G parameter removed from ThresholdKey

G _MUST_ be always n+1 to make the threshold encryption algorithm safe. We assume G=n+1 both for standard and threshold version.

paillier.go

@@ -37,6 +37,9 @@ func (pub *PublicKey) Encrypt(m *big.Int, random io.Reader) (*Cypher, error) {
 	}
 	nSquare := pub.GetNSquare()
 
+	// g is _always_ equal n+1
+	// Threshold encryption is safe only for g=n+1 choice.
+	// See [DJN 10], section 5.1
 	g := new(big.Int).Add(pub.N, big.NewInt(1))
 	gm := new(big.Int).Exp(g, m, nSquare)
 	rn := new(big.Int).Exp(r, pub.N, nSquare)