JVMTI实现SpringBoot的jar加密，防止反编译

1.背景

ToB项目私有化部署，携带有项目jar包，防止别人下载jar，反编译出源码

2.JVMTI解释

JVMTI（Java Virtual Machine Tool Interface）即指 Java 虚拟机工具接口，它是一套由虚拟机直接提供的 native 接口，它处于整个 JPDA（Java Platform Debugger Architecture） 体系的最底层，所有调试功能本质上都需要通过 JVMTI 来提供。通过这些接口，开发人员不仅调试在该虚拟机上运行的 Java 程序，还能查看它们运行的状态，设置回调函数，控制某些环境变量，从而优化程序性能。

3.使用JVMTI思路

在SpringBoot项目打包后，通过dll动态链接库（so共享对象）加密生成新的jar，在启动jar时，让jvm启动时调用jvmti提供的Agent_OnLoad方法，用c++去实现，去解密对应的class文件。利用c++编译型语言特性，无法反编译出对应的加密解密方法。

4.实现源码

c++加密实现和jvm启动监听，需要jni.h，jvmti.h，jni_md.h三个头文件，分别在java环境变量下include和include/linux（win32）下

// c++加密头文件
#include 
 
#ifndef _Included_com_cxp_demo_encrypt_ByteCodeEncryptor
#define _Included_com_cxp_demo_encrypt_ByteCodeEncryptor
#ifdef __cplusplus
extern "C"
{
#endif
    JNIEXPORT jbyteArray JNICALL Java_com_cxp_demo_encrypt_ByteCodeEncryptor_encrypt(JNIEnv *, jclass, jbyteArray);
 
#ifdef __cplusplus
}
#endif
#endif
#ifndef CONST_HEADER_H_  
#define CONST_HEADER_H_   
const int k = 4;
const int compare_length = 18;
const char* package_prefix= "com/cxp/demo";
#endif

// c++加密解密源码
#include 
 
#include 
#include 
#include 
#include "demo_bytecode_encryptor.h"
 
void encode(char *str)
{
    unsigned int m = strlen(str);
    for (int i = 0; i < m; i++)
    {
        str[i] = str[i] + k;
    }
}
 
void decode(char *str)
{
    unsigned int m = strlen(str);
    for (int i = 0; i < m; i++)
    {
        str[i] = str[i] - k;
    }
}
 
extern"C" JNIEXPORT jbyteArray JNICALL Java_com_cxp_demo_encrypt_ByteCodeEncryptor_encrypt(JNIEnv * env, jclass cla, jbyteArray text)
{
    char* dst = (char*)env->GetByteArrayElements(text, 0);
    encode(dst);
    env->SetByteArrayRegion(text, 0, strlen(dst), (jbyte *)dst);
    return text;
}
 
void JNICALL ClassDecryptHook(
    jvmtiEnv *jvmti_env,
    JNIEnv* jni_env,
    jclass class_being_redefined,
    jobject loader,
    const char* name,
    jobject protection_domain,
    jint class_data_len,
    const unsigned char* class_data,
    jint* new_class_data_len,
    unsigned char** new_class_data
)
{
    *new_class_data_len = class_data_len;
    jvmti_env->Allocate(class_data_len, new_class_data);
 
    unsigned char* _data = *new_class_data;
 
    if (name && strncmp(name, package_prefix, compare_length) == 0 && strstr(name, "BySpringCGLIB") == NULL)
    {
        for (int i = 0; i < class_data_len; i++)
        {
            _data[i] = class_data[i];
        }
        decode((char*)_data);
    }
    else {
        for (int i = 0; i < class_data_len; i++)
        {
            _data[i] = class_data[i];
        }
    }
 
}
 
JNIEXPORT jint JNICALL Agent_OnLoad(JavaVM *vm, char *options, void *reserved)
{
 
    jvmtiEnv *jvmti;
    jint ret = vm->GetEnv((void **)&jvmti, JVMTI_VERSION);
    if (JNI_OK != ret)
    {
        printf("ERROR: Unable to access JVMTI!\n");
        return ret;
    }
    jvmtiCapabilities capabilities;
    (void)memset(&capabilities, 0, sizeof(capabilities));
 
    capabilities.can_generate_all_class_hook_events = 1;
    capabilities.can_tag_objects = 1;
    capabilities.can_generate_object_free_events = 1;
    capabilities.can_get_source_file_name = 1;
    capabilities.can_get_line_numbers = 1;
    capabilities.can_generate_vm_object_alloc_events = 1;
 
    jvmtiError error = jvmti->AddCapabilities(&capabilities);
    if (JVMTI_ERROR_NONE != error)
    {
        printf("ERROR: Unable to AddCapabilities JVMTI!\n");
        return error;
    }
 
    jvmtiEventCallbacks callbacks;
    (void)memset(&callbacks, 0, sizeof(callbacks));
 
    callbacks.ClassFileLoadHook = &ClassDecryptHook;
    error = jvmti->SetEventCallbacks(&callbacks, sizeof(callbacks));
    if (JVMTI_ERROR_NONE != error)
    {
        printf("ERROR: Unable to SetEventCallbacks JVMTI!\n");
        return error;
    }
 
    error = jvmti->SetEventNotificationMode(JVMTI_ENABLE, JVMTI_EVENT_CLASS_FILE_LOAD_HOOK, NULL);
    if (JVMTI_ERROR_NONE != error)
    {
        printf("ERROR: Unable to SetEventNotificationMode JVMTI!\n");
        return error;
    }
 
    return JNI_OK;
}

 java加密逻辑：

// JNI调用c++代码
public class ByteCodeEncryptor {
 
    static {
        String currentPath = ByteCodeEncryptor.class.getResource("").getPath().split("SpringBootJarEncryptor.jar!")[0];
        if (currentPath.startsWith("file:")) {
            currentPath = currentPath.substring(5);
        }
        String dllPath;
        String os = System.getProperty("os.name");
        if (os.toLowerCase().startsWith("win")) {
            dllPath = currentPath + "SpringBootJarEncryptor.dll";
        } else {
            dllPath = currentPath + "SpringBootJarEncryptor.so";
        }
        System.load(dllPath);
    }
 
    public native static byte[] encrypt(byte[] text);
 
