如何使用自定义类加载器防止代码被反编译破解

前言

最近和朋友聊天,他接了个外包项目,他问我有没有办法让自己的源码不被反编译破解,我就跟他说可以对代码进行混淆和加密。今天我们就来聊聊如何通过对代码进行加密实现代码防反编译,至于混淆因为可以直接利用proguard-maven-plugin进行配置实现,相对比较简单,就不在本文论述

代码防编译整体套路

1、编写加密工具类

@Slf4j
public class EncryptUtils {

    private static String secretKey = "test123456lyb-geek"+System.currentTimeMillis();

    private EncryptUtils(){}


    public static void encrypt(String classFileSrcPath,String classFileDestPath) {
        System.out.println(secretKey);
        FileInputStream fis = null;
        FileOutputStream fos = null;

        try {
            fis = new FileInputStream(classFileSrcPath);
            fos = new FileOutputStream(classFileDestPath);
            int len;
            String[] arrs = secretKey.split("lyb-geek");
            long key = Long.valueOf(arrs[1]);
            System.out.println("key:"+key);
            while((len = fis.read())!=-1){
              byte data = (byte)(len + key + secretKey.length());
              fos.write(data);
            }
        } catch (Exception e) {
           log.error("encrypt fail:"+e.getMessage(),e);
        }finally {
            if(fis != null){
                try {
                    fis.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }

            if(fos != null){
                try {
                    fos.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }

    }

}

2、对需要防止被反编译代码加密

 public static void main(String[] args) {
        String classFileSrcPath = classFileSrcPath("UserServiceImpl");
        System.out.println("classFileSrcPath:--->"+classFileSrcPath);
        String classFileDestDir = ServiceGenerate.class.getClassLoader().getResource("META-INF/services/").getPath();
        System.out.println("classFileDestDir:--->"+classFileDestDir);
        String classFileDestPath = classFileDestDir + "com.github.lybgeek.user.service.impl.UserServiceImpl.lyb";
        EncryptUtils.encrypt(classFileSrcPath,classFileDestPath);
    }

3、对加密代码进行反编译验证

打开反编译工具jd-gui,把加密的代码拖入jd-gui

如何使用自定义类加载器防止代码被反编译破解_第1张图片
打不开,至少说明不能用jd-gui来反编译加密过的代码。

我们打开正常的编译的class文件,其内容形如下
image.png
内容宛若天书

思考一:代码都被加密了,那jvm如何识别?

答案:既然有加密,自然可以通过解密来使用。那这个解密得存放在什么地方进行解密?

如果对类加载有一定了解的朋友,就会知道java的class文件是通过类加载器把class加载入jvm内存中,因此我们可以考虑把解密放在类加载器中。常用的类加载有启动类加载器、扩展类加载器、系统类加载。我们正常classpath路径下的类都是通过系统类加载器进行加载。而不巧这三个jdk提供的加载器没法满足我们的需求。因此我们只能自己实现我们的类加载器。其自定义加载器代码如下

@Slf4j
public class CustomClassLoader extends ClassLoader{

    /**
     * 授权码
     */
    private String secretKey;

    private String SECRETKEY_PREFIX = "lyb-geek";


    /**
     * class文件的根目录
     */
    private String classRootDir = "META-INF/services/";

    public CustomClassLoader(String secretKey) {
        this.secretKey = secretKey;
    }


    public String getClassRootDir() {
        return classRootDir;
    }

    public void setClassRootDir(String classRootDir) {
        this.classRootDir = classRootDir;
    }

    @Override
    protected Class findClass(String name) throws ClassNotFoundException {

        Class clz = findLoadedClass(name);
        //先查询有没有加载过这个类。如果已经加载,则直接返回加载好的类。如果没有,则加载新的类。
        if(clz != null){
            return clz;
        }else{
            ClassLoader parent = this.getParent();
            clz = getaClass(name, clz, parent);

            if(clz != null){
                return clz;
            }else{
                clz = getaClass(name);
            }

        }

        return clz;

    }

    private Class getaClass(String name) throws ClassNotFoundException {
        Class clz;
        byte[] classData = getClassData(name);
        if(classData == null){
            throw new ClassNotFoundException();
        }else{
            clz = defineClass(name, classData, 0,classData.length);
        }
        return clz;
    }

    private Class getaClass(String name, Class clz, ClassLoader parent) {
        try {
            //委派给父类加载
            clz = parent.loadClass(name);
        } catch (Exception e) {
           //log.warn("parent load class fail:"+ e.getMessage(),e);
        }
        return clz;
    }

    private byte[] getClassData(String classname){
        if(StringUtils.isEmpty(secretKey) || !secretKey.contains(SECRETKEY_PREFIX) || secretKey.split(SECRETKEY_PREFIX).length != 2){
            throw new RuntimeException("secretKey is illegal");
        }
        String path = CustomClassLoader.class.getClassLoader().getResource("META-INF/services/").getPath() +"/"+ classname+".lyb";
        InputStream is = null;
        ByteArrayOutputStream bas = null;
        try{
            is  = new FileInputStream(path);
            bas = new ByteArrayOutputStream();
            int len;
            //解密
            String[] arrs = secretKey.split(SECRETKEY_PREFIX);
            long key = Long.valueOf(arrs[1]);
          //  System.out.println("key:"+key);
            while((len = is.read())!=-1){
                byte data = (byte)(len - key - secretKey.length());
                bas.write(data);
            }
            return bas.toByteArray();
        }catch(Exception e){
            e.printStackTrace();
            return null;
        }finally{
            try {
                if(is!=null){
                    is.close();
                }
            } catch (IOException e) {
                log.error("encrypt fail:"+e.getMessage(),e);
            }
            try {
                if(bas!=null){
                    bas.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

