Security Of Advanced Access Content System
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Advanced Access Content System The Advanced Access Content System (AACS) is a 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 ...
(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 The Content Scramble System (CSS) is a digital rights management (DRM) and encryption system employed on many commercially produced DVD-Video discs. CSS utilizes a proprietary 40-bit stream cipher algorithm. The system was introduced around ...
(CSS), the
digital rights management Digital rights management (DRM) is the management of legal access to digital content. Various tools or technological protection measures, such as access control technologies, can restrict the use of proprietary hardware and copyrighted works. DRM ...
mechanism used by commercial
DVD The DVD (common abbreviation for digital video disc or digital versatile disc) is a digital optical disc data storage format. It was invented and developed in 1995 and first released on November 1, 1996, in Japan. The medium can store any ki ...
s, AACS was intended to improve upon the design of CSS by addressing flaws which had led to the total circumvention of CSS in 1999. The AACS system relies on a subset difference tree combined with a
certificate revocation In public key cryptography, a public key certificate, certificate may be revoked before it expires, which signals that it is no longer valid. Without revocation, an attacker could exploit such a compromised or misissued certificate until expiry. ...
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.


Comparison of CSS and AACS


History of attacks

The AACS proposal was voted one of the technologies most likely to fail by ''
IEEE Spectrum ''IEEE Spectrum'' is a magazine edited and published by the Institute of Electrical and Electronics Engineers. The first issue of ''IEEE Spectrum'' was published in January 1964 as a successor to ''Electrical Engineering''. In 2010, ''IEEE Spe ...
'' magazine's readers in the January 2005 issue. 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 Jon Lech Johansen (born November 18, 1983, in Harstad, Norway), also known as DVD Jon, is a Norwegian programmer who has worked on reverse engineering data formats. He wrote the DeCSS software, which decodes the Content Scramble System used fo ...
, 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. In late 2006, security expert 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 Windows Vista is a major release of the Windows NT operating system developed by Microsoft. It was the direct successor to Windows XP, released five years earlier, which was then the longest time span between successive releases of Microsoft W ...
. Microsoft later claimed that the paper contained various factual errors. 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 A display device is an output device for presentation of information in visual or tactile form (the latter used for example in tactile electronic displays for blind people). When the input information that is supplied has an electrical signa ...
, it was discovered in July 2006 that a perfect copy of any still frame from a film could be captured from certain
Blu-ray Blu-ray (Blu-ray Disc or BD) is a digital optical disc data storage format designed to supersede the DVD format. It was invented and developed in 2005 and released worldwide on June 20, 2006, capable of storing several hours of high-defin ...
and
HD DVD HD DVD (short for High Density Digital Versatile Disc) is an obsolete high-density optical disc format for storing data and playback of high-definition video.
software players by using the Print Screen function of the Windows
operating system An operating system (OS) is system software that manages computer hardware and software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ...
. 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 The analog hole (also known as the analog loophole or analog gap) is a perceived fundamental and inevitable vulnerability in copy protection schemes for noninteractive works in digital formats which can be exploited to duplicate copy-protected ...
. 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. Hackers also found Device Keys, which are used to calculate the Processing Key, and a Host Private Key (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 A BitTorrent tracker is a special type of server that assists in the communication between peers using the BitTorrent protocol. In peer-to-peer file sharing, a software client on an end-user PC requests a file, and portions of the requested ...
s soon afterwards. 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 Doom9 is a website featuring information on digital audio and video manipulation (mostly video) and digital copyrights. It is also the forum username of the author of the page, an Austrian who was a college student at the time of the creation of ...
forums. AACS Licensing Authority sent multiple
DMCA takedown notice The Online Copyright Infringement Liability Limitation Act (OCILLA) is United States federal law that creates a conditional 'safe harbor' for online service providers (OSP), a group which includes Internet service providers (ISP) and other Inte ...
s to web sites hosting the key. Some administrators of sites which consist of user-submitted content, such as
Digg Digg (stylized in lowercase as digg) is an American news aggregator with a curated front page, aiming to select articles specifically for the Internet audience such as science, trending political issues, and viral phenomenon, viral Internet iss ...
and
Wikipedia Wikipedia is a free content, free Online content, online encyclopedia that is written and maintained by a community of volunteers, known as Wikipedians, through open collaboration and the wiki software MediaWiki. Founded by Jimmy Wales and La ...
, tried to remove mentions of the key fearing reprisals from AACS LA. Both sites' administrators eventually decided to allow publication of the key.
Cyberlink CyberLink Corp. () is a Taiwanese multimedia software company headquartered in New Taipei City, Taiwan. Its products include PC and mobile applications for playback of movies and media, editing of videos and photos, and disc burning and backup s ...
, the company which sells the
PowerDVD PowerDVD is a media player software for Microsoft Windows created by CyberLink, for DVD movie discs, Blu-ray movie discs, and digital video files, photos and music. PowerDVD is offered in various versions, which vary greatly in terms of fun ...
player, stated that their software could not have been used as part of these exploits. On April 16, 2007, the AACS consortium announced that it had revoked the Device Keys used by both Cyberlink PowerDVD and InterVideo
WinDVD WinDVD (owned by Alludo, formerly Corel Corporation, which acquired InterVideo in 2006) is a commercial DVD video player software for Microsoft Windows. Features and functions Features and functions supported by InterVideo WinDVD version 8.0 du ...
, and patches were made available for users which provided uncompromised encryption keys and better security for the keys. 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. 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 In computing, a virtual machine (VM) is the virtualization or emulator, emulation of a computer system. Virtual machines are based on computer architectures and provide the functionality of a physical computer. Their implementations may involve ...
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 Trusted Computing (TC) is a technology developed and promoted by the Trusted Computing Group. The term is taken from the field of trusted systems and has a specialized meaning that is distinct from the field of confidential computing. With Trust ...
) 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 The Digital Millennium Copyright Act (DMCA) is a 1998 United States copyright law that implements two 1996 treaties of the World Intellectual Property Organization (WIPO). It criminalizes production and dissemination of technology, devices, or ...
complaint).
SlySoft RedFox (formerly SlySoft) was a software development company based in Belize. The company is most prominently known for its software AnyDVD, which can be used to bypass copy protection measures on optical media, including DVD and Blu-ray Disc ...
has released
AnyDVD AnyDVD is a device driver for Microsoft Windows which allows decryption of DVDs on the fly, as well as targeted removal of copy preventions and user operation prohibitions (UOPs). With an upgrade, it will also do the same for HD DVD and Blu-ray ...
HD which allows users to watch HD DVD and Blu-ray movies on non-
HDCP High-bandwidth Digital Content Protection (HDCP) is a form of digital copy protection developed by Intel Corporation to prevent copying of digital audio and video content as it travels across connections. Types of connections include DisplayPort ...
-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, but they will release no details on their implementation. Users at Doom9 claim that the program makes use of the host certificate of
PowerDVD PowerDVD is a media player software for Microsoft Windows created by CyberLink, for DVD movie discs, Blu-ray movie discs, and digital video files, photos and music. PowerDVD is offered in various versions, which vary greatly in terms of fun ...
version 6.5, but SlySoft has claimed that the program would be unaffected by the AACS revocation system.


Media key block renewals


See also

*
AnyDVD AnyDVD is a device driver for Microsoft Windows which allows decryption of DVDs on the fly, as well as targeted removal of copy preventions and user operation prohibitions (UOPs). With an upgrade, it will also do the same for HD DVD and Blu-ray ...


References

{{reflist Advanced Access Content System