wpa_supplicant: isn't "802.1x Start" required for WPA?

Jouni Malinen jkmaline
Tue Apr 19 19:45:26 PDT 2005

On Tue, Apr 19, 2005 at 08:07:50PM +0200, Arjan van Bentem wrote:

> Trying to figger out why my Linksys card works on Windows, but not on 
> Linux I used Ethereal to see what's actually sent. I noticed some 
> differences. Any comment?

Getting a raw Ethereal capture file would be helpful..

> As a response to the initial key as sent by the access point, the 
> Windows XP driver first seems to send a "Start", shown by Ethereal like:
> 802.1x Authentication
>    Version: 1
>    Type: Start (1)
>    Length: 0
> Does anyone know if this "Start" might be required for some access 
> points (in my case: a Speedtouch 580 access point)? wpa_supplicant / 
> ndiswrapper do not send such "Start" but sends the EAPOL WPA key right 
> away.

EAPOL-Start frame is not part of WPA-PSK and I'm not aware of any AP
requiring it. Yes, I know that Microsoft supplicant sent this, but it is
not correct behavior as far as I can tell.

> The first EAPOL WPA key message as sent by wpa_supplicant is almost the 
> same as the Windows message. However: the value for "Key Length" is zero 
> on Windows, but not in wpa_supplicant.

This field is not really used in WPA and as such, I would not expect
authenticator to verify that it is zero. Anyway, I did actually change
wpa_supplicant to use zero in this field. This change is currently only
in the development branch, so you would need to download a development
snapshot in order to test this.

> And the Windows driver sends a 
> value for "WPA Key" that is 2 bytes longer and ends in two zero bytes:

This is fine. The difference is in whether the optional WPA capabilities
field is included in WPA IE or not.

> whereas the response when using wpa_supplicant does not have the 
> "Install flag"and "Key Ack flag" set:

This packets looks odd.. I would need to see full headers to see what it
is, but it looks more like a reply from the client (i.e., msg 2/4) than
anything from the AP..

Jouni Malinen                                            PGP id EFC895FA

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