Physical layer security

Implementing Physical Layer Security in Military Embedded Systems


In the high-stakes arena of military technology, the safeguarding of sensitive defense systems from adversaries is a critical task. This detailed article delves into the nuanced practices for ensuring robust physical security in the design of printed circuit boards (PCBs) for military embedded computing systems. It focuses on a comprehensive strategy that integrates advanced PCB layout techniques with strategic enclosure design, aiming to fortify critical systems against potential threats.

Leveraging PCB Design for Security

Military systems are repositories of sensitive technology and critical data, making them prime targets for adversaries. The PCBs within these systems are particularly vulnerable to physical tampering and reverse engineering efforts. To counteract these threats, several innovative techniques in PCB layout are employed:

Optimize Design to Minimize Attack Surface

To minimize the attack surface, designers should strategically reduce the number of exposed interfaces that offer physical access to the PCB. This involves a meticulous design process where each port, connector, test point, and debugging feature is evaluated for its necessity. Non-essential interfaces should be eliminated or combined to reduce potential access points. For instance, combining data and power ports can significantly reduce the number of external connectors.

Harden Against Physical Access

To combat physical probing and data theft, it's essential to physically protect any exposed interfaces. Techniques such as applying underfill around components can prevent their removal. Designers should route critical nets on inner layers of the PCB, making them inaccessible from the surface. Opting for chip-on-board designs, which leave no exposed die contacts, significantly reduces the attack surface. Additionally, potting the entire PCB assembly in epoxy resin effectively blocks physical access. This resin should be chosen for its durability and resistance to solvents and other tampering methods.

Obfuscate Critical Components

Disguising the location of sensitive components involves a strategic layout where these components are interspersed with non-critical ones, making it difficult to identify them. Avoiding silkscreen markings that identify major ICs is a start. Designers should use identical footprints and packages for different types of components, making it challenging to distinguish between them. Distributing functionality across multiple ICs rather than centralizing it in one main processor also adds a layer of complexity for anyone attempting to reverse engineer the PCB.

Securing Interfaces and External Connections

The security of external interfaces is critical in preventing unauthorized access. Implementing encrypted protocols for all wired and wireless interfaces is essential to maintain the confidentiality of communications. Mutual authentication is also vital to ensure the integrity of data transfers.

Encrypt Network Communications

To safeguard data in transit, all external wired and wireless interfaces must employ robust encryption. Designers should implement common protocols such as TLS/SSL, IPsec, and WPA2, which offer strong encryption algorithms to secure network links. Additionally, developing proprietary encryption protocols tailored to specific application requirements can provide an extra layer of security. These protocols should be regularly updated and tested against emerging threats.

Authenticate Endpoints

Beyond encryption, authentication plays a crucial role in verifying the identity of endpoints. Techniques such as using pre-shared keys, certificates, and authentication protocols like RADIUS enable mutual authentication between devices. This is vital to ensure that rogue devices cannot join the network or impersonate trusted endpoints. Implementing a robust key management system that regularly updates and manages these keys and certificates is essential.

Limit Debug and Test Interfaces

While debugging and test ports are invaluable during development, they pose significant security risks. These interfaces should be either eliminated or disabled in final board assemblies. If necessary for field diagnostics, they must be secured through authentication and physical access control. Implementing a hardware switch or jumper that physically disconnects these interfaces when not in use can be an effective measure.

Enclosure Design for PCB Protection

The design of the enclosure is as critical as the PCB layout, providing an additional layer of defense. Tamper-evident seals, robust construction, and access control mechanisms are key to mitigating the risk of physical attacks on internal electronics.

Tamper Evident Enclosure

Implementing visible indicators that reveal unauthorized entry attempts serves as an active deterrent. Tamper-evident labels, screws, and meshes alert operators to any compromise of the system. Once a sealed enclosure is breached, the tamper evidence is permanently altered, indicating the security breach. Designers should ensure that these indicators are designed in such a way that they cannot be replicated or reset without authorized access.

Rugged, Robust Construction

Military enclosures must be designed to endure harsh environments and safeguard internal components. Thick metallic construction offers resistance against drilling, cutting, and penetration attacks. Designing compartments within the enclosure isolates and protects individual PCB assemblies. Additionally, RFI/EMI shielding is crucial to prevent side-channel emissions analysis. The materials used should be selected for their durability and resistance to environmental factors such as temperature extremes, moisture, and electromagnetic interference.

Controlled Access

Implementing strict physical access control is essential to limit who can access the enclosures and the PCBs within. Electronic locks keyed to specific operators, logged access, and video surveillance are effective measures against unauthorized access. Establishing proper access control policies and conducting regular audits are fundamental to maintaining security. Access logs should be regularly reviewed, and any anomalies investigated promptly.


The integration of advanced PCB layout techniques with strategic enclosure design forms a robust multilayered defense mechanism for sensitive defense electronics. This comprehensive approach, which encompasses optimizing, hardening, and obfuscating PCB designs along with implementing robust, tamper-evident enclosures, is crucial in protecting critical embedded computing systems. Such measures are indispensable in preventing adversaries from gaining physical access to steal data and compromise technology, thereby ensuring the integrity and security of military embedded systems.


Whether you're designing an ultra-rugged aerospace system or feature-rich embedded computing products, make sure your design firm understands how to coordinate with electronics manufacutring services and contract manufacturers to help you produce military embedded systems with maximum quality. NWES helps aerospace OEMs, defense primes, and private companies in multiple industries design modern PCBs and create cutting-edge embedded technology, including power systems for high reliability applications and precision control systems. We've also partnered directly with EDA companies and advanced ITAR-compliant PCB manufacturers, and we'll make sure your next high speed digital system is fully manufacturable at scale. Contact NWES for a consultation.


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