}

import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.util.Enumeration;
import java.util.jar.JarEntry;
import java.util.jar.JarFile;
import java.util.jar.JarOutputStream;
 
// 加密jar代码
public class JarEncryptor {
 
    public static void encrypt(String fileName, String dstName) {
        try {
            ByteArrayOutputStream bos = new ByteArrayOutputStream();
            byte[] buf = new byte[1024];
            File srcFile = new File(fileName);
            File dstFile = new File(dstName);
            FileOutputStream dstFos = new FileOutputStream(dstFile);
            JarOutputStream dstJar = new JarOutputStream(dstFos);
            JarFile srcJar = new JarFile(srcFile);
            for (Enumeration enumeration = srcJar.entries(); enumeration.hasMoreElements(); ) {
                JarEntry entry = enumeration.nextElement();
                InputStream is = srcJar.getInputStream(entry);
                int len;
                while ((len = is.read(buf, 0, buf.length)) != -1) {
                    bos.write(buf, 0, len);
                }
                byte[] bytes = bos.toByteArray();
                String name = entry.getName();
                if (name.startsWith("com/cxp/demo") && name.endsWith(".class")) {
                    try {
                        bytes = ByteCodeEncryptor.encrypt(bytes);
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }
                JarEntry ne = new JarEntry(name);
                dstJar.putNextEntry(ne);
                dstJar.write(bytes);
                bos.reset();
            }
            srcJar.close();
            dstJar.close();
            dstFos.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
 
    public static void main(String[] args) {
        if (args == null || args.length == 0) {
            System.out.println("please input parameter");
            return;
        }
        if (args[0].endsWith(".jar")) {
            JarEncryptor.encrypt(args[0], args[0].substring(0, args[0].lastIndexOf(".")) + "_encrypted.jar");
        } else {
            File file = new File(args[0]);
            if (file.isDirectory()) {
                String[] list = file.list();
                if (list != null) {
                    for (String jarFilePath : list) {
                        if (jarFilePath.endsWith(".jar")) {
                            JarEncryptor.encrypt(args[0] + "/" + jarFilePath, args[0] + "_encrypted/" + jarFilePath);
                        }
                    }
                }
            } else {
                System.out.println("this is not a folder or folder is empty");
            }
        }
    }
 
}

实现步骤：

1.先把c++打成dll（so）动态链接库

2.通过java调用dll文件，加密jar

3.启动加密后的jar，加上启动参数-agentpath:*.dll

gradle.build打包：

task copyJar(type: Copy) {
    delete "$buildDir/libs/lib"
    from configurations.runtime
    into "$buildDir/libs/lib"
}
 
jar {
    enabled = true
    dependsOn copyJar
    archivesBaseName = "app"
    archiveVersion = ""
    manifest {
        attributes 'Main-Class': "主类全限定名",
                'Class-Path': configurations.runtime.files.collect { "lib/$it.name" }.join(' ')
    }
}

 Dockerfile文件：

# 加密jar
RUN mkdir ./build/libs/lib_encrypted
RUN java -jar ./encrypt/SpringBootJarEncryptor.jar ./build/libs/app.jar
RUN java -jar ./encrypt/SpringBootJarEncryptor.jar ./build/libs/lib
RUN rm -r ./build/libs/lib
RUN rm ./build/libs/app.jar
RUN mv ./build/libs/lib_encrypted ./build/libs/lib
RUN mv ./build/libs/app_encrypted.jar ./build/libs/app.jar
 
# --- java ---
FROM java8
# 提取启动需要的资源
COPY --from=builder /build/libs/app.jar /application/app.jar
COPY --from=builder /build/libs/lib /application/lib
COPY --from=builder /encrypt /encrypt
COPY --from=builder /start.sh start.sh
ENTRYPOINT ["sh", "start.sh"]

启动命令：

java -agentpath:./SpringBootJarEncryptor.dll -jar app.jar

5.踩坑

• java使用jni调用c++函数，c++被调用的函数名要与java方法全限定名一致，如：com.cxp.demo.encrypt.ByteCodeEncryptor#encrypt=》Java_com_cxp_demo_encrypt_ByteCodeEncryptor_encrypt，注意java和c++数据类型的对应关系
• JVMTI只能作用Java原生启动类加载器，而SpringBoot有自己启动类加载器，读取SpringBoot规定的原文件路径（BOOT-INF/classes）和依赖路径（BOOT-INF/lib），所以SpringBoot要打包成普通jar方式，bootjar是SpringBoot默认的打包方式，改为jar打包方式无法打入依赖包，只能把依赖包打到同文件夹下，修改MANIFEST.MF文件的CLass-Path属性，把依赖包添加进去。可以看下SpringBoot的启动jar和普通jar区别。
• c++在linux下打成so库，可以自行搜索下，推荐使用cmake
• java引入dll动态库，只能放在java的classpath下或绝对路径
• 引包方式改为可以打出依赖包的方式，如compile，运行时不需要的可以不用