Armor key negotiation in FAST

[Simon.Jansen@t-systems.com]

Hi,

I have a further question referring to the following part of the previous conversation.

>> So the security of the whole tunnel is based on the strength of the long-term host key.
>
>Yes.

Why is the armor built and why don't they use simply the long-term key of the host? 
>From my current point of view they want a fresh armorkey for each conversation to decrease the vulnerability to replay attacks. But referring to page 31 of the RFC 6113 a nonce is included in the client request. So the chance to mount a replay attack should be decreased already. Are there any other advantages that come up with the generation of the armor key?


Regards,
Simon