Internet DRAFT - draft-tschofenig-uta-tls13-profile
draft-tschofenig-uta-tls13-profile
UTA H. Tschofenig
Internet-Draft T. Fossati
Updates: 7925 (if approved) Arm Limited
Intended status: Standards Track 22 April 2020
Expires: 24 October 2020
TLS/DTLS 1.3 Profiles for the Internet of Things
draft-tschofenig-uta-tls13-profile-04
Abstract
This document is a companion to RFC 7925 and defines TLS/DTLS 1.3
profiles for Internet of Things devices. It also updates RFC 7925
with regards to the X.509 certificate profile.
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
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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 24 October 2020.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Simplified BSD License text
as described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Simplified BSD License.
Tschofenig & Fossati Expires 24 October 2020 [Page 1]
Internet-Draft TLS/DTLS 1.3 IoT Profiles April 2020
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Conventions and Terminology . . . . . . . . . . . . . . . 3
2. Credential Types . . . . . . . . . . . . . . . . . . . . . . 3
3. Error Handling . . . . . . . . . . . . . . . . . . . . . . . 3
4. Session Resumption . . . . . . . . . . . . . . . . . . . . . 4
5. Compression . . . . . . . . . . . . . . . . . . . . . . . . . 4
6. Perfect Forward Secrecy . . . . . . . . . . . . . . . . . . . 4
7. Keep-Alive . . . . . . . . . . . . . . . . . . . . . . . . . 4
8. Timeouts . . . . . . . . . . . . . . . . . . . . . . . . . . 4
9. Random Number Generation . . . . . . . . . . . . . . . . . . 4
10. Server Name Indication (SNI) . . . . . . . . . . . . . . . . 4
11. Maximum Fragment Length Negotiation . . . . . . . . . . . . . 5
12. Crypto Agility . . . . . . . . . . . . . . . . . . . . . . . 5
13. Key Length Recommendations . . . . . . . . . . . . . . . . . 5
14. 0-RTT Data . . . . . . . . . . . . . . . . . . . . . . . . . 5
15. Certificate Profile . . . . . . . . . . . . . . . . . . . . . 6
15.1. Compression . . . . . . . . . . . . . . . . . . . . . . 6
16. Security Considerations . . . . . . . . . . . . . . . . . . . 6
17. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
18. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
18.1. Normative References . . . . . . . . . . . . . . . . . . 7
18.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
This document defines a profile of DTLS 1.3 [I-D.ietf-tls-dtls13] and
TLS 1.3 [RFC8446] that offers communication security services for IoT
applications and is reasonably implementable on many constrained
devices. Profile thereby means that available configuration options
and protocol extensions are utilized to best support the IoT
environment.
For IoT profiles using TLS/DTLS 1.2 please consult [RFC7925]. This
document re-uses the communication pattern defined in [RFC7925] and
makes IoT-domain specific recommendations for version 1.3 (where
necessary).
TLS 1.3 has been re-designed and several previously defined
extensions are not applicable to the new version of TLS/DTLS anymore.
This clean-up also simplifies this document. Furthermore, many
outdated ciphersuites have been omitted from the TLS/DTLS 1.3
specification.
Tschofenig & Fossati Expires 24 October 2020 [Page 2]
Internet-Draft TLS/DTLS 1.3 IoT Profiles April 2020
1.1. Conventions and Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. Credential Types
In accordance with the recommendations in [RFC7925], a compliant
implementation MUST implement TLS_AES_128_CCM_8_SHA256. It SHOULD
implement TLS_CHACHA20_POLY1305_SHA256.
Pre-shared key based authentication is integrated into the main TLS/
DTLS 1.3 specification and has been harmonized with session
resumption.
A compliant implementation supporting authentication based on
certificates and raw public keys MUST support digital signatures with
ecdsa_secp256r1_sha256. A compliant implementation MUST support the
key exchange with secp256r1 (NIST P-256) and SHOULD support key
exchange with X25519.
A plain PSK-based TLS/DTLS client or server MUST implement the
following extensions:
* supported_versions
* cookie
* server_name
* pre_shared_key
* psk_key_exchange_modes
For TLS/DTLS clients and servers implementing raw public keys and/or
certificates the guidance for mandatory-to-implement extensions
described in Section 9.2 of [RFC8446] MUST be followed.
