Tools to help reverse engineer binary file formats

Question

What tools are available to aid in decoding unknown binary data formats?

I know Hex Workshop and 010 Editor both support structures. These are okay

Answer 1

Here are some tips that come to mind:

From my experience, interactive scripting languages (I use Python) can be a great help. You can write a simple framework to deal with binary streams and some simple algorithms. Then you can write scripts that will take your binary and check various things. For example:

Do some statistical analysis on various parts. Random data, for example, will tell you that this part is probably compressed/encrypted. Zeros may mean padding between parts. Scattered zeros may mean integer values or Unicode strings and so on. Try to spot various offsets. Try to convert parts of the binary into 2 or 4 byte integers or into floats, print them and see if they make sence. Write some functions that will search for repeating or very similar parts in the data, this way you can easily spot headers.

Try to find as many strings as possible, try different encodings (c strings, pascal strings, utf8/16, etc.). There are some good tools for that (I think that Hex Workshop has such a tool). Strings can tell you a lot.

Good luck!

Answer 2

Tupni; to my knowledge not directly available out of Microsoft Research, but there is a paper about this tool which can be of interest to someone wanting to write a similar program (perhaps open source):

Tupni: Automatic Reverse Engineering of Input Formats (@ ACM digital library)

Abstract

Recent work has established the importance of automatic reverse engineering of protocol or file format specifications. However, the formats reverse engineered by previous tools have missed important information that is critical for security applications. In this paper, we present Tupni, a tool that can reverse engineer an input format with a rich set of information, including record sequences, record types, and input constraints. Tupni can generalize the format specification over multiple inputs. We have implemented a prototype of Tupni and evaluated it on 10 different formats: five file formats (WMF, BMP, JPG, PNG and TIF) and five network protocols (DNS, RPC, TFTP, HTTP and FTP). Tupni identified all record sequences in the test inputs. We also show that, by aggregating over multiple WMF files, Tupni can derive a more complete format specification for WMF. Furthermore, we demonstrate the utility of Tupni by using the rich information it provides for zeroday vulnerability signature generation, which was not possible with previous reverse engineering tools.

Answer 3

There is Hachoir which is a Python library for parsing any binary format into fields, and then browse the fields. It has lots of parsers for common formats, but you can also write own parsers for your files (eg. when working with code that reads or writes binary files, I usually write a Hachoir parser first to have a debugging aid). Looks like the project is pretty much inactive by now, though.

Answer 4

For Mac OS X, there's a new great tool that's even better than my iBored: Synaliyze It! (http://www.synalysis.net/)

Compared to iBored, it is better suited for non-blocked files, while also giving full control over structures, including scriptability (with Lua). And it visualizes structures better, too.

Answer 5

My project icebuddha.com supports this using python to describe the format in the browser.

Answer 6

A cut'n'paste of my answer to a similar question:

One tool is WinOLS, which is designed for interpreting and editing vehicle engine managment computer binary images (mostly the numeric data in their lookup tables). It has support for various endian formats (though not PDP, I think) and viewing data at various widths and offsets, defining array areas (maps) and visualising them in 2D or 3D with all kinds of scaling and offset options. It also has a heuristic/statistical automatic map finder, which might work for you.

It's a commercial tool, but the free demo will let you do everything but save changes to the binary and use engine management features you don't need.