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AACS Specifications Released
Posted by
CowboyNeal
on Fri Apr 15, 2005 12:46 AM
from the meet-the-new-css dept.
from the meet-the-new-css dept.
An anonymous reader writes "AACS, the proposed key management scheme for HD DVD, has finally released preliminary (ver 0.9) specifications. The specs look like CSS on steroids: they use AES instead of proprietary crypto, but other than that they're basically the same. The main difference appears to be that AACS can revoke an entire player model if a hack appears against it, which I guess sucks if you own that kind of player."
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Manufacturers (Score:5, Insightful)
In that case, why would any manufacturer in their right mind produce anything under such terms? That would just be insane
Re:Manufacturers (Score:5, Interesting)
If a set of Device Keys is compromised in a way that threatens the integrity of the system, an updated MKB can be released that causes a device with the compromised set of Device Keys to be unable to calculate the correct Km. In this way, the compromised Device Keys are "revoked" by the new MKB.
If I read this right (which is not guaranteed this early in the morning), only hacked devices would be revoked. So it wouldn't be insane for manufacturers to use this scheme, and in fact would make them discourage hacks rather than making them easy as they do with many DVD players. Bad for fair use, but no problem for manufacturers.
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Re:Manufacturers (Score:5, Insightful)
I'm not sure that creating a product that another entity can simply break is a great way to go. Can you imagine how irate all the innocent users would be? Man, I'd hate to be tech support at any of the companies that make these.
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Re:Manufacturers (Score:4, Interesting)
The way this worked in CSS and probably works similarly here is that at the begining to the disk they encrypt a disk key with many different device keys. Then each device decrypts the disk key using their own device key.
However if you work out the math it simply isn't plausible to include a seperate key for every HD DVD player that might ever be sold (imagine 128 bits for an AES key). Instead each manufacturer, or perhaps even DVD player model in this new system, gets one key. They can then 'revoke' these keys by just refusing to encrypt future DVD keys with these device keys but since each DVD player doesn't have its own key they can't disable movies player by player.
On another point I would find it to be really unlikely that any major DVD player would truly get this penalty imposed against it. It would be a huge loss to be the first movie that doesn't work on sony blah players so no movie company is going to be the one who takes that first step.
Instead this is really a measure to deter manufacturers from 'accidently' making their DVD players ignore copy protection or otherwise violate their rules. Thus it is likely to be used when a player first hits the market or not at all.
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Re:Manufacturers (Score:5, Insightful)
In the end, revoking player keys is stupid. It comes back to the whole point that DRM is not only a stupid idea but fundamentally flawed. It also creates an interesting situation for the key licensing organisation. Don't like a competitor or just want them to pay higher licensing fees? Threaten to cancel all their keys.
If the consumer association in your country has any sense whatsoever, they won't play along with this at all.
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Re:Manufacturers (Score:5, Informative)
"... with the compromised set of keys
Nasty. DVD is offensive enough already ("You may not skip this!"), this will just make it worse. Argh.
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Re:Manufacturers (Score:5, Informative)
With that in mind, it's clear that you can read what you quoted in the above sense, and indeed it's the plausible way to read it: it's not "causes a compromised device to be unable...", it's "causes a device with the compromised set of Device Keys to be unable...". Any device using this set of keys--whether it's superDeCSS or any particular machine of the sort that was compromised, or any other machine that shares the same set of keys--will no longer be able to view content--presumably only new content created after the revocation.
Related, from the spec:
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Extortion Opprotunity (Score:5, Interesting)
To me, this seems to be a golden opprotunity for organized crime, assuming they hire hackers good enough to reverse engineer a particular DVD player.
For example, say Sony make a really popular player, so organized crime get the AACS code hacked and then turn around and extort Sony - give us a lot of money or we'll release the key. If they release the key and this device blocking kicks in, Sony are going to have a lot of angry custumers demanding their money back.
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force obsolescence == forced "upgrades"!! (Score:4, Insightful)
What better way to keep people purchasing hardware than to force obsolescence?
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Let me be the first to hack it.. (Score:5, Informative)
Re:Let me be the first to hack it.. (Score:5, Insightful)
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Player Model? (Score:5, Insightful)
"The main difference appears to be that AACS can revoke an entire player model if a hack appears against it, which I guess sucks if you own that kind of player."
Player model? What if a hack comes out for PC that allows you to circumvent the copy protection: Does it revoke PCs altogether, only certain disk drives, or what?
