From b56db814255256e9cc73c8f91c77936062ed2e5e Mon Sep 17 00:00:00 2001
From: Vinnie Ryan <vinnie@openjdk.org>
Date: Thu, 24 Sep 2009 22:50:41 +0100
Subject: [PATCH] 6863503: SECURITY: MessageDigest.isEqual introduces timing
 attack vulnerabilities

Reviewed-by: mullan, wetmore
---
 .../classes/java/security/MessageDigest.java  | 19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/jdk/src/share/classes/java/security/MessageDigest.java b/jdk/src/share/classes/java/security/MessageDigest.java
index 9ff8390d92d..f08b6fd9502 100644
--- a/jdk/src/share/classes/java/security/MessageDigest.java
+++ b/jdk/src/share/classes/java/security/MessageDigest.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 1996-2006 Sun Microsystems, Inc.  All Rights Reserved.
+ * Copyright 1996-2009 Sun Microsystems, Inc.  All Rights Reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -414,16 +414,17 @@ public abstract class MessageDigest extends MessageDigestSpi {
      *
      * @return true if the digests are equal, false otherwise.
      */
-    public static boolean isEqual(byte digesta[], byte digestb[]) {
-        if (digesta.length != digestb.length)
+    public static boolean isEqual(byte[] digesta, byte[] digestb) {
+        if (digesta.length != digestb.length) {
             return false;
-
-        for (int i = 0; i < digesta.length; i++) {
-            if (digesta[i] != digestb[i]) {
-                return false;
-            }
         }
-        return true;
+
+        int result = 0;
+        // time-constant comparison
+        for (int i = 0; i < digesta.length; i++) {
+            result |= digesta[i] ^ digestb[i];
+        }
+        return result == 0;
     }
 
     /**