Content-scrambling system
From Wikipedia, the free encyclopedia.
Content-Scrambling System (CSS) is an encryption system used on some DVDs. It uses weak 40-bit proprietary encryption algorithm. Technical terms are explained in the specification section.
The system was introduced circa 1996. In October 1999, the algorithm was reverse engineered and DeCSS source code was released. It was soon revealed to be susceptible to a brute force attack. The weakness of the protection is due to US government crypto-export regulations.
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.
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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 manufactuer is allocated one of approximately 400 player keys to incorportate in its players.
Due to inherent weaknesses in the system, many modern Open Source decryption components bypass the above procedure and determine title keys by examining the encrypted titles on the disc, without the need for access to disc or player keys.
Reference
- IEEE - Copy Protection for DVD Video
- Cryptanalysis of Contents Scrambling System by Frank A. Stevenson
Work note
The part about the specification is based on CSS PROCEDURAL SPECIFICATIONS 1.1, which is supposed to disclose only to CSS Licensees, most of which are DVD drive manufactures, DVD player manufactures and the productions of DVD disc products.