Need help in understanding the "Signature Generation" for SMB packets

["Narendra Kumar S.S" <ssnkumar () gmail com>]

Hi,

     I have a pcap file with smb traffic and I am trying to understand how
the signature is generated.
     Using wireshark GUI, I have opened the pcap file and have put a filter,
so that I can see the relevant tcp stream only.
     In this stream, the initial authentication is done using NTLMSSP.
     But, after nearly 100 smb packets, suddenly I see a SetupAndX
Request/Response, with krb5 AP_REQ and AP_REP.
     I have used the keytab file to decrypt the AP_REP and get the session
key.
     Now, the sequence number starts with 0 and I have used that counter to
calculate the signature.
     But, the signature that I am getting doesn't match with the original
signature.
     I also, tried to count the sequence number starting from the NTLM
Request/Response and with that also, the signature doesn't match.

     So, can somebody tell me, if this kind of mixup of NTLM and kerberos
packets in a single tcp stream is common?
     And how to get the right signature in this case?

Warm Regards,
Narendra

Visit my blogs at:
http://ssnarendrakumar.blogspot.com/
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