View source for Security of Advanced Access Content System

The '''security of [[Advanced Access Content System]]''' (AACS) has been a subject of discussion amongst security researchers, high definition video enthusiasts, and consumers at large since its inception. A successor to [[Content Scramble System]] (CSS), the [[digital rights management]] mechanism used by commercial [[DVD]]s, AACS was intended to improve upon the design of CSS by addressing flaws which had led to the [[DeCSS|total circumvention of CSS]] in 1999. The AACS system relies on a [[Tree (set theory)|subset difference tree]] combined with a [[certificate revocation]] mechanism to ensure the security of high definition video content in the event of a compromise.

Even before AACS was put into use, security researchers expressed doubts about the system's ability to withstand attacks.

[[Image:AACS dataflow.svg|right|thumb|AACS decryption process]]

==Comparison of CSS and AACS==

{| class="wikitable" 
|- style="background:Gainsboro;font-size: 115%;height:30px;"
!
! [[Content Scramble System]]
! [[Advanced Access Content System]]
|-
| style="background:#EAEAEA;"| '''[[Cryptography|Algorithm]]'''
| Proprietary [[Linear-feedback shift register|LFSR]]-based
| [[Advanced Encryption Standard|AES]]
|-
| style="background:#EAEAEA;"| '''[[Key size|Key strength]]'''
| 40-bit
| 128-bit
|-
| style="background:#EAEAEA;"| '''[[Certificate revocation]]'''
| No
| Yes
|}

==History of attacks==
{{wikinews|High definition anti-piracy DRM possibly hacked}}

The AACS proposal was voted one of the technologies most likely to fail by ''[[IEEE Spectrum]]'' magazine's readers in the January 2005 issue.<ref>{{cite web
 |url         = http://www.spectrum.ieee.org/jan05/2703
 |title       = Loser: DVD Copy Protection, Take 2
 |accessdate  = 2007-05-04
 |author      = Tekla S. Perry
 |date        = January 2007
 |work        = Spectrum Online
 |url-status     = dead
 |archiveurl  = https://web.archive.org/web/20070608074811/http://spectrum.ieee.org/jan05/2703
 |archivedate = 2007-06-08
}}</ref> 
Concerns about the approach included its similarity to past systems that failed, such as CSS, and the inability to preserve security against attacks that compromise large numbers of players. [[Jon Lech Johansen]], who was part of the team that circumvented CSS, said he expected AACS to be cracked by the end of 2006 or the beginning of 2007.<ref>{{cite web 
| url = http://nanocrew.net/2006/01/08/deaacscom/ 
| title = DeAACS.com 
| accessdate = 2007-05-04 
| last = Johansen 
| first = Jon Lech 
| date = 2006-01-08 
|work=So sue me}}</ref>
 
In late 2006, security expert [[Peter Gutmann (computer scientist)|Peter Gutmann]] released "''A Cost Analysis of Windows Vista Content Protection''", a technical paper criticizing the implementation of various content protection technologies in [[Windows Vista]].<ref name=vista-cost>{{cite web 
| author = Peter Gutmann
| date = 2006-12-26 
| title = A Cost Analysis of Windows Vista Content Protection 
| url = http://www.cs.auckland.ac.nz/~pgut001/pubs/vista_cost.html 
| accessdate = 2007-01-28 
| authorlink = Peter Gutmann (computer scientist) }}</ref>
{{cquote|
Providing this protection incurs considerable costs in terms of system performance, system stability, technical support overhead, and hardware and software cost.  These issues affect not only users of Vista but the entire PC industry, since the effects of the protection measures extend to cover all hardware and software that will ever come into contact with Vista, even if it's not used directly with Vista (for example hardware in a Macintosh computer or on a Linux server).
}}

