Moto perpetuo

It occurs to me that unbreakable copy protection is the perpetual motion of our day.

Back at the beginnings of the industrial revolution, when inventions like the steam engine and electrical generator were making new and mysterious things possible and were not widely understood, people were constantly coming up with perpetual motion schemes. And why not? If you can generate more power than hundreds of strong men and horses can produce just by burning coal, and transmit that power miles and miles away with simple metal wires, is it so implausible that some arrangement of magnets and overbalanced wheels could generate endless power from nothing?

Eventually, in the early 1800s, after commercial steam power had been around for about a century, the principle of conservation of energy came to be widely accepted and by the the middle of the century the familiar laws of thermodynamics were established, including the crucial first two:

1. You can't win (conservation of energy).
2. You can't break even (entropy increases in a closed system).

These two principles explain why perpetual motion schemes don't work. That hasn't stopped people from coming up with them, but it has stopped knowledgeable engineers and scientists from wasting time on them. It hasn't completely stopped investors from investing in them, but the long and sorry track record of such schemes probably has been a deterrent.

Why do people still bother, then? Because if it were possible, large-scale perpetual motion would do away with energy shortages forever. It woudn't necessarily make any money, infinite supply implying zero price, and an energy surplus would have drawbacks of its own, but we could probably deal with those problems when they came up. The point is that people try to prove that perpetual motion is possible because they really, really want it to be.

Anyone in the business of selling information would really, really like to be able to control the propagation of that information. You do the math.

I don't know of any specific principle of information theory that explains why this will never work, but there's a growing body of empirical evidence to that effect. Intuitively, copying bits costs much less than the price sellers would like to charge, so the protection has to come in the conversion of those bits into usable form. That runs you right in to the analog reconversion problem, of which "camming" (sneaking cameras into movie theaters) is a crude but effective example.

Clearly none of this is currently stopping people from trying to come up with copy protection schemes, or people from paying for them. The track record probably isn't quite long or sorry enough yet. I suspect it eventually will be.

Fortunately, selling bits and making them impossible to copy are two different things.

We want the world and we want it reasonably soon

One of the nice features of digital TV is that you can decide when to watch a given program. This isn't a new feature, but digital delivery makes it a lot easier. Anyone remember VCR Plus?

In fact, you can time-shift in two different ways with a typical digital cable setup (at least, I think mine is fairly typical):

• Record a program and watch it at your leisure
• Get it on demand

In either case, you watch the show when you want. The difference is when the bits arrive. In the first case, they arrive when the broadcaster decides to send them. In the second case, they arrive when you ask for them.

What determines which way the bits get to you?

• Storage space: Your DVR will only hold so much. If you try to record everything you might possibly be interested in, you're liable to run out of space. This factor is rapidly changing.
• Broadcast bandwidth: There's only so much spectrum available. With infinite bandwidth, a provider could broadcast every piece of video/film ever made at 1,000,000x speed on an infinite loop and everyone could grab what they wanted as it came by [See this post for some implications of that].
• Copy protection: A provider might prefer that you not store a copy of the bits. Instead, it would prefer to send encrypted bits to a box that decodes them, without offering a ready way to store the results. This factor is also subject to change as the whole copy protection issue shakes out.
• Time sensitivity. A live event has to go out live. Even pre-recorded material can have more impact if everyone gets it at the same time -- the water-cooler effect.

The broadcast-and-record model doesn't require a data network. Traditional TV/Radio broadcasting, whether from towers or satellites, works just fine. VHF and UHF together comprise around 3GHz of bandwidth, readily available without building out a "last mile". At the moment, that's still quite a bit of bandwidth. Even if the broadcast is via a data network, there's no requirement that said network be connected to or behave like the internet.

The downside is that (for the most part) you don't get to choose when the bits are sent. But how much of a downside is that? It's not a problem for live content -- quite the opposite. It's not a problem for not-so-live content either, as long as you can still choose when you watch.

Again, the connection between receiving and watching has been loosening over time as storage gets cheaper and easier. Maybe this is just me, but if my favorite show comes in while I'm asleep and I can watch it whenever I want the next day, I've got no problem. On the other hand, if it's something that everyone just absolutely has to watch at a given time, that's essentially live content.

The upshot is this: Given ample cheap storage, it would appear worthwhile to broadcast anything new that lots of people want to see, regardless of whether they want to see right at that moment.

I haven't paid a lot of attention to satellite TV lately, having had cable for the past few years, but I could imagine someone shipping out a set-top box pre-loaded with a huge video library and space for plenty more. Only new content gets broadcast.

Live content comes in as it happens. Pre-recorded content comes in whenever the bandwidth is available. Everything gets stored on the box, using double-secret heavy encryption mojo. You can have whatever you want, and reasonably soon. The result would be pretty much indistinguishable from a cable set-up.

