LWIG Working Group                                     J. Preuß Mattsson
Internet-Draft                                              F. Palombini
Intended status: Informational                                  Ericsson
Expires: 28 June 2023                                         M. Vučinić
                                                                   INRIA
                                                        25 December 2022


                 Comparison of CoAP Security Protocols
            draft-ietf-lwig-security-protocol-comparison-06

Abstract

   This document analyzes and compares the sizes of key exchange flights
   and the per-packet message size overheads when using different
   security protocols to secure CoAP.  Small message sizes are very
   important for reducing energy consumption, latency, and time to
   completion in constrained radio network such as Low-Power Wide Area
   Networks (LPWANs).  The analyzed security protocols are DTLS 1.2,
   DTLS 1.3, TLS 1.2, TLS 1.3, cTLS, EDHOC, OSCORE, and Group OSCORE.
   The DTLS and TLS record layers are analyzed with and without 6LoWPAN-
   GHC compression.  DTLS is analyzed with and without Connection ID.

Status of This Memo

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   This Internet-Draft will expire on 28 June 2023.

Copyright Notice

   Copyright (c) 2022 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.



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   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Overhead of Key Exchange Protocols  . . . . . . . . . . . . .   4
     2.1.  Summary . . . . . . . . . . . . . . . . . . . . . . . . .   5
     2.2.  DTLS 1.3  . . . . . . . . . . . . . . . . . . . . . . . .   6
       2.2.1.  Message Sizes RPK + ECDHE . . . . . . . . . . . . . .   6
       2.2.2.  Message Sizes PSK + ECDHE . . . . . . . . . . . . . .  12
       2.2.3.  Message Sizes PSK . . . . . . . . . . . . . . . . . .  13
       2.2.4.  Cached Information  . . . . . . . . . . . . . . . . .  14
       2.2.5.  Resumption  . . . . . . . . . . . . . . . . . . . . .  15
       2.2.6.  DTLS Without Connection ID  . . . . . . . . . . . . .  16
       2.2.7.  Raw Public Keys . . . . . . . . . . . . . . . . . . .  16
     2.3.  TLS 1.3 . . . . . . . . . . . . . . . . . . . . . . . . .  17
       2.3.1.  Message Sizes RPK + ECDHE . . . . . . . . . . . . . .  18
       2.3.2.  Message Sizes PSK + ECDHE . . . . . . . . . . . . . .  24
       2.3.3.  Message Sizes PSK . . . . . . . . . . . . . . . . . .  25
     2.4.  TLS 1.2 and DTLS 1.2  . . . . . . . . . . . . . . . . . .  26
     2.5.  EDHOC . . . . . . . . . . . . . . . . . . . . . . . . . .  26
       2.5.1.  Message Sizes RPK . . . . . . . . . . . . . . . . . .  26
       2.5.2.  Summary . . . . . . . . . . . . . . . . . . . . . . .  27
     2.6.  Conclusion  . . . . . . . . . . . . . . . . . . . . . . .  28
   3.  Overhead for Protection of Application Data . . . . . . . . .  28
     3.1.  Summary . . . . . . . . . . . . . . . . . . . . . . . . .  29
     3.2.  DTLS 1.2  . . . . . . . . . . . . . . . . . . . . . . . .  30
       3.2.1.  DTLS 1.2  . . . . . . . . . . . . . . . . . . . . . .  31
       3.2.2.  DTLS 1.2 with 6LoWPAN-GHC . . . . . . . . . . . . . .  31
       3.2.3.  DTLS 1.2 with Connection ID . . . . . . . . . . . . .  32
       3.2.4.  DTLS 1.2 with Connection ID and 6LoWPAN-GHC . . . . .  33
     3.3.  DTLS 1.3  . . . . . . . . . . . . . . . . . . . . . . . .  33
       3.3.1.  DTLS 1.3  . . . . . . . . . . . . . . . . . . . . . .  33
       3.3.2.  DTLS 1.3 with 6LoWPAN-GHC . . . . . . . . . . . . . .  34
       3.3.3.  DTLS 1.3 with Connection ID . . . . . . . . . . . . .  34
       3.3.4.  DTLS 1.3 with Connection ID and 6LoWPAN-GHC . . . . .  35
     3.4.  TLS 1.2 . . . . . . . . . . . . . . . . . . . . . . . . .  35
       3.4.1.  TLS 1.2 . . . . . . . . . . . . . . . . . . . . . . .  35
       3.4.2.  TLS 1.2 with 6LoWPAN-GHC  . . . . . . . . . . . . . .  36
     3.5.  TLS 1.3 . . . . . . . . . . . . . . . . . . . . . . . . .  36
       3.5.1.  TLS 1.3 . . . . . . . . . . . . . . . . . . . . . . .  36
       3.5.2.  TLS 1.3 with 6LoWPAN-GHC  . . . . . . . . . . . . . .  37
     3.6.  OSCORE  . . . . . . . . . . . . . . . . . . . . . . . . .  37
     3.7.  Group OSCORE  . . . . . . . . . . . . . . . . . . . . . .  39



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     3.8.  Conclusion  . . . . . . . . . . . . . . . . . . . . . . .  40
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .  41
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  41
   6.  Informative References  . . . . . . . . . . . . . . . . . . .  41
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  45
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  45

1.  Introduction

   Small message sizes are very important for reducing energy
   consumption, latency, and time to completion in constrained radio
   network such as Low-Power Personal Area Networks (LPPANs) and Low-
   Power Wide Area Networks (LPWANs).  Constrained radio networks are
   not only characterized by very small frame sizes on the order of tens
   of bytes transmitted a few times per day at ultra-low speeds, but
   also high latency, and severe duty cycles constraints.  Some
   constrained radio networks are also multi-hop where the already small
   frame sizes are additionally reduced for each additional hop.  Too
   large payload sizes can easily lead to unacceptable completion times
   due to fragmentation into a large number of frames and long waiting
   times between frames can be sent (or resent in the case of
   transmission errors).  In constrained radio networks, the processing
   energy costs are typically almost negligible compared to the energy
   costs for radio and the energy costs for sensor measurement.  Keeping
   the number of bytes or frames low is also essential for low latency
   and time to completion as well as efficient use of spectrum to
   support a large number of devices.  For an overview of LPWANs and
   their limitations, see [RFC8376].

   To reduce overhead, processing, and energy consumption in constrained
   radio networks, IETF has created several working groups and
   technologies for constrained networks, e.g., (here technologies in
   parenthesis when the name is different from the working group): 6lo,
   6LoWPAN, 6TiSCH, ACE, CBOR, CoRE (CoAP, OSCORE), COSE, LAKE (EDHOC),
   LPWAN (SCHC), ROLL (RPL), and TLS (cTLS).  Compact formats and
   protocol have also been suggested as a way to decrease the energy
   consumption of Internet Applications and Systems in general
   [E-impact].

   This document analyzes and compares the sizes of key exchange flights
   and the per-packet message size overheads when using different
   security protocols to secure CoAP over UPD [RFC7252] and TCP
   [RFC8323].  The analyzed security protocols are DTLS 1.2 [RFC6347],
   DTLS 1.3 [RFC9147], TLS 1.2 [RFC5246], TLS 1.3 [RFC8446], cTLS
   [I-D.ietf-tls-ctls], EDHOC [I-D.ietf-lake-edhoc]
   [I-D.ietf-core-oscore-edhoc], OSCORE [RFC8613], and Group OSCORE
   [I-D.ietf-core-oscore-groupcomm].




