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{{Use dmy dates|date=February 2020}}
[[Image:AACS dataflow.svg|right|thumb|AACS decryption process]]
The '''Advanced Access Content System''' ('''AACS''') is a [[standardization|standard]] for [[content distribution]] and [[digital rights management]], intended to restrict access to and copying of the post-[[DVD]] generation of optical discs. The specification was publicly released in April 2005. The standard has been adopted as the access restriction scheme for [[HD DVD]] and [[Blu-ray Disc]] (BD). It is developed by [[AACS LA|AACS Licensing Administrator, LLC]] (AACS LA), a [[consortium]] that includes [[The Walt Disney Company|Disney]], [[Intel]], [[Microsoft]], [[Panasonic Corporation|Panasonic]], [[Warner Bros.]], [[IBM]], [[Toshiba]] and [[Sony]]. AACS has been operating under an "interim agreement" since the final specification (including provisions for [[#Managed Copy|Managed Copy]]) has not yet been finalized.
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==System overview==
===Encryption===
AACS uses [[cryptography]] to control and restrict the use of digital media. It encrypts content under one or more ''title keys'' using the [[Advanced Encryption Standard]] (AES). Title keys are decrypted using
The principal difference between AACS and [[Content Scramble System|CSS]] (the DRM system used on DVDs) lies in how the device decryption keys and codes are organized.
Under CSS, all players of a given model group are provisioned with the same shared activated decryption key. Content is encrypted
In principle, this approach allows licensors to "revoke" a given player model (prevent it from playing back future content) by omitting to encrypt future title keys with the player model's key. In practice, however, revoking all players of a particular model is costly, as it causes many users to lose playback capability. Furthermore, the inclusion of a shared key across many players makes key compromise significantly more likely, as was demonstrated by a number of compromises in the mid-1990s.
The approach of AACS provisions each individual player with a unique set of decryption keys which are used in a [[broadcast encryption]] scheme. This approach allows licensors to "revoke" individual players, or more specifically, the decryption keys associated with the player. Thus, if a given player's keys are compromised and published, the AACS LA can simply revoke those keys in future content,
AACS also incorporates [[traitor tracing]] techniques. The standard allows for multiple versions of short sections of a movie to be encrypted with different keys, while a given player will only be able to decrypt one version of each section. The manufacturer embeds varying [[Digital watermarking|digital watermarks]] (such as [[Cinavia]]) in these sections, and upon subsequent analysis of the pirated release the compromised keys can be identified and revoked (this feature is called ''Sequence keys'' in the AACS specifications).<ref>{{cite web |author=Hongxia Jin |author2=Jeffery Lotspiech |author3-link=Nimrod Megiddo |author3=Nimrod Megiddo |title=Efficient Traitor Tracing |date=4 October 2006 |url=http://domino.watson.ibm.com/library/cyberdig.nsf/papers/AF8C220CB33D5A98852571FF00570458/$File/rj10390.pdf |access-date=2 May 2007 |archive-date=5 February 2012 |archive-url=https://web.archive.org/web/20120205202528/http://domino.watson.ibm.com/library/cyberdig.nsf/papers/AF8C220CB33D5A98852571FF00570458/$File/rj10390.pdf |url-status=live }}</ref><ref>{{cite web
|title = AACS Reference: Pre-recorded Video Book
|url = http://www.aacsla.com/specifications/specs091/AACS_Spec_Prerecorded_0.91.pdf
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=== Volume IDs ===
Volume IDs are unique identifiers or [[serial number]]s that are stored on pre-recorded discs with special hardware. They cannot be duplicated on consumers' [[Blu-ray Disc recordable|recordable media]]. The point of this is to prevent simple bit-by-bit copies, since the Volume ID is required (though not sufficient) for decoding content. On Blu-ray discs, the Volume ID is stored in the [[ROM-Mark|BD-ROM Mark]].<ref>{{cite web |url=http://www.aacsla.com/specifications/AACS_Spec_BD_Prerecorded_0.912.pdf |title=Blu-ray Disc Pre-recorded Book |access-date=1 November 2007 |date=27 July 2006 |publisher=AACS LA |page=15 |archive-url=https://web.archive.org/web/20071106065659/http://www.aacsla.com/specifications/AACS_Spec_BD_Prerecorded_0.912.pdf |archive-date=6 November 2007 |url-status=dead}}</ref>
To read the Volume ID, a cryptographic [[Public key certificate|certificate]] (the ''Private Host Key'') signed by the AACS LA is required. However, this has been circumvented by modifying the firmware of some HD DVD and Blu-ray drives.<ref name=arstechnica-aacs>{{cite web
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=== Decryption process ===
To view the movie, the player must first decrypt the content on the disc. The decryption process is somewhat convoluted. The disc contains 4 items—the Media Key Block (MKB), the Volume ID, the [[Encrypted Title Key|Encrypted Title Keys]], and the Encrypted Content. The MKB is encrypted in a subset difference tree approach. Essentially, a set of keys are arranged in a tree such that any given key can be used to find every other key except its parent keys. This way, to revoke a given [[Device Keys|device key]], the MKB needs only be encrypted with that device key's parent key.
