| // Copyright 2022 The Go Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style |
| // license that can be found in the LICENSE file. |
| |
| //go:build ignore |
| |
| package main |
| |
| // Running this generator requires addchain v0.4.0, which can be installed with |
| // |
| // go install github.com/mmcloughlin/addchain/cmd/addchain@v0.4.0 |
| // |
| |
| import ( |
| "bytes" |
| "crypto/elliptic" |
| "fmt" |
| "go/format" |
| "io" |
| "log" |
| "math/big" |
| "os" |
| "os/exec" |
| "strings" |
| "text/template" |
| ) |
| |
| var curves = []struct { |
| P string |
| Element string |
| Params *elliptic.CurveParams |
| BuildTags string |
| }{ |
| { |
| P: "P224", |
| Element: "fiat.P224Element", |
| Params: elliptic.P224().Params(), |
| }, |
| { |
| P: "P256", |
| Element: "fiat.P256Element", |
| Params: elliptic.P256().Params(), |
| BuildTags: "!amd64 && !arm64 && !ppc64le", |
| }, |
| { |
| P: "P384", |
| Element: "fiat.P384Element", |
| Params: elliptic.P384().Params(), |
| }, |
| { |
| P: "P521", |
| Element: "fiat.P521Element", |
| Params: elliptic.P521().Params(), |
| }, |
| } |
| |
| func main() { |
| t := template.Must(template.New("tmplNISTEC").Parse(tmplNISTEC)) |
| |
| tmplAddchainFile, err := os.CreateTemp("", "addchain-template") |
| if err != nil { |
| log.Fatal(err) |
| } |
| defer os.Remove(tmplAddchainFile.Name()) |
| if _, err := io.WriteString(tmplAddchainFile, tmplAddchain); err != nil { |
| log.Fatal(err) |
| } |
| if err := tmplAddchainFile.Close(); err != nil { |
| log.Fatal(err) |
| } |
| |
| for _, c := range curves { |
| p := strings.ToLower(c.P) |
| elementLen := (c.Params.BitSize + 7) / 8 |
| B := fmt.Sprintf("%#v", c.Params.B.FillBytes(make([]byte, elementLen))) |
| Gx := fmt.Sprintf("%#v", c.Params.Gx.FillBytes(make([]byte, elementLen))) |
| Gy := fmt.Sprintf("%#v", c.Params.Gy.FillBytes(make([]byte, elementLen))) |
| |
| log.Printf("Generating %s.go...", p) |
| f, err := os.Create(p + ".go") |
| if err != nil { |
| log.Fatal(err) |
| } |
| defer f.Close() |
| buf := &bytes.Buffer{} |
| if err := t.Execute(buf, map[string]interface{}{ |
| "P": c.P, "p": p, "B": B, "Gx": Gx, "Gy": Gy, |
| "Element": c.Element, "ElementLen": elementLen, |
| "BuildTags": c.BuildTags, |
| }); err != nil { |
| log.Fatal(err) |
| } |
| out, err := format.Source(buf.Bytes()) |
| if err != nil { |
| log.Fatal(err) |
| } |
| if _, err := f.Write(out); err != nil { |
| log.Fatal(err) |
| } |
| |
| // If p = 3 mod 4, implement modular square root by exponentiation. |
| mod4 := new(big.Int).Mod(c.Params.P, big.NewInt(4)) |
| if mod4.Cmp(big.NewInt(3)) != 0 { |
| continue |
| } |
| |
| exp := new(big.Int).Add(c.Params.P, big.NewInt(1)) |
| exp.Div(exp, big.NewInt(4)) |
| |
| tmp, err := os.CreateTemp("", "addchain-"+p) |
| if err != nil { |
