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