/**
 * 对字符串md5加密
 *
 * @param str
 * @return
 */
import java.security.MessageDigest;
public static String getMD5(String str) {
 try {
  // 生成一个MD5加密计算摘要
  MessageDigest md = MessageDigest.getInstance("MD5");
  // 计算md5函数
  md.update(str.getBytes());
  // digest()最后确定返回md5 hash值，返回值为8为字符串。因为md5 hash值是16位的hex值，实际上就是8位的字符
  // BigInteger函数则将8位的字符串转换成16位hex值，用字符串来表示；得到字符串形式的hash值
  return new BigInteger(1, md.digest()).toString(16);
 } catch (Exception e) {
  throw new SpeedException("MD5加密出现错误");
 }
}

package com.zyg.security.md5;

import java.io.UnsupportedEncodingException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import java.util.Arrays;

public class MyMD5Util {
 
 private static final String HEX_NUMS_STR="0123456789ABCDEF";
 private static final Integer SALT_LENGTH = 12;
 
 /** 
 * 将16进制字符串转换成字节数组 
 * @param hex 
 * @return 
 */
 public static byte[] hexStringToByte(String hex) {
 int len = (hex.length() / 2);
 byte[] result = new byte[len];
 char[] hexChars = hex.toCharArray();
 for (int i = 0; i < len; i++) {
 int pos = i * 2;
 result[i] = (byte) (HEX_NUMS_STR.indexOf(hexChars[pos]) << 4 
  | HEX_NUMS_STR.indexOf(hexChars[pos + 1]));
 }
 return result;
 }

 
 /**
 * 将指定byte数组转换成16进制字符串
 * @param b
 * @return
 */
 public static String byteToHexString(byte[] b) {
 StringBuffer hexString = new StringBuffer();
 for (int i = 0; i < b.length; i++) {
 String hex = Integer.toHexString(b[i] & 0xFF);
 if (hex.length() == 1) {
 hex = '0' + hex;
 }
 hexString.append(hex.toUpperCase());
 }
 return hexString.toString();
 }
 
 /**
 * 验证口令是否合法
 * @param password
 * @param passwordInDb
 * @return
 * @throws NoSuchAlgorithmException
 * @throws UnsupportedEncodingException
 */
 public static boolean validPassword(String password, String passwordInDb)
 throws NoSuchAlgorithmException, UnsupportedEncodingException {
 //将16进制字符串格式口令转换成字节数组
 byte[] pwdInDb = hexStringToByte(passwordInDb);
 //声明盐变量
 byte[] salt = new byte[SALT_LENGTH];
 //将盐从数据库中保存的口令字节数组中提取出来
 System.arraycopy(pwdInDb, 0, salt, 0, SALT_LENGTH);
 //创建消息摘要对象
 MessageDigest md = MessageDigest.getInstance("MD5");
 //将盐数据传入消息摘要对象
 md.update(salt);
 //将口令的数据传给消息摘要对象
 md.update(password.getBytes("UTF-8"));
 //生成输入口令的消息摘要
 byte[] digest = md.digest();
 //声明一个保存数据库中口令消息摘要的变量
 byte[] digestInDb = new byte[pwdInDb.length - SALT_LENGTH];
 //取得数据库中口令的消息摘要
 System.arraycopy(pwdInDb, SALT_LENGTH, digestInDb, 0, digestInDb.length);
 //比较根据输入口令生成的消息摘要和数据库中消息摘要是否相同
 if (Arrays.equals(digest, digestInDb)) {
 //口令正确返回口令匹配消息
 return true;
 } else {
 //口令不正确返回口令不匹配消息
 return false;
 }
 }


 /**
 * 获得加密后的16进制形式口令
 * @param password
 * @return
 * @throws NoSuchAlgorithmException
 * @throws UnsupportedEncodingException
 */
 public static String getEncryptedPwd(String password)
 throws NoSuchAlgorithmException, UnsupportedEncodingException {
 //声明加密后的口令数组变量
 byte[] pwd = null;
 //随机数生成器
 SecureRandom random = new SecureRandom();
 //声明盐数组变量
 byte[] salt = new byte[SALT_LENGTH];
 //将随机数放入盐变量中
 random.nextBytes(salt);

 //声明消息摘要对象
 MessageDigest md = null;
 //创建消息摘要
 md = MessageDigest.getInstance("MD5");
 //将盐数据传入消息摘要对象
 md.update(salt);
 //将口令的数据传给消息摘要对象
 md.update(password.getBytes("UTF-8"));
 //获得消息摘要的字节数组
 byte[] digest = md.digest();

 //因为要在口令的字节数组中存放盐，所以加上盐的字节长度
 pwd = new byte[digest.length + SALT_LENGTH];
 //将盐的字节拷贝到生成的加密口令字节数组的前12个字节，以便在验证口令时取出盐
 System.arraycopy(salt, 0, pwd, 0, SALT_LENGTH);
 //将消息摘要拷贝到加密口令字节数组从第13个字节开始的字节
 System.arraycopy(digest, 0, pwd, SALT_LENGTH, digest.length);
 //将字节数组格式加密后的口令转化为16进制字符串格式的口令
 return byteToHexString(pwd);
 }
}

package com.zyg.security.md5;

import java.io.UnsupportedEncodingException;
import java.security.NoSuchAlgorithmException;
import java.util.HashMap;
import java.util.Map;

public class Client {
 private static Map users = new HashMap();
 
 public static void main(String[] args){
 String userName = "zyg";
 String password = "123";
 registerUser(userName,password);
 
 userName = "changong";
 password = "456";
 registerUser(userName,password);
 
 String loginUserId = "zyg";
 String pwd = "1232";
 try {
  if(loginValid(loginUserId,pwd)){
  System.out.println("欢迎登陆！！！");
  }else{
  System.out.println("口令错误，请重新输入！！！");
  }
 } catch (NoSuchAlgorithmException e) {
  // TODO Auto-generated catch block
  e.printStackTrace();
 } catch (UnsupportedEncodingException e) {
  // TODO Auto-generated catch block
  e.printStackTrace();
 } 
 }
 
 /**
 * 注册用户
 * 
 * @param userName
 * @param password
 */
 public static void registerUser(String userName,String password){
 String encryptedPwd = null;
 try {
  encryptedPwd = MyMD5Util.getEncryptedPwd(password);
  
  users.put(userName, encryptedPwd);
  
 } catch (NoSuchAlgorithmException e) {
  // TODO Auto-generated catch block
  e.printStackTrace();
 } catch (UnsupportedEncodingException e) {
  // TODO Auto-generated catch block
  e.printStackTrace();
 }
 }
 
 /**
 * 验证登陆
 * 
 * @param userName
 * @param password
 * @return
 * @throws UnsupportedEncodingException 
 * @throws NoSuchAlgorithmException 
 */
 public static boolean loginValid(String userName,String password) 
  throws NoSuchAlgorithmException, UnsupportedEncodingException{
 String pwdInDb = (String)users.get(userName);
 if(null!=pwdInDb){ // 该用户存在
  return MyMD5Util.validPassword(password, pwdInDb);
 }else{
  System.out.println("不存在该用户！！！");
  return false;
 }
 }
}