AACS decrypted... keys in memory

[Steve]

A doom9 user by the name of muslix64 has published a Java application that can decrypt AACS encrypted HD content.

He got miffed when he couldn't play HD-DVDs on his PC because his graphics card didn't support HDCP, so like any good programmer, he stuck two fingers up at the "fair use" management and found a way to decrypt it anyway.

It looks like PowerDVD was the key, literally, keeping the title keys in memory. He found them, then used them. Took him 8 days to do.

It's an interesting breakthrough, provided somebody can verify it. The MPAA will be rallying their lawyers as we speak, no doubt. Good luck to muslix64 on that front, then.

Read his post on Doom9, found via The Inquirer.

[pak000]

The movie industry has a real problem, it needs to wise up to the fact that people do not appreciate having restrictions stuffed down their throat. I would be understandably annoyed if I owned a computer with hd player and couldn't play a hd movie because my monitor didnt support hdcp.

I think it is inevitable that anything that has to be decrypted at the user end will always be open to attack.

The doom9 forum talks of it being a problem as soon as its put on a computer and out of a closed hardware solution...Even that isn't the case, intelligent people will always find a way around the problem - take a look at all the chipped games consoles.

[Steve]

As long there's something beaming light towards my eyes, copy protection is pretty much pointless.

[pak000]

that doesn't make it pointless, it makes it transparent.

The point is i want something to be beamed to my eyes through a system of my choice, copy protection stops that....for instance - why should i have to upgrade from a dell 2405 to a 2407 to watch hd content because the the 05 doesn't have hdcp?

[JPreston]

Since the MPAA etc insist on hobbling paying customers with restrictive encryption and copy protection (that apparently doesn't prevent copying anyway), why don't they require the disks to weigh 23kg to discourage shoplifters nicking them from HMV?

[UltraMagnus]

Since the MPAA etc insist on hobbling paying customers with restrictive encryption and copy protection (that apparently doesn't prevent copying anyway), why don't they require the disks to weigh 23kg to discourage shoplifters nicking them from HMV?

because depleated uranium is expensive (and still not heavy enough) not to mention how big the motor would have to be to spin up such a thing

and POWNED! when will the stupid movie industry realise how stupid this all is, all they do is put off paying customers and make people want to download unrestricted versions on P2P rather than buy a crippled version

[badass]

This is a good result but won't be for long. AACS allows for "revoking" keys form software/hardware that is known to be compromised. However all current discs in the shops will be decryptable!
I dont know of the finalised spec but I saw discussion of software players checking a CRL (certificate revocation list) on the internet before palying and if their certificate is revoked, the player refuses to work.
This means potentially anyone with powerDVD will require an update to play any HD movies now. AFAIK, the hardware players would read a CRL on any disc inserted and keep in NVRAM all of the revoked certificates read from the discs.

[manwithnoname]

This is a good result but won't be for long. AACS allows for "revoking" keys form software/hardware that is known to be compromised. However all current discs in the shops will be decryptable!
I dont know of the finalised spec but I saw discussion of software players checking a CRL (certificate revocation list) on the internet before palying and if their certificate is revoked, the player refuses to work.
This means potentially anyone with powerDVD will require an update to play any HD movies now. AFAIK, the hardware players would read a CRL on any disc inserted and keep in NVRAM all of the revoked certificates read from the discs.

Trying to get my head round the keys for decrypting, if a key is published it could be 'black listed' so a newly released HD-DVD disc contains info to stop it playing.

If I publish all the keys for all Toshiba players, then newly released discs will be prevented from playing on them? That got to be a great selling point or have I missed something...

btw I don't have the keys to publish

[badass]

Trying to get my head round the keys for decrypting, if a key is published it could be 'black listed' so a newly released HD-DVD disc contains info to stop it playing.

Yes

If I publish all the keys for all Toshiba players, then newly released discs will be prevented from playing on them? That got to be a great selling point or have I missed something...

btw I don't have the keys to publish

I dont see how this is practically possible, but that was the gist of the article I read. I suspect its only the software players that'll check for CRL's.
However the keys in the players are stored in a TPM style Chip that is supposedly impossible to get the key from.

[chrestomanci]

Trying to get my head round the keys for decrypting, if a key is published it could be 'black listed' so a newly released HD-DVD disc contains info to stop it playing.

If I publish all the keys for all Toshiba players, then newly released discs will be prevented from playing on them? That got to be a great selling point or have I missed something...

As you say, Holywood can blacklist a player if it's key gets cracked, but if it is a hardware player, then every one out there will become useless for new releases which would lead to a lot of pissed of consumers who paid good money for those players.

In a similar situation, the USA addopted HD TV much earlier than Europe, and there are a lot of pissed off early adopters in America who paid $10K+ for large HD plasmas, that don't have HDCP compliant inputs, so cannot be used to watch HD-DVD or Blu-Ray content.

