SpringBoot自定义classloader加密保护class文件

背景

最近针对公司框架进行关键业务代码进行加密处理，防止通过jd-gui等反编译工具能够轻松还原工程代码，相关混淆方案配置使用比较复杂且针对springboot项目问题较多，所以针对class文件加密再通过自定义的classloder进行解密加载，此方案并不是绝对安全，只是加大反编译的困难程度，防君子不防小人，整体加密保护流程图如下图所示

maven插件加密

使用自定义maven插件对编译后指定的class文件进行加密，加密后的class文件拷贝到指定路径，这里是保存到resource/coreclass下，删除源class文件，加密使用的是简单的DES对称加密

 @Parameter(name = "protectClassNames", defaultValue = "")
 private List<String> protectClassNames;
 @Parameter(name = "noCompileClassNames", defaultValue = "")
 private List<String> noCompileClassNames;
 private List<String> protectClassNameList = new ArrayList<>();
 private void protectCore(File root) throws IOException {
        if (root.isDirectory()) {
            for (File file : root.listFiles()) {
                protectCore(file);
            }
        }
        String className = root.getName().replace(".class", "");
        if (root.getName().endsWith(".class")) {
            //class筛选
            boolean flag = false;
            if (protectClassNames!=null && protectClassNames.size()>0) {
                for (String item : protectClassNames) {
                    if (className.equals(item)) {
                        flag = true;
                    }
                }
            }
            if(noCompileClassNames.contains(className)){
                boolean deleteResult = root.delete();
                if(!deleteResult){
                    System.gc();
                    deleteResult = root.delete();
                }
                System.out.println("【noCompile-deleteResult】:" + deleteResult);
            }
            if (flag && !protectClassNameList.contains(className)) {
                protectClassNameList.add(className);
                System.out.println("【protectCore】:" + className);
                FileOutputStream fos = null;
                try {
                    final byte[] instrumentBytes = doProtectCore(root);
                    //加密后的class文件保存路径
                    String folderPath = output.getAbsolutePath() + "\\" + "classes";
                    File  folder = new File(folderPath);
                    if(!folder.exists()){
                        folder.mkdir();
                    }
                    folderPath = output.getAbsolutePath() + "\\" + "classes"+ "\\" + "coreclass" ;
                    folder = new File(folderPath);
                    if(!folder.exists()){
                        folder.mkdir();
                    }
                    String filePath = output.getAbsolutePath() + "\\" + "classes" + "\\" + "coreclass" + "\\" + className + ".class";
                    System.out.println("【filePath】：" + filePath);
                    File protectFile = new File(filePath);
                    if (protectFile.exists()) {
                        protectFile.delete();
                    }
                    protectFile.createNewFile();
                    fos = new FileOutputStream(protectFile);
                    fos.write(instrumentBytes);
                    fos.flush();
                } catch (MojoExecutionException e) {
                    System.out.println("【protectCore-exception】:" + className);
                    e.printStackTrace();
                } finally {
                    if (fos != null) {
                        fos.close();
                    }
                    if(root.exists()){
                        boolean deleteResult = root.delete();
                        if(!deleteResult){
                            System.gc();
                            deleteResult = root.delete();
                        }
                        System.out.println("【protectCore-deleteResult】:" + deleteResult);
                    }
                }
            }
        }
    }

    private byte[] doProtectCore(File clsFile) throws MojoExecutionException {
        try {
            FileInputStream inputStream = new FileInputStream(clsFile);
            byte[] content = ProtectUtil.encrypt(inputStream);
            inputStream.close();
            return content;
        } catch (Exception e) {
            throw new MojoExecutionException("doProtectCore error", e);
        }
    }

注意事项

1.加密后的文件也是class文件，为了防止在递归查找中重复加密，需要对已经加密后的class名称记录防止重复

2.在删除源文件时可能出现编译占用的情况，执行System.gc()后方可删除

3.针对自定义插件的列表形式的configuration节点可以使用List来映射

插件使用配置如图所示

自定义classloader

创建CustomClassLoader继承自ClassLoader，重写findClass方法只处理装载加密后的class文件，其他class交有默认加载器处理，需要注意的是默认处理不能调用super.finclass方法，在idea调试没问题，打成jar包运行就会报加密的class中的依赖class无法加载（ClassNoDefException/ClassNotFoundException），这里使用的是当前线程的上下文的类加载器就没有问题（Thread.currentThread().getContextClassLoader()）

public class CustomClassLoader extends ClassLoader {

    @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;
        }
        String[] classNameList = name.split("\\.");
        String classFileName = classNameList[classNameList.length - 1];
        if (classFileName.endsWith("MethodAccess") || !classFileName.endsWith("CoreUtil")) {
            return Thread.currentThread().getContextClassLoader().loadClass(name);
        }
        ClassLoader parent = this.getParent();
        try {
            //委派给父类加载
            clz = parent.loadClass(name);
        } catch (Exception e) {
            //log.warn("parent load class fail："+ e.getMessage(),e);
        }
        if (clz != null) {
            return clz;
        } else {
            byte[] classData = null;
            ClassPathResource classPathResource = new ClassPathResource("coreclass/" + classFileName + ".class");
            InputStream is = null;
            try {
                is = classPathResource.getInputStream();
                classData = DESEncryptUtil.decryptFromByteV2(FileUtil.convertStreamToByte(is), "xxxxxxx");
            } catch (Exception e) {
                e.printStackTrace();
                throw new ProtectClassLoadException("getClassData error");
            } finally {
                try {
                    if (is != null) {
                        is.close();
                    }
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (classData == null) {
                throw new ClassNotFoundException();
            } else {
                clz = defineClass(name, classData, 0, classData.length);
            }
            return clz;
        }
    }