Microsoft later claimed that the paper contained various factual errors.<ref>{{cite web|url=http://windowsvistablog.com/blogs/windowsvista/archive/2007/01/20/windows-vista-content-protection-twenty-questions-and-answers.aspx|title=Windows Vista Content Protection - Twenty Questions (and Answers)|url-status=dead|archiveurl=https://web.archive.org/web/20130121121652/http://blogs.windows.com/windows/archive/b/windowsvista/archive/2007/01/20/windows-vista-content-protection-twenty-questions-and-answers.aspx|archivedate=2013-01-21}}</ref><ref>[[Peter Gutmann (computer scientist)#Criticism of Peter Gutmann.27s analysis of Vista DRM]]</ref>

While great care had been taken with AACS to ensure that content was encrypted along the entire path from the disc to the [[display device]], it was discovered in July 2006 that a perfect copy of any still frame from a film could be captured from certain [[Blu-ray]] and [[HD DVD]] software players by using the [[Print Screen]] function of the Windows [[operating system]].<ref>{{cite web 
| url = http://hardware.slashdot.org/article.pl?sid=06/07/07/1255224 
| title = Work Around for New DVD Format Protections 
| date = 2006-06-07 
| accessdate = 2007-05-02 
| work = [[Slashdot]]}}</ref>
<ref>{{cite web 
| url =  http://www.heise-online.co.uk/security/Copy-protection-hole-in-Blu-ray-and-HD-DVD-movies--/news/75103 
| title = Copy protection hole in Blu-ray and HD DVD movies 
| accessdate = 2007-05-02 
| date = 2006-07-07 
| author = Edward Henning ("ehe") 
| work = heise Security}}</ref>
It was suggested that this approach could be automated to allow a perfect copy of an entire film to be made, in much the same way that DVD films were copied before the CSS was cracked, but to date no such copy has been discovered. This exploit has been closed in subsequent software versions.

Such approaches do not constitute compromises of the AACS encryption itself, relying instead on an officially licensed software player to perform the decryption. As such, the output data will not be in the form of the compressed video from the disc, but rather decompressed video. This is an example of the [[analog hole]].

