Cocos2dlua手游 Lua解密与资源解密实战

Posted 2021-08-06 看雪学院

发过理论篇 浅谈Cocos2d-x下Lua文件的保护方式 – 翻车鱼 (blog.shi1011.cn) ，是时候来实战一番了。

起因： 一位不知是港澳台哪地的师傅，加了我的QQ：

于是我和他进行了一场漫长的探讨， 尽管轮子在手，但是依旧无法反编译出.lua（因为加了一层自定义加密）。

 

结果就是：喜提样本一份。

1

样本树

大致结构如下：

.├── assets│ ├── res│ │ ├── ani│ │ │ └── logo│ │ │ └── logo.png│ ├── src│ │ ├── main.lua│ │ └── main.lua64├── lib│ ├── arm64-v8a│ │ ├── libBugly.so│ │ └── libcocos2dlua.so│ └── armeabi-v7a│ ├── libBugly.so│ └── libcocos2dlua.so└── stamp-cert-sha256

其中.lua64为标准LuaJit文件， 而.lua的文件头有点奇怪。

.lua文件头：abcd，再看资源文件.png，发现也是加密的：

综上，我们需要实现的目标：1、 解密.lua文件；2、 解密.png文件。

2

LuaJit 反汇编

这个不多介绍了窝，在理论篇中已经提到了。对于此样本的LuaJit的版本是2.1.0-Beta2，并且没有魔改Opcode。

Lua文件加载流程：想要解密.lua文件，了解coco2d-x加载Lua的流程必不可少。

Cocos2d-x环境搭建：参考官方Docs，搭建所需环境：

3

从android Activity揭秘cocos2d-x的世界

由于Android的应用层是从Activity开始的，也就是创建完一个Cocos2dx后src文件夹下的Java文件，其中主要看Activity创建时的操作。

package org.cocos2dx.lua; import android.os.Bundle;import org.cocos2dx.lib.Cocos2dxActivity; public class AppActivity extends Cocos2dxActivity{ @Override protected void onCreate(Bundle savedInstanceState) { super.setEnableVirtualButton(false); super.onCreate(savedInstanceState); // Workaround in https://stackoverflow.com/questions/16283079/re-launch-of-activity-on-home-button-but-only-the-first-time/16447508 if (!isTaskRoot()) { // Android launched another instance of the root activity into an existing task // so just quietly finish and go away, dropping the user back into the activity // at the top of the stack (ie: the last state of this task) // Don't need to finish it again since it's finished in super.onCreate . return; }  // DO OTHER INITIALIZATION BELOW  }}

这个方法很简单，就只调用了父类Cocos2dxActivity的onCreate方法：

@Override protected void onCreate(final Bundle savedInstanceState) { super.onCreate(savedInstanceState);  // Workaround in https://stackoverflow.com/questions/16283079/re-launch-of-activity-on-home-button-but-only-the-first-time/16447508 if (!isTaskRoot()) { // Android launched another instance of the root activity into an existing task // so just quietly finish and go away, dropping the user back into the activity // at the top of the stack (ie: the last state of this task) finish(); Log.w(TAG, "[Workaround] Ignore the activity started from icon!"); return; }  this.hideVirtualButton();  onLoadNativeLibraries();  sContext = this; this.mHandler = new Cocos2dxHandler(this);  Cocos2dxHelper.init(this);  this.mGLContextAttrs = getGLContextAttrs(); this.init();  if (mVideoHelper == null) { mVideoHelper = new Cocos2dxVideoHelper(this, mFrameLayout); }  if(mWebViewHelper == null){ mWebViewHelper = new Cocos2dxWebViewHelper(mFrameLayout); }  if(mEditBoxHelper == null){ mEditBoxHelper = new Cocos2dxEditBoxHelper(mFrameLayout); }  Window window = this.getWindow(); window.setSoftInputMode(WindowManager.LayoutParams.SOFT_INPUT_ADJUST_PAN);  // Audio configuration this.setVolumeControlStream(AudioManager.STREAM_MUSIC); }

在这个方法中主要看Cocos2dxActivity的初始化方法init，Cocos2dxHandler是工具辅助类，不是重点。

public Cocos2dxGLSurfaceView onCreateView() { Cocos2dxGLSurfaceView glSurfaceView = new Cocos2dxGLSurfaceView(this); //this line is need on some device if we specify an alpha bits // FIXME: is it needed? And it will cause afterimage. // if(this.mGLContextAttrs[3] > 0) glSurfaceView.getHolder().setFormat(PixelFormat.TRANSLUCENT);  // use custom EGLConfigureChooser Cocos2dxEGLConfigChooser chooser = new Cocos2dxEGLConfigChooser(this.mGLContextAttrs); glSurfaceView.setEGLConfigChooser(chooser);  return glSurfaceView; }// ......public void init() {  // FrameLayout 初始化窗口布局 ViewGroup.LayoutParams framelayout_params = new ViewGroup.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT);  mFrameLayout = new ResizeLayout(this);  mFrameLayout.setLayoutParams(framelayout_params);  // Cocos2dxEditText layout 初始化Cocos2dx的文本编辑布局 ViewGroup.LayoutParams edittext_layout_params = new ViewGroup.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.WRAP_CONTENT); Cocos2dxEditBox edittext = new Cocos2dxEditBox(this); edittext.setLayoutParams(edittext_layout_params);   mFrameLayout.addView(edittext);  // Cocos2dxGLSurfaceView 初始化Cocos2dx视图 this.mGLSurfaceView = this.onCreateView();  // ...add to FrameLayout 将Cocos2dxGLSurfaceView加入到当前的窗口布局中 mFrameLayout.addView(this.mGLSurfaceView);  // Switch to supported OpenGL (ARGB888) mode on emulator // this line dows not needed on new emulators and also it breaks stencil buffer //if (isAndroidEmulator()) // 在模拟器中切换支持OpenGL模式的渲染(ARGB888) // this.mGLSurfaceView.setEGLConfigChooser(8, 8, 8, 8, 16, 0);  // 设置Cocos2dx的渲染器 this.mGLSurfaceView.setCocos2dxRenderer(new Cocos2dxRenderer()); //设置Cocos2dx的文本编辑 this.mGLSurfaceView.setCocos2dxEditText(edittext);  // Set framelayout as the content view // 把显示布局（即Cocos2dx的视图）绑定到Activity上，建立显示窗口 setContentView(mFrameLayout); }

首先在init中先看this.mGLSurfaceView = this.onCreateView();this.mGLSurfaceView是一个Cocos2dxGLSurfaceView类。

