md5.java

Java Mail Server JAVA编写的邮件服务器

/****************************************************************
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.     *
 *                                                              *
 * Copyright 2008 Jun Li(SiChuan University, the School of      *
 * Software Engineering). All rights reserved.                  *
 *                                                              *
 * Licensed to the JMS under one  or more contributor license   *
 * agreements.  See the LICENCE file  distributed with this     *
 * work for additional information regarding copyright          *
 * ownership.  The JMS licenses this file  you may not use this *
 * file except in compliance  with the License.                 *
 *                                                              *
 * 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.jpxx.mail.Util.Security;

import java.security.MessageDigest;

/**
 * The algorithm takes as input a message of arbitrary length and produces
 * as output a 128-bit "fingerprint" or "message digest" of the input.
 * It is conjectured that it is computationally infeasible to produce
 * two messages having the same message digest, or to produce any
 * message having a given prespecified target message digest. The MD5
 * algorithm is intended for digital signature applications, where a
 * large file must be "compressed" in a secure manner before being
 * encrypted with a private (secret) key under a public-key cryptosystem
 * such as RSA.
 * 
 * The MD5 algorithm is designed to be quite fast on 32-bit machines. In
 * addition, the MD5 algorithm does not require any large substitution
 * tables; the algorithm can be coded quite compactly.
 * 
 * The MD5 algorithm is an extension of the MD4 message-digest algorithm
 * 1,2]. MD5 is slightly slower than MD4, but is more "conservative" in
 * design. MD5 was designed because it was felt that MD4 was perhaps
 * being adopted for use more quickly than justified by the existing
 * critical review; because MD4 was designed to be exceptionally fast,
 * it is "at the edge" in terms of risking successful cryptanalytic
 * attack. MD5 backs off a bit, giving up a little in speed for a much
 * greater likelihood of ultimate security. It incorporates some
 * suggestions made by various reviewers, and contains additional
 * optimizations. The MD5 algorithm is being placed in the public domain
 * for review and possible adoption as a standard.
 * 
 *
 * @author Jun Li
 * @version $Revision: 0.0.1 $, $Date: 2008/04/28 23:09:00 $
 * @since JMS 0.0.1
 */
public class MD5 {

    /**
     * Encode String with MD5
     * @param s String. 
     * @return Encoded String
     */
    public final static String encode(String s) {
        char hexDigits[] = {'0', '1', '2', '3', '4', '5', '6', '7',
            '8', '9', 'a', 'b', 'c', 'd', 'e', 'f'
        };
        try {
            byte[] strTemp = s.getBytes();
            MessageDigest mdTemp = MessageDigest.getInstance("MD5");
            mdTemp.update(strTemp);
            byte[] md = mdTemp.digest();
            int j = md.length;
            char str[] = new char[j * 2];
            int k = 0;
            for (int i = 0; i < j; i++) {
                byte byte0 = md[i];
                str[k++] = hexDigits[byte0 >>> 4 & 0xf];
                str[k++] = hexDigits[byte0 & 0xf];
            }
            return new String(str);
        } catch (Exception e) {
            return null;
        }
    }
}