Has there been any serious effort made to reverse engineer the Amazon MP3 store azn file format?

Question

Since the Amazon MP3 store launched in the UK, I really want to write a downloader application for my phone so I can buy mp3s wherever I am and listen to them without hassle. However, first I need to reverse engineer the amazon .azn file format it supplies to the downloader app. The outer layer is obvious, it is simply base 64 encoded. However, the next layer in is a little more mysterious. It isn't deflated as far as I can tell, nor any other obvious compression algorithm.

I'm going to try a few tricks to see if I can use the downloader app itself to help me figure it out, but I wonder if I'm reproducing work someone else has done out there in an obscure corner of the internet? Anyone know of any work that has previously gone in to this?

Answer 1

Be careful here - I'm not sure what kind of laws are enforced in the UK, but in the US an attempt to circumvent copyright protection schemes (in this instance Digital Rights Management) is a violation of the DCMA.

That being said, if you are doing this solely for personal/academic use I doubt anyone would mind. Still, none of this should be construed as legal advice.

Answer 2

I may well have answered my own question anyway. The software uses OpenSSL for various things, including BIO base 64 decode. I believe the inner layer is actually encrypted (wtf?) However, while the windows version of the downloader statically links to OpenSSL, the Linux version dynamically links to it. This should mean not only do I know which functions the binary imports from the import table, I should simply be able to throw an instrumented version of OpenSSL at it and have it print out all the parameters I need. MWAHAHAHA. Sorry, evil genius moment.

Answer 3

it's not hard

base-64 encoded single-DES CBC

constant key 29ab9d18b2449e315e72

fixed IV 5e72d79a11b34fee

merry xmas

Answer 4

There is an free software project to download mp3 albums from amazon. In playlist.c they decrypt the amz file: http://code.google.com/p/clamz/