Coordinates conversion from/to twisted Edwards to Weierstass form

[gogost.git] / src / cypherpunks.ru / gogost / gost3410 / curve.go

diff --git a/src/cypherpunks.ru/gogost/gost3410/curve.go b/src/cypherpunks.ru/gogost/gost3410/curve.go
index b25131636f3605fdea75c2adeef6dfc3a88219ea..6b371a2bdc21fc28db22481fa3978cab9eb97d21 100644 (file)
--- a/src/cypherpunks.ru/gogost/gost3410/curve.go
+++ b/src/cypherpunks.ru/gogost/gost3410/curve.go
@@ -36,6 +36,10 @@ type Curve struct {
        A *big.Int
        B *big.Int
 
+       // Equation coefficients of the elliptic curve in twisted Edwards form
+       E *big.Int
+       D *big.Int
+
        // Basic point X and Y coordinates
        X *big.Int
        Y *big.Int
@@ -44,9 +48,13 @@ type Curve struct {
        t  *big.Int
        tx *big.Int
        ty *big.Int
+
+       // Cached s/t parameters for Edwards curve points conversion
+       edS *big.Int
+       edT *big.Int
 }
 
-func NewCurve(p, q, a, b, x, y *big.Int) (*Curve, error) {
+func NewCurve(p, q, a, b, x, y, e, d *big.Int) (*Curve, error) {
        c := Curve{
                P:  p,
                Q:  q,
@@ -71,6 +79,9 @@ func NewCurve(p, q, a, b, x, y *big.Int) (*Curve, error) {
        if r1.Cmp(r2) != 0 {
                return nil, errors.New("Invalid curve parameters")
        }
+       if e != nil && d != nil {
+               c.E = e
+               c.D = d
        }
        return &c, nil
 }