Refactoring for go1.15+

- use elliptic.MarshalCompressed
- use elliptic.UnmarshalCompressed
- for older go versions use old methods
- update dependencies
  - github.com/mr-tron/base58 v1.2.0
  - github.com/pkg/errors v0.9.1
  - github.com/stretchr/testify v1.7.0

Signed-off-by: Evgeniy Kulikov <kim@nspcc.ru>

ecdsa.go

@@ -70,75 +70,6 @@ func unmarshalXY(data []byte) (x *big.Int, y *big.Int) {
 	return
 }
 
-// decompressPoints using formula y² = x³ - 3x + b
-// crypto/elliptic/elliptic.go:55
-func decompressPoints(x *big.Int, yBit uint) (*big.Int, *big.Int) {
-	params := curve.Params()
-
-	x3 := new(big.Int).Mul(x, x)
-	x3.Mul(x3, x)
-
-	threeX := new(big.Int).Lsh(x, 1)
-	threeX.Add(threeX, x)
-
-	x3.Sub(x3, threeX)
-	x3.Add(x3, params.B)
-	x3.Mod(x3, params.P)
-
-	// y = √(x³ - 3x + b) mod p
-	y := new(big.Int).ModSqrt(x3, params.P)
-
-	// big.Int.Jacobi(a, b) can return nil
-	if y == nil {
-		return nil, nil
-	}
-
-	if y.Bit(0) != (yBit & 0x1) {
-		y.Neg(y)
-		y.Mod(y, params.P)
-	}
-
-	return x, y
-}
-
-func encodePoint(x, y *big.Int) []byte {
-	data := make([]byte, PublicKeyCompressedSize)
-	i := PublicKeyCompressedSize - len(x.Bytes())
-	copy(data[i:], x.Bytes())
-
-	if y.Bit(0) == 0x1 {
-		data[0] = 0x3
-	} else {
-		data[0] = 0x2
-	}
-
-	return data
-}
-
-func decodePoint(data []byte) (*big.Int, *big.Int) {
-	// empty data
-	if len(data) == 0 {
-		return nil, nil
-	}
-
-	switch prefix := data[0]; prefix {
-	case 0x02, 0x03: // compressed key
-		// Incorrect length for compressed encoding
-		if len(data) != PublicKeyCompressedSize {
-			return nil, nil
-		}
-
-		return decompressPoints(new(big.Int).SetBytes(data[1:]), uint(prefix))
-	case 0x04: // uncompressed key
-		// To get the public key, besides getting it from the data and checking,
-		// we also must to check that the points are on an elliptic curve
-		return unmarshalXY(data)
-	}
-
-	// unknown type
-	return nil, nil
-}
-
 // MarshalPublicKey to bytes.
 func MarshalPublicKey(key *ecdsa.PublicKey) []byte {
 	if key == nil || key.X == nil || key.Y == nil {
@@ -150,7 +81,7 @@ func MarshalPublicKey(key *ecdsa.PublicKey) []byte {
 
 // UnmarshalPublicKey from bytes.
 func UnmarshalPublicKey(data []byte) *ecdsa.PublicKey {
-	if x, y := decodePoint(data); x != nil && y != nil && curve.IsOnCurve(x, y) {
+	if x, y := decodePoint(data); x != nil && y != nil {
 		return &ecdsa.PublicKey{
 			Curve: curve,
 			X:     x,

ecdsa_go1.15.go

@@ -0,0 +1,34 @@
+// +build go1.15
+
+package crypto
+
+import (
+	"crypto/elliptic"
+	"math/big"
+)
+
+func encodePoint(x, y *big.Int) []byte {
+	return elliptic.MarshalCompressed(curve, x, y)
+}
+
+func decodePoint(data []byte) (x *big.Int, y *big.Int) {
+	// empty data
+	if len(data) == 0 {
+		return
+	}
+
+	// tries to unmarshal compressed form
+	// returns (nil, nil) when:
+	// - wrong len(data)
+	// - data[0] != 2 && data[0] != 3
+	if x, y = elliptic.UnmarshalCompressed(curve, data); x != nil && y != nil {
+		return x, y
+	}
+
+	// tries to unmarshal uncompressed form and check that points on curve
+	if x, y = unmarshalXY(data); x == nil || y == nil || !curve.IsOnCurve(x, y) {
+		x, y = nil, nil
+	}
+
+	return x, y
+}

