Several people have pointed me to the news that claims of cracking AACS (the content protection system protecting both Blu-Ray and HD-DVD discs) have been leveled. Here is a doom9 thread on the matter. My first reaction was, “What took so long?” Conceptually, it should have been pretty straightforward to understand the entire system and recover secret keys since technical documents on the matter are quite openly available. I always considered that rather odd since a large part of DRM’s efficacy hinges on obscurity.
Good news, nonetheless, if it’s accurate.
My understanding is that this AACS decrypter isn’t any real breakthrough. It simply uses the published specs to decrypt it the same way an HD-DVD player would. You still have to provide it with the disk’s title key yourself.
The “new” part is how he got the title keys from the disks. My understanding is that the title key is encrypted on the disk, and each player has its own key which can be used to decrypt the title key (or *a* title key which can decrypt the stream – maybe there are multiple ones? I don’t know), but part of the agreement to get such a key is that you keep it hard to get at.
So probably he used a software player, and rather than grabbing the player key which was well protected, found the title key left in memory after it was decrypted off the disk.
Everybody so far seems to be hailing this as a way around the key revocation scheme, but I’m not sure if it is. It’s probably only one software player that’s been used so far to grab the title keys – if they can figure out which player (possibly by looking at the title key it managed to get, assuming I’m right that there are multiple valid title keys), then they can still revoke that player’s key for future disks. In which case, this is still non-news.