ascii-zip's Introduction

ascii-zip

A deflate compressor that emits compressed data that is in the [A-Za-z0-9] ASCII byte range.

Example

$ echo 'Hello ASCII world!' >hello
$ ./compress.py --mode raw --output ./hello.infalted ./hello >/dev/null
$ cat ./hello.infalted
D0Up0IZUnnnnnnnnnnnnnnnnnnnUU5nnnnnn3SUUnUUUwCiudIbEAtwwwEt333
G0GDGGDtGptw0GwDDDGtDGDt33333www03333sDdFPsgWWwackSKKaowOWGQ4

Why?

It can be used for bypassing certain filters in certain applications :)

This algorithm is at the heart of the Rosetta Flash vulnerability. For additional information, see

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ascii-zip's Issues

Variable scoping

I created a new brute-force mode for the tool (it is not pretty yet as it simply works but is a huge hack). I was able to find what I did (a deflated stream that includes the string "5#"), however, there were many issues and the ASCIICompressor code throws a couple of exceptions:

floyd-fuh@b181fe8

So I'm generally a little confused about the scope of your variables, for example "huffman". It is set here (but due to python's scoping, will live in the function as variable if I got that right): https://github.com/molnarg/ascii-zip/blob/master/compress.py#L67 . But of course if "cursor" was below 0, the variable is still uninitialized. Something similar happens on https://github.com/molnarg/ascii-zip/blob/master/compress.py#L81 . But then you just use the maybe-uninitialized variable "huffman" here https://github.com/molnarg/ascii-zip/blob/master/compress.py#L96 .

This is all problematic as some of the functions actually return None, such as here:
https://github.com/molnarg/ascii-zip/blob/master/compress.py#L139 or https://github.com/molnarg/ascii-zip/blob/master/compress.py#L159

I'm not enough into the topic of the deflate algorithm, so it is hard for me to fully undestand the code and fix it. Any chance you'll have a look?

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