3. Error Handling
TLS 1.3 simplified the Alert protocol but the underlying challenge in
an embedded context remains unchanged, namely what should an IoT
device do when it encounters an error situation. The classical
approach used in a desktop environment where the user is prompted is
often not applicable with unattended devices. Hence, it is more
important for a developer to find out from which error cases a device
can recover from.
Tschofenig & Fossati Expires 24 October 2020 [Page 3]
Internet-Draft TLS/DTLS 1.3 IoT Profiles April 2020
4. Session Resumption
TLS 1.3 has built-in support for session resumption by utilizing PSK-
based credentials established in an earlier exchange.
5. Compression
TLS 1.3 does not have support for compression.
6. Perfect Forward Secrecy
TLS 1.3 allows the use of PFS with all ciphersuites since the support
for it is negotiated independently.
7. Keep-Alive
The discussion in Section 10 of [RFC7925] is applicable.
8. Timeouts
The recommendation in Section 11 of [RFC7925] is applicable. In
particular this document RECOMMENDED to use an initial timer value of
9 seconds with exponential back off up to no less then 60 seconds.
Question: DTLS 1.3 now offers per-record retransmission and therefore
introduces much less congestion risk associated with spurious
retransmissions. Hence, should we relax the 9s initial timeout?
9. Random Number Generation
The discussion in Section 12 of [RFC7925] is applicable with one
exception: the ClientHello and the ServerHello messages in TLS 1.3 do
not contain gmt_unix_time component anymore.
10. Server Name Indication (SNI)
This specification mandates the implementation of the SNI extension.
Where privacy requirements require it, the encrypted SNI extension
[I-D.ietf-tls-esni] prevents an on-path attacker to determine the
domain name the client is trying to connect to. Note, however, that
the extension is still at an experimental state.
Tschofenig & Fossati Expires 24 October 2020 [Page 4]
Internet-Draft TLS/DTLS 1.3 IoT Profiles April 2020
11. Maximum Fragment Length Negotiation
The Maximum Fragment Length Negotiation (MFL) extension has been
superseded by the Record Size Limit (RSL) extension [RFC8449].
Implementations in compliance with this specification MUST implement
the RSL extension and SHOULD use it to indicate their RAM
limitations.
12. Crypto Agility
The recommendations in Section 19 of [RFC7925] are applicable.
13. Key Length Recommendations
The recommendations in Section 20 of [RFC7925] are applicable.
14. 0-RTT Data
When clients and servers share a PSK, TLS/DTLS 1.3 allows clients to
send data on the first flight ("early data"). This features reduces
communication setup latency but requires application layer protocols
to define its use with the 0-RTT data functionality.
For HTTP this functionality is described in [RFC8470]. This document
specifies the application profile for CoAP, which follows the design
of [RFC8470].
For a given request, the level of tolerance to replay risk is
specific to the resource it operates upon (and therefore only known
to the origin server). In general, if processing a request does not
have state-changing side effects, the consequences of replay are not
significant. The server can choose whether it will process early
data before the TLS handshake completes.
It is RECOMMENDED that origin servers allow resources to explicitly
configure whether early data is appropriate in requests.
This specification specifies the Early-Data option, which indicates
that the request has been conveyed in early data and that a client
understands the 4.25 (Too Early) status code. The semantic follows
[RFC8470].
Tschofenig & Fossati Expires 24 October 2020 [Page 5]
Internet-Draft TLS/DTLS 1.3 IoT Profiles April 2020
+-----+---+---+---+---+-------------+--------+--------+---------+---+
| No. | C | U | N | R | Name | Format | Length | Default | E |
+-----+---+---+---+---+-------------+--------+--------+---------+---+
| TBD | x | | | | Early-Data | empty | 0 | (none) | x |
+-----+---+---+---+---+-------------+--------+--------+---------+---+
C=Critical, U=Unsafe, N=NoCacheKey, R=Repeatable,
E=Encrypt and Integrity Protect (when using OSCORE)
Figure 1: Early-Data Option
15. Certificate Profile
This section is intended for discussing updates to the certificate
profile defined in [RFC7925]. Initial set of things to consider:
* pathLenConstraint
Question: should also we move the ASN.1 schema from Appendix B of
[I-D.raza-ace-cbor-certificates] here and let it have it by
reference?