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   The DTLS and TLS record layers are analyzed with and without 6LoWPAN-
   GHC compression.  DTLS is analyzed with and without Connection ID
   [RFC9146].  Readers are expected to be familiar with some of the
   terms described in RFC 7925 [RFC7925], such as ICV.  Section 2
   compares the overhead of key exchange, while Section 3 covers the
   overhead for protection of application data.

   Readers of this document also might be interested in the following
   documents: [Illustrated-TLS12], [Illustrated-TLS13],
   [Illustrated-DTLS13], and [I-D.ietf-lake-traces] gives an explanation
   of every byte in example TLS 1.2, TLS 1.3, DTLS 1.3, and EDHOC
   instances.  [RFC9191] looks at potential tools available for
   overcoming the deployment challenges induced by large certificates
   and long certificate chains and discusses solutions available to
   overcome these challenges.  [I-D.ietf-cose-cbor-encoded-cert] gives
   examples of IoT and Web certificates as well as examples on how
   effective C509 an TLS certificate compression [RFC8879] is at
   compressing example certificate and certificate chains.

2.  Overhead of Key Exchange Protocols

   This section analyzes and compares the sizes of key exchange flights
   for different protocols.

   To enable a fair comparison between protocols, the following
   assumptions are made:

   *  All the overhead calculations in this section use AES-CCM with a
      tag length of 8 bytes (e.g., AES_128_CCM_8 or AES-CCM-16-64-128).

   *  A minimum number of algorithms and cipher suites is offered.  The
      algorithm used/offered are Curve25519 or P-256, ECDSA with P-256,
      AES-CCM_8, and SHA-256.

   *  The length of key identifiers are 1 byte.

   *  The length of connection identifiers are 1 byte.

   *  DTLS handshake message fragmentation is not considered.

   *  Several DTLS handshake messages are sent in a single record.

   *  Only mandatory (D)TLS extensions are included.

   Section 2.1 gives a short summary of the message overhead based on
   different parameters and some assumptions.  The following sections
   detail the assumptions and the calculations.




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2.1.  Summary

   The DTLS overhead is dependent on the parameter Connection ID.  The
   following overheads apply for all Connection IDs of the same length,
   when Connection ID is used.

   The EDHOC overhead is dependent on the key identifiers included.  The
   following overheads apply for Sender IDs of the same length.

   All the overhead are dependent on the tag length.  The following
   overheads apply for tags of the same length.

   Figure 1 compares the message sizes of DTLS 1.3 [RFC9147] and EDHOC
   [I-D.ietf-lake-edhoc] handshakes with connection ID.  EDHOC is
   typically sent over CoAP which would add 4 bytes to flight #1 and #2
   and 5 bytes to flight #3 (4 byte CoAP header and 1 byte Connection
   ID).

   =====================================================================
    Flight                                   #1      #2      #3   Total
   ---------------------------------------------------------------------
    DTLS 1.3 - RPKs, ECDHE                  152     414     248     814
    DTLS 1.3 - Compressed RPKs, ECDHE       152     382     216     750
    DTLS 1.3 - Cached RPK, ECDHE            191     362     248     801
    DTLS 1.3 - Cached X.509, RPK, ECDHE     185     356     248     789
    DTLS 1.3 - PSK, ECDHE                   186     193      56     435
    DTLS 1.3 - PSK                          136     153      56     345
   ---------------------------------------------------------------------
    EDHOC - X.509, Signature, x5t, ECDHE     37     115      90     242
    EDHOC - X.509, Signature, kid, ECDHE     37     102      77     216
    EDHOC - RPK, Static DH, x5t, ECDHE       37      58      33     128
    EDHOC - RPK, Static DH, kid, ECDHE       37      45      19     101
   =====================================================================

     Figure 1: Comparison of message sizes in bytes with Connection ID

   Figure 2 compares of message sizes of DTLS 1.3 [RFC9147] and TLS 1.3
   [RFC8446] handshakes without connection ID.













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   =====================================================================
    Flight                                   #1      #2      #3   Total
   ---------------------------------------------------------------------
    DTLS 1.3 - RPK, ECDHE                   146     407     247     800
    DTLS 1.3 - PSK, ECDHE                   180     186      55     421
    DTLS 1.3 - PSK                          130     146      55     331
   ---------------------------------------------------------------------
    TLS 1.3  - RPK, ECDHE                   129     354     226     709
    TLS 1.3  - PSK, ECDHE                   163     157      50     370
    TLS 1.3  - PSK                          113     117      50     280
   ---------------------------------------------------------------------
    cTLS - X.509s by reference, ECDHE        71     143      78     292
   =====================================================================

    Figure 2: Comparison of message sizes in bytes without Connection ID

   The cTLS example in Figure 2. is taken from [I-D.ietf-tls-ctls].  The
   details of the other message size calculations are given in the
   following sections.

2.2.  DTLS 1.3

   This section gives an estimate of the message sizes of DTLS 1.3 with
   different authentication methods.  Note that the examples in this
   section are not test vectors, the cryptographic parts are just
   replaced with byte strings of the same length, while other fixed
   length fields are replace with arbitrary strings or omitted, in which
   case their length is indicated.  Values that are not arbitrary are
   given in hexadecimal.

2.2.1.  Message Sizes RPK + ECDHE

   In this section, a Connection ID of 1 byte is used.

2.2.1.1.  Flight #1

   Record Header - DTLSPlaintext (13 bytes):
   16 fe fd EE EE SS SS SS SS SS SS LL LL

     Handshake Header - Client Hello (12 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



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       Legacy Session ID (1 bytes):
       00

       Legacy Cookie (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 + 12 + 2 + 32 + 1 + 1 + 4 + 2 + 2 + 8 + 8 + 42 + 7 + 6 + 6 + 6
   = 152 bytes

   DTLS 1.3 RPK + ECDHE flight #1 gives 152 bytes of overhead.

2.2.1.2.  Flight #2






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   Record Header - DTLSPlaintext (13 bytes):
   16 fe fd EE EE SS SS SS SS SS SS LL LL

     Handshake Header - Server Hello (12 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 (3 bytes):
   HH 42 SS

     Handshake Header - Encrypted Extensions (12 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




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         Extension - Server Certificate Type (Raw Public Key) (6 bytes):
         00 14 00 01 01 02

     Handshake Header - Certificate Request (12 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 (12 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 (91 bytes): \\ 91 byte RPK see Section 2.2.7.
       ....

       Certificate Extensions (2 bytes):
       00 00

     Handshake Header - Certificate Verify (12 bytes):
     0f LL LL LL SS SS 00 00 00 LL LL LL

       Signature  (68 bytes):
       ZZ ZZ 00 40 ....

     Handshake Header - Finished (12 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):



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     16

   Auth Tag (8 bytes):
   e0 8b 0e 45 5a 35 0a e5

   13 + 104 + 3 + 26 + 23 + 112 + 80 + 44 + 1 + 8 = 414 bytes

   DTLS 1.3 RPK + ECDHE flight #2 gives 414 bytes of overhead.  With a
   point compressed RPK the overhead is 414 - 32 = 382 bytes, see
   Section 2.2.7.

