The Blank DVD-R was one of the first recordable DVD formats to debut, arriving to an enthusiastic reception by a public eager for a chance to create its own high-definition video. While family vacations and birthday parties remain the top subjects of many home-made discs, one of the most popular uses of blank DVD-R media was to back up commercial content to which the rights were owned.
When talking about DVDs, one eventually comes to discussing the various anti-copying mechanisms which have been used. Blank DVD-R media was in such high demand because suddenly such content could be copied. Article Twenty in this series will take a quick look back at one of the very first that was employed – and compromised.
The Content Scramble System, or CSS, was a 40-bit stream encryption algorithm used on practically all commercially produced DVDs for sale since the mid-’90s, when DVDs first entered the marketplace. CSS keys were licensed in sets by the DVD Copy Control Association to manufacturers who incorporated the software onto the discs and into the players. These keys can be stored anywhere on a disc, though often wind up on the lead-in section that is only read by compliant players. Most DVD players are equipped with a decryption module. A CSS key set could include an authentication key, a disc key, player keys, title keys, and others.
Authentication is a process where a DVD drive and its CSS Decryption Module recognizes, or authenticates, one another. This necessary step takes place before any reading of data from a DVD even occurs. As might be expected, an authentication key is used for this process. Player keys decrypt the disc keys; each DVD player manufacturer is allocated one of approximately four hundred player keys for use inside its players. Disc keys are used to decrypt title keys. Title keys scramble and descramble data on DVDs called titles, which could be anything from the whole motion picture itself to just its trailer (titles are generally self-contained units).
CSS worked because unauthorized copies did not include such keys. However, only three years after its debut, CSS was cracked by Jon Lech Johansen and two anonymous helpers who reverse-engineered the algorithm with their DeCSS program. 40-bit algorithms had by then become relatively weak in the face of the much increased processing power available to personal computers, and CSS was found to be wide open to a simple “brute force” attack whereby various combinations were thrown at it. Indeed, any computer that could play a DVD could also crack one. Many other CSS decrypting software followed, many of which even played DVD movies. Some even allowed an originally region-specific DVD to be copied as an all-region DVD. Others went even further in removing the Macrovision anti-copying system as well.
Thus CSS has long been superceded by the various new ciphers. Indeed, the successor format to today’s standard DVD, Blu-ray Disc, had even won out over its rival, HD DVD, in large part due to industry favoring its more robust anti-copying mechanisms.