Thanks to everybody else who got in touch to help me with this situation. I 
will explain in detail the DRM at the end of the post, so people living in 
restricted countries can tune out and avoid the thought police, but you all 
played your part in helping me understand how it worked.

My brother got his account back. For whatever reason, his pleading with Amazon 
got his account reopened. Maybe it was that he mentioned that he was blind. The 
memo went all the way up to the CEO of Amazon in the UK, which might have meant 
that the RNIB got involved after all. Whatever the reason, he can now log in to 
his account, make and return purchases and access his Audible content on any 
device once again. Cheers all round. Well, except for the disappointment that 
is DRM, of course. I'll never be grateful for that. We've all learned an 
important lesson. As soon as my brother gets the gumption together, and now 
that he has the time, I'm going to help him download all his books and strip 
out the DRM. That way this can't happen to him again.

For myself, I have already completely stripped the DRM from my Audible books 
collection, with no loss of quality whatsoever, and maintaining the original 
format and encoding. I was too late to return my Audible credits, but I would 
have, if I could have; Amazon didn't notify me, in December, when the renewal 
happened, and you only get 14 days to cancel your membership. Dirty trick, 
that. Still, with these credits on hand, I might as well stock up on books that 
I've already paid for. The removal of the DRM means, quite simply, that Audible 
has a great deal more value to me than it otherwise would have. I can buy 
timeless books I will actually value for eternity because they don't have DRM 
to make them rot, I can get access to Audible exclusives, and I can use my USB 
MP3 player to play the books in the other room, which ironically probably means 
I'll have more time for listening. Naturally, though, I don't reward bad 
behaviour when I can possibly help it, so I'm going to try and avoid them for 
new purchases, just as I promised to. These bastards can only hurt people 
because we let them, so I'm going to try the various alternatives that have 
been suggested, particularly Downpour. Oh, and no, piracy isn't an option I'm 
happy with, no matter the provocation; at best it's something to be resorted to 
if there are no other options for obtaining the content and there is a 
specific, compelling reason to have it.

Now, what follows is a discussion of the DRM itself. If you're living in an 
uncivilised nation where corporations write the rules (i.e. the US), then you 
can stop reading now and avoid a visit from the thought police.

The tool of choice is called Inaudible. It is somewhat hard to find, but 
happily, the news is spreading, if you know where to look, and as always, 
especially among Open Sourcerers who don't mind getting their hands dirty. It 
can perform lossless decryption of Audible book files. The latest format, 
Audible Enhanced (file extension .aax) is an MPEG4 container with chapter 
markings in the metadata atoms, encrypted with a per-subscriber key. On 
Windows, Inaudible is pretty much a point-and-click affair, and can be 
automated entirely. On OS X, Inaudible includes the tools required, but not the 
shell scripting knowledge to do bulk conversions, and its UI seems to be 
limited specifically to converting one book at a time, although it is still 
useful for discovering keys and testing the tools.

The basic idea of breaking the DRM is first to find your four-byte "Activation 
secret" and then to convert the audible file into a regular MPEG4 container 
using that secret. The secret is the golden key with which your files are 
encrypted for all of a subscriber's files. There are three ways to find it: 
from your existing player, from Audible's own activation server, and by 
brute-force. Inaudible seems to be using the third method, and has rainbow 
tables with precomputed keys and a custom implementation for the Audible 
algorithm for the open-source rcrack tool. It seems to work well, even without 
access to iTunes or Audible Manager, as was apparently required in the past. I 
suppose we should be glad that DRM purveyors are stupid as well as malicious; 
the key is 64 bits and is usually found in seconds. However, for a fully 
networked solution, there is the "Audible activator" from the same open-source 
inaudible-ng project--basically a tool for sending the username and password 
query to Audible's server for activation, just as your client would.

Now you have your secret, store it away in a safe place. This is your ultimate 
weapon, together with your Audible files, if you should get disconnected from 
Audible. Next comes the actual decryption process. This part I learned from the 
Mac Inaudible tool: ffmpeg is, as it is so often, your friend. Ffmpeg is a 
well-known general-purpose audio/video manipulation tool. The Audible format is 
essentially encrypted MPEG4 with AAC data and metadata atoms, and ffmpeg has 
support for it, specifically. Using a command like
ffmpeg -activation_bytes 00112233 -i input.aax -codec:a copy -sn -vn output.m4a
will get you a decrypted Audible file, with the original AAC audio data 
untouched and all metadata, including chapter markings, ported across to the 
new, unencrypted container. There is no transcoding of any sort involved, so 
the process is very quick, even for 32 GB of files, as was my case. If you were 
to rename a decrypted file to have a .m4b extension, you would find that, 
imported into iTunes, it would work exactly like the real deal--it simply won't 
have the DRM anymore. The -vn and -sn switches drop video and subtitles, 
respectively; this includes cover art. Now you just have to figure out how to 
do this for multiple files, including those with spaces and other shell 
characters in their filenames, and you can process your entire collection. This 
is left as an exercise for the reader, but I used the find command to great 
effect here.

I hope this helps the poor souls out there with Audible content they wish to 
liberate. I can tell you now that it's made me very happy, because it is so 
perfect and flawless, and produces files that are actually indistinguishable 
from the originals. I'm very grateful to the awesome people who 
reverse-engineered the format and turned what has long been a pillar of despair 
involving crusty old versions of Windows software producing huge files that are 
poorly re-encoded, into a simple, one-step process for producing files as they 
were meant to be, without loss of quality, with chapter markings, that can be 
converted however I wish if need be. It really is awesome to experience Audible 
without the DRM; it's just Audible, only better.

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