Title: Producing Trustworthy Hardware Using Untrusted Components, Personnel and Resources
Description: Computer security is a full-system property, and attackers will always go after the weakest link in a system. In modern computer systems, the hardware supply chain is an obvious and vulnerable point of attack. The ever-increasing complexity of hardware systems, along with the globalization of the hardware supply chain, has made it unreasonable to trust hardware. Hardware-based attacks, known as backdoors, are easy to implement and can undermine the security of systems built on top of compromised hardware. Operating systems and other software can only be secure if they can trust the underlying hardware systems. The full supply chain for creating hardware includes multiple processes, which are often addressed in disparate threads of research, but which we consider as one unified process. On the front-end side, there is the soft design of hardware, along with validation and synthesis, to ultimately create a netlist, the document that defines the physical layout of hardware. On the back-end side, there is a physical fabrication process, where a chip is produced at a foundry from a supplied netlist, followed in some cases by post-fabrication testing.

Producing a trustworthy chip means securing the process from the early design stages through to the post-fabrication tests. We propose, implement and analyze a series of methods for making the hardware supply chain resilient against a wide array of known and possible attacks. These methods allow for the design and fabrication of hardware using untrustworthy personnel, designs, tools and resources, while protecting the final product from large classes of attacks, some known previously and some discovered and taxonomized in this work. The overarching idea in this work is to take a full-process view of the hardware supply chain. We begin by securing the hardware design and synthesis processes uses a defense-in-depth approach. We combine this work with foundry-side techniques to prevent malicious modifications and counterfeiting, and finally apply novel attestation techniques to ensure that hardware is trustworthy when it reaches users. For our design-side security approach, we use defense-in-depth because in practice, any security method can potentially subverted, and defense-in-depth is the best way to handle that assumption.

Our approach involves three independent steps. The first is a functional analysis tool (called FANCI), applied statically to designs during the coding and validation stages to remove any malicious circuits. The second step is to include physical security circuits that operate at runtime. These circuits, which we call trigger obfuscation circuits, scramble data at the microarchitectural level so that any hardware backdoors remaining in the design cannot be triggered at runtime. The third and final step is to include a runtime monitoring system that detects any backdoor payloads that might have been achieved despite the previous two steps. We design two different versions of this monitoring system. The first, TrustNet, is extremely lightweight and protects against an important class of attacks called emitter backdoors. The second, DataWatch, is slightly more heavyweight (though still efficient and low overhead) that can catch a wider variety of attacks and can be adapted to protect against nearly any type of digital payload.

We taxonomize the types of attacks that are possible against each of the three steps of our defense-in-depth system and show that each defense provides strong coverage with low (or negligible) overheads to performance, area and power consumption. For our foundry-side security approach, we develop the first foundry-side defense system that is aware of design-side security. We create a power-based side-channel, called a beacon. This beacon is essentially a benign backdoor. It can be turned on by a special key (not provided to the foundry), allowing for security attestation during post-fabrication testing. By designing this beacon into the design itself, the beacon requires neither keys nor storage, and as such exists in the final chip purely by virtue of existing in the netlist. We further obfuscate the netlist itself, rendering the task of reverse engineering the beacon (for a foundry-side adversary) intractable. Both the inclusion of the beacon and the obfuscation process add little to area and power costs and have no impact on performance.

All together, these methods provide a foundation on which hardware security can be developed and enhanced. They are low overhead and practical, making them suitable for inclusion in next generation hardware. Moving forward, the criticality of having trustworthy hardware can only increase. Ensuring that the hardware supply chain can be trusted in the face of sophisticated adversaries is vital. Both hardware design and hardware fabrication are increasingly international processes, and we believe continuing with this unified approach is the correct path for future research. In order for companies and governments to place trust in mission-critical hardware, it is necessary for hardware to be certified as secure and trustworthy. The methods we propose can be the first steps toward making this certification a reality.