Re: [Ace] (details on use case scenario?) Re: [Lwip] EDHOC standardization

Göran Selander <goran.selander@ericsson.com> Tue, 05 March 2019 11:42 UTC

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From: =?utf-8?B?R8O2cmFuIFNlbGFuZGVy?= <goran.selander@ericsson.com>
To: Rene Struik <rstruik.ext@gmail.com>, John Mattsson <john.mattsson@ericsson.com>
CC: "secdispatch@ietf.org" <secdispatch@ietf.org>, 'Benjamin Kaduk' <kaduk@mit.edu>, "ace@ietf.org" <ace@ietf.org>
Thread-Topic: (details on use case scenario?) Re: [Lwip] [Ace] EDHOC standardization
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Date: Tue, 5 Mar 2019 11:41:58 +0000
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Subject: Re: [Ace] (details on use case scenario?) Re: [Lwip] EDHOC standardization
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Hi Rene,

From: Rene Struik <rstruik.ext@gmail.com>
Date: Monday, 4 March 2019 at 22:57
To: John Mattsson <john.mattsson@ericsson.com>
Cc: "secdispatch@ietf.org" <secdispatch@ietf.org>rg>, Göran Selander <goran.selander@ericsson.com>om>, 'Benjamin Kaduk' <kaduk@mit.edu>du>, "ace@ietf.org" <ace@ietf.org>
Subject: (details on use case scenario?) Re: [Lwip] [Ace] EDHOC standardization

Hi John, Goran:

It is not easy to follow the discussion on EDHOC (except for witnessing a byte-count slinging contest on the mailing list).

I think it would be good to look at the big picture, i.e., which problem does one solve and/or does one solve the right problem.

I would like to understand somewhat better how the scheme suggested in [1] could help in facilitating fast network enrollment and network  formation.

Could you describe how to use this in the following scenario:
1) Network with one central manager and N=1,000 nodes that wish to join the network roughly at the same time, where the network manager is, say, 10 hops away from the joining nodes;
2) Authenticated key agreement using cert-based key agreement;
3) Network uses time-synchronized scheduling (such as in 6tisch) - where local single-hop communication time latency is 10 seconds);
4) The network manager may have high-bandwidth with outside world, but joining node/network manager path uses relatively low-bandwidth pipe that may only be available intermittently, with preset schedule);
5) It is unknown beforehand which entry point the joining nodes will pick when trying to enroll to the network?

Something like this is briefly discussed under the benchmarking subject on today’s agenda, but with PSK/RPK ECHDE instead of certificates.
This is an excellent use case where message sizes is expected to have a large impact and simulations can be made, e.g. using https://bitbucket.org/6tisch/simulator/


While the draft refers to lots of details from other protocols that are used under the hood, it would be good to abstract from this for now and describe basics first.

We have considered this. Our conclusion at the time was the having a precise description of an abstract protocol, in addition to the concrete mapping to COSE would perhaps be more confusing, and instead we tried to introduce people to CBOR and COSE in Appendix A. Considering the positive outcome from the CFRG Crypto Panel, I assume the protocol is sufficient readable for review. Please let us know if you have further issues reading it.

I tend to agree with others that lossless data compression could result in some savings, with some give and take re encoding rules (see also [2]). Even if one finds a magic compression bullet at zero incremental cost, though, the more important question is what problem one solves and/or whether one solves the right problem. {As an aside, 802.15.4 (which is the MAC with the 127-byte payload limit mentioned) does not easily allow mixed secured/unsecured communications (but I do not think it is useful to have a side-discussion on that detail right now).}

Some things cannot be compressed, like e.g. nonces, they can only be omitted by removing them at design time. Compression algorithms in themselves also add to the footprint. The approach of OSCORE and EDHOC has been to elide redundant information and define a compact format from the start. Do you think a lossless data compression performs better?

The other question I have is whether it would be more important to hide the identity of the joining node in a network enrollment scenario than to hide the network manager's identity, or the other way around.

There are different options to embed EDHOC in CoAP, the first request could be message_1 and the last response just an empty payload. Or the first request can be a trigger and message_1 carried in the first response.

Hope that helps,
Göran



From [1], Section 1.1:
EDHOC is optimized for small message sizes and can therefore be sent over a small number of radio frames. The message size of a key exchange protocol may have a large impact on the performance of an IoT deployment, especially in noisy environments. For example, in a network bootstrapping setting a large number of devices turned on in a short period of time may result in large latencies caused by parallel key exchanges.

