1 /*
2  * Copyright (c) 2021, Oracle and/or its affiliates. All rights reserved.
3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4  *
5  * This code is free software; you can redistribute it and/or modify it
6  * under the terms of the GNU General Public License version 2 only, as
7  * published by the Free Software Foundation.  Oracle designates this
8  * particular file as subject to the "Classpath" exception as provided
9  * by Oracle in the LICENSE file that accompanied this code.
10  *
11  * This code is distributed in the hope that it will be useful, but WITHOUT
12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
14  * version 2 for more details (a copy is included in the LICENSE file that
15  * accompanied this code).
16  *
17  * You should have received a copy of the GNU General Public License version
18  * 2 along with this work; if not, write to the Free Software Foundation,
19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20  *
21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22  * or visit www.oracle.com if you need additional information or have any
23  * questions.
24  */
25 
26 package sun.security.util;
27 
28 /**
29  * A time-instance comparison of two byte arrays.
30  */
31 public class ByteArrays {
32     // See the MessageDigest.isEqual(byte[] digesta, byte[] digestb)
33     // implementation.  This is a potential enhancement of the
34     // MessageDigest class.
isEqual(byte[] a, int aFromIndex, int aToIndex, byte[] b, int bFromIndex, int bToIndex)35     public static boolean isEqual(byte[] a, int aFromIndex, int aToIndex,
36                                  byte[] b, int bFromIndex, int bToIndex) {
37         if (a == b) {
38             return true;
39         }
40 
41         if (a == null || b == null) {
42             return false;
43         }
44 
45         if (a.length == 0) {
46             return b.length == 0;
47         }
48 
49         int lenA = aToIndex - aFromIndex;
50         int lenB = bToIndex - bFromIndex;
51 
52         if (lenB == 0) {
53             return lenA == 0;
54         }
55 
56         int result = 0;
57         result |= lenA - lenB;
58 
59         // time-constant comparison
60         for (int indexA = 0; indexA < lenA; indexA++) {
61             int indexB = ((indexA - lenB) >>> 31) * indexA;
62             result |= a[aFromIndex + indexA] ^ b[bFromIndex + indexB];
63         }
64 
65         return result == 0;
66     }
67 }
68