"They're not that hard to mitigate": What Cryptographic Library Developers Think About Timing Attacks

Jan Jancar (1) , Marcel Fourné (2) , Daniel de Almeida Braga (3, 4, 5, 6) , Mohamed Sabt (3, 4, 5, 6) , Peter Schwabe (2, 7) , Gilles Barthe (2, 8) , Pierre-Alain Fouque (9, 4, 5, 6) , Yasemin Acar (10, 2)

1 MUNI - Masaryk University [Brno]
2 MPI SP - Max Planck Institute for Security and Privacy
3 SPICY - Security & PrIvaCY
4 UR - Université de Rennes
5 CNRS - Centre National de la Recherche Scientifique
6 IRISA - Institut de Recherche en Informatique et Systèmes Aléatoires
7 Radboud University [Nijmegen]
8 Institute IMDEA Software [Madrid]
9 CAPSULE - Applied Cryptography and Implementation Security
10 GW - The George Washington University

Timing attacks are among the most devastating side-channel attacks, allowing remote attackers to retrieve secret material, including cryptographic keys, with relative ease. In principle, “these attacks are not that hard to mitigate”: the basic intuition, captured by the constant-time criterion, is that control-flow and memory accesses should be independent from secrets. Furthermore, there is a broad range of tools for automatically checking adherence to this intuition. Yet, these attacks still plague popular crypto libraries twenty-five years after their discovery, reflecting a dangerous gap between academic research and crypto engineering. This gap can potentially undermine the emerging shift towards high-assurance, formally verified crypto libraries. However, the causes for this gap remain uninvestigated. To understand the causes of this gap, we conducted a survey with 44 developers of 27 prominent open source cryptographic libraries. The goal of the survey was to analyze if and how the developers ensure that their code executes in constant time. Our main findings are that developers are aware of timing attacks and of their potentially dramatic consequences and yet often prioritize other issues over the perceived huge investment of time and resources currently needed to make their code resistant to timing attacks. Based on the survey, we identify several shortcomings in existing analysis tools for constant-time, and issue recommendations that can make writing constant-time libraries less difficult. Our recommendations can inform future development of analysis tools, security-aware compilers, and crypto libraries, not only for constant-timeness, but in the broader context of side-channel attacks, in particular for micro-architectural side-channel attacks.

Mots clés: constant-time; timing-attacks; cryptographic-library; survey; developer-survey; expert-survey; usable-security; human-factors; cryptography

Domaines: Cryptographie et sécurité [cs.CR]; Autre [cs.OH]

Jan Jancar, Marcel Fourné, Daniel de Almeida Braga, Mohamed Sabt, Peter Schwabe, et al.. "They're not that hard to mitigate": What Cryptographic Library Developers Think About Timing Attacks. 2022 IEEE Symposium on Security and Privacy, May 2022, San Francisco, United States. pp.755-772, ⟨10.1109/SP46214.2022.9833713⟩. ⟨hal-03694811⟩