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iBooks DRM has been cracked.

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Re: iBooks DRM has been cracked.

#31

Post by tzs »

There's one thing about cracking DRM that has me puzzled. Consider DRM on music, for instance. Suppose we have a 4 minute song, stored as an MP3 with DRM.

The ideal crack results in a 4 minute audio file, without DRM, that is the same audio quality as the input MP3, and is about the same size.

If we didn't care about size, there would be an easy way to crack the DRM. Just play back to music and capture the digital audio stream, and store that as a WAV file, or compress it with a lossless compressor. That preserves the audio quality, but the file is bigger.

If we are willing to give up some audio quality, we can do the above, but use an MP3 encoder. That should get is back down to near the original size, but the decoding and re-encoding as MP3 will cause some audio degradation.

Let's think about the MP3 format in an abstract way for a moment. Consider the set of all possible 4 minute audio streams. Define a given stream as being "perfectly representable" as an MP3 of bit rate B if there exists an MP3 encoding at a rate of B that decodes perfectly to that stream.

A general purpose MP3 encoder takes an input stream, and produces an MP3 file that decodes to a perfectly representable stream that is close to the input stream--ideally only differing in ways that people can't hear.

So here's the question--if the input stream to an MP3 encoder is perfectly representable, why is the output usually a file that decodes to a different perfectly representable stream?

It seems to me it should be possible to design an MP3 encoder with the property that under the operation of encoding followed by decoding, the perfectly representable streams are fixed points. I'll call such an encoder "representation preserving".

With such an encoder, removing DRM from an MP3 file consists simply of playing it back using whatever is normally used to play files with that DRM system, capturing the digital output stream, and then re-encoding with a representation preserving MP3 encoder. The result will by a DRM-free MP3 with exactly the same quality as the MP3 you started with, and compressed to about the same file size.

Re: iBooks DRM has been cracked.

#32

Post by mikeash »

tptacek wrote: post #18
mikeash wrote: post #17

Earlier quoted context omitted.

I think this is what shows that DRM really is hopeless. For DRM to work, it has to work every time. For DRM to be broken, it only needs to fail once. After one guy has extracted the media, it can then be distributed to the world even if nobody else can break the DRM.

Not really. The content providers only have to hold the line (a) on high-quality and (b) during the new-release window. It's true that eventual failure is inevitable, but the economic case for DRM doesn't rely on permanent protection.

Maybe my statement needs to be modified a bit, but the general idea still holds. DRM needs to work to prevent (a) and (b) for everybody, whereas if just one person can break the DRM with high-quality results during the new-release window, they lose.

Re: iBooks DRM has been cracked.

#33

Post by tptacek »

mikeash wrote: post #32
tptacek wrote: post #18

Earlier quoted context omitted.

Not really. The content providers only have to hold the line (a) on high-quality and (b) during the new-release window. It's true that eventual failure is inevitable, but the economic case for DRM doesn't rely on permanent protection.

Maybe my statement needs to be modified a bit, but the general idea still holds. DRM needs to work to prevent (a) and (b) for everybody , whereas if just one person can break the DRM with high-quality results during the new-release window, they lose.

That's true, of course, but modern DRM schemes anticipate exactly that, and so they put lots of effort into making it cost-prohibitive to break the scheme in under 2 weeks.

Maybe it's the case that everyone has backed off Blu-Ray because of Slysoft, but either way: BD+ has protected the new-release window for Blu-Ray disks in several instances (you can check out the Slysoft message boards to see when that's happening).

If you want to see an example of an (as far as I know) unbroken DRM scheme, look at the modern crypto cards in satellite TV systems.

Re: iBooks DRM has been cracked.

#34

Post by daeken »

tptacek wrote: post #33
mikeash wrote: post #32

Earlier quoted context omitted.

Maybe my statement needs to be modified a bit, but the general idea still holds. DRM needs to work to prevent (a) and (b) for everybody , whereas if just one person can break the DRM with high-quality results during the new-release window, they lose.

That's true, of course, but modern DRM schemes anticipate exactly that, and so they put lots of effort into making it cost-prohibitive to break the scheme in under 2 weeks. Maybe it's the case that everyone has backed off Blu-Ray because of Slysoft, but either way: BD+ has protected the new-release window for Blu-Ray disks in several instances (you can check out the Slysoft message boards to see when that's happening…

You totally hit the nail on the head: DRM 'works' if it makes it difficult to get access to content, not impossible. And of course, I say that having spent the majority of my teenage years reversing DRM. Nobody believes that DRM will hold up forever, but there's a huuuuge imbalance here that favors the DRM creators, which is that it's really, really easy to put together modifications on a DRM system that make a reverser's life hell. For a while, iTunes was rolling out a new version of their store page crypto with every release (and deprecating the old one) so I'd have to go and reverse it to keep my iTMS client working; I may have kept up for a while, but eventually I stopped because it simply took too much damn time, and they won in the end with a fairly small amount of work from their side.

That imbalance means that DRM will always work, even if it doesn't 'work'.

Re: iBooks DRM has been cracked.

#35

Post by mikeash »

daeken wrote: post #34
tptacek wrote: post #33

Earlier quoted context omitted.

