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bstree

bstree is Lua source code obfuscator. It analyzes Lua files in source code and outputs an encoder and a decoder.

BS stands for Bit Stream or Bull Shit, depending on your mood.

Usage

$ lua bstree.lua <input.lua>+

This command will analyze all given Lua files and output two files:

  1. bsenc.lua: Lua application that obfuscates the given source code
  2. bsdec.lua: Lua application that decodes the given obfuscated code
  3. bstree.h: header file with the decode tree, used by bsreader.c

bsenc.lua

$ lua bsenc.lua <input.lua> <output.bs>

Obfuscates the given Lua file in source code format, producing output.bs. Use output.bs in your applications.

bsdec.lua

$ lua bsenc.lua <input.bs> <output.lua>

Decodes the given .bs file, producing output.lua which should be identical to the original Lua source code.

bsreader.c

To read the obfuscated files in your application, use bsreader.c. It requires bstree.h, created by running bstree.lua. bsreader.h provides two functions:

  • void* bsnew( void* data );: creates a structure used by bsread.
  • const char* bsread( lua_State* L, void* data, size_t* size );: a lua_Reader function that takes the structure created by bsnew and produces Lua source code. bsread is meant to be used with lua_load.

See testdec.c for a decoder example.

Details

bstree.lua analyzes Lua source code and creates a Huffman tree. Identifiers, numbers, strings and comments are all encoded as literals, with the characters following the encoding, and the remaining Lua keywords and symbols are encoded as themselves. self, despiting begin an identifier, is encoded as a keyword. A special keyword, eof is also added to the tree to mark the end of the encoded data.

bstree.lua then outputs bsenc.lua, bsdec.lua, and bstree.h, all with the Huffman tree embeded. They must be used together, i.e. files encoded by bsenc.lua can only be decoded by bsdec.lua or by using bstree.h that were created during the same bstree.lua run.

The bsread function uses a predefined buffer during the decoding process. Its size if 512 bytes by default, make sure you edit bsread.c and change MAX_LITERAL_SIZE according to your needs. The default size should be enough for most applications, but if you have large string literals or comments it won't be able to decode the entire literal and bad things will happen.

The encoded files are easily decoded if bstree.h or bsdec.lua are available, or if the Huffman tree is recreated via reverse engineering. This utility should not be used if you require absolute secrecy about your Lua source code. Also, compression is just a by-product of the obfuscation process, if you need real compression you're better off using a compression utility like gzip or bzip2.

bstree.lua and the generated bsenc.lua files uses Penlight's lexer.lua, modified to include the integer division symbol // from Lua version 5.3. lexer.lua is included verbatim where it's used because I hate LUA_PATH.

License

bstree.lua is released under the zlib/libpng license. bsenc.lua, bsdec.lua and bstree.h are not subject to this license, and can be used according to your own terms. bsreader.c and bsreader.h are in the public domain.