Both title keys and one of the keys used to decrypt them (known as ''Processing Keys'' in the AACS specifications) have been found by using debuggers to inspect the memory space of running HD-DVD and Blu-ray player programs.<ref>{{cite web 
|  url = http://www.techamok.com/?pid=1849 
| title = HD-DVD Content Protection already hacked? 
| work = TechAmok 
| date = 2006-12-28 
| accessdate = 2007-01-02 }}</ref><ref>{{cite web 
| url = http://news.bbc.co.uk/2/hi/technology/6301301.stm 
| title = Hi-def DVD security is bypassed 
| date = 2007-01-26 
|accessdate=2007-05-02 
|work=[[BBC News]]}}</ref><ref>{{cite web 
| last = Block 
| first = Ryan 
| url = https://www.engadget.com/2007/01/20/blu-ray-cracked-too/ 
| title = Blu-ray cracked too? 
| date = 2007-01-20 
| accessdate = 2007-01-22 
|work=Engadget }}</ref><ref>{{cite web 
| url = https://www.theregister.co.uk/2007/01/23/blu-ray_drm_cracked/ 
| first = John 
| last = Leyden 
| work = The Register 
| title = Blu-ray DRM defeated 
| date = 2007-01-23 
| accessdate = 2007-01-22}}</ref>
Hackers also found Device Keys,<ref>{{cite web 
|url=http://forum.doom9.org/showthread.php?t=122664 
|title=WinDVD 8 Device Key Found! 
|accessdate=2007-05-04 
|author=ATARI Vampire 
|date=2007-02-24 
|work=Doom9.net forums}}</ref>
which are used to calculate the Processing Key, and a Host Private Key<ref>{{cite web 
|url=http://forum.doom9.org/showthread.php?t=122969 
|title=PowerDVD private key 
|accessdate=2007-05-04 
|author=jx6bpm 
|date=2007-03-03 
|work=Doom9.net forums}}</ref>
(a key signed by the AACS LA used for hand-shaking between host and HD drive; required for reading the Volume ID). The first unprotected HD DVD movies appeared on [[BitTorrent tracker]]s soon afterwards.<ref>{{cite web 
|url=http://www.dailytech.com/article.aspx?newsid=5747 
|title=First Pirated HD DVDs Released 
|accessdate=2007-05-03 
|first=Marcus 
|last=Yam 
|date=2007-01-17 
|work=DailyTech 
|archive-date=2007-02-19 
|archive-url=https://web.archive.org/web/20070219103102/http://www.dailytech.com/article.aspx?newsid=5747 
|url-status=dead 
}}</ref> 
The Processing Key for the first Media Key Block version, which could be used to decrypt any AACS protected content released up to that point, was found and published on the Internet at the [[Doom9]] forums. AACS Licensing Authority sent multiple [[DMCA takedown notice]]s to web sites hosting the key.<ref>{{cite web 
|url=http://www.chillingeffects.org/notice.cgi?sID=3218 
|title=AACS licensor complains of posted key 
|accessdate=2007-05-02}}</ref> 
Some administrators of sites which consist of user-submitted content, such as [[Digg]] and [[Wikipedia]], tried to remove mentions of the key fearing reprisals from AACS LA.<ref>{{cite web 
|url=http://blog.wired.com/business/2007/05/wikipedia_locks.html 
|title=Wikipedia Locks Out "The Number" 
|first=Paul 
|last=Boutin 
|accessdate=2007-05-02 
|date=2007-05-01 }}</ref>
<ref>{{cite web 
|title=Digg's DRM Revolt 
|first=Andy 
|last=Greenberg 
|date=2007-05-02
|work=[[Forbes]]
|url=https://www.forbes.com/technology/2007/05/02/digital-rights-management-tech-cx_ag_0502digg.html 
|accessdate=2007-05-04|archiveurl=https://web.archive.org/web/20070504173353/http://www.forbes.com/technology/2007/05/02/digital-rights-management-tech-cx_ag_0502digg.html|archivedate=2007-05-04}}</ref> 
Both sites' administrators eventually decided to allow publication of the key.<ref>{{cite web 
|url=http://news.bbc.co.uk/2/hi/technology/6615047.stm 
|title=DVD DRM row sparks user rebellion 
|accessdate = 2007-05-02 
|date=2007-05-02 
|work=[[BBC News]]}}</ref>

{{Further|AACS encryption key controversy}}

[[Cyberlink]], the company which sells the [[PowerDVD]] player, stated that their software could not have been used as part of these exploits.<ref>{{cite web
 |date        = 2007-01-02
 |first       = Chris
 |last        = Lanier
 |url         = http://msmvps.com/blogs/chrisl/archive/2007/01/02/463980.aspx
 |title       = Cyberlink Responds to Alleged AACS Crack
 |accessdate  = 2007-05-02
 |url-status     = dead
 |archiveurl  = https://web.archive.org/web/20070616212554/http://msmvps.com/blogs/chrisl/archive/2007/01/02/463980.aspx
 |archivedate = 2007-06-16
}}</ref>

On April 16, 2007, the AACS consortium announced that it had revoked the Device Keys used by both Cyberlink PowerDVD and InterVideo [[WinDVD]], and patches were made available for users which provided uncompromised encryption keys and better security for the keys.<ref>{{cite web 
|url=http://www.aacsla.com/press/ 
|title=Press Messages: AACS - Advanced Access Content System 
|accessdate=2007-05-02 
|archive-date=2007-04-30 
|archive-url=https://web.archive.org/web/20070430070403/http://www.aacsla.com/press/ 
|url-status=dead 
}}</ref>
<ref>{{cite web 
|url=http://dailytech.com/AACS+Responds+to+Cracked+HD+DVD+and+Bluray+Disc+Protections/article5879.htm 
|title=AACS Responds to Cracked HD DVD and Blu-ray Disc Protections 
|accessdate=2007-05-03 
|first=Marcus 
|last=Yam 
|date=2007-01-26 
|work=DailyTech }}</ref>
To continue having the ability to view new content users were forced to apply the patches, which also hardened the security of player applications.

