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pairing.go
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pairing.go
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// Copyright 2020 ConsenSys AG
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package bw6633
import (
"errors"
"github.com/consensys/gnark-crypto/ecc/bw6-633/fp"
"github.com/consensys/gnark-crypto/ecc/bw6-633/internal/fptower"
)
// GT target group of the pairing
type GT = fptower.E6
type lineEvaluation struct {
r0 fp.Element
r1 fp.Element
r2 fp.Element
}
// Pair calculates the reduced pairing for a set of points
// ∏ᵢ e(Pᵢ, Qᵢ).
//
// This function doesn't check that the inputs are in the correct subgroup. See IsInSubGroup.
func Pair(P []G1Affine, Q []G2Affine) (GT, error) {
f, err := MillerLoop(P, Q)
if err != nil {
return GT{}, err
}
return FinalExponentiation(&f), nil
}
// PairingCheck calculates the reduced pairing for a set of points and returns True if the result is One
// ∏ᵢ e(Pᵢ, Qᵢ) =? 1
//
// This function doesn't check that the inputs are in the correct subgroup. See IsInSubGroup.
func PairingCheck(P []G1Affine, Q []G2Affine) (bool, error) {
f, err := Pair(P, Q)
if err != nil {
return false, err
}
var one GT
one.SetOne()
return f.Equal(&one), nil
}
// FinalExponentiation computes the exponentiation (∏ᵢ zᵢ)ᵈ
// where d = (p^6-1)/r = (p^6-1)/Φ_6(p) ⋅ Φ_6(p)/r = (p^3-1)(p+1)(p^2 - p +1)/r
// we use instead d=s ⋅ (p^3-1)(p+1)(p^2 - p +1)/r
// where s is the cofactor 3(x_0+1) (El Housni and Guillevic)
func FinalExponentiation(z *GT, _z ...*GT) GT {
var result GT
result.Set(z)
for _, e := range _z {
result.Mul(&result, e)
}
var buf GT
// Easy part
// (p^3-1)(p+1)
buf.Conjugate(&result)
result.Inverse(&result)
buf.Mul(&buf, &result)
result.Frobenius(&buf).
Mul(&result, &buf)
var one GT
one.SetOne()
if result.Equal(&one) {
return result
}
// Hard part (up to permutation)
// El Housni and Guillevic
// https://eprint.iacr.org/2021/1359.pdf
var m [11]GT
var f10, _m1, _m3, _m4, _m5, _m7, _m8, _m8m5, _m6, f11, f11f10, f12, f1, f1u, f1q, f1a GT
m[0].Set(&result)
for i := 1; i < 11; i++ {
m[i].Expt(&m[i-1])
}
result.Mul(&m[3], &m[1]).
Conjugate(&result).
Mul(&result, &m[2]).
Mul(&result, &m[0]).
CyclotomicSquare(&result).
Mul(&result, &m[4])
buf.Frobenius(&m[0]).Conjugate(&buf)
result.Mul(&result, &buf)
buf.CyclotomicSquare(&result).
CyclotomicSquare(&buf).
CyclotomicSquare(&buf)
result.Mul(&result, &buf)
_m1.Conjugate(&m[1])
_m3.Conjugate(&m[3])
_m4.Conjugate(&m[4])
_m5.Conjugate(&m[5])
_m7.Conjugate(&m[7])
f10.Mul(&m[4], &_m3).
CyclotomicSquare(&f10).
Mul(&f10, &m[2]).
Mul(&f10, &m[6]).
Mul(&f10, &_m5).
CyclotomicSquare(&f10).
Mul(&f10, &_m1).
Mul(&f10, &_m5).
Mul(&f10, &_m7).
CyclotomicSquare(&f10).
Mul(&f10, &m[0]).
Mul(&f10, &m[2]).
Mul(&f10, &m[3]).
Mul(&f10, &_m1).
CyclotomicSquare(&f10).
Mul(&f10, &m[0]).
Mul(&f10, &m[8]).
Mul(&f10, &_m4)
_m8.Conjugate(&m[8])
_m6.Conjugate(&m[6])
_m8m5.Mul(&m[5], &_m8)
f11.Mul(&m[7], &_m6).
