In AACS, each player device is assigned a DeviceID (which might not be unique to that device), and is given decryption keys that correspond to its DeviceID. When a disc is made, a random ‘title key’ is generated and the video content on the disc is encrypted under the title key. The title key is encrypted in a special way that specifies exactly which devices’ decryption keys are able to extract the title key, and the result is then written into a header field on the disc.
When a player device wants to read a disc, the player first uses its own decryption keys (which are specific to the player’s DeviceID) to extract the title key from the disc’s header; then it uses the title key to unlock the content.
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