初步认识cocos2d-x
先clone到本地
git clone https://github.com/cocos2d/cocos2d-x.git
Cocos2d-x是一个开源的移动2D游戏框架，底层支持各种平台，核心用c++封装了各种库，外面给了lua和c++的接口，所以关键代码可能在lua中，很多安卓游戏的逻辑也基本都在lua脚本里，盗用官网这张图
framework_architecture_v4.png (63.04 KB, 下载次数: 0)
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从c++进入lua世界
lua虚拟机相关代码在cocos2d-x\cocos\scripting\lua-bindings\manual里
CCLuaEngine.h lua引擎相关
CCLuaStack.h lua栈相关
进入虚拟机
cocos2d-x\templates\lua-template-default\frameworks\runtime-src\Classes\AppDelegate.cpp\AppDelegate::applicationDidFinishLaunching
applicationDidFinishLaunching函数
应用结束加载中进入lua虚拟机
bool AppDelegate::applicationDidFinishLaunching()
{
// set default FPS
Director::getInstance()->setAnimationInterval(1.0 / 60.0f);//设置fps刷新率
// register lua module
auto engine = LuaEngine::getInstance();//创建lua虚拟机引擎
ScriptEngineManager::getInstance()->setScriptEngine(engine);//设置脚本引擎为lua引擎
lua_State* L = engine->getLuaStack()->getLuaState();//创建lua虚拟机环境lua_State
lua_module_register(L); //分配网络，控制台，ui界面等相关联的寄存器
register_all_packages();
LuaStack* stack = engine->getLuaStack();
stack->setXXTEAKeyAndSign("2dxLua", strlen("2dxLua"), "XXTEA", strlen("XXTEA"));
//这一步很关键，获取栈结构并调用setXXTEAKeyAndSign设置加密算法为xxtea，sign为XXTEA,KEY为2dxlua，很多游戏lua脚本都用的默认的sign和key
//如果没有用默认的，ida打开libxxxluaxxx.so直接搜索applicationDidFinishLaunching导出函数也基本都能直接找到
//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"); //lua源码在src文件夹，资源在res文件夹
FileUtils::getInstance()->addSearchPath("res");
if (engine->executeScriptFile("main.lua")) //直接通过lua引擎调用main.lua进入lua的世界
{
return false;
}
return true;
}
这句engine->executeScriptFile("main.lua")调用了cocos2d-x\cocos\scripting\lua-bindings\manual\CCLuaEngine.cpp的executeScriptFile调用了CCLuaStack.cpp的executeScriptFile
LuaStack::executeScriptFile
int LuaStack::executeScriptFile(const char* filename)
{
CCAssert(filename, "CCLuaStack::executeScriptFile() - invalid filename");
std::string buf(filename);
//
// remove .lua or .luac
//
size_t pos = buf.rfind(BYTECODE_FILE_EXT);//BYTECODE_FILE_EXT就是lua字节码，NOT_BYTECODE_FILE_EXT就是lua脚本源码
//static const std::string BYTECODE_FILE_EXT = ".luac";
if (pos != std::string::npos)
{
buf = buf.substr(0, pos);//截取前缀
}
else
{
pos = buf.rfind(NOT_BYTECODE_FILE_EXT);
if (pos == buf.length() - NOT_BYTECODE_FILE_EXT.length())
{
buf = buf.substr(0, pos);
}
}
FileUtils *utils = FileUtils::getInstance();
//
// 1. check .luac suffix
// 2. check .lua suffix
//
std::string tmpfilename = buf + BYTECODE_FILE_EXT;
if (utils->isFileExist(tmpfilename))
{
buf = tmpfilename;
}
else
{
tmpfilename = buf + NOT_BYTECODE_FILE_EXT;
if (utils->isFileExist(tmpfilename))
{
buf = tmpfilename;
}
}
std::string fullPath = utils->fullPathForFilename(buf);//获取绝对路径
Data data = utils->getDataFromFile(fullPath);//通过getDataFromFile读取lua文件到data
int rn = 0;
if (!data.isNull())
{
if (luaLoadBuffer(_state, (const char*)data.getBytes(), (int)data.getSize(), fullPath.c_str()) == 0)//通过luaLoadBuffer加载data
{
rn = executeFunction(0);
}
}
return rn;
}
LuaStack::luaLoadBuffer
luaLoadBuffer里调用xxtea_decrypt解密了lua脚本，然后调用luaL_loadbuffer加载解密后的脚本，所以直接hook 这个函数luaL_loadbuffer把(char*)content这个字符dump出来就得到解密过的lua脚本了
