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g1.go
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g1.go
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package bn256
import (
"crypto/rand"
"errors"
"io"
"math/big"
"math/bits"
"sync"
)
func randomK(r io.Reader) (k *big.Int, err error) {
for {
k, err = rand.Int(r, Order)
if err != nil || k.Sign() > 0 {
return
}
}
}
// G1 is an abstract cyclic group. The zero value is suitable for use as the
// output of an operation, but cannot be used as an input.
type G1 struct {
p *curvePoint
}
// Gen1 is the generator of G1.
var Gen1 = &G1{curveGen}
var g1GeneratorTable *[32 * 2]curvePointTable
var g1GeneratorTableOnce sync.Once
func (g *G1) generatorTable() *[32 * 2]curvePointTable {
g1GeneratorTableOnce.Do(func() {
g1GeneratorTable = new([32 * 2]curvePointTable)
base := NewCurveGenerator()
for i := 0; i < 32*2; i++ {
g1GeneratorTable[i][0] = &curvePoint{}
g1GeneratorTable[i][0].Set(base)
for j := 1; j < 15; j += 2 {
g1GeneratorTable[i][j] = &curvePoint{}
g1GeneratorTable[i][j].Double(g1GeneratorTable[i][j/2])
g1GeneratorTable[i][j+1] = &curvePoint{}
g1GeneratorTable[i][j+1].Add(g1GeneratorTable[i][j], base)
}
base.Double(base)
base.Double(base)
base.Double(base)
base.Double(base)
}
})
return g1GeneratorTable
}
// RandomG1 returns x and g₁ˣ where x is a random, non-zero number read from r.
func RandomG1(r io.Reader) (*big.Int, *G1, error) {
k, err := randomK(r)
if err != nil {
return nil, nil, err
}
g1, err := new(G1).ScalarBaseMult(NormalizeScalar(k.Bytes()))
return k, g1, err
}
func (g *G1) String() string {
return "sm9.G1" + g.p.String()
}
func NormalizeScalar(scalar []byte) []byte {
if len(scalar) == 32 {
return scalar
}
s := new(big.Int).SetBytes(scalar)
if len(scalar) > 32 {
s.Mod(s, Order)
}
out := make([]byte, 32)
return s.FillBytes(out)
}
// ScalarBaseMult sets e to scaler*g where g is the generator of the group and then
// returns e.
func (e *G1) ScalarBaseMult(scalar []byte) (*G1, error) {
if len(scalar) != 32 {
return nil, errors.New("invalid scalar length")
}
if e.p == nil {
e.p = &curvePoint{}
}
//e.p.Mul(curveGen, k)
tables := e.generatorTable()
// This is also a scalar multiplication with a four-bit window like in
// ScalarMult, but in this case the doublings are precomputed. The value
// [windowValue]G added at iteration k would normally get doubled
// (totIterations-k)×4 times, but with a larger precomputation we can
// instead add [2^((totIterations-k)×4)][windowValue]G and avoid the
// doublings between iterations.
t := NewCurvePoint()
e.p.SetInfinity()
tableIndex := len(tables) - 1
for _, byte := range scalar {
windowValue := byte >> 4
tables[tableIndex].Select(t, windowValue)
e.p.Add(e.p, t)
tableIndex--
windowValue = byte & 0b1111
tables[tableIndex].Select(t, windowValue)
e.p.Add(e.p, t)
tableIndex--
}
return e, nil
}
// ScalarMult sets e to a*k and then returns e.
func (e *G1) ScalarMult(a *G1, scalar []byte) (*G1, error) {
if e.p == nil {
e.p = &curvePoint{}
}
//e.p.Mul(a.p, k)
// Compute a curvePointTable for the base point a.
var table = curvePointTable{NewCurvePoint(), NewCurvePoint(), NewCurvePoint(),
NewCurvePoint(), NewCurvePoint(), NewCurvePoint(), NewCurvePoint(),
NewCurvePoint(), NewCurvePoint(), NewCurvePoint(), NewCurvePoint(),
NewCurvePoint(), NewCurvePoint(), NewCurvePoint(), NewCurvePoint()}
table[0].Set(a.p)
for i := 1; i < 15; i += 2 {
table[i].Double(table[i/2])
table[i+1].Add(table[i], a.p)
}
// Instead of doing the classic double-and-add chain, we do it with a
// four-bit window: we double four times, and then add [0-15]P.
