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Quick Start

This guide walks through writing and running your first timing test. You’ve seen the basic pattern on the landing page; now let’s create a complete, runnable test.

Add the dependencies

Section titled “Add the dependencies”
Terminal window
cargo add tacet --dev
cargo add rand --dev  # For random input generation
cargo add subtle --dev  # For the constant-time comparison example

Write a test

Section titled “Write a test”

Create a test file (e.g., tests/timing.rs):

use tacet::{TimingOracle, AttackerModel, helpers::InputPair};
use std::time::Duration;


#[test]
fn test_constant_time_compare() {
    let secret = [0u8; 32];


    // Baseline matches secret (slow path if leaky)
    // Sample is random (fast path if leaky)
    let inputs = InputPair::new(
        || [0u8; 32],
        || rand::random::<[u8; 32]>(),
    );


    let outcome = TimingOracle::for_attacker(AttackerModel::AdjacentNetwork)
        .time_budget(Duration::from_secs(30))
        .test(inputs, |input| {
            // Test your comparison function
            constant_time_eq(&secret, &input);
        });


    // Display prints nicely formatted output with colors
    println!("{outcome}");


    // Assert the test passed (panics on Fail, warns on Inconclusive/Unmeasurable)
    assert!(outcome.passed(), "Timing leak detected");
}


fn constant_time_eq(a: &[u8], b: &[u8]) -> bool {
    // Your constant-time comparison implementation
    subtle::ConstantTimeEq::ct_eq(a, b).into()
}

Run the test

Section titled “Run the test”
Terminal window
cargo test --test timing -- --test-threads=1 --nocapture

You should see output like:

[test_constant_time_compare]
tacet
──────────────────────────────────────────────────────────────


  Samples: 6000 per class
  Quality: Good


  ✓ No timing leak detected


    Probability of leak: 0.0%
    95% CI: 0.0–12.5 ns


──────────────────────────────────────────────────────────────

What just happened

Section titled “What just happened”

The library ran your function thousands of times with two types of inputs (baseline zeros and random samples), measured execution times, and compared the timing distributions using Bayesian statistics. The result tells you whether there’s a security-relevant timing difference above your chosen threshold.

For details on the statistical methodology, see How It Works.

Next steps

Section titled “Next steps”