Media Key Block

The Media Key Block (MKB) is one of the keys included inside the copying protection system (DRM) AACS. This system is used to protect Blu-ray and HD DVD formats from being copied. The system was developed by companies from the film industry and the electronics industry including IBM, Intel, Microsoft, Matsushita (Panasonic), Sony, Toshiba, The Walt Disney Company and Warner Bros.

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 (Km).

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.

The reproduction device will have available its own keys, uniques for each model, called Device Keys. 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 together with the VID (Volume ID) and as a result we obtain the Volume Unique Key (Kvu). With the Kvu 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 protect 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.

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