Comparison of CoAP Security Protocols
draft-ietf-iotops-security-protocol-comparison-06
| Document | Type | Active Internet-Draft (iotops WG) | |
|---|---|---|---|
| Authors | John Preuß Mattsson , Francesca Palombini , Mališa Vučinić | ||
| Last updated | 2024-04-17 (Latest revision 2024-03-20) | ||
| Replaces | draft-ietf-lwig-security-protocol-comparison | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | Informational | ||
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draft-ietf-iotops-security-protocol-comparison-06
IOTOPS Working Group J. Preuß Mattsson
Internet-Draft F. Palombini
Intended status: Informational Ericsson
Expires: 22 September 2024 M. Vučinić
INRIA
21 March 2024
Comparison of CoAP Security Protocols
draft-ietf-iotops-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.
About This Document
This note is to be removed before publishing as an RFC.
Status information for this document may be found at
https://datatracker.ietf.org/doc/draft-ietf-iotops-security-protocol-
comparison/.
Discussion of this document takes place on the IOT Operations
(iotops) Working Group mailing list (mailto:iotops@ietf.org), which
is archived at https://mailarchive.ietf.org/arch/browse/iotops/.
Subscribe at https://www.ietf.org/mailman/listinfo/iotops/.
Source for this draft and an issue tracker can be found at
https://github.com/lwig-wg/protocol-comparison.
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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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Underlying Layers . . . . . . . . . . . . . . . . . . . . . . 5
3. Overhead of Authenticated Key Exchange Protocols . . . . . . 6
3.1. Summary . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.2. DTLS 1.3 . . . . . . . . . . . . . . . . . . . . . . . . 9
3.2.1. Message Sizes RPK + ECDHE . . . . . . . . . . . . . . 9
3.2.2. Message Sizes PSK + ECDHE . . . . . . . . . . . . . . 15
3.2.3. Message Sizes PSK . . . . . . . . . . . . . . . . . . 16
3.2.4. Cached Information . . . . . . . . . . . . . . . . . 17
3.2.5. Resumption . . . . . . . . . . . . . . . . . . . . . 18
3.2.6. DTLS Without Connection ID . . . . . . . . . . . . . 19
3.2.7. Raw Public Keys . . . . . . . . . . . . . . . . . . . 19
3.3. TLS 1.3 . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.3.1. Message Sizes RPK + ECDHE . . . . . . . . . . . . . . 21
3.3.2. Message Sizes PSK + ECDHE . . . . . . . . . . . . . . 27
3.3.3. Message Sizes PSK . . . . . . . . . . . . . . . . . . 28
3.4. TLS 1.2 and DTLS 1.2 . . . . . . . . . . . . . . . . . . 29
3.5. cTLS . . . . . . . . . . . . . . . . . . . . . . . . . . 29
3.6. EDHOC . . . . . . . . . . . . . . . . . . . . . . . . . . 30
3.6.1. Message Sizes RPK . . . . . . . . . . . . . . . . . . 30
3.6.2. Summary . . . . . . . . . . . . . . . . . . . . . . . 31
3.7. Summary . . . . . . . . . . . . . . . . . . . . . . . . . 31
4. Overhead for Protection of Application Data . . . . . . . . . 32
4.1. Summary . . . . . . . . . . . . . . . . . . . . . . . . . 32
4.2. DTLS 1.2 . . . . . . . . . . . . . . . . . . . . . . . . 34
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4.2.1. DTLS 1.2 . . . . . . . . . . . . . . . . . . . . . . 34
4.2.2. DTLS 1.2 with 6LoWPAN-GHC . . . . . . . . . . . . . . 35
4.2.3. DTLS 1.2 with Connection ID . . . . . . . . . . . . . 36
4.2.4. DTLS 1.2 with Connection ID and 6LoWPAN-GHC . . . . . 36
4.3. DTLS 1.3 . . . . . . . . . . . . . . . . . . . . . . . . 37
4.3.1. DTLS 1.3 . . . . . . . . . . . . . . . . . . . . . . 37
4.3.2. DTLS 1.3 with 6LoWPAN-GHC . . . . . . . . . . . . . . 37
4.3.3. DTLS 1.3 with Connection ID . . . . . . . . . . . . . 38
4.3.4. DTLS 1.3 with Connection ID and 6LoWPAN-GHC . . . . . 38
4.4. TLS 1.2 . . . . . . . . . . . . . . . . . . . . . . . . . 39
4.4.1. TLS 1.2 . . . . . . . . . . . . . . . . . . . . . . . 39
4.4.2. TLS 1.2 with 6LoWPAN-GHC . . . . . . . . . . . . . . 40
4.5. TLS 1.3 . . . . . . . . . . . . . . . . . . . . . . . . . 40
4.5.1. TLS 1.3 . . . . . . . . . . . . . . . . . . . . . . . 40
4.5.2. TLS 1.3 with 6LoWPAN-GHC . . . . . . . . . . . . . . 41
4.6. OSCORE . . . . . . . . . . . . . . . . . . . . . . . . . 41
4.7. Group OSCORE . . . . . . . . . . . . . . . . . . . . . . 42
4.8. Summary . . . . . . . . . . . . . . . . . . . . . . . . . 43
5. Security Considerations . . . . . . . . . . . . . . . . . . . 44
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 44
7. Informative References . . . . . . . . . . . . . . . . . . . 44
Appendix A. EDHOC Over CoAP and OSCORE . . . . . . . . . . . . . 51
Change Log . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 53
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 54
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] and [I-D.ietf-lake-reqs].
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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 (COSE, C509),
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 [RFC9547].
