of the larger of a and b. func (x *Nat) GCDVarTime(a, b *Nat) (*Nat, error) { u, _, err := extendedGCD(a, b) if err != nil { return nil, err } return x.set(u), nil } // extendedGCD computes u and A such that u = GCD(a, m) = A*a - B*m. // // u will have the size of the larger of a and m, and A will have the size of m. // // It is an error if either a or m is zero, or if they are both even. func extendedGCD(a, m *Nat) (u, A *Nat, err error) { // This is the extended binary GCD algorithm described in...