ltn12ce

ltn12ce is a Lua module which provides compression, decompression, encryption, decryption and hashing using a common interface. These are provided using the following libraries:

The list of currently supported algorithms:

Compression - bzip2 (.bz2), LZMA (.lzma), LZMA2 (.xz), DEFLATE, gzip (.gz)
Encryption - AES, Blowfish, Camellia, DES, 3-DES
Hashing - MD4, MD5, SHA1, SHA-224/256/385/512

One of the design goals of this module is to have no external dependencies. This means that every dependent library code is embedded and there are no prerequisites (except for Lua). In addition with CMake, this is a very portable way to handle compressed and/or encrypted data.

This is not a module to handle compressed archives (.zip, .rar, .tar), only compressed streams.

Installing

This module is created with LuaDist in mind, so once it is in the LuaDist package repository, you can simply install it using:

luadist install ltn12ce

Building

It is possible to build ltn12ce separately from LuaDist. The build process is based on CMake. All external libraries' build processes have been converted to CMake, so there are no autotools/configure scripts necessary. It should be possible to build the module for every build system CMake supports, which includes building for Windows, Linux and Mac OS X (in case of problems, please report).

The preferred way to build ltn12ce is using an out-of-source directory and running cmake inside it:

ltn12ce$ mkdir build; cd build
ltn12ce/build$ cmake ..
ltn12ce/build$ make

Installation is simply by copying the build/src/ltn12 somewhere into your Lua package.cpath.

It is possible to selectively compile the libraries in case of size/memory constraints. The following CMake variables control what gets built:

BUILD_CRYPTO - encryption and hashing using PolarSSL
BUILD_BZIP2 - bzip2 compression
BUILD_LZMA - LZMA and XZ compression
BUILD_ZLIB - zlib compression

All flags are turned on by default.

API

All algorithms implement a common API. An algorithm constructor creates an object, which acts as a filter that takes string input and returns processed string output. True LTN12 filter interface will be implemented later using pure Lua module.

The object (let's name it filter), when initialized, provides the following methods:

filter:update(data : string) : string - call this method (at least once, but maybe repeatedly) to provide additional input to the filter. data must be a string, but it may be an empty string (#data == 0). It returns a string representing additional output from this filter. Given the nature of the algorithms, which may buffer the data until something can be processed, update may return an empty string, but it never returns nil.
filter:finish() : string - after the entire input has been consumed, there may be some data which is buffered. Call this method to finish the processing and return any leftover data. This may be an empty string.

Imagine a process input -> filter -> output. input can be provided in one or multiple chunks by calls to filter:update(chunk) followed by filter:finish(). The concatenation of the results of update() and finish() calls is the entire output of the filter.

ltn12.core

This module is a C binding to the embedded libraries. Here is a list of functions/objects/methods it provides. Every object implements the update and finish functions documented above, and they are not repeated here.

core.ciphers() : { string } - an array of valid cipher identifiers for core.cipher.
core.cipher(cipherid : string) : cipher - create a cipher, where cipherid is one of the identifiers from core.ciphers(). An example of such cipherid is "AES-256-CBC". cipherid is case-insensitive. The operation (encryption/decryption) and keys are set using cipher:setkeys().
cipher:name() : string - the cipher identifier of the given object (in case you forget ;-)
cipher:keysize() : number - the length of expected encryption/decryption key.
cipher:setkey(key : string, operation : string) - sets the keys and operation for the given cipher. operation is one of two strings "encrypt" and "decrypt", and key is the binary encryption/decryption key. It must be of the length reported by cipher:keysize().
core.digests() : { string } - an array of valid digest identifiers for core.digest().
core.digest(digestid : string) : digest - create a digest (hash) algorithm using a digest identifier reported by core.digests(). digestid is case-insensitive.
digest:name() : string - the digest identifier.
digest:size() : number - the size of the resulting digest in bytes.
digest:update(data : string) : string - a little implementation note on this method - this always returns an empty string. No output is produced until digest:finish(), which returns the resulting digest.

Compression constructors (bzip2, lzma, zlib) have the following interface:

core.compressor(operation : string, level : number) : filter - create a (de)compressor, where compressor is one of bzip2, lzma, zlib. operation must be one of "compress" or "decompress". When compressing, the second parameter represents the compression level, and is a number between 1 and 9 including.

Sample

function makekey(key, bits)
	return key .. string.rep('0', bits/8 - #key)
end
local compressor = core.zlib('compress', 9)
local encrypter = core.cipher('aes-256-cbc')
encrypter:setkey(makekey('12345678', 256), 'encrypt')

function runthrough(f, data) return f:update(data) .. f:finish() end

local input = 'xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx'
local compressed = runthrough(compressor, input)
local output = runthrough(encrypter, compressed)

License

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.