Advanced Access Content System

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 post-DVD generation of optical discs. 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, Panasonic, Warner Bros., IBM, Toshiba and Sony. AACS has been operating under an "interim agreement" since the final specification (including provisions for Managed Copy) has not yet been finalized.

Since appearing in devices in 2006, several AACS decryption keys have been extracted from software players and published on the Internet, allowing decryption by unlicensed software.

AACS uses cryptography to control and restrict the use of digital media. It encrypts content under one or more title keys using the Advanced Encryption Standard (AES). Title keys are decrypted using a combination of a media key (encoded in a Media Key Block) and the Volume ID of the media (e.g., a physical serial number embedded on a pre-recorded disc).

The principal difference between AACS and CSS, the DRM system used on DVDs and CDs, lies in how the device decryption keys and codes are organized.

Under CSS, all players of a given model group are provisioned with the same shared activated 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.

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