Testing side-channel security of cryptographic implementations against future microarchitectures

TL;DR

This paper introduces a framework to evaluate how future microarchitectural optimizations might compromise the security of cryptographic implementations by revealing secret information through side channels.

Contribution

The authors develop LmSpec and LmTest to systematically analyze the security impact of microarchitectural optimizations on cryptographic code.

Findings

All tested implementations showed potential secret-dependent leaks.

Some leaks only occur due to coding practices that prevent leaks under standard models.

Leaks could be sufficient to recover secret keys in future microarchitectures.

Abstract

How will future microarchitectures impact the security of existing cryptographic implementations? As we cannot keep reducing the size of transistors, chip vendors have started developing new microarchitectural optimizations to speed up computation. A recent study (Sanchez Vicarte et al., ISCA 2021) suggests that these optimizations might open the Pandora's box of microarchitectural attacks. However, there is little guidance on how to evaluate the security impact of future optimization proposals. To help chip vendors explore the impact of microarchitectural optimizations on cryptographic implementations, we develop (i) an expressive domain-specific language, called LmSpec, that allows them to specify the leakage model for the given optimization and (ii) a testing framework, called LmTest, to automatically detect leaks under the specified leakage model within the given implementation. Using this framework, we conduct an empirical study of 18 proposed microarchitectural optimizations on 25 implementations of eight cryptographic primitives in five popular libraries. We find that every implementation would contain secret-dependent leaks, sometimes sufficient to recover a victim's secret key, if these optimizations were realized. Ironically, some leaks are possible only because of coding idioms used to prevent leaks under the standard constant-time model.