Construction of Response-Authenticator

[Theresa Otte]

Hello,

I use FreeRADIUS 2.1.8 on Ubuntu 10.4. For my course at university I 
have to write a program in which I need to re-calculate the 
response-authenticator 
(MD5(Code+ID+Length+Request-Auth.+Attributes+Secret)). Does anybody know 
how FreeRADIUS calculates it? Does it take the binary code of the 
message fields or an other encoding? When I try to re-calculate it, I 
never get the same Response-Authenticator as in the Access-Accept-Message.
I'm programming with Python and using the libraries of scapy and 
hashlib. Perhaps anyone of you can help me.

Thank you very much!