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Versions: (draft-mattsson-lwig-security-protocol-comparison) 00 01 02 03

LWIG Working Group                                           J. Mattsson
Internet-Draft                                              F. Palombini
Intended status: Informational                               Ericsson AB
Expires: September 12, 2019                               March 11, 2019


                 Comparison of CoAP Security Protocols
            draft-ietf-lwig-security-protocol-comparison-03

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.  The analyzed security protocols
   are DTLS 1.2, DTLS 1.3, TLS 1.2, TLS 1.3, 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

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   Drafts is at https://datatracker.ietf.org/drafts/current/.

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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on September 12, 2019.

Copyright Notice

   Copyright (c) 2019 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
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   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   include Simplified BSD License text as described in Section 4.e of



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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Overhead of Key Exchange Protocols  . . . . . . . . . . . . .   3
     2.1.  Summary . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.2.  DTLS 1.3  . . . . . . . . . . . . . . . . . . . . . . . .   5
       2.2.1.  Message Sizes RPK + ECDHE . . . . . . . . . . . . . .   5
       2.2.2.  Message Sizes PSK + ECDHE . . . . . . . . . . . . . .  10
       2.2.3.  Message Sizes PSK . . . . . . . . . . . . . . . . . .  11
       2.2.4.  Cached Information  . . . . . . . . . . . . . . . . .  12
       2.2.5.  Resumption  . . . . . . . . . . . . . . . . . . . . .  13
       2.2.6.  Without Connection ID . . . . . . . . . . . . . . . .  14
       2.2.7.  DTLS Raw Public Keys  . . . . . . . . . . . . . . . .  15
     2.3.  TLS 1.3 . . . . . . . . . . . . . . . . . . . . . . . . .  16
       2.3.1.  Message Sizes RPK + ECDHE . . . . . . . . . . . . . .  16
       2.3.2.  Message Sizes PSK + ECDHE . . . . . . . . . . . . . .  22
       2.3.3.  Message Sizes PSK . . . . . . . . . . . . . . . . . .  23
     2.4.  EDHOC . . . . . . . . . . . . . . . . . . . . . . . . . .  24
       2.4.1.  Message Sizes RPK . . . . . . . . . . . . . . . . . .  24
       2.4.2.  Message Sizes Certificates  . . . . . . . . . . . . .  26
       2.4.3.  Message Sizes PSK . . . . . . . . . . . . . . . . . .  26
       2.4.4.  message_1 . . . . . . . . . . . . . . . . . . . . . .  26
       2.4.5.  message_2 . . . . . . . . . . . . . . . . . . . . . .  26
       2.4.6.  message_3 . . . . . . . . . . . . . . . . . . . . . .  27
       2.4.7.  Summary . . . . . . . . . . . . . . . . . . . . . . .  27
     2.5.  Conclusion  . . . . . . . . . . . . . . . . . . . . . . .  27
   3.  Overhead for Protection of Application Data . . . . . . . . .  28
     3.1.  Summary . . . . . . . . . . . . . . . . . . . . . . . . .  28
     3.2.  DTLS 1.2  . . . . . . . . . . . . . . . . . . . . . . . .  30
       3.2.1.  DTLS 1.2  . . . . . . . . . . . . . . . . . . . . . .  30
       3.2.2.  DTLS 1.2 with 6LoWPAN-GHC . . . . . . . . . . . . . .  30
       3.2.3.  DTLS 1.2 with Connection ID . . . . . . . . . . . . .  31
       3.2.4.  DTLS 1.2 with Connection ID and 6LoWPAN-GHC . . . . .  32
     3.3.  DTLS 1.3  . . . . . . . . . . . . . . . . . . . . . . . .  32
       3.3.1.  DTLS 1.3  . . . . . . . . . . . . . . . . . . . . . .  32
       3.3.2.  DTLS 1.3 with 6LoWPAN-GHC . . . . . . . . . . . . . .  33
       3.3.3.  DTLS 1.3 with Connection ID . . . . . . . . . . . . .  33
       3.3.4.  DTLS 1.3 with Connection ID and 6LoWPAN-GHC . . . . .  34
     3.4.  TLS 1.2 . . . . . . . . . . . . . . . . . . . . . . . . .  34
       3.4.1.  TLS 1.2 . . . . . . . . . . . . . . . . . . . . . . .  34
       3.4.2.  TLS 1.2 with 6LoWPAN-GHC  . . . . . . . . . . . . . .  35
     3.5.  TLS 1.3 . . . . . . . . . . . . . . . . . . . . . . . . .  35
       3.5.1.  TLS 1.3 . . . . . . . . . . . . . . . . . . . . . . .  35
       3.5.2.  TLS 1.3 with 6LoWPAN-GHC  . . . . . . . . . . . . . .  36
     3.6.  OSCORE  . . . . . . . . . . . . . . . . . . . . . . . . .  36



