why "underflow" happens?

Jouni Malinen j at w1.fi
Wed Oct 12 16:44:17 EDT 2011

On Sun, Oct 09, 2011 at 09:25:28PM -0700, hong zhang wrote:
> When wpa-psk TKIP key rotation happens during connection, "underflow" is complained and then disconnected. What does it means?

> 10-08 08:27:51.153 D/wpa_supplicant( 1791): WPA: RX message 1 of Group Key Handshake from 58:8d:09:b1:14:00 (ver=1)
> 10-08 08:27:51.153 D/wpa_supplicant( 1791): WPA: EAPOL-Key Key Data underflow (ie=29 len=72 pos=0)

This indicates that the received EAPOL-Key frame was considered to be
invalid. The following debug entry from wpa_hexdump_key would have been
quite useful in figuring out what exactly was in the message (it looks
like you are running wpa_supplicant on a system that does not show that
in the default debug info, so some additional effort would be needed to
get that information, I'd guess).

What AP were you using when this happened? The OUI in the MAC address
seems to indicate that it would be a Cisco device. I have not seen this
type of interop issue with any Cisco AP that I've tested with.

Jouni Malinen                                            PGP id EFC895FA

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