Ref: [1] draft-selander-ace-cose-ecdhe-12
        [2] Email RS as of October 31, 2018, 2.32pm EDT, subject: https://mailarchive.ietf.org/arch/browse/ace/?q=struik

On 11/22/2018 10:43 AM, Rene Struik wrote:
Hi John:

When comparing protocols, it would be useful to protocol flows optimization, as follows:
a) optimized for parallelized online computations;
b) optimized for minimization of message flows.
See also slide 6 of my CFRG-83 presentation of March 30, 2012 (slides-83-cfrg-05 attached; I could not find CFRG records online).

The current draft-selander-ace-cose-ecdhe-10 document considers optimization b), which minimizes the number of message flows, but does require each party to compute the shared key consecutively, rather than in parallel (as in optimization a).

With option a), if one really wishes to squeeze as much info into a 128-octet datagram, one can already send A's ephemeral ECDSA signature key in message flow 1, thereby cutting down the
size of the second message flow of the Sigma protocol depicted in Fig. 1 (https://tools.ietf.org/html/draft-selander-ace-cose-ecdhe-10#page-11) by 32 octets. This tackles the 120-octet byte count for the second flow of Fig. 1 quite simply, while leading to a 4-pass protocol flow (with roughly 70/70/55/55 bytes in flows 1/2/3/4).

Obviously, this presents a trade-off, but quite well be worth it in settings where online key computations are quite slow on some platforms and where scheduling (e.g., with TSCH) can now be done with less consideration of the individual computational capabilities of devices (since now one does not need to build-in a worst-case 2 x "key computation back-off" for least capable devices, but can just use the 1x contingency for this).

The parallel version is depicted below.

Party
U Party V | C_U, X_U, ALG_1, UAD_1, R_Sig(U;...) | +--------------------------------------------------------------------->| | message_1 | | | | C_U, C_V, X_V, ALG_2, R_Sig(V; ...) | |<---------------------------------------------------------------------+ |
message_2 | | | | S_U, AEAD(K_3; ID_CRED_U, s_Sig(U; CRED_U, aad_3), PAD_3) | +--------------------------------------------------------------------->+ | message_3 |
|
| | S_V, AEAD(K_2;
ID_CRED_V, s_Sig(V; CRED_V, aad_2), UAD_2)| | +<---------------------------------------------------------------------| | message_4 |
==============================================================================

Flight                                #1         #2        #3    #4    Total

------------------------------------------------------------------------------

DTLS 1.3 RPK + ECDHE                 143        364       212     -     721

TLS 1.3  RPK + ECDHE                 129        322       194     -     645

EDHOC    RPK + ECDHE                  37        120        85     -     242

--> EDHOC parallel flow                 70         70        55     55    250
On 11/22/2018 7:23 AM, John Mattsson wrote:

Hi Jim,



In the analysis that I did I very deliberately used TLS not DTLS.  The main reason for using DTLS is because one is operating in the UDP environment and one cannot have reliable in order delivery.  Since EDHOC is being built on top of CoAP, one can use CoAP to create reliable in order delivery.  Thus, the extra bytes that DTLS has to deal with this are not needed.

I started with DTLS as that was what was discussion between Salvador and Benjamin. Below are numbers for TLS 1.3. Changes compared to DTLS 1.3 are that the record header is smaller, handshake headers are smaller, and that Connection ID is not supported in TLS 1.3. The numbers I get for TLS 1.3 are overall slightly bigger than the numbers in your estimate (but for PSK Flight #3 I get slightly smaller numbers). I think the difference is due to many smaller things like handshake headers and fields in the certificate structure that adds up. I plan to add TLS 1.3 numbers to draft-ietf-lwig-security-protocol-comparison as well.



I agree with your comment Jim. Just now, I am just trying to count the number of bytes of the security protocol. To do a fair comparison, you have to choose a specific deployment and look at the topology, the whole protocol stack, frame sizes (e.g. 128 bytes), how and where in the protocol stack fragmentation is done, and the expected packet loss. There is ongoing work on such simulations for 6tisch. Fragmentation and/or packet loss lead to the total number of bytes in the table below has to be multiplied by some linear factor. And as more bytes often lead to increased packet loss, you often see a non-linear relation between logical number of bytes on the transport/application layer as shown in the table below and physical number of bytes and/or time from completion of the protocol. Any realistic comparison over constrained radio would make the difference between TLS 1.3 and EDHOC larger. A problem with TLS is that it does not support Connection ID.



