The Advanced Access Content System (AACS) is a standard for content distribution and digital rights management (DRM). Developed by AACS Licensing Administrator, LLC (AACS LA), a consortium including Disney, Intel, Microsoft, Panasonic, Warner Bros., IBM, Toshiba and Sony, and publicly released in April 2005, the standard has been employed in HD DVD and Blu-ray Disc as the access restriction scheme.

AACS Encryption
AACS encrypts content under one or more title keys which are decrypted using a combination of a Media Key and the Volume ID of the media. The Media Key is encoded in a Media Key Block (MKB); and the Volume ID is a serial number stored on a pre-recorded disc with special hardware and cannot be duplicated on consumers' recordable media.

AACS Decryption
If you want to watch an AACS encrypted disc, the player must first decrypt it. The disc contains 4 items -- the Media Key Block (MKB), the Volume ID, the Encrypted Title Keys, and the Encrypted Content. Once the MKB is decrypted, it provides the Media Key. The Media Key is combined with the Volume ID to produce the Volume Unique Key. The Volume Unique Key is used to decrypt the encrypted Title Keys, and the Title Key is used to decrypt the encrypted content.

Passkey Solution
Passkey has the capability to manage MKB up to the newest MKB v25, and is powerful to remove all known AACS protections for Blu-ray and HD DVD. So anyone can go ahead to copy/clone/convert/rip AACS protected Blu-rays using other software after the decryption work of Passkey.