Re:Player Model? (Score:4, Informative)
So they revoke a player model as follows (omitting lots of details that aren't important to the big picture, and oversimplifying):
Each player model gets its own key ("set of Device Keys" in the specification). Data on the disc is encoded with a disc-specific data key. Given N player models, there are also N encrypted master keys, one for each (non-revoked) player model.
If a player model is compromised and the key from it used in a DeCSS-like program, they will "revoke" that key and, on all future releases, not include a copy of the disc-data key encrypted for that player.
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Re:It's all about firmware? (Score:4, Insightful)
Most people won't even know what you are talking about.
Now having new DVDs automatically update the firmware is easy, stealthy, evil, and effective. I think some DRM systems use such an idea.
The user merely watches a movie, and their player gets reflashed in the process. That could work.
Expecting the average movie watcher to even know what to do with a USB cable and how to boot something off an external drive won't.
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I accept? (Score:4, Funny)
No Thanks. I'll just wait for it to get posted to
Mark my words. (Score:5, Funny)
There's no way they'll make the same mistake twice. DirecTV upgraded all their smart cards 2 or 3 years ago and it has yet to be broken. Bell Canada's expressvu is adopting the same technology because _everybody_ and their mom is pirating the signals.
Re:Mark my words. (Score:5, Insightful)
Here's the big difference...
Gaining access to DirecTV's signal requires hacking proprietary hardware. If PC-based players are ever allowed, reverse engineering will be along the same lines as last time around. It's just so easy to monitor everything your computer is doing in real-time, especially with the help of emulators like QEMU, Bochs, VMware, or Virtual PC.
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Re:Mark my words. (Score:5, Funny)
If they do it right, pirate copies will be truly impossible. Granted, no one will be able to play the legit copies either, but it's my impression that this is only a minor concern to the companies involved.
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Re:Mark my words. (Score:4, Insightful)
"Adult film producer"
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Okay, DVD Jon... (Score:5, Funny)
You have your work cut out for you!
Just kidding. :)
What will the packaging say? (Score:5, Interesting)
Now, how does this scale, suppose players AAA through ZZZ have been revoked. Do we need larger DVD cases just so we can fit a list of all the players that won't work on it?
Owning a model player that get's revoked .... (Score:5, Insightful)
Even worse : you have no way of knowing if the player you are going to buy is on the list of players shortly-to-be-revoked, or worse yet : allready revoked.
How's the "you should be able to use a bought commodity for a reasonable time"-law come in play here ?
Re:Owning a model player that get's revoked .... (Score:4, Insightful)
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Re:Owning a model player that get's revoked .... (Score:4, Funny)
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Well then... (Score:5, Funny)
Re:Higher unit cost for Blu-Ray (Score:5, Informative)
Also, contrary to what you may have heard, Blu-Ray discs will not require a cartridge. [blu-ray.com] Blu-Ray discs should be more scratch-resistant than even current CDs and DVDs.
And about capacity: HD-DVD can only hold 30GB(15GB per layer) [nec.co.jp], but Blu-Ray can hold 54GB(27GB per layer) [blu-ray.com]. In the future, Blu-Ray discs could even hold up to 200GB.
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Content scrambling is stupid... (Score:5, Insightful)
I wish they simply wouldn't scramble content in the first place. 99.9% of the people who buy the dvd and would need to break the encoding have a LEGITIMATE reason to break said encoding (backup, copying to laptop so it's not necessary to carry discs on trips, etc).
Re:Content scrambling is stupid... (Score:4, Informative)
When a video recorder receives the signal, it normalises the incoming signal, resulting in the signal sent in the flyback period (which is not used for the image) being awarded most of the signal bandwidth, and the image proportion being awarded approximately none.
Bypassing such a system is left as an exercise to the reader, however it should be fairly obvious.
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Can Slash stop with the obscure acronymns (Score:5, Informative)
AACS= Advanced Access Content System.
Maybe I am an idiot but i had to actually read the article to know what the posted article was talking about.
Re:Can Slash stop with the obscure acronymns (Score:5, Funny)
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key revocation (Score:4, Insightful)
How many people are still running windows 98? How many people know how to set the clock on their vcr?
You DoS the keyspace eventually people won't be able to play commercials. Then the productions don't get their money. Then the system does either of 2 things. 1: every screen goes black and there is no tv or 2: they give up and take off the crypto so the ads work again.
