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

[Eric Rescorla <[e-mail]>]

At Wed, 17 Jun 2009 08:41:52 -0700,
Joe Touch wrote:
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> Eric Rescorla wrote:
> > 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.
> 
> That is only possible with either non-overlapping or ordering to resolve
> overlaps.

I don't see why this is true. Any time a new key is entered, you
find all other keys that overlap with it and verify that they
have distinct key-ids. If so, the entry fails. If that's what
you mean by "prohibit overlaps", yes, I think we should
prohibit overlaps. 

If what you mean is that two MKTs with different key-ids can't overlap
the same socket pair space, I don't see a problem with that.

-Ekr