1 files changed, 93 insertions, 0 deletions
diff --git a/src/crypto/internal/edwards25519/scalar_alias_test.go b/src/crypto/internal/edwards25519/scalar_alias_test.go
new file mode 100644
index 0000000..827153b
--- /dev/null
+++ b/src/crypto/internal/edwards25519/scalar_alias_test.go
@@ -0,0 +1,93 @@
+// Copyright (c) 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package edwards25519
+
+import (
+	"testing"
+	"testing/quick"
+)
+
+func TestScalarAliasing(t *testing.T) {
+	checkAliasingOneArg := func(f func(v, x *Scalar) *Scalar, v, x Scalar) bool {
+		x1, v1 := x, x
+
+		// Calculate a reference f(x) without aliasing.
+		if out := f(&v, &x); out != &v || !isReduced(out) {
+			return false
+		}
+
+		// Test aliasing the argument and the receiver.
+		if out := f(&v1, &v1); out != &v1 || v1 != v || !isReduced(out) {
+			return false
+		}
+
+		// Ensure the arguments was not modified.
+		return x == x1
+	}
+
+	checkAliasingTwoArgs := func(f func(v, x, y *Scalar) *Scalar, v, x, y Scalar) bool {
+		x1, y1, v1 := x, y, Scalar{}
+
+		// Calculate a reference f(x, y) without aliasing.
+		if out := f(&v, &x, &y); out != &v || !isReduced(out) {
+			return false
+		}
+
+		// Test aliasing the first argument and the receiver.
+		v1 = x
+		if out := f(&v1, &v1, &y); out != &v1 || v1 != v || !isReduced(out) {
+			return false
+		}
+		// Test aliasing the second argument and the receiver.
+		v1 = y
+		if out := f(&v1, &x, &v1); out != &v1 || v1 != v || !isReduced(out) {
+			return false
+		}
+
+		// Calculate a reference f(x, x) without aliasing.
+		if out := f(&v, &x, &x); out != &v || !isReduced(out) {
+			return false
+		}
+
+		// Test aliasing the first argument and the receiver.
+		v1 = x
+		if out := f(&v1, &v1, &x); out != &v1 || v1 != v || !isReduced(out) {
+			return false
+		}
+		// Test aliasing the second argument and the receiver.
+		v1 = x
+		if out := f(&v1, &x, &v1); out != &v1 || v1 != v || !isReduced(out) {
+			return false
+		}
+		// Test aliasing both arguments and the receiver.
+		v1 = x
+		if out := f(&v1, &v1, &v1); out != &v1 || v1 != v || !isReduced(out) {
+			return false
+		}
+
+		// Ensure the arguments were not modified.
+		return x == x1 && y == y1
+	}
+
+	for name, f := range map[string]any{
+		"Negate": func(v, x Scalar) bool {
+			return checkAliasingOneArg((*Scalar).Negate, v, x)
+		},
+		"Multiply": func(v, x, y Scalar) bool {
+			return checkAliasingTwoArgs((*Scalar).Multiply, v, x, y)
+		},
+		"Add": func(v, x, y Scalar) bool {
+			return checkAliasingTwoArgs((*Scalar).Add, v, x, y)
+		},
+		"Subtract": func(v, x, y Scalar) bool {
+			return checkAliasingTwoArgs((*Scalar).Subtract, v, x, y)
+		},
+	} {
+		err := quick.Check(f, &quick.Config{MaxCountScale: 1 << 5})
+		if err != nil {
+			t.Errorf("%v: %v", name, err)
+		}
+	}
+}