fix: missing validation in scalar range check (#417)

core/vm/privacy/ringct.go

@@ -513,6 +513,11 @@ func Verify(sig *RingSignature, verifyMes bool) bool {
 	for j := 0; j < ringsize; j++ {
 		var l []byte
 		for i := 0; i < numRing; i++ {
+			// Validate S[i][j] and C[j]
+			if !isValidScalar(S[i][j], curve) || !isValidScalar(C[j], curve) {
+				return false // Or handle the error as required
+			}
+
 			// calculate L[i][j] = s[i][j]*G + c[j]*Ring[i][j]
 			px, py := curve.ScalarMult(rings[i][j].X, rings[i][j].Y, C[j].Bytes()) // px, py = c_i*P_i
 			sx, sy := curve.ScalarBaseMult(S[i][j].Bytes())                        // sx, sy = s[i]*G
@@ -524,6 +529,11 @@ func Verify(sig *RingSignature, verifyMes bool) bool {
 			// calculate R_i = s[i][j]*H_p(Ring[i][j]) + c[j]*I[j]
 			px, py = curve.ScalarMult(image[i].X, image[i].Y, C[j].Bytes()) // px, py = c[i]*I
 			hx, hy := HashPoint(rings[i][j])
+
+			// Validate S[i][j], hx, and hy
+			if !isValidScalar(S[i][j], curve) || !isValidScalar(hx, curve) || !isValidScalar(hy, curve) {
+				return false // Or handle the error as required
+			}
 			//log.Info("H[i][j]", "i", i, "j", j, "x.input", common.Bytes2Hex(rings[i][j].X.Bytes()), "y.input", common.Bytes2Hex(rings[i][j].Y.Bytes()))
 			//log.Info("H[i][j]", "i", i, "j", j, "x", common.Bytes2Hex(hx.Bytes()), "y", common.Bytes2Hex(hy.Bytes()))
 			sx, sy = curve.ScalarMult(hx, hy, S[i][j].Bytes()) // sx, sy = s[i]*H_p(P[i])
@@ -549,6 +559,10 @@ func Verify(sig *RingSignature, verifyMes bool) bool {
 	return bytes.Equal(sig.C.Bytes(), C[ringsize].Bytes())
 }
 
+func isValidScalar(scalar *big.Int, curve elliptic.Curve) bool {
+	return scalar.Sign() >= 0 && scalar.Cmp(curve.Params().N) < 0
+}
+
 func Link(sig_a *RingSignature, sig_b *RingSignature) bool {
 	for i := 0; i < len(sig_a.I); i++ {
 		for j := 0; j < len(sig_b.I); j++ {

core/vm/privacy/ringct_test.go

@@ -4,8 +4,10 @@ import (
 	"bytes"
 	"encoding/binary"
 	"fmt"
+	"math/big"
 	"testing"
 
+	"github.com/XinFinOrg/XDPoSChain/crypto"
 	"github.com/stretchr/testify/assert"
 )
 
@@ -127,3 +129,46 @@ func TestPadTo32Bytes(t *testing.T) {
 	assert.True(t, bytes.Equal(PadTo32Bytes(arr[10:40]), arr[8:40]), "Test PadTo32Bytes shorter than 32 bytes #9")
 	assert.True(t, bytes.Equal(PadTo32Bytes(arr[10:41]), arr[9:41]), "Test PadTo32Bytes shorter than 32 bytes #10")
 }
+
+func TestCurveScalarMult(t *testing.T) {
+	curve := crypto.S256()
+
+	x, y := curve.ScalarBaseMult(curve.Params().N.Bytes())
+	if x == nil && y == nil {
+		fmt.Println("Scalar multiplication with base point returns nil when scalar is the scalar field")
+	}
+
+	x2, y2 := curve.ScalarMult(new(big.Int).SetUint64(uint64(100)), new(big.Int).SetUint64(uint64(2)), curve.Params().N.Bytes())
+	if x2 == nil && y2 == nil {
+		fmt.Println("Scalar multiplication with a point (not necessarily on curve) returns nil when scalar is the scalar field")
+	}
+}
+
+func TestNilPointerDereferencePanic(t *testing.T) {
+	numRing := 5
+	ringSize := 10
+	s := 7
+	rings, privkeys, m, err := GenerateMultiRingParams(numRing, ringSize, s)
+
+	ringSig, err := Sign(m, rings, privkeys, s)
+	if err != nil {
+		fmt.Println("Failed to set up")
+	}
+
+	ringSig.S[0][0] = curve.Params().N // change one sig to the scalar field
+
+	sig, err := ringSig.Serialize()
+	if err != nil {
+		t.Error("Failed to Serialize input Ring signature")
+	}
+
+	deserializedSig, err := Deserialize(sig)
+	if err != nil {
+		t.Error("Failed to Deserialize Ring signature")
+	}
+
+	verified := Verify(deserializedSig, false)
+	if verified {
+		t.Error("Should failed to verify Ring signature as the signature is invalid")
+	}
+}