How to Implement Constant-Time Comparison in Rust

Use the constant_time_eq function from the crypto-common crate to compare byte slices in constant time, preventing timing attacks. This function returns true if the slices are equal and false otherwise, regardless of where they differ.

use constant_time_eq::constant_time_eq;

fn main() {
    let a = b"secret";
    let b = b"secret";
    let c = b"public";

    assert!(constant_time_eq(a, b));
    assert!(!constant_time_eq(a, c));
}

Add constant_time_eq = "0.3" to your Cargo.toml dependencies.

Constant-time comparison in Rust compares two pieces of data in a way that takes the exact same amount of time, no matter how similar or different they are. It matters because attackers can sometimes guess secrets by measuring how long a comparison takes. Think of it like checking a combination lock where the mechanism makes the same sound whether you get the first digit right or wrong.