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Old 5th February 2007, 20:42   #8  |  Link
arnezami
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Join Date: Sep 2006
Posts: 390
Quote:
Originally Posted by evdberg View Post
Sorry for sounding a bit ignorant, but how does the Volume ID and MKB lead to the Volume Unique Key?
I'm sorry for not explaining. The Media Key is a key resulting from the MKB (Media Key Block) and the Device keys. When combined with the Volume ID it gives the Volume Unique key.

Here is the part from the Pre-recorded Video Book section 3.3:

Quote:
2. Calculate the Volume Unique Key (Kvu):
The licensed replicator chooses a Volume ID (IDv) to be placed on the pre-recorded media and calculates a
Volume Unique Key (Kvu) as follows:
Kvu = AES-G(Km, IDv)
where AES-G represents the AES-based one-way function defined in the Introduction and Common
Cryptographic Elements book.
That basicly means that having a Volume ID (IDv) and a Media Key (Km) you can calculate the Volume Unique Key (Kvu).

Or to illustrate it (I removed the currently unused parts):



The red part is the hard part: getting the Media Key** (usually from a software player by debugging/memory snooping). But this only has to be done once per MKB and can be done by a pro.

The yellow part is what I described above: we either can (nearly) predict the Volume ID or we can get it via simple USB sniffing (the software player can't do much about that apart from bus encryption which is not implemented yet).

The blue part is the easiest: if we have the Volume ID (also called IDv) and the Media Key (Km) we can calculate the Volume Unique Key (Kvu) and then the Title Keys (Kt). This of course enables us to decrypt the content itself.

Hope that clarifies a bit.

Regards,

arnezami

** Later in this thread it became clear we need a Processing Key. But it amounts to basicly the same thing.

Last edited by arnezami; 11th February 2007 at 15:40.
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