On 23 May 2007 the Processing Key for the next version of the Media Key Block was posted to the comments page of a Freedom to Tinker blog post.<ref>{{cite web
 |url         = http://www.freedom-to-tinker.com/?p=1155
 |title       = You Can Own an Integer Too
 |accessdate  = 2007-06-09
 |url-status     = bot: unknown
 |archiveurl  = https://web.archive.org/web/20070824092116/http://www.freedom-to-tinker.com/?p=1155#comment-367359
 |archivedate = 2007-08-24
}}  (original link dead)</ref>

The use of encryption does not offer any true protection against memory snooping, since the software player must have the encryption key available somewhere in memory and there is no way to protect against a determined PC owner extracting the encryption key (if everything else fails the user could run the program in a [[virtual machine]] making it possible to freeze the program and inspect all memory addresses without the program knowing).

The only way to wholly prevent attacks like this would require changes to the PC platform (see [[Trusted Computing]]) or that the content distributors do not permit their content to be played on PCs at all (by not providing the companies making software players with the needed encryption keys).

On January 15, 2007 a website launched at HDKeys.com containing a database of HD DVD title keys. It also featured a modified copy of the BackupHDDVD software allowing for online key retrieval (the latter was later removed after a [[DMCA]] complaint).

[[SlySoft]] has released [[AnyDVD]] HD which allows users to watch HD DVD and Blu-ray movies on non-[[HDCP]]-compliant PC hardware. The movies can be decrypted on the fly directly from the disc, or can be copied to another medium. AnyDVD HD is also capable of automatically removing any unwanted logos and trailers. Slysoft has stated that AnyDVD HD uses several different mechanisms to disable the encryption, and is not dependent on the use of compromised encryption keys. They have also stated that AACS has even more flaws in its implementation than CSS; this renders it highly vulnerable,<ref>{{cite web
 |url         = http://forum.slysoft.com/showpost.php?s=dd10095bbb7307dcbb16168166d2087e&p=9286&postcount=2
 |title       = Device key revokation
 |accessdate  = 2007-04-09
 |date        = 2007-02-13
 |author      = peer
 |work        = Slysoft forums
 |url-status     = dead
 |archiveurl  = https://web.archive.org/web/20070927092642/http://forum.slysoft.com/showpost.php?s=dd10095bbb7307dcbb16168166d2087e&p=9286&postcount=2
 |archivedate = 2007-09-27
}}</ref> 
but they will release no details on their implementation.  Users at Doom9 claim that the program makes use of the host certificate of [[PowerDVD]] version 6.5,<ref>{{cite web 
| url = http://forum.doom9.org/showthread.php?t=122272 
| title = AnyDVD method of operation 
| accessdate = 2007-04-09 
| date = 2007-02-15
| author = evdberg 
| work = Doom9.net Forums }}</ref> 
but SlySoft has claimed that the program would be unaffected by the AACS revocation system.<ref>{{cite web
 |url         = http://forum.slysoft.com/showpost.php?p=15263&postcount=10
 |title       = And after the process. key is revoked?
 |accessdate  = 2007-04-09
 |date        = 2007-03-02
 |author      = James
 |work        = Slysoft forums
 |url-status     = dead
 |archiveurl  = https://web.archive.org/web/20070927092544/http://forum.slysoft.com/showpost.php?p=15263&postcount=10
 |archivedate = 2007-09-27
}}</ref>

