TLS/DTLS 1.3 Profiles for the Internet of Things
draft-ietf-uta-tls13-iot-profile-01
UTA H. Tschofenig
Internet-Draft T. Fossati
Updates: 7925 (if approved) Arm Limited
Intended status: Standards Track 22 February 2021
Expires: 26 August 2021
TLS/DTLS 1.3 Profiles for the Internet of Things
draft-ietf-uta-tls13-iot-profile-01
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.
Discussion Venues
This note is to be removed before publishing as an RFC.
Source for this draft and an issue tracker can be found at
https://github.com/thomas-fossati/draft-tls13-iot
(https://github.com/thomas-fossati/draft-tls13-iot).
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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This Internet-Draft will expire on 26 August 2021.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Conventions and Terminology . . . . . . . . . . . . . . . 3
2. Credential Types . . . . . . . . . . . . . . . . . . . . . . 3
3. Error Handling . . . . . . . . . . . . . . . . . . . . . . . 4
4. Session Resumption . . . . . . . . . . . . . . . . . . . . . 4
5. Compression . . . . . . . . . . . . . . . . . . . . . . . . . 4
6. Perfect Forward Secrecy . . . . . . . . . . . . . . . . . . . 4
7. Keep-Alive . . . . . . . . . . . . . . . . . . . . . . . . . 4
8. Timeouts . . . . . . . . . . . . . . . . . . . . . . . . . . 4
9. Random Number Generation . . . . . . . . . . . . . . . . . . 5
10. Server Name Indication (SNI) . . . . . . . . . . . . . . . . 5
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. All Certificates . . . . . . . . . . . . . . . . . . . . 6
15.1.1. Version . . . . . . . . . . . . . . . . . . . . . . 6
15.1.2. Serial Number . . . . . . . . . . . . . . . . . . . 6
15.1.3. Signature . . . . . . . . . . . . . . . . . . . . . 6
15.1.4. Issuer . . . . . . . . . . . . . . . . . . . . . . . 6
15.1.5. Validity . . . . . . . . . . . . . . . . . . . . . . 7
15.1.6. subjectPublicKeyInfo . . . . . . . . . . . . . . . . 7
15.2. Root CA Certificate . . . . . . . . . . . . . . . . . . 7
15.3. Intermediate CA Certificate . . . . . . . . . . . . . . 7
15.4. End Entity Certificate . . . . . . . . . . . . . . . . . 7
15.4.1. Client Certificate Subject . . . . . . . . . . . . . 8
16. Certificate Revocation Checks . . . . . . . . . . . . . . . . 8
16.1. Open Issues . . . . . . . . . . . . . . . . . . . . . . 8
17. Security Considerations . . . . . . . . . . . . . . . . . . . 9
18. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
19. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
20. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
20.1. Normative References . . . . . . . . . . . . . . . . . . 9
20.2. Informative References . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
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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.
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
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* 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.
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?
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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.
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.
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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].
+-----+---+---+---+---+-------------+--------+--------+---------+---+
| 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 contains updates and clarifications to the certificate
profile defined in [RFC7925]. The content of Table 1 of [RFC7925]
has been split by certificate "type" in order to clarify exactly what
requirements and recommendations apply to which entity in the PKI
hierarchy.
15.1. All Certificates
15.1.1. Version
Certificates MUST be of type X.509 v3.
15.1.2. Serial Number
CAs SHALL generate non-sequential Certificate serial numbers greater
than zero (0) containing at least 64 bits of output from a CSPRNG
(cryptographically secure pseudo-random number generator).
15.1.3. Signature
The signature MUST be ecdsa-with-SHA256 or stronger [RFC5758].
15.1.4. Issuer
Contains the DN of the issuing CA.
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15.1.5. Validity
No maximum validity period is mandated. Validity values are
expressed as UTCTime in notBefore and notAfter fields, as mandated in
[RFC5280].
In many cases it is necessary to indicate that a certificate does not
expire. This is likely to be the case for manufacturer-provisioned
certificates. RFC 5280 provides a simple solution to convey the fact
that a certificate has no well-defined expiration date by setting the
notAfter to the GeneralizedTime value of 99991231235959Z.
Some devices might not have a reliable source of time and for those
devices it is also advisable to use certificates with no expiration
date and to let a device management solution manage the lifetime of
all the certificates used by the device. While this approach does
not utilize certificates to its widest extent, it is a solution that
extends the capabilities offered by a raw public key approach.
