With the Content ScramblingSystem (CSS), copy protection is achieved using a scrambling technique in which the data is encoded. The decoding of the scrambled signals is done by the DVD video player or a decoder card. The CSS process prevents the copying of video and audio data from a DVD, as well as the storage of this data on hard disk.
The CSS system uses a proprietary encryption method with a 40-bit key; it can be used license-free and is used in all DVDs. Playback of encrypted video sequences is possible only in conjunction with CSS decoding.
Content Scrambling System was developed by the Content Protection Technical Working Group( CPTWG). Since the procedure contains some weak points and can be cracked with brute force attacks, an improved copy protection for digital rights management was developed with Advanced Access Content System( AACS) which works with the Advanced Encryption Standard( AES).