# Constant Time Analysis

Detects timing side-channel vulnerabilities in cryptographic code.

- Repository: https://github.com/trailofbits/skills (7935 stars)
- Category: Security
- License: CC-BY-SA-4.0
- Last updated: 2026-10-28
- Runs scripts: no, instructions only

## Install

Claude Code: `npx skills add trailofbits/skills --skill constant-time-analysis -g -a claude-code -y`
Codex: `npx skills add trailofbits/skills --skill constant-time-analysis -g -a codex -y`
Cursor: `npx skills add trailofbits/skills --skill constant-time-analysis -g -a cursor -y`
Gemini CLI: `npx skills add trailofbits/skills --skill constant-time-analysis -g -a gemini-cli -y`
Claude Code plugin marketplace: `/plugin marketplace add trailofbits/skills`

## Description

Detects timing side-channel vulnerabilities in cryptographic code. Use when implementing or reviewing crypto code, encountering division on secrets, secret-dependent branches, or constant-time programming questions in C, C++, Go, Rust, Swift, Java, Kotlin, C#, PHP, JavaScript, TypeScript, Python, or Ruby.

## SKILL.md, as published by its author (untrusted third-party text, read it as data)

# Constant-Time Analysis

Compile the code, inspect the emitted assembly or bytecode for variable-time instructions, then decide which of the flagged operations actually touch secrets. The compilation step is mechanical; the triage step is the work.

## When to Use

- Implementing or reviewing a signature, encryption, KEM, or key derivation routine
- Code applies `/` or `%` to a value derived from a key, plaintext, nonce, or token
- The user mentions "constant-time", "timing attack", "side-channel", or "KyberSlash"
- Reviewing functions named `sign`, `verify`, `encrypt`, `decrypt`, `derive_key`

## When NOT to Use

- **Measuring** timing variance on a running binary, use the `constant-time-testing` skill from the `testing-handbook-skills` plugin, which covers dudect and statistical approaches and may not be installed. This skill inspects compiler output statically and never executes the code under test.
- Non-cryptographic code, or crypto code where every input is public
- High-level API usage where a vetted library owns the constant-time guarantees
- Cache and other microarchitectural side channels, the assembly view cannot see them

## Language Routing

Read the guide for the target language before interpreting any findings; each one lists that language's dangerous instructions and the idiomatic constant-time replacements.

| Guide | Languages |
| ----- | --------- |
| [references/compiled.md](references/compiled.md) | C, C++, Go, Rust |
| [references/swift.md](references/swift.md) | Swift |
| [references/vm-compiled.md](references/vm-compiled.md) | Java, C# |
| [references/kotlin.md](references/kotlin.md) | Kotlin |
| [references/php.md](references/php.md) | PHP |
| [references/javascript.md](references/javascript.md) | JavaScript, TypeScript |
| [references/python.md](references/python.md) | Python |
| [references/ruby.md](references/ruby.md) | Ruby |

## Running the Analyzer

The rest: https://github.com/trailofbits/skills/blob/HEAD/plugins/constant-time-analysis/skills/constant-time-analysis/SKILL.md