This document analyzes and compares the sizes of Authenticated Key
Exchange (AKE) 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 [RFC9528]
[I-D.ietf-core-oscore-edhoc], OSCORE [RFC8613], and Group OSCORE
[I-D.ietf-core-oscore-groupcomm]. An AKE and a protocol for the
protection of application data serve distinct purposes. An AKE is
responsible for establishing secure communication channels between
parties and negotiating cryptographic keys used for authenticated
encryption. AKE protocols typically involve a series of messages
exchanged between communicating parties to authenticate each other's
identities and derive shared secret keys. TLS, DTLS, and cTLS
handshakes as well as EDHOC are examples of AKEs. Protocols for
protection of application data are responsible for encrypting and
authenticating application-layer data to ensure its confidentiality,
integrity, and replay protection during transmission. The TLS and
DTLS record layers, OSCORE, and Group OSCORE are examples of
protocols for protection of application data. Section 3 compares the
overhead of mutually authenticated key exchange protocols, while
Section 4 covers the overhead of protocols for protection of
application data. The protocols are analyzed with different
algorithms and options. The DTLS and TLS record layers are analyzed
with and without 6LoWPAN-GHC compression [RFC7400]. 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 Integrity Check Value (ICV).
Readers of this document also might be interested in the following
documents: [Illustrated-TLS12], [Illustrated-TLS13],
[Illustrated-DTLS13], and [RFC9529] explain 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 and TLS
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certificate compression [RFC8879] is at compressing example
certificate and certificate chains. [I-D.ietf-tls-cert-abridge] and
[I-D.kampanakis-tls-scas-latest] describe how TLS clients or servers
can reduce the size of the TLS handshake by not sending certificate
authority certificates. [I-D.mattsson-tls-compact-ecc] proposes new
optimized encodings for key exchange and signatures with P-256 in TLS
1.3.
2. Underlying Layers
The described overheads in Section 3 and Section 4 are independent of
the underlying layers as they do not consider DTLS handshake message
fragmentation, how to compose DTLS handshake messages into records,
and how the underlying layers influence the choice of application
plaintext sizes. The complete overhead for all layers depends on the
combination of layers as well as assumptions regarding the devices
and applications and is out of scope of the document. This section
give a short overview of the overheads of UDP, TCP, and CoAP to give
the reader a high-level overview.
DTLS and cTLS are typically sent over 8 bytes UDP datagram headers
while TLS is typically sent over 20 bytes TCP segment headers. TCP
also uses some more bytes for additional messages used in TCP
internally. EDHOC is typically sent over CoAP which would typically
add 12 bytes to flight #1, 5 bytes to flight #2, and 1 byte to flight
#3 when used in the combined mode with OSCORE according to
[I-D.ietf-core-oscore-edhoc], see Appendix A. If EDHOC is used
without OSCORE, the overhead would typically be 12 bytes to flight #1
and #3 and 5 bytes to flight #2. OSCORE and Group OSCORE is part of
CoAP and are typically sent over UDP. A comparison of the total size
for DTLS and EDHOC when transported over IEEE 802.15.4 and 6LoWPAN is
provided in [Performance].
IPv6, UDP, and CoAP can be compressed with the Static Context Header
Compression (SCHC) for the Constrained Application Protocol (CoAP)
[RFC8824][I-D.ietf-schc-8824-update]. Use of SCHC can significantly
reduce the overhead. [SCHC-eval] gives an evaluation of how SCHC
reduces this overhead for OSCORE and the DTLS 1.2 record layer when
used in four of the most widely used LPWAN radio technologies
Fragmentation can significantly increase the total overhead as many
more packet headers have to be sent. CoAP, (D)TLS handshake, and IP
supports fragmentation. If, how, and where fragmentation is done
depends heavily on the underlying layers.
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3. Overhead of Authenticated Key Exchange Protocols
This section analyzes and compares the sizes of key exchange flights
for different protocols.
To enable a comparison between protocols, the following assumptions
are made:
* The overhead calculations in this section use an 8 bytes ICV
(e.g., AES_128_CCM_8 [RFC6655] or AES-CCM-16-64-128 [RFC9053]) or
16 bytes e.g., AES-CCM [SP-800-38C], AES-GCM [SP-800-38D], or
ChaCha20-Poly1305 [RFC7539]).
* A minimum number of algorithms and cipher suites is offered. The
algorithm used/offered are P-256 [SP-800-186] or Curve25519
[RFC7748], ECDSA [FIPS-186-5] with P-256 and SHA-256 or Ed25519
[RFC8032], AES-CCM_8, and SHA-256 [FIPS-180-4].
* The length of key identifiers are 1 byte.
* The length of connection identifiers are 1 byte.
* DTLS handshake message fragmentation is not considered.
* As many (D)TLS handshake messages as possible are sent in a single
record.
* Only mandatory (D)TLS extensions are included.
* DoS protection with DTLS HelloRetryRequest or the CoAP Echo Option
is not considered.
The choices of algorithms are based on the profiles in [RFC7925],
[I-D.ietf-uta-tls13-iot-profile], and [I-D.ietf-core-oscore-edhoc].
Many DTLS implementations splits flight #2 in two records.
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, EDHOC, and cTLS overhead is dependent on the parameter
Connection ID. The EDHOC and cTLS overhead is dependent on the key
or certificate identifiers included. Key identifiers are byte
strings used to identity a cryptographic key and certificate
identifiers are used to identify a certificate. If 8 bytes
identifiers are used instead of 1 byte, the RPK numbers for flight #2
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and #3 increases with 7 bytes and the PSK numbers for flight #1
increases with 7 bytes.
