Tools to help reverse engineer binary file formats

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!

My own tool "iBored", which I released just recently, can do parts of this. I wrote the tool to visualize and debug file system formats (UDF, HFS, ISO9660, FAT etc.), and implemented search, copy and later even structure and templates support. The structure support is pretty straight-forward, and the templates are a way to identify structures dynamically.

The entire thing is programmable in a Visual BASIC dialect, allowing you to test values, read specific blocks, and all.

The tool is free, works on all platforms (Win, Mac, Linux), but as it's personal tool which I just released to the public to share it, it's not much documented.

However, if you want to give it a try, and like to give feedback, I might add more useful features.

I'd even open source it, but as it's written in REALbasic, I doubt many people will join such a project.

Link: iBored home page

I still occasionally use an old hex editor called A.X.E., Advanced Hex Editor. It seems to have largely disappeared from the Internet now, though Google should still be able to find it for you. The last version I know of was version 3.4, but I've really only used the free-for-personal-use version 2.1.

Its most interesting feature, and the one I've had the most use for deciphering various game and graphics formats, is its graphical view mode. That basically just shows you the file with each byte turned into a color-coded pixel. And as simple as that sounds, it has made my reverse-engineering attempts a lot easier at times.

I suppose doing it by eye is quite the opposite of doing automatic analysis, though, and the graphical mode won't be much use for finding and following offsets...

The later version has some features that sound like they could fit your needs (scripts, regularity finder, grammar generator), but I have no idea how good they are.

Kaitai is an open-source language for describing binary structures in data streams. It comes with a translator that can output parsing code for many programming languages, for inclusion in your own program code.