Introduction
The AACS’s cryptographic key management procedure uses Device Keys to decrypt one or more elements of a Media Key Block (MKB), in order to extract a secret Media Key (Km). A MKB is located on the physical support (the disc) together with the content of the disc encrypted. MKB enables system renewability. The MKB is generated by AACS LA, and allows all compliant devices, each using their set of secret Device Keys, to calculate the same Media Key (Km).
If a set of Device Keys is compromised in a way that threatens the integrity of the system, an updated MKB can be released that causes a device with the compromised set of Device Keys to be unable to calculate the correct Km. In this way, the compromised Device Keys are “revoked” by the new MKB.
| Key or Variable | Size |
|---|---|
| Device Keys (Kd0,Kd1,…,Kdn-1) | 128 bits each |
| Media Key Block (MKB) | Variable, multiple of 4 bytes |
| Media Key (Km) | 128 bits |
Read more about this topic: Device Keys
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