ecdsa_older_go.go

@@ -0,0 +1,79 @@
+// +build !go1.15
+
+package crypto
+
+import "math/big"
+
+// decompressPoints using formula y² = x³ - 3x + b
+// crypto/elliptic/elliptic.go:55
+func decompressPoints(x *big.Int, yBit uint) (*big.Int, *big.Int) {
+	params := curve.Params()
+
+	x3 := new(big.Int).Mul(x, x)
+	x3.Mul(x3, x)
+
+	threeX := new(big.Int).Lsh(x, 1)
+	threeX.Add(threeX, x)
+
+	x3.Sub(x3, threeX)
+	x3.Add(x3, params.B)
+	x3.Mod(x3, params.P)
+
+	// y = √(x³ - 3x + b) mod p
+	y := new(big.Int).ModSqrt(x3, params.P)
+
+	// big.Int.Jacobi(a, b) can return nil
+	if y == nil {
+		return nil, nil
+	}
+
+	if y.Bit(0) != (yBit & 0x1) {
+		y.Neg(y)
+		y.Mod(y, params.P)
+	}
+
+	return x, y
+}
+
+func encodePoint(x, y *big.Int) []byte {
+	data := make([]byte, PublicKeyCompressedSize)
+	i := PublicKeyCompressedSize - len(x.Bytes())
+	copy(data[i:], x.Bytes())
+
+	if y.Bit(0) == 0x1 {
+		data[0] = 0x3
+	} else {
+		data[0] = 0x2
+	}
+
+	return data
+}
+
+func decodePoint(data []byte) (x *big.Int, y *big.Int) {
+	// empty data
+	if len(data) == 0 {
+		return
+	}
+
+	switch prefix := data[0]; prefix {
+	case 0x02, 0x03: // compressed key
+		// Incorrect length for compressed encoding
+		if len(data) != PublicKeyCompressedSize {
+			return nil, nil
+		}
+
+		x, y = decompressPoints(new(big.Int).SetBytes(data[1:]), uint(prefix))
+	case 0x04: // uncompressed key
+		// To get the public key, besides getting it from the data and checking,
+		// we also must to check that the points are on an elliptic curve
+		x, y = unmarshalXY(data)
+	default: // unknown type
+		return
+	}
+
+	if x == nil || y == nil || !curve.IsOnCurve(x, y) {
+		x, y = nil, nil
+	}
+
+	return
+}

ecdsa_older_go_test.go

@@ -0,0 +1,28 @@
+// +build !go1.15
+
+package crypto
+
+import (
+	"crypto/ecdsa"
+	"encoding/hex"
+	"math/big"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func Test_decompressPoints(t *testing.T) {
+	t.Run("prepared public keys: decompressPoints", func(t *testing.T) {
+		for i := range testKeys {
+			bytes, err := hex.DecodeString(testKeys[i])
+			require.NoErrorf(t, err, testKeys[i])
+
+			x, y := decompressPoints(new(big.Int).SetBytes(bytes[1:]), uint(bytes[0]))
+			require.NotNil(t, x)
+			require.NotNil(t, y)
+
+			res := MarshalPublicKey(&ecdsa.PublicKey{Curve: curve, X: x, Y: y})
+			require.Equal(t, testKeys[i], hex.EncodeToString(res))
+		}
+	})
+}

ecdsa_test.go

@@ -30,22 +30,6 @@ var testKeys = [...]string{
 	"02a33413277a319cc6fd4c54a2feb9032eba668ec587f307e319dc48733087fa61",
 }
 