 

进入到Cocos2dxGLSurfaceView这个类，可以看到时继承于GLSurfaceView（可以把GLSurfaceView看成一个视图，里面有个方法设置了这个视图的渲染器，然后通过这个渲染器来进行画面的渲染）。

在Android中，GLSurfaceView是一个支持OpenGL的渲染视图，通过继承SurfaceView中的surface来渲染OpenGL。

并提供了以下特性（来源于网上）：

1. 管理一个surface，这个surface就是一块特殊的内存，能直接排版到android的视图view上
2. 管理一个EGL display，它能让opengl把内容渲染到上述的surface上
3. 用户自定义渲染器(render)
4. 让渲染器在独立的线程里运作，和UI线程分离
5. 支持按需渲染(on-demand)和连续渲染(continuous)
6. 一些可选工具，如调试
   
   

重点是自定义的渲染器，也就是Cocos2dx引擎封装的渲染器。

 

进入Cocos2dxRenderer类，看到他是继承GLSurfaceView.Renderer接口，这个接口定义了三个方法：

• onSurfaceCreated: 创建GLSurfaceView时被调用，只调用一次，做初始化工作
• onSurfaceChanged: 当GLSurfaceView的几何体被改变时被调用
• onDrawFrame: 绘制渲染GLSurfaceView

onSurfaceCreated：

@Override public void onSurfaceCreated(final GL10 GL10, final EGLConfig EGLConfig) { Cocos2dxRenderer.nativeInit(this.mScreenWidth, this.mScreenHeight); this.mLastTickInNanoSeconds = System.nanoTime(); mNativeInitCompleted = true; }

nativeInit是一个Native函数：

private static native void nativeInit(final int width, final int height);

具体实现在frameworks\cocos2d-x\cocos\platform\android\javaactivity-android.cpp中：

JNIEXPORT void Java_org_cocos2dx_lib_Cocos2dxRenderer_nativeInit(JNIEnv* env, jobject thiz, jint w, jint h){ auto director = cocos2d::Director::getInstance(); auto glview = director->getOpenGLView(); if (!glview) { glview = cocos2d::GLViewImpl::create("Android app"); glview->setFrameSize(w, h); director->setOpenGLView(glview);  cocos2d::Application::getInstance()->run(); } else { cocos2d::Director::getInstance()->resetMatrixStack(); cocos2d::EventCustom recreatedEvent(EVENT_RENDERER_RECREATED); director->getEventDispatcher()->dispatchEvent(&recreatedEvent); director->setGLDefaultValues(); cocos2d::VolatileTextureMgr::reloadAllTextures(); } cocos2d::network::_preloadJavaDownloaderClass();}

重点是cocos2d::Application::getInstance()->run()。

int Application::run(){ // Initialize instance and cocos2d. if (! applicationDidFinishLaunching()) { return 0; }  return -1;}

applicationDidFinishLaunching，没错这就是游戏逻辑的入口了：

bool AppDelegate::applicationDidFinishLaunching(){ // set default FPS Director::getInstance()->setAnimationInterval(1.0 / 60.0f);  // register lua module  // 初始化 LuaEngine, 在 getInstance 中会初始化 LuaStack, LuaStack 初始化 Lua 环境相关 auto engine = LuaEngine::getInstance(); // 将 LuaEngine 添加到脚本引擎管理器 ScriptEngineManager 中 ScriptEngineManager::getInstance()->setScriptEngine(engine); // 获取 Lua 环境 lua_State* L = engine->getLuaStack()->getLuaState(); // 注册额外的 C++ API 相关，比如 cocosstudio, spine, audio 相关 lua_module_register(L);  // 设置 cocos 自带的加密相关 register_all_packages();  // 在 LuaStack::executeScriptFile 执行脚本文件时，会通过 LuaStack::luaLoadBuffer 对文件进行解密 LuaStack* stack = engine->getLuaStack(); stack->setXXTEAKeyAndSign("2dxLua", strlen("2dxLua"), "XXTEA", strlen("XXTEA"));  //register custom function //LuaStack* stack = engine->getLuaStack(); //register_custom_function(stack->getLuaState()); #if CC_64BITS FileUtils::getInstance()->addSearchPath("src/64bit");#endif FileUtils::getInstance()->addSearchPath("src"); FileUtils::getInstance()->addSearchPath("res"); if (engine->executeScriptFile("main.lua")) { return false; }  return true;}

LuaEngine::getInstance();这段代码实例化了LuaEngine。

 

下面分析LuaEngine初始化过程：

LuaEngine* LuaEngine::getInstance(void){ if (!_defaultEngine) { _defaultEngine = new (std::nothrow) LuaEngine(); _defaultEngine->init(); } return _defaultEngine;}

接下来是_defaultEngine->init()：

bool LuaEngine::init(void){ _stack = LuaStack::create(); _stack->retain(); return true;}

继续进入：

LuaStack *LuaStack::create(){ LuaStack *stack = new (std::nothrow) LuaStack(); stack->init(); stack->autorelease(); return stack;}

下面是stack->init()：

bool LuaStack::init(){ // 初始化Lua环境并打开标准库 _state = lua_open(); luaL_openlibs(_state); toluafix_open(_state);  // Register our version of the global "print" function // 注册全局函数print到lua中，它会覆盖lua库中的print方法 const luaL_Reg global_functions [] = { {"print", lua_print}, {"release_print",lua_release_print}, {nullptr, nullptr} }; // 注册全局变量 luaL_register(_state, "_G", global_functions);  // 注册cocos2d-x引擎的API到lua环境中 g_luaType.clear(); register_all_cocos2dx(_state); register_all_cocos2dx_backend(_state); register_all_cocos2dx_manual(_state); register_all_cocos2dx_module_manual(_state); register_all_cocos2dx_math_manual(_state); register_all_cocos2dx_shaders_manual(_state); register_all_cocos2dx_bytearray_manual(_state);  tolua_luanode_open(_state); register_luanode_manual(_state);#if CC_USE_PHYSICS // 导入使用的physics相关API register_all_cocos2dx_physics(_state); register_all_cocos2dx_physics_manual(_state);#endif #if (CC_TARGET_PLATFORM == CC_PLATFORM_ios || CC_TARGET_PLATFORM == CC_PLATFORM_MAC) // 导入ios下调用object-c相关API LuaObjcBridge::luaopen_luaoc(_state);#endif #if (CC_TARGET_PLATFORM == CC_PLATFORM_ANDROID) // 导入android下调用java相关API LuaJavaBridge::luaopen_luaj(_state);#endif register_all_cocos2dx_deprecated(_state); register_all_cocos2dx_manual_deprecated(_state);  tolua_script_handler_mgr_open(_state);  // add cocos2dx loader // 添加Lua的加载器,该方法将cocos2dx_lua_loader方法添加到Lua全局变量package下的loaders成员中　　 // 当requires加载脚本时，Lua会使用package下的loaders中的加载器，即cocos2dx_lua_loader来加载 // 设定cocos2dx_lua_loader，可以使得我们自定义设置搜索路径相关，且拓展实现对脚本的加密解密相关 addLuaLoader(cocos2dx_lua_loader);  return true;}