TLS Assumptions:

- Minimum number of algorithms and cipher suites offered

- Curve25519, ECDSA with P-256, AES-CCM_8, SHA-256

- Length of key identifiers: 4 bytes

- TLS RPK with point compression (saves 32 bytes)

- Only mandatory TLS extentions



==============================================================================

Flight                                #1         #2        #3       Total

------------------------------------------------------------------------------

DTLS 1.3 RPK + ECDHE                 143        364       212        721

TLS 1.3  RPK + ECDHE                 129        322       194        645

EDHOC    RPK + ECDHE                  37        120        85        242

------------------------------------------------------------------------------

DTLS 1.3 PSK + ECDHE                 180        183        56        419

TLS 1.3  PSK + ECDHE                 166        157        50        373

EDHOC    PSK + ECDHE                  42         46        11         99

------------------------------------------------------------------------------

DTLS 1.3 PSK                         130        143        56        329

TLS 1.3  PSK                         116        117        50        283

==============================================================================

                        Number of bytes (No connection ID)



Below is detailed information about the different flights:



======================================================

TLS 1.3 Flight #1 RPK + ECDHE

======================================================



Record Header - TLSPlaintext (5 bytes)

16 03 03 LL LL



     Handshake Header - Client Hello (4 bytes)

     01 LL LL LL



             Legacy Version (2 bytes)

             03 03



             Client Random (32 bytes)

             00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f



             Legacy Session ID (1 bytes)

             00



             Cipher Suites (TLS_AES_128_CCM_8_SHA256) (4 bytes)

             00 02 13 05



             Compression Methods (null) (2 bytes)

             01 00



             Extensions Length (2 bytes)

             LL LL



                    Extension - Supported Groups (x25519) (8 bytes)

                    00 0a 00 04 00 02 00 1d



                    Extension - Signature Algorithms (ecdsa_secp256r1_sha256) (8 bytes)

                    00 0d 00 04 00 02 08 07



                    Extension - Key Share (42 bytes)

                    00 33 00 26 00 24 00 1d 00 20

                    00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f



                    Extension - Supported Versions (1.3) (7 bytes)

                    00 2b 00 03 02 03 04



                    Extension - Client Certificate Type (Raw Public Key) (6 bytes)

                    00 13 00 01 01 02



                    Extension - Server Certificate Type (Raw Public Key) (6 bytes)

                    00 14 00 01 01 02



5 + 4 + 2 + 32 + 1 + 4 + 2 + 2 + 8 + 8 + 42 + 7 + 6 + 6 = 129 bytes



------------------------------------------------------

TLS 1.3 Flight #1 PSK + ECDHE

------------------------------------------------------



Differences compared to RPK + ECDHE



+ Extension - PSK Key Exchange Modes (6 bytes)

  00 2d 00 02 01 01



+ Extension - Pre Shared Key (51 bytes)

  00 29 00 2F

  00 0a 00 04 ID ID ID ID 00 00 00 00

  00 21 20 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f



- Extension - Signature Algorithms (ecdsa_secp256r1_sha256) (8 bytes)



- Extension - Client Certificate Type (Raw Public Key) (6 bytes)



- Extension - Server Certificate Type (Raw Public Key) (6 bytes)



129 + 6 + 51 - 8 - 6 - 6 = 166 bytes



------------------------------------------------------

TLS 1.3 Flight #1 PSK

------------------------------------------------------



Differences compared to PSK + ECDHE



- Extension - Supported Groups (x25519) (8 bytes)



- Extension - Key Share (42 bytes)



166 - 8 - 42 = 116 bytes







======================================================

TLS 1.3 Flight #2  RPK + ECDHE

======================================================



Record Header - TLSPlaintext (5 bytes)

16 03 03 LL LL



     Handshake Header - Server Hello (4 bytes)

     02 LL LL LL



             Legacy Version (2 bytes)

             fe fd



             Server Random (32 bytes)

             00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f



             Legacy Session ID (1 bytes)

             00



             Cipher Suite (TLS_AES_128_CCM_8_SHA256) (2 bytes)

             13 05



             Compression Method (null) (1 bytes)

             00



             Extensions Length (2 bytes)

             LL LL



                    Extension - Key Share (40 bytes)

                    00 33 00 24 00 1d 00 20

                    00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f



                    Extension - Supported Versions (1.3) (6 bytes)

                    00 2b 00 02 03 04



Record Header - TLSCiphertext (5 bytes)

17 03 03 LL LL



     Handshake Header - Encrypted Extensions (4 bytes)

     08 LL LL LL



             Extensions Length (2 bytes)

             LL LL



                    Extension - Client Certificate Type (Raw Public Key) (6 bytes)

                    00 13 00 01 01 02



                    Extension - Server Certificate Type (Raw Public Key) (6 bytes)

                    00 14 00 01 01 02



     Handshake Header - Certificate Request (4 bytes)

     0d LL LL LL



             Request Context (1 bytes)

             00



             Extensions Length (2 bytes)

             LL LL



                    Extension - Signature Algorithms (ecdsa_secp256r1_sha256) (8 bytes)

                    00 0d 00 04 00 02 08 07



     Handshake Header - Certificate (4 bytes)

     0b LL LL LL



             Request Context (1 bytes)

             00



             Certificate List Length (3 bytes)

             LL LL LL



             Certificate Length (3 bytes)

             LL LL LL



             Certificate (59 bytes) // Point compression

             ....



