fn multiscalar_consistency_iter()

in src/edwards.rs [1265:1294]

• 19 lines of code
• 1 McCabe index (conditional complexity)

    fn multiscalar_consistency_iter(n: usize) {
        use core::iter;
        let mut rng = rand::thread_rng();

        // Construct random coefficients x0, ..., x_{n-1},
        // followed by some extra hardcoded ones.
        let xs = (0..n)
            .map(|_| Scalar::random(&mut rng))
            // The largest scalar allowed by the type system, 2^255-1
            .chain(iter::once(Scalar::from_bits([0xff; 32])))
            .collect::<Vec<_>>();
        let check = xs.iter()
            .map(|xi| xi * xi)
            .sum::<Scalar>();

        // Construct points G_i = x_i * B
        let Gs = xs.iter()
            .map(|xi| xi * &constants::ED25519_BASEPOINT_TABLE)
            .collect::<Vec<_>>();

        // Compute H1 = <xs, Gs> (consttime)
        let H1 = EdwardsPoint::multiscalar_mul(&xs, &Gs);
        // Compute H2 = <xs, Gs> (vartime)
        let H2 = EdwardsPoint::vartime_multiscalar_mul(&xs, &Gs);
        // Compute H3 = <xs, Gs> = sum(xi^2) * B
        let H3 = &check * &constants::ED25519_BASEPOINT_TABLE;

        assert_eq!(H1, H3);
        assert_eq!(H2, H3);
    }