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Re: [STDS-802-11-TGBI] What happens when a non-AP MLD changes EDP epoch group?

Hi Antonio, I have responses inline below (in green font starting [PH]) to your questions about generation of EDP FA Block. Cheers,Phil
From: Antonio DeLaOlivaDelgado <aoliva@xxxxxxxx>
Sent: Wednesday, July 2, 2025 4:43 PM
To: STDS-802-11-TGBI@xxxxxxxxxxxxxxxxx <STDS-802-11-TGBI@xxxxxxxxxxxxxxxxx>
Subject: [STDS-802-11-TGBI] What happens when a non-AP MLD changes EDP epoch group?
 

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Dear, 
I have several CIDs asking to describe what happens when a non-AP MLD changes its group, maybe after receiving an EDP Epoch Request frame.

In my understanding, the EDP Epoch Response frame should be received well in advance so that the non-AP MLD is able to compute all its FA parameters. Then it will wait until the time of the next epoch change and apply them. first question is what happens if the response frame arrives so that the non-AP MLD does not have time to change its parameters? it aborts? disassociate?

I have also noticed that the calculation of the FA parameters, which is the following:

EDP FA block =KDF-Hash-Length( KDK, "EDP CPE frame anonymization", n)

Will result on the same parameters for the same user in the same relative n, is not it?
[PH] According to current definition: yes.

So if we have one user in EDP epoch 1 with relative number 10, which has been there during epoch with relative number 9, and changes to a new epoch group 2 which next relative epoch number is 7, in two epochs (relative epoch number 9) its EDP FA block in epoch group 2 will be the same as in the epoch group 1, relative number 9. 
Is my interpretation correct?
[PH] According to current definition: I believe so.

is this what we want?
[PH] No! As you point out, this can result in an epoch deriving an EDP FA block identical to the EDP FA block of an earlier epoch of another epoch group, which will be easily detectable since all affiliated STAs of all non-AP MLDs will using identical MAC addresses in both epochs.
There are two changes help avoid such scenarios:
1. In the place of (n) in the KDF context, use EpochTSFStartTime(n) or PlannedTSFStartTime(n) (defined in 10.71.2.4 EDP Epoch Start Time Computation)). This was the original proposal for generation of EDP FA block.
2. Include the EDP Group ID  (defined in (9.4.1.84 EDP Epoch Settings field)) in the KDF context

One or both of these changes could be applied.

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