重点在cocos2dx_lua_loader方法(这个方法在frameworks\cocos2d-x\cocos\scripting\lua-bindings\manual\Cocos2dxLuaLoader.cpp)：

int cocos2dx_lua_loader(lua_State *L){ // 后缀为luac和lua static const std::string BYTECODE_FILE_EXT = ".luac"; static const std::string NOT_BYTECODE_FILE_EXT = ".lua";  // require传入的要加载的文件名，例如：require("a.b") 查找文件为：a/b.lua std::string filename(luaL_checkstring(L, 1)); size_t pos = filename.rfind(BYTECODE_FILE_EXT); // 去掉后缀名".luac"或“.lua” if (pos != std::string::npos && pos == filename.length() - BYTECODE_FILE_EXT.length()) filename = filename.substr(0, pos); else { pos = filename.rfind(NOT_BYTECODE_FILE_EXT); if (pos != std::string::npos && pos == filename.length() - NOT_BYTECODE_FILE_EXT.length()) filename = filename.substr(0, pos); }  // 将 "." 替换为 "/" pos = filename.find_first_of('.'); while (pos != std::string::npos) { filename.replace(pos, 1, "/"); pos = filename.find_first_of('.'); }  // search file in package.path Data chunk; std::string chunkName; FileUtils* utils = FileUtils::getInstance();  // 获取 package.path 的变量 lua_getglobal(L, "package"); lua_getfield(L, -1, "path"); // 通过 package.path 获取搜索路径相关，该路径为模版路径，格式类似于： // ?; ?.lua; c:\Users\?; /usr/local/lua/lua/?/?.lua 以“;”作为分割符 std::string searchpath(lua_tostring(L, -1)); lua_pop(L, 1); size_t begin = 0; size_t next = searchpath.find_first_of(';', 0);  // 遍历 package.path 中的所有路径，查找文件是否存在，若文件存在则通过 getDataFromFile 读取文件数据 do { if (next == std::string::npos) next = searchpath.length(); std::string prefix = searchpath.substr(begin, next-begin); if (prefix[0] == '.' && prefix[1] == '/') prefix = prefix.substr(2);  pos = prefix.rfind(BYTECODE_FILE_EXT); if (pos != std::string::npos && pos == prefix.length() - BYTECODE_FILE_EXT.length()) { prefix = prefix.substr(0, pos); } else { pos = prefix.rfind(NOT_BYTECODE_FILE_EXT); if (pos != std::string::npos && pos == prefix.length() - NOT_BYTECODE_FILE_EXT.length()) prefix = prefix.substr(0, pos); } pos = prefix.find_first_of('?', 0); while (pos != std::string::npos) { prefix.replace(pos, 1, filename); pos = prefix.find_first_of('?', pos + filename.length() + 1); }  chunkName = prefix + BYTECODE_FILE_EXT; if (utils->isFileExist(chunkName)) // && !utils->isDirectoryExist(chunkName)) { chunk = utils->getDataFromFile(chunkName); break; } else { chunkName = prefix + NOT_BYTECODE_FILE_EXT; if (utils->isFileExist(chunkName) ) //&& !utils->isDirectoryExist(chunkName)) { chunk = utils->getDataFromFile(chunkName); break; } else { chunkName = prefix; if (utils->isFileExist(chunkName)) // && !utils->isDirectoryExist(chunkName)) { chunk = utils->getDataFromFile(chunkName); break; } } }  // 指定搜素路径下不存在该文件, 下一个 begin = next + 1; next = searchpath.find_first_of(';', begin); } while (begin < searchpath.length()); // 判断文件内容是否获取成功 if (chunk.getSize() > 0) { // 加载文件 LuaStack* stack = LuaEngine::getInstance()->getLuaStack(); stack->luaLoadBuffer(L, reinterpret_cast<const char*>(chunk.getBytes()), static_cast<int>(chunk.getSize()), chunkName.c_str()); } else { CCLOG("can not get file data of %s", chunkName.c_str()); return 0; }  return 1; }

通过此处的代码，可以了解到cocos2d-x是如何搜索指定的lua文件。

 

同时也会明白require为何可以使用 "." 来设定文件路径了，比如：

require "cocos.cocos2d.Cocos2d"require "cocos.cocos2d.Cocos2dConstants"require "cocos.cocos2d.functions"

再来看下stack->luaLoadBuffer的实现：

int LuaStack::luaLoadBuffer(lua_State *L, const char *chunk, int chunkSize, const char *chunkName){ int r = 0;  // 判断是否加密，若lua脚本加密，则解密后在加载脚本文件 // luaL_loadbuffer 用于加载并编译Lua代码，并将其压入栈中 if (_xxteaEnabled && strncmp(chunk, _xxteaSign, _xxteaSignLen) == 0) { // decrypt XXTEA xxtea_long len = 0; unsigned char* result = xxtea_decrypt((unsigned char*)chunk + _xxteaSignLen, (xxtea_long)chunkSize - _xxteaSignLen, (unsigned char*)_xxteaKey, (xxtea_long)_xxteaKeyLen, &len); unsigned char* content = result; xxtea_long contentSize = len; skipBOM((const char*&)content, (int&)contentSize); r = luaL_loadbuffer(L, (char*)content, contentSize, chunkName); free(result); } else { skipBOM(chunk, chunkSize); r = luaL_loadbuffer(L, chunk, chunkSize, chunkName); } // 判定内容是否存在错误#if defined(COCOS2D_DEBUG) && COCOS2D_DEBUG > 0 if (r) { switch (r) { case LUA_ERRSYNTAX: // 语法错误 CCLOG("[LUA ERROR] load \"%s\", error: syntax error during pre-compilation.", chunkName); break;  case LUA_ERRMEM: // 内存分配错误 CCLOG("[LUA ERROR] load \"%s\", error: memory allocation error.", chunkName); break;  case LUA_ERRFILE: // 文件错误 CCLOG("[LUA ERROR] load \"%s\", error: cannot open/read file.", chunkName); break;  default: // 未知错误 CCLOG("[LUA ERROR] load \"%s\", error: unknown.", chunkName); } }#endif return r;}

