125 lines
3.3 KiB
Go
125 lines
3.3 KiB
Go
package curve25519
|
|
|
|
import (
|
|
"crypto/elliptic"
|
|
"math/big"
|
|
"sync"
|
|
)
|
|
|
|
var cv25519 cv25519Curve
|
|
|
|
type cv25519Curve struct {
|
|
*elliptic.CurveParams
|
|
}
|
|
|
|
func copyReverse(dst []byte, src []byte) {
|
|
// Curve 25519 multiplication functions expect scalars in reverse
|
|
// order than PGP. To keep the curve25519Curve type consistent
|
|
// with other curves, we reverse it here.
|
|
for i, j := 0, len(src)-1; j >= 0 && i < len(dst); i, j = i+1, j-1 {
|
|
dst[i] = src[j]
|
|
}
|
|
}
|
|
|
|
func copyTruncate(dst []byte, src []byte) {
|
|
lenDst, lenSrc := len(dst), len(src)
|
|
if lenDst == lenSrc {
|
|
copy(dst, src)
|
|
} else if lenDst > lenSrc {
|
|
copy(dst[lenDst-lenSrc:lenDst], src)
|
|
} else if lenDst < lenSrc {
|
|
copy(dst, src[:lenDst])
|
|
}
|
|
}
|
|
|
|
func (cv25519Curve) ScalarMult(x1, y1 *big.Int, scalar []byte) (x, y *big.Int) {
|
|
// Assume y1 is 0 with cv25519.
|
|
var dst [32]byte
|
|
var x1Bytes [32]byte
|
|
var scalarBytes [32]byte
|
|
|
|
copyTruncate(x1Bytes[:], x1.Bytes())
|
|
copyReverse(scalarBytes[:], scalar)
|
|
|
|
scalarMult(&dst, &scalarBytes, &x1Bytes)
|
|
|
|
x = new(big.Int).SetBytes(dst[:])
|
|
y = new(big.Int)
|
|
return x, y
|
|
}
|
|
|
|
func (cv25519Curve) ScalarBaseMult(scalar []byte) (x, y *big.Int) {
|
|
var dst [32]byte
|
|
var scalarBytes [32]byte
|
|
copyReverse(scalarBytes[:], scalar[:32])
|
|
scalarMult(&dst, &scalarBytes, &basePoint)
|
|
x = new(big.Int).SetBytes(dst[:])
|
|
y = new(big.Int)
|
|
return x, y
|
|
}
|
|
|
|
func (cv25519Curve) IsOnCurve(bigX, bigY *big.Int) bool {
|
|
return bigY.Sign() == 0 // bigY == 0 ?
|
|
}
|
|
|
|
// More information about 0x40 point format:
|
|
// https://tools.ietf.org/html/draft-koch-eddsa-for-openpgp-00#section-3
|
|
// In addition to uncompressed point format described here:
|
|
// https://tools.ietf.org/html/rfc6637#section-6
|
|
|
|
func (cv25519Curve) MarshalType40(x, y *big.Int) []byte {
|
|
byteLen := 32
|
|
|
|
ret := make([]byte, 1+byteLen)
|
|
ret[0] = 0x40
|
|
|
|
xBytes := x.Bytes()
|
|
copyTruncate(ret[1:], xBytes)
|
|
return ret
|
|
}
|
|
|
|
func (cv25519Curve) UnmarshalType40(data []byte) (x, y *big.Int) {
|
|
if len(data) != 1+32 {
|
|
return nil, nil
|
|
}
|
|
if data[0] != 0x40 {
|
|
return nil, nil
|
|
}
|
|
x = new(big.Int).SetBytes(data[1:])
|
|
// Any x is a valid curve point.
|
|
return x, new(big.Int)
|
|
}
|
|
|
|
// ToCurve25519 casts given elliptic.Curve type to Curve25519 type, or
|
|
// returns nil, false if cast was unsuccessful.
|
|
func ToCurve25519(cv elliptic.Curve) (cv25519Curve, bool) {
|
|
cv2, ok := cv.(cv25519Curve)
|
|
return cv2, ok
|
|
}
|
|
|
|
func initCv25519() {
|
|
cv25519.CurveParams = &elliptic.CurveParams{Name: "Curve 25519"}
|
|
// Some code relies on these parameters being available for
|
|
// checking Curve coordinate length. They should not be used
|
|
// directly for any calculations.
|
|
cv25519.P, _ = new(big.Int).SetString("7fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffed", 16)
|
|
cv25519.N, _ = new(big.Int).SetString("1000000000000000000000000000000014def9dea2f79cd65812631a5cf5d3ed", 16)
|
|
cv25519.Gx, _ = new(big.Int).SetString("9", 16)
|
|
cv25519.Gy, _ = new(big.Int).SetString("20ae19a1b8a086b4e01edd2c7748d14c923d4d7e6d7c61b229e9c5a27eced3d9", 16)
|
|
cv25519.BitSize = 256
|
|
}
|
|
|
|
var initonce sync.Once
|
|
|
|
// Cv25519 returns a Curve which (partially) implements Cv25519. Only
|
|
// ScalarMult and ScalarBaseMult are valid for this curve. Add and
|
|
// Double should not be used.
|
|
func Cv25519() elliptic.Curve {
|
|
initonce.Do(initCv25519)
|
|
return cv25519
|
|
}
|
|
|
|
func (curve cv25519Curve) Params() *elliptic.CurveParams {
|
|
return curve.CurveParams
|
|
}
|