Questions on using EAP-AKA

Ben Greear greearb
Tue Dec 24 05:40:09 PST 2013

I've some questions from a user trying to get our product
(which uses wpa_supplicant) to associate with EAP-AKA and
the USIM simulator.  I'm working on getting access to logs,
packet captures and such.  Any help would be greatly appreciated.

Now we have started receiving EAP-AKA-challenge message from DUT to station; but the latter is replying
back with Authentication-Rejection. To narrow down the issue, we would like to understand key configuration at station side.

As per our understanding, the station required  'k' : 'OPc' : 'SQN' in its configuration. Right ?

Question is why do we need to configure SQN at UE side ? Shouldn't UE extract it from Received challenge (AUTN) ?

On the UE side, on receiving AKA-Challenge, following calculations should be done:

1) Calculate  AK = F5 (K, RAND);   where 'k' is pre-shared between UE and Network and RAND is received in AKA-challenge message.

2) Extract  SQN = Xor(AK, AUTN[1-6]); where AUTN[1-6] are first 6-bytes from received AUTN

3) Extract AMF which is AUTN[7-8]

4)  Verify AUTN[9-16] using K, RAND, SQN, AMF using another Milenage function.

Thus UE only needs 'k' value to authenticate AUTN and it does so by extracting AMF, SQN, RAND from received challenge message.


Ben Greear <greearb at>
Candela Technologies Inc

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