至此，Lua文件的加载流程结束。

 

下面是Lua文件主要加载流程图：

4

Lua解密之自定义文件头

了解了Coco2d-x Lua文件基本的加载流程，可以帮助我们很快的定位关键方法。

快速定位：由于所有的Lua文件加载必定经过cocos2d::LuaStack::luaLoadBuffer，所以可以直接定位，进行回溯。

 

定位至cocos2dx_lua_loader：

在luaLoadBuffer前调用了decodeLuaData，怀疑这就是解密Lua的关键方法。

 

下面是伪代码：

_BYTE *__fastcall decodeLuaData(cocos2d::Data *a1, int *size){ _BYTE *v3; // r0 _BYTE *v4; // r5 int v6; // r0 int v7; // r2 int v8; // r3 bool v9; // cc unsigned int v10; // r1 _BYTE *v11; // r12 _BYTE *v12; // r0 char v13; // t1 _BYTE *v14; // r0 char v15[4]; // [sp+0h] [bp-18h]  v3 = (_BYTE *)cocos2d::Data::getBytes(a1); v4 = v3; if ( *size > 8 && *v3 == 'a' && v3[1] == 'b' && v3[2] == 'c' && v3[3] == 'd' ) { v6 = _hexToDecimal(v3 + 4, 4); v7 = *size; v8 = 0; v9 = *size <= 8; v15[3] = v6; v15[2] = (unsigned __int16)(v6 - 2048) >> 8; v10 = (unsigned int)(v6 - 2048) >> 24; v15[1] = (unsigned int)(v6 - 2048) >> 16; v15[0] = (unsigned int)(v6 - 2048) >> 24; if ( !v9 ) { v11 = v4 - 1; v12 = v4 + 7; while ( 1 ) { v13 = *++v12; ++v8; *++v11 = v13 ^ v10; v7 = *size; if ( *size <= v8 + 8 ) break; LOBYTE(v10) = v15[v8 & 3]; } } v14 = &v4[v7 - 8]; *v14 = 0; v14[1] = 0; v14[2] = 0; v14[3] = 0; v14[4] = 0; v14[5] = 0; v14[6] = 0; v14[7] = 0; *size -= 8; } return v4;}

此方法首先获取文件数据，而后判断文件头，文件头正是abcd。

 

可以肯定这就是解密.lua的算法。如果不确定，我们可以使用Frida进行Hook验证猜想，我这里就不Hook了。

算法还原： 要实现算法的还原，我们就要依据伪代码或是汇编代码翻译成可用代码，可以发现IDA所反汇编的伪代码中包含了一些特定的宏，例如：LOBYTE

 

要了解这些宏的用途，我们可以参考ida_root/plugins/def.h

我这里使用了Python：

import structfrom loguru import logger  def _hexToDecimal(data, offset): if offset <= 0: return 0 return struct.unpack(">I", data[:offset])[0]  def LOBYTE(d): return d & 0xff  def decodeLuaData(data, size): v4 = bytearray(data) v15 = [0] * 4 if size > 8 and data[0] == ord('a') and data[1] == ord('b') and data[2] == ord('c') and data[3] == ord('d'): logger.info("find special exts") v6 = _hexToDecimal(data[4:], 4)  v15[3] = v6 v15[2] = (v6 - 2048) >> 8 v10 = (v6 - 2048) >> 24 v15[1] = (v6 - 2048) >> 16 v15[0] = (v6 - 2048) >> 24  if size > 8: i = 0 while 1: v13 = v4[8 + i] v4[i] = v13 ^ v10 i += 1 if size <= i + 8: break v10 = LOBYTE(v15[i & 3]) size -= 8  return v4[:-8]