The TLS, DTLS, and cTLS overhead is dependent on the group used for
key exchange and the signature algorithm. secp256r1 and
ecdsa_secp256r1_sha256 have less optimized encoding than x25519,
ed25519, and [I-D.mattsson-tls-compact-ecc].
Figure 1 compares the message sizes of DTLS 1.3, cTLS, and EDHOC
handshakes with connection ID and the mandatory to implement
algorithms CCM_8, P-256, and ECDSA [I-D.ietf-uta-tls13-iot-profile]
[I-D.ietf-core-oscore-edhoc].
Editor's note: This version of the document analyses the -09 version
of cTLS, which seems relatively stable. It is uncertain if the TLS
WG will adopt more compact encoding for P-256 and ECDSA such as
secp256r1_compact and ecdsa_secp256r1_sha256_compact
[I-D.mattsson-tls-compact-ecc].
=====================================================================
Flight #1 #2 #3 Total
---------------------------------------------------------------------
DTLS 1.3 - RPKs, ECDHE 185 454 255 894
DTLS 1.3 - Compressed RPKs, ECDHE 185 422 223 830
DTLS 1.3 - Cached RPK, PRK, ECDHE 224 402 255 881
DTLS 1.3 - Cached X.509, RPK, ECDHE 218 396 255 869
DTLS 1.3 - PSK, ECDHE 219 226 56 501
DTLS 1.3 - PSK 136 153 56 345
---------------------------------------------------------------------
EDHOC - Signature X.509s, x5t, ECDHE 37 115 90 242
EDHOC - Signature RPKs, kid, ECDHE 37 102 77 216
EDHOC - Static DH X.509s, x5t, ECDHE 37 58 33 128
EDHOC - Static DH RPKs, kid, ECDHE 37 45 19 101
=====================================================================
Figure 1: Comparison of message sizes in bytes with CCM_8, P-256,
and ECDSA and with Connection ID
Figure 2 compares of message sizes of DTLS 1.3 [RFC9147] and TLS 1.3
[RFC8446] handshakes without connection ID but with the same
algorithms CCM_8, P-256, and ECDSA.
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=====================================================================
Flight #1 #2 #3 Total
---------------------------------------------------------------------
DTLS 1.3 - RPKs, ECDHE 179 447 254 880
DTLS 1.3 - PSK, ECDHE 213 219 55 487
DTLS 1.3 - PSK 130 146 55 331
---------------------------------------------------------------------
TLS 1.3 - RPKs, ECDHE 162 394 233 789
TLS 1.3 - PSK, ECDHE 196 190 50 436
TLS 1.3 - PSK 113 117 50 280
---------------------------------------------------------------------
cTLS-09 - X.509s by reference, ECDHE 107 200 98 405
cTLS-09 - PSK, ECDHE 108 120 20 250
cTLS-09 - PSK 43 57 20 120
=====================================================================
Figure 2: Comparison of message sizes in bytes with CCM_8,
secp256r1, and ecdsa_secp256r1_sha256 or PSK and without
Connection ID
Figure 3 is the same as Figure 2 but with more efficiently encoded
key shares and signatures such as x25519 and ed25519. The algorithms
in [I-D.mattsson-tls-compact-ecc] with point compressed secp256r1
RPKs would add 15 bytes to #2 and #3 in the rows with RPKs.
=====================================================================
Flight #1 #2 #3 Total
---------------------------------------------------------------------
DTLS 1.3 - RPKs, ECDHE 146 360 200 706
DTLS 1.3 - PSK, ECDHE 180 186 55 421
DTLS 1.3 - PSK 130 146 55 331
---------------------------------------------------------------------
TLS 1.3 - RPKs, ECDHE 129 307 179 615
TLS 1.3 - PSK, ECDHE 163 157 50 370
TLS 1.3 - PSK 113 117 50 280
---------------------------------------------------------------------
cTLS-09 - X.509s by reference, ECDHE 74 160 91 325
cTLS-09 - PSK, ECDHE 75 89 20 186
cTLS-09 - PSK 43 57 20 120
=====================================================================
Figure 3: Comparison of message sizes in bytes with CCM_8,
x25519, and ed25519 or PSK and without Connection ID
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The numbers in Figure 2, Figure 2, and Figure 3 were calculated with
8 bytes tags which is the mandatory to implement in
[I-D.ietf-uta-tls13-iot-profile] and [I-D.ietf-core-oscore-edhoc].
If 16 bytes tag are used, the numbers in the #2 and #3 columns
increases with 8 and the numbers in the Total column increases with
16.
The numbers in Figure 1, Figure 2, and Figure 3 do not consider
underlying layers, see Section 2.
3.2. 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 replaced with arbitrary strings or omitted, in
which case their length is indicated. Values that are not arbitrary
are given in hexadecimal.
3.2.1. Message Sizes RPK + ECDHE
In this section, CCM_8, P-256, and ECDSA and a Connection ID of 1
byte are used.
3.2.1.1. 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
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
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Compression Methods (null) (2 bytes):
01 00
Extensions Length (2 bytes):
LL LL
Extension - Supported Groups (secp256r1) (8 bytes):
00 0a 00 04 00 02 00 17
Extension - Signature Algorithms (ecdsa_secp256r1_sha256)
(8 bytes):
00 0d 00 04 00 02 04 03
Extension - Key Share (secp256r1) (75 bytes):
00 33 00 27 00 25 00 1d 00 41
04 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
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 02 01 02
Extension - Server Certificate Type (Raw Public Key) (6 bytes):
00 14 00 02 01 02
Extension - Connection Identifier (42) (6 bytes):
00 36 00 02 01 42
13 + 12 + 2 + 32 + 1 + 1 + 4 + 2 + 2 + 8 + 8 + 75 + 7 + 6 + 6 + 6
= 185 bytes
DTLS 1.3 RPK + ECDHE flight #1 gives 185 bytes of overhead. With
efficiently encoded key share such as x25519 or
[I-D.mattsson-tls-compact-ecc] the overhead is 185 - 33 = 152 bytes.
