Failure due to bad EAPOL-Key descriptor version(3)

Jouni Malinen j
Fri Nov 14 11:33:17 PST 2014

On Fri, Nov 14, 2014 at 10:34:06AM -0800, Ben Greear wrote:
> I reproduced the same general issue using hostapd as AP.

Could you please send me a hostapd configuration file that you used to
reproduce this? I could not get hostapd to misbehave in the same way
without modifying the implementation..

> I have since fixed my tool to enforce only the SHA256 are enabled when .11w is enabled,
> but if you tell supplicant and hostapd to enable .11w, but also give
> them an option to use SHA128 and SHA256, then it appears supplicant and/or hostapd
> will not properly choose the SHA256 variants.

SHA1 is certainly supposed to work with PMF.

> It is still possible I have just completely broken config files,
> but I suspect that is not the full problem since I too saw some bug reports
> on the web that looked similar...

There is certainly some interop issues in this area. So far, I've only
seen signs pointing towards AP misbehavior, but I do not have verbose
log or capture file to confirm my assumptions. Anyway, I expect this
commit to address most, if not all, of these issues:

> >> network={
> >>     ieee80211w=2
> >>     proto=RSN
> >>     key_mgmt=WPA-PSK
> > 
> > Please note that this would be a pretty strange configuration for PMF.
> > When PMF is required (ieee80211w=2), a SHA256-based AKM (WPA-PSK-SHA256)
> > should be used. With that AKM, EAPOL-Key descriptor version should
> > indeed be 3, but this configuration is forcing the station to use
> > SHA1-based AKM and that AKM would use descriptor version 2.
> If it is totally broken config, should supplicant just fail to start
> with a big error explaining the issue in this case?

It is not broken as far as the IEEE 802.11 standard is concerned, i.e.,
that is an allowed combination and it is supposed to work (and I just
added a hwsim test case to confirm that this works and will continue to
work in the future). That said, there is not much point in using
SHA1-based AKM with PMF required since all PMF capable devices will be
able to support SHA256-based AKM. In other words, I'd use SHA1-based AKM
with PMF only in case PMF is set as optional on the AP.

Jouni Malinen                                            PGP id EFC895FA

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