Latest AACS crack 'beyond revocation'

Hackers have found a way of circumventing the AACS copy prevention technology used by next-generation DVD disks. Unlike earlier breaks, the latest crack can't be papered over simply by pushing key revocation updates.

Advanced Access Content System (AACS) encryption forms the cornerstone of the content protection technology on high-definition DVD formats such as Blu-Ray and HD-DVD. The technology includes a system for revoking keys, making it impossible to play newly released high-definition movies via versions of playback software known to be weak or flawed.

For example, last month WinDVD 8 users need to update their software, after crackers worked out a way to grab content protection keys. Hackers sniffed out the keys using an approach based on figuring out memory changes made after playing high-def discs on their PCs.

The latest crack, once again formulated by the denizens of the Doom9 forums, is said to be immune to key revocation. The hardware hack involves tampering with the HD DVD add-on drive of an Xbox 360 to capture the "Volume Unique Keys", Ars Technica reports.

The key can be extracted after de-soldering the HD DVD drive's firmware chip, reading its contents, and then reconnecting it. The approach bypasses the encryption performed by the Device Keys, so revoking these keys as applied by the WinDVD update. Although the latest approach involves voided warranties and potential solder burns, Ars Technica adds that the ruse takes hackers one step closer to using software to achieve the same ends.

The attack caps a miserable week for the Advanced Access Content System Licensing Administrator (AACS LA), the custodian of the AACS encryption. The organisation has been busy sending out legal nastygrams to websites that published a 32-digit hexadecimal number that represented one of the keys for cracking AACS involved in last month's attack. Predictably the move chiefly served to publicise the infamous number.

Now AACS LA has got an even more serious chink in the armour of AACS to contend with. ®