| log.Fatal(err) |
| } |
| defer os.Remove(tmp.Name()) |
| cmd := exec.Command("addchain", "search", fmt.Sprintf("%d", exp)) |
| cmd.Stderr = os.Stderr |
| cmd.Stdout = tmp |
| if err := cmd.Run(); err != nil { |
| log.Fatal(err) |
| } |
| if err := tmp.Close(); err != nil { |
| log.Fatal(err) |
| } |
| cmd = exec.Command("addchain", "gen", "-tmpl", tmplAddchainFile.Name(), tmp.Name()) |
| cmd.Stderr = os.Stderr |
| out, err = cmd.Output() |
| if err != nil { |
| log.Fatal(err) |
| } |
| out = bytes.Replace(out, []byte("Element"), []byte(c.Element), -1) |
| out = bytes.Replace(out, []byte("sqrtCandidate"), []byte(p+"SqrtCandidate"), -1) |
| out, err = format.Source(out) |
| if err != nil { |
| log.Fatal(err) |
| } |
| if _, err := f.Write(out); err != nil { |
| log.Fatal(err) |
| } |
| } |
| } |
| |
| const tmplNISTEC = `// Copyright 2022 The Go Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style |
| // license that can be found in the LICENSE file. |
| |
| // Code generated by generate.go. DO NOT EDIT. |
| |
| {{ if .BuildTags }} |
| //go:build {{ .BuildTags }} |
| {{ end }} |
| |
| package nistec |
| |
| import ( |
| "crypto/internal/nistec/fiat" |
| "crypto/subtle" |
| "errors" |
| "sync" |
| ) |
| |
| // {{.p}}ElementLength is the length of an element of the base or scalar field, |
| // which have the same bytes length for all NIST P curves. |
| const {{.p}}ElementLength = {{ .ElementLen }} |
| |
| // {{.P}}Point is a {{.P}} point. The zero value is NOT valid. |
| type {{.P}}Point struct { |
| // The point is represented in projective coordinates (X:Y:Z), |
| // where x = X/Z and y = Y/Z. |
| x, y, z *{{.Element}} |
| } |
| |
| // New{{.P}}Point returns a new {{.P}}Point representing the point at infinity point. |
| func New{{.P}}Point() *{{.P}}Point { |
| return &{{.P}}Point{ |
| x: new({{.Element}}), |
| y: new({{.Element}}).One(), |
| z: new({{.Element}}), |
| } |
| } |
| |
| // SetGenerator sets p to the canonical generator and returns p. |
| func (p *{{.P}}Point) SetGenerator() *{{.P}}Point { |
| p.x.SetBytes({{.Gx}}) |
| p.y.SetBytes({{.Gy}}) |
| p.z.One() |
| return p |
| } |
| |
| // Set sets p = q and returns p. |
| func (p *{{.P}}Point) Set(q *{{.P}}Point) *{{.P}}Point { |
| p.x.Set(q.x) |
| p.y.Set(q.y) |
| p.z.Set(q.z) |
| return p |
| } |
| |
| // SetBytes sets p to the compressed, uncompressed, or infinity value encoded in |
| // b, as specified in SEC 1, Version 2.0, Section 2.3.4. If the point is not on |
| // the curve, it returns nil and an error, and the receiver is unchanged. |
| // Otherwise, it returns p. |
| func (p *{{.P}}Point) SetBytes(b []byte) (*{{.P}}Point, error) { |
| switch { |
| // Point at infinity. |
| case len(b) == 1 && b[0] == 0: |
| return p.Set(New{{.P}}Point()), nil |
| |
| // Uncompressed form. |
