Re: [STDS-802-11-TGM] TGmc CID 13

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On Fri, Dec 14, 2012 at 1:47 PM, Mark Rison <m.rison@xxxxxxxxxxx> wrote:

--- This message came from the IEEE 802.11 Task Group M Technical Reflector ---
1) 11.6.1.4 Group key hierarchy says that the size of the GTK is
256 + TK_bits, where TK_bits is in Table 11-4

That looks broken to me. There are no other components apart from the TK in the GTK, i.e., that "256 +" part should not really be there. That extra 256 bits of "something" was not there in 802.11i-2004 and it was not there in 802.11-2007 either.. I don't know how exactly this got added in 802.11-2012, but I'd assume it was a copy-paste error from PTK description in 09-601r2 that got accepted for CID 1115. Anyway, TGmc should consider reverting that change of adding the extra 256 bits, i.e., that text in 11.6.1.4 should really be "X = TK_bits" instead of "X = 256 + TK_bits".

2) So the size of the GTK is 32+5 octets for WEP-40, 32+13 octets

for WEP-104, 32+32 octets for TKIP and 32+16 octets for CCMP/BIP,
right?

Well, based on that description in 802.11-2012, yes, that would be what 11.6.1.4 claims, but the real GTK lengths based on the way this was designed in 802.11i would be 5, 13, 32, 16..

3) So if the thing being distributed is the GTK (rather than the TK,

which does have a size of TK_bits, as the name suggests):

GTK is indeed distributed, but GTK = TK once that +32 part is fixed.

b) The value of the Length field below should be 11+32+5, 11+32+13,
11+32+16 or 11+32+32 (except that I hope/think we've managed to agree

to delete such sentences)

It should be noted that the standard allows use of vendor specific cipher suites and those could have other key lengths than the ones listed here. Anyway, the clearest option would be to just get rid of the goal of listing all possible Length field values and describe it as variable (or as a function of the GTK length if really needed).

- Jouni

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Re: [STDS-802-11-TGM] TGmc CID 13 - Proposed resolution