3.2.1.2. Flight #2
Record Header - DTLSPlaintext (13 bytes):
16 fe fd EE EE SS SS SS SS SS SS LL LL
Handshake Header - Server Hello (12 bytes):
02 LL LL LL SS SS 00 00 00 LL LL LL
Legacy Version (2 bytes):
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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 (secp256r1) (73 bytes):
00 33 00 45 00 1d 00 41
04 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
Extension - Supported Versions (1.3) (6 bytes):
00 2b 00 02 03 04
Extension - Connection Identifier (43) (6 bytes):
00 36 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
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
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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 (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 (Uncompressed secp256r1 RPK) (91 bytes):
30 59 30 13 ... // DER encoded 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 (ecdsa_secp256r1_sha256) (average 75 bytes):
04 03 LL LL
30 LL 02 LL ... 02 LL ... // DER encoded signature
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):
16
Auth Tag (8 bytes):
e0 8b 0e 45 5a 35 0a e5
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13 + 137 + 3 + 26 + 23 + 112 + 87 + 44 + 1 + 8 = 454 bytes
DTLS 1.3 RPK + ECDHE flight #2 gives 454 bytes of overhead. With a
point compressed secp256r1 RPK the overhead is 454 - 32 = 422 bytes,
see Section 3.2.7. With an ed25519 RPK and signature the overhead is
454 - 47 - 7 = 400 bytes. With an efficiently encoded key share such
as x25519 or [I-D.mattsson-tls-compact-ecc] the overhead is 454 - 33
= 421 bytes. With an efficiently encoded signature such
[I-D.mattsson-tls-compact-ecc] the overhead is 454 - 7 = 447 bytes.
With x25519 and ed25519 he overhead is 454 - 47 - 33 - 7 = 367 bytes.
3.2.1.3. 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 (Uncompressed secp256r1 RPK) (91 bytes):
30 59 30 13 ... // DER encoded 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 (ecdsa_secp256r1_sha256) (average 75 bytes):
04 03 LL LL
30 LL 02 LL ... 02 LL ... // // DER encoded signature
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 + 87 + 44 + 1 + 8 = 255 bytes
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DTLS 1.3 RPK + ECDHE flight #3 gives 255 bytes of overhead. With a
point compressed secp256r1 RPK the overhead is 255 - 32 = 223 bytes,
see Section 3.2.7. With an ed25519 RPK and signature the overhead is
255 - 47 - 7 = 201 bytes. With an efficiently encoded signature such
as [I-D.mattsson-tls-compact-ecc] the overhead is 255 - 7 = 248
bytes.
3.2.2. Message Sizes PSK + ECDHE
3.2.2.1. Flight #1
The differences in overhead compared to Section 3.2.1.1 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:
185 + 6 + 48 - 8 - 6 - 6 = 219 bytes
DTLS 1.3 PSK + ECDHE flight #1 gives 219 bytes of overhead.
3.2.2.2. Flight #2
The differences in overhead compared to Section 3.2.1.2 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 (87 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:
454 + 6 - 112 - 87 - 23 - 6 - 6 = 226 bytes
DTLS 1.3 PSK + ECDHE flight #2 gives 226 bytes of overhead.
3.2.2.3. Flight #3
The differences in overhead compared to Section 3.2.1.3 are:
The following is removed:
- Handshake Message Certificate (112 bytes)
- Handshake Message Certificate Verify (87 bytes)
In total:
255 - 112 - 87 = 56 bytes
DTLS 1.3 PSK + ECDHE flight #3 gives 56 bytes of overhead.
3.2.3. Message Sizes PSK
3.2.3.1. Flight #1
The differences in overhead compared to Section 3.2.2.1 are:
The following is removed:
- Extension - Supported Groups (x25519) (8 bytes)
- Extension - Key Share (75 bytes)
In total:
219 - 8 - 75 = 136 bytes
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DTLS 1.3 PSK flight #1 gives 136 bytes of overhead.
3.2.3.2. Flight #2
The differences in overhead compared to Section 3.2.2.2 are:
The following is removed:
- Extension - Key Share (73 bytes)
In total:
226 - 73 = 153 bytes
DTLS 1.3 PSK flight #2 gives 153 bytes of overhead.
3.2.3.3. Flight #3
There are no differences in overhead compared to Section 3.2.2.3.
DTLS 1.3 PSK flight #3 gives 56 bytes of overhead.
3.2.4. 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 certificate
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 3.2.1 are the following.
3.2.4.1. 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:
185 + 39 = 224 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:
224 - 6 = 218 bytes
3.2.4.2. 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:
454 + 7 - 59 = 402 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:
402 - 6 = 396 bytes
3.2.5. Resumption
To enable resumption, a 4th flight with 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 ordinary PSK handshake with or without
ECDHE.
3.2.6. 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
3.2.7. Raw Public Keys
Raw Public Keys in TLS consists of a DER encoded ASN.1
SubjectPublicKeyInfo structure [RFC7250]. This section illustrates
the format of P-256 (secp256r1) SubjectPublicKeyInfo [RFC5480] with
and without point compression as well as an ed25519
SubjectPublicKeyInfo. 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 seem
to be supported by (D)TLS implementations.
