the level of rigor as project needs evolve.

Commensurate Rigor in Action

To see this principle in action, consider the development of autonomous vehicles. These systems require substantial rigor in their engineering processes to ensure safety and reliability under all conditions.

Example:

1. Risk Assessment: Identifying potential hazards, such as system failure leading to accidents.
2. High Rigor Application: Testing under diverse conditions, from extreme weather to dense traffic scenarios.
3. Evidence Generation: Collecting data from simulations and real-world tests to validate system performance.
   
   

By applying Commensurate Rigor, manufacturers build trust in their vehicles while minimizing risks to passengers and the public.

Commensurate Rigor as a Tool for Innovation

While rigor might sound like a constraint, it’s a powerful enabler of innovation. By ensuring confidence in system reliability, rigorous processes free engineers to focus on pushing boundaries and exploring new possibilities.

For example, the aerospace industry relies on rigorous testing to certify cutting-edge technologies, enabling breakthroughs that redefine what’s possible.

Key Takeaways

• Commensurate Rigor ensures engineering activities are proportional to the potential impact of system failures.
• It supports confidence-building, risk mitigation, and informed decision-making.
• Implementing rigor requires balancing thoroughness with practical constraints like cost and schedule.
• By aligning rigor with the stakes, teams can secure critical systems while fostering innovation.