Decrypting Lua Files from game

Question

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);

Answer 1

  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/