1
// Copyright 2012 The Go Authors. All rights reserved.
2
// Use of this source code is governed by a BSD-style
3
// license that can be found in the LICENSE file.
11
// twistPoint implements the elliptic curve y²=x³+3/ξ over GF(p²). Points are
12
// kept in Jacobian form and t=z² when valid. The group G₂ is the set of
13
// n-torsion points of this curve over GF(p²) (where n = Order)
14
type twistPoint struct {
19
bigFromBase10("6500054969564660373279643874235990574282535810762300357187714502686418407178"),
20
bigFromBase10("45500384786952622612957507119651934019977750675336102500314001518804928850249"),
23
// twistGen is the generator of group G₂.
24
var twistGen = &twistPoint{
26
bigFromBase10("21167961636542580255011770066570541300993051739349375019639421053990175267184"),
27
bigFromBase10("64746500191241794695844075326670126197795977525365406531717464316923369116492"),
30
bigFromBase10("20666913350058776956210519119118544732556678129809273996262322366050359951122"),
31
bigFromBase10("17778617556404439934652658462602675281523610326338642107814333856843981424549"),
43
func newTwistPoint(pool *bnPool) *twistPoint {
52
func (c *twistPoint) String() string {
53
return "(" + c.x.String() + ", " + c.y.String() + ", " + c.z.String() + ")"
56
func (c *twistPoint) Put(pool *bnPool) {
63
func (c *twistPoint) Set(a *twistPoint) {
70
// IsOnCurve returns true iff c is on the curve where c must be in affine form.
71
func (c *twistPoint) IsOnCurve() bool {
73
yy := newGFp2(pool).Square(c.y, pool)
74
xxx := newGFp2(pool).Square(c.x, pool)
75
xxx.Mul(xxx, c.x, pool)
79
return yy.x.Sign() == 0 && yy.y.Sign() == 0
82
func (c *twistPoint) SetInfinity() {
86
func (c *twistPoint) IsInfinity() bool {
90
func (c *twistPoint) Add(a, b *twistPoint, pool *bnPool) {
91
// For additional comments, see the same function in curve.go.
102
// See http://hyperelliptic.org/EFD/g1p/auto-code/shortw/jacobian-0/addition/add-2007-bl.op3
103
z1z1 := newGFp2(pool).Square(a.z, pool)
104
z2z2 := newGFp2(pool).Square(b.z, pool)
105
u1 := newGFp2(pool).Mul(a.x, z2z2, pool)
106
u2 := newGFp2(pool).Mul(b.x, z1z1, pool)
108
t := newGFp2(pool).Mul(b.z, z2z2, pool)
109
s1 := newGFp2(pool).Mul(a.y, t, pool)
111
t.Mul(a.z, z1z1, pool)
112
s2 := newGFp2(pool).Mul(b.y, t, pool)
114
h := newGFp2(pool).Sub(u2, u1)
118
i := newGFp2(pool).Square(t, pool)
119
j := newGFp2(pool).Mul(h, i, pool)
123
if xEqual && yEqual {
127
r := newGFp2(pool).Add(t, t)
129
v := newGFp2(pool).Mul(u1, i, pool)
131
t4 := newGFp2(pool).Square(r, pool)
133
t6 := newGFp2(pool).Sub(t4, j)
137
t4.Mul(s1, j, pool) // t8
139
t4.Mul(r, t, pool) // t10
142
t.Add(a.z, b.z) // t11
143
t4.Square(t, pool) // t12
144
t.Sub(t4, z1z1) // t13
145
t4.Sub(t, z2z2) // t14
164
func (c *twistPoint) Double(a *twistPoint, pool *bnPool) {
165
// See http://hyperelliptic.org/EFD/g1p/auto-code/shortw/jacobian-0/doubling/dbl-2009-l.op3
166
A := newGFp2(pool).Square(a.x, pool)
167
B := newGFp2(pool).Square(a.y, pool)
168
C := newGFp2(pool).Square(B, pool)
170
t := newGFp2(pool).Add(a.x, B)
171
t2 := newGFp2(pool).Square(t, pool)
174
d := newGFp2(pool).Add(t2, t2)
176
e := newGFp2(pool).Add(t, A)
177
f := newGFp2(pool).Square(e, pool)
189
t.Mul(a.y, a.z, pool)
202
func (c *twistPoint) Mul(a *twistPoint, scalar *big.Int, pool *bnPool) *twistPoint {
203
sum := newTwistPoint(pool)
205
t := newTwistPoint(pool)
207
for i := scalar.BitLen(); i >= 0; i-- {
209
if scalar.Bit(i) != 0 {
222
func (c *twistPoint) MakeAffine(pool *bnPool) *twistPoint {
227
zInv := newGFp2(pool).Invert(c.z, pool)
228
t := newGFp2(pool).Mul(c.y, zInv, pool)
229
zInv2 := newGFp2(pool).Square(zInv, pool)
230
c.y.Mul(t, zInv2, pool)
231
t.Mul(c.x, zInv2, pool)
243
func (c *twistPoint) Negative(a *twistPoint, pool *bnPool) {