Self-Protecting Digital Content

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Self Protecting Digital Content(SPDC), is a copy protection (DRM) architecture used by the Advanced Access Content System (AACS).

[edit] Overview

SPDC executes code from the protected content on the DVD player, enabling the content providers to change protection systems in case an existing protection system is compromised and adds functionality to make the system "dynamic", as opposed to "static" systems in which the system and keys for encryption and decryption do not change, thus enabling one compromised key to decode all content released using that encryption system. "Dynamic" protection systems attempt to make future content released immune to attack using an existing method of circumvention.

Playback Method

If a method of playback used in previously released content is revealed to have a weakness, either by review or because it has already been exploited, code embedded into content released in the future will change the method, and any attackers will have to start over and attack it again.

Targeting Compromised Players

If a certain model of players are compromised, code specific to the model can be activated to verify that the particular player has not been compromised. The player can be "fingerprinted" if found to be compromised and the information can be used later.

Forensic Marking

Code inserted into content can add information to the output that specifically identifies the player, and in a large-scale distribution of the content, can be used to trace the player. This may include the fingerprint of a specific player.

[edit] Weaknesses

If an entire class of players is compromised, it is infeasible to revoke the ability to use the content on the entire class because of legitimate users that may have purchased the player. A fingerprint may be used to try to work around this limitation, but an attacker with access to multiple sources of video may "scrub" the fingerprint, removing the fingerprint entirely or rendering it useless at the very least.