}

隐藏classloader

classloader加密class文件处理方案的漏洞在于自定义类加载器是完全暴露的，只需进行分析解密流程就能获取到原始class文件，所以我们需要对classloder的内容进行隐藏

1.把classloader的源文件在编译期间进行删除（maven自定义插件实现）

2.将classloder的内容进行base64编码后拆分内容寻找多个系统启动注入点写入到loader.key文件中（拆分时写入的路径和文件名需要进行base64加密避免全局搜索），例如

    private static void init() {
        String source = "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";
        String filePath = "";
        try{
            filePath = new String(Base64.decodeBase64("dGVtcGZpbGVzL2R5bmFtaWNnZW5zZXJhdGUvbG9hZGVyLmtleQ=="),"utf-8");
        }catch (Exception e){
            e.printStackTrace();
        }
        FileUtil.writeFile(filePath, source,true);
    }

3.通过GroovyClassLoader对classloder的内容（字符串）进行动态编译获取到对象，删除loader.key文件

pom文件增加动态编译依赖

        <dependency>
            <groupId>org.codehaus.groovy</groupId>
            <artifactId>groovy-all</artifactId>
            <version>2.4.13</version>
        </dependency>

获取文件内容进行编译代码如下（写入/读取注意utf-8处理防止乱码）

public class CustomCompile {
    private static Object Compile(String source){
        Object instance = null;
        try{
            // 编译器
            CompilerConfiguration config = new CompilerConfiguration();
            config.setSourceEncoding("UTF-8");
            // 设置该GroovyClassLoader的父ClassLoader为当前线程的加载器(默认)
            GroovyClassLoader groovyClassLoader = new GroovyClassLoader(Thread.currentThread().getContextClassLoader(), config);
            Class<?> clazz = groovyClassLoader.parseClass(source);
            // 创建实例
            instance = clazz.newInstance();
        }catch (Exception e){
            e.printStackTrace();
        }
        return instance;
    }

    public static  ClassLoader getClassLoader(){
        String filePath = "tempfiles/dynamicgenserate/loader.key";
        String source = FileUtil.readFileContent(filePath);
        byte[] decodeByte = Base64.decodeBase64(source);
        String str = "";
        try{
            str = new String(decodeByte, "utf-8");
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            FileUtil.deleteDirectory("tempfiles/dynamicgenserate/");
        }
        return (ClassLoader)Compile(str);
    }
}

被保护class手动加壳

因为相关需要加密的class文件都是通过customerclassloder加载的，获取不到显示的class类型，所以我们实际的业务类只能通过反射的方法进行调用，例如业务工具类LicenseUtil，加密后类为LicenseCoreUtil，我们在LicenseUtil的方法中需要反射调用，LicenseCoreUtil中的方法，例如

@Component
public class LicenseUtil {
    private String coreClassName = "com.haopan.frame.core.util.LicenseCoreUtil";

    public String getMachineCode() throws Exception {
        return (String) CoreLoader.getInstance().executeMethod(coreClassName, "getMachineCode");
    }

    public boolean checkLicense(boolean startCheck) {
        return (boolean)CoreLoader.getInstance().executeMethod(coreClassName, "checkLicense",startCheck);
    }
}

为了避免反射调用随着调用次数的增加损失较多的性能，使用了一个第三方的插件reflectasm，pom增加依赖

        <dependency>
            <groupId>com.esotericsoftware</groupId>
            <artifactId>reflectasm</artifactId>
            <version>1.11.0</version>
        </dependency>

reflectasm使用了MethodAccess快速定位方法并在字节码层面进行调用，CoreLoader的代码如下

public class CoreLoader {
    private ClassLoader classLoader;

    private CoreLoader() {
        classLoader = CustomCompile.getClassLoader();
    }

    private static class SingleInstace {
        private static final CoreLoader instance = new CoreLoader();
    }

    public static CoreLoader getInstance() {
        return SingleInstace.instance;
    }

    public Object executeMethod(String className,String methodName, Object... args) {
        Object result = null;
        try {
            Class clz = classLoader.loadClass(className);
            MethodAccess access = MethodAccess.get(clz);
            result = access.invoke(clz.newInstance(), methodName, args);

        } catch (Exception e) {
            e.printStackTrace();
            throw  new ProtectClassLoadException("executeMethod error");
        }
        return result;
    }
}

总结

自定义classloder并不是一个完美的代码加密保护的解决方案，但就改造工作量与对项目的影响程度来说是最小的，只需要针对关键核心逻辑方法进行保护，不会对系统运行逻辑产生影响制造bug，理论上来说只要classloder的拆分越小，系统启动注入点隐藏的越多，那破解的成本就会越高，如果有不足之处还请见谅