Content Scrambling System (CSS)

Content Scrambling System (CSS) is a data encryption and authentication method used to protect digital versatile disk (DVD) movies from being illegally copied, distributed, and viewed from other devices, such as computer hard drives.

Content Scrambling System (CSS) is a data encryption and authentication method used to protect digital versatile disk (DVD) movies from being illegally copied, distributed, and viewed from other devices, such as computer hard drives. CSS is one of several copy-protection methods currently used in today's DVDs.

The CSS method was developed by members of the DVD Copy Control Association (DVDCCA). This association includes companies in the U.S. motion picture industry (members of the MPAA) and the consumer electronics industry. The Matsushita and Toshiba companies are largely credited with the first main development efforts of the CSS method for encryption and decryption of DVD movies.

In general, the CSS method encrypts (scrambles) the video files on a DVD to prevent illegal viewing or copying. In order to view any video files found on the DVD, the user must use a hardware device that is CSS-licensed to decrypt, or decode, the data in the video file. One such hardware device is a DVD-ROM (DVD-read only memory) device that can be installed with a computer or a specially designed TV in order to view DVD movies. Another possible device could be the hard disk of a personal computer.

DVD disc manufacturers or DVD-ROM manufacturers must first be licensed to use CSS before they can produce discs or DVD-ROMs that will successfully encrypt or decrypt CSS-protected video files. Once a DVD-ROM manufacturer is licensed to use CSS, the manufacturer receives one of 400 keys which are stored in a locked section on every CSS-supported disc.

The DVD-ROM then uses this key information to decode the video file on the DVD and display the related movie. The actual operation of CSS involves the use of a decryption algorithm that mixes the key information exchanged between the disc and the hardware device in order to produce a unique key that will successfully decrypt the movie or video file for viewing.

As with many encryption methods of the past, CSS came under intense scrutiny in October 1999 when it was reported that a 16-year-old Norwegian programmer cracked the CSS code and posted the decryption method (quickly coined DeCSS) on the Internet. This action, and the subsequent postings of DeCSS code elsewhere on the Internet, heralded a series of lawsuits from the DVDCCA. In response, some pro-DeCSS organizations also sprouted up to protest what they perceived of as a lack of rights to freely distribute the reverse-engineered, CSS code for other programming uses.

Lawsuits over the future rights to access the CSS/deCSS code are still being waged today. The DVDCCA maintains that CSS can be licensed for free to any manufacturer who agrees to follow the terms of its CSS license.

This was first published in April 2005

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