CyclotomicSquare(&f11).
Mul(&f11, &m[2]).
Mul(&f11, &_m3).
Mul(&f11, &_m8m5).
CyclotomicSquare(&f11).
Mul(&f11, &_m8m5).
Mul(&f11, &m[9]).
Mul(&f11, &_m1)
buf.CyclotomicSquare(&f11)
f11.Mul(&buf, &f11)
f11f10.Mul(&f11, &f10)
buf.CyclotomicSquare(&f11f10)
f11f10.Mul(&f11f10, &buf)
f12.Mul(&m[0], &m[1]).
Mul(&f12, &m[2]).
Mul(&f12, &m[8]).
Mul(&f12, &m[10])
buf.CyclotomicSquare(&m[5])
f12.Mul(&f12, &buf)
buf.CyclotomicSquare(&m[9]).
Mul(&buf, &m[6]).
Mul(&buf, &m[4]).
Conjugate(&buf)
f12.Mul(&f12, &buf)
buf.CyclotomicSquare(&f12). // cyclo exp by 13: (ht**2+3*hy**2)//4
Mul(&buf, &f12).
CyclotomicSquare(&buf).
CyclotomicSquare(&buf)
f12.Mul(&f12, &buf)
f1.Mul(&f11f10, &f12)
f1u.Expt(&f1)
f1q.Mul(&f1u, &f1).
Frobenius(&f1q)
f1a.Conjugate(&f1u).
Mul(&f1a, &f1).
Expt(&f1a).
Expt(&f1a).
Expt(&f1a).
Expt(&f1a)
f1.Conjugate(&f1)
f1a.Mul(&f1a, &f1)
result.Mul(&result, &f1a).
Mul(&result, &f1q)
return result
}
// MillerLoop Optimal Tate alternative (or twisted ate or Eta revisited)
// computes the multi-Miller loop ∏ᵢ MillerLoop(Pᵢ, Qᵢ)
// Alg.2 in https://eprint.iacr.org/2021/1359.pdf
func MillerLoop(P []G1Affine, Q []G2Affine) (GT, error) {
// check input size match
n := len(P)
if n == 0 || n != len(Q) {
return GT{}, errors.New("invalid inputs sizes")
}
// filter infinity points
p0 := make([]G1Affine, 0, n)
q := make([]G2Affine, 0, n)
for k := 0; k < n; k++ {
if P[k].IsInfinity() || Q[k].IsInfinity() {
continue
}
p0 = append(p0, P[k])
q = append(q, Q[k])
}
n = len(q)
// precomputations
pProj0 := make([]g1Proj, n)
p1 := make([]G1Affine, n)
pProj01 := make([]g1Proj, n) // P0+P1
pProj10 := make([]g1Proj, n) // P0-P1
l01 := make([]lineEvaluation, n)
l10 := make([]lineEvaluation, n)
for k := 0; k < n; k++ {
p1[k].Y.Set(&p0[k].Y)
p1[k].X.Mul(&p0[k].X, &thirdRootOneG1)
p0[k].Neg(&p0[k])
pProj0[k].FromAffine(&p0[k])
// l_{p0,p1}(q)
pProj01[k].Set(&pProj0[k])
pProj01[k].addMixedStep(&l01[k], &p1[k])
l01[k].r1.Mul(&l01[k].r1, &q[k].X)
l01[k].r0.Mul(&l01[k].r0, &q[k].Y)
// l_{-p0,p1}(q)
pProj10[k].Neg(&pProj0[k])
pProj10[k].addMixedStep(&l10[k], &p1[k])
l10[k].r1.Mul(&l10[k].r1, &q[k].X)
l10[k].r0.Mul(&l10[k].r0, &q[k].Y)
}
p01 := BatchProjectiveToAffineG1(pProj01)
p10 := BatchProjectiveToAffineG1(pProj10)
// f_{a0+λ*a1,P}(Q)
var result GT
result.SetOne()
var l, l0 lineEvaluation
var prodLines [5]fp.Element
var j int8
if n >= 1 {
// i = len(loopCounter0) - 2, separately to avoid an E12 Square
// (Square(res) = 1² = 1)
// j = 0
// k = 0, separately to avoid MulBy034 (res × ℓ)
// (assign line to res)
// pProj0[0] ← 2pProj0[0] and l0 the tangent ℓ passing 2pProj0[0]
pProj0[0].doubleStep(&l0)
// line evaluation at Q[0] (assign)
