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AP: Extend EAPOL-Key msg 1/4 retry workaround for changing SNonce

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If the 4-way handshake ends up having to retransmit the EAPOL-Key
message 1/4 due to a timeout on waiting for the response, it is possible
for the Supplicant to change SNonce between the first and second
EAPOL-Key message 2/4. This is not really desirable due to extra
complexities it causes on the Authenticator side, but some deployed
stations are doing this.

This message sequence looks like this:
AP->STA: EAPOL-Key 1/4 (replay counter 1, ANonce)
AP->STA: EAPOL-Key 1/4 (replay counter 2, ANonce)
STA->AP: EAPOL-Key 2/4 (replay counter 1, SNonce 1)
AP->STA: EAPOL-Key 3/4 (replay counter 3, ANonce)
STA->AP: EAPOL-Key 2/4 (replay counter 2, SNonce 2)
followed by either:
STA->AP: EAPOL-Key 4/4 (replay counter 3 using PTK from SNonce 1)
or:
AP->STA: EAPOL-Key 3/4 (replay counter 4, ANonce)
STA->AP: EAPOL-Key 4/4 (replay counter 4, using PTK from SNonce 2)

Previously, Authenticator implementation was able to handle the cases
where SNonce 1 and SNonce 2 were identifical (i.e., Supplicant did not
update SNonce which is the wpa_supplicant behavior) and where PTK
derived using SNonce 2 was used in EAPOL-Key 4/4. However, the case of
using PTK from SNonce 1 was rejected ("WPA: received EAPOL-Key 4/4
Pairwise with unexpected replay counter" since EAPOL-Key 3/4 TX and
following second EAPOL-Key 2/4 invalidated the Replay Counter that was
used previously with the first SNonce).

This commit extends the AP/Authenticator workaround to keep both SNonce
values in memory if two EAPOL-Key 2/4 messages are received with
different SNonce values. The following EAPOL-Key 4/4 message is then
accepted whether the MIC has been calculated with the latest SNonce (the
previously existing behavior) or with the earlier SNonce (the new
extension). This makes 4-way handshake more robust with stations that
update SNonce for each transmitted EAPOL-Key 2/4 message in cases where
EAPOL-Key message 1/4 needs to be retransmitted.

Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>
This commit is contained in:
Jouni Malinen 2014-11-21 17:02:00 +02:00 • committed by Jouni Malinen
parent db099951cb
commit f23c5b17e1
2 changed files with 77 additions and 7 deletions
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3
src/ap/wpa_auth_i.h
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@ -58,6 +58,8 @@ struct wpa_state_machine {
Boolean GUpdateStationKeys;
u8 ANonce[WPA_NONCE_LEN];
u8 SNonce[WPA_NONCE_LEN];
u8 alt_SNonce[WPA_NONCE_LEN];
u8 alt_replay_counter[WPA_REPLAY_COUNTER_LEN];
u8 PMK[PMK_LEN];
struct wpa_ptk PTK;
Boolean PTK_valid;
@ -84,6 +86,7 @@ struct wpa_state_machine {
unsigned int mgmt_frame_prot:1;
unsigned int rx_eapol_key_secure:1;
unsigned int update_snonce:1;
unsigned int alt_snonce_valid:1;
#ifdef CONFIG_IEEE80211R
unsigned int ft_completed:1;
unsigned int pmk_r1_name_valid:1;