Key revocation is a bigger security risk than keys in software dvd players because you can do more than opening up a file to everybody. You can lock everybody out of it as well.
This idea (starting with hdcp I guess) just opens up more vectors for attack. Now we have a social engineering vector and a keyspace vector in additon to a locally stored key vector (css).
Re:key revocation (Score:5, Insightful)
We're talking about attacking the subset of deployed keys. We don't need these keys at all to get them revoked.
The device itself will decrypt the stream. All you need is access to the output to reencode and share. Copyright cops detect the share, lift whatever watermark may be in the stream, finger the device and revoke the key.
There you go. You just DoS'd a production run of playstations from decrypting movies. All without having any knowlege of any keys.
When I say DoS the keyspace I don't mean exhausting the theoretical keyspace of a 128 bit cryptosystem. You're right, that'd be hard. You don't have to discover keys to DoS the subset of deployed keys via third party revocation. You need only make it seem as if the key was compromised to the revocation authority, thus prompting revocation.
So long as the stream will exist in a decrypted form so the user can watch it, then no knowlege of keys is needed to perform this attack.
Also. If the revocation authority becomes wary of such attacks it acts as a bunny rabbit attack. When keys are legitimately compromised they may do nothing thinking it's just another dupe.
The keyspace isn't the weakness here. It's people.
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Re:key revocation (Score:5, Insightful)
You don't need to DoS the whole keyspace, or even any significant fraction of it. You only need to DoS the keys that are actually in use.
Imagine there are 100 different models of DVD player on the market. You just get those 100 keys revoked and suddenly no-one can watch any DVDs
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Hey... If there are hacks against it? (Score:5, Insightful)
We have seen that play before, cripple the next hot DVD to hit the market and what do you get? A ton of product returns and pissed off customers. The encryption may be more advanced, but when you want to give everyone consumer devices with the universal key to the castle... It's only a matter of time before someone figures out a way to copy it.
Re:Hey... If there are hacks against it? (Score:5, Insightful)
I think this will be the major reason that you _won't_ see key revocation, ever. It sounds like a very costly ordeal for all involved. The costs of tech support at the DVD player manufacturer and customer service at the disc producer will be enormous.
This would also be unwise for the branding concept as a whole. Branding, say, with the DVD-Video logo, is supposed to assure consumers that the product they get is system-interoperable with the other products bearing said brand. Imagine if there was a "hard incompatibility" issue between two products.
I think the first key revocation will be a seriously expensive endeavour, and the lawsuits will fly fast and furious. Customers will initiate class-action suits against the player manufacturers and disc producers, and the trademark owner who's assurance of interoperability has been proven a false representation. Player manufacturers will in turn sue the licensing authority for the harm their trademarks will suffer, as well as costs of tech support and lawsuits.
Disc producers may be SOL as far as suing anyone: They chose to release the discs without the complete keyset. Retailers will demand that returned product must be refunded; despite the fact that it is currently not industry practice. (Laws will force retailers to accept returned product that is defective.)
This is really a train wreck in the making. Bad medicine.
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This isn't new news... (Score:5, Interesting)
When will they learn? (Score:5, Insightful)
Remember Apple IIe games that wrote bad sectors or extra sectors and other such nasties to try and stop people copying 5-1/4 inch floppies?
Remember SecureROM and others making CD copy protection by intentionally leaving broken sectors on CDs - making them unburnable in nearly all of the burners at that time?
Remember that DVD's were once uncopyable?
Remember when Pay TV signals were encrypted by obfuscating their signal with some analogue hardware?
Remember when they started using proprietary digital encryption for Pay TV (Irdeto)?
Every time someone offers up content in some protected form, someone is going to break it. Period. Even if they can't break it, someone will use a legitimate DVD player and screen/sound grab their favorite movies using a capture card.
The only difference I see now is that the companies implementing these measures are monopolies whereas they used to smaller players in their respective markets. This might mean that they can push some legislation through to discourage copying but nothing will ever stop it IMHO.
Definition of insanity? (Score:4, Insightful)
people will just go old school then (Score:4, Insightful)
It doesn't suck - it's perfect! (Score:5, Interesting)
At that point the bottom will fall out of the market.
Proof: see what DVD players sell best: those with zone restrictions or those without. The irony is that that does not happen because of piracy (pirated DVD appear to be generally set to zone 0 so zone selection is irrelevant) but because of legitimate purchases made elsewhere in the world.
