Re: [tcpm] question about TCP-AO and rekeying

[Eric Rescorla <[e-mail]>]

At Tue, 16 Jun 2009 23:24:55 -0700,
Joe Touch wrote:
> Eric Rescorla wrote:
> ...
> >> However, the invariant is twofold:
> >>
> >> 	a) for a given packet, only one MKT applies
> >>
> >> 	b) for two endpoints with multiple MKTs,
> >> 	the *same* MKT applies.
> > 
> > I don't see that this is true. As I understand the current design
> > there's no reason that both sides can't use different MKTs
> > indefinitely.
> 
> Each side can use a different MKT to transmit. However, if side A uses
> MKT X to transmit, then side B needs to know to use MKT X to receive. If
> side A matches MKT X on transmit and side B matches MKT Y on receive,
> then there's a problem for that connection.
> 
> So let's rephrase, recognizing that there are two MKTs at any given time
> (one for transmit on each side, and the same pair for receive on the
> opposite side).
> 
> b) for two endpoints, if a given packet matches MKT on one side during
> transmit, it must match the corresponding MKT on the other side during
> receive.

Right, but this doesn't require ordering or non-overlapping, as far as
I can tell.  It merely requires that at any time there only be one MKT
corresponding to any given socketpair/key-id.
       
-Ekr