What is CSS? ( Content Scrambling System for DVD Video )

From Wikipedia

Content-Scrambling System (CSS) is an encryption system used on some DVDs. It uses a weak, proprietary 40-bit encryption algorithm. The system was introduced circa 1996.

The CSS key sets are licensed to manufactors 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, the algorithm was reverse engineered by Jon Johansen 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 of CSS
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.