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Article Abstract In this article I will cover the basics of reverse-engineering binary file formats, starting with the simple archive format used in the popular game EverQuest II known as VPK. This is the first of many articles I'll be writing on the subject as time goes on. You can find VPK files in any EverQuest II installation, and any will do for the purposes of this article. For the purposes of this article, I will assume the reader has knowledge of programming in C. The architecture being used is x86, and thus, everything is unsigned and little-endian. The tools you will need to follow along with this article are a decent hex editor (I recommend "HexEditor" for Mac OS X) and a copy of Python.

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Article Comments
drew Posted: Tuesday, September 6 2005 18:45.26 CDT
For file format RE, my favorite hex editor is Hex Workshop:
http://www.hexworkshop.com/

It has tons of features for REing file formats.  Simply highlight some bytes and it will instantly tell you info about the bytes.  It lets you easily calculate checksums of all sorts, int/uint values, digests, byte lengths, etc.

However Hex Workshop won't let the user comment locations of the file, nor does it have any features to deal directly with compressed data.

0xebfe Posted: Tuesday, September 6 2005 19:57.01 CDT
So basically, generically speaking, you looked for zlib blocks, and length:data like structures. Cool.. do post any attempts at structured network protocol reversing..

hoglund Posted: Monday, October 10 2005 01:12.42 CDT
What is your favorite feature of HexWorkshop?

luis Posted: Monday, October 10 2005 22:51.38 CDT
Hi hoglund. Personally my favorite feature of HexWorkshop is the structure editor. It is very useful in reversing file format, as it also serves as your notes. HexWorshop includes some samples like pkzip and others.

I do wish it had some kind of api or scripting mechanism such as IDA.

rfreeman Posted: Wednesday, October 12 2005 17:42.19 CDT
Two I have used extensively:

1) The CopyAs function. Output options include C array.
2) Resyncronizing compare.

drew Posted: Thursday, October 13 2005 03:47.55 CDT
The ability to highlight a chunk of bytes and quickly get info on them is simple but wonderful.  Being able to quickly see the length, casted values, CRC, MD5, etc of a chunk of bytes definitely speeds up my file format reversing.

drew Posted: Friday, January 20 2006 08:54.49 CST
Someone mentioned to me that the 010 editor was also good for file format RE:
http://www.sweetscape.com/010editor/

klondikemarlen Posted: Thursday, September 30 2010 20:12.57 CDT
Would the following code do the same thing with bzip2 as your code did with zlib?

import bz2, sys

def main(args):
    f = file(args[0], 'rb').read()
    size = len(f)

    i = 0
    while i < size:
        try:
            de = bz2.decompress(f[i:])
        except IOError:
            i += 1
            continue

        print 'Found a compressed block starting at', i

        i += 1

if __name__=='__main__':
    sys.exit(main(sys.argv[1:]))



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wedikes Posted: Thursday, November 7 2013 02:46.26 CST
It is interesting article and what about RE any binary file? That is, given a binary file which we do not have any clue using what tool it has been created, how we could reverse engineer it?


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