result.B1.A0.Mul(&l0.r1, &q[0].X)
result.B0.A0.Mul(&l0.r0, &q[0].Y)
result.B1.A1.Set(&l0.r2)
}
// k = 1
if n >= 2 {
// pProj0[1] ← 2pProj0[1] and l0 the tangent ℓ passing 2pProj0[1]
pProj0[1].doubleStep(&l0)
// line evaluation at Q[0]
l0.r1.Mul(&l0.r1, &q[1].X)
l0.r0.Mul(&l0.r0, &q[1].Y)
// ℓ × res
prodLines = fptower.Mul034By034(&l0.r0, &l0.r1, &l0.r2, &result.B0.A0, &result.B1.A0, &result.B1.A1)
result.B0.A0 = prodLines[0]
result.B0.A1 = prodLines[1]
result.B0.A2 = prodLines[2]
result.B1.A0 = prodLines[3]
result.B1.A1 = prodLines[4]
}
// k >= 2
for k := 2; k < n; k++ {
// pProj0[1] ← 2pProj0[1] and l0 the tangent ℓ passing 2pProj0[1]
pProj0[k].doubleStep(&l0)
// line evaluation at Q[k]
l0.r1.Mul(&l0.r1, &q[k].X)
l0.r0.Mul(&l0.r0, &q[k].Y)
// ℓ × res
result.MulBy034(&l0.r0, &l0.r1, &l0.r2)
}
var tmp G1Affine
for i := len(loopCounter0) - 3; i >= 1; i-- {
// (∏ᵢfᵢ)²
// mutualize the square among n Miller loops
result.Square(&result)
j = loopCounter0[i]*3 + loopCounter1[i]
for k := 0; k < n; k++ {
// pProj0[1] ← 2pProj0[1] and l0 the tangent ℓ passing 2pProj0[1]
pProj0[k].doubleStep(&l0)
// line evaluation at Q[k]
l0.r1.Mul(&l0.r1, &q[k].X)
l0.r0.Mul(&l0.r0, &q[k].Y)
switch j {
case -4:
tmp.Neg(&p01[k])
// pProj0[k] ← pProj0[k]-p01[k] and
// l the line ℓ passing pProj0[k] and -p01[k]
pProj0[k].addMixedStep(&l, &tmp)
// line evaluation at Q[k]
l.r1.Mul(&l.r1, &q[k].X)
l.r0.Mul(&l.r0, &q[k].Y)
// ℓ × ℓ
prodLines = fptower.Mul034By034(&l.r0, &l.r1, &l.r2, &l01[k].r0, &l01[k].r1, &l01[k].r2)
// ℓ × res
result.MulBy034(&l0.r0, &l0.r1, &l0.r2)
// (ℓ × ℓ) × res
result.MulBy01234(&prodLines)
case -3:
tmp.Neg(&p1[k])
// pProj0[k] ← pProj0[k]-p1[k] and
// l the line ℓ passing pProj0[k] and -p1[k]
pProj0[k].addMixedStep(&l, &tmp)
// line evaluation at Q[k]
l.r1.Mul(&l.r1, &q[k].X)
l.r0.Mul(&l.r0, &q[k].Y)
// ℓ × ℓ
prodLines = fptower.Mul034By034(&l.r0, &l.r1, &l.r2, &l0.r0, &l0.r1, &l0.r2)
// (ℓ × ℓ) × res
result.MulBy01234(&prodLines)
case -2:
// pProj0[k] ← pProj0[k]+p10[k] and
// l the line ℓ passing pProj0[k] and p10[k]
pProj0[k].addMixedStep(&l, &p10[k])
// line evaluation at Q[k]
l.r1.Mul(&l.r1, &q[k].X)
l.r0.Mul(&l.r0, &q[k].Y)
// ℓ × ℓ
prodLines = fptower.Mul034By034(&l.r0, &l.r1, &l.r2, &l01[k].r0, &l01[k].r1, &l01[k].r2)
// ℓ × res
result.MulBy034(&l0.r0, &l0.r1, &l0.r2)
// (ℓ × ℓ) × res
result.MulBy01234(&prodLines)
case -1:
tmp.Neg(&p0[k])
// pProj0[k] ← pProj0[k]-p0[k] and
// l the line ℓ passing pProj0[k] and -p0[k]
pProj0[k].addMixedStep(&l, &tmp)
// line evaluation at Q[k]
l.r1.Mul(&l.r1, &q[k].X)
l.r0.Mul(&l.r0, &q[k].Y)
// ℓ × ℓ
prodLines = fptower.Mul034By034(&l.r0, &l.r1, &l.r2, &l0.r0, &l0.r1, &l0.r2)