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     3.7.  Group OSCORE  . . . . . . . . . . . . . . . . . . . . . .  38
     3.8.  Conclusion  . . . . . . . . . . . . . . . . . . . . . . .  38
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .  39
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  39
   6.  Informative References  . . . . . . . . . . . . . . . . . . .  39
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  41
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  41

1.  Introduction

   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 [I-D.ietf-tls-dtls13], TLS 1.2 [RFC5246], TLS 1.3 [RFC8446],
   EDHOC [I-D.selander-ace-cose-ecdhe], OSCORE
   [I-D.ietf-core-object-security], and Group OSCORE
   [I-D.ietf-core-oscore-groupcomm].

   The DTLS and TLS record layers are analyzed with and without 6LoWPAN-
   GHC compression.  DTLS is anlyzed with and without Connection ID
   [I-D.ietf-tls-dtls-connection-id].  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.

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:

   o  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).

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

   o  The length of key identifiers are 1 byte.

   o  The length of connection identifiers are 1 byte.

   o  DTLS RPK makes use of point compression, which saves 32 bytes.

   o  DTLS handshake message fragmentation is not considered.



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   o  Only the DTLS mandatory extensions are considered, except for
      Connection ID.

   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.

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 EDHOC
   [I-D.selander-ace-cose-ecdhe] with the DTLS 1.3 [I-D.ietf-tls-dtls13]
   and TLS 1.3 [RFC8446] handshakes with connection ID.

   =====================================================================
   Flight                             #1         #2        #3      Total
   ---------------------------------------------------------------------
   DTLS 1.3 RPK + ECDHE              150        373       213        736
   DTLS 1.3 Cached X.509/RPK + ECDHE 182        347       213        742
   DTLS 1.3 PSK + ECDHE              184        190        57        431
   DTLS 1.3 PSK                      134        150        57        341
   ---------------------------------------------------------------------
   EDHOC RPK + ECDHE                  39        114        80        233
   EDHOC PSK + ECDHE                  41         45        11         97
   =====================================================================

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

   Figure 2 compares of message sizes of DTLS 1.3 [I-D.ietf-tls-dtls13]
   and TLS 1.3 [RFC8446] handshakes without connection ID.












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   =====================================================================
   Flight                             #1         #2        #3      Total
   ---------------------------------------------------------------------
   DTLS 1.3 RPK + ECDHE              144        364       212        722
   DTLS 1.3 PSK + ECDHE              178        183        56        417
   DTLS 1.3 PSK                      128        143        56        327
   ---------------------------------------------------------------------
   TLS 1.3  RPK + ECDHE              129        322       194        645
   TLS 1.3  PSK + ECDHE              163        157        50        370
   TLS 1.3  PSK                      113        117        50        280
   =====================================================================

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

   The details of the 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 (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



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     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 + 10 + 2 + 32 + 1 + 1 + 4 + 2 + 2 + 8 + 8 + 42 + 7 + 6 + 6 + 6 = 150
 bytes

   DTLS 1.3 RPK + ECDHE flight_1 gives 150 bytes of overhead.

2.2.1.2.  flight_2

 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



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     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




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     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



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   DTLS 1.3 RPK + ECDHE flight_2 gives 373 bytes of overhead.

