How does Audible.com DRM work with iTunes?

Factual Questions
1

To be clear, I’m not interested in how to circumvent any such DRM, just curious about the mechanics and the business.

Here’s what I know, or think I know: With my audible.com membership, I can download audiobooks, which come in a .aa file, and have some kind of DRM on them. If I open them in iTunes, iTunes asks me for my audible account info, and once I’ve input it, it will play the files. As far as I know, Apple has never licensed its iTunes DRM to any other company, and Audible is owned by Amazon. Are there hooks in iTunes to require authentication to decrypt files? Can anyone use them, or is Audible special? How does the DRM work with iPods? Or are the files just copied in the clear?

The reason I’m confused is that a while ago, Real tried to get its DRMed files to play in iTunes by emulating the iTunes DRM, and Apple just kept changing things and pushing updates regularly until Real’s solution wouldn’t work. They wouldn’t have had to do that if iTunes had authentication hooks, so Audible must be special in some way. But I can figure out why Apple would go to extra lengths to help Amazon, a major competitor in the downloaded content business.

2

The audio books sold by the iTunes store are actually provided by audible.com, so I presume they’ve worked out a deal.

3

I’ve had an Audible account for some time, and from what I can understand:

It’s a specially worked-out section built into (or maybe a plug-in) iTunes. I’m not sure if it uses Fairplay (Apple’s DRM); possibly it’s different if you buy it via the iTMS or through Audible.com directly. On Windows, there is (or was, been a while since I’ve used it on Windows) a separate program that authorizes the books.

As for iPods - the files themselves are transferred and playable on an iPod (not sure how, but it works with any iPod). The DRM is not exactly stripped, though. I found this out when I moved files from an old iPod to a new computer. The salvaged Audible files showed up as “not authorized to play on this computer”.

4

I’ve been an Audible member for years now, I believe that they have a proprietary format with DRM that they’ve managed to include in iTunes, on ipods, and on many other MP3 players from different vendors.

When you transfer the audible file from itunes on your desktop to the ipod, it also copies over a version of the DRM authentication codes I believe.

5

Ah, thank you. That does explain it, if Audible and Apple have a deal going, there.