keys: check length first, then do things in WIFDecode

Otherwise we can easily panic there on bad input.

pkg/crypto/keys/private_key.go

@@ -110,7 +110,9 @@ func NewPrivateKeyFromWIF(wif string) (*PrivateKey, error) {
 // Good documentation about this process can be found here:
 // https://en.bitcoin.it/wiki/Wallet_import_format
 func (p *PrivateKey) WIF() string {
-	w, err := WIFEncode(p.Bytes(), WIFVersion, true)
+	pb := p.Bytes()
+	defer slice.Clean(pb)
+	w, err := WIFEncode(pb, WIFVersion, true)
 	// The only way WIFEncode() can fail is if we're to give it a key of
 	// wrong size, but we have a proper key here, aren't we?
 	if err != nil {

pkg/crypto/keys/wif.go

@@ -59,36 +59,31 @@ func WIFDecode(wif string, version byte) (*WIF, error) {
 	if version == 0x00 {
 		version = WIFVersion
 	}
+	w := &WIF{
+		Version: version,
+		S:       wif,
+	}
+	switch len(b) {
+	case 33: // OK, uncompressed public key.
+	case 34: // OK, compressed public key.
+		// Check the compression flag.
+		if b[33] != 0x01 {
+			return nil, fmt.Errorf("invalid compression flag %d expecting %d", b[33], 0x01)
+		}
+		w.Compressed = true
+	default:
+		return nil, fmt.Errorf("invalid WIF length %d, expecting 33 or 34", len(b))
+	}
+
 	if b[0] != version {
 		return nil, fmt.Errorf("invalid WIF version got %d, expected %d", b[0], version)
 	}
 
 	// Derive the PrivateKey.
-	privKey, err := NewPrivateKeyFromBytes(b[1:33])
+	w.PrivateKey, err = NewPrivateKeyFromBytes(b[1:33])
 	if err != nil {
 		return nil, err
 	}
-	w := &WIF{
-		Version:    version,
-		PrivateKey: privKey,
-		S:          wif,
-	}
 
-	// This is an uncompressed WIF.
-	if len(b) == 33 {
-		w.Compressed = false
-		return w, nil
-	}
-
-	if len(b) != 34 {
-		return nil, fmt.Errorf("invalid WIF length: %d expecting 34", len(b))
-	}
-
-	// Check the compression flag.
-	if b[33] != 0x01 {
-		return nil, fmt.Errorf("invalid compression flag %d expecting %d", b[34], 0x01)
-	}
-
-	w.Compressed = true
 	return w, nil
 }

pkg/crypto/keys/wif_test.go

@@ -4,6 +4,7 @@ import (
 	"encoding/hex"
 	"testing"
 
+	"github.com/nspcc-dev/neo-go/pkg/encoding/base58"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
@@ -65,3 +66,35 @@ func TestWIFEncodeDecode(t *testing.T) {
 	_, err := WIFEncode(wifInv, 0, true)
 	require.Error(t, err)
 }
+
+func TestBadWIFDecode(t *testing.T) {
+	_, err := WIFDecode("garbage", 0)
+	require.Error(t, err)
+
+	s := base58.CheckEncode([]byte{})
+	_, err = WIFDecode(s, 0)
+	require.Error(t, err)
+
+	uncompr := make([]byte, 33)
+	compr := make([]byte, 34)
+
+	s = base58.CheckEncode(compr)
+	_, err = WIFDecode(s, 0)
+	require.Error(t, err)
+
+	s = base58.CheckEncode(uncompr)
+	_, err = WIFDecode(s, 0)
+	require.Error(t, err)
+
+	compr[33] = 1
+	compr[0] = WIFVersion
+	uncompr[0] = WIFVersion
+
+	s = base58.CheckEncode(compr)
+	_, err = WIFDecode(s, 0)
+	require.NoError(t, err)
+
+	s = base58.CheckEncode(uncompr)
+	_, err = WIFDecode(s, 0)
+	require.NoError(t, err)
+}