| case len(b) == 1+2*{{.p}}ElementLength && b[0] == 4: |
| x, err := new({{.Element}}).SetBytes(b[1 : 1+{{.p}}ElementLength]) |
| if err != nil { |
| return nil, err |
| } |
| y, err := new({{.Element}}).SetBytes(b[1+{{.p}}ElementLength:]) |
| if err != nil { |
| return nil, err |
| } |
| if err := {{.p}}CheckOnCurve(x, y); err != nil { |
| return nil, err |
| } |
| p.x.Set(x) |
| p.y.Set(y) |
| p.z.One() |
| return p, nil |
| |
| // Compressed form. |
| case len(b) == 1+{{.p}}ElementLength && (b[0] == 2 || b[0] == 3): |
| x, err := new({{.Element}}).SetBytes(b[1:]) |
| if err != nil { |
| return nil, err |
| } |
| |
| // y² = x³ - 3x + b |
| y := {{.p}}Polynomial(new({{.Element}}), x) |
| if !{{.p}}Sqrt(y, y) { |
| return nil, errors.New("invalid {{.P}} compressed point encoding") |
| } |
| |
| // Select the positive or negative root, as indicated by the least |
| // significant bit, based on the encoding type byte. |
| otherRoot := new({{.Element}}) |
| otherRoot.Sub(otherRoot, y) |
| cond := y.Bytes()[{{.p}}ElementLength-1]&1 ^ b[0]&1 |
| y.Select(otherRoot, y, int(cond)) |
| |
| p.x.Set(x) |
| p.y.Set(y) |
| p.z.One() |
| return p, nil |
| |
| default: |
| return nil, errors.New("invalid {{.P}} point encoding") |
| } |
| } |
| |
| |
| var _{{.p}}B *{{.Element}} |
| var _{{.p}}BOnce sync.Once |
| |
| func {{.p}}B() *{{.Element}} { |
| _{{.p}}BOnce.Do(func() { |
| _{{.p}}B, _ = new({{.Element}}).SetBytes({{.B}}) |
| }) |
| return _{{.p}}B |
| } |
| |
| // {{.p}}Polynomial sets y2 to x³ - 3x + b, and returns y2. |
| func {{.p}}Polynomial(y2, x *{{.Element}}) *{{.Element}} { |
| y2.Square(x) |
| y2.Mul(y2, x) |
| |
| threeX := new({{.Element}}).Add(x, x) |
| threeX.Add(threeX, x) |
| y2.Sub(y2, threeX) |
| |
| return y2.Add(y2, {{.p}}B()) |
| } |
| |
| func {{.p}}CheckOnCurve(x, y *{{.Element}}) error { |
| // y² = x³ - 3x + b |
| rhs := {{.p}}Polynomial(new({{.Element}}), x) |
| lhs := new({{.Element}}).Square(y) |
| if rhs.Equal(lhs) != 1 { |
| return errors.New("{{.P}} point not on curve") |
| } |
| return nil |
| } |
| |
| // Bytes returns the uncompressed or infinity encoding of p, as specified in |
| // SEC 1, Version 2.0, Section 2.3.3. Note that the encoding of the point at |
| // infinity is shorter than all other encodings. |
| func (p *{{.P}}Point) Bytes() []byte { |
| // This function is outlined to make the allocations inline in the caller |
| // rather than happen on the heap. |
| var out [1+2*{{.p}}ElementLength]byte |
| return p.bytes(&out) |
| } |
| |
| func (p *{{.P}}Point) bytes(out *[1+2*{{.p}}ElementLength]byte) []byte { |
| if p.z.IsZero() == 1 { |
| return append(out[:0], 0) |
| } |
| |
| zinv := new({{.Element}}).Invert(p.z) |
| x := new({{.Element}}).Mul(p.x, zinv) |
| y := new({{.Element}}).Mul(p.y, zinv) |
| |
| buf := append(out[:0], 4) |
