Content Scramble System
Content Scramble System (CSS) is an encryption system used on some DVDs. It uses a weak, proprietary 40-bit encryption stream cipher algorithm. The system was introduced circa 1996. This has no relation to cascading style sheets.
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 three people, Jon Lech Johansen and two 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.
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.
See also
- DVD Copy Control Association
- Advanced Access Content System
- DeCSS, DVD Decrypter and libdvdcss
- Content Protection for Prerecorded Media (CPPM)