Content Scramble System

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This article is about Content Scramble System (CSS). For Cascading Style Sheets (CSS), see Cascading Style Sheets.

Content Scramble System (CSS) is a Digital Rights Management (DRM) scheme used on almost all DVDs. It utilizes a weak, proprietary 40-bit stream cipher algorithm that has subsequently been compromised. The system was introduced around 1996.

The CSS key sets are licensed to manufacturers who incorporate them into products such as DVD drives, DVD players and DVD movie releases. Most DVD players are equipped with a CSS Decryption module. CSS key is a collective term for authentication key, disc key, player key, title key, second disk key set, and/or encrypted key.

In October 1999, Jon Lech Johansen and two people who remained anonymous reverse engineered the algorithm and DeCSS was released. The CSS algorithm was soon revealed to be easily susceptible to a brute force attack. The weakness of the protection is due to US government crypto-export regulations, apart from being an example of the trusted client problem. The CSS algorithm has been superseded by the Cryptomeria cipher in newer DRM schemes such as CPRM/CPPM.

[edit] Specification

Authentication is a process for a DVD drive and CSS Decryption module to recognize (or authenticate) each other. It is necessary before reading data from DVD discs. Authentication keys are used for this process.

Title keys are used for scrambling and descrambling actual data on DVD discs called titles. A title could be a complete motion picture, a trailer or similar self-contained unit.

Disc keys are used for decrypting title keys on DVD discs.

Player keys are used for decrypting disc keys on DVD discs. Each DVD player manufacturer is allocated one of approximately 400 player keys to incorporate in its players.

CSS decrypting software (such as DVD Decrypter, AnyDVD, DVD43, Smartripper and DVD Shrink) allows a region-specific DVD to be copied as an all-region DVD. It also removes Macrovision, Content Scrambling System (CSS), region codes, and disabled user operations (UOPs).