| buf = append(buf, x.Bytes()...) |
| buf = append(buf, y.Bytes()...) |
| return buf |
| } |
| |
| // BytesX returns the encoding of the x-coordinate of p, as specified in SEC 1, |
| // Version 2.0, Section 2.3.5, or an error if p is the point at infinity. |
| func (p *{{.P}}Point) BytesX() ([]byte, error) { |
| // This function is outlined to make the allocations inline in the caller |
| // rather than happen on the heap. |
| var out [{{.p}}ElementLength]byte |
| return p.bytesX(&out) |
| } |
| |
| func (p *{{.P}}Point) bytesX(out *[{{.p}}ElementLength]byte) ([]byte, error) { |
| if p.z.IsZero() == 1 { |
| return nil, errors.New("{{.P}} point is the point at infinity") |
| } |
| |
| zinv := new({{.Element}}).Invert(p.z) |
| x := new({{.Element}}).Mul(p.x, zinv) |
| |
| return append(out[:0], x.Bytes()...), nil |
| } |
| |
| // BytesCompressed returns the compressed or infinity encoding of p, as |
| // specified in SEC 1, Version 2.0, Section 2.3.3. Note that the encoding of the |
| // point at infinity is shorter than all other encodings. |
| func (p *{{.P}}Point) BytesCompressed() []byte { |
| // This function is outlined to make the allocations inline in the caller |
| // rather than happen on the heap. |
| var out [1 + {{.p}}ElementLength]byte |
| return p.bytesCompressed(&out) |
| } |
| |
| func (p *{{.P}}Point) bytesCompressed(out *[1 + {{.p}}ElementLength]byte) []byte { |
| if p.z.IsZero() == 1 { |
| return append(out[:0], 0) |
| } |
| |
| zinv := new({{.Element}}).Invert(p.z) |
| x := new({{.Element}}).Mul(p.x, zinv) |
| y := new({{.Element}}).Mul(p.y, zinv) |
| |
| // Encode the sign of the y coordinate (indicated by the least significant |
| // bit) as the encoding type (2 or 3). |
| buf := append(out[:0], 2) |
| buf[0] |= y.Bytes()[{{.p}}ElementLength-1] & 1 |
| buf = append(buf, x.Bytes()...) |
| return buf |
| } |
| |
| // Add sets q = p1 + p2, and returns q. The points may overlap. |
| func (q *{{.P}}Point) Add(p1, p2 *{{.P}}Point) *{{.P}}Point { |
| // Complete addition formula for a = -3 from "Complete addition formulas for |
| // prime order elliptic curves" (https://eprint.iacr.org/2015/1060), §A.2. |
| |
| t0 := new({{.Element}}).Mul(p1.x, p2.x) // t0 := X1 * X2 |
| t1 := new({{.Element}}).Mul(p1.y, p2.y) // t1 := Y1 * Y2 |
| t2 := new({{.Element}}).Mul(p1.z, p2.z) // t2 := Z1 * Z2 |
| t3 := new({{.Element}}).Add(p1.x, p1.y) // t3 := X1 + Y1 |
| t4 := new({{.Element}}).Add(p2.x, p2.y) // t4 := X2 + Y2 |
| t3.Mul(t3, t4) // t3 := t3 * t4 |
| t4.Add(t0, t1) // t4 := t0 + t1 |
| t3.Sub(t3, t4) // t3 := t3 - t4 |
| t4.Add(p1.y, p1.z) // t4 := Y1 + Z1 |
| x3 := new({{.Element}}).Add(p2.y, p2.z) // X3 := Y2 + Z2 |
| t4.Mul(t4, x3) // t4 := t4 * X3 |
| x3.Add(t1, t2) // X3 := t1 + t2 |
| t4.Sub(t4, x3) // t4 := t4 - X3 |
