3) Content Scramble System (CSS)Because of the potential for perfect digital copies, paranoid movie studios forced a deeper copy protection requirement into the DVD standard. Content Scramble System (CSS) is a data encryption and authentication scheme intended to prevent copying video files directly from DVD-Video discs. CSS was developed primarily by Matsushita and Toshiba. Each CSS player licensee is given a key from a master set of 409 keys stored on every CSS-encrypted disc. The theory was to allow a license to be revoked by removing its key from future discs. The CSS decryption algorithm exchanges keys with the drive unit to generate an encryption key that is then used to obfuscate the exchange of disc keys and title keys that are needed to decrypt data from the disc. DVD players have CSS circuitry that decrypts the data before it's decoded and displayed, and computer DVD decoder hardware and software must include a CSS decryption module. All DVD-ROM drives have extra firmware to exchange authentication and decryption keys with the CSS module in the computer. As of 2000 DVD-ROM drives are required to support regional management in conjunction with CSS (see 1.10 and 4.1). Makers of equipment used to display DVD-Video (drives, decoder chips, decoder software, display adapters, etc.) must license CSS. There is an annual $15,000 fee for the CSS license, and qualification is a lengthy process, so it's recommended that interested parties apply early. CSS is administered by the DVD Copy Control Association (DVD CCA). Near the end of May 1997, CSS licenses were finally granted for software decoding. The license is extremely restrictive in an attempt to keep the CSS algorithm and keys secret. Of course, nothing that's used on millions of players and drives worldwide could be kept secret for long. In October 1999, the CSS algorithm was cracked and posted on the Internet, triggering endless controversies and legal battles (see 4.8).
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