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package brainpool
import (
"crypto/elliptic"
"math/big"
)
var _ elliptic.Curve = (*rcurve)(nil)
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
}
var (
two = big.NewInt(2)
three = big.NewInt(3)
)
func newrcurve(twisted elliptic.Curve, params *elliptic.CurveParams, z *big.Int) *rcurve {
zinv := new(big.Int).ModInverse(z, params.P)
return &rcurve{
twisted: twisted,
params: params,
z: z,
zinv: zinv,
z2: new(big.Int).Exp(z, two, params.P),
z3: new(big.Int).Exp(z, three, params.P),
zinv2: new(big.Int).Exp(zinv, two, params.P),
zinv3: new(big.Int).Exp(zinv, three, params.P),
}
}
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))
}
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