Stealthy Opaque Predicates in Hardware -- Obfuscating Constant Expressions at Negligible Overhead

TL;DR

This paper introduces a new hardware technique for implementing resource-efficient opaque predicates that are difficult to reverse engineer, enhancing hardware security with minimal overhead.

Contribution

It presents a novel method for hardware opaque predicates that are resource-efficient and resistant to dynamic analysis, addressing a gap in hardware obfuscation research.

Findings

Stealthy opaque predicates can be implemented with minimal area overhead.

The technique effectively obfuscates cryptographic hardware Trojans.

No impact on latency was observed in the implementations.

Abstract

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.