Lately, I’ve been thinking a lot about hardware supply chain security and how the risks and controls differ from software supply chain security. As a CSO, one of your responsibilities is to ensure your supply chain is secure, yet the distributed nature of our global supply chain makes this a challenging endeavor. In this post I’ll explore how a CSO should think about the risks of hardware supply chain security, how they should think about governing this problem and some techniques for implementing security assurance within your hardware supply chain.
What Is Hardware Supply Chain?
Hardware supply chain relates to the manufacturing, assembly, distribution and logistics of physical systems. This includes the physical components and the underlying software that comes together to make a functioning system. A real world example could be something as complex as an entire server or something as simple as a USB drive. Your company can be at the start of the supply chain by sourcing and producing raw materials like copper and silicon, at the middle of the supply chain producing individual components like microchips, or at the end of the supply chain assembling and integrating components into an end product for customers.
What Are The Risks?
There are a lot of risks when it comes to the security of hardware supply chains. Hardware typically has longer lead times and longer shelf life than software. This means compromises can be harder to detect (due to all the stops along the way) and can persist for a long time (e.g. decades in cases like industrial control systems). It can be extremely difficult or impossible to mitigate a compromise in hardware without replacing the entire system (or requiring downtime), which is costly to a business or deadly to a mission critical system.
The risk of physical or logical compromise can happen in two ways – interdiction and seeding. Both involve physically tampering with a hardware device, but occur at different points in the supply chain. Seeding occurs during the physical manufacture of components and involves someone inserting something malicious (like a backdoor) into a design or component. Insertion early in the process means the compromise can persist for a long period of time if it is not detected before final assembly.
Interdiction happens later in the supply chain when the finished product is being shipped from the manufacturer to the end customer. During interdiction the product is intercepted en route, opened, altered and then sent to the end customer in an altered or compromised state. The hope is the recipient won’t detect the slight shipping delay or the compromised product, which will allow anything from GPS location data to full remote access.
Governance
CSOs should take a comprehensive approach to manage the risks associated with hardware supply chain security that includes policies, processes, contractual language and technology.
Policies
CSOs should establish and maintain policies specifying the security requirements at every step of the hardware supply chain. This starts at the requirements gathering phase and includes design, sourcing, manufacturing, assembly and shipping. These policies should align to the objectives and risks of the overall business with careful consideration for how to control risk at each step. An example policy could be your business requires independent validation and verification of your hardware design specification to make sure it doesn’t include malicious components or logic. Or, another example policy can require all personnel who physically manufacture components in your supply chain receive periodic background checks.
Processes
Designing and implementing secure processes can help manage the risks in your supply chain and CSOs should be involved in the design and review these processes. Processes can help detect compromises in your supply chain and can create or reduce friction where needed (depending on risk). For example, if your company is involved in national security programs you may establish processes that perform verification and validation of components prior to assembly. You also may want to establish robust processes and security controls related to intellectual property (IP) and research and development (R&D). Controlling access to and dissemination of IP and R&D can make it more difficult to seed or interdict hardware components later on.
Contractual Language
An avenue CSOs should regularly review with their legal department are the contractual clauses used by your company for the companies and suppliers in your supply chain. Contractual language can extend your security requirements to these third parties and even allow your security team to audit and review their manufacturing processes to make sure they are secure.
Technology
The last piece of governance CSOs should invest in is technology. These are the specific technology controls to ensure physical and logical security of the manufacturing and assembly facilities that your company operates. Technology can include badging systems, cameras, RFID tracking, GPS tracking, anti-tamper controls and even technology to help assess the security assurance of components and products. The technologies a CSO selects should complement and augment their entire security program in addition to normal security controls like physical security, network security, insider threat, RBAC, etc.
Detecting Compromises
One aspect of hardware supply chain that is arguably more challenging than software supply chain is detection of compromise. With the proliferation of open source software and technologies like sandboxing, it is possible to review and understand how a software program behaves. Yet, it is much more difficult to do this at the hardware layer. There are some techniques that I have discovered while thinking about and researching this problem and they all relate back to how to detect if a hardware component has been compromised or is not performing as expected.
Basic Techniques
Some of the more simple techniques for detecting if hardware has been modified is via imaging. After the design and prototype is complete you can image the finished product and then compare all products produced against this image. This can tell you if the product has had any unauthorized components added or removed, but it won’t tell you if the internal logic has been compromised.
Another technique for detecting compromised components is similar to unit testing in software and is known as functional verification. In functional verification, individual components have their logic and sub-logic tested against known inputs and outputs to verify they are functioning properly. This may be impractical to do with every component if they are manufactured at scale so statistical sampling may be needed to probabilistically ensure all of the components in a batch are good. The assumption here is if all of your components pass functional verification or statistic sampling then the overall system has the appropriate level of integrity.
To detect interdiction or logistics compromises companies can implement logistics tracking such as unique serial numbers (down to the component level), tamper evident seals, anti-tamper technology that renders the system inoperable if tampered with or makes it difficult to tamper with something without destroying it and even shipping thresholds to detect shipping delay abnormalities.
Advanced Techniques
More advanced detection techniques for detecting compromise can include destructive testing. Similar to statistical sampling, destructive testing involves physically breaking apart a component to make sure nothing malicious has been inserted. Destructive testing makes sure the component was physically manufactured and assembled properly.
In addition to destructive testing, companies can create hardware signatures that include expected patterns of behavior for how a system should physically behave. This is a more advanced method of functional testing where multiple components or even finished products are analyzed together for known patterns of behavior to make sure they are functioning as designed and not compromised. Some hardware components that can assist with this validation are technologies like Trusted Platform Modules (TPM).
Continuing with functional operation, a more advanced method of security assurance for hardware components is function masking and isolation. Function masking attempts to mask a function so it is more difficult to reverse engineer the component. Isolation limits how components can behave with other components and usually has to be done at the design level, which effectively begins to sandbox components at the hardware level. Isolation could rely on TPM to limit functionality of components until the integrity of the system can be verified, or it could just limit functionality of one component with another.
Lastly, one of the most advanced techniques for detecting compromise is called 2nd order analysis and validation. 2nd order analysis looks at the byproduct of the component when it is operating by looking at things like power consumption, thermal signatures, electromagnetic emissions, acoustic properties and photonic (light) emissions. These 2nd order emissions can be analyzed to see if they are within expected limits and if not it could indicate the component is compromised.
Wrapping Up
Hardware supply chain security is a complex space given the distributed nature of hardware supply chains and the variety of attack vectors spanning physical and logical realms. A comprehensive security program needs to weigh the risks of supply chain compromise against the risks and objectives of the business. For companies that operate in highly secure environments, investing in advanced techniques ranging from individual component testing to logistics security is absolutely critical and can help ensure your security program is effectively managing the risks to your supply chain.
References:
Guarding Against Supply Chain Attacks Part 2 (Microsoft)
Long-Term Strategy for DoD Trusted Foundry Needs (ITEA)
370 Security Blog 