2.2.1.3.  flight_3

   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



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   DTLS 1.3 RPK + ECDHE flight_2 gives 213 bytes of overhead.

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:

   150 + 6 + 48 - 8 - 6 - 6 = 184 bytes

   DTLS 1.3 PSK + ECDHE flight_1 gives 184 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 (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)

   In total:

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

   DTLS 1.3 PSK + ECDHE flight_2 gives 190 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 (78 bytes)

   - Handshake Message Certificate Verify (78 bytes)

   In total:

   213 - 78 - 78 = 57 bytes

   DTLS 1.3 PSK + ECDHE flight_3 gives 57 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:

   184 - 8 - 42 = 134 bytes




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   DTLS 1.3 PSK flight_1 gives 134 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:

   190 - 40 = 150 bytes

   DTLS 1.3 PSK flight_2 gives 150 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 57 bytes of overhead.

2.2.4.  Cached Information

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

   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).

   The differences compared to Section 2.2.1 are the following.

   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

   And the following is removed:

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

   Giving a total of:

   150 + 33 = 183 bytes




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   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 removed:

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

   - Server Certificate (59 bytes -> 32 bytes)

   Giving a total of:

   373 - 26 = 347 bytes

   A summary of the calculation is given in Figure 3.

 ======================================================================
 Flight                             #1         #2        #3      Total
 ----------------------------------------------------------------------
 DTLS 1.3 Cached X.509/RPK + ECDHE 183        347       213       743
 DTLS 1.3 RPK + ECDHE              150        373       213       736
 =======================================================================

     Figure 3: Comparison of message sizes in bytes for DTLS 1.3 RPK +
                    ECDH with and without cached X.509

2.2.5.  Resumption

   To enable resumption, a 4th flight (New Session Ticket) is added to
   the PSK handshake.




















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   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 initial handshake when resumption is enabled is just a PSK
   handshake with 134 + 150 + 57 + 42 = 383 bytes.

2.2.6.  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

 =======================================================================
 Flight                                #1         #2       #3    Total
 -----------------------------------------------------------------------
 DTLS 1.3 RPK + ECDHE (no cid)        144        364       212    722
 DTLS 1.3 PSK + ECDHE (no cid)        178        183        56    417
 DTLS 1.3 PSK (no cid)                128        143        56    327
 =======================================================================

    Figure 4: Comparison of message sizes in bytes for DTLS 1.3 without
                               Connection ID




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2.2.7.  DTLS Raw Public Keys

   TODO

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
   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








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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 that the record header is
   smaller, 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.schaad-ace-tls-cbor-handshake] ).

   TLS Assumptions:

   o  Minimum number of algorithms and cipher suites offered

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

   o  Length of key identifiers: 1 bytes

   o  TLS RPK with point compression (saves 32 bytes)

   o  Only mandatory TLS extensions

   For the PSK calculations, [Ulfheim-TLS13] was a useful resource,
   while for RPK calculations we followed the work of [IoT-Cert].

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

   TLS 1.3 RPK + ECDHE flight_1 gives 129 bytes of overhead.



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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

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



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      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




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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 RPK + ECDHE flight_2 gives 322 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 (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 RPK + ECDHE flight_3 gives 194 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 166 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 (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)

   In total:

   322 - 72 - 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 (72 bytes)

   - Handshake Message Certificate Verify (72 bytes)

   In total:

   194 - 72 - 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 116 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 57 bytes of overhead.

2.4.  EDHOC

   This section gives an estimate of the message sizes of EDHOC 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.  All examples are
   given in CBOR diagnostic notation and hexadecimal.