int LuaStack::luaLoadBuffer(lua_State L, const char chunk, int chunkSize, const char *chunkName)
{
int r = 0;
if (_xxteaEnabled && strncmp(chunk, _xxteaSign, _xxteaSignLen) == 0)//这里判断是否开启xxtea加密，如果开启就需要解密
{
// 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);//调用xxtea_decrypt解密脚本，这个函数在cocos2d-x\external\xxtea\xxtea.cpp里，加解密都在这个cpp里
unsigned char* content = result;
xxtea_long contentSize = len;
skipBOM((const char*&)content, (int&)contentSize);//忽略utf8的bom
r = luaL_loadbuffer(L, (char*)content, contentSize, chunkName);//无论是否加密，解密后都会调用luaL_loadbuffer函数，所以直接hook这个函数把(char*)content这个字符dump出来就是解密过的lua脚本了
free(result);
}
else
{
skipBOM(chunk, chunkSize);
r = luaL_loadbuffer(L, chunk, chunkSize, chunkName);//这个返回值r会反映加载失败的类型，在下面的switch中打印出来
}
#if defined(COCOS2D_DEBUG) && COCOS2D_DEBUG > 0
if (r)
{
switch (r)
{
case LUA_ERRSYNTAX:
CCLOG("[LUA ERROR] load \"%s\", error: syntax error during pre-compilation.", chunkName);
break;
case LUA_ERRMEM:
CCLOG("[LUA ERROR] load \"%s\", error: memory allocation error.", chunkName);
break;
case LUA_ERRFILE:
CCLOG("[LUA ERROR] load \"%s\", error: cannot open/read file.", chunkName);
break;
default:
CCLOG("[LUA ERROR] load \"%s\", error: unknown.", chunkName);
}
}
#endif
return r;
}
而luaL_loadbuffer的源码没有，只有编译过的库cocos2d-x\external\lua\luajit\prebuilt\android\armeabi-v7a\libluajit.a，
要找它的实现需要下载luajit源代码分析了，这就完全进入了lua虚拟机的实现
a Just-In-Time Compiler for Lua. 采用C语言写的Lua的解释器的代码
总结
1.从c++进入lua世界的调用逻辑
AppDelegate::applicationDidFinishLaunching
{
setXXTEAKeyAndSign
executeScriptFile
{
getDataFromFile
luaLoadBuffer
{
xxtea_decrypt
luaL_loadbuffer
{
luajit
}
}
executeFunction
}
}
2.加密算法为xxtea，如果没有修改，sign为XXTEA,KEY为2dxlua，如果有修改，可以ida打开libxxluaxx.so在applicationDidFinishLaunching里找到
3.无论是否加密，解密后都会调用luaL_loadbuffer函数，所以直接hook这个函数把(char*)content这个字符dump出来就是解密过的lua脚本了，缺点是要把游戏运行一遍，只能搞出执行过的代码
4.cocos2d-x\external\xxtea\xxtea.cpp里有完整的加密解密算法，逻辑清晰，可以写个python脚本直接本地解密，也可以在这里hook获取key和sign或者解密后脚本
实战
某捕鱼游戏，下载安装apk后，再其内部内置了捕鱼、麻将等十几款小游戏，嘿嘿，懂得都懂这是干啥的，直接点击捕鱼游戏下载，
下载后的游戏源码在/data/data/com.q8wdw6.gyll9spfo.nycatp9/files/download/里
adb pull 出来，files文件夹里面已经暴露很多信息了，配置，下载的游戏，更新等等
QQ图片20210720113613.png (25.4 KB, 下载次数: 0)
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进入files\download\107\res\就可以看到luac，很明显crash里面存储了所有碰撞，model_path_crash和path里存储的是移动路径，我们可以看到所有的鱼的移动路径都是tm设定好的，models里面存储着游戏逻辑，views里面存储着界面显示逻辑
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随机打开一个luac加密了，开头的ZX_CS@56#D~d@dud明显就是加密sign
QQ图片20210719213107.png (20.34 KB, 下载次数: 0)
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根据之前对cocos2d引擎的分析，找到apk下面带有lua也是最大的一个so libqpry_lua.so，用ida直接打开，定位到AppDelegate::applicationDidFinishLaunching函数，直接拖到最下面，看到这句
(*(v7 + 1) + 116))((v7 + 1), "ZX_01RdsF~@!R8", 14, "ZX_CS@56#D~d@dud", 16);很明显是调用了stack->setXXTEAKeyAndSign
对比源码stack->setXXTEAKeyAndSign("2dxLua", strlen("2dxLua"), "XXTEA", strlen("XXTEA"));
解密key为ZX_01RdsF~@!R8，sign为ZX_CS@56#D~d@dud
也可以直接搜索字符串，因为key和sign在一个函数调用，所以一般离的很近，base/src/main.lua这个字符串进一步验证了正确性
QQ图片20210719214220.png (24.92 KB, 下载次数: 0)
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int __fastcall AppDelegate::applicationDidFinishLaunching(AppDelegate *this)
{
//前面是一堆初始化啥的没用的
....
