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To: Damion Wilson <dwilson,AT,ibl,DOT,bm>
Subject: Re: CIPE-Win32: communication breakdown
From: Alan Stern <stern,AT,rowland,DOT,harvard,DOT,edu>
Date: Mon, 9 Jun 2003 15:56:38 -0400 (EDT)
Cc: CIPE List <cipe-l,AT,inka,DOT,de>

On Mon, 9 Jun 2003, Damion Wilson wrote:

> Christof is saying that the peer starts using the new key without the ACK. 
> I'm 
> the one saying that CIPE-Win32 doesn't use its newly generated key until 
> the 
> ACK is sent back. Who are you agreeing with ?
> 
> DKW

Sorry, I think we got a little confused over which CIPE is doing what.  If 
it helps, here is a direct quote from cipe.texinfo:

  The key negotiation procedure normally runs as follows: The sender
  sends a NK_IND with the new key, then invalidates its own sending key.
  Upon receipt of NK_IND, the receiver starts using this key as its
  receiving key and sends a NK_ACK. When the sender receives NK_ACK, it
  starts using the new key as its sending key. If either of NK_IND or
  NK_ACK is lost in transmission, no new key will be used. The sender
  should send a new NK_IND (with new key) if no matching NK_ACK is
  received within a reasonable amount of time (current specification: 10
  seconds).

The unmentioned implication is that during the period when the old and new
sending keys are both invalid, the sender falls back on the static key.

That should clear things up.

Alan Stern

> On Friday 06 June 2003 04:31 pm, Alan Stern wrote:
> > On Fri, 6 Jun 2003, Damion K. Wilson wrote:
> > > I don't think that this approach is wrong, and it's intentionally 
> > > written
> > > that way. If A says to B: "I'm changing my  key, here it is" and B never
> > > says: "I got it, go ahead" then there has been no successful key 
> > > exchange
> > > so both A and B must try again.
> > >
> > > I didn't know that CIPE invalidates the key before receipt of the NK_IND
> > > has been acknowledged by the peer. It the NK_ACK wasn't necessary, why
> > > have it at all ?
> > >
> > > Olaf, if you're listening, do you have any guidance ?
> >
> > My memory may be a little rusty, but I think Christof was right.  The
> > reason for the NK_ACK message is that CIPE won't start to use the new key
> > until the NK_ACK is received.  Until then it will fall back on the static
> > key.
> >
> > At least, that's what the documentation says.  Maybe the implementation is
> > different.
> >
> > Alan Stern
> 
> 
> 


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