             Certificate Extensions (2 bytes)

             00 00



     Handshake Header - Certificate Verify (4 bytes)

     0f LL LL LL



             Signature  (68 bytes)

             ZZ ZZ 00 40 ....



     Handshake Header - Finished (4 bytes)

     14 LL LL LL



             Verify Data (32 bytes)

             00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f



     Record Type (1 byte)

     16



Auth Tag (8 bytes)

e0 8b 0e 45 5a 35 0a e5



5 + 90 + 5 + 18 + 15 + 72 + 72 + 36 + 1 + 8 = 322 bytes



------------------------------------------------------

TLS 1.3 Flight #2 PSK + ECDHE

------------------------------------------------------



Differences compared to RPK + ECDHE



- Handshake Message Certificate (72 bytes)



- Handshake Message CertificateVerify (72 bytes)



- Handshake Message CertificateRequest (15 bytes)



- Extension - Client Certificate Type (Raw Public Key) (6 bytes)



- Extension - Server Certificate Type (Raw Public Key) (6 bytes)



+ Extension - Pre Shared Key (6 bytes)

  00 29 00 02 00 00



322 - 72 - 72 - 15 - 6 - 6  + 6 = 157 bytes



------------------------------------------------------

TLS 1.3 Flight #2 PSK

------------------------------------------------------



Differences compared to PSK + ECDHE



- Extension - Key Share (40 bytes)



157 - 40 = 117 bytes







======================================================

TLS 1.3 Flight #3 RPK + ECDHE

======================================================



Record Header - TLSCiphertext (5 bytes)

17 03 03 LL LL



     Handshake Header - Certificate (4 bytes)

     0b LL LL LL



             Request Context (1 bytes)

             00



             Certificate List Length (3 bytes)

             LL LL LL



             Certificate Length (3 bytes)

             LL LL LL



             Certificate (59 bytes) // Point compression

             ....



             Certificate Extensions (2 bytes)

             00 00



     Handshake Header - Certificate Verify (4 bytes)

     0f LL LL LL



             Signature  (68 bytes)

             04 03 LL LL //ecdsa_secp256r1_sha256

             00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f

             00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f



     Handshake Header - Finished (4 bytes)

     14 LL LL LL



             Verify Data (32 bytes) // SHA-256

             00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f



     Record Type (1 byte)

     16



Auth Tag (8 bytes) // AES-CCM_8

00 01 02 03 04 05 06 07



5 + 72 + 72 + 36 + 1 + 8 = 194 bytes



------------------------------------------------------

TLS 1.3 Flight #3 PSK + ECDHE

-----------------------------------------------------



Differences compared to RPK + ECDHE



- Handshake Message Certificate (72 bytes)



- Handshake Message Certificate Verify (72 bytes)



194 - 72 - 72 = 50 bytes



------------------------------------------------------

TLS 1.3 Flight #3 PSK

-----------------------------------------------------



Differences compared to PSK + ECDHE



None



50 bytes





-----Original Message-----

From: Jim Schaad <ietf@augustcellars.com><mailto:ietf@augustcellars.com>

Date: Wednesday, 21 November 2018 at 16:25

To: John Mattsson <john.mattsson@ericsson.com><mailto:john.mattsson@ericsson.com>, "ace@ietf.org"<mailto:ace@ietf.org> <ace@ietf.org><mailto:ace@ietf.org>, "lwip@ietf.org"<mailto:lwip@ietf.org> <lwip@ietf.org><mailto:lwip@ietf.org>

Cc: 'Benjamin Kaduk' <kaduk@mit.edu><mailto:kaduk@mit.edu>, "salvador.p.f@um.es"<mailto:salvador.p.f@um.es> <salvador.p.f@um.es><mailto:salvador.p.f@um.es>

Subject: RE: [Ace] EDHOC standardization



John,



In the analysis that I did I very deliberately used TLS not DTLS.  The main reason for using DTLS is because one is operating in the UDP environment and one cannot have reliable in order delivery.  Since EDHOC is being built on top of CoAP, one can use CoAP to create reliable in order delivery.  Thus the extra bytes that DTLS has to deal with this are not needed.



