The Power of Trustworthy System Control: Designing Resilient Security Systems

Jan 9 / Chris Pujara

Trustworthy System Control: Building Resilience into Security Design

In the realm of system security, one principle stands as a beacon for ensuring that systems can withstand both deliberate and accidental threats: Trustworthy System Control. This critical security design principle, as outlined in NIST SP 800-160, Volume 1, plays a pivotal role in protecting high-value assets, particularly those within the U.S. critical infrastructure. Systems that rely on trustworthy control mechanisms are less susceptible to malicious adversaries, reducing the risks of catastrophic failures that could have national or economic consequences.

What is Trustworthy System Control?

At its core, Trustworthy System Control is a design principle that ensures system control functions adhere to the foundational properties of a generalized reference monitor. A reference monitor is an abstract security mechanism that mediates access to system resources, ensuring that only authorized entities can access sensitive information. The principle emphasizes that the control mechanisms should not only be secure but also resilient, non-bypassable, and continuously operational. This concept is crucial in preventing unauthorized access, ensuring systems are not easily subverted or compromised.

The main objective of trustworthy system control is to design systems in such a way that they are resistant to external and internal threats, capable of enforcing control and maintaining security without relying on detailed knowledge about potential adversaries. It allows systems to function with integrity even when they face hostile attacks.

The Four Essential Criteria for Trustworthy System Control

To implement trustworthy system control effectively, systems must satisfy four essential design criteria:

  1. Non-bypassability: A protection mechanism should be impossible to circumvent. In other words, it should be designed in a way that an attacker cannot bypass or bypass a particular safeguard. This ensures that security functions are consistently applied without shortcuts.

  2. Evaluability: Protection mechanisms must be simple enough to be evaluated and assessed for effectiveness. The smaller and simpler the protection mechanism, the easier it is to evaluate its strength and ensure it is functioning as intended. This reduces the risk of overlooked vulnerabilities or inefficiencies in the protection system.

  3. Continuous Invocation: The protection mechanisms should always be invoked and active. This guarantees that there is no point during the operation of the system when protection is not in place. Continuous protection ensures that vulnerabilities are closed off at all times, preventing adversaries from exploiting gaps in security.

  4. Tamper-proofing: A protection mechanism must be tamper-proof, meaning that neither the mechanism nor the data it relies on can be altered or modified without authorization. This ensures that the integrity of the system is upheld and cannot be easily undermined by malicious insiders or external attackers.

By adhering to these principles, trustworthy system control ensures that the system remains secure, resilient, and capable of handling adversity.

Trustworthy System Control: Enforcing Constraints and Providing Self-Protection

The Trustworthy System Control principle is more than just a set of guidelines for access control. It extends to the broader system’s ability to enforce constraints, ensuring that systems operate only within the bounds of authorized and intended behaviors. This helps prevent misuse, accidents, or malicious activity.

Some additional elements of trustworthy system control include:

  • Enforcing Constraints: Every system is designed to function within a defined set of constraints, and any behavior outside these boundaries is considered undesirable. This means only approved actions and outcomes should be permitted within the system. The implementation of these constraints ensures that no unauthorized activity can take place.

  • Self-Protection: Trustworthy system control goes beyond merely defending against external threats. It also includes mechanisms for self-protection. These systems are designed to withstand and recover from attacks, providing built-in defense capabilities. Whether it's a denial-of-service attack or a targeted attempt to breach security, these systems can resist and mitigate these threats, ensuring minimal disruption to the system's functionality.

  • Absence of Emergent, Erroneous, and Unsafe Actions: A trustworthy system should be free from emergent issues that could compromise its security. This includes unintended or self-induced errors that could expose vulnerabilities. Systems designed with this principle in mind are not only secure from external threats but also resilient against internal faults or misconfigurations.

Real-World Application of Trustworthy System Control

The principles of trustworthy system control are particularly vital for high-stakes environments like critical infrastructure, defense systems, and healthcare networks, where failure could have dire consequences. For instance, a power grid or a transportation system that is designed with trustworthy system control principles can better withstand cyberattacks or hardware failures that could otherwise cripple service.

One application of this principle is in critical infrastructure protection, where systems are often exposed to both physical and cyber threats. By ensuring that the system design includes the above-mentioned criteria, such systems can maintain operational continuity even in the face of adversarial attacks or natural disasters.

Full-Spectrum Security

One of the key aspects of trustworthy system control is its ability to contribute to a full-spectrum security approach. Rather than merely defending against specific threats, the system’s design anticipates a range of possible attack vectors, ensuring that it is resilient to all forms of adversity.

This full-spectrum approach includes:

  • Penetration Resistance: The system is designed to resist penetration attempts, whether they are external threats like hackers or internal breaches by malicious insiders.

  • Damage Limitation: Even when an attack occurs, the system can limit the damage, preventing a complete breach or shutdown of services.

  • System Resilience: Beyond resisting attacks, the system must also be resilient, meaning that it can recover quickly from any damage or disruption caused by threats.

Conclusion: Why Trustworthy System Control is Non-Negotiable

In today’s interconnected world, where cyber threats are ever-present and sophisticated, implementing trustworthy system control is no longer optional. It is essential for the protection of critical infrastructure, the maintenance of national security, and the protection of organizational assets.

By following the guidelines set forth in NIST SP 800-160, Volume 1, organizations can design systems that are not only secure but resilient, capable of withstanding both expected and unforeseen threats. The principles of non-bypassability, evaluability, continuous invocation, and tamper-proofing are foundational to achieving trustworthy system control, ensuring that systems are both strong and adaptable in an increasingly volatile security landscape.