Re: [TLS] DTLS 1.3 AEAD additional data

[Thomas Fossati <[e-mail]>]

On 25/04/2020, 11:11, "Thomas Fossati" <[e-mail]> wrote:
> On 25/04/2020, 01:30, "Christopher Wood" <[e-mail]> wrote:
> > On Thu, Apr 23, 2020, at 2:17 PM, Eric Rescorla wrote:
> > > 1. Allowing implicit CIDs is very recent (it was introduced in
> > > -34)
> > > 2. The CID specification explicitly prohibits it for DTLS 1.2.  3.
> > > I haven't really heard a very compelling argument for this and I
> > > note that QUIC forbids it [and in fact has much worse problems
> > > when you mix epochs because the long header is so long]
> > >
> > > So, given that the simplest and most consistent thing is to simply
> > > forbid it: can someone make an argument for why this is important
> > > to permit?
> >
> > Thanks to everyone who participated in this thread so far! Given the
> > points above, the chairs would like to hear arguments in favor of
> > implicit CIDs. Absent substantial rationale, we'll assume rough
> > consensus for explicit CIDs.
>
> Hi Chris, I think implicit CID needs to be considered in the wider
> scope of unified_hdr compression, together with implicit length and
> shortened epoch.  In particular, from Chris P's emails I understand
> that being able to authenticate records' length is a core assumption
> in the security proof of TLS.  Therefore leaving it out from DTLS AAD
> when it's not in the header looks like a pretty bad idea.  If this is
> the case (i.e. the fact that the wire image by itself is not
> sufficient input to the AAD), then authenticating implicit CIDs should
> just come in the same bundle.

Sorry, scratch that for the moment - I had missed the most recent emails
on this thread :-(

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