| x3.Add(p1.x, p1.z) // X3 := X1 + Z1 |
| y3 := new({{.Element}}).Add(p2.x, p2.z) // Y3 := X2 + Z2 |
| x3.Mul(x3, y3) // X3 := X3 * Y3 |
| y3.Add(t0, t2) // Y3 := t0 + t2 |
| y3.Sub(x3, y3) // Y3 := X3 - Y3 |
| z3 := new({{.Element}}).Mul({{.p}}B(), t2) // Z3 := b * t2 |
| x3.Sub(y3, z3) // X3 := Y3 - Z3 |
| z3.Add(x3, x3) // Z3 := X3 + X3 |
| x3.Add(x3, z3) // X3 := X3 + Z3 |
| z3.Sub(t1, x3) // Z3 := t1 - X3 |
| x3.Add(t1, x3) // X3 := t1 + X3 |
| y3.Mul({{.p}}B(), y3) // Y3 := b * Y3 |
| t1.Add(t2, t2) // t1 := t2 + t2 |
| t2.Add(t1, t2) // t2 := t1 + t2 |
| y3.Sub(y3, t2) // Y3 := Y3 - t2 |
| y3.Sub(y3, t0) // Y3 := Y3 - t0 |
| t1.Add(y3, y3) // t1 := Y3 + Y3 |
| y3.Add(t1, y3) // Y3 := t1 + Y3 |
| t1.Add(t0, t0) // t1 := t0 + t0 |
| t0.Add(t1, t0) // t0 := t1 + t0 |
| t0.Sub(t0, t2) // t0 := t0 - t2 |
| t1.Mul(t4, y3) // t1 := t4 * Y3 |
| t2.Mul(t0, y3) // t2 := t0 * Y3 |
| y3.Mul(x3, z3) // Y3 := X3 * Z3 |
| y3.Add(y3, t2) // Y3 := Y3 + t2 |
| x3.Mul(t3, x3) // X3 := t3 * X3 |
| x3.Sub(x3, t1) // X3 := X3 - t1 |
| z3.Mul(t4, z3) // Z3 := t4 * Z3 |
| t1.Mul(t3, t0) // t1 := t3 * t0 |
| z3.Add(z3, t1) // Z3 := Z3 + t1 |
| |
| q.x.Set(x3) |
| q.y.Set(y3) |
| q.z.Set(z3) |
| return q |
| } |
| |
| // Double sets q = p + p, and returns q. The points may overlap. |
| func (q *{{.P}}Point) Double(p *{{.P}}Point) *{{.P}}Point { |
| // Complete addition formula for a = -3 from "Complete addition formulas for |
| // prime order elliptic curves" (https://eprint.iacr.org/2015/1060), §A.2. |
| |
| t0 := new({{.Element}}).Square(p.x) // t0 := X ^ 2 |
| t1 := new({{.Element}}).Square(p.y) // t1 := Y ^ 2 |
| t2 := new({{.Element}}).Square(p.z) // t2 := Z ^ 2 |
| t3 := new({{.Element}}).Mul(p.x, p.y) // t3 := X * Y |
| t3.Add(t3, t3) // t3 := t3 + t3 |
| z3 := new({{.Element}}).Mul(p.x, p.z) // Z3 := X * Z |
| z3.Add(z3, z3) // Z3 := Z3 + Z3 |
| y3 := new({{.Element}}).Mul({{.p}}B(), t2) // Y3 := b * t2 |
| y3.Sub(y3, z3) // Y3 := Y3 - Z3 |
| x3 := new({{.Element}}).Add(y3, y3) // X3 := Y3 + Y3 |
| y3.Add(x3, y3) // Y3 := X3 + Y3 |
| x3.Sub(t1, y3) // X3 := t1 - Y3 |
| y3.Add(t1, y3) // Y3 := t1 + Y3 |
| y3.Mul(x3, y3) // Y3 := X3 * Y3 |
| x3.Mul(x3, t3) // X3 := X3 * t3 |
| t3.Add(t2, t2) // t3 := t2 + t2 |
| t2.Add(t2, t3) // t2 := t2 + t3 |
| z3.Mul({{.p}}B(), z3) // Z3 := b * Z3 |
| z3.Sub(z3, t2) // Z3 := Z3 - t2 |
| z3.Sub(z3, t0) // Z3 := Z3 - t0 |
| t3.Add(z3, z3) // t3 := Z3 + Z3 |
| z3.Add(z3, t3) // Z3 := Z3 + t3 |
| t3.Add(t0, t0) // t3 := t0 + t0 |
| t0.Add(t3, t0) // t0 := t3 + t0 |
| t0.Sub(t0, t2) // t0 := t0 - t2 |
| t0.Mul(t0, z3) // t0 := t0 * Z3 |
| y3.Add(y3, t0) // Y3 := Y3 + t0 |
| t0.Mul(p.y, p.z) // t0 := Y * Z |
| t0.Add(t0, t0) // t0 := t0 + t0 |
| z3.Mul(t0, z3) // Z3 := t0 * Z3 |
| x3.Sub(x3, z3) // X3 := X3 - Z3 |
| z3.Mul(t0, t1) // Z3 := t0 * t1 |