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3.2.7.1. secp256r1 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
3.2.7.2. secp256r1 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
3.2.7.3. ed25519 SubjectPublicKeyInfo
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0x30 // Sequence
0x2A // Size 42
0x30 // Sequence
0x05 // Size 5
0x06 0x03 0x2B 0x65 0x70
// OID 1.3.101.112 (ed25519)
0x03 // Bit string
0x21 // Size 33
0x00 // Unused bits 0
...... 32 bytes
Total of 44 bytes
3.3. 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]).
3.3.1. Message Sizes RPK + ECDHE
In this section, CCM_8, x25519, and ed25519 are used.
3.3.1.1. 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 (ed25519)
(8 bytes):
00 0d 00 04 00 02 08 07
Extension - Key Share (x25519) (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.
3.3.1.2. 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 (x25519) (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 (ed25519)
(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 (ed25519 RPK) (44 bytes):
30 2A 30 05 ... // DER encoded RPK, see Section 2.2.7.
Certificate Extensions (2 bytes):
00 00
Handshake Header - Certificate Verify (4 bytes):
0f LL LL LL
Signature (ed25519) (68 bytes):
08 07 LL LL
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):
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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Record Type (1 byte):
16
Auth Tag (8 bytes):
e0 8b 0e 45 5a 35 0a e5
5 + 90 + 5 + 18 + 15 + 57 + 72 + 36 + 1 + 8 = 307 bytes
TLS 1.3 RPK + ECDHE flight #2 gives 307 bytes of overhead.
3.3.1.3. 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 (ed25519 RPK) (44 bytes):
30 2A 30 05 ... // DER encoded RPK, see Section 2.2.7.
Certificate Extensions (2 bytes):
00 00
Handshake Header - Certificate Verify (4 bytes):
0f LL LL LL
Signature (ed25519) (68 bytes):
08 07 LL LL
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 + 57 + 72 + 36 + 1 + 8 = 179 bytes
TLS 1.3 RPK + ECDHE flight #3 gives 179 bytes of overhead.
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3.3.2. Message Sizes PSK + ECDHE
3.3.2.1. Flight #1
The differences in overhead compared to Section 3.3.1.3 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.
3.3.2.2. Flight #2
The differences in overhead compared to Section 3.3.1.2 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 (57 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:
307 - 57 - 72 - 15 - 6 - 6 + 6 = 157 bytes
TLS 1.3 PSK + ECDHE flight #2 gives 157 bytes of overhead.
3.3.2.3. Flight #3
The differences in overhead compared to Section 3.3.1.3 are:
The following is removed:
- Handshake Message Certificate (57 bytes)
- Handshake Message Certificate Verify (72 bytes)
In total:
179 - 57 - 72 = 50 bytes
TLS 1.3 PSK + ECDHE flight #3 gives 50 bytes of overhead.
3.3.3. Message Sizes PSK
3.3.3.1. Flight #1
The differences in overhead compared to Section 3.3.2.1 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.
3.3.3.2. Flight #2
The differences in overhead compared to Section 3.3.2.2 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.
3.3.3.3. Flight #3
There are no differences in overhead compared to Section 3.3.2.3.
TLS 1.3 PSK flight #3 gives 50 bytes of overhead.
3.4. 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.
3.5. cTLS
Version -09 of the cTLS specification [I-D.ietf-tls-ctls] has a
single example with CCM_8, x25519, and ed25519 in Appendix A. This
document uses that example and calculates numbers for different
parameters as follows:
Using secp256r1 instead x25519 add 33 bytes to the
KeyShareEntry.key_exchange in flight #1 and flight #2.
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Using ecdsa_secp256r1_sha256 instead ed25519 add an average of 7
bytes to CertificateVerify.signature in flight #2 and flight #3.
Using PSK authentication instead of ed25519 add 1 byte (psk
identifier) to flight #1 and removes 71 bytes (certificate and
certificate_verify) from flight #2 and #3.
Using PSK key exchange x25519 removes 32 bytes
(KeyShareEntry.key_exchange) from flight #1 and #2.
Using Connection ID adds 1 byte to flight #1 and #3, and 2 bytes to
flight #2.
3.6. EDHOC
This section gives an estimate of the message sizes of EDHOC
[RFC9528] 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 [RFC9529].
3.6.1. Message Sizes RPK
3.6.1.1. 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
3.6.1.2. message_2
message_2 = (
h'419701D7F00A26C2DC587A36DD752549F33763C893422C8EA0F955A13A4F
F5D5042459E2DA6C75143F35',
-8
)
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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
3.6.1.3. 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
3.6.2. 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 increases the size with 13-14 bytes. The typical
message sizes for the previous example and for the other combinations
are summarized in Figure 4. Note that EDHOC treats authentication
keys stored in RPK and X.509 in the same way. More detailed examples
can be found in [RFC9529].
==========================================================
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 4: Typical message sizes in bytes
3.7. Summary
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
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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.
4. Overhead for Protection of Application Data
To enable comparison, all the overhead calculations in this section
use an 8 bytes ICV (e.g., AES_128_CCM_8 [RFC6655] or AES-CCM-
16-64-128 [RFC9053]) or 16 bytes (e.g., AES-CCM [SP-800-38C], AES-GCM
[SP-800-38D], or ChaCha20-Poly1305 [RFC7539]), 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.
Section 4.1 gives a short summary of the message overhead based on
different parameters and some assumptions. The following sections
detail the assumptions and the calculations.
