OSPF MAC calculation

["Charis" <cycharis () yahoo gr>]

Dear List,
I would like to ask for some information regarding the OSPF MAC calculation.
I am doing my thesis on OSPF attacks and I am trying to implement a tool for
OSPF packet injection.
I am trying to calculate the MAC value of an OSPF packet in order to verify
the MAC.
Although that I read the RFCs I still can't get the same MAC. What I am
doing now, I take the packet bytes in HEX and I remove the Auth data that is
appended at the end. I finally take this value to a hash calculator and I
use the key that is known to me to check the result with the MAC that is on
the packet. These two values are never equal for me! 
I hope that you will be able to help me, 
Thanks in advance, 
Charis Florides