2.2.1.3.  Flight #3







































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   Record Header (3 bytes): // DTLSCiphertext
   ZZ 43 SS

     Handshake Header - Certificate (12 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 (91 bytes): \\ 91 byte RPK see Section 2.2.7.
       ....

       Certificate Extensions (2 bytes):
       00 00

     Handshake Header - Certificate Verify (12 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 (12 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

   3 + 112 + 80 + 44 + 1 + 8 = 248 bytes






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   DTLS 1.3 RPK + ECDHE flight #3 gives 248 bytes of overhead.  With a
   point compressed RPK the overhead is 248 - 32 = 216 bytes, see
   Section 2.2.7.

2.2.2.  Message Sizes PSK + ECDHE

2.2.2.1.  Flight #1

   The differences in overhead compared to Section 2.2.1.1 are:

   The following is added:

   + Extension - PSK Key Exchange Modes (6 bytes):
     00 2d 00 02 01 01

   + Extension - Pre Shared Key (48 bytes):
     00 29 00 2F
     00 0a 00 01 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

   The following is removed:

   - 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)

   In total:

   152 + 6 + 48 - 8 - 6 - 6 = 186 bytes

   DTLS 1.3 PSK + ECDHE flight #1 gives 186 bytes of overhead.

2.2.2.2.  Flight #2

   The differences in overhead compared to Section 2.2.1.2 are:

   The following is added:

   + Extension - Pre Shared Key (6 bytes)
     00 29 00 02 00 00

   The following is removed:






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   - Handshake Message Certificate (112 bytes)

   - Handshake Message CertificateVerify (80 bytes)

   - Handshake Message CertificateRequest (23 bytes)

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

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

   In total:

   414 + 6 - 112 - 80 - 23 - 6 - 6 = 193 bytes

   DTLS 1.3 PSK + ECDHE flight #2 gives 193 bytes of overhead.

2.2.2.3.  Flight #3

   The differences in overhead compared to Section 2.2.1.3 are:

   The following is removed:

   - Handshake Message Certificate (112 bytes)

   - Handshake Message Certificate Verify (80 bytes)

   In total:

   248 - 112 - 80 = 56 bytes

   DTLS 1.3 PSK + ECDHE flight #3 gives 56 bytes of overhead.

2.2.3.  Message Sizes PSK

2.2.3.1.  Flight #1

   The differences in overhead compared to Section 2.2.2.1 are:

   The following is removed:

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

   - Extension - Key Share (42 bytes)

   In total:

   186 - 8 - 42 = 136 bytes




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   DTLS 1.3 PSK flight #1 gives 136 bytes of overhead.

2.2.3.2.  Flight #2

   The differences in overhead compared to Section 2.2.2.2 are:

   The following is removed:

   - Extension - Key Share (40 bytes)

   In total:

   193 - 40 = 153 bytes

   DTLS 1.3 PSK flight #2 gives 153 bytes of overhead.

2.2.3.3.  Flight #3

   There are no differences in overhead compared to Section 2.2.2.3.

   DTLS 1.3 PSK flight #3 gives 56 bytes of overhead.

2.2.4.  Cached Information

   In this section, we consider the effect of [RFC7924] on the message
   size overhead.

   Cached information can be used to use a cached server cerificate from
   a previous connection and move bytes from flight #2 to flight #1.
   The cached certificate can be a RPK or X.509.

   The differences compared to Section 2.2.1 are the following.

2.2.4.1.  Flight #1

   For the flight #1, the following is added:

   + 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

   Giving a total of:

   152 + 39 = 191 bytes

   In the case the cached certificate is X.509 the following is removed:




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

   Giving a total of:

   191 - 6 = 185 bytes

2.2.4.2.  Flight #2

   For the flight #2, the following is added:

   + Extension - Server Cashed Information (7 bytes):
     00 19 LL LL LL LL 01

   And the following is reduced:

   - Server Certificate (91 bytes -> 32 bytes)

   Giving a total of:

   414 + 7 - 59 = 362 bytes

   In the case the cached certificate is X.509 the following is removed:

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

   Giving a total of:

   362 - 6 = 356 bytes

2.2.5.  Resumption

   To enable resumption, a 4th flight with a the handshake message New
   Session Ticket is added to the DTLS handshake.


















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   Record Header - DTLSCiphertext (3 bytes):
   HH 42 SS

     Handshake Header - New Session Ticket (12 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

   3 + 12 + 4 + 4 + 2 + 6 + 2 + 8 = 41 bytes

   Enabling resumption adds 41 bytes to the initial DTLS handshake.  The
   resumption handshake is an ordinaty PSK handshake with our without
   ECDHE.

2.2.6.  DTLS Without 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

2.2.7.  Raw Public Keys

   This sections illustrates the format of P-256 (secp256r1)
   SubjectPublicKeyInfo [RFC5480] with and without point compression.
   Point compression in SubjectPublicKeyInfo is standardized in
   [RFC5480] and is therefore theoretically possible to use in PRKs and
   X.509 certificates used in (D)TLS but does not seems to be supported
   by (D)TLS implementations.





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2.2.7.1.  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

2.2.7.2.  SubjectPublicKeyInfo With Point Compression

   0x30 // Sequence
   0x39 // Size 57

   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
   0x22 // Size 34
   0x00 // Unused bits 0
   0x03 // Compressed
   ...... 32 bytes X

   Total of 59 bytes

2.3.  TLS 1.3

   In this section, the message sizes are calculated for TLS 1.3.  The
   major changes compared to DTLS 1.3 are a different record header, the
   handshake headers is smaller, and that Connection ID is not
   supported.  Recently, additional work has taken shape with the goal
   to further reduce overhead for TLS 1.3 (see [I-D.ietf-tls-ctls]).




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2.3.1.  Message Sizes RPK + ECDHE

2.3.1.1.  Flight #1
















































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   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




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   TLS 1.3 RPK + ECDHE flight #1 gives 129 bytes of overhead.

2.3.1.2.  Flight #2

   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



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         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 (91 bytes): \\ 91 byte RPK see Section 2.2.7.
       ....

       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):



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     16

   Auth Tag (8 bytes):
   e0 8b 0e 45 5a 35 0a e5

   5 + 90 + 5 + 18 + 15 + 104 + 72 + 36 + 1 + 8 = 354 bytes

   TLS 1.3 RPK + ECDHE flight #2 gives 354 bytes of overhead.

2.3.1.3.  Flight #3









































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   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 (91 bytes): \\ 91 byte RPK see Section 2.2.7.
       ....

       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 + 104 + 72 + 36 + 1 + 8 = 226 bytes

   TLS 1.3 RPK + ECDHE flight #3 gives 226 bytes of overhead.



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2.3.2.  Message Sizes PSK + ECDHE

2.3.2.1.  Flight #1

   The differences in overhead compared to Section 2.3.1.3 are:

   The following is added:

   + Extension - PSK Key Exchange Modes (6 bytes):
     00 2d 00 02 01 01

   + Extension - Pre Shared Key (48 bytes):
     00 29 00 2F
     00 0a 00 01 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

   The following is removed:

   - 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)

   In total:

   129 + 6 + 48 - 8 - 6 - 6 = 163 bytes

   TLS 1.3 PSK + ECDHE flight #1 gives 163 bytes of overhead.

