let x = self.get_user_hash(salt);
let gx = self.g.modpow(&x, &self.n);
let kgx = (&self.k * &gx) % &self.n;
let bkgx =
    if server_public_key > &kgx {
        server_public_key - kgx
    } else {
        &self.n + server_public_key - kgx
    };

let diff = bkgx % &self.n;
let ux = (u * x) % &self.n;
let aux = (&self.client_private_key + &ux) % &self.n;
let secret = diff.modpow(&aux, &self.n);