解密后，发现还是LuaJit，那么直接类同.lua64反汇编即可。

5

Lua资源加载流程

回到Lua文件加载流程分析时提到的LuaStack::init()方法中，调用了：register_all_cocos2dx

TOLUA_API int register_all_cocos2dx(lua_State* tolua_S){ tolua_open(tolua_S);  tolua_module(tolua_S,"cc",0); tolua_beginmodule(tolua_S,"cc");  lua_register_cocos2dx_Ref(tolua_S); lua_register_cocos2dx_Material(tolua_S); lua_register_cocos2dx_Console(tolua_S); lua_register_cocos2dx_Node(tolua_S); lua_register_cocos2dx_Scene(tolua_S); lua_register_cocos2dx_TransitionScene(tolua_S); lua_register_cocos2dx_TransitionEaseScene(tolua_S); lua_register_cocos2dx_TransitionMoveInL(tolua_S); lua_register_cocos2dx_TransitionMoveInB(tolua_S); lua_register_cocos2dx_AtlasNode(tolua_S); lua_register_cocos2dx_TileMapAtlas(tolua_S); lua_register_cocos2dx_TransitionMoveInT(tolua_S); lua_register_cocos2dx_TMXTilesetInfo(tolua_S); lua_register_cocos2dx_TransitionMoveInR(tolua_S); lua_register_cocos2dx_Action(tolua_S); lua_register_cocos2dx_FiniteTimeAction(tolua_S); lua_register_cocos2dx_ActionInstant(tolua_S); lua_register_cocos2dx_Hide(tolua_S); lua_register_cocos2dx_ParticleSystem(tolua_S); lua_register_cocos2dx_ParticleSystemQuad(tolua_S); lua_register_cocos2dx_ParticleSpiral(tolua_S); lua_register_cocos2dx_GridBase(tolua_S); lua_register_cocos2dx_AnimationCache(tolua_S); lua_register_cocos2dx_ActionInterval(tolua_S); lua_register_cocos2dx_ActionCamera(tolua_S); lua_register_cocos2dx_ProgressFromTo(tolua_S); lua_register_cocos2dx_MoveBy(tolua_S); lua_register_cocos2dx_MoveTo(tolua_S); lua_register_cocos2dx_JumpBy(tolua_S); lua_register_cocos2dx_EventListener(tolua_S); lua_register_cocos2dx_EventListenerKeyboard(tolua_S); lua_register_cocos2dx_EventListenerMouse(tolua_S); lua_register_cocos2dx_TransitionRotoZoom(tolua_S); lua_register_cocos2dx_Event(tolua_S); lua_register_cocos2dx_EventController(tolua_S); lua_register_cocos2dx_Director(tolua_S); lua_register_cocos2dx_Scheduler(tolua_S); lua_register_cocos2dx_ActionEase(tolua_S); lua_register_cocos2dx_EaseElastic(tolua_S); lua_register_cocos2dx_EaseElasticOut(tolua_S); lua_register_cocos2dx_EaseQuadraticActionInOut(tolua_S); lua_register_cocos2dx_EaseBackOut(tolua_S); lua_register_cocos2dx_Texture2D(tolua_S); lua_register_cocos2dx_TransitionSceneOriented(tolua_S); lua_register_cocos2dx_TransitionFlipX(tolua_S); lua_register_cocos2dx_CameraBackgroundBrush(tolua_S); lua_register_cocos2dx_CameraBackgroundDepthBrush(tolua_S); lua_register_cocos2dx_CameraBackgroundColorBrush(tolua_S); lua_register_cocos2dx_GridAction(tolua_S); lua_register_cocos2dx_TiledGrid3DAction(tolua_S); lua_register_cocos2dx_FadeOutTRTiles(tolua_S); lua_register_cocos2dx_FadeOutUpTiles(tolua_S); lua_register_cocos2dx_FadeOutDownTiles(tolua_S); lua_register_cocos2dx_StopGrid(tolua_S); lua_register_cocos2dx_Technique(tolua_S); lua_register_cocos2dx_SkewTo(tolua_S); lua_register_cocos2dx_SkewBy(tolua_S); lua_register_cocos2dx_EaseQuadraticActionOut(tolua_S); lua_register_cocos2dx_TransitionProgress(tolua_S); lua_register_cocos2dx_TransitionProgressVertical(tolua_S); lua_register_cocos2dx_Layer(tolua_S); lua_register_cocos2dx_TMXTiledMap(tolua_S); lua_register_cocos2dx_Grid3DAction(tolua_S); lua_register_cocos2dx_BaseLight(tolua_S); lua_register_cocos2dx_SpotLight(tolua_S); lua_register_cocos2dx_FadeTo(tolua_S); lua_register_cocos2dx_FadeIn(tolua_S); lua_register_cocos2dx_DirectionLight(tolua_S); lua_register_cocos2dx_EventListenerCustom(tolua_S); lua_register_cocos2dx_FlipX3D(tolua_S); lua_register_cocos2dx_FlipY3D(tolua_S); lua_register_cocos2dx_EaseSineInOut(tolua_S); lua_register_cocos2dx_TransitionFlipAngular(tolua_S); lua_register_cocos2dx_EaseElasticInOut(tolua_S); lua_register_cocos2dx_EaseBounce(tolua_S); lua_register_cocos2dx_Show(tolua_S); lua_register_cocos2dx_FadeOut(tolua_S); lua_register_cocos2dx_CallFunc(tolua_S); lua_register_cocos2dx_EventMouse(tolua_S); lua_register_cocos2dx_GLView(tolua_S); lua_register_cocos2dx_EaseBezierAction(tolua_S); lua_register_cocos2dx_ParticleFireworks(tolua_S); lua_register_cocos2dx_MenuItem(tolua_S); lua_register_cocos2dx_MenuItemSprite(tolua_S); lua_register_cocos2dx_MenuItemImage(tolua_S); lua_register_cocos2dx_AutoPolygon(tolua_S); lua_register_cocos2dx_ParticleSmoke(tolua_S); lua_register_cocos2dx_TransitionZoomFlipAngular(tolua_S); lua_register_cocos2dx_EaseRateAction(tolua_S); lua_register_cocos2dx_EaseIn(tolua_S); lua_register_cocos2dx_EaseExponentialInOut(tolua_S); lua_register_cocos2dx_CardinalSplineTo(tolua_S); lua_register_cocos2dx_CatmullRomTo(tolua_S); lua_register_cocos2dx_Waves3D(tolua_S); lua_register_cocos2dx_EaseExponentialOut(tolua_S); lua_register_cocos2dx_Label(tolua_S); lua_register_cocos2dx_Application(tolua_S); lua_register_cocos2dx_DelayTime(tolua_S); lua_register_cocos2dx_LabelAtlas(tolua_S); lua_register_cocos2dx_EaseCircleActionOut(tolua_S); lua_register_cocos2dx_SpriteBatchNode(tolua_S); lua_register_cocos2dx_TMXLayer(tolua_S); lua_register_cocos2dx_AsyncTaskPool(tolua_S); lua_register_cocos2dx_ParticleSnow(tolua_S); lua_register_cocos2dx_EaseElasticIn(tolua_S); lua_register_cocos2dx_EaseCircleActionInOut(tolua_S); lua_register_cocos2dx_TransitionFadeTR(tolua_S); lua_register_cocos2dx_EaseQuarticActionOut(tolua_S); lua_register_cocos2dx_EventAcceleration(tolua_S); lua_register_cocos2dx_EaseCubicActionIn(tolua_S); lua_register_cocos2dx_TextureCache(tolua_S); lua_register_cocos2dx_ActionTween(tolua_S); lua_register_cocos2dx_TransitionFadeDown(tolua_S); lua_register_cocos2dx_ParticleSun(tolua_S); lua_register_cocos2dx_TransitionProgressHorizontal(tolua_S); lua_register_cocos2dx_ParticleFire(tolua_S); lua_register_cocos2dx_FlipX(tolua_S); lua_register_cocos2dx_FlipY(tolua_S); lua_register_cocos2dx_EventKeyboard(tolua_S); lua_register_cocos2dx_TransitionSplitCols(tolua_S); lua_register_cocos2dx_Timer(tolua_S); lua_register_cocos2dx_RepeatForever(tolua_S); lua_register_cocos2dx_Place(tolua_S); lua_register_cocos2dx_EventListenerAcceleration(tolua_S); lua_register_cocos2dx_TiledGrid3D(tolua_S); lua_register_cocos2dx_EaseBounceOut(tolua_S); lua_register_cocos2dx_RenderTexture(tolua_S); lua_register_cocos2dx_TintBy(tolua_S); lua_register_cocos2dx_TransitionShrinkGrow(tolua_S); lua_register_cocos2dx_ClippingNode(tolua_S); lua_register_cocos2dx_ActionFloat(tolua_S); lua_register_cocos2dx_ParticleFlower(tolua_S); lua_register_cocos2dx_EaseCircleActionIn(tolua_S); lua_register_cocos2dx_Image(tolua_S); // 