WPS: Incorrect Authenticator at STA [wps_process_m2]

[hari.c36 at wipro.com]

Hi

We are able to send M1 packet and got the M2 packet from AP.STA is failing to send M3 due to Authenticator Mismatch.Instead STA sends the WSC_NACK packets to AP.
The function wps_process_authenticator[wps_process_m2] returns NULL because of Authenticator mismatch.ie., the hash generated by HMAC-SHA-256 with last message and msg excluding authenticator is mismatching with the M2 Authenticator value.
So what can be the reasons for this mismatch.we are trying to port the supplicant wps code to an embedded platform.Verified the HMAC-SHA-256,sha256_vector,and all the inputs to this algorithms.Seems to be ok.
Not checked crypto_mod_exp[libtomath.c] but its returning public key.

Please help me how can we go forward to debug this issue.

Regards
Hari

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