Black listing players will probably be a bit of a game of chicken. If Hollywood are too eager blacklist then they will prevent the HD formats from being addopted, because the early adopters who get burned will warn their friends, but if they don't black list, they may as well not have the feature at all. The old DVD technology also supports blacklisting, but it was never used, partly for that reason, and partly because all 400 or so player keys where deduced by reverse engineering fairly soon after DeCSS was released.

[manwithnoname]

I appreciate Hollywood would want to take steps to protect their copyright material, but having a system where Joe public can spend cash on something in good faith that can then be potentially rendered useless for new discs doesn't appear to be a great way to treat the average Joe. I'm not sure what protect would work, is some better than none?

I guess it is unlikely the keys to hardware players will be found and published, but someone could cause a bit of chaos by spreading a few rumours about HD-DVD players been rendered useless, playing into the hands of the Blue-ray side, but I assuming the same thing could happen with Blue-ray.

[JPreston]

Do I understand this right:

1. You can buy a HD DVD player but it can effectively be bricked wrt new titles at the drop of a hat, and the onus will be on the end user to update the firmware/keys/whatever, somehow.

2. But if you have a software player and a suitably equipped PC, all you would have to do is replace the keys as and when they are revoked (and presumably the new keys will be circulated on P2P etc, as soon as they are produced in which case they get revoked and replaced and revoked and replaced...)

It seems that the only people that would be able to update their keys easily and frequently enough would be the second lot, who are more likely to be pirates (YAAAAARRRRR!!!). While Auntie Doris is supposed to spend £500 on a box she will have to drag to a telephone socket (or something) every other day to update the keys. How do they expect this to catch on (or have I missed the point altogether)?

[Steve]

This is a good result but won't be for long. AACS allows for "revoking" keys form software/hardware that is known to be compromised. However all current discs in the shops will be decryptable!
I dont know of the finalised spec but I saw discussion of software players checking a CRL (certificate revocation list) on the internet before palying and if their certificate is revoked, the player refuses to work.
This means potentially anyone with powerDVD will require an update to play any HD movies now. AFAIK, the hardware players would read a CRL on any disc inserted and keep in NVRAM all of the revoked certificates read from the discs.

That's all good and well, except the player's key remains unknown; it's the keys from the disc that have been discovered in memory. All they can do now is try their best to hide the keys, but they'll be there, somewhere, and the revocation list can't fix that.

[badass]

That's all good and well, except the player's key remains unknown; it's the keys from the disc that have been discovered in memory. All they can do now is try their best to hide the keys, but they'll be there, somewhere, and the revocation list can't fix that.

Yeah - I know that - what I was saying there is as a result of PowerDVD being used to get the keys, they could revoke PowerDVD's keys for that version, forcing people to download an update that fixes this problem. Of course the more savy amongst us might just block the player from accessing the CRL, however if the behaviour is like in a PKI then the player will refuse to run unless it can read the CRL every time it is started.
This does prove one thing though - all of this HDCP b0llocks is a complete waste of time and an inconveninece to the consumer and for what?
People that pirate these films dont have mega budgets to use specialist kit to record straight from the HDMI signal. They will rely on others hacking some software and then do it themselves.
all they have achieved from this is the same poor protection that is almost as bad as DVD's and annoyed consumers enough with the HDCP rubbish that they have cracked it when they may well have not done so if it weren;t for the HDCP.
Shot themselves in the foot

[chrestomanci]

I think it is worth explaining how the encryption on DVDs (both Old and new) works.

There are several different keys. Firstly there is the disc key. This is used to encrypt all the content on the disc, it unique to each disc, and totally random. In order for the player to recover the disc key, there are copies of the disc key stored on the disc encrypted using all the different player keys out there (about 400). The player uses it's key to decrypt the disc key so that it can play the disc.

So for example, if you have a Panasonic player, One of those encrypted keys will be for Panasonic players, so your player will be able to recover the disc key and play the disc. If in the future the Panasonic key gets leaked, future DVDs can omit the disc key that has been encrypted with the Panasonic key, so that pirates with that key will not be able to use it. Unfortunately it also means that Panasonic owners will not be able to play those discs either.

All this description applies to both old DVDs and the newer HD formats.

What muslix64 has done is exploited a weakness in a software player on his PC to recover the disc key for the HD-DVDs he has. It appears that his software player is keeping the disc key in memory without encrypting it, and at a predictable address. By reading the address using a debugger, muslix64 was able to recover that key. He then wrote a simple java program that uses the AACS java libraries to decrypt his disc. It is that java program that is circulating.

muslix64 has not actually done anything terribly clever, other than demonstrate than one software player is crackable, and stimulated a debate. The software player will be patched shortly, and in any case when Windows Vista comes out, it will be able to protect player software from having their memory read by other programs, so this hack will be impossible.

