package paillier

import (
	"crypto/rand"
	"io"
	"math/big"
)

var ZERO = big.NewInt(0)
var ONE = big.NewInt(1)
var TWO = big.NewInt(2)
var FOUR = big.NewInt(4)

// Generate a random element in the group of all the elements in Z/nZ that
// has a multiplicative inverse.
func GetRandomNumberInMultiplicativeGroup(n *big.Int, random io.Reader) (*big.Int, error) {
	r, err := rand.Int(random, n)
	if err != nil {
		return nil, err
	}
	zero := big.NewInt(0)
	one := big.NewInt(1)
	if zero.Cmp(r) == 0 || one.Cmp(new(big.Int).GCD(nil, nil, n, r)) != 0 {
		return GetRandomNumberInMultiplicativeGroup(n, random)
	}
	return r, nil

}