/*
 * Copyright [2020] [MaxKey of copyright http://www.maxkey.top]
 * 
 * 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
 * 
 *     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 org.maxkey.crypto.password;

 
import org.springframework.security.crypto.codec.Utf8;

import java.security.MessageDigest;

/**
 * Utility for constant time comparison to prevent against timing attacks.
 *
 * @author Rob Winch
 */
public class PasswordEncoderUtils {

    /**
     * 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);

        return MessageDigest.isEqual(expectedBytes, actualBytes);
    }

    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() {
    }
}