Once the MKB is decrypted, it provides the Media Key, or the ''km''. The ''km'' is combined with the Volume ID (which the program can only get by presenting a cryptographic certificate to the drive, as described above) in a one-way encryption scheme (AES-G) to produce the Volume Unique Key (''Kvu''). The ''Kvu'' is used to decrypt the encrypted title keys, and that is used to decrypt the encrypted content.<ref name=arstechnica-aacs /><ref>{{cite web
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=== Audio watermarking ===
On 5 June 2009, the licensing agreements for AACS were finalized, which were updated to make [[Cinavia]] [[audio watermark]] detection on commercial Blu-ray disc players a requirement.<ref>{{Cite press release | title = AACS Issues Final Agreements, Enabling Commercial Deployment of Cinavia in Blu-ray Disc Players | publisher = Verance | date = 5 June 2009 | url = http://www.verance.com/AdminSavR/news/news_item.php?news_id=42 | access-date = 11 October 2010 | archive-url = https://web.archive.org/web/20091009025320/http://www.verance.com/AdminSavR/news/news_item.php?news_id=42 | archive-date = 9 October 2009 | url-status = dead | df = dmy-all }}</ref>
===Managed Copy===
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|title=HD DVD, Blu-ray "Managed Copy" coming later this year
|work=arstechnica.com
|date=24 May 2007
|access-date=29 June 2010
| archive-url= https://web.archive.org/web/20100526040122/http://arstechnica.com/gadgets/news/2007/05/hd-dvd-blu-ray-managed-copy-coming-later-this-year.ars| archive-date= 26 May 2010 | url-status= live}}</ref>
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== History ==
On 24 February 2001, Dalit Naor, Moni Naor and Jeff Lotspiech published a paper entitled "Revocation and Tracing Schemes for Stateless Receivers", where they described a [[broadcast encryption]] scheme using a construct called Naor-Naor-Lotspiech subset-difference trees. That paper laid the theoretical foundations of AACS.<ref>{{cite web|url=http://www.playfuls.com/news_05648_HD_DVDs_AACS_Protection_Bypassed_In_Only_8_Days.html |title=HD DVD's AACS Protection Bypassed. In Only 8 Days?! |access-date=25 October 2007 |author=Dan Nicolae Alexa |date=28 December 2006 |work=playfuls.com |url-status=dead |archive-url=https://web.archive.org/web/20080210005229/http://www.playfuls.com/news_05648_HD_DVDs_AACS_Protection_Bypassed_In_Only_8_Days.html |archive-date=10 February 2008 }}</ref>
The AACS LA consortium was founded in 2004.<ref>{{cite magazine |url=http://archive.wired.com/entertainment/music/news/2004/07/64212 |title=Can Odd Alliance Beat Pirates? |access-date=20 January 2015 |author
|url = http://www.spectrum.ieee.org/jan05/2703
|title = Loser: DVD Copy Protection, Take 2
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|archive-date = 8 June 2007
|url-status = dead
}}</ref> The final AACS standard was delayed,<ref>{{cite web|url=http://www.pcworld.com/article/id,123924-page,1/article.html |title=Toshiba Hints at HD-DVD Delay |access-date=19 October 2007 |author=Martyn Williams |date=14 December 2005 |work=pcworld.com |archive-url=https://web.archive.org/web/20071005171717/http://www.pcworld.com/article/id%2C123924-page%2C1/article.html |archive-date=5 October 2007 |url-status=live }}</ref> and then delayed again when an important member of the Blu-ray group voiced concerns.