MessageDigest 加密和解密2

package com.drawthink.platform.util;

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

/**
 * MD5類:加密
 */
public class MD5Util {
    //獲取字符串的MD5串
    public static String Md5(//
            String plainText //原字符串
    ) {
        if (plainText == null) {
            return null;
        }
        StringBuffer buf = new StringBuffer();
        try {
            MessageDigest md = MessageDigest.getInstance("MD5");
            md.update(plainText.getBytes());
            md.reset();
            byte b[] = md.digest();
            int i;
            for (int offset = 0; offset < b.length; offset++) {
                i = b[offset];
                if (i < 0) {
                    i += 256;
                }
                if (i < 16) {
                    buf.append("0");
                }
                buf.append(Integer.toHexString(i));
            }
        } catch (NoSuchAlgorithmException ex) {
            ex.printStackTrace();
        }
        return buf.toString();
    }
}

-------------------解密---------------------------
package com.drawthink.platform.util;

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;
    
    /** 
    * 將16進制字符串轉換成字節數組 
    * @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;
    }


    /**
     * 將指定byte數組轉換成16進制字符串
     * @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();
     }
     /**
     * 驗證口令是否合法
     * @param password
     * @param passwordInDb
     * @return
     * @throws NoSuchAlgorithmException
     * @throws UnsupportedEncodingException
     */
     public static boolean validPassword(String password, String passwordInDb)throws NoSuchAlgorithmException, UnsupportedEncodingException {
         //將16進制字符串格式口令轉換成字節數組
         byte[] pwdInDb = hexStringToByte(passwordInDb);
         //聲明鹽變量
         byte[] salt = new byte[SALT_LENGTH];
         //將鹽從數據庫中保存的口令字節數組中提取出來
         System.arraycopy(pwdInDb, 0, salt, 0, SALT_LENGTH);
         //創建消息摘要對象
         MessageDigest md = MessageDigest.getInstance("MD5");
         //將鹽數據傳入消息摘要對象
         md.update(salt);
         //將口令的數據傳給消息摘要對象
         md.update(password.getBytes("UTF-8"));
         //生成輸入口令的消息摘要
         byte[] digest = md.digest();
         //聲明一個保存數據庫中口令消息摘要的變量
         byte[] digestInDb = new byte[pwdInDb.length - SALT_LENGTH];
         //取得數據庫中口令的消息摘要
         System.arraycopy(pwdInDb, SALT_LENGTH, digestInDb, 0, digestInDb.length);
         //比較根據輸入口令生成的消息摘要和數據庫中消息摘要是否相同
         if (Arrays.equals(digest, digestInDb)) {
             //口令正確返回口令匹配消息
             return true;
         } else {
             //口令不正確返回口令不匹配消息
             return false;
         }
     }
 
 
     /**
     * 獲得加密后的16進制形式口令
     * @param password
     * @return
     * @throws NoSuchAlgorithmException
     * @throws UnsupportedEncodingException
     */
     public static String getEncryptedPwd(String password) throws NoSuchAlgorithmException, UnsupportedEncodingException {
         //聲明加密后的口令數組變量
         byte[] pwd = null;
         //隨機數生成器
         SecureRandom random = new SecureRandom();
         //聲明鹽數組變量
         byte[] salt = new byte[SALT_LENGTH];
         //將隨機數放入鹽變量中
         random.nextBytes(salt);
         
         //聲明消息摘要對象
         MessageDigest md = null;
         //創建消息摘要
         md = MessageDigest.getInstance("MD5");
         //將鹽數據傳入消息摘要對象
         md.update(salt);
         //將口令的數據傳給消息摘要對象
         md.update(password.getBytes("UTF-8"));
         //獲得消息摘要的字節數組
         byte[] digest = md.digest();
         
         //因為要在口令的字節數組中存放鹽，所以加上鹽的字節長度
         pwd = new byte[digest.length + SALT_LENGTH];
         //將鹽的字節拷貝到生成的加密口令字節數組的前12個字節，以便在驗證口令時取出鹽
         System.arraycopy(salt, 0, pwd, 0, SALT_LENGTH);
         //將消息摘要拷貝到加密口令字節數組從第13個字節開始的字節
         System.arraycopy(digest, 0, pwd, SALT_LENGTH, digest.length);
         //將字節數組格式加密后的口令轉化為16進制字符串格式的口令
         return byteToHexString(pwd);
     }
     
     //測試方法
     public static void main(String[] args) {
        try {
            String password = "5a105e8b9d40e1329780d62ea2265d8a";
            boolean encryptedPwd = MyMD5Util.validPassword(password,password);
            System.out.println(encryptedPwd);
        } catch (NoSuchAlgorithmException | UnsupportedEncodingException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
}