Java code example sharing for MD5 encryption and decryption

Basics: Use of MessageDigest class

In fact, MD5 encryption needs to be completed in Java. Most of the MessageDigest class can help you implement it. A few lines of code are enough:

/**
 * 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");
 }
}

Advanced: Encryption and Decryption Class
Java implements MD5 encryption and decryption classes, with test classes attached, see the code for details.

MD5 encryption and decryption class——MyMD5Util, the code is as follows

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 = &#39;0&#39; + 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);
 }
}

##Test class——Client, the code is as follows:

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;
 }
 }
}

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