So, in summary, let them progress down this route. Eventually the market will die as alternatives pick up the revenue.
As an example: how many of you buy protected contents or media in non-Open formats?
I have looked at pirated DVDs and they are indeed not worth the money - if you're in a country with sane media prices. If they really, really, really wanted to address piracy all they need to do is become more sensible with the prices, that has already proved to work (hello MS, are you listening?). The increase in revenue more than offsets the expenditure they have to put in on lobbying, researching formats that don't work or get broken in a rainy weekend by a couple of bored teenagers.
Hell, it'll probably even keep them in cocaine and limos.
Actual quotes (Score:5, Insightful)
Page 24: Each compliant device is given a set of secret Device keys when manufactured. ...The set of device keys may either be unique per device, or used commonly by multiple devices. ...The [Media Key Block] system is based on a large master tree of keys, with each set of Device Keys being associated with a leaf node of the tree... Further, corresponding to every sub-tree in the master tree is another set of system keys... Thus, the subset-difference tree has to store one encryption per Device Key set revoked, and occasionally additional encryptions to pick up non-revoked sets not covered by the smaller sub-trees. On average, there are 1.28 enrcryptions per revocation.
The document goes on to mention around pages 27 and 28 that devices obtain key conversion data by mechanisms called out in the AACS liscense, and recording devices must verify the signature and determine by its version number field whether a Media Key Block is more recent than the one currently on the media. "Each time the AACS LA changes the revocation, it increments the version number and inserts the new value in subsequent Media Key Blocks."
This says to me that the DVDs you buy will in fact be the transport mechanism for updated revocation keys, and presumably your player will be able to store a lot of them. So movie production companies and distributors must conspire to continually subvert the functionality of a consumer's device, and this does not require the player to be online nor will a firewall help. Once you get yourself locked into the prison of this coded delivery system, your own buying habits will keep adding additional chains to your cage. It is quite insidious, not only are they using military-level technology to control movies, the system is founded on the complicity of the entertainment industry, the electronics industry, and consumers themselves (and the consumer's PC if used) with constant policing and injection of targeted death-messages into the distribution channel. It also looks like the drive can potentially disable media (page 41) and even report hacked hosts/drives by recording onto the media (it seems kind of vague but it is writing a concatenation of the "Binding_Nonce", "Drive_Nonce" and "Host_Nonce" to the protected data area, whatever these things are), which if this is indeed true would I suppose be reported through other PCs/drives of people to whom you lend the media, or maybe through even a shared Internet connection, if you want to try extrapolating this.
Sorry I got ahead of myself. Page 55 talks a lot about online connections, online enabled content and streamed content. It talks about Title Keys and says "the word 'title' is often overloaded. For example a title can refer to a full-feature movie, a TV program, a music album, etc. ... however [we] .. define Title to be a distinct path.. That is, a Title is a logical grouping of content material to be presented in a specific order in time." It also mentions an "Enhanced Device" that is online and can then provide full access to Enhanced Titles that require online connections or extended player functionality. Page 56 mentions a Cacheable Permission that expires after a certain amount of time or include a "do not play until" date, and the XML based Title Usage File is based on global, not local time, which if used must be based on a "secure clock" whatever that is. Oh yeah, on page 59 it mentions the default connection protocol can operate (by https) over Ethernet, firewire, WLAN, etc. so you know this is not just about an HD DVD format but looks like it is trying to take over every device in the vicinity as well. How much you want to bet this will police titles not actually loaded in the player?
I think the cutest part is page 61, where it shows how you can go online with a PIN number and a remote Clearing House server can offer a title
So they are using AES? (Score:5, Funny)
There is no warranty on hardware in U.S.? (Score:4, Interesting)
So, that would be a legal massacre of retailers/vendors/manufacturers by consumers/consumers organisations.
Isn't it about time we lobbied for a fair use law? (Score:5, Insightful)
Isn't it about time that we, the people who are paying for this content get our fair use rights looked after. Anyone putting DRM controls in place should have a legal obligation to ensure that if if a customer has paid for the right to have access to the content that they also get their fair use rights as well.
It seems to me that the sorts of controlling technologies that are being envisaged here do not safeguard those rights. Isn't it about time we pressurised our democratic representives to ensure that we don't lose them?
