AACS stands for Advanced Access Content System. AACS is a form of Digital Rights Management (DRM) used currently to protect content on both HD DVD and Blu-ray Disc titles using cryptography. It has two main focuses; to effectively control access to the contents on a protected disc and to prevent unauthorized copying of the contents. The system was developed by Intel, Microsoft, Matsushita, Warner Brothers, Sony, IBM, Toshiba and The Walt Disney Company.
Each HD DVD and Blu-ray Disc player has a unique set of decryption keys, used in a broadcast encryption scheme. This makes it possible for the companies behind AACS to revoke a players' decryption keys if it is found to have been compromised. This means that future content cannot be decrypted by that player. Of course, to revoke the keys, the AACS LA (licensing authority) has to actually know what to revoke, which mostly depends on the compromised player's keys being published publicly.
Hacking / Cracking / Work-Around
Like all copy protection schemes, AACS is far from secure, but not because of any weakness in the AES encryption scheme, but more so software that is capable of decoding and playing AACS discs being insecure and potentially exposing sensitive data. The first claimed breach of AACS came with the release of BackupHDDVD and a video posted on YouTube that showed it in progress. A hacker, "muslix64" claimed the tool will strip AACS and rip content from HD DVD discs to a HDD if an appropriate Title key is used. Title keys are stored encrypted on protected discs (technically derived from a media key combined with other elements), but obviously need to be decrypted for the content to be accessed. Muslix64 claims he found such keys in system memory.
He did not lie. A newer version of the software also allowed the decryption of HD DVD titles using an acquired Volume Key. While many speculated whether or not muslix64 was telling the truth, the first key was posted onto the Internet by some anonymous source, proving that the keys could be gotten. Soon after, many more appeared and eventually the first HD DVD-rips were available via P2P, BitTorrent, Usenet etc.
muslix64 went another step further and released a tool BackupBluray that could decrypt Blu-ray titles. However, Blu-ray titles can use the extra BD+ layer of protection, which has not yet been compromised in any way.
AACS utilizes the Advanced Encryption Standard (AES). While a player's keys can be revoked, a hacker could use his compromised equipment to get the Title or Media keys of many different movies and distribute those. As long as his player's keys aren't distributed, he doesn't have to worry about revocation.
More recently, the software developer Slysoft has updated its popular AnyDVD HD program to natively rip any AACS protection. Beginning with v220.127.116.11 AnyDVD HD offers a support for upcoming high-definition discs and thus removes the need to update the playback software and/or hardware.
"This again is a great feature for our customers. Only a few days before the official release of new titles we already can say, you can continue to watch your favorite movies on your favorite equipment. Not only the equipment the industry forces you to use," added Fernando Cabezas from SlySoft with the update.
- HD DVD copy protection circumvented? (28 December 2006)
- Media companies probing AACS hack (1 January 2007)
- Cyberlink denies PowerDVD problem created BackupHDDVD (2 January 2007)
- Company uses BackupHDDVD to emphasize Blu-ray security (6 January 2007)
- Blu-ray Disc titles cracked (24 January 2007)