144 lines
4.7 KiB
Go
144 lines
4.7 KiB
Go
// Copyright 2013 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package elliptic
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import (
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"crypto/elliptic/internal/nistec"
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"crypto/rand"
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"math/big"
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)
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// p384Curve is a Curve implementation based on nistec.P384Point.
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//
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// It's a wrapper that exposes the big.Int-based Curve interface and encodes the
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// legacy idiosyncrasies it requires, such as invalid and infinity point
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// handling.
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//
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// To interact with the nistec package, points are encoded into and decoded from
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// properly formatted byte slices. All big.Int use is limited to this package.
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// Encoding and decoding is 1/1000th of the runtime of a scalar multiplication,
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// so the overhead is acceptable.
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type p384Curve struct {
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params *CurveParams
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}
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var p384 p384Curve
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var _ Curve = p384
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func initP384() {
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p384.params = &CurveParams{
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Name: "P-384",
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BitSize: 384,
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// FIPS 186-4, section D.1.2.4
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P: bigFromDecimal("394020061963944792122790401001436138050797392704654" +
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"46667948293404245721771496870329047266088258938001861606973112319"),
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N: bigFromDecimal("394020061963944792122790401001436138050797392704654" +
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"46667946905279627659399113263569398956308152294913554433653942643"),
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B: bigFromHex("b3312fa7e23ee7e4988e056be3f82d19181d9c6efe8141120314088" +
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"f5013875ac656398d8a2ed19d2a85c8edd3ec2aef"),
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Gx: bigFromHex("aa87ca22be8b05378eb1c71ef320ad746e1d3b628ba79b9859f741" +
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"e082542a385502f25dbf55296c3a545e3872760ab7"),
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Gy: bigFromHex("3617de4a96262c6f5d9e98bf9292dc29f8f41dbd289a147ce9da31" +
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"13b5f0b8c00a60b1ce1d7e819d7a431d7c90ea0e5f"),
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}
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}
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func (curve p384Curve) Params() *CurveParams {
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return curve.params
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}
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func (curve p384Curve) IsOnCurve(x, y *big.Int) bool {
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// IsOnCurve is documented to reject (0, 0), the conventional point at
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// infinity, which however is accepted by p384PointFromAffine.
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if x.Sign() == 0 && y.Sign() == 0 {
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return false
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}
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_, ok := p384PointFromAffine(x, y)
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return ok
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}
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func p384PointFromAffine(x, y *big.Int) (p *nistec.P384Point, ok bool) {
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// (0, 0) is by convention the point at infinity, which can't be represented
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// in affine coordinates. Marshal incorrectly encodes it as an uncompressed
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// point, which SetBytes would correctly reject. See Issue 37294.
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if x.Sign() == 0 && y.Sign() == 0 {
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return nistec.NewP384Point(), true
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}
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if x.Sign() < 0 || y.Sign() < 0 {
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return nil, false
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}
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if x.BitLen() > 384 || y.BitLen() > 384 {
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return nil, false
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}
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p, err := nistec.NewP384Point().SetBytes(Marshal(P384(), x, y))
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if err != nil {
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return nil, false
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}
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return p, true
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}
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func p384PointToAffine(p *nistec.P384Point) (x, y *big.Int) {
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out := p.Bytes()
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if len(out) == 1 && out[0] == 0 {
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// This is the correct encoding of the point at infinity, which
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// Unmarshal does not support. See Issue 37294.
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return new(big.Int), new(big.Int)
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}
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x, y = Unmarshal(P384(), out)
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if x == nil {
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panic("crypto/elliptic: internal error: Unmarshal rejected a valid point encoding")
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}
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return x, y
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}
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// p384RandomPoint returns a random point on the curve. It's used when Add,
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// Double, or ScalarMult are fed a point not on the curve, which is undefined
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// behavior. Originally, we used to do the math on it anyway (which allows
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// invalid curve attacks) and relied on the caller and Unmarshal to avoid this
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// happening in the first place. Now, we just can't construct a nistec.P384Point
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// for an invalid pair of coordinates, because that API is safer. If we panic,
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// we risk introducing a DoS. If we return nil, we risk a panic. If we return
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// the input, ecdsa.Verify might fail open. The safest course seems to be to
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// return a valid, random point, which hopefully won't help the attacker.
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func p384RandomPoint() (x, y *big.Int) {
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_, x, y, err := GenerateKey(P384(), rand.Reader)
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if err != nil {
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panic("crypto/elliptic: failed to generate random point")
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}
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return x, y
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}
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func (p384Curve) Add(x1, y1, x2, y2 *big.Int) (*big.Int, *big.Int) {
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p1, ok := p384PointFromAffine(x1, y1)
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if !ok {
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return p384RandomPoint()
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}
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p2, ok := p384PointFromAffine(x2, y2)
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if !ok {
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return p384RandomPoint()
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}
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return p384PointToAffine(p1.Add(p1, p2))
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}
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func (p384Curve) Double(x1, y1 *big.Int) (*big.Int, *big.Int) {
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p, ok := p384PointFromAffine(x1, y1)
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if !ok {
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return p384RandomPoint()
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}
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return p384PointToAffine(p.Double(p))
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}
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func (p384Curve) ScalarMult(Bx, By *big.Int, scalar []byte) (*big.Int, *big.Int) {
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p, ok := p384PointFromAffine(Bx, By)
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if !ok {
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return p384RandomPoint()
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}
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return p384PointToAffine(p.ScalarMult(p, scalar))
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}
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func (p384Curve) ScalarBaseMult(scalar []byte) (*big.Int, *big.Int) {
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p := nistec.NewP384Generator()
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return p384PointToAffine(p.ScalarMult(p, scalar))
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}
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