4.1. 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 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 5: Overhead (8 bytes ICV) 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
--------------------------------------------------------------
Group OSCORE pairwise request 14 15 16
Group OSCORE pairwise response 11 11 11
==============================================================
Figure 6: Overhead (8 bytes ICV) in bytes as a function of
Connection/Sender ID (Sequence Number = '05')
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=============================================================
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 6
Group OSCORE pairwise response 3
=============================================================
Figure 7: Overhead (excluding ICV) in bytes (Connection/Sender ID
= '', Sequence Number = '05')
The numbers in Figure 5, Figure 6, and {fig-overhead3} do 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.
The numbers in Figure 5 and Figure 6 were calculated with 8 bytes ICV
which is the mandatory to implement in
[I-D.ietf-uta-tls13-iot-profile], and [I-D.ietf-core-oscore-edhoc].
If 16 bytes tag are used, all numbers increases with 8.
The numbers in Figure 5, Figure 6, and Figure 7 do not consider
underlying layers, see Section 2.
4.2. DTLS 1.2
4.2.1. 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.
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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.
4.2.2. 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.
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
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When compressed with 6LoWPAN-GHC, DTLS 1.2 with the above parameters
(epoch, sequence number, length) gives 16 bytes overhead.
4.2.3. 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 record 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.
4.2.4. 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.
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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.
4.3. DTLS 1.3
4.3.1. 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]).
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.
4.3.2. DTLS 1.3 with 6LoWPAN-GHC
This section analyzes the overhead of DTLS 1.3 [RFC9147] when
compressed with 6LoWPAN-GHC [RFC7400] [OlegHahm-ghc].
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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.
4.3.3. 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.
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.
4.3.4. 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].
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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.
4.4. TLS 1.2
4.4.1. 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.
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.
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4.4.2. 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.
4.5. TLS 1.3
4.5.1. 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.
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.
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4.5.2. 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.
4.6. 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.
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.
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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’.
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.
4.7. 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. An additional requirement compared to
[RFC8613] is that ID Context is always included in requests.
Assuming 1 byte ID Context and Sender ID this adds 2 bytes to
requests.
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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.
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 pairwise mode OSCORE with the above parameters gives 15 bytes
overhead for requests and 11 bytes overhead for responses.
4.8. Summary
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.
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
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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 7, Group
OSCORE for pairwise communication increases the overhead of OSCORE
requests with 20%.
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.
5. Security Considerations
When using the security protocols outlined in this document, it is
important to adhere to the latest requirements and recommendations
for respective protocol. It is also crucial to utilize supported
versions of libraries that continue to receive security updates in
response to identified vulnerabilities.
While the security considerations provided in DTLS 1.2 [RFC6347],
DTLS 1.3 [RFC9147], TLS 1.2 [RFC5246], TLS 1.3 [RFC8446], cTLS
[I-D.ietf-tls-ctls], EDHOC [RFC9528] [I-D.ietf-core-oscore-edhoc],
OSCORE [RFC8613], Group OSCORE [I-D.ietf-core-oscore-groupcomm], and
X.509 [RFC5280] serve as a good starting point, they are not
sufficient due to the fact that some of these specifications were
authored many years ago. For instance, being compliant to the TLS
1.2 [RFC5246] specification is considered very poor security
practice, given that the mandatory-to-implement cipher suite
TLS_RSA_WITH_AES_128_CBC_SHA possesses at least three major
weaknesses.
Therefore, implementations and configurations must also align with
the latest recommendations and best practices. Notable examples when
this document was published include BCP 195 [RFC9325][RFC8996],
[SP-800-52], and [BSI-TLS].
6. IANA Considerations
This document has no actions for IANA.
7. Informative References
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[BSI-TLS] Bundesamt für Sicherheit in der Informationstechnik,
"Technical Guideline TR-02102-2 Cryptographic Mechanisms:
Recommendations and Key Lengths Part 2 – Use of Transport
Layer Security (TLS)", January 2023, <https://www.bsi.bund
.de/SharedDocs/Downloads/EN/BSI/Publications/
TechGuidelines/TG02102/BSI-TR-02102-2.pdf>.
[FIPS-180-4]
NIST, "Secure Hash Standard (SHS)", August 2015,
<https://doi.org/10.6028/NIST.FIPS.180-4>.
[FIPS-186-5]
NIST, "Digital Signature Standard (DSS)", February 2023,
<https://doi.org/10.6028/NIST.FIPS.186-5>.
[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-04, 21 February 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-core-
attacks-on-coap-04>.
[I-D.ietf-core-oscore-edhoc]
Palombini, F., Tiloca, M., Höglund, R., Hristozov, S., and
G. Selander, "Using Ephemeral Diffie-Hellman Over COSE
(EDHOC) with the Constrained Application Protocol (CoAP)
and Object Security for Constrained RESTful Environments
(OSCORE)", Work in Progress, Internet-Draft, draft-ietf-
core-oscore-edhoc-10, 29 November 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-core-
oscore-edhoc-10>.
[I-D.ietf-core-oscore-groupcomm]
Tiloca, M., Selander, G., Palombini, F., Mattsson, J. P.,
and R. Höglund, "Group Object Security for Constrained
RESTful Environments (Group OSCORE)", Work in Progress,
Internet-Draft, draft-ietf-core-oscore-groupcomm-21, 4
March 2024, <https://datatracker.ietf.org/doc/html/draft-
ietf-core-oscore-groupcomm-21>.
[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-09, 4 March 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-cose-
cbor-encoded-cert-09>.
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[I-D.ietf-lake-reqs]
Vučinić, M., Selander, G., Mattsson, J. P., and D. Garcia-
Carillo, "Requirements for a Lightweight AKE for OSCORE",
Work in Progress, Internet-Draft, draft-ietf-lake-reqs-04,
8 June 2020, <https://datatracker.ietf.org/doc/html/draft-
ietf-lake-reqs-04>.