Jim





-----Original Message-----

From: Ace <ace-bounces@ietf.org><mailto:ace-bounces@ietf.org> On Behalf Of John Mattsson

Sent: Wednesday, November 21, 2018 7:03 AM

To: ace@ietf.org<mailto:ace@ietf.org>; lwip@ietf.org<mailto:lwip@ietf.org>

Cc: Benjamin Kaduk <kaduk@mit.edu><mailto:kaduk@mit.edu>; salvador.p.f@um.es<mailto:salvador.p.f@um.es>

Subject: Re: [Ace] EDHOC standardization



Hi all,



Inspired by the discussion in this thread, I did more detailed calculations of the

number of bytes when DTLS 1.3 is used for typical IoT use cases (PSK, RPK,

Connection ID). The plan is to add this information to draft-ietf-lwig-security-

protocol-comparison as this has been requested by several people. I think some

bytes were missing in the earlier estimates for TLS 1.3, and as Ben commented,

DTLS 1.3 adds some bytes compared to TLS 1.3.



================================================================

==============

Flight                                #1         #2        #3       Total

------------------------------------------------------------------------------

DTLS 1.3 RPK + ECDHE                 149        373       213        735

DTLS 1.3 PSK + ECDHE                 186        190        57        433

DTLS 1.3 PSK                         136        150        57        343

------------------------------------------------------------------------------

EDHOC    RPK + ECDHE                  38        121        86        245

EDHOC    PSK + ECDHE                  43         47        12        102

================================================================

==============

                                 Number of bytes



Assumptions:

- Minimum number of algorithms and cipher suites offered

- Curve25519, ECDSA with P-256, AES-CCM_8, SHA-256

- Length of key identifiers: 4 bytes

- Connection identifiers: 1 byte

- The DTLS RPKs use point compression (saves 32 bytes)

- No DTLS handshake message fragmentation

- Only mandatory DTLS extentions, except for connection ID

- Version 30 https://tools.ietf.org/html/draft-ietf-tls-dtls13-30



(EDHOC numbers are for the soon to be published -11 version with cipher

suites)



I hope this information is useful for people. Please comment if I missed

something or if you have any suggestion of things to add or how to present

things. I do not know currently how these numbers compare to DTLS 1.2.



Below is detailed information about where the byte in different flights as well

as the RPKs (SubjectPublicKeyInfo). Most of the bytes should have the correct

value, but most of the length fields are just written as LL LL LL. Below is also

information about how resumption, cached information [RFC 7924], and not

using Connection ID affects the number of bytes.





======================================================

DTLS 1.3 Flight #1 RPK + ECDHE

======================================================



Record Header - DTLSPlaintext (13 bytes)

16 fe fd EE EE SS SS SS SS SS SS LL LL



       Handshake Header - Client Hello (10 bytes)

       01 LL LL LL SS SS 00 00 00 LL LL LL



              Legacy Version (2 bytes)

              fe fd



              Client Random (32 bytes)

              00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 14

15 16 17 18 19 1a 1b 1c 1d 1e 1f



              Legacy Session ID (1 bytes)

              00



              Cipher Suites (TLS_AES_128_CCM_8_SHA256) (4 bytes)

              00 02 13 05



              Compression Methods (null) (2 bytes)

              01 00



              Extensions Length (2 bytes)

              LL LL



                      Extension - Supported Groups (x25519) (8 bytes)

                      00 0a 00 04 00 02 00 1d



                      Extension - Signature Algorithms

(ecdsa_secp256r1_sha256) (8 bytes)

                      00 0d 00 04 00 02 08 07



                      Extension - Key Share (42 bytes)

                      00 33 00 26 00 24 00 1d 00 20

                      00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11

12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f



                      Extension - Supported Versions (1.3) (7 bytes)

                      00 2b 00 03 02 03 04



                      Extension - Client Certificate Type (Raw Public Key) (6

bytes)

                      00 13 00 01 01 02



                      Extension - Server Certificate Type (Raw Public Key) (6

bytes)

                      00 14 00 01 01 02



                      Extension - Connection Identifier (43) (6 bytes)

                      XX XX 00 02 01 42



13 + 10 + 2 + 32 + 1 + 4 + 2 + 2 + 8 + 8 + 42 + 7 + 6 + 6 + 6 = 149 bytes



------------------------------------------------------

DTLS 1.3 Flight #1 PSK + ECDHE

------------------------------------------------------



Differences compared to RPK + ECDHE



+ Extension - PSK Key Exchange Modes (6 bytes)

  00 2d 00 02 01 01



+ Extension - Pre Shared Key (51 bytes)

