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Old 23rd February 2007, 13:45   #70  |  Link
xyz987
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Join Date: Dec 2006
Posts: 142
Quote:
Originally Posted by FoxDisc View Post
The "master tree" for all possible devices is different from the "master tree" for any single device with a set of device keys. I just wanted to point out that we were referring to the larger tree. Maybe we should call the larger tree the "master master tree?"
Your tree is not mentioned at spec, so it has no name at spec. However I also think your tree exist, and the only problem is to agree a name for it. This tree has the root keys of master tree and subtrees, so we can call it "God tree" (or any other not used name, at your choice).

Spec doesn't say where root keys come from, may be they are ramdon or nodes of a higher level tree. However, it is true that there are 8 levels above master tree. It is also true that the number of subtrees is huge (there are millions), so getting ramdonly the root keys for all those subtrees is not an efficient method. That's why I think you are right and God tree exists.

Quote:
Again, I am just trying to get consistent terminology - nodes are parts of trees. Multiple keys are assigned to each node. There is only one large master tree with nodes below the root. In your convenient numbered tree, node 4 is node 4 for the entire tree (rooted at node 1), and for the subtree rooted at 2 and for the subtree rooted at 4 - it's always node 4. Yes, one can think of trees of keys, and the keys assigned to node 4 are different for each of those subtrees, I just think it's easier to look at nodes and subtrees of nodes that are part of the master tree.
The real problem is that "master tree" is an expresion used in AACS spec with a precise meaning. Imagine we start to talk about "master tree" in the same sense you use this expresion. Any guy who lands here simply won't understand what we are saying. He will probably think we have not read the spec. If we talk about "God tree", this guy knows at least we are talking about a different tree.

My numbered tree can be used in different ways. Note that each subtree corresponds to a node of master tree (this correspondence is to decide for which subtrees the device receives Device Keys), so you can assign numbers to subtrees. You can say "node 4 of subtree 2" for example. Again I am just trying to do things in the same way AACS does.

Quote:
I presume it's because they put the software players into the first subtree. They made the first S-D set as big as possible (all except one device). The first C-value is the media key encrypted with the processing key for that first S-D set. It does not seem like a coincidence to me.
and later you wrote:

Quote:
1) The first MKB entry is for an S-D set, not a full tree or subtree. It includes almost all devices except the lower left device, which would not be a real device.
So what are you saying?. Just soft players or all players?.

I say it includes all players, of course. And the tree that includes all players (spec says "master tree of keys, where each device is uniquely associated with a leaf node of the tree") is precisely master tree (22 levels hight).

Of course, God tree also includes all players (because it includes master tree), but it is 8 levels higher.

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2)The other entries are for similar S-D sets within the larger master tree.
The other entries are just not used nowadays.

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3) We do not know if the other entries are used by current devices, but I bet they are - by non-software players.
Here is the "big coincidence". Soft players are at the very first entry. Of course, it is not a coincidence if all players are there (master tree).

Quote:
4) Later PK keys will not be able to be derived by current devices if they are revoked by defining S-D sets in the MKB that do not include the revoked devices. The revocation will occur by adding one or more new S-D sets and media keys encrypted with the PKs for those S-D sets to the MKB (and eliminating the current S-D set which includes the current players).

Note it is posible to revoke a player just storing on MKB only one valid entry (player 12 will become revoked if Media Key is encrypted with key 12). AACS LA only needs to use 2 or more entries if they want to revoke noncontiguous players.

Also spec says "On average, there are 1.28 encryptions per revocation". You are saying they use 512 encryptions (512 valid entries) even if they have not revoked any player.

Last edited by xyz987; 23rd February 2007 at 13:52.
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