Timing Leaks and Coarse-Grained Clocks

Abstract

Timing-based side-channel attacks have matured from an academic exercise to a powerful attack vector in the hand of real-world adversaries. A widely deployed countermeausure against such attacks is to reduce the accuracy of the clocks that are available to adversaries. While a number of high-profile attacks show that this mitigation can be side-stepped, there has not been a principled analysis of the degree of security it provides until now.In this paper, we perform the first information-flow analysis with respect to adversaries with coarse-grained clocks. To this end, we define an adversary model that is parametric in the granularity of the clock and connect it with a system model based on timed automata. We present algorithms for translating such a system to an information-theoretic channel, which enables us to analyze the leakage using standard techniques from quantitative information-flow analysis.We use our techniques to derive insights about the effect of reducing clock resolution on security. In particular, (1) we show that a coarse-grained clock might leak more than a fine-grained one, (2) we give a sufficient condition for when increasing the grain of the clock we achieve better security, and (3) we show that the attack techniques used in the literature form a strict hierarchy in terms of the information an adversary can extract using them.Finally, we illustrate the expressiveness of our development on a case study of a system that uses RSA signatures.

Timed Automata as a Formalism for Expressing Security: A Survey on Theory and Practice

“…In [Vas+19], Vasilikos et al study the impact of clock granularity on timing channel attacks. Timing side-channels attacks are closely related to non-interference, as an attacker is able to deduce internal information about a system by accessing some publicly available data-notably time.…”

“…Here, by "clock granularity", we mean clock as in processor clock that ticks periodically (different from the abstract concept of "timed automata clocks"). The authors in [Vas+19] notably propose a modeling based on timed automata with stochastic conditions, and they provide sufficient conditions "for when one can achieve better security by increasing the grain of the clock". The authors describe stochastic systems with the help of probabilistic TAs, and provide an algorithm for obtaining, given an attack scenario on a deterministic system, the timing channels along with their respective probability of occurrence.…”

Clockwork: Tracking Remote Timing Attacks

“…Note that our attacker may combine both differential-and absolutetime capabilities because programs have access to real-time clocks. Vasilikos et al [59] utilize time automata to study adversaries parametrized in the granularity of the clock. Practical remote timing attacks Remote timing attacks are (still) practical [22], [23].…”

Colored Petri Net Based Cache Side Channel Vulnerability Evaluation

“…All of the cache side channel attacks need the high resolution timer to measure the time of cache accesses, thus some operating systems or browsers provide a coarse timer only to enhance security. But Schwarz et al propose that the attacker can utilize other timing primitives to build a new high resolution timer [22], and Vasilikos et al show that coarse timer may leak more information by analyzing the information flow model of the attacks [23].…”