加载图片资源 lua_register_cocos2dx_LayerMultiplex(tolua_S); lua_register_cocos2dx_Blink(tolua_S); lua_register_cocos2dx_ShaderCache(tolua_S); lua_register_cocos2dx_JumpTo(tolua_S); lua_register_cocos2dx_ParticleExplosion(tolua_S); lua_register_cocos2dx_TransitionJumpZoom(tolua_S); lua_register_cocos2dx_Pass(tolua_S); lua_register_cocos2dx_Touch(tolua_S); lua_register_cocos2dx_CardinalSplineBy(tolua_S); lua_register_cocos2dx_CatmullRomBy(tolua_S); lua_register_cocos2dx_NodeGrid(tolua_S); lua_register_cocos2dx_TMXLayerInfo(tolua_S); lua_register_cocos2dx_EaseSineIn(tolua_S); lua_register_cocos2dx_EaseBounceIn(tolua_S); lua_register_cocos2dx_Camera(tolua_S); lua_register_cocos2dx_TMXObjectGroup(tolua_S); lua_register_cocos2dx_FastTMXTiledMap(tolua_S); lua_register_cocos2dx_ParticleGalaxy(tolua_S); lua_register_cocos2dx_Twirl(tolua_S); lua_register_cocos2dx_MenuItemLabel(tolua_S); lua_register_cocos2dx_EaseQuinticActionIn(tolua_S); lua_register_cocos2dx_LayerColor(tolua_S); lua_register_cocos2dx_FadeOutBLTiles(tolua_S); lua_register_cocos2dx_LayerGradient(tolua_S); lua_register_cocos2dx_EventListenerTouchAllAtOnce(tolua_S); lua_register_cocos2dx_GLViewImpl(tolua_S); lua_register_cocos2dx_ToggleVisibility(tolua_S); lua_register_cocos2dx_Repeat(tolua_S); lua_register_cocos2dx_TransitionFlipY(tolua_S); lua_register_cocos2dx_TurnOffTiles(tolua_S); lua_register_cocos2dx_TintTo(tolua_S); lua_register_cocos2dx_EaseBackInOut(tolua_S); lua_register_cocos2dx_TransitionFadeBL(tolua_S); lua_register_cocos2dx_TargetedAction(tolua_S); lua_register_cocos2dx_DrawNode(tolua_S); lua_register_cocos2dx_TransitionTurnOffTiles(tolua_S); lua_register_cocos2dx_RotateTo(tolua_S); lua_register_cocos2dx_TransitionSplitRows(tolua_S); lua_register_cocos2dx_Device(tolua_S); lua_register_cocos2dx_TransitionProgressRadialCCW(tolua_S); lua_register_cocos2dx_ScaleTo(tolua_S); lua_register_cocos2dx_TransitionPageTurn(tolua_S); lua_register_cocos2dx_RenderState(tolua_S); lua_register_cocos2dx_Properties(tolua_S); lua_register_cocos2dx_BezierBy(tolua_S); lua_register_cocos2dx_BezierTo(tolua_S); lua_register_cocos2dx_ParticleMeteor(tolua_S); lua_register_cocos2dx_SpriteFrame(tolua_S); lua_register_cocos2dx_Liquid(tolua_S); lua_register_cocos2dx_UserDefault(tolua_S); lua_register_cocos2dx_FastTMXLayer(tolua_S); lua_register_cocos2dx_TransitionZoomFlipX(tolua_S); lua_register_cocos2dx_EventFocus(tolua_S); lua_register_cocos2dx_TransitionFade(tolua_S); lua_register_cocos2dx_EaseQuinticActionInOut(tolua_S); lua_register_cocos2dx_SpriteFrameCache(tolua_S); lua_register_cocos2dx_PointLight(tolua_S); lua_register_cocos2dx_TransitionCrossFade(tolua_S); lua_register_cocos2dx_Ripple3D(tolua_S); lua_register_cocos2dx_Lens3D(tolua_S); lua_register_cocos2dx_EventListenerFocus(tolua_S); lua_register_cocos2dx_Spawn(tolua_S); lua_register_cocos2dx_EaseQuarticActionInOut(tolua_S); lua_register_cocos2dx_ShakyTiles3D(tolua_S); lua_register_cocos2dx_PageTurn3D(tolua_S); lua_register_cocos2dx_PolygonInfo(tolua_S); lua_register_cocos2dx_TransitionSlideInL(tolua_S); lua_register_cocos2dx_TransitionSlideInT(tolua_S); lua_register_cocos2dx_Grid3D(tolua_S); lua_register_cocos2dx_EventListenerController(tolua_S); lua_register_cocos2dx_TransitionProgressInOut(tolua_S); lua_register_cocos2dx_EaseCubicActionInOut(tolua_S); lua_register_cocos2dx_ParticleData(tolua_S); lua_register_cocos2dx_EaseBackIn(tolua_S); lua_register_cocos2dx_SplitRows(tolua_S); lua_register_cocos2dx_Follow(tolua_S); lua_register_cocos2dx_Animate(tolua_S); lua_register_cocos2dx_ShuffleTiles(tolua_S); lua_register_cocos2dx_CameraBackgroundSkyBoxBrush(tolua_S); lua_register_cocos2dx_ProgressTimer(tolua_S); lua_register_cocos2dx_EaseQuarticActionIn(tolua_S); lua_register_cocos2dx_Menu(tolua_S); lua_register_cocos2dx_EaseInOut(tolua_S); lua_register_cocos2dx_TransitionZoomFlipY(tolua_S); lua_register_cocos2dx_ScaleBy(tolua_S); lua_register_cocos2dx_EventTouch(tolua_S); lua_register_cocos2dx_Animation(tolua_S); lua_register_cocos2dx_TMXMapInfo(tolua_S); lua_register_cocos2dx_EaseExponentialIn(tolua_S); lua_register_cocos2dx_ReuseGrid(tolua_S); lua_register_cocos2dx_EaseQuinticActionOut(tolua_S); lua_register_cocos2dx_EventDispatcher(tolua_S); lua_register_cocos2dx_MenuItemAtlasFont(tolua_S); lua_register_cocos2dx_ActionManager(tolua_S); lua_register_cocos2dx_OrbitCamera(tolua_S); lua_register_cocos2dx_ClippingRectangleNode(tolua_S); lua_register_cocos2dx_EventCustom(tolua_S); lua_register_cocos2dx_ParticleBatchNode(tolua_S); lua_register_cocos2dx_Component(tolua_S); lua_register_cocos2dx_EaseCubicActionOut(tolua_S); lua_register_cocos2dx_EventListenerTouchOneByOne(tolua_S); lua_register_cocos2dx_Renderer(tolua_S); lua_register_cocos2dx_ParticleRain(tolua_S); lua_register_cocos2dx_Waves(tolua_S); lua_register_cocos2dx_ComponentLua(tolua_S); lua_register_cocos2dx_MotionStreak3D(tolua_S); lua_register_cocos2dx_EaseOut(tolua_S); lua_register_cocos2dx_MenuItemFont(tolua_S); lua_register_cocos2dx_TransitionFadeUp(tolua_S); lua_register_cocos2dx_LayerRadialGradient(tolua_S); lua_register_cocos2dx_EaseSineOut(tolua_S); lua_register_cocos2dx_JumpTiles3D(tolua_S); lua_register_cocos2dx_MenuItemToggle(tolua_S); lua_register_cocos2dx_RemoveSelf(tolua_S); lua_register_cocos2dx_SplitCols(tolua_S); lua_register_cocos2dx_ProtectedNode(tolua_S); lua_register_cocos2dx_MotionStreak(tolua_S); lua_register_cocos2dx_RotateBy(tolua_S); lua_register_cocos2dx_FileUtils(tolua_S); lua_register_cocos2dx_Sprite(tolua_S); lua_register_cocos2dx_ProgressTo(tolua_S); lua_register_cocos2dx_TransitionProgressOutIn(tolua_S); lua_register_cocos2dx_AnimationFrame(tolua_S); lua_register_cocos2dx_Sequence(tolua_S); lua_register_cocos2dx_Shaky3D(tolua_S); lua_register_cocos2dx_TransitionProgressRadialCW(tolua_S); lua_register_cocos2dx_EaseBounceInOut(tolua_S); lua_register_cocos2dx_TransitionSlideInR(tolua_S); lua_register_cocos2dx_AmbientLight(tolua_S); lua_register_cocos2dx_ParallaxNode(tolua_S); lua_register_cocos2dx_EaseQuadraticActionIn(tolua_S); lua_register_cocos2dx_WavesTiles3D(tolua_S); lua_register_cocos2dx_TransitionSlideInB(tolua_S); lua_register_cocos2dx_Speed(tolua_S); lua_register_cocos2dx_ShatteredTiles3D(tolua_S);  tolua_endmodule(tolua_S); return 1;}