t := &G1{NewCurvePoint()}
e.p.SetInfinity()
for i, byte := range scalar {
// No need to double on the first iteration, as p is the identity at
// this point, and [N]∞ = ∞.
if i != 0 {
e.Double(e)
e.Double(e)
e.Double(e)
e.Double(e)
}
windowValue := byte >> 4
table.Select(t.p, windowValue)
e.Add(e, t)
e.Double(e)
e.Double(e)
e.Double(e)
e.Double(e)
windowValue = byte & 0b1111
table.Select(t.p, windowValue)
e.Add(e, t)
}
return e, nil
}
// Add sets e to a+b and then returns e.
func (e *G1) Add(a, b *G1) *G1 {
if e.p == nil {
e.p = &curvePoint{}
}
e.p.Add(a.p, b.p)
return e
}
// Double sets e to [2]a and then returns e.
func (e *G1) Double(a *G1) *G1 {
if e.p == nil {
e.p = &curvePoint{}
}
e.p.Double(a.p)
return e
}
// Neg sets e to -a and then returns e.
func (e *G1) Neg(a *G1) *G1 {
if e.p == nil {
e.p = &curvePoint{}
}
e.p.Neg(a.p)
return e
}
// Set sets e to a and then returns e.
func (e *G1) Set(a *G1) *G1 {
if e.p == nil {
e.p = &curvePoint{}
}
e.p.Set(a.p)
return e
}
// Marshal converts e to a byte slice.
func (e *G1) Marshal() []byte {
// Each value is a 256-bit number.
const numBytes = 256 / 8
ret := make([]byte, numBytes*2)
e.fillBytes(ret)
return ret
}
// MarshalUncompressed converts e to a byte slice with prefix
func (e *G1) MarshalUncompressed() []byte {
// Each value is a 256-bit number.
const numBytes = 256 / 8
ret := make([]byte, numBytes*2+1)
ret[0] = 4
e.fillBytes(ret[1:])
return ret
}
// MarshalCompressed converts e to a byte slice with compress prefix.
// If the point is not on the curve (or is the conventional point at infinity), the behavior is undefined.
func (e *G1) MarshalCompressed() []byte {
// Each value is a 256-bit number.
const numBytes = 256 / 8
ret := make([]byte, numBytes+1)
if e.p == nil {
e.p = &curvePoint{}
}
e.p.MakeAffine()
temp := &gfP{}
montDecode(temp, &e.p.y)
temp.Marshal(ret[1:])
ret[0] = (ret[numBytes] & 1) | 2
montDecode(temp, &e.p.x)
temp.Marshal(ret[1:])
return ret
}
// UnmarshalCompressed sets e to the result of converting the output of Marshal back into
// a group element and then returns e.
func (e *G1) UnmarshalCompressed(data []byte) ([]byte, error) {
// Each value is a 256-bit number.
const numBytes = 256 / 8
if len(data) < 1+numBytes {
return nil, errors.New("sm9.G1: not enough data")
}
if data[0] != 2 && data[0] != 3 { // compressed form
return nil, errors.New("sm9.G1: invalid point compress byte")
}
if e.p == nil {
e.p = &curvePoint{}
} else {
e.p.x, e.p.y = gfP{0}, gfP{0}
}
e.p.x.Unmarshal(data[1:])
montEncode(&e.p.x, &e.p.x)
x3 := e.p.polynomial(&e.p.x)
e.p.y.Sqrt(x3)
montDecode(x3, &e.p.y)
if byte(x3[0]&1) != data[0]&1 {
gfpNeg(&e.p.y, &e.p.y)
}
if e.p.x == *zero && e.p.y == *zero {
// This is the point at infinity.
