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The Advanced Access Content System ('''AACS''') is a Standard for Content Distribution and Digital Rights Management , intended to restrict access to and Copying of the next Generation of optical discs and DVD s. The specification was publicly released in April 2005 and the standard has been adopted as the access restriction scheme for HD DVD and Blu-ray Disc (BD). It is developed by '''AACS Licensing Administrator, LLC''' ('''AACS LA'''), a Consortium that includes Disney , Intel , Microsoft , Matsushita (Panasonic), Warner Brothers , IBM , Toshiba and Sony . Since appearing in devices in 2006, several AACS decryption keys have been extracted from weakly protected software players and published on the Internet. SYSTEM OVERVIEW Encryption AACS uses Cryptography to control the use of digital media. It encrypts content under one or more ''title keys'' using the Advanced Encryption Standard (AES). Title keys are derived from a combination of a ''media key'' and several elements, including the ''volume ID'' of the media (e.g., a physical serial number embedded on a DVD), and a Cryptographic Hash of the title's ''usage rules''. The principal difference between AACS and CSS , the DRM system used on DVD s, lies in how the device decryption keys are organized. Under CSS , all players of a given model are provisioned with the same, shared decryption key. Content is encrypted under the title-specific key, which is itself encrypted under each model's key. Thus each disc contains a collection of several hundred encrypted keys, one for each licensed player model. In principle, this approach allows licensors to "revoke" a given player model (prevent it from playing back future content) by omitting to encrypt future title keys with the player model's key. In practice, however, revoking all players of a particular model is costly, as it causes many users to lose playback capability. Furthermore, the inclusion of a shared key across many players makes key compromise significantly more likely, as was demonstrated by a number of compromises in the mid-1990s. The approach of AACS provisions each individual player with a unique set of decryption keys which are used in a Broadcast Encryption scheme. This approach allows licensors to "revoke" individual players, or more specifically, the decryption keys associated with the player. Thus, if a given player's keys are compromised and published, the AACS licensing authority can simply revoke those keys in future content, making the keys/player useless for decrypting new titles. |
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