<ref>{{cite web |url=http://www.heise.de/english/newsticker/news/69559 |title=AACS copy protection for Blu-ray disc and HD DVD delayed again |access-date=19 October 2007 |author =Craig Morris |date=14 February 2006 |work=heise.de | archive-url= https://web.archive.org/web/20071102222432/http://www.heise.de/english/newsticker/news/69559| archive-date= 2 November 2007 | url-status= live}}</ref> At the request of Toshiba, an interim standard was published which did not include some features, like managed copy.<ref name=pcworld-burning-questions /> On July 5, 2009 the license of AACS1 went online.<ref>{{Cite web |last=Calonge |first=Juan |date=8 June 2009 |title=AACS Final License Goes Online |url=https://www.blu-ray.com/news/?id=2849 |access-date=11 March 2023 |website=blu-ray.com |archive-date=11 March 2023 |archive-url=https://web.archive.org/web/20230311133556/https://www.blu-ray.com/news/?id=2849 |url-status=live }}</ref>▼
}}</ref>▼
▲The final AACS standard was delayed,<ref>{{cite web|url=http://www.pcworld.com/article/id,123924-page,1/article.html |title=Toshiba Hints at HD-DVD Delay |access-date=19 October 2007 |author=Martyn Williams |date=14 December 2005 |work=pcworld.com |archive-url=https://web.archive.org/web/20071005171717/http://www.pcworld.com/article/id%2C123924-page%2C1/article.html |archive-date=5 October 2007 |url-status=live }}</ref> and then delayed again when an important member of the Blu-ray group voiced concerns.<ref>{{cite web |url=http://www.heise.de/english/newsticker/news/69559 |title=AACS copy protection for Blu-ray disc and HD DVD delayed again |access-date=19 October 2007 |author =Craig Morris |date=14 February 2006 |work=heise.de | archive-url= https://web.archive.org/web/20071102222432/http://www.heise.de/english/newsticker/news/69559| archive-date= 2 November 2007 | url-status= live}}</ref> At the request of Toshiba, an interim standard was published which did not include some features, like managed copy.<ref name=pcworld-burning-questions /> On July 5, 2009 the license of AACS1 went online.<ref>{{Cite web |last=Calonge |first=Juan |date=8 June 2009 |title=AACS Final License Goes Online |url=https://www.blu-ray.com/news/?id=2849 |access-date=11 March 2023 |website=blu-ray.com}}</ref>
==Unlicensed decryption==
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| access-date = 3 May 2007
|date=24 January 2007
| work = Engadget| archive-url= https://web.archive.org/web/20070516060453/http://www.engadget.com/2007/01/24/backupbluray-available-now-too/| archive-date= 16 May 2007 | url-status= live}}</ref> Blu-ray Copy is a program capable of copying Blu-rays to the [[hard drive]] or to blank BD-R discs.<ref>{{cite news|title=Get Blu-ray Copy (Win) for free|url=http://reviews.cnet.com/8301-33153_7-57468788-10391733/get-blu-ray-copy-win-for-free/|first=Rick|last=Broida|date=9 July 2012|work=[[CNET]]|access-date=18 July 2013|archive-date=26 July 2013|archive-url=https://web.archive.org/web/20130726081316/http://reviews.cnet.com/8301-33153_7-57468788-10391733/get-blu-ray-copy-win-for-free/|url-status=live}}</ref>
==Security==
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| title = HD-DVD Content Protection already hacked?
| work = TechAmok
| date = 28 December 2006
| access-date = 2 January 2007
| archive-date = 10 September 2023
| archive-url = https://web.archive.org/web/20230910210905/http://www.techamok.com/?pid=1849
| url-status = live
}}</ref><ref>{{cite news
| url = http://news.bbc.co.uk/2/hi/technology/6301301.stm
| title = Hi-def DVD security is bypassed
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|title=WinDVD 8 Device Key Found!