(**(v7 + 1) + 116))(*(v7 + 1), "ZX_01RdsF~@!R8", 14, "ZX_CS@56#D~d@dud", 16);
if ( (*(*v7 + 28))(v7, "base/src/main.lua") )
return 0;
v26 = GetMCKernel();
if ( !v26 )
return 0;
v27 = *(this + 145); if ( v27 ) v27 += 580; v28 = (*(*v26 + 20))(v26, v27);
v29 = *(cocos2d::Director::getInstance(v28) + 152);
v32[0] = AppDelegate::GlobalUpdate;
v32[1] = -8;
cocos2d::Scheduler::schedule(v29, AppDelegate::GlobalUpdate, -8, this + 4, 0.0, 0xFFFFFFFE, 0.0, 0);
return v25;
}
有了key和sign就可以直接解密luac脚本了，照着写，很简单，可以看到sign的作用就是被忽略，只有长度有用，尴尬，解密用的主要是key
unsigned char* result = xxtea_decrypt((unsigned char*)chunk + _xxteaSignLen,
(xxtea_long)chunkSize - _xxteaSignLen,
(unsigned char*)_xxteaKey,
(xxtea_long)_xxteaKeyLen,
&len);
unsigned char *xxtea_decrypt(unsigned char *data, xxtea_long data_len, unsigned char *key, xxtea_long key_len, xxtea_long *ret_length)
{
unsigned char *result;
*ret_length = 0;
if (key_len
或者直接pip install xxtea-py
然后直接python，自己写个循环实现批量解密吧
import xxtea
import os
orig_path=“”//初始路径
new_path=“”//存储路径
xxtea_sign=“”
xxtea_key=“”
orig_file = open(orig_path, "rb")
encrypt_bytes = orig_file.read()
orig_file.close()
decrypt_bytes = xxtea.decrypt(encrypt_bytes[len(xxtea_sign):], xxtea_key)
new_file = open(new_path, "wb")
new_file.write(decrypt_bytes)
new_file.close()
下面开始分析lua，这个最简单，我们想分析子弹打到鱼的逻辑，直接找src\views\layer\BulletLayer.luac
直接找子弹打到鱼的函数，很清晰，第一个参数为子弹对象，第二个为鱼列表，这里看到只有master_id == self_player_id才会调用
on_self_bullet_crash_fish当自己的子弹击中了鱼最后会调用加金币等，否则只调用on_bullet_crash_fish显示效果，这里可以也改成on_self_bullet_crash_fish就可以加金币了
function BulletLayer:on_bullet_crash_fish(bullet_obj, t_fish_list)
local scene = self:get_scene()
local master_id = bullet_obj:get_master_id()
local bullet_uid = bullet_obj:get_bullet_uid()
local self_player_id = self:get_self_player_id()
local num = #t_fish_list
if(num >= 2) then
local fish_layer = self:get_fish_layer()
table.sort(t_fish_list, function(uid1, uid2)
local fish_obj1 = fish_layer:get_fish_by_uid(uid1);local fish_obj2 = fish_layer:get_fish_by_uid(uid2)
local zorder1 = fish_obj1:getLocalZOrder();local zorder2 = fish_obj2:getLocalZOrder()
if(zorder1 > zorder2) then return true end
end)
end
local fish_uid = t_fish_list[1]
if(master_id == self_player_id) then
scene:on_self_bullet_crash_fish(master_id, bullet_uid, fish_uid)
--scene:on_self_bullet_crash_fish_test(master_id, bullet_uid, fish_uid)
end
scene:on_bullet_crash_fish(master_id, bullet_uid, t_fish_list)
end
在定位一下加钱的函数，fish_gold是鱼的钱，fish_odds是鱼的剩余 ，这句 local one_add_gold = math.floor(fish_gold/12)就是一个鱼加的钱，我们把这个/12改为*12就可以修改倍数了
function AnimationLayer:play_catch_fish_earn_money_self(fish_gold, fish_odds)
local earn_money_node = self:reuse_new_earn_money_view_node('zhuanqianle_buyu', self, 0)
local pos = cc.p(sizeVisble.width/2, sizeVisble.height/2)
local one_add_gold = math.floor(fish_gold/12)
local min = self:get_earn_money_one_add_gold_min()
if(one_add_gold
