The Content Scrambling System, or CSS, is a Digital Rights Management, or DRM, encryption system that encrypts data on commercially-available DVDs and prevents users from copying the disc’s data to a computer file or another disc. The Content Scrambling System is also used to require all media player manufacturers to produce devices that are compatible with the Content Scrambling System because the encrypted discs will not stream to a non-compatible device.
How A Content Scrambling System Works
The Content Scrambling System depends on three keys and a process known as “authentication”. The first key used by CSS is the “Title Key”, which is used to scramble or unscramble the contents of a movie or other copyrighted material. The next key is called the “Disc Key” and is used to decrypt the Title Key. The final key, which is known as the “Player Key”, is used to decrypt the Disc Key. Authentication describes how the CSS-protected disc and the disc reader work together to ensure that the content can be played.
When a CSS-protected disc is inserted in a compatible disc reader, the disc reader, or “player”, uses its allocated key to decrypt the disc key and have access to the contents of the disc. While the contents of the disc will still be encrypted by the Title key, the player will be able to locate the Disc Key and use it to unscramble the contents of the disc and allow the user to access the copyrighted material.
Applications
The Content Scrambling System is widely used for copyright protection schemes that prevent users from playing movies and other copyrighted materials on incompatible devices or copying the files to a different location. While the user may be able to copy the file itself, the data stream of the file will remain encrypted without the decryption keys that are hidden in a separate part of the disc. Although the Content Scrambling System is still used today, users have been using Brute-Force Attacks (a technique that tries every possible combination of characters to guess a password) to decrypt CSS-protected discs since 1999. Today, CSS has been widely replaced by other DRM techniques, such as CPRM (Content Protection for Recordable Media), AES (Advanced Encryption Standard), and AACS (Advanced Access Content System), which are used by HD DVDs and Blu-Ray Discs.
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