15.1.6. subjectPublicKeyInfo
The SubjectPublicKeyInfo structure indicates the algorithm and any
associated parameters for the ECC public key. This profile uses the
id-ecPublicKey algorithm identifier for ECDSA signature keys, as
defined and specified in [RFC5480].
15.2. Root CA Certificate
* basicConstraints MUST be present and MUST be marked critical. The
cA field MUST be set true. The pathLenConstraint field SHOULD NOT
be present.
* keyUsage MUST be present and MUST be marked critical. Bit
position for keyCertSign MUST be set.
* extendedKeyUsage MUST NOT be present.
15.3. Intermediate CA Certificate
* basicConstraints MUST be present and MUST be marked critical. The
cA field MUST be set true. The pathLenConstraint field MAY be
present.
* keyUsage MUST be present and MUST be marked critical. Bit
position for keyCertSign MUST be set.
* extendedKeyUsage MUST NOT be present.
15.4. End Entity Certificate
* extendedKeyUsage MUST be present and contain at least one of id-
kp-serverAuth or id-kp-clientAuth.
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* keyUsage MAY be present and contain one of digitalSignature or
keyAgreement.
* Domain names MUST NOT be encoded in the subject commonName,
instead they MUST be encoded in a subjectAltName of type DNS-ID.
Domain names MUST NOT contain wildcard ("*") characters.
subjectAltName MUST NOT contain multiple names.
15.4.1. Client Certificate Subject
The requirement in Section 4.4.2 of [RFC7925] to only use EUI-64 for
client certificates is lifted.
If the EUI-64 format is used to identify the subject of a client
certificate, it MUST be encoded in a subjectAltName of type DNS-ID as
a string of the form "HH-HH-HH-HH-HH-HH-HH-HH" where 'H' is one of
the symbols '0'-'9' or 'A'-'F'.
16. Certificate Revocation Checks
The considerations in Section 4.4.3 of [RFC7925] hold.
Since the publication of RFC 7925 the need for firmware update
mechanisms has been reinforced and the work on standardizing a secure
and interoperable firmware update mechanism has made substantial
progress, see [I-D.ietf-suit-architecture]. RFC 7925 recommends to
use a software / firmware update mechanism to provision devices with
new trust anchors.
The use of device management protocols for IoT devices, which often
include an onboarding or bootstrapping mechanism, has also seen
considerable uptake in deployed devices and these protocols, some of
which are standardized, allow provision of certificates on a regular
basis. This enables a deployment model where IoT device utilize end-
entity certificates with shorter lifetime making certificate
revocation protocols, like OCSP and CRLs, less relevant.
Hence, instead of performing certificate revocation checks on the IoT
device itself this specification recommends to delegate this task to
the IoT device operator and to take the necessary action to allow IoT
devices to remain operational.
16.1. Open Issues
A list of open issues can be found at https://github.com/thomas-
fossati/draft-tls13-iot/issues
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17. Security Considerations
This entire document is about security.
18. Acknowledgements
We would like to thank Ben Kaduk and John Mattsson.
19. IANA Considerations
IANA is asked to add the Option defined in Figure 2 to the CoAP
Option Numbers registry.
+--------+------------+-----------+
| 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
20. References
20.1. 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-
dtls13-40, 20 January 2021, <http://www.ietf.org/internet-
drafts/draft-ietf-tls-dtls13-40.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>.
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[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>.
[RFC5758] Dang, Q., Santesson, S., Moriarty, K., Brown, D., and T.
Polk, "Internet X.509 Public Key Infrastructure:
Additional Algorithms and Identifiers for DSA and ECDSA",
RFC 5758, DOI 10.17487/RFC5758, January 2010,
<https://www.rfc-editor.org/info/rfc5758>.
[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>.
[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>.
20.2. Informative References
[I-D.ietf-suit-architecture]
Moran, B., Tschofenig, H., Brown, D., and M. Meriac, "A
Firmware Update Architecture for Internet of Things", Work
in Progress, Internet-Draft, draft-ietf-suit-architecture-
15, 17 January 2021, <http://www.ietf.org/internet-drafts/
draft-ietf-suit-architecture-15.txt>.
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[I-D.ietf-tls-esni]
Rescorla, E., Oku, K., Sullivan, N., and C. Wood, "TLS
Encrypted Client Hello", Work in Progress, Internet-Draft,
draft-ietf-tls-esni-09, 16 December 2020,
<http://www.ietf.org/internet-drafts/draft-ietf-tls-esni-
09.txt>.
Authors' Addresses
Hannes Tschofenig
Arm Limited
Email: Hannes.Tschofenig@gmx.net
Thomas Fossati
Arm Limited
Email: Thomas.Fossati@arm.com
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