Add some utilities for comparing arrays without data-dependent branches

Lets arrays be compared without leaking information about their
contents caused by early exits etc.

1 files changed, 38 insertions, 0 deletions

diff --git a/security-utils/src/test/java/com/yahoo/security/SideChannelSafeTest.java b/security-utils/src/test/java/com/yahoo/security/SideChannelSafeTest.java
new file mode 100644
index 00000000000..7a66ed6eb7f
--- /dev/null
+++ b/security-utils/src/test/java/com/yahoo/security/SideChannelSafeTest.java
@@ -0,0 +1,38 @@
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+package com.yahoo.security;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+/**
+ * _Functional_ test of side channel safe utility functions. Testing that they're actually
+ * (probably) side channel safe would be too flaky since it's inherently timing-dependent.
+ */
+public class SideChannelSafeTest {
+
+    @Test
+    void all_zeros_checks_length_and_array_contents() {
+        assertFalse(SideChannelSafe.allZeros(new byte[0]));
+        assertFalse(SideChannelSafe.allZeros(new byte[]{ 1 }));
+        assertTrue(SideChannelSafe.allZeros(new byte[]{ 0 }));
+        assertFalse(SideChannelSafe.allZeros(new byte[]{ 0, 0, 127, 0 }));
+        assertFalse(SideChannelSafe.allZeros(new byte[]{ 0, 0, -1, 0 }));
+        assertTrue(SideChannelSafe.allZeros(new byte[]{ 0, 0, 0 }));
+    }
+
+    @Test
+    void arrays_equal_checks_length_and_array_contents() {
+        assertTrue(SideChannelSafe.arraysEqual(new byte[0], new byte[0]));
+        assertFalse(SideChannelSafe.arraysEqual(new byte[] { 0 }, new byte[0]));
+        assertFalse(SideChannelSafe.arraysEqual(new byte[0], new byte[]{ 0 }));
+        assertTrue(SideChannelSafe.arraysEqual(new byte[] { 0, 0, 0 }, new byte[] { 0, 0, 0 }));
+        assertTrue(SideChannelSafe.arraysEqual(new byte[] { 0x7, 0xe }, new byte[] { 0x7, 0xe }));
+        assertFalse(SideChannelSafe.arraysEqual(new byte[] { 0xe, 0x7 }, new byte[] { 0x7, 0xe }));
+        assertFalse(SideChannelSafe.arraysEqual(new byte[] { -1, 127 }, new byte[] { 127, -1 }));
+        assertFalse(SideChannelSafe.arraysEqual(new byte[] { -1, -1, 1 }, new byte[] { -1, -1, 2 }));
+        assertFalse(SideChannelSafe.arraysEqual(new byte[] { 0, -1, 1 }, new byte[] { 0, -1, 3 }));
+    }
+
+}