-
Notifications
You must be signed in to change notification settings - Fork 45
/
g2.go
456 lines (422 loc) · 11.3 KB
/
g2.go
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
// Copyright 2020 The CortexTheseus Authors
// This file is part of the CortexTheseus library.
//
// The CortexTheseus library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The CortexTheseus library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the CortexTheseus library. If not, see <http://www.gnu.org/licenses/>.
package bls12381
import (
"errors"
"math"
"math/big"
)
// PointG2 is type for point in G2.
// PointG2 is both used for Affine and Jacobian point representation.
// If z is equal to one the point is considered as in affine form.
type PointG2 [3]fe2
// Set copies valeus of one point to another.
func (p *PointG2) Set(p2 *PointG2) *PointG2 {
p[0].set(&p2[0])
p[1].set(&p2[1])
p[2].set(&p2[2])
return p
}
// Zero returns G2 point in point at infinity representation
func (p *PointG2) Zero() *PointG2 {
p[0].zero()
p[1].one()
p[2].zero()
return p
}
type tempG2 struct {
t [9]*fe2
}
// G2 is struct for G2 group.
type G2 struct {
f *fp2
tempG2
}
// NewG2 constructs a new G2 instance.
func NewG2() *G2 {
return newG2(nil)
}
func newG2(f *fp2) *G2 {
if f == nil {
f = newFp2()
}
t := newTempG2()
return &G2{f, t}
}
func newTempG2() tempG2 {
t := [9]*fe2{}
for i := 0; i < 9; i++ {
t[i] = &fe2{}
}
return tempG2{t}
}
// Q returns group order in big.Int.
func (g *G2) Q() *big.Int {
return new(big.Int).Set(q)
}
func (g *G2) fromBytesUnchecked(in []byte) (*PointG2, error) {
p0, err := g.f.fromBytes(in[:96])
if err != nil {
return nil, err
}
p1, err := g.f.fromBytes(in[96:])
if err != nil {
return nil, err
}
p2 := new(fe2).one()
return &PointG2{*p0, *p1, *p2}, nil
}
// FromBytes constructs a new point given uncompressed byte input.
// FromBytes does not take zcash flags into account.
// Byte input expected to be larger than 96 bytes.
// First 192 bytes should be concatenation of x and y values
// Point (0, 0) is considered as infinity.
func (g *G2) FromBytes(in []byte) (*PointG2, error) {
if len(in) != 192 {
return nil, errors.New("input string should be equal or larger than 192")
}
p0, err := g.f.fromBytes(in[:96])
if err != nil {
return nil, err
}
p1, err := g.f.fromBytes(in[96:])
if err != nil {
return nil, err
}
// check if given input points to infinity
if p0.isZero() && p1.isZero() {
return g.Zero(), nil
}
p2 := new(fe2).one()
p := &PointG2{*p0, *p1, *p2}
if !g.IsOnCurve(p) {
return nil, errors.New("point is not on curve")
}
return p, nil
}
// DecodePoint given encoded (x, y) coordinates in 256 bytes returns a valid G1 Point.
func (g *G2) DecodePoint(in []byte) (*PointG2, error) {
if len(in) != 256 {
return nil, errors.New("invalid g2 point length")
}
pointBytes := make([]byte, 192)
x0Bytes, err := decodeFieldElement(in[:64])
if err != nil {
return nil, err
}
x1Bytes, err := decodeFieldElement(in[64:128])
if err != nil {
return nil, err
}
y0Bytes, err := decodeFieldElement(in[128:192])
if err != nil {
return nil, err
}
y1Bytes, err := decodeFieldElement(in[192:])
if err != nil {
return nil, err
}
copy(pointBytes[:48], x1Bytes)
copy(pointBytes[48:96], x0Bytes)
copy(pointBytes[96:144], y1Bytes)
copy(pointBytes[144:192], y0Bytes)
return g.FromBytes(pointBytes)
}
// ToBytes serializes a point into bytes in uncompressed form,
// does not take zcash flags into account,
// returns (0, 0) if point is infinity.
func (g *G2) ToBytes(p *PointG2) []byte {
out := make([]byte, 192)
if g.IsZero(p) {
return out
}
g.Affine(p)
copy(out[:96], g.f.toBytes(&p[0]))
copy(out[96:], g.f.toBytes(&p[1]))
return out
}
// EncodePoint encodes a point into 256 bytes.
func (g *G2) EncodePoint(p *PointG2) []byte {
// outRaw is 96 bytes
outRaw := g.ToBytes(p)
out := make([]byte, 256)
// encode x
copy(out[16:16+48], outRaw[48:96])
copy(out[80:80+48], outRaw[:48])
// encode y
copy(out[144:144+48], outRaw[144:])
copy(out[208:208+48], outRaw[96:144])
return out
}
// New creates a new G2 Point which is equal to zero in other words point at infinity.
func (g *G2) New() *PointG2 {
return new(PointG2).Zero()
}
// Zero returns a new G2 Point which is equal to point at infinity.