2.3.2.2.  Flight #2

   The differences in overhead compared to Section 2.3.1.2 are:

   The following is added:

   + Extension - Pre Shared Key (6 bytes)
     00 29 00 02 00 00

   The following is removed:










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   - Handshake Message Certificate (104 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)

   In total:

   354 - 104 - 72 - 15 - 6 - 6  + 6 = 157 bytes

   TLS 1.3 PSK + ECDHE flight #2 gives 157 bytes of overhead.

2.3.2.3.  Flight #3

   The differences in overhead compared to Section 2.3.1.3 are:

   The following is removed:

   - Handshake Message Certificate (104 bytes)

   - Handshake Message Certificate Verify (72 bytes)

   In total:

   226 - 104 - 72 = 50 bytes

   TLS 1.3 PSK + ECDHE flight #3 gives 50 bytes of overhead.

2.3.3.  Message Sizes PSK

2.3.3.1.  Flight #1

   The differences in overhead compared to Section 2.3.2.1 are:

   The following is removed:

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

   - Extension - Key Share (42 bytes)

   In total:

   163 - 8 - 42 = 113 bytes




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   TLS 1.3 PSK flight #1 gives 113 bytes of overhead.

2.3.3.2.  Flight #2

   The differences in overhead compared to Section 2.3.2.2 are:

   The following is removed:

   - Extension - Key Share (40 bytes)

   In total:

   157 - 40 = 117 bytes

   TLS 1.3 PSK flight #2 gives 117 bytes of overhead.

2.3.3.3.  Flight #3

   There are no differences in overhead compared to Section 2.3.2.3.

   TLS 1.3 PSK flight #3 gives 50 bytes of overhead.

2.4.  TLS 1.2 and DTLS 1.2

   The TLS 1.2 and DTLS 1.2 handshakes are not analyzed in detail in
   this document.  One rough comparison on expected size between the TLS
   1.2 and TLS 1.3 handshakes can be found by counting the number of
   bytes in the example handshakes of [Illustrated-TLS12] and
   [Illustrated-TLS13].  In these examples the server authenticates with
   a certificate and the client is not authenticated.

   In TLS 1.2 the number of bytes in the four flights are 170, 1188,
   117, and 75 for a total of 1550 bytes.  In TLS 1.3 the number of
   bytes in the three flights are 253, 1367, and 79 for a total of 1699
   bytes.  In general, the (D)TLS 1.2 and (D)TLS 1.3 handshakes can be
   expected to have similar number of bytes.

2.5.  EDHOC

   This section gives an estimate of the message sizes of EDHOC
   [I-D.ietf-lake-edhoc] authenticated with static Diffie-Hellman keys
   and where the static Diffie-Hellman are identified with a key
   identifier (kid).  All examples are given in CBOR diagnostic notation
   and hexadecimal, and are based on the test vectors in Section 4 of
   [I-D.ietf-lake-traces].

2.5.1.  Message Sizes RPK




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2.5.1.1.  message_1

   message_1 = (
     3,
     2,
     h'8af6f430ebe18d34184017a9a11bf511c8dff8f834730b96c1b7c8dbca2f
       c3b6',
     -24
   )

   message_1 (37 bytes):
   03 02 58 20 8a f6 f4 30 eb e1 8d 34 18 40 17 a9 a1 1b f5 11 c8
   df f8 f8 34 73 0b 96 c1 b7 c8 db ca 2f c3 b6 37

2.5.1.2.  message_2

   message_2 = (
     h'419701D7F00A26C2DC587A36DD752549F33763C893422C8EA0F955A13A4F
       F5D5042459E2DA6C75143F35',
     -8
   )

   message_2 (45 bytes):
    58 2a 41 97 01 d7 f0 0a 26 c2 dc 58 7a 36 dd 75 25 49 f3 37
    63 c8 93 42 2c 8e a0 f9 55 a1 3a 4f f5 d5 04 24 59 e2 da 6c
    75 14 3f 35 27

2.5.1.3.  message_3

   message_3 = (
     h'C2B62835DC9B1F53419C1D3A2261EEED3505'
   )

   message_3 (19 bytes):
   52 c2 b6 28 35 dc 9b 1f 53 41 9c 1d 3a 22 61 ee ed 35 05

2.5.2.  Summary

   Based on the example above it is relatively easy to calculate numbers
   also for EDHOC authenticated with signature keys and for
   authentication keys identified with a SHA-256/64 hash (x5t).
   Signatures increase the size of flight #2 and #3 with (64 - 8 + 1)
   bytes while x5t inceases the size with 13-14 bytes.  The typical
   message sizes for the previous example and for the other combinations
   are summarized in Figure 3.  Note that EDHOC treats authentication
   keys stored in RPK and X.509 in the same way.  More detailed examples
   can be found in [I-D.ietf-lake-traces].




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        ==========================================================
                             Static DH Keys        Signature Keys
                            ----------------      ----------------
                             kid        x5t        kid        x5t
        ----------------------------------------------------------
         message_1            37         37         37         37
         message_2            45         58        102        115
         message_3            19         33         77         90
        ----------------------------------------------------------
         Total               101        128        216        242
        ==========================================================

                  Figure 3: Typical message sizes in bytes

2.6.  Conclusion

   To do a fair comparison, one has to choose a specific deployment and
   look at the topology, the whole protocol stack, frame sizes (e.g., 51
   or 128 bytes), how and where in the protocol stack fragmentation is
   done, and the expected packet loss.  Note that the number of bytes in
   each frame that is available for the key exchange protocol may depend
   on the underlying protocol layers as well as on the number of hops in
   multi-hop networks.  The packet loss may depend on how many other
   devices are transmitting at the same time, and may increase during
   network formation.  The total overhead will be larger due to
   mechanisms for fragmentation, retransmission, and packet ordering.
   The overhead of fragmentation is roughly proportional to the number
   of fragments, while the expected overhead due to retransmission in
   noisy environments is a superlinear function of the flight sizes.

3.  Overhead for Protection of Application Data

   To enable comparison, all the overhead calculations in this section
   use AES-CCM with a tag length of 8 bytes (e.g., AES_128_CCM_8 or AES-
   CCM-16-64), a plaintext of 6 bytes, and the sequence number '05'.
   This follows the example in [RFC7400], Figure 16.

   Note that the compressed overhead calculations for DLTS 1.2, DTLS
   1.3, TLS 1.2 and TLS 1.3 are dependent on the parameters epoch,
   sequence number, and length (where applicable), and all the overhead
   calculations are dependent on the parameter Connection ID when used.
   Note that the OSCORE overhead calculations are dependent on the CoAP
   option numbers, as well as the length of the OSCORE parameters Sender
   ID, ID Context, and Sequence Number (where applicable). cTLS uses the
   DTLS 1.3 record layer.  The following calculations are only examples.






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   Section 3.1 gives a short summary of the message overhead based on
   different parameters and some assumptions.  The following sections
   detail the assumptions and the calculations.

3.1.  Summary

   The DTLS overhead is dependent on the parameter Connection ID.  The
   following overheads apply for all Connection IDs with the same
   length.

   The compression overhead (GHC) is dependent on the parameters epoch,
   sequence number, Connection ID, and length (where applicable).  The
   following overheads should be representative for sequence numbers and
   Connection IDs with the same length.