| z3.Add(z3, z3) // Z3 := Z3 + Z3 |
| z3.Add(z3, z3) // Z3 := Z3 + Z3 |
| |
| q.x.Set(x3) |
| q.y.Set(y3) |
| q.z.Set(z3) |
| return q |
| } |
| |
| // Select sets q to p1 if cond == 1, and to p2 if cond == 0. |
| func (q *{{.P}}Point) Select(p1, p2 *{{.P}}Point, cond int) *{{.P}}Point { |
| q.x.Select(p1.x, p2.x, cond) |
| q.y.Select(p1.y, p2.y, cond) |
| q.z.Select(p1.z, p2.z, cond) |
| return q |
| } |
| |
| // A {{.p}}Table holds the first 15 multiples of a point at offset -1, so [1]P |
| // is at table[0], [15]P is at table[14], and [0]P is implicitly the identity |
| // point. |
| type {{.p}}Table [15]*{{.P}}Point |
| |
| // Select selects the n-th multiple of the table base point into p. It works in |
| // constant time by iterating over every entry of the table. n must be in [0, 15]. |
| func (table *{{.p}}Table) Select(p *{{.P}}Point, n uint8) { |
| if n >= 16 { |
| panic("nistec: internal error: {{.p}}Table called with out-of-bounds value") |
| } |
| p.Set(New{{.P}}Point()) |
| for i := uint8(1); i < 16; i++ { |
| cond := subtle.ConstantTimeByteEq(i, n) |
| p.Select(table[i-1], p, cond) |
| } |
| } |
| |
| // ScalarMult sets p = scalar * q, and returns p. |
| func (p *{{.P}}Point) ScalarMult(q *{{.P}}Point, scalar []byte) (*{{.P}}Point, error) { |
| // Compute a {{.p}}Table for the base point q. The explicit New{{.P}}Point |
| // calls get inlined, letting the allocations live on the stack. |
| var table = {{.p}}Table{New{{.P}}Point(), New{{.P}}Point(), New{{.P}}Point(), |
| New{{.P}}Point(), New{{.P}}Point(), New{{.P}}Point(), New{{.P}}Point(), |
| New{{.P}}Point(), New{{.P}}Point(), New{{.P}}Point(), New{{.P}}Point(), |
| New{{.P}}Point(), New{{.P}}Point(), New{{.P}}Point(), New{{.P}}Point()} |
| table[0].Set(q) |
| for i := 1; i < 15; i += 2 { |
| table[i].Double(table[i/2]) |
| table[i+1].Add(table[i], q) |
| } |
| |
| // 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 := New{{.P}}Point() |
| p.Set(New{{.P}}Point()) |
| 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 { |
| p.Double(p) |
| p.Double(p) |
| p.Double(p) |
| p.Double(p) |
| } |
| |
| windowValue := byte >> 4 |
| table.Select(t, windowValue) |
| p.Add(p, t) |
| |
| p.Double(p) |
| p.Double(p) |
| p.Double(p) |
| p.Double(p) |
| |
| windowValue = byte & 0b1111 |
| table.Select(t, windowValue) |
| p.Add(p, t) |
| } |
| |
| return p, nil |
| } |
| |
| var {{.p}}GeneratorTable *[{{.p}}ElementLength * 2]{{.p}}Table |
| var {{.p}}GeneratorTableOnce sync.Once |
| |
| // generatorTable returns a sequence of {{.p}}Tables. The first table contains |
| // multiples of G. Each successive table is the previous table doubled four |
| // times. |
| func (p *{{.P}}Point) generatorTable() *[{{.p}}ElementLength * 2]{{.p}}Table { |
| {{.p}}GeneratorTableOnce.Do(func() { |
