Of the legal and ideological issues spawned by the Internet, the one that is raising a lot of dust is the de-scrambling of DVD (Digital Video Disk) content. This can be done with a utility called DeCSS (De Content Scrambling System), which allows DVDs that have support for Windows and Mac systems to be played on Linux systems. This utility breaks the encryption of DVDs, and allows you to store the unencrypted content on your hard disk. You can then do anything you want with it—play it, make copies and distribute them, etc.

This decryption of DVDs has resulted in the movie industry filing cases of copyright infringement and stealing of trade secrets in the courts of New York and California, even as DeCSS is available for download at various Internet sites. While the industry alleges that the utility would lead to large-scale piracy and claims theft of intellectual property, counter-allegations range from the fact that the industry is trying to control the Internet, to that they’re depriving consumers of their right to use products they have legitimately paid for. So, what does the utility do, and what’s the brouhaha about?

DVD is a medium of optical storage technology that can hold lots of data and give superior audio and video. It’s most popularly used for distributing movies for home viewing. Within three years of the introduction of this technology, DVDs have become a rage in many countries, though they’re still to find their feet in India. You can play DVDs using a DVD drive on your PC, a specialized DVD player, or software-based DVD playback utilities, like WinDVD, ATI DVD, and XingDVD.

Scramble with CSS…

A Content Protection System Architecture (CPSA) protects DVDs against content copying and piracy. The CPSA comprises six forms of content protection, one of which, called Content Scrambling System (CSS), is the eye of this storm. The CSS is a data encryption and authentication system that was intended to prevent the copying of files directly from the DVD. It’s a licensed system, and those who want to develop DVD players or DVD-ROM drives have to apply for CSS licenses to the DVD Copy Control Association (DVD CCA), the licensing authority.

The data on the DVD is encrypted and the decryption keys are stored on the disk in an ‘obfuscated’ form, that is, they’re hidden in locations that can’t be directly read by an ordinary DVD drive. To play back a DVD, the CSS decryption algorithm exchanges keys with the drive unit. This generates an encryption key that is used to obfuscate the next exchange of keys—called disk keys and title keys. These are used to actually decrypt and play back the contents of the DVD.

The DVD’s contents are decrypted using the title key, which is encrypted with a disk key. The disk key in turn is encrypted with around 400 player keys. All these encrypted disk keys are stored on the DVD itself, in obfuscated form. At the same time, each CSS licensee is also given one of these player keys. So, each player uses its key to decrypt and play back the DVD’s contents. The advantage of using so many player keys is that if any licensee’s license is revoked, or one of the keys is discovered by an unauthorized person, the particular key can be removed from future disks.