15.1. Compression
The compression methods defined in
[I-D.ietf-tls-certificate-compression] do not seem to deal
effectively with [RFC7925] profiled certificates: zlib compresses the
example cert by 9%, but other certificates and compression algorithms
do in many cases increase the overall size. On the other hand,
[I-D.raza-ace-cbor-certificates] provides a more efficient scheme,
yielding to compression rates higher than 50% (see Section 3 of
[I-D.mattsson-cose-cbor-cert-compress]).
Question: should we RECOMMEND CBOR compression? How is that
negotiated?
16. Security Considerations
This entire document is about security.
17. IANA Considerations
IANA is asked to add the Option defined in Figure 2 to the CoAP
Option Numbers registry.
Tschofenig & Fossati Expires 24 October 2020 [Page 6]
Internet-Draft TLS/DTLS 1.3 IoT Profiles April 2020
+--------+------------+-----------+
| Number | Name | Reference |
+--------+------------+-----------+
| TBD | Early-Data | RFCThis |
+--------+------------+-----------+
Figure 2: Early-Data Option
IANA is asked to add the Response Code defined in Figure 3 to the
CoAP Response Code registry.
+--------+-------------+-----------+
| Code | Description | Reference |
+--------+-------------+-----------+
| 4.25 | Too Early | RFCThis |
+--------+-------------+-----------+
Figure 3: Too Early Response Code
18. References
18.1. Normative References
[I-D.ietf-tls-dtls13]
Rescorla, E., Tschofenig, H., and N. Modadugu, "The
Datagram Transport Layer Security (DTLS) Protocol Version
1.3", Work in Progress, Internet-Draft, draft-ietf-tls-
dtls13-37, 9 March 2020, <http://www.ietf.org/internet-
drafts/draft-ietf-tls-dtls13-37.txt>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[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>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[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>.
Tschofenig & Fossati Expires 24 October 2020 [Page 7]
Internet-Draft TLS/DTLS 1.3 IoT Profiles April 2020
[RFC8449] Thomson, M., "Record Size Limit Extension for TLS",
RFC 8449, DOI 10.17487/RFC8449, August 2018,
<https://www.rfc-editor.org/info/rfc8449>.
[RFC8470] Thomson, M., Nottingham, M., and W. Tarreau, "Using Early
Data in HTTP", RFC 8470, DOI 10.17487/RFC8470, September
2018, <https://www.rfc-editor.org/info/rfc8470>.
18.2. Informative References
[I-D.ietf-tls-certificate-compression]
Ghedini, A. and V. Vasiliev, "TLS Certificate
Compression", Work in Progress, Internet-Draft, draft-
ietf-tls-certificate-compression-10, 6 January 2020,
<http://www.ietf.org/internet-drafts/draft-ietf-tls-
certificate-compression-10.txt>.
[I-D.ietf-tls-esni]
Rescorla, E., Oku, K., Sullivan, N., and C. Wood,
"Encrypted Server Name Indication for TLS 1.3", Work in
Progress, Internet-Draft, draft-ietf-tls-esni-06, 9 March
2020, <http://www.ietf.org/internet-drafts/draft-ietf-tls-
esni-06.txt>.
[I-D.mattsson-cose-cbor-cert-compress]
Mattsson, J., Selander, G., Raza, S., Hoglund, J., and M.
Furuhed, "CBOR Object Signing and Encryption (COSE):
Headers for Carrying CBOR Compressed Certificates", Work
in Progress, Internet-Draft, draft-mattsson-cose-cbor-
cert-compress-00, 9 March 2020, <http://www.ietf.org/
internet-drafts/draft-mattsson-cose-cbor-cert-compress-
00.txt>.
[I-D.raza-ace-cbor-certificates]
Raza, S., Hoglund, J., Selander, G., Mattsson, J., and M.
Furuhed, "CBOR Profile of X.509 Certificates", Work in
Progress, Internet-Draft, draft-raza-ace-cbor-
certificates-04, 9 March 2020, <http://www.ietf.org/
internet-drafts/draft-raza-ace-cbor-certificates-04.txt>.
Authors' Addresses
Hannes Tschofenig
Arm Limited
Email: Hannes.Tschofenig@gmx.net
Tschofenig & Fossati Expires 24 October 2020 [Page 8]
Internet-Draft TLS/DTLS 1.3 IoT Profiles April 2020
Thomas Fossati
Arm Limited
Email: Thomas.Fossati@arm.com
Tschofenig & Fossati Expires 24 October 2020 [Page 9]
