imported from https://bitbucket.org/ustraca/crypto

utils.go

@@ -0,0 +1,28 @@
+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
+
+}