[I-D.ietf-schc-8824-update]
Tiloca, M., Toutain, L., Martinez, I., and A. Minaburo,
"Static Context Header Compression (SCHC) for the
Constrained Application Protocol (CoAP)", Work in
Progress, Internet-Draft, draft-ietf-schc-8824-update-01,
4 March 2024, <https://datatracker.ietf.org/doc/html/
draft-ietf-schc-8824-update-01>.
[I-D.ietf-tls-cert-abridge]
Jackson, D., "Abridged Compression for WebPKI
Certificates", Work in Progress, Internet-Draft, draft-
ietf-tls-cert-abridge-00, 6 September 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-tls-
cert-abridge-00>.
[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-09, 23 October 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-tls-
ctls-09>.
[I-D.ietf-uta-tls13-iot-profile]
Tschofenig, H., Fossati, T., and M. Richardson, "TLS/DTLS
1.3 Profiles for the Internet of Things", Work in
Progress, Internet-Draft, draft-ietf-uta-tls13-iot-
profile-09, 3 March 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-uta-
tls13-iot-profile-09>.
[I-D.kampanakis-tls-scas-latest]
Kampanakis, P., Bytheway, C., Westerbaan, B., and M.
Thomson, "Suppressing CA Certificates in TLS 1.3", Work in
Progress, Internet-Draft, draft-kampanakis-tls-scas-
latest-03, 5 January 2023,
<https://datatracker.ietf.org/doc/html/draft-kampanakis-
tls-scas-latest-03>.
[I-D.mattsson-tls-compact-ecc]
Mattsson, J. P. and H. Tschofenig, "Compact ECDHE and
ECDSA Encodings for TLS 1.3", Work in Progress, Internet-
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Draft, draft-mattsson-tls-compact-ecc-06, 23 February
2024, <https://datatracker.ietf.org/doc/html/draft-
mattsson-tls-compact-ecc-06>.
[Illustrated-DTLS13]
Driscoll, M., "The Illustrated DTLS 1.3 Connection", n.d.,
<https://dtls.xargs.org/>.
[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>.
[Performance]
Fedrecheski, G., Vučinić, M., and T. Watteyne,
"Performance Comparison of EDHOC and DTLS 1.3 in Internet-
of-Things Environments", January 2024,
<https://hal.science/hal-04382397>.
[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>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/info/rfc5280>.
[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>.
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[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>.
[RFC6655] McGrew, D. and D. Bailey, "AES-CCM Cipher Suites for
Transport Layer Security (TLS)", RFC 6655,
DOI 10.17487/RFC6655, July 2012,
<https://www.rfc-editor.org/info/rfc6655>.
[RFC7250] Wouters, P., Ed., Tschofenig, H., Ed., Gilmore, J.,
Weiler, S., and T. Kivinen, "Using Raw Public Keys in
Transport Layer Security (TLS) and Datagram Transport
Layer Security (DTLS)", RFC 7250, DOI 10.17487/RFC7250,
June 2014, <https://www.rfc-editor.org/info/rfc7250>.
[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>.
[RFC7539] Nir, Y. and A. Langley, "ChaCha20 and Poly1305 for IETF
Protocols", RFC 7539, DOI 10.17487/RFC7539, May 2015,
<https://www.rfc-editor.org/info/rfc7539>.
[RFC7748] Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves
for Security", RFC 7748, DOI 10.17487/RFC7748, January
2016, <https://www.rfc-editor.org/info/rfc7748>.
[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>.
[RFC8032] Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital
Signature Algorithm (EdDSA)", RFC 8032,
DOI 10.17487/RFC8032, January 2017,
<https://www.rfc-editor.org/info/rfc8032>.
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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>.
[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>.
[RFC8824] Minaburo, A., Toutain, L., and R. Andreasen, "Static
Context Header Compression (SCHC) for the Constrained
Application Protocol (CoAP)", RFC 8824,
DOI 10.17487/RFC8824, June 2021,
<https://www.rfc-editor.org/info/rfc8824>.
[RFC8879] Ghedini, A. and V. Vasiliev, "TLS Certificate
Compression", RFC 8879, DOI 10.17487/RFC8879, December
2020, <https://www.rfc-editor.org/info/rfc8879>.
[RFC8996] Moriarty, K. and S. Farrell, "Deprecating TLS 1.0 and TLS
1.1", BCP 195, RFC 8996, DOI 10.17487/RFC8996, March 2021,
<https://www.rfc-editor.org/info/rfc8996>.
[RFC9053] Schaad, J., "CBOR Object Signing and Encryption (COSE):
Initial Algorithms", RFC 9053, DOI 10.17487/RFC9053,
August 2022, <https://www.rfc-editor.org/info/rfc9053>.
[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>.
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[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>.
[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>.
[RFC9325] Sheffer, Y., Saint-Andre, P., and T. Fossati,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 9325, DOI 10.17487/RFC9325, November
2022, <https://www.rfc-editor.org/info/rfc9325>.
[RFC9528] Selander, G., Preuß Mattsson, J., and F. Palombini,
"Ephemeral Diffie-Hellman Over COSE (EDHOC)", RFC 9528,
DOI 10.17487/RFC9528, March 2024,
<https://www.rfc-editor.org/info/rfc9528>.
