1 // GoGOST -- Pure Go GOST cryptographic functions library
2 // Copyright (C) 2015-2019 Sergey Matveev <stargrave@stargrave.org>
4 // This program is free software: you can redistribute it and/or modify
5 // it under the terms of the GNU General Public License as published by
6 // the Free Software Foundation, either version 3 of the License, or
7 // (at your option) any later version.
9 // This program is distributed in the hope that it will be useful,
10 // but WITHOUT ANY WARRANTY; without even the implied warranty of
11 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 // GNU General Public License for more details.
14 // You should have received a copy of the GNU General Public License
15 // along with this program. If not, see <http://www.gnu.org/licenses/>.
23 func (c *Curve) IsEdwards() bool {
27 func (c *Curve) EdwardsST() (*big.Int, *big.Int) {
36 c.t.ModInverse(c.t, c.P)
43 c.t.ModInverse(c.t, c.P)
49 // Convert Weierstrass X,Y coordinates to twisted Edwards U,V
50 func XY2UV(curve *Curve, x, y *big.Int) (*big.Int, *big.Int) {
51 if !curve.IsEdwards() {
52 panic("non twisted Edwards curve")
54 edS, edT := curve.EdwardsST()
58 u.ModInverse(y, curve.P)
61 v := big.NewInt(0).Set(curve.t)
64 curve.t.Add(curve.t, edS)
65 curve.t.ModInverse(curve.t, curve.P)
71 // Convert twisted Edwards U,V coordinates to Weierstrass X,Y
72 func UV2XY(curve *Curve, u, v *big.Int) (*big.Int, *big.Int) {
73 if !curve.IsEdwards() {
74 panic("non twisted Edwards curve")
76 edS, edT := curve.EdwardsST()
77 curve.tx.Add(bigInt1, v)
78 curve.tx.Mul(curve.tx, edS)
79 curve.tx.Mod(curve.tx, curve.P)
80 curve.ty.Sub(bigInt1, v)
83 x.ModInverse(curve.ty, curve.P)
89 y.ModInverse(y, curve.P)