139 lines
4.4 KiB
Go
139 lines
4.4 KiB
Go
// Copyright 2013 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.
|
|
|
|
package elliptic
|
|
|
|
import (
|
|
"crypto/elliptic/internal/nistec"
|
|
"crypto/rand"
|
|
"math/big"
|
|
)
|
|
|
|
// p224Curve is a Curve implementation based on nistec.P224Point.
|
|
//
|
|
// It's a wrapper that exposes the big.Int-based Curve interface and encodes the
|
|
// legacy idiosyncrasies it requires, such as invalid and infinity point
|
|
// handling.
|
|
//
|
|
// To interact with the nistec package, points are encoded into and decoded from
|
|
// properly formatted byte slices. All big.Int use is limited to this package.
|
|
// Encoding and decoding is 1/1000th of the runtime of a scalar multiplication,
|
|
// so the overhead is acceptable.
|
|
type p224Curve struct {
|
|
params *CurveParams
|
|
}
|
|
|
|
var p224 p224Curve
|
|
var _ Curve = p224
|
|
|
|
func initP224() {
|
|
p224.params = &CurveParams{
|
|
Name: "P-224",
|
|
BitSize: 224,
|
|
// FIPS 186-4, section D.1.2.2
|
|
P: bigFromDecimal("26959946667150639794667015087019630673557916260026308143510066298881"),
|
|
N: bigFromDecimal("26959946667150639794667015087019625940457807714424391721682722368061"),
|
|
B: bigFromHex("b4050a850c04b3abf54132565044b0b7d7bfd8ba270b39432355ffb4"),
|
|
Gx: bigFromHex("b70e0cbd6bb4bf7f321390b94a03c1d356c21122343280d6115c1d21"),
|
|
Gy: bigFromHex("bd376388b5f723fb4c22dfe6cd4375a05a07476444d5819985007e34"),
|
|
}
|
|
}
|
|
|
|
func (curve p224Curve) Params() *CurveParams {
|
|
return curve.params
|
|
}
|
|
|
|
func (curve p224Curve) IsOnCurve(x, y *big.Int) bool {
|
|
// IsOnCurve is documented to reject (0, 0), the conventional point at
|
|
// infinity, which however is accepted by p224PointFromAffine.
|
|
if x.Sign() == 0 && y.Sign() == 0 {
|
|
return false
|
|
}
|
|
_, ok := p224PointFromAffine(x, y)
|
|
return ok
|
|
}
|
|
|
|
func p224PointFromAffine(x, y *big.Int) (p *nistec.P224Point, ok bool) {
|
|
// (0, 0) is by convention the point at infinity, which can't be represented
|
|
// in affine coordinates. Marshal incorrectly encodes it as an uncompressed
|
|
// point, which SetBytes would correctly reject. See Issue 37294.
|
|
if x.Sign() == 0 && y.Sign() == 0 {
|
|
return nistec.NewP224Point(), true
|
|
}
|
|
if x.Sign() < 0 || y.Sign() < 0 {
|
|
return nil, false
|
|
}
|
|
if x.BitLen() > 224 || y.BitLen() > 224 {
|
|
return nil, false
|
|
}
|
|
p, err := nistec.NewP224Point().SetBytes(Marshal(P224(), x, y))
|
|
if err != nil {
|
|
return nil, false
|
|
}
|
|
return p, true
|
|
}
|
|
|
|
func p224PointToAffine(p *nistec.P224Point) (x, y *big.Int) {
|
|
out := p.Bytes()
|
|
if len(out) == 1 && out[0] == 0 {
|
|
// This is the correct encoding of the point at infinity, which
|
|
// Unmarshal does not support. See Issue 37294.
|
|
return new(big.Int), new(big.Int)
|
|
}
|
|
x, y = Unmarshal(P224(), out)
|
|
if x == nil {
|
|
panic("crypto/elliptic: internal error: Unmarshal rejected a valid point encoding")
|
|
}
|
|
return x, y
|
|
}
|
|
|
|
// p224RandomPoint returns a random point on the curve. It's used when Add,
|
|
// Double, or ScalarMult are fed a point not on the curve, which is undefined
|
|
// behavior. Originally, we used to do the math on it anyway (which allows
|
|
// invalid curve attacks) and relied on the caller and Unmarshal to avoid this
|
|
// happening in the first place. Now, we just can't construct a nistec.P224Point
|
|
// for an invalid pair of coordinates, because that API is safer. If we panic,
|
|
// we risk introducing a DoS. If we return nil, we risk a panic. If we return
|
|
// the input, ecdsa.Verify might fail open. The safest course seems to be to
|
|
// return a valid, random point, which hopefully won't help the attacker.
|
|
func p224RandomPoint() (x, y *big.Int) {
|
|
_, x, y, err := GenerateKey(P224(), rand.Reader)
|
|
if err != nil {
|
|
panic("crypto/elliptic: failed to generate random point")
|
|
}
|
|
return x, y
|
|
}
|
|
|
|
func (p224Curve) Add(x1, y1, x2, y2 *big.Int) (*big.Int, *big.Int) {
|
|
p1, ok := p224PointFromAffine(x1, y1)
|
|
if !ok {
|
|
return p224RandomPoint()
|
|
}
|
|
p2, ok := p224PointFromAffine(x2, y2)
|
|
if !ok {
|
|
return p224RandomPoint()
|
|
}
|
|
return p224PointToAffine(p1.Add(p1, p2))
|
|
}
|
|
|
|
func (p224Curve) Double(x1, y1 *big.Int) (*big.Int, *big.Int) {
|
|
p, ok := p224PointFromAffine(x1, y1)
|
|
if !ok {
|
|
return p224RandomPoint()
|
|
}
|
|
return p224PointToAffine(p.Double(p))
|
|
}
|
|
|
|
func (p224Curve) ScalarMult(Bx, By *big.Int, scalar []byte) (*big.Int, *big.Int) {
|
|
p, ok := p224PointFromAffine(Bx, By)
|
|
if !ok {
|
|
return p224RandomPoint()
|
|
}
|
|
return p224PointToAffine(p.ScalarMult(p, scalar))
|
|
}
|
|
|
|
func (p224Curve) ScalarBaseMult(scalar []byte) (*big.Int, *big.Int) {
|
|
p := nistec.NewP224Generator()
|
|
return p224PointToAffine(p.ScalarMult(p, scalar))
|
|
}
|