Subject: #5 [*] When 3-way, is responder's nonce MUST or SHOULD?

From: Shoichi Sakane <[email-masked]>
Date: Fri, 04 Feb 2005 20:04:06 +0900

> #5 [*] When 3-way, is responder's nonce MUST or SHOULD? (section 4.3 and 7.3)
> (solution proposed)
> 
> 	Sec 4.3 and 7.3 use SHOULD and MUST respectively regarding when the 
> 	nonce should be used.  If the circumstances they're describing are 
> 	different, that's okay, but if so, I missed it on first reading.
> 	(Ken Raeburn)
> 
> 	They are talking the same situation and the requirement levels should
> 	be aligned.  I think SHOULD is appropriate because non-returning
> 	responder's nonce does not break interoperabilities.
> 	(Message-ID: <[email-masked]>)
> 
> 	If the initiator receives a responder's nonce, she MUST use
> 	it in the KEYMAT calculation.

I think it is also editorial issue.  anyway, the behavior depends on
condition.  if a responder does not agree with the initiator's proposal,
AND if the responder wants to continue the transaction, then the responder
MUST send back a message with ACK request bit, and MAY contain a nonce.
There is a case when the responder wants to use same KEYMAT of the
initiator, but just doesn't want to use the initiator's proposal.
It is not always required to add a nonce.

When the initiator receives a nonce as the reply from the responder,
AND the initiator wants to continue the transaction, then the initiator
MUST reculculates KEYMAT with the nonce, and MUST send back a ACK message.