A method to fully crack the Advanced Access Content System (AACS) has been found, according to some media reports and forum posts, which means that it is now possible to extract copy-protected content from Blu-ray discs (BDs) and HD DVDs and copy it without compromising quality. Earlier it was possible to copy only limited amount of movies, which AACS keys had been leaked.
While it is still not completely clear how AACS works, certain documents that are publicly available, such as “Introduction and Common Cryptographic Elements” gives some ideas that Doom9 forum member, who identifies himself as Arnezami, used to create a method for decrypting both Blu-ray and HD DVD movies.
The AACS copy protection system implemented into current BDs and HD DVDs includes Device Keys, Media Key Block (MKB), Media Key, Processing Keys, Volume IDs and Volume Unique Keys (VUKs) among others. Previously the "crack" of the high definition video discs’ AACS was based on knowledge of the VUKs, which are needed to access the content, however, right now a way to calculate the VUK for every single disc has been found.
Arnezami has found a Processing Key, which should work on any BD or HD DVD, whereas Volume ID key appeared to be date and time of the disc production (e.g. Volume ID for King Kong movie is 09 18 20 06 08 41, which means that the date and time of its production is 09/18/2006, 08:41). Using the Processing Key and some other data, the BD or HD DVD device calculates the Media Key, which, when combined with the Volume ID, gives the Volume Unique Key (which are also referred to as "Title Keys") needed for decryption of the protected content.
Potentially, Arnezami’s discovery means that it is now possible to create a software that would calculate all the keys using publicly available algorithms, which means that, if AACS licensing agent (AACS LA) and content producers do not change the processing key and the Volume ID keys, all the future BD and HD DVD releases face possibility of replication using already available burners, sharing or even pirating.
“Most of the time I spend studying the AACS papers. A good understanding of how the things worked has helped me greatly in knowing what to find in the first place (and how to recognize something),” Arnezami wrote in a forum post, explaining how he managed to unlock AACS.