  00 29 00 2F

  00 0a 00 04 ID ID ID ID 00 00 00 00

  00 21 20 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 14 15

16 17 18 19 1a 1b 1c 1d 1e 1f



- Extension - Signature Algorithms (ecdsa_secp256r1_sha256) (8 bytes)



- Extension - Client Certificate Type (Raw Public Key) (6 bytes)



- Extension - Server Certificate Type (Raw Public Key) (6 bytes)



149 + 6 + 51 - 8 - 6 - 6 = 186 bytes



------------------------------------------------------

DTLS 1.3 Flight #1 PSK

------------------------------------------------------



Differences compared to PSK + ECDHE



- Extension - Supported Groups (x25519) (8 bytes)



- Extension - Key Share (42 bytes)



186 - 8 - 42 = 136 bytes







======================================================

DTLS 1.3 Flight #2  RPK + ECDHE

======================================================



Record Header - DTLSPlaintext (13 bytes)

16 fe fd EE EE SS SS SS SS SS SS LL LL



       Handshake Header - Server Hello (10 bytes)

       02 LL LL LL SS SS 00 00 00 LL LL LL



              Legacy Version (2 bytes)

              fe fd



              Server Random (32 bytes)

              00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 14

15 16 17 18 19 1a 1b 1c 1d 1e 1f



              Legacy Session ID (1 bytes)

              00



              Cipher Suite (TLS_AES_128_CCM_8_SHA256) (2 bytes)

              13 05



              Compression Method (null) (1 bytes)

              00



              Extensions Length (2 bytes)

              LL LL



                      Extension - Key Share (40 bytes)

                      00 33 00 24 00 1d 00 20

                      00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11

12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f



                      Extension - Supported Versions (1.3) (6 bytes)

                      00 2b 00 02 03 04



                      Extension - Connection Identifier (43) (6 bytes)

                      XX XX 00 02 01 43



Record Header - DTLSCiphertext, Full (6 bytes) HH ES SS 43 LL LL



       Handshake Header - Encrypted Extensions (10 bytes)

       08 LL LL LL SS SS 00 00 00 LL LL LL



              Extensions Length (2 bytes)

              LL LL



                      Extension - Client Certificate Type (Raw Public Key) (6

bytes)

                      00 13 00 01 01 02



                      Extension - Server Certificate Type (Raw Public Key) (6

bytes)

                      00 14 00 01 01 02



       Handshake Header - Certificate Request (10 bytes)

       0d LL LL LL SS SS 00 00 00 LL LL LL



              Request Context (1 bytes)

              00



              Extensions Length (2 bytes)

              LL LL



                      Extension - Signature Algorithms

(ecdsa_secp256r1_sha256) (8 bytes)

                      00 0d 00 04 00 02 08 07



       Handshake Header - Certificate (10 bytes)

       0b LL LL LL SS SS 00 00 00 LL LL LL



              Request Context (1 bytes)

              00



              Certificate List Length (3 bytes)

              LL LL LL



              Certificate Length (3 bytes)

              LL LL LL



              Certificate (59 bytes) // Point compression

              ....



              Certificate Extensions (2 bytes)

              00 00



       Handshake Header - Certificate Verify (10 bytes)

       0f LL LL LL SS SS 00 00 00 LL LL LL



              Signature  (68 bytes)

              ZZ ZZ 00 40 ....



       Handshake Header - Finished (10 bytes)

       14 LL LL LL SS SS 00 00 00 LL LL LL



              Verify Data (32 bytes)

              00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 14

15 16 17 18 19 1a 1b 1c 1d 1e 1f



       Record Type (1 byte)

       16



Auth Tag (8 bytes)

e0 8b 0e 45 5a 35 0a e5



13 + 102 + 6 + 24 + 21 + 78 + 78 + 42 + 1 + 8 = 373 bytes



------------------------------------------------------

DTLS 1.3 Flight #2 PSK + ECDHE

------------------------------------------------------



Differences compared to RPK + ECDHE



- Handshake Message Certificate (78 bytes)



- Handshake Message CertificateVerify (78 bytes)



- Handshake Message CertificateRequest (21 bytes)



- Extension - Client Certificate Type (Raw Public Key) (6 bytes)



- Extension - Server Certificate Type (Raw Public Key) (6 bytes)



+ Extension - Pre Shared Key (6 bytes)

  00 29 00 02 00 00



373 - 78 - 78 - 21 - 6 - 6  + 6 = 190 bytes



------------------------------------------------------

DTLS 1.3 Flight #2 PSK

------------------------------------------------------



Differences compared to PSK + ECDHE



- Extension - Key Share (40 bytes)



190 - 40 = 150 bytes







======================================================

DTLS 1.3 Flight #3 RPK + ECDHE

======================================================



Record Header (6 bytes) // DTLSCiphertext, Full ZZ ES SS 42 LL LL



       Handshake Header - Certificate (10 bytes)

       0b LL LL LL SS SS XX XX XX LL LL LL



              Request Context (1 bytes)

              00



              Certificate List Length (3 bytes)

              LL LL LL



              Certificate Length (3 bytes)

              LL LL LL



              Certificate (59 bytes) // Point compression

              ....



