/*
* Copyright 2016 The Netty Project
*
* The Netty Project licenses this file to you under the Apache License,
* version 2.0 (the "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at:
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations
* under the License.
*/
package io.netty.util.internal;
public final class ConstantTimeUtils {
private ConstantTimeUtils() { }
/**
* Compare two {@code int}s without leaking timing information.
* <p>
* The {@code int} return type is intentional and is designed to allow cascading of constant time operations:
* <pre>
* int v1 = 1;
* int v1 = 1;
* int v1 = 1;
* int v1 = 500;
* boolean equals = (equalsConstantTime(l1, l2) & equalsConstantTime(l3, l4)) != 0;
* </pre>
* @param x the first value.
* @param y the second value.
* @return {@code 0} if not equal. {@code 1} if equal.
*/
public static int equalsConstantTime(int x, int y) {
int z = -1 ^ (x ^ y);
z &= z >> 16;
z &= z >> 8;
z &= z >> 4;
z &= z >> 2;
z &= z >> 1;
return z & 1;
}
/**
* Compare two {@code longs}s without leaking timing information.
* <p>
* The {@code int} return type is intentional and is designed to allow cascading of constant time operations:
* <pre>
* long v1 = 1;
* long v1 = 1;
* long v1 = 1;
* long v1 = 500;
* boolean equals = (equalsConstantTime(l1, l2) & equalsConstantTime(l3, l4)) != 0;
* </pre>
* @param x the first value.
* @param y the second value.
* @return {@code 0} if not equal. {@code 1} if equal.
*/
public static int equalsConstantTime(long x, long y) {
long z = -1L ^ (x ^ y);
z &= z >> 32;
z &= z >> 16;
z &= z >> 8;
z &= z >> 4;
z &= z >> 2;
z &= z >> 1;
return (int) (z & 1);
}
/**
* Compare two {@code byte} arrays for equality without leaking timing information.
* For performance reasons no bounds checking on the parameters is performed.
* <p>
* The {@code int} return type is intentional and is designed to allow cascading of constant time operations:
* <pre>
* byte[] s1 = new {1, 2, 3};
* byte[] s2 = new {1, 2, 3};
* byte[] s3 = new {1, 2, 3};
* byte[] s4 = new {4, 5, 6};
* boolean equals = (equalsConstantTime(s1, 0, s2, 0, s1.length) &
* equalsConstantTime(s3, 0, s4, 0, s3.length)) != 0;
* </pre>
* @param bytes1 the first byte array.
* @param startPos1 the position (inclusive) to start comparing in {@code bytes1}.
* @param bytes2 the second byte array.
* @param startPos2 the position (inclusive) to start comparing in {@code bytes2}.
* @param length the amount of bytes to compare. This is assumed to be validated as not going out of bounds
* by the caller.
* @return {@code 0} if not equal. {@code 1} if equal.
*/
public static int equalsConstantTime(byte[] bytes1, int startPos1,
byte[] bytes2, int startPos2, int length) {
// Benchmarking demonstrates that using an int to accumulate is faster than other data types.
int b = 0;
final int end = startPos1 + length;
for (; startPos1 < end; ++startPos1, ++startPos2) {
b |= bytes1[startPos1] ^ bytes2[startPos2];
}
return equalsConstantTime(b, 0);
}
/**
* Compare two {@link CharSequence} objects without leaking timing information.
* <p>
* The {@code int} return type is intentional and is designed to allow cascading of constant time operations:
* <pre>
* String s1 = "foo";
* String s2 = "foo";
* String s3 = "foo";
* String s4 = "goo";
* boolean equals = (equalsConstantTime(s1, s2) & equalsConstantTime(s3, s4)) != 0;
* </pre>
* @param s1 the first value.
* @param s2 the second value.
* @return {@code 0} if not equal. {@code 1} if equal.
*/
public static int equalsConstantTime(CharSequence s1, CharSequence s2) {
if (s1.length() != s2.length()) {
return 0;
}
// Benchmarking demonstrates that using an int to accumulate is faster than other data types.
int c = 0;
for (int i = 0; i < s1.length(); ++i) {
c |= s1.charAt(i) ^ s2.charAt(i);
}
return equalsConstantTime(c, 0);
}
}