Constant-Time Code: The Pessimist Case

Thomas Pornin

Paper 2025/435

Constant-Time Code: The Pessimist Case

Thomas Pornin

, NCC Group

Abstract

This note discusses the problem of writing cryptographic implementations in software, free of timing-based side-channels, and many ways in which that endeavour can fail in practice. It is a pessimist view: it highlights why such failures are expected to become more common, and how constant-time coding is, or will soon become, infeasible in all generality.

Metadata

Available format(s): PDF
Category: Implementation
Publication info: Preprint.
Keywords: constant-time compiler JIT
Contact author(s): thomas pornin @ nccgroup com
History: 2025-03-08: approved; 2025-03-06: received; See all versions
Short URL: https://ia.cr/2025/435
License: CC BY

BibTeX

@misc{cryptoeprint:2025/435,
      author = {Thomas Pornin},
      title = {Constant-Time Code: The Pessimist Case},
      howpublished = {Cryptology {ePrint} Archive, Paper 2025/435},
      year = {2025},
      url = {https://eprint.iacr.org/2025/435}
}