=== Media key block renewals ===
{{Expand section|with=missing details, especially media key blocks #13–#64|small=no|date=December 2022}}
{| class="wikitable"
|-
! Version
! First titles
! Date released
! Date circumvented
|-
| [[AACS encryption key controversy|1]]
| ''[[The Last Samurai]]'', ''[[Million Dollar Baby]]''
| 2006-04-18
| 2007-02-13<ref>{{cite web |url=http://sww.engadgethd.com/2007/02/13/hackers-discover-hd-dvd-and-blu-ray-processing-key-all-hd-t/ |title=Hackers discover HD DVD and Blu-ray "processing key" -- all HD titles now exposed |accessdate=2007-11-02 |author=Thomas Ricker |date=2007-02-13 |work=engadgethd.com |publisher=}}</ref>
|-
| 2
| colspan="3" | Never used<ref>{{cite web |url=http://forum.doom9.org/showthread.php?p=1009643#post1009643 |title= New Processing Key found!! (MKB v3 is now open) |accessdate=2007-11-02 |author=aKzenT |date=2007-06-01 |work=doom9.org forums}}</ref>
|-
| [[AACS encryption key controversy#2007|3]]
| [[The Matrix Trilogy|The ''Matrix'' Trilogy]]
| 2007-05-22
| 2007-05-17<ref>{{cite web |url=http://www.engadgethd.com/2007/05/17/newest-aacs-circumvented-the-matrix-trilogy-set-free/ |title=Newest AACS circumvented: The Matrix Trilogy set free |accessdate=2007-11-02 |author=Thomas Ricker |date=2007-05-17 |work=engadgethd.com}}</ref>
|-
| [[AACS encryption key controversy#2008|4]]
| ''[[Transformers (film)|Transformers]]'', ''[[Spider-Man 3]]''
|
| 2007-10-30
|-
| 5
| colspan="3" | Never used<ref name="forum.slysoft.com">{{cite web |url=http://forum.slysoft.com/showthread.php?t=15550 |title=AVP: Requiem/Alvin and the Cipmunks logfiles |accessdate=2008-04-09 |author= |date= }}</ref>
|-
| [[AACS encryption key controversy#2008|6]]
| colspan="3" | Never used<ref name="forum.slysoft.com"/>
|-
| [[AACS encryption key controversy#2008|7]]
| ''[[Alvin and the Chipmunks (film)|Alvin and the Chipmunks]]'', ''[[Aliens vs. Predator: Requiem]]''
| 2008-04-06<ref>{{cite web |url=http://forum.slysoft.com/showthread.php?t=15550 |title=AVP: Requiem/Alvin and the Cipmunks logfiles |accessdate=2008-04-09 |author= |date= |publisher=}}</ref>
| 2008-04-11<ref>{{cite web |url=http://forum.slysoft.com/showthread.php?t=15698 |title=AnyDVD (HD) 6.4.1.1 released |accessdate=2008-04-11 |author= |date= |publisher=}}</ref>
|-
| [[AACS encryption key controversy#2008|8]]
| ''[[The Forbidden Kingdom]]''
| 2008-08-26<ref>{{cite web |url=http://forum.slysoft.com/showthread.php?t=19612 |title=The Forbidden Kingdom (2008) - MKBv8 - Update server down?  |accessdate=2008-04-09 |author= |date= |publisher=}}</ref>
| 2008-08-26<ref>{{cite web |url=http://forum.slysoft.com/showthread.php?t=19612 |title=The Forbidden Kingdom (2008) - MKBv8 - Update server down?  |accessdate=2008-04-11 |author= |date= |publisher=}}</ref>
|-
| [[AACS encryption key controversy#2009|9]]
| ?
| Approximately 2008-09-03<ref>{{cite web |url=http://forum.slysoft.com/showthread.php?t=19806&highlight=MKBV9 |title=Blu-ray YELLOW DRAGON'S COLORS Read Error |accessdate=2009-03-28 |author= |date= |publisher=}}</ref>
| 2009-03-20<ref name="MKBvand">{{cite web |url=http://forum.doom9.org/showthread.php?t=145789 |title=MKBv9 and MKBv10 Processing Keys found