In the meantime it is possible to recover all the disc keys for all the HD-DVD titles currently available. Some people have suggested that even without a complete crack for AACS, this would be effective, because a continuously updated list of all disc keys could be published, and circulated via Warez newsgroups and P2P. Some people have also suggested that next time someone cracks a player, they should keep quiet about which player they cracked, and just publish disc keys. That way Hollywood will not know which player to blacklist.

Hollywood could could prevent that from working, by realeasing hundreds of versions of each popular movie, each with a different disc key, so when you go on-line to get a disc key for the movie you have just brought, you will probably not find one for the disc you have. Hollywood could also attempt to find out where in the world the crackers are by keeping records of which discs where sent to which regions, and correlating with the cracked disc keys that appear. This would force the cracker to travel to a different town to buy each disc, to prevent his address being narrowed down to much.

The problem for Hollywood with having hundreds of different versions of each disc is that it would cause logistics problems and drive up their costs. For popular movies, the hackers would find most of the keys anyway, and for less popular ones, there would only be one version. If the DVD Disc manufacturers found a way to individually burn each disc instead of pressing them, they could all be different, but that would require much higher security at the manufacturing plant as all the player keys would need to be known to the manufacturer instead of just giving them a disc image. None of that would affect comercal pirates anyway, as all they want to do is decrypt the disc they have, not all the others out there.

1. You can buy a HD DVD player but it can effectively be bricked writ new titles at the drop of a hat, and the onus will be on the end user to update the firmware/keys/whatever, somehow.

As you can see from the description above, it would not be bricked in the sense that it would stop working entirely, it would still play old discs that Prue-dated the blacklisting fine, as well as non protected content such as home movies, just not newer material.

Auntie Doris is supposed to spend £500 on a box she will have to drag to a telephone socket (or something) every other day to update the keys. How do they expect this to catch on (or have I missed the point altogether)?

Not necessarily. There is a lot of space on the new HD discs, so one suggestion is to routinely put firmware updates there. If the player key is part of the firmware, then it can be included in that update, so after a blacklisting, all new Movie discs for a year or so would contain a firmware update for the blacklisted player. In the case of Auntie Doris, the first time she plays a new disc after her old firmware was blacklisted, the player would automatically update and take slightly longer to start up and show the disc menu.

The problem with this is that the player key is in the firmware, and someone sufficiently determined could reverse engineer the binary to recover that key, and force the whole cycle to start again.

An alternative would be to put the player key inside the player's CPU. The only way to read it then would be to open it, and use an electron microscope to see the logic circits as they operate. Needless to say that would be a lot harder and more expensive, but if the hackers managed it, there would be no way to update the key, so any blacklisting would be permanent. Because of that it would be unlikely to get blacklisted, especially if the player in question was a popular model from a big name manufacturer.

A third way would be to put the key on a smart card similar to a Sky viewing card. This would be harder to crack than a key in the firmware, but could be updated by sending out new cards to the public. The problem with this is that the card and reader would add at least $10 to the cost of a player, which will be seen as a lot when players go mainstream and only cost $100 or so.

In practise we are likely to see a mix of all three solutions in the market in a few years time.

2. But if you have a software player and a suitably equipped PC, all you would have to do is replace the keys as and when they are revoked (and presumably the new keys will be circulated on P2P etc, as soon as they are produced in which case they get revoked and replaced and revoked and replaced...)

Not necessarily. It depends how they handle player keys for software players. Old DVDs where cracked via the Xing software player. Someone reverse engineered the player software and recovered the Xing player key. (It was supposed be to obfuscated in the binary but was not). Then because the CSS crypto was weak once one player key was recovered, it became possible to calculate all the others. Since then other Cypto researchers have shown weaknesses in CSS so it can be brute forced fairly easily anyway.

Hollywood does not intend to make the same mistake again. Firstly, the AACS cypto is much stronger, so if one player key is recovered, it will be impossible to get the others, and the crypto has no known weaknesses so probably can't be brute forced. Secondly they are thinking of doing away with player keys for software players. Instead the idea would be for the player software to phone home via the internet, Report it's version and the serial number of the disc, and be told the disc key. If the software has been cracked, an update can be forced. The problem with that is that it will prevent people watching HD movies on their laptops when they are on aircraft or at remote places with no phone coverage. One solution to that would be to allow player keys for sufficiently secure laptops such as those running Windows Vista 64 bit, or with hardware decryption such as TPM modules, but force windows XP users to phone home.

Hackers might be able to subvert the phone home system by writing programs that pretend to be player software in order to request a disc key.

(Yikes!, that was a much longer post than I expected)

[Funkstar]

(Yikes!, that was a much longer post than I expected)

very interesting though