              Certificate Extensions (2 bytes)

              00 00



       Handshake Header - Certificate Verify (10 bytes)

       0f LL LL LL SS SS 00 00 00 LL LL LL



              Signature  (68 bytes)

              04 03 LL LL //ecdsa_secp256r1_sha256

              00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 14

15 16 17 18 19 1a 1b 1c 1d 1e 1f

              00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 14

15 16 17 18 19 1a 1b 1c 1d 1e 1f



       Handshake Header - Finished (10 bytes)

       14 LL LL LL SS SS 00 00 00 LL LL LL



              Verify Data (32 bytes) // SHA-256

              00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 14

15 16 17 18 19 1a 1b 1c 1d 1e 1f



       Record Type (1 byte)

       16



Auth Tag (8 bytes) // AES-CCM_8

00 01 02 03 04 05 06 07



6 + 78 + 78 + 42 + 1 + 8 = 213 bytes



------------------------------------------------------

DTLS 1.3 Flight #3 PSK + ECDHE

-----------------------------------------------------



Differences compared to RPK + ECDHE



- Handshake Message Certificate (78 bytes)



- Handshake Message Certificate Verify (78 bytes)



213 - 78 - 78 = 57 bytes



------------------------------------------------------

DTLS 1.3 Flight #3 PSK

-----------------------------------------------------



Differences compared to PSK + ECDHE



None



57 bytes















======================================================

DTLS 1.3 - Cached information [RFC 7924]

======================================================



- Cached information together with server X.509 can be used to move bytes

from flight #2 to flight #1

  (cached RPK increases the number of bytes compared to cached X.509)



Differences compared to RPK + ECDHE



Flight #1



- Extension - Server Certificate Type (Raw Public Key) (6 bytes)



+ Extension - Client Cashed Information (39 bytes)

  00 19 LL LL LL LL

  01 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 14 15 16 17

18 19 1a 1b 1c 1d 1e 1f



149 + 33 = 182 bytes



Flight #2



- Extension - Server Certificate Type (Raw Public Key) (6 bytes)



+ Extension - Server Cashed Information (7 bytes)

  00 19 LL LL LL LL 01



- Server Certificate (59 bytes -> 32 bytes)



373 - 26 = 347 bytes



================================================================

==============

Flight                                #1         #2        #3       Total

------------------------------------------------------------------------------

DTLS 1.3 Cached X.509/RPK + ECDHE    182        347       213        742

DTLS 1.3 RPK + ECDHE                 149        373       213        735

================================================================

==============







======================================================

DTLS 1.3 - Resumption

======================================================



To enable resumption, a 4th flight (New Session Ticket) is added



Flight #4 - New Session Ticket



Record Header - DTLSCiphertext, Full (6 bytes) HH ES SS 43 LL LL



       Handshake Header - New Session Ticket (10 bytes)

       04 LL LL LL SS SS 00 00 00 LL LL LL



              Ticket Lifetime (4 bytes)

              00 01 02 03



              Ticket Age Add (4 bytes)

              00 01 02 03



              Ticket Nonce (2 bytes)

              01 00



              Ticket (6 bytes)

              00 04 ID ID ID ID



              Extensions (2 bytes)