That's true, of course, but modern DRM schemes anticipate exactly that, and so they put lots of effort into making it cost-prohibitive to break the scheme in under 2 weeks. Maybe it's the case that everyone has backed off Blu-Ray because of Slysoft, but either way: BD+ has protected the new-release window for Blu-Ray disks in several instances (you can check out the Slysoft message boards to see when that's happening…

You totally hit the nail on the head: DRM 'works' if it makes it difficult to get access to content, not impossible. And of course, I say that having spent the majority of my teenage years reversing DRM. Nobody believes that DRM will hold up forever, but there's a huuuuge imbalance here that favors the DRM creators, which is that it's really, really easy to put together modifications on a DRM system that make a rever…

This actually seems to paint a nice picture where everybody wins. Content producers win because DRM only needs to work for a short time. Everybody else wins because it can still be cracked in relatively short order.

Re: iBooks DRM has been cracked.

#36

Post by tptacek »

daeken wrote: post #34
tptacek wrote: post #33

Earlier quoted context omitted.

That's true, of course, but modern DRM schemes anticipate exactly that, and so they put lots of effort into making it cost-prohibitive to break the scheme in under 2 weeks. Maybe it's the case that everyone has backed off Blu-Ray because of Slysoft, but either way: BD+ has protected the new-release window for Blu-Ray disks in several instances (you can check out the Slysoft message boards to see when that's happening…

You totally hit the nail on the head: DRM 'works' if it makes it difficult to get access to content, not impossible. And of course, I say that having spent the majority of my teenage years reversing DRM. Nobody believes that DRM will hold up forever, but there's a huuuuge imbalance here that favors the DRM creators, which is that it's really, really easy to put together modifications on a DRM system that make a rever…

While I'm pretty sure you already know this, I doubt many people on this thread do:

The BD+ scheme that protects Blu-Ray disks was designed by very, very smart people (outside the content industry) to make it maximally easy to update the protection scheme, potentially on a title-by-title basis, without ever having to ship new players (and ideally never having to update player firmware).

Re: iBooks DRM has been cracked.

#37

Post by mikeash »

tptacek wrote: post #36
daeken wrote: post #34

Earlier quoted context omitted.

You totally hit the nail on the head: DRM 'works' if it makes it difficult to get access to content, not impossible. And of course, I say that having spent the majority of my teenage years reversing DRM. Nobody believes that DRM will hold up forever, but there's a huuuuge imbalance here that favors the DRM creators, which is that it's really, really easy to put together modifications on a DRM system that make a rever…

While I'm pretty sure you already know this, I doubt many people on this thread do: The BD+ scheme that protects Blu-Ray disks was designed by very, very smart people (outside the content industry) to make it maximally easy to update the protection scheme, potentially on a title-by-title basis, without ever having to ship new players (and ideally never having to update player firmware).

I read the Wikipedia entry on BD+ to see what made it special. Sounds like it's essentially a way to implement DRM on the disc rather than in the player by having the player provide a virtual machine which executes arbitrary DRM code on the disc. However, it seems like this would be defeated permanently by simply implementing the virtual machine in the hypothetical DRM unlocker. Has it simply been too difficult to fully reverse engineer, or is there some other hurdle in the way beyond that?

Re: iBooks DRM has been cracked.

#38

Post by tptacek »

mikeash wrote: post #37
tptacek wrote: post #36

Earlier quoted context omitted.

While I'm pretty sure you already know this, I doubt many people on this thread do: The BD+ scheme that protects Blu-Ray disks was designed by very, very smart people (outside the content industry) to make it maximally easy to update the protection scheme, potentially on a title-by-title basis, without ever having to ship new players (and ideally never having to update player firmware).

I read the Wikipedia entry on BD+ to see what made it special. Sounds like it's essentially a way to implement DRM on the disc rather than in the player by having the player provide a virtual machine which executes arbitrary DRM code on the disc. However, it seems like this would be defeated permanently by simply implementing the virtual machine in the hypothetical DRM unlocker. Has it simply been too difficult to fu…

I can't comment in any detail here, but the problem of implementing the particular VM that BD+ programs are written to is not a trivial one, more akin to implementing a simulator for an entire X86 execution stack including the chipset, microarchitecture, and all the MSRs than it is to writing a JVM. Get anything wrong and you fail to derive keys.

Re: iBooks DRM has been cracked.

#39

Post by Natsu »

tptacek wrote: post #28
Natsu wrote: post #25

Earlier quoted context omitted.

In other words, they only have to fool themselves into thinking it's doing them any good?

I'm not sure what this comment is supposed to mean. Maybe if you rephrased it?

I don't believe it actually helps them economically, though Hollywood has a pretty funky take on accounting so you never know. I can't imagine a sane business being glad that they were able to successfully delay selling things for X months.

I understand the rational explanations for that, but I'm just as sure that people aren't that rational. Essentially, they're trying to be too good at the negotiating game. Ever been too good at a game? Nobody wants to play with you any more.

Re: iBooks DRM has been cracked.

#40

Post by easp »

jonny_eh wrote: post #6
DarkShikari wrote: post #5

I’ve always thought that DRM only remained unbroken so long as no hacker was interested in breaking it This has always been true; why break the weak DRM on a low-quality 'Netflix' stream when you can do an HDTV rip or even a Blu-ray rip? But the instant you create exclusive content that everyone wants on such a service, the DRM will be broken faster than you can say "DMCA". The downside of this is it lets companies d…

Now that Netflix has original exclusive content, can we look forward to someone hacking the Netflix stream?

It'll have to wait for something better than Lillyhammer to come along...
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