The Media Key Block (MKB) is one of the keys included inside the copying protection system (
DRM
DRM may refer to:
Government, military and politics
* Defense reform movement, U.S. campaign inspired by Col. John Boyd
* Democratic Republic of Madagascar, a former socialist state (1975–1992) on Madagascar
* Direction du renseignement militai ...
)
AACS. This system is used to prevent
Blu-ray
The Blu-ray Disc (BD), often known simply as Blu-ray, is a digital optical disc data storage format. It was invented and developed in 2005 and released on June 20, 2006 worldwide. It is designed to supersede the DVD format, and capable of sto ...
and
HD DVD
HD DVD (short for High Definition Digital Versatile Disc) is an obsolete high-density optical disc format for storing data and playback of high-definition video. Supported principally by Toshiba, HD DVD was envisioned to be the successor to th ...
formats from being copied. The system was developed by companies from the film industry and the electronics industry including
IBM,
Intel
Intel Corporation is an American multinational corporation and technology company headquartered in Santa Clara, California. It is the world's largest semiconductor chip manufacturer by revenue, and is one of the developers of the x86 seri ...
,
Microsoft
Microsoft Corporation is an American multinational technology corporation producing computer software, consumer electronics, personal computers, and related services headquartered at the Microsoft Redmond campus located in Redmond, Washing ...
,
Matsushita (Panasonic),
Sony
, commonly stylized as SONY, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan. As a major technology company, it operates as one of the world's largest manufacturers of consumer and professional ...
,
Toshiba
, commonly known as Toshiba and stylized as TOSHIBA, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan. Its diversified products and services include power, industrial and social infrastructure system ...
,
The Walt Disney Company
The Walt Disney Company, commonly known as Disney (), is an American multinational mass media and entertainment conglomerate headquartered at the Walt Disney Studios complex in Burbank, California. Disney was originally founded on October ...
and
Warner Bros.
Warner Bros. Entertainment Inc. (commonly known as Warner Bros. or abbreviated as WB) is an American film and entertainment studio headquartered at the Warner Bros. Studios complex in Burbank, California, and a subsidiary of Warner Bros. Di ...
The MKB key is found in the physical support (the disc) together with the content of the disc encrypted. The ''MKB'' has the function of validating the reproduction devices on which the disc is being played and obtaining, from the devices codes, the key that will allow the decryption of the disc content. That is the
Media Key (
). , version 78 has been the most recent MKB version.
How it works
''Blu-Ray'' or ''HD-DVD'' have as content the encrypted data (usually video), the
Volume ID (VID), the
Encrypted Title Key(s) and the ''MKB''. The ''MKB'' is also found encrypted in the disc to prevent it from being extracted off the disc and being manipulated and/or reproduced by another non authorized device.
![MKB obtencion](https://upload.wikimedia.org/wikipedia/commons/4/40/MKB_obtencion.jpg)
The reproduction device will have available its own keys, uniques for each model, called
Device Keys
Device Keys play a role in the cryptographic key management procedure in the Advanced Access Content System (AACS) specification. This specification defines a method for protecting audiovisual entertainment content, including high-definition conte ...
. These keys are conceded by the ''AACS'' organization. In the moment of the reproduction, one of these keys will decrypt the ''MKB'' contained on the disc and as a result of this process we obtain the ''Media key''.
The ''Media key'' is combined with the ''VID'' (Volume ID) and as a result we obtain the
Volume Unique Key (
). With the
we are able to decrypt the ''Encrypted Title Key'' and obtain the
Title keys which finally allows to decrypt the content of the disc and view it.
This way the system can prevent contents from being viewed in devices that have not been authorized. Therefore, the system allows modifying the ''MKB'' in future relaunch of a determined content in order to select the devices in which this content can be viewed.
Key structure
Even though it seems a simple mechanism the ''MKB'' key which is found in the physical support of the disc follows a complex structure. The ''MKB'' is distributed in blocks that contain the version of the ''Media key'', the list of devices that have been revoked, a field to authenticate the ''MKB'', and other fields that specify parameters corresponding to the decrypting algorithm and define the structure of the own ''Media Key'' and also the ''Media key'' itself.
The ''MKB'' itself is found inside the field Media Key Data Record and has a variable length but it is always a multiple of 4 bytes.
Advantages and disadvantages
Many consumer associations have complained against this system since it can lead to a situation where physical devices cannot reproduce contents even though they do not infringe any
intellectual property
Intellectual property (IP) is a category of property that includes intangible creations of the human intellect. There are many types of intellectual property, and some countries recognize more than others. The best-known types are patents, cop ...
. This situation can be achieved either by trying to reproduce some content in old devices, therefore not certified by the ''AACS'', or because the device model has been disallowed by AACS, as a result all the owners of that device model will not be able to view contents encrypted with the ''MKB''.
This situation has become even worse with the recent publication in multiple web sites of the Media Key, that is, the key that allows decrypting the ''Volume ID''
and at the same time, the encrypted content, without the need of using a certified device by the AACS or a valid MKB. This is especially critical because nowadays the Volume ID is the same in all the Blu-ray or HD-DVDs with equal content.
References
{{Reflist
External links
AACS web page.Guide to understand AACS.Introduction and Common Cryptographic Elements.Rev. 0.91.
AACS Technical Overview.7/2004.
Key management
Advanced Access Content System