Function ecdlp_bsgs 

pub fn ecdlp_bsgs(
    curve: &Curve,
    base: &Point,
    target: &Point,
    n: u64,
) -> Option<BigInt>

Solve the elliptic-curve discrete log Q = k·P by baby-step/giant-step, given the order n of P. O(√n) group operations — the best generic attack, and exponential in the bit length. This is exactly why a sound (large prime-order) curve resists, and why ECC uses far smaller keys than RSA. None if Q is not a multiple of P.