Stealthy Opaque Predicates in Hardware -- Obfuscating Constant Expressions at Negligible Overhead
This work addresses hardware security challenges for protecting intellectual property and obfuscating cryptographic hardware Trojans, representing a novel application in an underexplored domain.
The paper tackles the problem of implementing opaque predicates in hardware for obfuscation, proposing a novel technique that achieves minimal area overhead and no latency impact.
Opaque predicates are a well-established fundamental building block for software obfuscation. Simplified, an opaque predicate implements an expression that provides constant Boolean output, but appears to have dynamic behavior for static analysis. Even though there has been extensive research regarding opaque predicates in software, techniques for opaque predicates in hardware are barely explored. In this work, we propose a novel technique to instantiate opaque predicates in hardware, such that they (1) are resource-efficient, and (2) are challenging to reverse engineer even with dynamic analysis capabilities. We demonstrate the applicability of opaque predicates in hardware for both, protection of intellectual property and obfuscation of cryptographic hardware Trojans. Our results show that we are able to implement stealthy opaque predicates in hardware with minimal overhead in area and no impact on latency.