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Update and add test for PackSignY & UnpackSignY

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- Update PackSignY & UnpackSignY interface and description
- Add test for UnpackSignY & PackPoint
This commit is contained in:
arnaucube
2020-12-21 16:53:02 +01:00
parent a0722b9e8f
commit 2318fd7044
3 changed files with 48 additions and 26 deletions
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52
babyjub/babyjub.go
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@@ -203,37 +203,24 @@ func PointCoordSign(c *big.Int) bool {
return c.Cmp(new(big.Int).Rsh(constants.Q, 1)) == 1
}
// PackPoint packs a point into a 32 byte array
func PackPoint(ay *big.Int, sign bool) [32]byte {
leBuf := utils.BigIntLEBytes(ay)
// PackSignY packs the given sign and the coordinate Y of a point into a 32
// byte array. This method does not check that the values belong to a valid
// Point in the curve.
func PackSignY(sign bool, y *big.Int) [32]byte {
leBuf := utils.BigIntLEBytes(y)
if sign {
leBuf[31] = leBuf[31] | 0x80 //nolint:gomnd
}
return leBuf
}
// Compress the point into a 32 byte array that contains the y coordinate in
// little endian and the sign of the x coordinate.
func (p *Point) Compress() [32]byte {
sign := PointCoordSign(p.X)
return PackPoint(p.Y, sign)
}
// Decompress a compressed Point into p, and also returns the decompressed
// Point. Returns error if the compressed Point is invalid.
func (p *Point) Decompress(leBuf [32]byte) (*Point, error) {
var sign bool
sign, p.Y = CompressedPointToSignAndY(leBuf)
return PointFromSignAndY(sign, p.Y)
}
// CompressedPointToSignAndY returns the sign and coordinate Y from a given
// compressed point. This method does not check that the Point belongs to the
// BabyJubJub curve, thus does not return error in such case. This method is
// intended to obtain the sign and the Y coordinate without checking if the
// point belongs to the curve, if the objective is to uncompress a point
// Decompress method should be used instead.
func CompressedPointToSignAndY(leBuf [32]byte) (bool, *big.Int) {
// UnpackSignY returns the sign and coordinate Y from a given compressed point.
// This method does not check that the Point belongs to the BabyJubJub curve,
// thus does not return error in such case. This method is intended to obtain
// the sign and the Y coordinate without checking if the point belongs to the
// curve, if the objective is to uncompress a point, Decompress method should
// be used instead.
func UnpackSignY(leBuf [32]byte) (bool, *big.Int) {
sign := false
y := big.NewInt(0)
if (leBuf[31] & 0x80) != 0x00 { //nolint:gomnd
@@ -244,6 +231,21 @@ func CompressedPointToSignAndY(leBuf [32]byte) (bool, *big.Int) {
return sign, y
}
// Compress the point into a 32 byte array that contains the y coordinate in
// little endian and the sign of the x coordinate.
func (p *Point) Compress() [32]byte {
sign := PointCoordSign(p.X)
return PackSignY(sign, p.Y)
}
// Decompress a compressed Point into p, and also returns the decompressed
// Point. Returns error if the compressed Point is invalid.
func (p *Point) Decompress(leBuf [32]byte) (*Point, error) {
var sign bool
sign, p.Y = UnpackSignY(leBuf)
return PointFromSignAndY(sign, p.Y)
}
// PointFromSignAndY returns a Point from a Sign and the Y coordinate
func PointFromSignAndY(sign bool, y *big.Int) (*Point, error) {
var p Point