core/src/main/java/org/apache/ftpserver/usermanager/SaltedPasswordEncryptor.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF 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 org.apache.ftpserver.usermanager;

import java.security.SecureRandom;

import org.apache.ftpserver.util.EncryptUtils;
import org.apache.ftpserver.util.PasswordUtil;

/**
 * Password encryptor that hashes a salt together with the password using MD5.
 * Using a salt protects against birthday attacks. The hashing is also made in
 * iterations, making lookup attacks much harder.
 *
 * The algorithm is based on the principles described in
 * http://www.jasypt.org/howtoencryptuserpasswords.html
 * 
 * @author <a href="http://mina.apache.org">Apache MINA Project</a>
 */
public class SaltedPasswordEncryptor implements PasswordEncryptor {

	private SecureRandom rnd = new SecureRandom();

	private static final int MAX_SEED = 99999999;
	private static final int HASH_ITERATIONS = 1000;

	private String encrypt(String password, String salt) {
		String hash = salt + password;
		for (int i = 0; i < HASH_ITERATIONS; i++) {
			hash = EncryptUtils.encryptMD5(hash);
		}
		return salt + ":" + hash;
	}

	/**
	 * Encrypts the password using a salt concatenated with the password and a
	 * series of MD5 steps.
	 */
	public String encrypt(String password) {
		String seed = Integer.toString(rnd.nextInt(MAX_SEED));

		return encrypt(password, seed);
	}

	/**
	 * {@inheritDoc}
	 */
	public boolean matches(String passwordToCheck, String storedPassword) {
		if (storedPassword == null) {
			throw new NullPointerException("storedPassword can not be null");
		}
		if (passwordToCheck == null) {
			throw new NullPointerException("passwordToCheck can not be null");
		}

		// look for divider for hash
		int divider = storedPassword.indexOf(':');

		if (divider < 1) {
			throw new IllegalArgumentException("stored password does not contain salt");
		}

		String storedSalt = storedPassword.substring(0, divider);

		return PasswordUtil.secureCompareFast(encrypt(passwordToCheck, storedSalt).toLowerCase(),
				storedPassword.toLowerCase());
	}

}