2.4.1.  Message Sizes RPK

2.4.1.1.  message_1

   message_1 = (
     1,
     0,
     h'000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d
       1e1f',
     h'c3'
   )

   message_1 (38 bytes):
   01 00 58 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 41 C3






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2.4.1.2.  message_2

   plaintext = <<
     h'a1',
     h'000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d
       1e1f202122232425262728292a2b2c2d2e2f303132333435363738393a3b
       3c3d3e3f'
   >>

   The header map { 4 : h'a1' } is encoded as the two bytes h'a1'.  The
   length of plaintext is 68 bytes so assuming a 64-bit MAC value the
   length of ciphertext is 76 bytes.

   message_2 = (
     h'000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d
       1e1f',
     h'c4',
     h'000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d
       1e1f202122232425262728292a2b2c2d2e2f303132333435363738393a3b
       3c3d3e3f404142434445464748494a4b'
   )

   message_2 (114 bytes):
   58 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 41 C4 58 51 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 20 21 22 23 24 25 26 27 28 29
   2A 2B 2C 2D 2E 2F 30 31 32 33 34 35 36 37 38 39 3A 3B 3C 3D
   3E 3F 40 41 42 43 44 45 46 47 48 49 4A 4B

2.4.1.3.  message_3

   The plaintext and ciphertext in message_3 are assumed to be of equal
   sizes as in message_2.

   message_3 = (
     h'c4',
     h'000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d
       1e1f202122232425262728292a2b2c2d2e2f303132333435363738393a3b
       3c3d3e3f404142434445464748494a4b'
   )

   message_3 (80 bytes):
   41 C4 58 51 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 20 21 22 23
   24 25 26 27 28 29 2A 2B 2C 2D 2E 2F 30 31 32 33 34 35 36 37
   38 39 3A 3B 3C 3D 3E 3F 40 41 42 43 44 45 46 47 48 49 4A 4B




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2.4.2.  Message Sizes Certificates

   When the certificates are distributed out-of-band and identified with
   the x5t header parameter and a SHA256/64 hash value, the header map
   will be 13 bytes (assuming labels in the range -24...23).

   { TDB1 : [ TDB6, h'0001020304050607' ] }

   When the certificates are identified with the x5chain header
   parameter, the message sizes depends on the size of the (truncated)
   certificate chains.  The header map will be 3 bytes + the size of the
   certificate chain (assuming a label in the range -24...23).

   { TDB3 : h'0001020304050607...' }

2.4.3.  Message Sizes PSK

2.4.4.  message_1

   message_1 = (
     4,
     0,
     h'000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d
       1e1f',
     h'c3',
     h'a2'
   )

   message_1 (40 bytes):
   04 00 58 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 41 C3 41 A2

2.4.5.  message_2

   Assuming a 0 byte plaintext and a 64-bit MAC value the ciphertext is
   8 bytes

   message_2 = (
     h'000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d
       1e1f',
     h'c4',
     h'0001020304050607'
   )

   message_2 (45 bytes):
   58 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 41 C4 48 61 62 63
   64 65 66 67 68



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2.4.6.  message_3

   The plaintext and ciphertext in message_3 are assumed to be of equal
   sizes as in message_2.

   message_3 = (
     h'c4',
     h'0001020304050607'
   )

   message_3 (11 bytes):
   41 C4 48 00 01 02 03 04 05 06 07

2.4.7.  Summary

   The previous examples of typical message sizes are summarized in
   Figure 5.

   =====================================================================
                  PSK       RPK       x5t     x5chain
   ---------------------------------------------------------------------
   message_1       40        38        38        38
   message_2       45       114       126       116 + Certificate chain
   message_3       11        80        91        81 + Certificate chain
   ---------------------------------------------------------------------
   Total           96       232       255       235 + Certificate chains
   =====================================================================

                 Figure 5: Typical message sizes in bytes

2.5.  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 byte in
   each frame that is available for the key exchange protocol may depend
   on the underlying protocol layers as well as the number of hops in
   multi-hop networks.  The packet loss depends may depend on how many
   other devices that 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.





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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, 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 and
   Sequence Number.  The following calculations are only examples.

   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.

















