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I'm truing to decrypt LUA scrpits from cocos2dx game (for wiki).

Links to files of game: libhellolua.so (cocos2dx external library) example encrypted LUA-scripts (*.abc files)

I was reading a library in IDA Pro. This library don't have mention "xxtea".

And i found function getEncyptedFileData: pastebin getEncyptedFileData

This function is not in the original source code of Cocos2d-x. I think this function is related to decryption (since this function is called nearby with the variable "*.abc"). I can not understand the some lines in this function:

1: I think that this function CCFileUtils:getFileData.

v5 = (_BYTE *)(*(int (__fastcall **)(cocos2d::CCFileUtils *, const char *, const char *, unsigned int *))(*(_DWORD *)this + 16))(this, a2, "rb", &v26);

2: This loop not readeable. The result of the first line is used in this loop.

do
  {
    v6[(signed int)v17 * (signed __int64)v11 % (unsigned __int64)v14] = *(_BYTE *)(v13 + v16) ^ v15[v17];
    ++v17;
    v16 = (v16 + 1) % v10;
  }
  while ( v17 < v14 );

3: function getEncyptedFileData return result of this line:

v19 = (*(int (__cdecl **)(cocos2d::CCFileUtils *, _BYTE *))(*(_DWORD *)v21 + 24))(v21, v6);
  • bbs.pediy.com/thread-188534-1.htm#1293990 password to unzip: cocos2d: ERROR: Invalid filename <filename without path and extension>, ex: cocos2d: ERROR: Invalid filename DailyLoginReward – user29082 Aug 4 '19 at 14:48
  • Are those links valid now? I can't download those and can't understand russian! – Biswapriyo Aug 6 '19 at 4:01
  • @Biswapriyo, yes. Links valid. – Azat Idrisov Aug 6 '19 at 9:33
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  v5 = (_BYTE *)(*(int (__fastcall **)(cocos2d::CCFileUtils *, const char *, const char *, unsigned int *))(*(_DWORD *)this + 16))(
                  this,
                  a2,
                  "rb",
                  &v26);

This is a signature xxtea encryption with the sign rb. Now you need to find the xxtea encryption key in this method. You can either dig a little bit more from CCFileUtils or AppDelegate(As this article: https://boards.libre.io/threads/decrypt-xxtea-block-cipher-in-lua-file-from-cocos2d-lua-games.297552/)

Another way (my favorite way), is to use frida and hook to the method, print out this (arg[0]) using this guide: https://boards.libre.io/threads/decrypting-lua-files.238916/

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