// (ℓ × ℓ) × res
result.MulBy01234(&prodLines)
case 0:
// ℓ × res
result.MulBy034(&l0.r0, &l0.r1, &l0.r2)
case 1:
// pProj0[k] ← pProj0[k]+p0[k] and
// l the line ℓ passing pProj0[k] and p0[k]
pProj0[k].addMixedStep(&l, &p0[k])
// line evaluation at Q[k]
l.r1.Mul(&l.r1, &q[k].X)
l.r0.Mul(&l.r0, &q[k].Y)
// ℓ × ℓ
prodLines = fptower.Mul034By034(&l.r0, &l.r1, &l.r2, &l0.r0, &l0.r1, &l0.r2)
// (ℓ × ℓ) × res
result.MulBy01234(&prodLines)
case 2:
tmp.Neg(&p10[k])
// pProj0[k] ← pProj0[k]-p10[k] and
// l the line ℓ passing pProj0[k] and -p10[k]
pProj0[k].addMixedStep(&l, &tmp)
// line evaluation at Q[k]
l.r1.Mul(&l.r1, &q[k].X)
l.r0.Mul(&l.r0, &q[k].Y)
// ℓ × ℓ
prodLines = fptower.Mul034By034(&l.r0, &l.r1, &l.r2, &l01[k].r0, &l01[k].r1, &l01[k].r2)
// ℓ × res
result.MulBy034(&l0.r0, &l0.r1, &l0.r2)
// (ℓ × ℓ) × res
result.MulBy01234(&prodLines)
case 3:
// pProj0[k] ← pProj0[k]+p1[k] and
// l the line ℓ passing pProj0[k] and p1[k]
pProj0[k].addMixedStep(&l, &p1[k])
// line evaluation at Q[k]
l.r1.Mul(&l.r1, &q[k].X)
l.r0.Mul(&l.r0, &q[k].Y)
// (ℓ × ℓ) × res
prodLines = fptower.Mul034By034(&l.r0, &l.r1, &l.r2, &l0.r0, &l0.r1, &l0.r2)
// (ℓ × ℓ) × res
result.MulBy01234(&prodLines)
case 4:
// pProj0[k] ← pProj0[k]+p01[k] and
// l the line ℓ passing pProj0[k] and p01[k]
pProj0[k].addMixedStep(&l, &p01[k])
// line evaluation at Q[k]
l.r1.Mul(&l.r1, &q[k].X)
l.r0.Mul(&l.r0, &q[k].Y)
// ℓ × ℓ
prodLines = fptower.Mul034By034(&l.r0, &l.r1, &l.r2, &l01[k].r0, &l01[k].r1, &l01[k].r2)
// ℓ × res
result.MulBy034(&l0.r0, &l0.r1, &l0.r2)
// (ℓ × ℓ) × res
result.MulBy01234(&prodLines)
default:
return GT{}, errors.New("invalid loopCounter")
}
}
}
// i = 0, separately to avoid a point addition
// j = 1
result.Square(&result)
for k := 0; k < n; k++ {
// pProj0[k] ← 2pProj0[k] and l0 the tangent ℓ passing 2pProj0[k]
pProj0[k].doubleStep(&l0)
// line evaluation at Q[k]
l0.r1.Mul(&l0.r1, &q[k].X)
l0.r0.Mul(&l0.r0, &q[k].Y)
// l the line passing pProj0[k] and p0
pProj0[k].lineCompute(&l, &p0[k])
// line evaluation at Q[k]
l.r1.Mul(&l.r1, &q[k].X)
l.r0.Mul(&l.r0, &q[k].Y)
// ℓ × ℓ
prodLines = fptower.Mul034By034(&l.r0, &l.r1, &l.r2, &l0.r0, &l0.r1, &l0.r2)
// (ℓ × ℓ) × res
result.MulBy01234(&prodLines)
}
return result, nil
}
// doubleStep doubles a point in Homogenous projective coordinates, and evaluates the line in Miller loop
// https://eprint.iacr.org/2013/722.pdf (Section 4.3)
func (p *g1Proj) doubleStep(evaluations *lineEvaluation) {
// get some Element from our pool
var t1, A, B, C, D, E, EE, F, G, H, I, J, K fp.Element
A.Mul(&p.x, &p.y)
A.Halve()
B.Square(&p.y)
C.Square(&p.z)
D.Double(&C).
