Paper 2025/435 Constant-Time Code: The Pessimist Case 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. BibTeX @misc{cryptoeprint:2025/435, author = {Thomas Pornin}, title = {Constant...