Re: [TLS] SCHC for DTLS

We spent a fair bit of time working to shrink the DTLS 1.3 record layer, so
I'm not sure how much room there is for optimization.
See: https://www.rfc-editor.org/rfc/rfc9147.html#name-the-dtls-record-layer

Specifically, the longest header (w/o CID) is 5 octets and the shortest is
2 octets. The sequence number is used for the IV, so there's no extra there.

-Ekr

On Mon, May 30, 2022 at 6:28 AM Robert Moskowitz <rgm-sec@htt-consult.com>
wrote:

> Greetings Hannes,
>
> This is for the record layer.  And I really don't know how much would be
> gained.
>
> But as I would see it, this use of SCHC would be for UDP/DTLS/cipher.
> Since it is starting with UDP, SCHC would have to be an IP Protocol (not
> currently defined as such).  So you loose 1 byte for the SCHC rule, against
> the 8 probably saved in compressing UDP to 0 bytes.  Then there is the
> cipher.  Try AES-GCM-12; what is currently used for the IV?  Can something
> like rfc8750 be added to use the seq # in the DTLS header and gain maybe 16
> bytes?  I really don't know the DTLS header at all.  I have tried to find
> some decent layout as I am use to for ESP in 4303 (Fig 1) for side-by-side
> comparison.
>
> But if it means being able to fit over some UHF carrier for unmanned
> aircraft (UA) Network Remote ID (Net-RID) and Command and Control (C2)?
> Worth the effort.
>
> So this is not something I could do myself, but something that I see using
> and thus pitching in on doing it.
>
> On 5/30/22 05:33, Hannes Tschofenig wrote:
>
> Bob, is this about compressing the DTLS record layer or the DTLS handshake
> protocol?
>
> For the former, I wonder how much is there actually to compress (when
> using DTLS 1.3)?
>
>
>
> *From:* TLS <tls-bounces@ietf.org> <tls-bounces@ietf.org> *On Behalf Of *
> Eric Rescorla
> *Sent:* Friday, May 27, 2022 5:30 PM
> *To:* Robert Moskowitz <rgm-sec@htt-consult.com> <rgm-sec@htt-consult.com>
> *Cc:* <tls@ietf.org> <tls@ietf.org> <tls@ietf.org> <tls@ietf.org>
> *Subject:* Re: [TLS] SCHC for DTLS
>
>
>
>
>
>
>
> On Fri, May 27, 2022 at 6:27 AM Robert Moskowitz <rgm-sec@htt-consult.com>
> wrote:
>
> Is there any activity to define SCHC rules for DTLS?
>
>
>
> Not to my knowledge.
>
>
>
> -Ekr
>
>
>
>
> I want this for Unmanned Aircraft (UA) Network Remote ID (Net-RID)
> communications from the UA to the Net-RID Service Provider (SP).
>
> See
>
> https://datatracker.ietf.org/doc/draft-moskowitz-drip-secure-nrid-c2/
>
> I am compressing ESP traffic using rfc 8750 and:
>
> https://datatracker.ietf.org/doc/draft-mglt-ipsecme-diet-esp/
>
> SCHC is negotiated in IKE (and will be in HIP) and SA tables allow the
> ESP receiver to recognize a SCHC compressed ESP Header and act properly.
>
> It is not so simple with DTLS.  First UDP is below DTLS, so how do you
> compress it?  The way I see it, SCHC would need to be assigned an IP
> Protocol type so that the transport processing can start right up with
> the SCHC rule for UDP and then on to DTLS and then the cipher.
>
> Or at least how I see the challenge.
>
> So I am looking for any extant work on SCHC for DTLS and/or interest in
> this activity.
>
> The CoAP SCHC work, rfc 8824, dodge DTLS compression.  Or that is how I
> read it.
>
> Thanks
>
> Bob
>
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