It’s worth noting that the licensing protections on home users making playable CSS-encrypted disks go beyond just the manufacture of recordable disks, but also involve design constraints on licensed recorders. For example, I believe DVD+R disks *don’t* come from the factory with the lead-in sectors zeroed out, meaning that if you could burn a key there, you could make bit-for-bit copies of a prerecorded disk. See here:

http://www.cdfreaks.com/reviews/Increased-compatibility-DVD-bitsetting

The reason why DVD+R recorders aren’t a massive security breach is that there’s an additional protection, which is that licensed recorders aren’t supposed to *write* to the lead-in area where the disk key is located, even if it is blank. Evidently they can, however, write to the lead-in area that contains the DVD+R’s “book type,” which I believe was also supposed to be an additional protection — licensed players and drives should ignore CSS data present on a recordable book type. In all, I think the DVD+R situation shows that, although you refer to a “DVD cartel,” it’s a pretty reluctant and unruly cartel.

So it’s true that the whole system depends not just on technology, but also licensing requirements and legal protections. I’m curious, why do you describe that as a “trap”? It could be described as “blocking” or “inhibiting,” maybe, but I don’t get what the “trap” is that catches the unwary. No one hopes for a license violation.

[I]t’s unclear why the cartel expected CSS to survive first contact with the general-purpose computer. It’s “secure” as long as all DVD-reading hardware consists of sealed special-purpose boxes, but once you put a computer in the process, it’s obviously feasible to control the decryption process or monitor the playback.

“Hoped” might be a better word here than “expected.” Playback in computers was still relatively new in the mid-1990s. Obviously monitoring decryption and playback is easier in a computer than it would be in a stand-alone machine. But “easier” doesn’t mean “easy.” The CSS hack resulted from a particular implementation in one software player. It might be more accurate to say that the reluctant nature of the “cartel” was more the problem than a technological flaw in CSS.

Re: Archit’s comment: The DVD people could require the OS to provide some protected output and limit software playback licensees to using that output.

The politics of the DVD “cartel” wouldn’t allow this. Computer manufacturers, including OS manufacturers, are typically adamant that there be no obligation on their part to scan all content to figure out what it is just by virtue of their handling it (but not decrypting or otherwise using it). So content is protected as it transits through a computer either by encryption or by being transmitted through channels that are thought to be physically difficult to tap. Each device or program that decrypts CSS data must have a license and thereby play by the license rules, which include restrictions on outputs (from the device or program, not necessarily from the piece of tin that wraps the computer). But there’s no general obligation on the part of an operating system manufacturer, just from the fact that the OS handles communications between devices and programs, to determine what is in the communication and protect it accordingly.

One way of putting it might be that it’s unclear why the cartel expected CSS to survive first contact with the general-purpose computer. It’s “secure” as long as all DVD-reading hardware consists of sealed special-purpose boxes, but once you put a computer in the process, it’s obviously feasible to control the decryption process or monitor the playback.