WPA with TKIP done

Andriy Tkachuk andriy.v.tkachuk
Wed Sep 2 04:09:49 PDT 2009

Basically it looks like the very same chopchop attack described by Beck 
& Tews in theirs paper at Nov 2008 
(http://dl.aircrack-ng.org/breakingwepandwpa.pdf) but the special 
man-in-the-middle case which is also mentioned in theirs paper:

> Even if the network does not support the IEEE 802.11e QoS features, 
> the attack still
> seems to be possible. Here, the attacker needs to prevent the client 
> from receiving the
> data packet he chooses for the chopchop attack, and must disconnect 
> the client from
> the access point for the time of the attack, so that the TSC counter 
> is not increased
> by the packet or following packets. After the attacker has 
> successfully executed the
> chopchop attack, he can send a single data packet to the client. 
> However, we did not
> implement this attack mode.

So it does not look like an sensation (at least for me).

If sincerely, I can not imagine how an attacker could organize 
man-in-the-middle attack to the setup where the AP directly see the 
STAtion staying physically unnoticeable.

As Beck & Tews suggested in theirs paper, to countermeasure these type 
of attacks users can decrease rekeying time from default 10 minutes to 2 
or less minutes (wpa_ptk_rekey parameter starting from hostapd-0.6.6 
version). Also Beck & Tews suggest to avoid sending MIC failure report 
frames by clients at all. Instead, Jouni only added an optional 
mitigation mechanism to wpa_supplicant starting from 0.6.6 version for 
such type of attack by delaying Michael MIC error reports by a random 
amount of time between 0 and 60 seconds. Jouni, could you comment, why 
we just can't follow Beck & Tews suggestion here and just avoid sending 
of MIC failure report frames at all (at least make this approach 
configurable, since it looks like WFA certification testplan checks it)?

Thank you,

On 2009-08-29 00:45, Cristian Ionescu-Idbohrn wrote:
> Seen articles like this one:
> 	http://isc.sans.org/diary.html?storyid=7027
> and:
> 	http://www.h-online.com/security/Attack-on-WPA-refined--/news/114105
> circulating.  "researchers in Japan describe how to perform the Beck-Tews
> style attack against any WPA-TKIP implementation, in under a minute".
> Jouni, would you please comment?
> Cheers,

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