Subject: [Roll] How is the Message Authentication Code field computed?

From: Alexandru Petrescu <[email-masked]>
Date: Sun, 25 Jul 2010 02:31:08 +0200

> 9.6. Coverage of Integrity and Confidentiality
>
>
> For a RPL ICMPv6 message, the entire packet is within the scope of
> RPL security.

Well yes and no, because draft says "The body of the RPL ICMPv6 message 
MAY be encrypted, starting from the first byte after the security 
section" - that is not the entire packet.

> The message authentication code is calculated over the entire IPv6
> packet.

I need to understand this in more detail, and I don't find in draft (or
I don't understand):

How is the MAC computed?  Which fields are covered?  Which are mutable?
  What's the initialization?

How is the ICMP Checksum field covered by the MAC?  First compute the
Checksum or first the MAC?

Please give an example.

(I could give similar with AH HMAC-MD5 and SHA1)
(I may not be aware of a ton of security RFCs and terminology - sorry
  Michael about HMAC-MD5 vs MD5).

Alex