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/*_############################################################################
  _## 
  _##  SNMP4J - Salt.java  
  _## 
  _##  Copyright (C) 2003-2018  Frank Fock and Jochen Katz (SNMP4J.org)
  _##  
  _##  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.snmp4j.security;

import java.io.Serializable;
import java.util.Random;
import java.security.SecureRandom;
import java.security.NoSuchAlgorithmException;

import org.snmp4j.log.*;

/**
 * Class that holds a 64 bit salt value for crypto operations.
 * 
 * This class tries to use the SecureRandom class to initialize
 * the salt value. If SecureRandom is not available the class Random
 * is used.
 *
 * @author Jochen Katz
 * @version 1.0
 */
public class Salt implements Serializable {
    private static final long serialVersionUID = -912647364914316367L;
    private long salt;

    private static Salt instance = null;
    private static final LogAdapter logger = LogFactory.getLogger(Salt.class);

    /**
     * Default constructor, initializes the salt to a random value.
     */
    protected Salt() {
        byte[] rnd = new byte[8];

        try {
            SecureRandom sr = SecureRandom.getInstance("SHA1PRNG");
            sr.nextBytes(rnd);
        } catch (NoSuchAlgorithmException nsae) {
            logger.warn("Could not use SecureRandom. Using Random instead.");
            Random r = new Random();
            r.nextBytes(rnd);
        }

        salt = rnd[0];

        for (int i = 0; i < 7; i++) {
            salt = (salt * 256) + ((int) rnd[i]) + 128;
        }
        if (logger.isDebugEnabled()) {
            logger.debug("Initialized Salt to " + Long.toHexString(salt) + ".");
        }
    }

    /**
     * Get a initialized Salt object.
     *
     * @return the Salt object
     */
    public static Salt getInstance() {
        if (instance == null) {
            instance = new Salt();
        }
        return instance;
    }

    /**
     * Get the next value of the salt by adding one to its current value.
     * This might result in a predictable salt value if it is not combined with
     * other somehow unpredictable (random) data.
     *
     * @return previous value increased by one.
     */
    public synchronized long getNext() {
        return salt++;
    }
}