ramp_mul.rs

extern crate ramp;

use ramp::Int;

#[derive(PartialEq, Clone, Debug)]
struct Point {
    x: Int,
    y: Int,
}

fn point_add(
    &Point {
        x: ref p_x,
        y: ref p_y,
    }: &Point,
    &Point {
        x: ref q_x,
        y: ref q_y,
    }: &Point,
) -> Point {
    let P = &Int::from_str_radix(
        "115792089237316195423570985008687907853269984665640564039457584007908834671663",
        10,
    ).unwrap();
    let P2 = &(P - Int::from(2));

    let lam = if p_x == q_x && p_y == q_y {
        Int::from(3) * p_x.pow(2) * ((p_y + p_y) % P).pow_mod(P2, P)
    } else {
        (q_x - p_x).pow_mod(P2, P) * (q_y - p_y) % P
    };

    let rx = (lam.pow(2) - p_x - q_x) % P;

    let mut ry = (&lam * (p_x - &rx) - p_y) % P;
    if ry < 0 {
        ry = ry + P;
    }

    Point { x: rx, y: ry }
}

fn point_mul(p: &Point, mut d: u32) -> Point {
    let mut n = p.clone();
    let mut q = None;

    for _ in 0..256 {
        let last_bit = d & 1 == 1;
        d >>= 1;

        if last_bit {
            q = Some(q.map_or_else(|| n.clone(), |q| point_add(&q, &n)));
        }
        n = point_add(&n, &n);
    }
    q.unwrap()
}

fn main() {
    let g = Point {
        x: Int::from_str_radix(
            "79BE667EF9DCBBAC55A06295CE870B07029BFCDB2DCE28D959F2815B16F81798",
            16,
        ).unwrap(),
        y: Int::from_str_radix(
            "483ADA7726A3C4655DA4FBFC0E1108A8FD17B448A68554199C47D08FFB10D4B8",
            16,
        ).unwrap(),
    };

    let res = point_mul(&g, 125);
    println!(" {}", res.x);
    println!(" {}", res.y);
}