NOT HOW IT WORKS!!! (Score:5, Informative)
Almost all of the assumptions in this thread are wrong. The system does not work cryptographically in the way people imagine. The technology makes it possible to efficiently revoke INDIVIDUAL DEVICES, not entire model lines. Every device can have a unique key, even if there are millions of them. There is no necessity or desire to make people's non-hacked players stop working. As others have pointed out, this would be INSANE. That's not how it works!
Cryptographically, this system allows the data to be encrypted to any of millions or even billions of devices, using a very short encrypted key block. What happens is that if some of those (individual!) devices get revoked, the size of the key block increases. Amazingly, the size is dependent on how many devices get revoked, not on how many devices there are. If extracting keys from a device is complicated and expensive, and not too many need to get revoked over the lifetime of the system, it will be a success.
The cryptographic technique is described in a paper from Crypto 2001 called Revocation and Tracing Schemes for Stateless Receivers by Naor et al and is available from http://www.wisdom.weizmann.ac.il/~naor/PAPERS/2nl
Imagine creating a binary tree with enough leaf nodes to hold all of the devices (again, this is individual devices, not model lines). Each device is associated with a particular leaf node of the tree. Now we assign a random AES key to every node of the tree, leaf nodes and internal nodes.
At manufacture time, each device is given all of the keys corresponding to its branch of the tree; that is, the key for its leaf node, and the keys for the parent, grandparent, etc. of that node, all the way back to the root node of the tree. As long as the disk is encrypted to one of these keys, the device can play the disk. Note that even if there are a billion device nodes in the tree this is only about 30 keys that a device has to hold, which is trivial.
Now, to create a disk, initially it is encrypted to the root node of the tree. All devices have the key for that node so all devices can play it. The key block is very short. But now suppose that someone manages to extract the secret device keys in their device, they get published on the internet (as happened initially with DeCSS), and everyone is able to use them to decrypt HD-DVDs. (BTW this system is also being used for Blue-ray! Don't think that's going to be any different!) Now what do we do?
What happens is that new disks are no longer encrypted to the root key. Instead, we partition the tree into subtrees that include every leaf node except the one which got its keys published. Now we encrypt the disk data to the root nodes of those subtrees, rather than to the root node of the whole tree. This will allow every other device still to decrypt the data, but that one hacked device can no longer decrypt new disks. The size of the key block grows based on the number of hacked players.
This is an oversimplified version because the size of the key block is bigger than desired. The paper above shows a more complex system, which is actually being used, which makes the size of the key block linear in the number of hacked systems. Assuming that hacking them remains relatively difficult, this should be an effective and efficient content protection system.
Basically this is the same method being used in current satellite TV systems, and for the past few years it has been successful enough that satellite piracy in the U.S. at least is largely a thing of the past.
Re:Is this legal? (Score:5, Informative)
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Look to your own house (Score:5, Insightful)
Last I checked US troops aren't marching house to house in Australia, or occupying the Australian parliament.
Blame your own gutless politicians for your own mess. I don't blame Aussies for Bush being in office, despite the fact that one right-wing Aussie happens to own FOX and had no small part in running the propoganda machine that conviced approximately 50% of the US voters to vote the moron back into office.
You're responsible for your own mess, and the sooner you take your own leaders to task for it, rather than blaming a foreign power, the sooner you'll get it fixed. The same goes for us, by the way. The sooner we start blaming our own leaders for the current mess, rather than boogeymen in caves and Al Q'aide, the sooner our mess here in the states will get sorted out.
I don't expect either country's population to do this anytime soon, however.
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Re:wtf? (Score:5, Informative)
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Re:Protecting everyone's interests. (Score:5, Insightful)
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They aren't trying to stop piracy. (Score:5, Insightful)
What they care about is control.
They care about linux distributions adding support to play HD-DVD movies, but not paying license fees to the DVD forum.
They care about HD-DVD players cropping up that allow you to fast-forward past the trailers at the beginning of the movie, the ones where a licensed player, when you say "fast forward", says "no".
They care about people making players behind their back which openly flaunt the "region locking" mechanisms that make regional price discrimination possible.
They care about products like DVDXCopy which allow consumers to exercise their fair use rights and do God knows what with the products they purchase.
These are the things they're trying to stop or hinder. Their choice of technology simply reflects that. AACS will do little in the short run and nothing in the long run to prevent piracy. But the legal barriers the media companies paid to erect will allow AACS to keep all four of the above things off of the general commercial market.
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