constant-time-testing

An agent skill by trailofbits, from trailofbits/skills. Tags: analysis, crypto, security, testing.

What it does

Measures timing side channels in cryptographic implementations by running them, using dudect for statistical analysis and Timecop over Valgrind for dynamic tracing. Covers the formal, symbolic, dynamic, and statistical tool categories and how to read a result. Use when testing whether a running implementation is constant-time, measuring timing variance on a compiled binary, or investigating a suspected timing attack. Not for statically inspecting compiler output — the constant-time-analysis plugin covers that.

Install

With the skills CLI, which installs into Claude Code, Codex, Cursor and other agents:

npx skills add trailofbits/skills --skill constant-time-testing

Or copy the skill folder into Claude Code's skills directory by hand (~/.claude/skills for every project, or .claude/skills inside one):

git clone --depth 1 https://github.com/trailofbits/skills
cp -r skills/plugins/testing-handbook-skills/skills/constant-time-testing ~/.claude/skills/constant-time-testing

Safety box score

Not rated yet. A safety box score grades what a skill and its scripts can reach on the machine of whoever installs it, across eight categories from shell execution to secrets access. Anyone can request one from this page; it is saved for everyone. How the score works.

Source

Repository

trailofbits/skills (all skills from this repository)

Path

plugins/testing-handbook-skills/skills/constant-time-testing/SKILL.md

Branch

main

Collection

testing-handbook-skills

Updated

2026-09-19

Related skills

• wycheproof — Validates cryptographic implementations against Project Wycheproof's test vectors, which encode known attacks and edge cases across AES, RSA, ECDSA, ECDH.
• audit-prep-assistant — Prepares codebases for security review using Trail of Bits' checklist.
• constant-time-analysis — Detects timing side-channel vulnerabilities in cryptographic code.
• post-patch-validation — Validates security patches with reproducible baseline-versus-patched evidence, including original exploits, root-cause variants, behavior preservation.
• vector-forge — Mutation-driven test vector generation.
• qa-expert — This skill should be used when establishing comprehensive QA testing processes for any software project.