AACS

AACS, short for Advanced Access Content System, is a digital rights management (DRM) standard designed to protect high-definition video content on optical discs and related formats. It is primarily associated with Blu-ray Discs and was also used in the HD DVD format. The system aims to restrict unauthorized copying, distribution, and playback of protected content by controlling access to the decryption keys required to view the disc’s content.

The technology is governed by the Advanced Access Content System Licensing Authority (AACS LA), a consortium of studios and electronics companies that licenses the use of the system to manufacturers of players, software, and disc production tools. AACS defines a hierarchy of cryptographic keys and certificates, including device-specific keys and content-related keys, to regulate which devices can decrypt a given disc. Each disc contains encrypted content and key information, and licensed devices must present valid credentials to unlock the content. The framework also includes a mechanism to revoke compromised devices by distributing updated revocation lists, which are checked by players before decryption.

In practice, AACS provides the baseline DRM for Blu-ray Discs, complemented by additional protections such as BD+ in some discs. HD DVD employed a similar approach. Over time, the system has faced circumvention attempts, prompting updates to the revocation infrastructure and security requirements. Support for AACS continues to be maintained through licensing updates and compatibility efforts, involving hardware players, software players, and publishers that produce AACS-protected content.