func (g *G2) Zero() *PointG2 {
return new(PointG2).Zero()
}
// One returns a new G2 Point which is equal to generator point.
func (g *G2) One() *PointG2 {
p := &PointG2{}
return p.Set(&g2One)
}
// IsZero returns true if given point is equal to zero.
func (g *G2) IsZero(p *PointG2) bool {
return p[2].isZero()
}
// Equal checks if given two G2 point is equal in their affine form.
func (g *G2) Equal(p1, p2 *PointG2) bool {
if g.IsZero(p1) {
return g.IsZero(p2)
}
if g.IsZero(p2) {
return g.IsZero(p1)
}
t := g.t
g.f.square(t[0], &p1[2])
g.f.square(t[1], &p2[2])
g.f.mul(t[2], t[0], &p2[0])
g.f.mul(t[3], t[1], &p1[0])
g.f.mul(t[0], t[0], &p1[2])
g.f.mul(t[1], t[1], &p2[2])
g.f.mul(t[1], t[1], &p1[1])
g.f.mul(t[0], t[0], &p2[1])
return t[0].equal(t[1]) && t[2].equal(t[3])
}
// InCorrectSubgroup checks whether given point is in correct subgroup.
func (g *G2) InCorrectSubgroup(p *PointG2) bool {
tmp := &PointG2{}
g.MulScalar(tmp, p, q)
return g.IsZero(tmp)
}
// IsOnCurve checks a G2 point is on curve.
func (g *G2) IsOnCurve(p *PointG2) bool {
if g.IsZero(p) {
return true
}
t := g.t
g.f.square(t[0], &p[1])
g.f.square(t[1], &p[0])
g.f.mul(t[1], t[1], &p[0])
g.f.square(t[2], &p[2])
g.f.square(t[3], t[2])
g.f.mul(t[2], t[2], t[3])
g.f.mul(t[2], b2, t[2])
g.f.add(t[1], t[1], t[2])
return t[0].equal(t[1])
}
// IsAffine checks a G2 point whether it is in affine form.
func (g *G2) IsAffine(p *PointG2) bool {
return p[2].isOne()
}
// Affine calculates affine form of given G2 point.
func (g *G2) Affine(p *PointG2) *PointG2 {
if g.IsZero(p) {
return p
}
if !g.IsAffine(p) {
t := g.t
g.f.inverse(t[0], &p[2])
g.f.square(t[1], t[0])
g.f.mul(&p[0], &p[0], t[1])
g.f.mul(t[0], t[0], t[1])
g.f.mul(&p[1], &p[1], t[0])
p[2].one()
}
return p
}
// Add adds two G2 points p1, p2 and assigns the result to point at first argument.
func (g *G2) Add(r, p1, p2 *PointG2) *PointG2 {
// http://www.hyperelliptic.org/EFD/gp/auto-shortw-jacobian-0.html#addition-add-2007-bl
if g.IsZero(p1) {
return r.Set(p2)
}
if g.IsZero(p2) {
return r.Set(p1)
}
t := g.t
g.f.square(t[7], &p1[2])
g.f.mul(t[1], &p2[0], t[7])
g.f.mul(t[2], &p1[2], t[7])
g.f.mul(t[0], &p2[1], t[2])
g.f.square(t[8], &p2[2])
g.f.mul(t[3], &p1[0], t[8])
g.f.mul(t[4], &p2[2], t[8])
g.f.mul(t[2], &p1[1], t[4])
if t[1].equal(t[3]) {
if t[0].equal(t[2]) {
return g.Double(r, p1)
}
return r.Zero()
}
g.f.sub(t[1], t[1], t[3])
g.f.double(t[4], t[1])
g.f.square(t[4], t[4])
g.f.mul(t[5], t[1], t[4])
g.f.sub(t[0], t[0], t[2])
g.f.double(t[0], t[0])
g.f.square(t[6], t[0])
g.f.sub(t[6], t[6], t[5])
g.f.mul(t[3], t[3], t[4])
g.f.double(t[4], t[3])
g.f.sub(&r[0], t[6], t[4])
g.f.sub(t[4], t[3], &r[0])
g.f.mul(t[6], t[2], t[5])
g.f.double(t[6], t[6])
g.f.mul(t[0], t[0], t[4])
g.f.sub(&r[1], t[0], t[6])
g.f.add(t[0], &p1[2], &p2[2])
g.f.square(t[0], t[0])
g.f.sub(t[0], t[0], t[7])
g.f.sub(t[0], t[0], t[8])
g.f.mul(&r[2], t[0], t[1])
return r
}
// Double doubles a G2 point p and assigns the result to the point at first argument.
