Fixed VKO cofactor bug

[gogost.git] / gost3410 / curve.go

diff --git a/gost3410/curve.go b/gost3410/curve.go
index 696beabed9a68889675f9b96237a924fff30ea91..a3685ce047e7be3b7c11ea58f649c09761255d46 100644 (file)
--- a/gost3410/curve.go
+++ b/gost3410/curve.go
@@ -25,6 +25,7 @@ var (
        bigInt1 *big.Int = big.NewInt(1)
        bigInt2 *big.Int = big.NewInt(2)
        bigInt3 *big.Int = big.NewInt(3)
+       bigInt4 *big.Int = big.NewInt(4)
 )
 
 type Curve struct {
@@ -33,6 +34,8 @@ type Curve struct {
        P *big.Int // Characteristic of the underlying prime field
        Q *big.Int // Elliptic curve subgroup order
 
+       Co *big.Int // Cofactor
+
        // Equation coefficients of the elliptic curve in canonical form
        A *big.Int
        B *big.Int
@@ -55,7 +58,7 @@ type Curve struct {
        edT *big.Int
 }
 
-func NewCurve(p, q, a, b, x, y, e, d *big.Int) (*Curve, error) {
+func NewCurve(p, q, a, b, x, y, e, d, co *big.Int) (*Curve, error) {
        c := Curve{
                Name: "unknown",
                P:    p,
@@ -85,6 +88,11 @@ func NewCurve(p, q, a, b, x, y, e, d *big.Int) (*Curve, error) {
                c.E = e
                c.D = d
        }
+       if co == nil {
+               c.Co = bigInt1
+       } else {
+               c.Co = co
+       }
        return &c, nil
 }