Add(&D, &C)
// E.Mul(&D, &bCurveCoeff)
E.Double(&D).
Double(&E)
F.Double(&E).
Add(&F, &E)
G.Add(&B, &F)
G.Halve()
H.Add(&p.y, &p.z).
Square(&H)
t1.Add(&B, &C)
H.Sub(&H, &t1)
I.Sub(&E, &B)
J.Square(&p.x)
EE.Square(&E)
K.Double(&EE).
Add(&K, &EE)
// X, Y, Z
p.x.Sub(&B, &F).
Mul(&p.x, &A)
p.y.Square(&G).
Sub(&p.y, &K)
p.z.Mul(&B, &H)
// Line evaluation
evaluations.r0.Neg(&H)
evaluations.r1.Double(&J).
Add(&evaluations.r1, &J)
evaluations.r2.Set(&I)
}
// addMixedStep point addition in Mixed Homogenous projective and Affine coordinates
// https://eprint.iacr.org/2013/722.pdf (Section 4.3)
func (p *g1Proj) addMixedStep(evaluations *lineEvaluation, a *G1Affine) {
// get some Element from our pool
var Y2Z1, X2Z1, O, L, C, D, E, F, G, H, t0, t1, t2, J fp.Element
Y2Z1.Mul(&a.Y, &p.z)
O.Sub(&p.y, &Y2Z1)
X2Z1.Mul(&a.X, &p.z)
L.Sub(&p.x, &X2Z1)
C.Square(&O)
D.Square(&L)
E.Mul(&L, &D)
F.Mul(&p.z, &C)
G.Mul(&p.x, &D)
t0.Double(&G)
H.Add(&E, &F).
Sub(&H, &t0)
t1.Mul(&p.y, &E)
// X, Y, Z
p.x.Mul(&L, &H)
p.y.Sub(&G, &H).
Mul(&p.y, &O).
Sub(&p.y, &t1)
p.z.Mul(&E, &p.z)
t2.Mul(&L, &a.Y)
J.Mul(&a.X, &O).
Sub(&J, &t2)
// Line evaluation
evaluations.r0.Set(&L)
evaluations.r1.Neg(&O)
evaluations.r2.Set(&J)
}
// lineCompute computes the line through p in Homogenous projective coordinates
// and a in affine coordinates. It does not compute the resulting point p+a.
func (p *g1Proj) lineCompute(evaluations *lineEvaluation, a *G1Affine) {
// get some Element from our pool
var Y2Z1, X2Z1, O, L, t2, J fp.Element
Y2Z1.Mul(&a.Y, &p.z)
O.Sub(&p.y, &Y2Z1)
X2Z1.Mul(&a.X, &p.z)
L.Sub(&p.x, &X2Z1)
t2.Mul(&L, &a.Y)
J.Mul(&a.X, &O).
Sub(&J, &t2)
// Line evaluation
evaluations.r0.Set(&L)
evaluations.r1.Neg(&O)
evaluations.r2.Set(&J)
}