e.p.y = *newGFp(1)
e.p.z = gfP{0}
e.p.t = gfP{0}
} else {
e.p.z = *newGFp(1)
e.p.t = *newGFp(1)
if !e.p.IsOnCurve() {
return nil, errors.New("sm9.G1: malformed point")
}
}
return data[numBytes+1:], nil
}
func (e *G1) fillBytes(buffer []byte) {
const numBytes = 256 / 8
if e.p == nil {
e.p = &curvePoint{}
}
e.p.MakeAffine()
if e.p.IsInfinity() {
return
}
temp := &gfP{}
montDecode(temp, &e.p.x)
temp.Marshal(buffer)
montDecode(temp, &e.p.y)
temp.Marshal(buffer[numBytes:])
}
// Unmarshal sets e to the result of converting the output of Marshal back into
// a group element and then returns e.
func (e *G1) Unmarshal(m []byte) ([]byte, error) {
// Each value is a 256-bit number.
const numBytes = 256 / 8
if len(m) < 2*numBytes {
return nil, errors.New("sm9.G1: not enough data")
}
if e.p == nil {
e.p = &curvePoint{}
} else {
e.p.x, e.p.y = gfP{0}, gfP{0}
}
e.p.x.Unmarshal(m)
e.p.y.Unmarshal(m[numBytes:])
montEncode(&e.p.x, &e.p.x)
montEncode(&e.p.y, &e.p.y)
if e.p.x == *zero && e.p.y == *zero {
// This is the point at infinity.
e.p.y = *newGFp(1)
e.p.z = gfP{0}
e.p.t = gfP{0}
} else {
e.p.z = *newGFp(1)
e.p.t = *newGFp(1)
if !e.p.IsOnCurve() {
return nil, errors.New("sm9.G1: malformed point")
}
}
return m[2*numBytes:], nil
}
// Equal compare e and other
func (e *G1) Equal(other *G1) bool {
if e.p == nil && other.p == nil {
return true
}
return e.p.x == other.p.x &&
e.p.y == other.p.y &&
e.p.z == other.p.z &&
e.p.t == other.p.t
}
// IsOnCurve returns true if e is on the curve.
func (e *G1) IsOnCurve() bool {
return e.p.IsOnCurve()
}
type G1Curve struct {
params *CurveParams
g G1
}
var g1Curve = &G1Curve{
params: &CurveParams{
Name: "sm9",
BitSize: 256,
P: bigFromHex("B640000002A3A6F1D603AB4FF58EC74521F2934B1A7AEEDBE56F9B27E351457D"),
N: bigFromHex("B640000002A3A6F1D603AB4FF58EC74449F2934B18EA8BEEE56EE19CD69ECF25"),
B: bigFromHex("0000000000000000000000000000000000000000000000000000000000000005"),
Gx: bigFromHex("93DE051D62BF718FF5ED0704487D01D6E1E4086909DC3280E8C4E4817C66DDDD"),
Gy: bigFromHex("21FE8DDA4F21E607631065125C395BBC1C1C00CBFA6024350C464CD70A3EA616"),
},
g: G1{},
}
func (g1 *G1Curve) pointFromAffine(x, y *big.Int) (a *G1, err error) {
a = &G1{&curvePoint{}}
if x.Sign() == 0 {
a.p.SetInfinity()
return a, nil
}
// Reject values that would not get correctly encoded.
if x.Sign() < 0 || y.Sign() < 0 {
return a, errors.New("negative coordinate")
}
if x.BitLen() > g1.params.BitSize || y.BitLen() > g1.params.BitSize {
return a, errors.New("overflowing coordinate")
}
a.p.x = *fromBigInt(x)
a.p.y = *fromBigInt(y)
a.p.z = *newGFp(1)
a.p.t = *newGFp(1)
if !a.p.IsOnCurve() {
return a, errors.New("point not on G1 curve")
}
return a, nil
}
func (g1 *G1Curve) Params() *CurveParams {
return g1.params
}
// normalizeScalar brings the scalar within the byte size of the order of the
// curve, as expected by the nistec scalar multiplication functions.
