X-Git-Url: http://www.git.cypherpunks.ru/?a=blobdiff_plain;f=gost3410%2Fcurve.go;h=50d00719df9d2ac22c372efca96dfa9d31a9b081;hb=cd1b35daa4b2db076ed1613fc16b7341ca0f2c52;hp=6cc113548e3d6fff5a0d851408ad4a70dd8f434d;hpb=36499b404629e5bbc4969b2ccdb71eed8bbc64d8;p=gogost.git

diff --git a/gost3410/curve.go b/gost3410/curve.go
index 6cc1135..50d0071 100644
--- a/gost3410/curve.go
+++ b/gost3410/curve.go
@@ -63,17 +63,7 @@ func NewCurve(p, q, a, b, x, y, e, d, co *big.Int) (*Curve, error) {
 		X:    x,
 		Y:    y,
 	}
-	r1 := big.NewInt(0)
-	r2 := big.NewInt(0)
-	r1.Mul(c.Y, c.Y)
-	r1.Mod(r1, c.P)
-	r2.Mul(c.X, c.X)
-	r2.Add(r2, c.A)
-	r2.Mul(r2, c.X)
-	r2.Add(r2, c.B)
-	r2.Mod(r2, c.P)
-	c.pos(r2)
-	if r1.Cmp(r2) != 0 {
+	if !c.Contains(c.X, c.Y) {
 		return nil, errors.New("gogost/gost3410: invalid curve parameters")
 	}
 	if e != nil && d != nil {
@@ -88,6 +78,21 @@ func NewCurve(p, q, a, b, x, y, e, d, co *big.Int) (*Curve, error) {
 	return &c, nil
 }
 
+// Is point on curve?
+func (c *Curve) Contains(x, y *big.Int) bool {
+	r1 := big.NewInt(0)
+	r2 := big.NewInt(0)
+	r1.Mul(y, y)
+	r1.Mod(r1, c.P)
+	r2.Mul(x, x)
+	r2.Add(r2, c.A)
+	r2.Mul(r2, x)
+	r2.Add(r2, c.B)
+	r2.Mod(r2, c.P)
+	c.pos(r2)
+	return r1.Cmp(r2) == 0
+}
+
 // Get the size of the point's coordinate in bytes.
 // 32 for 256-bit curves, 64 for 512-bit ones.
 func (c *Curve) PointSize() int {