|accessdate=2009-03-28 |author= |date= |publisher=}}</ref>
|-
| [[AACS encryption key controversy#2009|10]]
| ?
| ?
| 2009-03-20<ref name="MKBvand" />
|-
| 11
| ?
| ?
| ?
|-
| [[AACS encryption key controversy#2009|12]]
| ''[[Body of Lies (film)|Body of Lies]]'', [[Baraka (film)|Baraka]]
| 2008-10-09
| 2009-04-06<ref>{{cite web |url=http://forum.doom9.org/showpost.php?p=1270338&postcount=156 |title=Disc using MKBv12 decrypted
|accessdate=2009-04-06 |author= |date= |publisher=}}</ref>
|-
| 13
|
|
|
|-
| 14
|
|
|
|-
| 15
|
|
|
|-
| 16
|
|
|
|-
| 17
|
|
|
|-
| 18
|
|
|
|-
|
|
|
|
|-
| 61
|
|
|
|-
| 62
|
|
|
|-
| 63
|
|
|
|-
| 64
|
|
|
|-
| 65
| ?
| Approximately 2018-06-19<ref>{{cite web |url=https://forum.doom9.org/showthread.php?p=1844914#post1844914 |title=Public MKBs |accessdate=2022-12-22 |date=2018-06-19}}</ref>
| ?
|-
| 66
| ?
| Approximately 2018-11-20<ref>{{cite web |url=https://forum.doom9.org/showthread.php?p=1858010#post1858010 |title=Public MKBs |accessdate=2022-12-22 |date=2018-11-20}}</ref>
| ?
|-
| 67
| colspan="3" | Never used<ref name="doom9-post1868374">{{cite web |url=https://forum.doom9.org/showthread.php?p=1868374#post1868374 |title=Public MKBs |accessdate=2022-12-22 |date=2019-03-11}}</ref>
|-
| 68
| ?
| Approximately 2019-03-11<ref name="doom9-post1868374" />
| ?
|-
| 69
| colspan="3" | Never used<ref name="doom9-post1878517">{{cite web |url=https://forum.doom9.org/showthread.php?p=1878517#post1878517 |title=Public MKBs |accessdate=2022-12-22 |date=2019-07-04 |work=doom9.org forums}}</ref>
|-
| 70
| ?
| Approximately 2019-07-04<ref name="doom9-post1878517" />
| ?
|-
| 71
| ?
| ?<ref>{{cite web |url=https://forum.doom9.org/showthread.php?p=1887549#post1887549 |title=Public MKBs |accessdate=2022-12-22 |date=2019-10-15 |work=doom9.org forums |quote=…&nbsp;MKBv71 was identical to MKBv70 as far as HRL/DRL&nbsp;…}}</ref>
| ?
|-
| 72
| ?
| Approximately 2019-10-15<ref name="doom9-post1887549">{{cite web |url=https://forum.doom9.org/showthread.php?p=1887549#post1887549 |title=Public MKBs |accessdate=2022-12-22 |date=2019-10-15 |work=doom9.org forums}}</ref>
| ?
|-
| 73
| colspan="3" | Never used<ref name="doom9-post1906427">{{cite web |url=https://forum.doom9.org/showthread.php?p=1906427#post1906427 |title=Public MKBs |accessdate=2022-12-22 |date=2020-04-05 |work=doom9.org forums}}</ref>
|-
| 74
| colspan="3" | Never used<ref name="doom9-post1906427" />
|-
| 75
| ?
| ?<ref name="doom9-post1970801">{{cite web |url=https://forum.doom9.org/showthread.php?p=1970801#post1970801 |title=Public MKBs |accessdate=2022-12-22 |date=2022-06-24 |work=doom9.org forums |quote=…&nbsp;I found out that MKBv75 does exist. However, HRL/DRL is identical to MKBv72}}</ref>
| ?
|-
| 76
| ?
| Approximately 2020-04-05<ref name="doom9-post1906427" />
| ?
|-
| 77
| ?
| Approximately 2022-06-24<ref name="doom9-post1970801" />
| ?
|-
| 78
| ?
| Approximately 2022-08-02<ref name="doom9-post1972563">{{cite web |url=https://forum.doom9.org/showthread.php?p=1972563#post1972563 |title=Public MKBs |accessdate=2022-12-22 |date=2022-08-02 |work=doom9.org forums}}</ref>
| ?
|}

==See also==
* [[AnyDVD]]

==References==
{{reflist}}

[[Category:Advanced Access Content System]]