wpa_supplicant: IBSS/RSN and node reboot

Antonio Quartulli ordex
Tue Dec 20 00:03:50 PST 2011

Hi Jouni and thank you for your reply,

On Tue, Dec 20, 2011 at 01:05:38 +0200, Jouni Malinen wrote:
> On Mon, Dec 19, 2011 at 09:59:49PM +0100, Antonio Quartulli wrote:
> > I'm trying to make IBSS/RSN work in various scenarios. 
> > 
> > In particular I'm now
> > focussing on the simple case of two nodes (say A and B) which get in sync and
> > where one of them (say B) suddenly reboots. After this event B tries to
> > renegotiate the key but, A (which didn't delete A's state since it haven't
> > received any IBSS_PEER_REMOVE) will drop its EAPOL packets due to wrong
> > replay_counter..is there any way to workaround this issue? Actually, since A is
> > never going to receive the IBSS_PEER_REMOVE (because A and B are again the same
> > IBSS), A is not going to delete/reinitiate B's state machine.
> The IEEE 802.11 standard provides a mechanism that could potentially be
> used to recover from this (well, at least if PMF is not used). Station B
> could send an Authentication frame here and that should make station A
> drop the current PTKSA. While the rules on Key Replay Counter do not
> strictly speaking discuss this IBSS use, I'd say it would be fine to
> allow this to be used to initialize key replay counter to 0 (this is
> describe beibg on on "(re)association" which does not really happen in
> IBSS).

You mean using the authentication frame to reset the replay counter? this should
straightforward (from the coder point of view :-))

> A more string way of interpreting the standard would point out that Key
> Replay Counter does not get re-initialized back to zero until PSK is
> changed (i.e., potentially never) and as such, the station better
> remember which counter value it has used in the past and never go back
> to zero..

This would probably be cleaner, but I don't think it is always applicable:
imagine a node being suddenly plugged off (which is actually the test I'm doing)


Antonio Quartulli

..each of us alone is worth nothing..
Ernesto "Che" Guevara

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