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rcurve.go
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rcurve.go
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package brainpool
import (
"crypto/elliptic"
"math/big"
)
type rcurve struct {
twisted elliptic.Curve
params elliptic.CurveParams
z *big.Int
zinv *big.Int
z2 *big.Int
z3 *big.Int
zinv2 *big.Int
zinv3 *big.Int
}
func newrcurve(twisted elliptic.Curve, gx, gy, z *big.Int) *rcurve {
var curve rcurve
curve.twisted = twisted
curve.params = *twisted.Params()
curve.params.B = nil // FIXME: crypto/elliptic assumes A=-3
curve.params.Gx = gx
curve.params.Gy = gy
two := big.NewInt(2)
three := big.NewInt(3)
curve.z = z
curve.zinv = new(big.Int).ModInverse(z, curve.params.P)
curve.z2 = new(big.Int).Exp(curve.z, two, curve.params.P)
curve.z3 = new(big.Int).Exp(curve.z, three, curve.params.P)
curve.zinv2 = new(big.Int).Exp(curve.zinv, two, curve.params.P)
curve.zinv3 = new(big.Int).Exp(curve.zinv, three, curve.params.P)
return &curve
}
func (curve *rcurve) toTwisted(x, y *big.Int) (*big.Int, *big.Int) {
var tx, ty big.Int
tx.Mul(x, curve.z2)
tx.Mod(&tx, curve.params.P)
ty.Mul(y, curve.z3)
ty.Mod(&ty, curve.params.P)
return &tx, &ty
}
func (curve *rcurve) fromTwisted(tx, ty *big.Int) (*big.Int, *big.Int) {
var x, y big.Int
x.Mul(tx, curve.zinv2)
x.Mod(&x, curve.params.P)
y.Mul(ty, curve.zinv3)
y.Mod(&y, curve.params.P)
return &x, &y
}
func (curve *rcurve) Params() *elliptic.CurveParams {
return &curve.params
}
func (curve *rcurve) IsOnCurve(x, y *big.Int) bool {
return curve.twisted.IsOnCurve(curve.toTwisted(x, y))
}
func (curve *rcurve) Add(x1, y1, x2, y2 *big.Int) (x, y *big.Int) {
tx1, ty1 := curve.toTwisted(x1, y1)
tx2, ty2 := curve.toTwisted(x2, y2)
return curve.fromTwisted(curve.twisted.Add(tx1, ty1, tx2, ty2))
}
func (curve *rcurve) Double(x1, y1 *big.Int) (x, y *big.Int) {
return curve.fromTwisted(curve.twisted.Double(curve.toTwisted(x1, y1)))
}
func (curve *rcurve) ScalarMult(x1, y1 *big.Int, scalar []byte) (x, y *big.Int) {
tx1, ty1 := curve.toTwisted(x1, y1)
return curve.fromTwisted(curve.twisted.ScalarMult(tx1, ty1, scalar))
}
func (curve *rcurve) ScalarBaseMult(scalar []byte) (x, y *big.Int) {
return curve.fromTwisted(curve.twisted.ScalarBaseMult(scalar))
}