在大量注册函数中寻找到关键方法lua_register_cocos2dx_Image：

int lua_register_cocos2dx_Image(lua_State* tolua_S){ tolua_usertype(tolua_S,"cc.Image"); tolua_cclass(tolua_S,"Image","cc.Image","cc.Ref",nullptr);  tolua_beginmodule(tolua_S,"Image"); tolua_function(tolua_S,"new",lua_cocos2dx_Image_constructor); tolua_function(tolua_S,"hasPremultipliedAlpha",lua_cocos2dx_Image_hasPremultipliedAlpha); tolua_function(tolua_S,"reversePremultipliedAlpha",lua_cocos2dx_Image_reversePremultipliedAlpha); tolua_function(tolua_S,"isCompressed",lua_cocos2dx_Image_isCompressed); tolua_function(tolua_S,"hasAlpha",lua_cocos2dx_Image_hasAlpha); tolua_function(tolua_S,"getPixelFormat",lua_cocos2dx_Image_getPixelFormat); tolua_function(tolua_S,"getHeight",lua_cocos2dx_Image_getHeight); tolua_function(tolua_S,"premultiplyAlpha",lua_cocos2dx_Image_premultiplyAlpha); tolua_function(tolua_S,"initWithImageFile",lua_cocos2dx_Image_initWithImageFile); // 初始化图片文件 tolua_function(tolua_S,"getWidth",lua_cocos2dx_Image_getWidth); tolua_function(tolua_S,"getBitPerPixel",lua_cocos2dx_Image_getBitPerPixel); tolua_function(tolua_S,"getFileType",lua_cocos2dx_Image_getFileType); tolua_function(tolua_S,"getFilePath",lua_cocos2dx_Image_getFilePath); tolua_function(tolua_S,"getNumberOfMipmaps",lua_cocos2dx_Image_getNumberOfMipmaps); tolua_function(tolua_S,"saveToFile",lua_cocos2dx_Image_saveToFile); tolua_function(tolua_S,"setPVRImagesHavePremultipliedAlpha", lua_cocos2dx_Image_setPVRImagesHavePremultipliedAlpha); tolua_function(tolua_S,"setPNGPremultipliedAlphaEnabled", lua_cocos2dx_Image_setPNGPremultipliedAlphaEnabled); tolua_endmodule(tolua_S); std::string typeName = typeid(cocos2d::Image).name(); g_luaType[typeName] = "cc.Image"; g_typeCast["Image"] = "cc.Image"; return 1;}

lua_cocos2dx_Image_initWithImageFile加载了我们的图片文件。

int lua_cocos2dx_Image_initWithImageFile(lua_State* tolua_S){ int argc = 0; cocos2d::Image* cobj = nullptr; bool ok = true; #if COCOS2D_DEBUG >= 1 tolua_Error tolua_err;#endif  #if COCOS2D_DEBUG >= 1 if (!tolua_isusertype(tolua_S,1,"cc.Image",0,&tolua_err)) goto tolua_lerror;#endif  cobj = (cocos2d::Image*)tolua_tousertype(tolua_S,1,0); #if COCOS2D_DEBUG >= 1 if (!cobj) { tolua_error(tolua_S,"invalid 'cobj' in function 'lua_cocos2dx_Image_initWithImageFile'", nullptr); return 0; }#endif  argc = lua_gettop(tolua_S)-1; if (argc == 1) { std::string arg0;  ok &= luaval_to_std_string(tolua_S, 2,&arg0, "cc.Image:initWithImageFile"); if(!ok) { tolua_error(tolua_S,"invalid arguments in function 'lua_cocos2dx_Image_initWithImageFile'", nullptr); return 0; } bool ret = cobj->initWithImageFile(arg0); tolua_pushboolean(tolua_S,(bool)ret); return 1; } luaL_error(tolua_S, "%s has wrong number of arguments: %d, was expecting %d \n", "cc.Image:initWithImageFile",argc, 1); return 0; #if COCOS2D_DEBUG >= 1 tolua_lerror: tolua_error(tolua_S,"#ferror in function 'lua_cocos2dx_Image_initWithImageFile'.",&tolua_err);#endif  return 0;}

下面看cobj->initWithImageFile：

bool Image::initWithImageFile(const std::string& path){ bool ret = false; _filePath = FileUtils::getInstance()->fullPathForFilename(path);  Data data = FileUtils::getInstance()->getDataFromFile(_filePath); // 获取文件数据  if (!data.isNull()) { ret = initWithImageData(data.getBytes(), data.getSize()); // 解码/解密 处理文件数据 }  return ret;}