   The OSCORE overhead is dependent on the included CoAP Option numbers
   as well as the length of the OSCORE parameters Sender ID and sequence
   number.  The following overheads apply for all sequence numbers and
   Sender IDs with the same length.

       Sequence Number                  '05'      '1005'    '100005'
      ---------------------------------------------------------------
       DTLS 1.2                          29         29         29
       DTLS 1.3                          11         11         11
      ---------------------------------------------------------------
       DTLS 1.2 (GHC)                    16         16         16
       DTLS 1.3 (GHC)                    12         12         12
      ---------------------------------------------------------------
       TLS  1.2                          21         21         21
       TLS  1.3                          14         14         14
      ---------------------------------------------------------------
       TLS  1.2 (GHC)                    17         18         19
       TLS  1.3 (GHC)                    15         16         17
      ---------------------------------------------------------------
       OSCORE request                    13         14         15
       OSCORE response                   11         11         11
      ---------------------------------------------------------------
       Group OSCORE pairwise request     14         15         16
       Group OSCORE pairwise response    11         11         11

           Figure 4: Overhead in bytes as a function of sequence
                 number       (Connection/ Sender ID = '')









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       Connection/Sender ID              ''        '42'      '4002'
      --------------------------------------------------------------
       DTLS 1.2                          29         30         31
       DTLS 1.3                          11         12         13
      --------------------------------------------------------------
       DTLS 1.2 (GHC)                    16         17         18
       DTLS 1.3 (GHC)                    12         13         14
      --------------------------------------------------------------
       OSCORE request                    13         14         15
       OSCORE response                   11         11         11
      --------------------------------------------------------------
       Group OSCORE pairwise request     14         15         16
       Group OSCORE pairwise response    11         13         14

       Figure 5: Overhead in bytes as a function of Connection/Sender
                     ID       (Sequence Number = '05')

        Protocol                       Overhead      Overhead (GHC)
       -------------------------------------------------------------
        DTLS 1.2                          21               8
        DTLS 1.3                           3               4
       -------------------------------------------------------------
        TLS  1.2                          13               9
        TLS  1.3                           6               7
       -------------------------------------------------------------
        OSCORE request                     5
        OSCORE response                    3
       -------------------------------------------------------------
        Group OSCORE pairwise request      7
        Group OSCORE pairwise response     4

                   Figure 6: Overhead (excluding ICV) in
       bytes                   (Connection/ Sender ID = '', Sequence
                               Number = '05')

   The numbers in Figure 4, Figure 5, and {fig-overhead3} does not
   consider the different Token processing requirements for clients
   [RFC9175] required for secure operation as motivated by
   [I-D.ietf-core-attacks-on-coap].  As reuse of Tokens is easier in
   OSCORE than DTLS, OSCORE might have slightly lower overhead than DTLS
   1.3 for long connection even if DTLS 1.3 has slightly lower overhead
   than OSCORE for short connections.

3.2.  DTLS 1.2







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3.2.1.  DTLS 1.2

   This section analyzes the overhead of DTLS 1.2 [RFC6347].  The nonce
   follow the strict profiling given in [RFC7925].  This example is
   taken directly from [RFC7400], Figure 16.

   DTLS 1.2 record layer (35 bytes, 29 bytes overhead):
   17 fe fd 00 01 00 00 00 00 00 05 00 16 00 01 00
   00 00 00 00 05 ae a0 15 56 67 92 4d ff 8a 24 e4
   cb 35 b9

   Content type:
   17
   Version:
   fe fd
   Epoch:
   00 01
   Sequence number:
   00 00 00 00 00 05
   Length:
   00 16
   Nonce:
   00 01 00 00 00 00 00 05
   Ciphertext:
   ae a0 15 56 67 92
   ICV:
   4d ff 8a 24 e4 cb 35 b9

   DTLS 1.2 gives 29 bytes overhead.

3.2.2.  DTLS 1.2 with 6LoWPAN-GHC

   This section analyzes the overhead of DTLS 1.2 [RFC6347] when
   compressed with 6LoWPAN-GHC [RFC7400].  The compression was done with
   [OlegHahm-ghc].

   Note that the sequence number '01' used in [RFC7400], Figure 15 gives
   an exceptionally small overhead that is not representative.

   Note that this header compression is not available when DTLS is used
   over transports that do not use 6LoWPAN together with 6LoWPAN-GHC.










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   Compressed DTLS 1.2 record layer (22 bytes, 16 bytes overhead):
   b0 c3 03 05 00 16 f2 0e ae a0 15 56 67 92 4d ff
   8a 24 e4 cb 35 b9

   Compressed DTLS 1.2 record layer header and nonce:
   b0 c3 03 05 00 16 f2 0e
   Ciphertext:
   ae a0 15 56 67 92
   ICV:
   4d ff 8a 24 e4 cb 35 b9

   When compressed with 6LoWPAN-GHC, DTLS 1.2 with the above parameters
   (epoch, sequence number, length) gives 16 bytes overhead.

3.2.3.  DTLS 1.2 with Connection ID

   This section analyzes the overhead of DTLS 1.2 [RFC6347] with
   Connection ID [RFC9146].  The overhead calculations in this section
   uses Connection ID = '42'.  DTLS recored layer with a Connection ID =
   '' (the empty string) is equal to DTLS without Connection ID.

   DTLS 1.2 record layer (36 bytes, 30 bytes overhead):
   17 fe fd 00 01 00 00 00 00 00 05 42 00 16 00 01
   00 00 00 00 00 05 ae a0 15 56 67 92 4d ff 8a 24
   e4 cb 35 b9

   Content type:
   17
   Version:
   fe fd
   Epoch:
   00 01
   Sequence number:
   00 00 00 00 00 05
   Connection ID:
   42
   Length:
   00 16
   Nonce:
   00 01 00 00 00 00 00 05
   Ciphertext:
   ae a0 15 56 67 92
   ICV:
   4d ff 8a 24 e4 cb 35 b9

   DTLS 1.2 with Connection ID gives 30 bytes overhead.





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3.2.4.  DTLS 1.2 with Connection ID and 6LoWPAN-GHC

   This section analyzes the overhead of DTLS 1.2 [RFC6347] with
   Connection ID [RFC9146] when compressed with 6LoWPAN-GHC [RFC7400]
   [OlegHahm-ghc].

   Note that the sequence number '01' used in [RFC7400], Figure 15 gives
   an exceptionally small overhead that is not representative.

   Note that this header compression is not available when DTLS is used
   over transports that do not use 6LoWPAN together with 6LoWPAN-GHC.

   Compressed DTLS 1.2 record layer (23 bytes, 17 bytes overhead):
   b0 c3 04 05 42 00 16 f2 0e ae a0 15 56 67 92 4d
   ff 8a 24 e4 cb 35 b9

   Compressed DTLS 1.2 record layer header and nonce:
   b0 c3 04 05 42 00 16 f2 0e
   Ciphertext:
   ae a0 15 56 67 92
   ICV:
   4d ff 8a 24 e4 cb 35 b9

   When compressed with 6LoWPAN-GHC, DTLS 1.2 with the above parameters
   (epoch, sequence number, Connection ID, length) gives 17 bytes
   overhead.

3.3.  DTLS 1.3

3.3.1.  DTLS 1.3

   This section analyzes the overhead of DTLS 1.3 [RFC9147].  The
   changes compared to DTLS 1.2 are: omission of version number, merging
   of epoch into the first byte containing signaling bits, optional
   omission of length, reduction of sequence number into a 1 or 2-bytes
   field.