入口代码在AnimationLayer.lua里，直接看接收到玩家捕到鱼的函数，分为网或者炸弹，里面还有一网打尽和大转盘之类的特效，这里可以把它全部改成高倍的特效
function AnimationLayer:on_recv_player_catch_fish(player_id, fish_uid, fish_gold)
local fish_layer = self:get_fish_layer()
local fish_obj = fish_layer:get_fish_by_uid(fish_uid)
if(fish_obj == nil) then return end
local data_center = self:get_data_center()
local fish_id = fish_obj:get_fish_id()
local fish_info = data_center:get_fish_info(fish_id)
if(fish_info == nil) then return end
local fish_type = fish_info.type
if(fish_type == GameDefine.fish_type.wang) then
local other_fish_obj_list = self:get_other_fish_yi_wang_da_jin_list(fish_obj, GameDefine.fish_type.wang)
local num = #other_fish_obj_list
if(num > 0) then
local fish_odds = self:get_catch_fish_odds(fish_obj, other_fish_obj_list)
self:on_player_catch_fish_yi_wang_da_jin(player_id, fish_obj, fish_gold, fish_odds, other_fish_obj_list)
end
self:on_player_catch_fish_drop_fish_gold(player_id, fish_obj, 0, 0)
return
end
if(fish_type == GameDefine.fish_type.bomb) then
play_drop_gold = 0
local other_fish_list = self:get_bomb_fish_effect_fish_list()
local num = #other_fish_list
if(num > 0) then
local fish_odds = self:get_catch_fish_odds(fish_obj, other_fish_list)
self:on_player_catch_fish_bomb(player_id, fish_obj, fish_gold, fish_odds, other_fish_list)
end
self:on_player_catch_fish_drop_fish_gold(player_id, fish_obj, 0, 0)
return
end
local fish_odds = fish_info.mulriple_max;local fish_name = fish_info.name
self:on_player_cath_fish_da_zhuan_pan(player_id, fish_type, fish_gold, fish_name)
self:on_player_catch_fish_drop_fish_gold(player_id, fish_obj, fish_gold, fish_odds)
end
src\models\DataCenter.lua里存储着鱼和子弹等参数，可以看到子弹最高9级，odds_min与odds_max应该就代表威力，改这里可以改子弹威力
{
room_style= 3,
cannon_id= 109,
odds_min= 7,
odds_max= 10,
level= 3,
res= "pao3_buyu",
bullet= "zd9",
net= "yuwang3_buyu",
time= 200,
sound= 109
}
self.fish_client存储不同鱼的参数，不同id对应不同鱼，mulriple_min与mulriple_max存储着金币的倍数最大与最小值，一般鱼都是2-3倍，大章鱼为300倍，改这里可以直接改鱼的倍数
{
id= 302,
name= "60倍组合鱼",
packet= "4lian_buyu",
crash_model= 101,
mulriple_min= 60,
mulriple_max= 60,
type= 101,
zoder= 21,
die_sound= "fish14_1",
die_type= 4,
copy_num= 4
},
{
id= 402,
name= "大章鱼",
packet= "yu22_buyu",
crash_model= 16,
mulriple_min= 300,
mulriple_max= 300,
type= 2,
zoder= 30,
bron_sound= "f_wb_3",
die_sound= "fish33_1",
die_type= 5,
copy_num= 4
},
其他的功能逻辑获得源码后都很清晰，改倍数改鱼改子弹什么都很简单，改完之后重新用sign和key加密之后push到相应文件夹下面就实现了破解
[md]# 个人想法
如何实现cocos2d反逆向，我的一些不成熟想法，由浅到深分层如下
1.修改xxtea的key和sign，就像这个游戏，需要分析so才能找到key
2.直接修改xxtea算法为其他可逆算法，这样逆向的时候还得逆加密算法
3.在进一步，修改luajit源码改动lua虚拟机，比如改变字节码指令顺序，或者改变数据读取顺序等，这样逆向的时候必须分析lua虚拟机的改动
4.把key，加密算法，虚拟机改动等的关键函数封装放到其他cpp或者其他so里，在加密一层，调用的时候在解密，这样需要先动态调试先分析调用逻辑
5.关键代码加入ollvm再编译或者直接vm掉，这样需要先去掉ollvm混淆或者分析vm
## 参考文章
[cocos2d 3.3 lua 代码加密 luac](https://www.cnblogs.com/lxjshuju/p/7028393.html)
[安卓逆向之Luac解密反编译](https://www.yuanrenxue.com/app-crawl/luac.html)[/md]