[RFC9529] Selander, G., Preuß Mattsson, J., Serafin, M., Tiloca, M.,
and M. Vučinić, "Traces of Ephemeral Diffie-Hellman Over
COSE (EDHOC)", RFC 9529, DOI 10.17487/RFC9529, March 2024,
<https://www.rfc-editor.org/info/rfc9529>.
[RFC9547] Arkko, J., Perkins, C. S., and S. Krishnan, "Report from
the IAB Workshop on Environmental Impact of Internet
Applications and Systems, 2022", RFC 9547,
DOI 10.17487/RFC9547, February 2024,
<https://www.rfc-editor.org/info/rfc9547>.
[SCHC-eval]
Dumay, M., Barthel, D., Toutain, L., and J. Lecoeuvre,
"Effective interoperability and security support for
constrained IoT networks", December 2021,
<https://ieeexplore.ieee.org/document/9685592>.
[SP-800-186]
Chen, L., Moody, D., Randall, K., Regenscheid, A., and A.
Robinson, "Recommendations for Discrete Logarithm-based
Cryptography: Elliptic Curve Domain Parameters",
NIST Special Publication 800-186, February 2023,
<https://doi.org/10.6028/NIST.SP.800-186>.
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[SP-800-38C]
Dworkin, M., "Recommendation for Block Cipher Modes of
Operation: the CCM Mode for Authentication and
Confidentiality", NIST Special Publication 800-38C, May
2004, <https://doi.org/10.6028/NIST.SP.800-38C>.
[SP-800-38D]
Dworkin, M., "Recommendation for Block Cipher Modes of
Operation: Galois/Counter Mode (GCM) and GMAC",
NIST Special Publication 800-38D, November 2007,
<https://doi.org/10.6028/NIST.SP.800-38D>.
[SP-800-52]
McKay, K. and D. Cooper, "Guidelines for the Selection,
Configuration, and Use of Transport Layer Security (TLS)
Implementations", NIST Special Publication 800-52 Revision
2, August 2019,
<https://doi.org/10.6028/NIST.SP.800-52r2>.
Appendix A. EDHOC Over CoAP and OSCORE
The overhead of CoAP and OSCORE when used to transport EDHOC is a bit
more complex than the overhead of UPD and TCP. Assuming a that the
CoAP Token has a length of 0 bytes, that CoAP Content-Format is not
used, that the EDHOC Initiator is the CoAP client, that the
connection identifiers have 1-byte encodings, and the CoAP URI path
is "edhoc", the additional overhead due to CoAP being used as
transport is:
For EDHOC message_1
--- CoAP header: 4 bytes
--- CoAP token: 0 bytes
--- URI-Path option with value "edhoc": 6 bytes
--- Payload marker 0xff: 1 byte
--- Dummy connection identifier "true": 1 byte
Total: 12 bytes
For EDHOC message_2
--- CoAP header: 4 bytes
--- CoAP token: 0 bytes
--- Payload marker 0xff: 1 byte
Total: 5 bytes
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For EDHOC message_3 without the combined request
--- CoAP header: 4 bytes
--- CoAP token: 0 bytes
--- URI-Path option with value "edhoc": 6 bytes
--- Payload marker 0xff: 1 byte
--- Connection identifier C_R (wire encoding): 1 byte
Total: 12 bytes
For EDHOC message_3 over OSCORE with the EDHOC + OSCORE combined
request [I-D.ietf-core-oscore-edhoc] all the overhead contributions
from the previous case is gone. The only additional overhead is 1
byte due to the EDHOC CoAP option.
Change Log
This section is to be removed before publishing as an RFC.
Changes from -05 to -06:
* Editorial changes.
Changes from -04 to -05:
* Editorial changes.
Changes from -03 to -04:
* Added change log
* Updated to cTLS-09, which seems relatively stable.
* Explained key and certificate identifiers.
* Added a paragraph to introduce the section on underlying layers.
* Added text explaining the difference between AKEs and protocols
for protection of application data.
* Added reference to RFC 7250, RFC 9547, and "Performance Comparison
of EDHOC and DTLS 1.3 in Internet-of-Things Environments".
* Editorial changes.
Changes from -02 to -03:
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* Security considerations linking to the security considerations for
the protocols as well as newer recommendations and best practices.
* Moved "EDHOC Over CoAP and OSCORE" subsection to appendix.
* References for the algorithms.
* Editorial changes.
Changes from -01 to -02:
* More information about overhead in underlying layers.
* New subsection "EDHOC Over CoAP and OSCORE" contributed by Marco.
* Editorial changes.
Changes from -00 to -01:
* Added links to the IOTOPS mailing list and the GitHub repository.
* Made it clearer that the document focuses on comparing the
security protocols and not underlying layers.
* Added a short section on underlying layers. Added references to
SCHC documents.
* Changed “Conclusion” to “Summary”.
* Corrected Group OSCORE numbers.
* Updated cTLS numbers to align with -08. Use “cTLS-08” in tables
to make it clear that numbers are for -08.
* cTLS is more stable now. Seems like cTLS will not optimize P-256/
ECDSA and instead focus on x25519 and EdDSA. The impact of any
cTLS changes are now much smaller than before.
* Editorial changes.
Acknowledgments
The authors want to thank Carsten Bormann, Russ Housley, Ari Keränen,
Erik Kline, Stephan Koch, Achim Kraus, Michael Richardsson, Göran
Selander, Bill Silverajan, Akram Sheriff, Marco Tiloca, and Hannes
Tschofenig for comments and suggestions on previous versions of the
draft.
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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
Email: john.mattsson@ericsson.com
Francesca Palombini
Ericsson
Email: francesca.palombini@ericsson.com
Mališa Vučinić
INRIA
Email: malisa.vucinic@inria.fr
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