   DTLS 1.3 is only analyzed with an omitted length field and with an
   8-bit sequence number (see Figure 4 of [RFC9147]).












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   DTLS 1.3 record layer (17 bytes, 11 bytes overhead):
   21 05 ae a0 15 56 67 92 ec 4d ff 8a 24 e4 cb 35 b9

   First byte (including epoch):
   21
   Sequence number:
   05
   Ciphertext (including encrypted content type):
   ae a0 15 56 67 92 ec
   ICV:
   4d ff 8a 24 e4 cb 35 b9

   DTLS 1.3 gives 11 bytes overhead.

3.3.2.  DTLS 1.3 with 6LoWPAN-GHC

   This section analyzes the overhead of DTLS 1.3 [RFC9147] when
   compressed with 6LoWPAN-GHC [RFC7400] [OlegHahm-ghc].

   Note that this header compression is not available when DTLS is used
   over transports that do not use 6LoWPAN together with 6LoWPAN-GHC.

   Compressed DTLS 1.3 record layer (18 bytes, 12 bytes overhead):
   11 21 05 ae a0 15 56 67 92 ec 4d ff 8a 24 e4 cb
   35 b9

   Compressed DTLS 1.3 record layer header and nonce:
   11 21 05
   Ciphertext (including encrypted content type):
   ae a0 15 56 67 92 ec
   ICV:
   4d ff 8a 24 e4 cb 35 b9

   When compressed with 6LoWPAN-GHC, DTLS 1.3 with the above parameters
   (epoch, sequence number, no length) gives 12 bytes overhead.

3.3.3.  DTLS 1.3 with Connection ID

   This section analyzes the overhead of DTLS 1.3 [RFC9147] with
   Connection ID [RFC9146].

   In this example, the length field is omitted, and the 1-byte field is
   used for the sequence number.  The minimal DTLSCiphertext structure
   is used (see Figure 4 of [RFC9147]), with the addition of the
   Connection ID field.






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   DTLS 1.3 record layer (18 bytes, 12 bytes overhead):
   31 42 05 ae a0 15 56 67 92 ec 4d ff 8a 24 e4 cb 35 b9

   First byte (including epoch):
   31
   Connection ID:
   42
   Sequence number:
   05
   Ciphertext (including encrypted content type):
   ae a0 15 56 67 92 ec
   ICV:
   4d ff 8a 24 e4 cb 35 b9

   DTLS 1.3 with Connection ID gives 12 bytes overhead.

3.3.4.  DTLS 1.3 with Connection ID and 6LoWPAN-GHC

   This section analyzes the overhead of DTLS 1.3 [RFC9147] with
   Connection ID [RFC9146] when compressed with 6LoWPAN-GHC [RFC7400]
   [OlegHahm-ghc].

   Note that this header compression is not available when DTLS is used
   over transports that do not use 6LoWPAN together with 6LoWPAN-GHC.

   Compressed DTLS 1.3 record layer (19 bytes, 13 bytes overhead):
   12 31 05 42 ae a0 15 56 67 92 ec 4d ff 8a 24 e4
   cb 35 b9

   Compressed DTLS 1.3 record layer header and nonce:
   12 31 05 42
   Ciphertext (including encrypted content type):
   ae a0 15 56 67 92 ec
   ICV:
   4d ff 8a 24 e4 cb 35 b9

   When compressed with 6LoWPAN-GHC, DTLS 1.3 with the above parameters
   (epoch, sequence number, Connection ID, no length) gives 13 bytes
   overhead.

3.4.  TLS 1.2

3.4.1.  TLS 1.2

   This section analyzes the overhead of TLS 1.2 [RFC5246].  The changes
   compared to DTLS 1.2 is that the TLS 1.2 record layer does not have
   epoch and sequence number, and that the version is different.




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   TLS 1.2 Record Layer (27 bytes, 21 bytes overhead):
   17 03 03 00 16 00 00 00 00 00 00 00 05 ae a0 15
   56 67 92 4d ff 8a 24 e4 cb 35 b9

   Content type:
   17
   Version:
   03 03
   Length:
   00 16
   Nonce:
   00 00 00 00 00 00 00 05
   Ciphertext:
   ae a0 15 56 67 92
   ICV:
   4d ff 8a 24 e4 cb 35 b9

   TLS 1.2 gives 21 bytes overhead.

3.4.2.  TLS 1.2 with 6LoWPAN-GHC

   This section analyzes the overhead of TLS 1.2 [RFC5246] when
   compressed with 6LoWPAN-GHC [RFC7400] [OlegHahm-ghc].

   Note that this header compression is not available when TLS is used
   over transports that do not use 6LoWPAN together with 6LoWPAN-GHC.

   Compressed TLS 1.2 record layer (23 bytes, 17 bytes overhead):
   05 17 03 03 00 16 85 0f 05 ae a0 15 56 67 92 4d
   ff 8a 24 e4 cb 35 b9

   Compressed TLS 1.2 record layer header and nonce:
   05 17 03 03 00 16 85 0f 05
   Ciphertext:
   ae a0 15 56 67 92
   ICV:
   4d ff 8a 24 e4 cb 35 b9

   When compressed with 6LoWPAN-GHC, TLS 1.2 with the above parameters
   (epoch, sequence number, length) gives 17 bytes overhead.

3.5.  TLS 1.3

3.5.1.  TLS 1.3

   This section analyzes the overhead of TLS 1.3 [RFC8446].  The change
   compared to TLS 1.2 is that the TLS 1.3 record layer uses a different
   version.



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   TLS 1.3 Record Layer (20 bytes, 14 bytes overhead):
   17 03 03 00 16 ae a0 15 56 67 92 ec 4d ff 8a 24
   e4 cb 35 b9

   Content type:
   17
   Legacy version:
   03 03
   Length:
   00 0f
   Ciphertext (including encrypted content type):
   ae a0 15 56 67 92 ec
   ICV:
   4d ff 8a 24 e4 cb 35 b9

   TLS 1.3 gives 14 bytes overhead.

3.5.2.  TLS 1.3 with 6LoWPAN-GHC

   This section analyzes the overhead of TLS 1.3 [RFC8446] when
   compressed with 6LoWPAN-GHC [RFC7400] [OlegHahm-ghc].

   Note that this header compression is not available when TLS is used
   over transports that do not use 6LoWPAN together with 6LoWPAN-GHC.

   Compressed TLS 1.3 record layer (21 bytes, 15 bytes overhead):
   14 17 03 03 00 0f ae a0 15 56 67 92 ec 4d ff 8a
   24 e4 cb 35 b9

   Compressed TLS 1.3 record layer header and nonce:
   14 17 03 03 00 0f
   Ciphertext (including encrypted content type):
   ae a0 15 56 67 92 ec
   ICV:
   4d ff 8a 24 e4 cb 35 b9

   When compressed with 6LoWPAN-GHC, TLS 1.3 with the above parameters
   (epoch, sequence number, length) gives 15 bytes overhead.

3.6.  OSCORE

   This section analyzes the overhead of OSCORE [RFC8613].

   The below calculation Option Delta = '9', Sender ID = '' (empty
   string), and Sequence Number = '05', and is only an example.  Note
   that Sender ID = '' (empty string) can only be used by one client per
   server.




