Metior: A Comprehensive Model to Evaluate Obfuscating Side-Channel Defense Schemes

Microarchitectural side-channels enable an attacker to exfiltrate information via the observable side-effects of a victim's execution. Obfuscating mitigation schemes have recently gained in popularity for their appealing performance characteristics. These schemes, including randomized caches and DRAM traffic shapers, limit, but do not completely eliminate, side-channel leakage. An important (yet under-explored) research challenge is the quantitative study of the security effectiveness of these schemes, identifying whether these obfuscating schemes help increase the security level of a system, and if so, by how much.

In this paper, we address this research challenge by presenting Metior, a comprehensive model to quantitatively evaluate the effectiveness of obfuscating side-channel mitigations. Metior offers a way to reason about the flow of information through obfuscating schemes. Metior builds upon existing information theoretic approaches, allowing for the comprehensive side-channel leakage evaluation of active attackers, real victim applications, and state-ofthe-art microarchitectural obfuscation schemes. We demonstrate the use of Metior in the concrete leakage evaluation of three microarchitectural obfuscation schemes (fully-associative random replacement caches, CEASER-S, and Camouflage), identifying unintuitive leakage behaviours across all three schemes.

• Security and privacy → Side-channel analysis and countermeasures.