|access-date=4 May 2007
|author
|date=24 February 2007
|work=Doom9.net forums
|archive-date=21 June 2007
|archive-url=https://web.archive.org/web/20070621014631/http://forum.doom9.org/showthread.php?t=122664
|url-status=live
▲}}</ref>
(used to calculate the Processing Key) and a Host Private Key<ref>{{cite web
|url=http://forum.doom9.org/showthread.php?t=122969
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|url=http://www.chillingeffects.org/notice.cgi?sID=3218
|title=AACS licensor complains of posted key
|access-date=2 May 2007
|archive-date=1 May 2007
|archive-url=https://web.archive.org/web/20070501142633/http://www.chillingeffects.org/notice.cgi?sID=3218
|url-status=live
}}</ref>
Some sites that rely on user-submitted content, like [[Digg]] and Wikipedia, tried to remove any mentions of the key.<ref>{{cite magazine
|url=http://blog.wired.com/business/2007/05/wikipedia_locks.html
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The AACS key extractions highlight the inherent weakness in any DRM system that permit software players for PCs to be used for playback of content. No matter how many layers of encryption are employed, it does not offer any true protection, since the keys needed to obtain the unencrypted content stream must be available somewhere in memory for playback to be possible. The PC platform offers no way to prevent memory snooping attacks on such keys, since a PC configuration can always be emulated by a [[virtual machine]], in theory without any running program or external system being able to detect the virtualization. The only way to wholly prevent attacks like this would require changes to the PC platform (see [[Trusted Computing]]) which could provide protection against such attacks. This would require that content distributors do not permit their content to be played on PCs without trusted computing technology, by not providing the companies making software players for non-trusted PCs with the needed encryption keys.
On 16 April 2007, the AACS consortium announced that it had expired certain encryption keys used by PC-based applications. Patches were available for [[WinDVD]] and [[PowerDVD]] which used new and uncompromised encryption keys.<ref>
{{cite web| url= http://www.aacsla.com/press/| title= Press Messages: AACS – Advanced Access Content System| access-date= 2 May 2007| archive-url= https://web.archive.org/web/20070430070403/http://www.aacsla.com/press/| archive-date= 30 April 2007| url-status= dead| df= dmy-all}}
</ref><ref>
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}}
</ref>
The AACS LA has sent [[DMCA takedown notice]]s to such sites on at least one occasion.<ref>{{cite web
|url=http://forum.doom9.org/attachment.php?attachmentid=7071&d=1176327932
|title=Illegal Offering of Title/Volume Keys to Circumvent AACS Copyright Protection: hdkeys.com
|format=pdf
|access-date=29 May 2007
|author
|date=5 April 2007
|work=DMCA takedown notice
|archive-date=26 September 2007
|archive-url=https://web.archive.org/web/20070926213835/http://forum.doom9.org/attachment.php?attachmentid=7071&d=1176327932
|url-status=live
}}</ref>
There is also commercial software ([[AnyDVD|AnyDVD HD]]) that can circumvent the AACS protection. Apparently this program works even with movies released after the AACS LA expired the first batch of keys.<ref>
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|work=US Patent Office
|display-authors=etal}}
</ref> and "Digital signatures on a Smartcard."<ref>{{cite web
|url=https://patents.google.com/patent/US6704870
|title=Digital signatures on a Smartcard
|access-date=31 May 2007
|author
|date=29 August 2001
|work=US Patent Office
|display-authors=etal
|archive-date=27 March 2019
</ref> The patents were filed in 1999 and 2001 respectively, and in 2003 the [[National Security Agency]] paid $25 million for the right to use 26 of Certicom's patents, including the two that Sony is alleged to have infringed on.<ref>▼
|archive-url=https://web.archive.org/web/20190327011204/https://patents.google.com/patent/US6704870
|url-status=live
▲}}</ref> The patents were filed in 1999 and 2001 respectively, and in 2003 the [[National Security Agency]] paid $25 million for the right to use 26 of Certicom's patents, including the two that Sony is alleged to have infringed on.<ref>
{{cite web
|url=https://arstechnica.com/news.ars/post/20070531-encryption-vendor-claims-aacs-infringes-its-patents-sues-sony.html
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| date=2009-05-27
| publisher=justia.com
| access-date=2013-08-12
| archive-date=18 September 2020
| archive-url=https://web.archive.org/web/20200918180848/https://dockets.justia.com/docket/texas/txedce/2:2007cv00216/103383
| url-status=live
}}</ref>
==See also==
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==External links==
{{wikinews|High definition anti-piracy DRM possibly hacked}}
* [https://web.archive.org/web/20100306013059/http://www.aacsla.com/home Old AACS homepage]
* [https://www.aacsla.com Current AACS homepage]
* [https://web.archive.org/web/20070128110342/http://www.aacsla.com/specifications/ AACS specifications]
* [http://forum.doom9.org/showthread.php?t=122363 Understanding AACS], an introductory forum thread. {{Webarchive|url=https://web.archive.org/web/20120205101739/http://forum.doom9.org/showthread.php?t=122363|date=dmy}} with the diagrams working.
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