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   OSCORE request (19 bytes, 13 bytes overhead):
   92 09 05
   ff ec ae a0 15 56 67 92 4d ff 8a 24 e4 cb 35 b9

   CoAP option delta and length:
   92
   Option value (flag byte and sequence number):
   09 05
   Payload marker:
   ff
   Ciphertext (including encrypted code):
   ec ae a0 15 56 67 92
   ICV:
   4d ff 8a 24 e4 cb 35 b9

   The below calculation Option Delta = '9', Sender ID = '42', and
   Sequence Number = '05', and is only an example.

   OSCORE request (20 bytes, 14 bytes overhead):
   93 09 05 42
   ff ec ae a0 15 56 67 92 4d ff 8a 24 e4 cb 35 b9

   CoAP option delta and length:
   93
   Option Value (flag byte, sequence number, and Sender ID):
   09 05 42
   Payload marker:
   ff
   Ciphertext (including encrypted code):
   ec ae a0 15 56 67 92
   ICV:
   4d ff 8a 24 e4 cb 35 b9

   The below calculation uses Option Delta = '9'.

















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   OSCORE response (17 bytes, 11 bytes overhead):
   90
   ff ec ae a0 15 56 67 92 4d ff 8a 24 e4 cb 35 b9

   CoAP delta and option length:
   90
   Option value:
   -
   Payload marker:
   ff
   Ciphertext (including encrypted code):
   ec ae a0 15 56 67 92
   ICV:
   4d ff 8a 24 e4 cb 35 b9

   OSCORE with the above parameters gives 13-14 bytes overhead for
   requests and 11 bytes overhead for responses.

   Unlike DTLS and TLS, OSCORE has much smaller overhead for responses
   than requests.

3.7.  Group OSCORE

   This section analyzes the overhead of Group OSCORE
   [I-D.ietf-core-oscore-groupcomm].  Group OSCORE defines a pairwise
   mode where each member of the group can efficiently derive a
   symmetric pairwise key with any other member of the group for
   pairwise OSCORE communication.  Additional requirements compared to
   [RFC8613] is that ID Context is always included in requests and that
   Sender ID is always included in responses.  Assuming 1 byte ID
   Context and Sender ID this adds 2 bytes to requests and 1 byte to
   responses.

   The below calculation Option Delta = '9', ID Context = '', Sender ID
   = '42', and Sequence Number = '05', and is only an example.  ID
   Context = '' would be the standard for local deployments only having
   a single group.














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   OSCORE request (21 bytes, 15 bytes overhead):
   93 09 05 42
   ff ec ae a0 15 56 67 92 4d ff 8a 24 e4 cb 35 b9

   CoAP option delta and length:
   93
   Option Value (flag byte, ID Context length, sequence nr, Sender ID):
   19 00 05 42
   Payload marker:
   ff
   Ciphertext (including encrypted code):
   ec ae a0 15 56 67 92
   ICV:
   4d ff 8a 24 e4 cb 35 b9

   The below calculation uses Option Delta = '9' and Sender ID = '69',
   and is only an example.

   OSCORE response (18 bytes, 12 bytes overhead):
   90
   ff ec ae a0 15 56 67 92 4d ff 8a 24 e4 cb 35 b9

   CoAP delta and option length:
   90
   Option value (flag byte, Sender ID):
   08 69
   Payload marker:
   ff
   Ciphertext (including encrypted code):
   ec ae a0 15 56 67 92
   ICV:
   4d ff 8a 24 e4 cb 35 b9

   The pairwise mode OSCORE with the above parameters gives 15 bytes
   overhead for requests and 12 bytes overhead for responses.

3.8.  Conclusion

   DTLS 1.2 has quite a large overhead as it uses an explicit sequence
   number and an explicit nonce.  TLS 1.2 has significantly less (but
   not small) overhead.  TLS 1.3 has quite a small overhead.  OSCORE and
   DTLS 1.3 (using the minimal structure) format have very small
   overhead.

   The Generic Header Compression (6LoWPAN-GHC) can in addition to DTLS
   1.2 handle TLS 1.2, and DTLS 1.2 with Connection ID.  The Generic
   Header Compression (6LoWPAN-GHC) works very well for Connection ID
   and the overhead seems to increase exactly with the length of the



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   Connection ID (which is optimal).  The compression of TLS 1.2 is not
   as good as the compression of DTLS 1.2 (as the static dictionary only
   contains the DTLS 1.2 version number).  Similar compression levels as
   for DTLS could be achieved also for TLS 1.2, but this would require
   different static dictionaries.  For TLS 1.3 and DTLS 1.3, GHC
   increases the overhead.  The 6LoWPAN-GHC header compression is not
   available when (D)TLS is used over transports that do not use 6LoWPAN
   together with 6LoWPAN-GHC.

   New security protocols like OSCORE, TLS 1.3, and DTLS 1.3 have much
   lower overhead than DTLS 1.2 and TLS 1.2.  The overhead is even
   smaller than DTLS 1.2 and TLS 1.2 over 6LoWPAN with compression, and
   therefore the small overhead is achieved even on deployments without
   6LoWPAN or 6LoWPAN without compression.  OSCORE is lightweight
   because it makes use of CoAP, CBOR, and COSE, which were designed to
   have as low overhead as possible.  As can be seen in Figure 6, Group
   OSCORE for pairwise communication increases the overhead of OSCORE
   requests with 20% and OSCORE responses with 33%.

   Note that the compared protocols have slightly different use cases.
   TLS and DTLS are designed for the transport layer and are terminated
   in CoAP proxies.  OSCORE is designed for the application layer and
   protects information end-to-end between the CoAP client and the CoAP
   server.  Group OSCORE is designed for communication in a group.

4.  Security Considerations

   This document is purely informational.

5.  IANA Considerations

   This document has no actions for IANA.

6.  Informative References

   [E-impact] Internet Architecture Board, "Workshop on Environmental
              Impact of Internet Applications and Systems", December
              2022,
              <https://www.iab.org/activities/workshops/e-impact/>.

   [I-D.ietf-core-attacks-on-coap]
              Mattsson, J. P., Fornehed, J., Selander, G., Palombini,
              F., and C. Amsüss, "Attacks on the Constrained Application
              Protocol (CoAP)", Work in Progress, Internet-Draft, draft-
              ietf-core-attacks-on-coap-02, 23 December 2022,
              <https://datatracker.ietf.org/api/v1/doc/document/draft-
              ietf-core-attacks-on-coap/>.




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   [I-D.ietf-core-oscore-edhoc]
              Palombini, F., Tiloca, M., Höglund, R., Hristozov, S., and
              G. Selander, "Profiling EDHOC for CoAP and OSCORE", Work
              in Progress, Internet-Draft, draft-ietf-core-oscore-edhoc-
              06, 23 November 2022, <https://www.ietf.org/archive/id/
              draft-ietf-core-oscore-edhoc-06.txt>.

   [I-D.ietf-core-oscore-groupcomm]
              Tiloca, M., Selander, G., Palombini, F., Mattsson, J. P.,
              and J. Park, "Group OSCORE - Secure Group Communication
              for CoAP", Work in Progress, Internet-Draft, draft-ietf-
              core-oscore-groupcomm-17, 20 December 2022,
              <https://www.ietf.org/archive/id/draft-ietf-core-oscore-
              groupcomm-17.txt>.