              00 00



Auth Tag (8 bytes) // AES-CCM_8

00 01 02 03 04 05 06 07



6 + 10 + 4 + 4 + 2 + 6 + 2 + 8 = 42 bytes



The resumption handshake is just a PSK handshake with 136 + 150 + 57 = 343

bytes



================================================================

==============

Flight                                      #1     #2     #3     #4    Total

------------------------------------------------------------------------------

DTLS 1.3 RPK + ECDHE + NewSessionTicket    149    373    213     42      777

DTLS 1.3 PSK (resumption)                  136    150     57             343

================================================================

==============







======================================================

DTLS 1.3 - Connection ID

======================================================



Without a Connection ID the DTLS 1.3 flight sizes changes as follows



DTLS 1.3 Flight #1:   -6 bytes

DTLS 1.3 Flight #2:   -7 bytes

DTLS 1.3 Flight #3:   -1 byte







================================================================

==============

Flight                                #1         #2        #3       Total

------------------------------------------------------------------------------

DTLS 1.3 RPK + ECDHE (no cid)        143        364       212        721

DTLS 1.3 PSK + ECDHE (no cid)        180        183        56        419

DTLS 1.3 PSK (no cid)                130        143        56        329

================================================================

==============











======================================================

DTLS Raw Public Keys

======================================================



SubjectPublicKeyInfo without point compression

-----------------------------------------------------



0x30 // Sequence

0x59 // Size 89



0x30 // Sequence

0x13 // Size 19

0x06 0x07 0x2A 0x86 0x48 0xCE 0x3D 0x02 0x01.     // OID 1.2.840.10045.2.1

(ecPublicKey)

0x06 0x08 0x2A 0x86 0x48 0xCE 0x3D 0x03 0x01 0x07 // OID

1.2.840.10045.3.1.7 (secp256r1)



0x03 // Bit string

0x42 // Size 66

0x00 // Unused bits 0

0x04 // Uncompressed

...... 64 bytes X and Y



Total of 91 bytes



SubjectPublicKeyInfo with point compression

-----------------------------------------------------



0x30 // Sequence

0x59 // Size 89



0x30 // Sequence

0x13 // Size 19

0x06 0x07 0x2A 0x86 0x48 0xCE 0x3D 0x02 0x01.     // OID 1.2.840.10045.2.1

(ecPublicKey)

0x06 0x08 0x2A 0x86 0x48 0xCE 0x3D 0x03 0x01 0x07 // OID

1.2.840.10045.3.1.7 (secp256r1)



0x03 // Bit string

0x42 // Size 66

0x00 // Unused bits 0

0x03 // Compressed

...... 32 bytes X



Total of 59 bytes





======================================================

Helpful Sources of Information

======================================================



In addition to relevant RFCs and the estimates done by Jim, the following

references were helpful:



Every Byte Explained: The Illustrated TLS 1.3 Connection

https://tls13.ulfheim.net/



Digital Certificates for the Internet of Things https://kth.diva-

portal.org/smash/get/diva2:1153958/FULLTEXT01.pdf



/John









-----Original Message-----

From: Benjamin Kaduk <kaduk@mit.edu><mailto:kaduk@mit.edu>

Date: Saturday, 3 November 2018 at 15:59

To: John Mattsson <john.mattsson@ericsson.com><mailto:john.mattsson@ericsson.com>

Cc: "salvador.p.f@um.es"<mailto:salvador.p.f@um.es> <salvador.p.f@um.es><mailto:salvador.p.f@um.es>, "ace@ietf.org"<mailto:ace@ietf.org>

<ace@ietf.org><mailto:ace@ietf.org>

Subject: Re: [Ace] EDHOC standardization



On Fri, Nov 02, 2018 at 02:55:54PM +0000, John Mattsson wrote:

Hi Benjamin, Salvador



While DTLS 1.3 have done a very good job of lowering the overhead of the

record layer when application data is sent (see e.g.

https://tools.ietf.org/html/draft-ietf-lwig-security-protocol-comparison-01 for a

comparison between different protocols), I do not think the handshake protocol

is much leaner (is it leaner at all?).



(There are some handshake messages that are removed entirely.)



We tried to make an fair comparison between EDHOC and TLS 1.3 in the

presentation at IETF 101 (see

https://datatracker.ietf.org/meeting/101/materials/slides-101-ace-key-

exchange-w-oscore-00). Since then, we have significantly optimized the

encoding in EDHOC and the upcoming version (-11) is expected to have the

following message sizes.

   Auth.               PSK       RPK       x5t     x5chain

   --------------------------------------------------------------------

   EDHOC message_1      43        38        38        38

   EDHOC message_2      47       121       127       117 + Certificate chain

   EDHOC message_3      12        86        92        82 + Certificate chain

   --------------------------------------------------------------------

   Total               102       245       257       237 + Certificate chains



As Salvador writes, the handshakes in TLS 1.3 and DTLS 1.3 are basically the

same, so the numbers presented at IETF 101 should be a good estimate also for

DTLS 1.3.

   Auth.                PSK       RPK

   --------------------------------------------------------------------

   (D)TLS message_1     142       107

   (D)TLS message_2     135       264

   (D)TLS message_3      51       167

   --------------------------------------------------------------------

   Total                328       538

Thanks for the numbers!



The numbers above include ECDHE. For handshake messages, my

understanding is that the DTLS 1.3 and TLS 1.3 record layer have exactly the

same size.



The DTLS 1.3 ones will be worse, due to the epoch and sequence number fields.



-Ben



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