下面是图片数据格式解码方法initWithImageData：

bool Image::initWithImageData(const unsigned char * data, ssize_t dataLen){ bool ret = false;  do { CC_BREAK_IF(! data || dataLen <= 0);  unsigned char* unpackedData = nullptr; ssize_t unpackedLen = 0;  //detect and unzip the compress file if (ZipUtils::isCCZBuffer(data, dataLen)) { unpackedLen = ZipUtils::inflateCCZBuffer(data, dataLen, &unpackedData); } else if (ZipUtils::isGZipBuffer(data, dataLen)) { unpackedLen = ZipUtils::inflateMemory(const_cast<unsigned char*>(data), dataLen, &unpackedData); } else { unpackedData = const_cast<unsigned char*>(data); unpackedLen = dataLen; }  _fileType = detectFormat(unpackedData, unpackedLen);  switch (_fileType) { case Format::PNG: ret = initWithPngData(unpackedData, unpackedLen); break; case Format::JPG: ret = initWithJpgData(unpackedData, unpackedLen); break; case Format::WEBP: ret = initWithWebpData(unpackedData, unpackedLen); break; case Format::PVR: ret = initWithPVRData(unpackedData, unpackedLen); break; case Format::ETC: ret = initWithETCData(unpackedData, unpackedLen); break; case Format::S3TC: ret = initWithS3TCData(unpackedData, unpackedLen); break; case Format::ATITC: ret = initWithATITCData(unpackedData, unpackedLen); break; default: { // load and detect image format tImageTGA* tgaData = tgaLoadBuffer(unpackedData, unpackedLen);  if (tgaData != nullptr && tgaData->status == TGA_OK) { ret = initWithTGAData(tgaData); } else { CCLOG("cocos2d: unsupported image format!"); }  free(tgaData); break; } }  if(unpackedData != data) { free(unpackedData); } } while (0);  return ret;}

图片资源的加载到这里就结束了。

6

图片资源解密

快速定位：根据调用流程，我们可以直接定位方法cocos2d::Image::initWithImageData。

 

向上可以追溯到cocos2d::Image::initWithImageFile：

看到了可疑函数cocos2d::Image::decodePngData

cocos2d *__fastcall cocos2d::Image::decodePngData(cocos2d::Image *this, cocos2d::Data *a2){ _BYTE *v4; // r7 int v5; // r5 signed int v6; // r0 bool v7; // cc int v8; // r4 void *v9; // r0 int v10; // r2 int v12; // r6 int v13; // r4 int v14; // r9 int v15; // r2 int v16; // r0 int v17; // r3 _BYTE *v18; // r5 unsigned int *v19; // r2 int v20; // r3 int v21; // [sp+8h] [bp-28h] BYREF  v4 = (_BYTE *)cocos2d::Data::getBytes(a2); v5 = cocos2d::Data::getSize(a2); sub_FBDCA8(&v21, (int *)this + 47); v6 = sub_FBC854((int)&v21, ".png", 0, 4u); v7 = v6 <= -1; if ( v6 != -1 ) v7 = v5 <= 24; v8 = !v7; v9 = (void *)(v21 - 12); if ( (int *)(v21 - 12) != &dword_12F6978 ) { if ( &pthread_create ) { v19 = (unsigned int *)(v21 - 4); __dmb(0xFu); do v20 = __ldrex(v19); while ( __strex(v20 - 1, v19) ); __dmb(0xFu); } else { v20 = *(_DWORD *)(v21 - 4); *(_DWORD *)(v21 - 4) = v20 - 1; } if ( v20 <= 0 ) operator delete(v9); } if ( v8 && memcmp(&unk_11CBE0C, v4, 8u) ) // PNG Header { v12 = v5 - 4; v13 = v5 - 8; v14 = cocos2d::hexToDecimal((cocos2d *)&v4[v5 - 4], (unsigned __int8 *)&byte_4, v10); v16 = cocos2d::hexToDecimal((cocos2d *)&v4[v5 - 8], (unsigned __int8 *)&byte_4, v15); if ( v5 >= v16 ) cocos2d::decodePng(v4, (unsigned __int8 *)(v14 - 2048), v16, v17); v18 = &v4[v5]; *(v18 - 1) = 130; *(v18 - 2) = 96; *(v18 - 3) = 66; v4[v12] = 174; *(v18 - 5) = 68; *(v18 - 6) = 78; *(v18 - 7) = 69; v4[v13] = 73; } return (cocos2d *)v4;}

明显是一个算法函数，看方法cocos2d::decodePng：

_BYTE *__fastcall cocos2d::decodePng(_BYTE *this, unsigned __int8 *a2, int a3, int a4){ char v4; // r12 unsigned int v5; // r1 int v6; // r12 char v7[4]; // [sp+0h] [bp-10h]  v7[1] = BYTE2(a2); v4 = BYTE1(a2); v7[3] = (char)a2; v5 = (unsigned int)a2 >> 24; v7[2] = v4; v6 = 0; v7[0] = v5; if ( a3 > 0 ) { while ( 1 ) { ++v6; *this++ ^= v5; if ( v6 == a3 ) break; LOBYTE(v5) = v7[v6 % 4]; } } return this;}

这里也可以尝试Frida Hook验证猜想，同样的，我就不Hook了。 算法还原：

def _hexToDecimal(data, offset): if offset <= 0: return 0 return struct.unpack(">I", data[:offset])[0]  def LOBYTE(d): return d & 0xff  def _decodePng(data, magic, rounds): dthis = bytearray(data)  v7 = [0] * 4 a2 = struct.pack("<i", magic) v7[1] = a2[2] v7[3] = a2[0] v7[0] = v5 = magic >> 24 v7[2] = a2[1]  i = 0 if rounds > 0: while 1: i += 1 dthis[i-1] ^= v5 if i == rounds: break v5 = LOBYTE(v7[i % 4]) return dthis  def decodePng(data, size): v14 = _hexToDecimal(data[-4:], 4) v16 = _hexToDecimal(data[-8:], 4) if size >= v16: ret = _decodePng(data, v14 - 2048, v16) ret[-1] = 130 ret[-2] = 96 ret[-3] = 66 ret[-4] = 174 ret[-5] = 68 ret[-6] = 78 ret[-7] = 69 ret[-8] = 73 return ret

解密结果：

最大的感想就是：对照源码逆向好爽！

 

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