   [I-D.ietf-cose-cbor-encoded-cert]
              Mattsson, J. P., Selander, G., Raza, S., Höglund, J., and
              M. Furuhed, "CBOR Encoded X.509 Certificates (C509
              Certificates)", Work in Progress, Internet-Draft, draft-
              ietf-cose-cbor-encoded-cert-04, 10 July 2022,
              <https://www.ietf.org/archive/id/draft-ietf-cose-cbor-
              encoded-cert-04.txt>.

   [I-D.ietf-lake-edhoc]
              Selander, G., Mattsson, J. P., and F. Palombini,
              "Ephemeral Diffie-Hellman Over COSE (EDHOC)", Work in
              Progress, Internet-Draft, draft-ietf-lake-edhoc-18, 28
              November 2022, <https://www.ietf.org/archive/id/draft-
              ietf-lake-edhoc-18.txt>.

   [I-D.ietf-lake-traces]
              Selander, G., Mattsson, J. P., Serafin, M., and M. Tiloca,
              "Traces of EDHOC", Work in Progress, Internet-Draft,
              draft-ietf-lake-traces-03, 24 October 2022,
              <https://www.ietf.org/archive/id/draft-ietf-lake-traces-
              03.txt>.

   [I-D.ietf-tls-ctls]
              Rescorla, E., Barnes, R., Tschofenig, H., and B. M.
              Schwartz, "Compact TLS 1.3", Work in Progress, Internet-
              Draft, draft-ietf-tls-ctls-06, 9 July 2022,
              <https://www.ietf.org/archive/id/draft-ietf-tls-ctls-
              06.txt>.

   [Illustrated-DTLS13]
              Driscoll, M., "The Illustrated DTLS 1.3 Connection", n.d.,
              <https://dtls.xargs.org/>.




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   [Illustrated-TLS12]
              Driscoll, M., "The Illustrated TLS 1.2 Connection", n.d.,
              <https://tls12.xargs.org/>.

   [Illustrated-TLS13]
              Driscoll, M., "The Illustrated TLS 1.3 Connection", n.d.,
              <https://tls13.xargs.org/>.

   [IoT-Cert] Forsby, F., "Digital Certificates for the Internet of
              Things", June 2017, <https://kth.diva-
              portal.org/smash/get/diva2:1153958/FULLTEXT01.pdf>.

   [OlegHahm-ghc]
              Hahm, O., "Generic Header Compression", July 2016,
              <https://github.com/OlegHahm/ghc>.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,
              <https://www.rfc-editor.org/info/rfc5246>.

   [RFC5480]  Turner, S., Brown, D., Yiu, K., Housley, R., and T. Polk,
              "Elliptic Curve Cryptography Subject Public Key
              Information", RFC 5480, DOI 10.17487/RFC5480, March 2009,
              <https://www.rfc-editor.org/info/rfc5480>.

   [RFC6347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
              January 2012, <https://www.rfc-editor.org/info/rfc6347>.

   [RFC7252]  Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
              Application Protocol (CoAP)", RFC 7252,
              DOI 10.17487/RFC7252, June 2014,
              <https://www.rfc-editor.org/info/rfc7252>.

   [RFC7400]  Bormann, C., "6LoWPAN-GHC: Generic Header Compression for
              IPv6 over Low-Power Wireless Personal Area Networks
              (6LoWPANs)", RFC 7400, DOI 10.17487/RFC7400, November
              2014, <https://www.rfc-editor.org/info/rfc7400>.

   [RFC7924]  Santesson, S. and H. Tschofenig, "Transport Layer Security
              (TLS) Cached Information Extension", RFC 7924,
              DOI 10.17487/RFC7924, July 2016,
              <https://www.rfc-editor.org/info/rfc7924>.







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   [RFC7925]  Tschofenig, H., Ed. and T. Fossati, "Transport Layer
              Security (TLS) / Datagram Transport Layer Security (DTLS)
              Profiles for the Internet of Things", RFC 7925,
              DOI 10.17487/RFC7925, July 2016,
              <https://www.rfc-editor.org/info/rfc7925>.

   [RFC8323]  Bormann, C., Lemay, S., Tschofenig, H., Hartke, K.,
              Silverajan, B., and B. Raymor, Ed., "CoAP (Constrained
              Application Protocol) over TCP, TLS, and WebSockets",
              RFC 8323, DOI 10.17487/RFC8323, February 2018,
              <https://www.rfc-editor.org/info/rfc8323>.

   [RFC8376]  Farrell, S., Ed., "Low-Power Wide Area Network (LPWAN)
              Overview", RFC 8376, DOI 10.17487/RFC8376, May 2018,
              <https://www.rfc-editor.org/info/rfc8376>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/info/rfc8446>.

   [RFC8613]  Selander, G., Mattsson, J., Palombini, F., and L. Seitz,
              "Object Security for Constrained RESTful Environments
              (OSCORE)", RFC 8613, DOI 10.17487/RFC8613, July 2019,
              <https://www.rfc-editor.org/info/rfc8613>.

   [RFC8879]  Ghedini, A. and V. Vasiliev, "TLS Certificate
              Compression", RFC 8879, DOI 10.17487/RFC8879, December
              2020, <https://www.rfc-editor.org/info/rfc8879>.

   [RFC9146]  Rescorla, E., Ed., Tschofenig, H., Ed., Fossati, T., and
              A. Kraus, "Connection Identifier for DTLS 1.2", RFC 9146,
              DOI 10.17487/RFC9146, March 2022,
              <https://www.rfc-editor.org/info/rfc9146>.

   [RFC9147]  Rescorla, E., Tschofenig, H., and N. Modadugu, "The
              Datagram Transport Layer Security (DTLS) Protocol Version
              1.3", RFC 9147, DOI 10.17487/RFC9147, April 2022,
              <https://www.rfc-editor.org/info/rfc9147>.

   [RFC9175]  Amsüss, C., Preuß Mattsson, J., and G. Selander,
              "Constrained Application Protocol (CoAP): Echo, Request-
              Tag, and Token Processing", RFC 9175,
              DOI 10.17487/RFC9175, February 2022,
              <https://www.rfc-editor.org/info/rfc9175>.







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   [RFC9191]  Sethi, M., Preuß Mattsson, J., and S. Turner, "Handling
              Large Certificates and Long Certificate Chains in TLS-
              Based EAP Methods", RFC 9191, DOI 10.17487/RFC9191,
              February 2022, <https://www.rfc-editor.org/info/rfc9191>.

Acknowledgments

   The authors want to thank Ari Keränen, Carsten Bormann, Stephan Koch,
   Göran Selander, and Hannes Tschofenig for comments and suggestions on
   previous versions of the draft.

   All 6LoWPAN-GHC compression was done with [OlegHahm-ghc].
   [Illustrated-TLS13] as a was a useful resource for the TLS handshake
   content and formatting and [IoT-Cert] was a useful resource for
   SubjectPublicKeyInfo formatting.

Authors' Addresses

   John Preuß Mattsson
   Ericsson AB
   Email: john.mattsson@ericsson.com


   Francesca Palombini
   Ericsson AB
   Email: francesca.palombini@ericsson.com


   Mališa Vučinić
   INRIA
   Email: malisa.vucinic@inria.fr




















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