func (g *G2) Double(r, p *PointG2) *PointG2 {
// http://www.hyperelliptic.org/EFD/gp/auto-shortw-jacobian-0.html#doubling-dbl-2009-l
if g.IsZero(p) {
return r.Set(p)
}
t := g.t
g.f.square(t[0], &p[0])
g.f.square(t[1], &p[1])
g.f.square(t[2], t[1])
g.f.add(t[1], &p[0], t[1])
g.f.square(t[1], t[1])
g.f.sub(t[1], t[1], t[0])
g.f.sub(t[1], t[1], t[2])
g.f.double(t[1], t[1])
g.f.double(t[3], t[0])
g.f.add(t[0], t[3], t[0])
g.f.square(t[4], t[0])
g.f.double(t[3], t[1])
g.f.sub(&r[0], t[4], t[3])
g.f.sub(t[1], t[1], &r[0])
g.f.double(t[2], t[2])
g.f.double(t[2], t[2])
g.f.double(t[2], t[2])
g.f.mul(t[0], t[0], t[1])
g.f.sub(t[1], t[0], t[2])
g.f.mul(t[0], &p[1], &p[2])
r[1].set(t[1])
g.f.double(&r[2], t[0])
return r
}
// Neg negates a G2 point p and assigns the result to the point at first argument.
func (g *G2) Neg(r, p *PointG2) *PointG2 {
r[0].set(&p[0])
g.f.neg(&r[1], &p[1])
r[2].set(&p[2])
return r
}
// Sub subtracts two G2 points p1, p2 and assigns the result to point at first argument.
func (g *G2) Sub(c, a, b *PointG2) *PointG2 {
d := &PointG2{}
g.Neg(d, b)
g.Add(c, a, d)
return c
}
// MulScalar multiplies a point by given scalar value in big.Int and assigns the result to point at first argument.
func (g *G2) MulScalar(c, p *PointG2, e *big.Int) *PointG2 {
q, n := &PointG2{}, &PointG2{}
n.Set(p)
l := e.BitLen()
for i := 0; i < l; i++ {
if e.Bit(i) == 1 {
g.Add(q, q, n)
}
g.Double(n, n)
}
return c.Set(q)
}
// ClearCofactor maps given a G2 point to correct subgroup
func (g *G2) ClearCofactor(p *PointG2) {
g.MulScalar(p, p, cofactorEFFG2)
}
// MultiExp calculates multi exponentiation. Given pairs of G2 point and scalar values
// (P_0, e_0), (P_1, e_1), ... (P_n, e_n) calculates r = e_0 * P_0 + e_1 * P_1 + ... + e_n * P_n
// Length of points and scalars are expected to be equal, otherwise an error is returned.
// Result is assigned to point at first argument.
func (g *G2) MultiExp(r *PointG2, points []*PointG2, powers []*big.Int) (*PointG2, error) {
if len(points) != len(powers) {
return nil, errors.New("point and scalar vectors should be in same length")
}
var c uint32 = 3
if len(powers) >= 32 {
c = uint32(math.Ceil(math.Log10(float64(len(powers)))))
}
bucketSize, numBits := (1<<c)-1, uint32(g.Q().BitLen())
windows := make([]*PointG2, numBits/c+1)
bucket := make([]*PointG2, bucketSize)
acc, sum := g.New(), g.New()
for i := 0; i < bucketSize; i++ {
bucket[i] = g.New()
}
mask := (uint64(1) << c) - 1
j := 0
var cur uint32
for cur <= numBits {
acc.Zero()
bucket = make([]*PointG2, (1<<c)-1)
for i := 0; i < len(bucket); i++ {
bucket[i] = g.New()
}
for i := 0; i < len(powers); i++ {
s0 := powers[i].Uint64()
index := uint(s0 & mask)
if index != 0 {
g.Add(bucket[index-1], bucket[index-1], points[i])
}
powers[i] = new(big.Int).Rsh(powers[i], uint(c))
}
sum.Zero()
for i := len(bucket) - 1; i >= 0; i-- {
g.Add(sum, sum, bucket[i])
g.Add(acc, acc, sum)
}
windows[j] = g.New()
windows[j].Set(acc)
j++
cur += c
}
acc.Zero()
for i := len(windows) - 1; i >= 0; i-- {
for j := uint32(0); j < c; j++ {
g.Double(acc, acc)
}
g.Add(acc, acc, windows[i])
}
return r.Set(acc), nil
}
// MapToCurve given a byte slice returns a valid G2 point.
// This mapping function implements the Simplified Shallue-van de Woestijne-Ulas method.
// https://tools.ietf.org/html/draft-irtf-cfrg-hash-to-curve-05#section-6.6.2
// Input byte slice should be a valid field element, otherwise an error is returned.
func (g *G2) MapToCurve(in []byte) (*PointG2, error) {
fp2 := g.f
u, err := fp2.fromBytes(in)
if err != nil {
return nil, err
}
x, y := swuMapG2(fp2, u)
isogenyMapG2(fp2, x, y)
z := new(fe2).one()
q := &PointG2{*x, *y, *z}
g.ClearCofactor(q)
return g.Affine(q), nil
}