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code-encryptor

Introduction

Encrypt bytecode using JNI, and decrypt it via JVMTI to protect the code.

Provides two DLL files, one for encryption and the other for decryption. For actual operation, only the decryption DLL is needed. Supports custom keys and package names.

The encrypted Class files become malformed and uninterpretable.

jd-gui

Apart from the initial Magic part, the subsequent bytes are uninterpretable.

hex

Launching with specified parameters can prevent Java Agent from dynamically dumping the bytecode.

For more experienced hackers, they might think of using sa-jdi's HSDB to dump the bytecode.

Taking inspiration from Master Beichen's discussion, I disabled the gHotSpotVMStructs function inside the JVM.

Supports Windows system.

WINDOWS

Supports Linux system.

LINUX

Quick Start

The encryption and decryption use C for one layer of encryption and assembly for bitwise operation in the second layer. Compiled Release versions of DLL/SO files are provided to embed in the Jar package.

Built-in support is for JDK-8; other versions have not been tested. In theory, it requires replacing the JNI.h header file and recompiling. It supports both Windows and Linux.

Encrypt your Jar package: (Specify Jar package, package encryption package name, and key)

 java -jar code-encryptor.jar patch --jar your-jar.jar --package com.your.pack --key your-key

Export the decryption DLL/SO file: (Default export to code-encryptor-temp directory, not recommended to modify)

java -jar code-encryptor.jar export

Launch the Jar package with the decryption DLL/SO: (Use the -agentpath parameter)

Note that two parameters PACKAGE_NAME and KEY are required.

Note: In some cases, it may not start the first time. Repeat the command to start.

java -XX:+DisableAttachMechanism -agentpath:D:\abs-path\decrypter.dll=PACKAGE_NAME=com.your.pack,KEY=your-key --jar your-jar.jar

Features

Compared to publicly available articles/codes on the internet, this project has the following advantages and features:

  • The original article fixed the package name, requiring users who want to encrypt their own package names to recompile the DLL.
  • In the original article, the encryption and decryption DLL were the same, making it vulnerable to simple JNI call decryption.
  • The original article's code was only at the Demo level and not ready for direct testing and use.
  • The original article lacked a specific encryption algorithm, only employing simple operations that needed strengthening.
  • There were some BUGs and optimization spaces in the original article's code.
  • Employing certain magic operations to prevent bytecode from being dumped, further ensuring security.

Current encryption and decryption algorithms:

  • Multiple bitwise operations, byte swapping, etc.
  • Based on the XXTEA algorithm, with multiple rounds of encryption.
  • Supports custom keys for further protection.

Building

Compilation Environment:

  • Windows 11 / Ubuntu 22.04
  • JDK 8 / Maven
  • MSVC + ml64 (Windows) / gcc + nasm (Linux)
  • CMake 3.x
  • Python 3.x

Others

Not suitable for projects that scan for class files at startup (typical projects like SpringBoot).

Currently working on solving this issue.

References

Thanks to the following projects or articles for their ideas: