Merge pull request #19 from bytemare/fix-nist-scalar-copy

Fix NIST scalar and element Copy() and Set() methods

internal/nist/element.go

@@ -140,7 +140,9 @@ func (e *Element[P]) Set(element internal.Element) internal.Element {
 		panic(internal.ErrCastElement)
 	}
 
-	return e.set(ec)
+	e.p.Set(ec.p)
+
+	return e
 }
 
 // Copy returns a copy of the receiver.

internal/nist/scalar.go

@@ -140,23 +140,24 @@ func (s *Scalar) set(scalar *Scalar) *Scalar {
 	return s
 }
 
-// Set sets the receiver to the argument scalar, and returns the receiver.
+// Set sets the receiver to the value of the argument scalar, and returns the receiver.
 func (s *Scalar) Set(scalar internal.Scalar) internal.Scalar {
 	if scalar == nil {
 		return s.set(nil)
 	}
 
 	ec := s.assert(scalar)
+	s.s.Set(&ec.s)
 
-	return s.set(ec)
+	return s
 }
 
 // Copy returns a copy of the Scalar.
 func (s *Scalar) Copy() internal.Scalar {
 	cpy := &Scalar{field: s.field}
 	cpy.s.Set(&s.s)
 
-	return s
+	return cpy
 }
 
 // Encode returns the compressed byte encoding of the scalar.

internal/ristretto/scalar.go

@@ -134,15 +134,16 @@ func (s *Scalar) set(scalar *Scalar) *Scalar {
 	return s
 }
 
-// Set sets the receiver to the argument, and returns the receiver.
+// Set sets the receiver to the value of the argument scalar, and returns the receiver.
 func (s *Scalar) Set(scalar internal.Scalar) internal.Scalar {
 	if scalar == nil {
 		return s.set(nil)
 	}
 
 	ec := assert(scalar)
+	s.scalar = ec.scalar
 
-	return s.set(ec)
+	return s
 }
 
 // Copy returns a copy of the receiver.

internal/scalar.go

@@ -41,7 +41,7 @@ type Scalar interface {
 	// IsZero returns whether the scalar is 0.
 	IsZero() bool
 
-	// Set sets the receiver to the argument, and returns the receiver.
+	// Set sets the receiver to the value of the argument scalar, and returns the receiver.
 	Set(Scalar) Scalar
 
 	// Copy returns a copy of the receiver.

scalar.go

@@ -94,7 +94,7 @@ func (s *Scalar) IsZero() bool {
 	return s.Scalar.IsZero()
 }
 
-// Set sets the receiver to the argument, and returns the receiver.
+// Set sets the receiver to the value of the argument scalar, and returns the receiver.
 func (s *Scalar) Set(scalar *Scalar) *Scalar {
 	s.Scalar.Set(scalar.Scalar)
 	return s

tests/element_test.go

@@ -21,20 +21,43 @@ const (
 	wrongGroup       = "wrong group"
 )
 
-func TestElement_SetCopy(t *testing.T) {
-	testAll(t, func(t2 *testing.T, group *testGroup) {
-		g := group.id
-		base := g.Base()
+func testElementCopySet(t *testing.T, element, other *crypto.Element) {
+	// Verify they don't point to the same thing
+	if &element == &other {
+		t.Fatalf("Pointer to the same scalar")
+	}
 
-		set := g.NewElement().Set(base)
-		if set.Equal(base) != 1 {
-			t.Fatal(expectedEquality)
-		}
+	// Verify whether they are equivalent
+	if element.Equal(other) != 1 {
+		t.Fatalf("Expected equality")
+	}
 
+	// Verify than operations on one don't affect the other
+	element.Add(element)
+	if element.Equal(other) == 1 {
+		t.Fatalf("Unexpected equality")
+	}
+
+	other.Double().Double()
+	if element.Equal(other) == 1 {
+		t.Fatalf("Unexpected equality")
+	}
+}
+
+func TestElementCopy(t *testing.T) {
+	testAll(t, func(t2 *testing.T, group *testGroup) {
+		base := group.id.Base()
 		cpy := base.Copy()
-		if cpy.Equal(base) != 1 {
-			t.Fatal(expectedEquality)
-		}
+		testElementCopySet(t, base, cpy)
+	})
+}
+
+func TestElementSet(t *testing.T) {
+	testAll(t, func(t2 *testing.T, group *testGroup) {
+		base := group.id.Base()
+		other := group.id.NewElement()
+		other.Set(base)
+		testElementCopySet(t, base, other)
 	})
 }
 

tests/scalar_test.go

@@ -65,6 +65,46 @@ func TestScalar_WrongInput(t *testing.T) {
 	})
 }
 
+func testScalarCopySet(t *testing.T, scalar, other *crypto.Scalar) {
+	// Verify they don't point to the same thing
+	if &scalar == &other {
+		t.Fatalf("Pointer to the same scalar")
+	}
+
+	// Verify whether they are equivalent
+	if scalar.Equal(other) != 1 {
+		t.Fatalf("Expected equality")
+	}
+
+	// Verify than operations on one don't affect the other
+	scalar.Add(scalar)
+	if scalar.Equal(other) == 1 {
+		t.Fatalf("Unexpected equality")
+	}
+
+	other.Invert()
+	if scalar.Equal(other) == 1 {
+		t.Fatalf("Unexpected equality")
+	}
+}
+
+func TestScalarCopy(t *testing.T) {
+	testAll(t, func(t2 *testing.T, group *testGroup) {
+		random := group.id.NewScalar().Random()
+		cpy := random.Copy()
+		testScalarCopySet(t, random, cpy)
+	})
+}
+
+func TestScalarSet(t *testing.T) {
+	testAll(t, func(t2 *testing.T, group *testGroup) {
+		random := group.id.NewScalar().Random()
+		other := group.id.NewScalar()
+		other.Set(random)
+		testScalarCopySet(t, random, other)
+	})
+}
+
 func TestScalar_Arithmetic(t *testing.T) {
 	testAll(t, func(t2 *testing.T, group *testGroup) {
 		scalarTestZero(t, group.id)

tests/utils_test.go

@@ -139,6 +139,7 @@ func TestEncoding(t *testing.T) {
 		scalar := group.id.NewScalar().Random()
 		testEncoding(t, scalar, group.id.NewScalar())
 
+		scalar = group.id.NewScalar().Random()
 		element := group.id.Base().Multiply(scalar)
 		testEncoding(t, element, group.id.NewElement())
 	})