Re: [TLS] SCHC for DTLS

On Mon, May 30, 2022 at 9:38 AM Robert Moskowitz <rgm-sec@htt-consult.com>
wrote:

> Great to know.  thanks.  My feable attempts to find this were coming up
> empty.  But now I should be able to put some things together.
>
> I am assuming that the DTLS header is part of the AEAD protection.  Thus I
> can squeeze out the UDP CRC?
>

The DTLS header is included in the AD, yes.

> I recall seeing length in the DTLS header, but I do not have it in front
> of me.  Also want to drop that from the UDP header...
>

DTLS 1.3 has a header mode in which it omits the length and just uses the
UDP length. That may be easier.

-Ekr

> Anyway, this is good info.
>
> On 5/30/22 12:12, Eric Rescorla wrote:
>
> 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
>>
>> _______________________________________________
>> TLS mailing list
>> TLS@ietf.org
>> https://www.ietf.org/mailman/listinfo/tls
>>
>> IMPORTANT NOTICE: The contents of this email and any attachments are
>> confidential and may also be privileged. If you are not the intended
>> recipient, please notify the sender immediately and do not disclose the
>> contents to any other person, use it for any purpose, or store or copy the
>> information in any medium. Thank you.
>>
>>
>>
>