-func Test_decompressPoints(t *testing.T) {
-	t.Run("prepared public keys: decompressPoints", func(t *testing.T) {
-		for i := range testKeys {
-			bytes, err := hex.DecodeString(testKeys[i])
-			require.NoErrorf(t, err, testKeys[i])
-
-			x, y := decompressPoints(new(big.Int).SetBytes(bytes[1:]), uint(bytes[0]))
-			require.NotNil(t, x)
-			require.NotNil(t, y)
-
-			res := MarshalPublicKey(&ecdsa.PublicKey{Curve: curve, X: x, Y: y})
-			require.Equal(t, testKeys[i], hex.EncodeToString(res))
-		}
-	})
-}
-
 func TestMarshalUnmarshal(t *testing.T) {
 	t.Run("prepared public keys: unmarshal / marshal", func(t *testing.T) {
 		for i := range testKeys {

go.mod

@@ -3,8 +3,8 @@ module github.com/nspcc-dev/neofs-crypto
 go 1.13
 
 require (
-	github.com/mr-tron/base58 v1.1.2
+	github.com/mr-tron/base58 v1.2.0
 	github.com/nspcc-dev/rfc6979 v0.2.0
-	github.com/pkg/errors v0.8.1
+	github.com/pkg/errors v0.9.1
-	github.com/stretchr/testify v1.4.0
+	github.com/stretchr/testify v1.7.0
 )

go.sum

@@ -2,16 +2,24 @@ github.com/davecgh/go-spew v1.1.0 h1:ZDRjVQ15GmhC3fiQ8ni8+OwkZQO4DARzQgrnXU1Liz8
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/mr-tron/base58 v1.1.2 h1:ZEw4I2EgPKDJ2iEw0cNmLB3ROrEmkOtXIkaG7wZg+78=
 github.com/mr-tron/base58 v1.1.2/go.mod h1:BinMc/sQntlIE1frQmRFPUoPA1Zkr8VRgBdjWI2mNwc=
+github.com/mr-tron/base58 v1.2.0 h1:T/HDJBh4ZCPbU39/+c3rRvE0uKBQlU27+QI8LJ4t64o=
+github.com/mr-tron/base58 v1.2.0/go.mod h1:BinMc/sQntlIE1frQmRFPUoPA1Zkr8VRgBdjWI2mNwc=
 github.com/nspcc-dev/rfc6979 v0.2.0 h1:3e1WNxrN60/6N0DW7+UYisLeZJyfqZTNOjeV/toYvOE=
 github.com/nspcc-dev/rfc6979 v0.2.0/go.mod h1:exhIh1PdpDC5vQmyEsGvc4YDM/lyQp/452QxGq/UEso=
 github.com/pkg/errors v0.8.1 h1:iURUrRGxPUNPdy5/HRSm+Yj6okJ6UtLINN0Q9M4+h3I=
 github.com/pkg/errors v0.8.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
+github.com/pkg/errors v0.9.1 h1:FEBLx1zS214owpjy7qsBeixbURkuhQAwrK5UwLGTwt4=
+github.com/pkg/errors v0.9.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
 github.com/stretchr/testify v1.4.0 h1:2E4SXV/wtOkTonXsotYi4li6zVWxYlZuYNCXe9XRJyk=
 github.com/stretchr/testify v1.4.0/go.mod h1:j7eGeouHqKxXV5pUuKE4zz7dFj8WfuZ+81PSLYec5m4=
+github.com/stretchr/testify v1.7.0 h1:nwc3DEeHmmLAfoZucVR881uASk0Mfjw8xYJ99tb5CcY=
+github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/yaml.v2 v2.2.2 h1:ZCJp+EgiOT7lHqUV2J862kp8Qj64Jo6az82+3Td9dZw=
 gopkg.in/yaml.v2 v2.2.2/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c h1:dUUwHk2QECo/6vqA44rthZ8ie2QXMNeKRTHCNY2nXvo=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=