Abstract & expose CompressedPointToSignAndY

Add scanner/valuer interface to babyjub.PublicKeyComp

babyjub/babyjub.go

@@ -222,13 +222,26 @@ func (p *Point) Compress() [32]byte {
 // 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) {
 	sign := false
+	y := big.NewInt(0)
 	if (leBuf[31] & 0x80) != 0x00 { //nolint:gomnd
 		sign = true
 		leBuf[31] = leBuf[31] & 0x7F //nolint:gomnd
 	}
-	utils.SetBigIntFromLEBytes(p.Y, leBuf[:])
-	return PointFromSignAndY(sign, p.Y)
+	utils.SetBigIntFromLEBytes(y, leBuf[:])
+	return sign, y
 }
 
 // PointFromSignAndY returns a Point from a Sign and the Y coordinate

babyjub/eddsa.go

@@ -354,3 +354,21 @@ func (pk PublicKey) Value() (driver.Value, error) {
 	comp := pk.Compress()
 	return comp[:], nil
 }
+
+// Scan implements Scanner for database/sql.
+func (pkComp *PublicKeyComp) Scan(src interface{}) error {
+	srcB, ok := src.([]byte)
+	if !ok {
+		return fmt.Errorf("can't scan %T into PublicKeyComp", src)
+	}
+	if len(srcB) != 32 {
+		return fmt.Errorf("can't scan []byte of len %d into PublicKeyComp, want %d", len(srcB), 32)
+	}
+	copy(pkComp[:], srcB)
+	return nil
+}
+
+// Value implements valuer for database/sql.
+func (pkComp PublicKeyComp) Value() (driver.Value, error) {
+	return pkComp[:], nil
+}

babyjub/eddsa_test.go

@@ -160,7 +160,7 @@ func TestSignatureScannerValuer(t *testing.T) {
 	assert.Equal(t, value, scan)
 }
 
-func TestPubKeyScannerValuer(t *testing.T) {
+func TestPublicKeyScannerValuer(t *testing.T) {
 	privKValue := NewRandPrivKey()
 	pubKValue := privKValue.Public()
 	privKScan := NewRandPrivKey()
@@ -175,6 +175,21 @@ func TestPubKeyScannerValuer(t *testing.T) {
 	assert.Equal(t, value, scan)
 }
 
+func TestPublicKeyCompScannerValuer(t *testing.T) {
+	privKValue := NewRandPrivKey()
+	pubKCompValue := privKValue.Public().Compress()
+	privKScan := NewRandPrivKey()
+	pubKCompScan := privKScan.Public().Compress()
+	var value driver.Valuer
+	var scan sql.Scanner
+	value = &pubKCompValue
+	scan = &pubKCompScan
+	fromDB, err := value.Value()
+	assert.Nil(t, err)
+	assert.Nil(t, scan.Scan(fromDB))
+	assert.Equal(t, value, scan)
+}
+
 func BenchmarkBabyjubEddsa(b *testing.B) {
 	var k PrivateKey
 	_, err := hex.Decode(k[:],