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       Sequence Number                '05'       '1005'     '100005'
       -------------------------------------------------------------
       DTLS 1.2                        29          29          29
       DTLS 1.3                        11          12          12
       -------------------------------------------------------------
       DTLS 1.2 (GHC)                  16          16          16
       DTLS 1.3 (GHC)                  12          13          13
       -------------------------------------------------------------
       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

       Figure 6: Overhead in bytes as a function of sequence number
                        (Connection/Sender ID = '')

       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

     Figure 7: 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

                Figure 8: Overhead (excluding ICV) in bytes
            (Connection/Sender ID = '', Sequence Number = '05')




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3.2.  DTLS 1.2

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 [I-D.ietf-tls-dtls-connection-id].  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 [I-D.ietf-tls-dtls-connection-id] 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 [I-D.ietf-tls-dtls13].
   The changes compared to DTLS 1.2 are: omission of version number,
   merging of epoch into the first byte containing signalling bits,
   optional omission of length, reduction of sequence number into a 1 or
   2-bytes field.

   Only the minimal header format for DTLS 1.3 is analyzed (see Figure 4
   of [I-D.ietf-tls-dtls13]).  The minimal header formal omit the length
   field and only a 1-byte field is used to carry the 8 low order bits
   of the sequence number










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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 [I-D.ietf-tls-dtls13]
   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 [I-D.ietf-tls-dtls13]
   with Connection ID [I-D.ietf-tls-dtls-connection-id].

   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 [I-D.ietf-tls-dtls13]), 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 [I-D.ietf-tls-dtls13]
   with Connection ID [I-D.ietf-tls-dtls-connection-id] 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
   [I-D.ietf-core-object-security].

   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].

   TODO

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
   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.



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   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.

   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 group communication and
   protects information between a CoAP client and any number of CoAP
   servers.

4.  Security Considerations

   This document is purely informational.

5.  IANA Considerations

   This document has no actions for IANA.

6.  Informative References

   [I-D.ietf-core-object-security]
              Selander, G., Mattsson, J., Palombini, F., and L. Seitz,
              "Object Security for Constrained RESTful Environments
              (OSCORE)", draft-ietf-core-object-security-15 (work in
              progress), August 2018.

   [I-D.ietf-core-oscore-groupcomm]
              Tiloca, M., Selander, G., Palombini, F., and J. Park,
              "Group OSCORE - Secure Group Communication for CoAP",
              draft-ietf-core-oscore-groupcomm-03 (work in progress),
              October 2018.

   [I-D.ietf-tls-dtls-connection-id]
              Rescorla, E., Tschofenig, H., Fossati, T., and T. Gondrom,
              "Connection Identifiers for DTLS 1.2", draft-ietf-tls-
              dtls-connection-id-02 (work in progress), October 2018.

   [I-D.ietf-tls-dtls13]
              Rescorla, E., Tschofenig, H., and N. Modadugu, "The
              Datagram Transport Layer Security (DTLS) Protocol Version
              1.3", draft-ietf-tls-dtls13-30 (work in progress),
              November 2018.



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   [I-D.schaad-ace-tls-cbor-handshake]
              Schaad, J., "TLS Handshake in CBOR", draft-schaad-ace-tls-
              cbor-handshake-00 (work in progress), March 2019.

   [I-D.selander-ace-cose-ecdhe]
              Selander, G., Mattsson, J., and F. Palombini, "Ephemeral
              Diffie-Hellman Over COSE (EDHOC)", draft-selander-ace-
              cose-ecdhe-12 (work in progress), February 2019.

   [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>.

   [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>.

   [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>.




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   [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>.

   [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>.

   [Ulfheim-TLS13]
              Driscoll, M., "Every Byte Explained The Illustrated TLS
              1.3 Connection", March 2018, <https://tls13.ulfheim.net>.

Acknowledgments

   The authors want to thank Ari Keraenen, Carsten Bormann, Goeran
   Selander, and Hannes Tschofenig for comments and suggestions on
   previous versions of the draft.

   All 6LoWPAN-GHC compression was done with [OlegHahm-ghc].

Authors' Addresses

   John Mattsson
   Ericsson AB

   Email: john.mattsson@ericsson.com


   Francesca Palombini
   Ericsson AB

   Email: francesca.palombini@ericsson.com

















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