/*
* Copyright 2002-2017 the original author or authors.
*
* Licensed 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
*
* https://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 org.springframework.security.crypto.password;
import org.springframework.security.crypto.codec.Utf8;
Utility for constant time comparison to prevent against timing attacks.
Author: Rob Winch
/**
* Utility for constant time comparison to prevent against timing attacks.
*
* @author Rob Winch
*/
class PasswordEncoderUtils {
Constant time comparison to prevent against timing attacks.
Params: - expected –
- actual –
Returns:
/**
* Constant time comparison to prevent against timing attacks.
* @param expected
* @param actual
* @return
*/
static boolean equals(String expected, String actual) {
byte[] expectedBytes = bytesUtf8(expected);
byte[] actualBytes = bytesUtf8(actual);
int expectedLength = expectedBytes == null ? -1 : expectedBytes.length;
int actualLength = actualBytes == null ? -1 : actualBytes.length;
int result = expectedLength == actualLength ? 0 : 1;
for (int i = 0; i < actualLength; i++) {
byte expectedByte = expectedLength <= 0 ? 0 : expectedBytes[i % expectedLength];
byte actualByte = actualBytes[i % actualLength];
result |= expectedByte ^ actualByte;
}
return result == 0;
}
private static byte[] bytesUtf8(String s) {
if (s == null) {
return null;
}
return Utf8.encode(s); // need to check if Utf8.encode() runs in constant time (probably not). This may leak length of string.
}
private PasswordEncoderUtils() {
}
}