You would even have on-demand viewing. This difference is that instead of demanding the bits, you're demanding authorization to decrypt the bits (for a while, at least). You might well obtain the decryption key via the web, in which case the web handles the transaction, but the heavy lifting of moving large hunks of video around can happen elsewhere if that makes sense.

Such a scheme would also have all of the usual data-protection problems, notably including analog conversion, but that comes with the territory. Whether it's less secure than an existing on-demand service depends on just how good the double-secret heavy encryption mojo is. I can see content providers being nervous about putting the keys to the kingdom directly in the hands of millions of subscribers, however well protected the data may be. But on the other hand, isn't the whole point of mass media to get the bits to as many people as possible?

Why is there still print?

The Newsweek article on Kindle quotes Jeff Bezos as saying "Books are the last bastion of analog." I take his point, but it seems an odd statement. Text, after all, is arguably the first real digital medium. What he means by "digital", of course, is "available to computers". Unlike music and video, which are now routinely released in computer-readable form, books are still released in a form you can't just download. Bezos aims to change this with the Kindle.

The interesting question is, why does print resist digitization so well? I've suggested that publishers like it because it provides copy protection, but why does it? The answer has to be economic, not technical. Technically, it's trivial to digitize a book. Just scan it in. Don't bother to try to convert the image back to text. If all that people want to do with the result is read it, the image should work fine.

There's an interesting subplot here. Optical character recognition (OCR) seems to do fairly well these days on well-printed books, judging by Google books and Amazon's own "Search inside the book" feature. On the other hand, the fully general problem of reading anything a person can make out still appears to be hard, which is why sites use distorted text CAPTCHAs to try to stop bots. This seems like the equivalent of anX-prize for freelance OCR hackers, and indeed the inevitable arms race appears to be well under way. Finally, bringing us full circle, one source of these CAPTCHAs is printed text that failed to scan correctly.

In any case, the difficulty doesn't seem to be digitizing text in a readable form. The problem is, what do you do with it once you've got it? It's technically trivial to scan a book, but it still takes some time and effort to flip through all the pages, at least without expensive specialized equipment. So if I've done this, I'd like to see some compensation -- assuming I don't mind violating copyright laws.

Can I put it on the web and sell it? Well, um, I've just brought it into digital form, thereby making it hugely easier to copy. In other words, I've just put myself in the position of the publisher whose print-based copy protection I've just broken. If copy-protection is out, there's always advertising. Except that's maybe not such a good idea given that I've just broken the law.

This same argument would seem to act as a counterbalance to all sorts of unauthorized copying, but obviously it doesn't apply as effectively to audio and video. This is probably because copying CDs and DVDs is much, much easier than scanning books, and also because books are simply a different medium. I'd expect that PhDs have already been earned on just such matters.

Analog reconversion and copy quality

All copy-protection schemes have at least one prominent hole. At some point, they have to deliver you something. A music player has to play music, a document viewer has to show you a document, and so forth.

There's nothing at all stopping you from recording the sound that comes out of the headphones, or taking a picture of a document on a screen (and in the Trusted Computing nightmare scenario of the disappearing order, that might be a very good idea).

Of course, the usual objection is that you've lost information in the process. You've lost sound quality in the case of music. In the case of a document, you're just seeing text on the screen, not the underlying markup or structure.

Well yes, but ... if all you can do with a piece of music is play it on your headphones, and you record the analog signal going to the headphones (or even coming out of the headphones), then you have copied all the information needed to listen to the music with the quality those headphones give. Which is all you had in the first place.

Similarly, if you capture the images on the screen as you view a document, then you can go back and re-read the document any time you want. With optical character recognition, you could even reconstruct the text with fair accuracy. The process in general is called analog reconversion.

If all you are granted is the ability to view images or listen to sound, then you have already lost information. Recording the analog signal results in further loss, but as playback and recording equipment gets better and better, the loss becomes less and less perceptible. The ultimate limit here is human bandwidth, not computer bandwidth.

At the moment, recapturing the full glory of an HD DVD is beyond most people's capability. There are just too many bits going up on the screen and compressing would take too long. But grabbing enough to re-sell as a cheap pirated copy is clearly within many people's capability, and Moore's law will come into play sooner or later.

Attempts to plug this "analog hole" tend to be draconian, e.g., restricting the use of digital recording devices, and don't tend to get very far. Not that that will keep people from trying.

Hypertext is an interesting counterexample. I could record my viewing of a web site, and probably even analyze the results and reconstruct the links I've followed. What I can't do, however, is know what's behind the links I didn't follow, or even where they point.