func (curve *G1Curve) normalizeScalar(scalar []byte) []byte {
byteSize := (curve.params.N.BitLen() + 7) / 8
s := new(big.Int).SetBytes(scalar)
if len(scalar) > byteSize {
s.Mod(s, curve.params.N)
}
out := make([]byte, byteSize)
return s.FillBytes(out)
}
func (g1 *G1Curve) ScalarBaseMult(scalar []byte) (*big.Int, *big.Int) {
scalar = g1.normalizeScalar(scalar)
p, err := g1.g.ScalarBaseMult(scalar)
if err != nil {
panic("sm9: g1 rejected normalized scalar")
}
res := p.Marshal()
return new(big.Int).SetBytes(res[:32]), new(big.Int).SetBytes(res[32:])
}
func (g1 *G1Curve) ScalarMult(Bx, By *big.Int, scalar []byte) (*big.Int, *big.Int) {
a, err := g1.pointFromAffine(Bx, By)
if err != nil {
panic("sm9: ScalarMult was called on an invalid point")
}
scalar = g1.normalizeScalar(scalar)
p, err := g1.g.ScalarMult(a, scalar)
if err != nil {
panic("sm9: g1 rejected normalized scalar")
}
res := p.Marshal()
return new(big.Int).SetBytes(res[:32]), new(big.Int).SetBytes(res[32:])
}
func (g1 *G1Curve) Add(x1, y1, x2, y2 *big.Int) (*big.Int, *big.Int) {
a, err := g1.pointFromAffine(x1, y1)
if err != nil {
panic("sm9: Add was called on an invalid point")
}
b, err := g1.pointFromAffine(x2, y2)
if err != nil {
panic("sm9: Add was called on an invalid point")
}
res := g1.g.Add(a, b).Marshal()
return new(big.Int).SetBytes(res[:32]), new(big.Int).SetBytes(res[32:])
}
func (g1 *G1Curve) Double(x, y *big.Int) (*big.Int, *big.Int) {
a, err := g1.pointFromAffine(x, y)
if err != nil {
panic("sm9: Double was called on an invalid point")
}
res := g1.g.Double(a).Marshal()
return new(big.Int).SetBytes(res[:32]), new(big.Int).SetBytes(res[32:])
}
func (g1 *G1Curve) IsOnCurve(x, y *big.Int) bool {
_, err := g1.pointFromAffine(x, y)
return err == nil
}
func lessThanP(x *gfP) int {
var b uint64
_, b = bits.Sub64(x[0], p2[0], b)
_, b = bits.Sub64(x[1], p2[1], b)
_, b = bits.Sub64(x[2], p2[2], b)
_, b = bits.Sub64(x[3], p2[3], b)
return int(b)
}
func (curve *G1Curve) UnmarshalCompressed(data []byte) (x, y *big.Int) {
if len(data) != 33 || (data[0] != 2 && data[0] != 3) {
return nil, nil
}
r := &gfP{}
r.Unmarshal(data[1:33])
if lessThanP(r) == 0 {
return nil, nil
}
x = new(big.Int).SetBytes(data[1:33])
p := &curvePoint{}
montEncode(r, r)
p.x = *r
p.z = *newGFp(1)
p.t = *newGFp(1)
y2 := &gfP{}
gfpMul(y2, r, r)
gfpMul(y2, y2, r)
gfpAdd(y2, y2, curveB)
y2.Sqrt(y2)
p.y = *y2
if !p.IsOnCurve() {
return nil, nil
}
montDecode(y2, y2)
ret := make([]byte, 32)
y2.Marshal(ret)
y = new(big.Int).SetBytes(ret)
if byte(y.Bit(0)) != data[0]&1 {
gfpNeg(y2, y2)
y2.Marshal(ret)
y.SetBytes(ret)
}
return x, y
}
func (curve *G1Curve) Unmarshal(data []byte) (x, y *big.Int) {
if len(data) != 65 || (data[0] != 4) {
return nil, nil
}
x1 := &gfP{}
x1.Unmarshal(data[1:33])
y1 := &gfP{}
y1.Unmarshal(data[33:])
if lessThanP(x1) == 0 || lessThanP(y1) == 0 {
return nil, nil
}
montEncode(x1, x1)
montEncode(y1, y1)
p := &curvePoint{
x: *x1,
y: *y1,
z: *newGFp(1),
t: *newGFp(1),
}
if !p.IsOnCurve() {
return nil, nil
}
x = new(big.Int).SetBytes(data[1:33])
y = new(big.Int).SetBytes(data[33:])
return x, y
}