| {{.p}}GeneratorTable = new([{{.p}}ElementLength * 2]{{.p}}Table) |
| base := New{{.P}}Point().SetGenerator() |
| for i := 0; i < {{.p}}ElementLength*2; i++ { |
| {{.p}}GeneratorTable[i][0] = New{{.P}}Point().Set(base) |
| for j := 1; j < 15; j++ { |
| {{.p}}GeneratorTable[i][j] = New{{.P}}Point().Add({{.p}}GeneratorTable[i][j-1], base) |
| } |
| base.Double(base) |
| base.Double(base) |
| base.Double(base) |
| base.Double(base) |
| } |
| }) |
| return {{.p}}GeneratorTable |
| } |
| |
| // ScalarBaseMult sets p = scalar * B, where B is the canonical generator, and |
| // returns p. |
| func (p *{{.P}}Point) ScalarBaseMult(scalar []byte) (*{{.P}}Point, error) { |
| if len(scalar) != {{.p}}ElementLength { |
| return nil, errors.New("invalid scalar length") |
| } |
| tables := p.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 := New{{.P}}Point() |
| p.Set(New{{.P}}Point()) |
| tableIndex := len(tables) - 1 |
| for _, byte := range scalar { |
| windowValue := byte >> 4 |
| tables[tableIndex].Select(t, windowValue) |
| p.Add(p, t) |
| tableIndex-- |
| |
| windowValue = byte & 0b1111 |
| tables[tableIndex].Select(t, windowValue) |
| p.Add(p, t) |
| tableIndex-- |
| } |
| |
| return p, nil |
| } |
| |
| // {{.p}}Sqrt sets e to a square root of x. If x is not a square, {{.p}}Sqrt returns |
| // false and e is unchanged. e and x can overlap. |
| func {{.p}}Sqrt(e, x *{{ .Element }}) (isSquare bool) { |
| candidate := new({{ .Element }}) |
| {{.p}}SqrtCandidate(candidate, x) |
| square := new({{ .Element }}).Square(candidate) |
| if square.Equal(x) != 1 { |
| return false |
| } |
| e.Set(candidate) |
| return true |
| } |
| ` |
| |
| const tmplAddchain = ` |
| // sqrtCandidate sets z to a square root candidate for x. z and x must not overlap. |
| func sqrtCandidate(z, x *Element) { |
| // Since p = 3 mod 4, exponentiation by (p + 1) / 4 yields a square root candidate. |
| // |
| // The sequence of {{ .Ops.Adds }} multiplications and {{ .Ops.Doubles }} squarings is derived from the |
| // following addition chain generated with {{ .Meta.Module }} {{ .Meta.ReleaseTag }}. |
| // |
| {{- range lines (format .Script) }} |
| // {{ . }} |
| {{- end }} |
| // |
| |
| {{- range .Program.Temporaries }} |
| var {{ . }} = new(Element) |
| {{- end }} |
| {{ range $i := .Program.Instructions -}} |
| {{- with add $i.Op }} |
| {{ $i.Output }}.Mul({{ .X }}, {{ .Y }}) |
| {{- end -}} |
| |
| {{- with double $i.Op }} |
| {{ $i.Output }}.Square({{ .X }}) |
| {{- end -}} |
| |
| {{- with shift $i.Op -}} |
| {{- $first := 0 -}} |
| {{- if ne $i.Output.Identifier .X.Identifier }} |
| {{ $i.Output }}.Square({{ .X }}) |
| {{- $first = 1 -}} |
| {{- end }} |
| for s := {{ $first }}; s < {{ .S }}; s++ { |
| {{ $i.Output }}.Square({{ $i.Output }}) |
| } |
| {{- end -}} |
| {{- end }} |
| } |
| ` |
