crypto/keys: implement NewPublicKeyFromBytes()

It is convenient to have a single function instead of
allocating new `PublicKey` and using `DecodeBytes()` on it.

pkg/core/interop_neo.go

@@ -628,8 +628,7 @@ func assetCreate(ic *interop.Context, v *vm.VM) error {
 	if amount != -util.Satoshi() && (int64(amount)%int64(math.Pow10(int(MaxAssetPrecision-precision))) != 0) {
 		return errors.New("given asset amount has fractional component")
 	}
-	owner := &keys.PublicKey{}
-	err := owner.DecodeBytes(v.Estack().Pop().Bytes())
+	owner, err := keys.NewPublicKeyFromBytes(v.Estack().Pop().Bytes())
 	if err != nil {
 		return gherr.Wrap(err, "failed to get owner key")
 	}

pkg/core/interop_system.go

@@ -324,8 +324,7 @@ func runtimeCheckWitness(ic *interop.Context, v *vm.VM) error {
 	hashOrKey := v.Estack().Pop().Bytes()
 	hash, err := util.Uint160DecodeBytesBE(hashOrKey)
 	if err != nil {
-		key := &keys.PublicKey{}
-		err = key.DecodeBytes(hashOrKey)
+		key, err := keys.NewPublicKeyFromBytes(hashOrKey)
 		if err != nil {
 			return errors.New("parameter given is neither a key nor a hash")
 		}

pkg/crypto/keys/publickey.go

@@ -83,14 +83,15 @@ func NewPublicKeyFromString(s string) (*PublicKey, error) {
 	if err != nil {
 		return nil, err
 	}
+	return NewPublicKeyFromBytes(b)
+}
 
+// NewPublicKeyFromBytes returns public key created from b.
+func NewPublicKeyFromBytes(b []byte) (*PublicKey, error) {
 	pubKey := new(PublicKey)
-	r := io.NewBinReaderFromBuf(b)
-	pubKey.DecodeBinary(r)
-	if r.Err != nil {
-		return nil, r.Err
+	if err := pubKey.DecodeBytes(b); err != nil {
+		return nil, err
 	}
-
 	return pubKey, nil
 }
 

pkg/crypto/keys/publickey_test.go

@@ -37,6 +37,16 @@ func TestEncodeDecodePublicKey(t *testing.T) {
 	}
 }
 
+func TestNewPublicKeyFromBytes(t *testing.T) {
+	priv, err := NewPrivateKey()
+	require.NoError(t, err)
+
+	b := priv.PublicKey().Bytes()
+	pub, err := NewPublicKeyFromBytes(b)
+	require.NoError(t, err)
+	require.Equal(t, priv.PublicKey(), pub)
+}
+
 func TestDecodeFromString(t *testing.T) {
 	str := "03b209fd4f53a7170ea4444e0cb0a6bb6a53c2bd016926989cf85f9b0fba17a70c"
 	pubKey, err := NewPublicKeyFromString(str)

pkg/vm/vm.go

@@ -1595,8 +1595,8 @@ func (v *VM) bytesToPublicKey(b []byte) *keys.PublicKey {
 	if v.keys[s] != nil {
 		pkey = v.keys[s]
 	} else {
-		pkey = &keys.PublicKey{}
-		err := pkey.DecodeBytes(b)
+		var err error
+		pkey, err = keys.NewPublicKeyFromBytes(b)
 		if err != nil {
 			panic(err.Error())
 		}