    }


}

通过如下方式进行调用

 public static void main(String[] args) throws Exception{
        CustomClassLoader customClassLoader = new CustomClassLoader("test123456lyb-geek1603895713759");
        Class clz = customClassLoader.loadClass("com.github.lybgeek.user.service.impl.UserServiceImpl");
        if(clz != null){
            Method method = clz.getMethod("list", User.class);
            method.invoke(clz.newInstance(),new User());
        }
    }

思考二:通过自定义加载器加载过的类如何整合进行spring?

答案: 通过spring提供的扩展点进行ioc容器注入

1、编写bean定义,并注册注册bean定义
@Component
public class ServiceBeanFactoryPostProcessor implements BeanFactoryPostProcessor {

    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
        Object secretKey = YmlUtils.getValue("lyb-geek.secretKey");
        if(ObjectUtils.isEmpty(secretKey)){
            throw new RuntimeException("secretKey can not be null,you maybe need to config in application.yml with key lyb-geek.secretKey");
        }
        registerBean(beanFactory,secretKey.toString());

//        setClassLoader(beanFactory,secretKey.toString());
    }

    /**
     * 如果项目中引入了>spring-boot-devtools,则默认加载器为org.springframework.boot.devtools.restart.classloader.RestartClassLoader
     * 此时如果使用自定加载器,则需把bean的类加载器变更为AppClassLoader
     * @param beanFactory
     */
    private void setClassLoader(ConfigurableListableBeanFactory beanFactory,String secretKey) {

        CustomClassLoader customClassLoader = new CustomClassLoader(secretKey);
        beanFactory.setBeanClassLoader(customClassLoader.getParent());
    }

    private void registerBean(ConfigurableListableBeanFactory beanFactory,String secretKey){
        DefaultListableBeanFactory defaultListableBeanFactory = (DefaultListableBeanFactory) beanFactory;
        BeanDefinitionBuilder builder = BeanDefinitionBuilder.genericBeanDefinition(UserService.class);
        GenericBeanDefinition definition = (GenericBeanDefinition) builder.getRawBeanDefinition();
        definition.getPropertyValues().add("serviceClz",UserService.class);
        definition.getPropertyValues().add("serviceImplClzName", "com.github.lybgeek.user.service.impl.UserServiceImpl");
        definition.getPropertyValues().add("secretKey", secretKey);
        definition.setBeanClass(ServiceFactoryBean.class);
        definition.setAutowireMode(GenericBeanDefinition.AUTOWIRE_BY_TYPE);
        String beanId = StringUtils.uncapitalize(UserService.class.getSimpleName());
        defaultListableBeanFactory.registerBeanDefinition(beanId, definition);
    }

}
2、如果是接口注入,还需通过FactoryBean进行狸猫换太子
@Data
@AllArgsConstructor
@NoArgsConstructor
public class ServiceFactoryBean  implements FactoryBean , ApplicationContextAware, InitializingBean {

    private ApplicationContext applicationContext;

    private Class serviceClz;

    private String serviceImplClzName;

    private String secretKey;

    private Object targetObj;

    @Override
    public T getObject() throws Exception {
        return (T) targetObj;
    }

    @Override
    public Class getObjectType() {
        return serviceClz;
    }

    @Override
    public void afterPropertiesSet() throws Exception {
        targetObj = ServiceFactory.create(secretKey,serviceImplClzName,applicationContext);

    }

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        this.applicationContext = applicationContext;
    }
}
3、验证是否整合成功

验证示例代码

@RestController
@RequestMapping("/user")
public class UserController {


    @Autowired
    private UserService userService;

    @PostMapping(value = "/save")
    public User save(User user){
        User newUser = userService.save(user);
        return newUser;
    }
    }

如何使用自定义类加载器防止代码被反编译破解_第2张图片
能够正常输出,说明整合成功

总结

上述的例子只是提供一个思路,并不能完全杜绝代码被反编译。因为如果真想进行反编译,其实可以先通过反编译你自定义的类加载器,然后通过解密方式,去逆推加密算法,从而还原加密类。要杜绝代码被反编译的思路有如下

  • 提高反编译的成本,比如对自定义类加载再次加密,编写复杂的加密算法

    • 编写让人没有欲望反编译的代码,比如写一堆垃圾代码

demo链接

https://github.com/lyb-geek/springboot-learning/tree/master/springboot-code-authorization

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