Subject: [Mip4] Query regarding MN-AAA authenticator calculation.

From: Archana <[email-masked]>
Date: Fri, 25 Feb 2005 15:08:18 +0530

Hi 
According to RFC 3012, the MN-AAA authenticator is computed by applying MD5
on the following data

      High-order byte from Challenge || Key ||
      MD5(Preceding Mobile IP data ||
      Type, Subtype (if present), Length, SPI) ||
      Least-order 237 bytes from Challenge

I have the following queries regarding the above computation. Any help in
the clarifying them will be highly appreciated.

1. What is meant by High-order and Least order ? 
2. How does the Radius MD5 algorithm differ in calculating the Authenticator
from a MD5 algorithm

Thanks in advance
Archana

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---

From: Pete McCann <[email-masked]>
Date: Fri, 25 Feb 2005 09:48:29 -0600

Hi, Archana,

 > 1. What is meant by High-order and Least order ? 

"High-order" means "most significant".  You can also interpret it as
"leftmost" when looking at the encoding of the Challenge in a Mobile
IP Extension.

 > 2. How does the Radius MD5 algorithm differ in calculating the Authenticator

There is no special "Radius MD5" as far as I know.

MD5 is specified in RFC3121.  It is a well-known hash function that
processes the input and produces a 16 octet hash.

The calculation shown above is compatible with existing RADIUS servers
that are used for authenticating PPP/CHAP, i.e., the code used for
PPP/CHAP can be re-used to compute the above authenticator, assuming
that the FA can precompute the inner MD5 and send it in an
Access-Request.

-Pete