Internet DRAFT - draft-lenders-core-dnr
draft-lenders-core-dnr
Constrained RESTful Environments M. S. Lenders
Internet-Draft TU Dresden
Intended status: Informational C. Amsüss
Expires: 5 September 2024
T. C. Schmidt
HAW Hamburg
M. Wählisch
TU Dresden & Barkhausen Institut
4 March 2024
Discovery of Network-designated CoRE Resolvers
draft-lenders-core-dnr-00
Abstract
This document specifies solutions to discover DNS resolvers that
support encrypted DNS resolution in constrained environments. The
discovery is based DNS SVCB records, Router Advertisements, or DHCP.
In particular, the proposed specification allows a host to learn DNS
over CoAP (DoC) servers, including configurations to use DoC over
TLS/DTLS, OSCORE, and EDHOC when resolving names.
About This Document
This note is to be removed before publishing as an RFC.
The latest revision of this draft can be found at https://anr-bmbf-
pivot.github.io/draft-lenders-core-dnr/draft-lenders-core-dnr.html.
Status information for this document may be found at
https://datatracker.ietf.org/doc/draft-lenders-core-dnr/.
Discussion of this document takes place on the Constrained RESTful
Environments Working Group mailing list (mailto:core@ietf.org), which
is archived at https://mailarchive.ietf.org/arch/browse/core/.
Subscribe at https://www.ietf.org/mailman/listinfo/core/.
Source for this draft and an issue tracker can be found at
https://github.com/anr-bmbf-pivot/draft-lenders-core-dnr.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Problem Space . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Solution Sketches . . . . . . . . . . . . . . . . . . . . . . 5
4.1. Unencrypted DoC . . . . . . . . . . . . . . . . . . . . . 6
4.2. DoC over TLS/DTLS . . . . . . . . . . . . . . . . . . . . 6
4.3. DoC over OSCORE using EDHOC . . . . . . . . . . . . . . . 7
4.4. DoC over ACE-OSCORE . . . . . . . . . . . . . . . . . . . 7
5. Security Considerations . . . . . . . . . . . . . . . . . . . 8
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
6.1. TLS ALPN for CoAP . . . . . . . . . . . . . . . . . . . . 8
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
7.1. Normative References . . . . . . . . . . . . . . . . . . 8
7.2. Informative References . . . . . . . . . . . . . . . . . 10
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
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1. Introduction
[RFC9461], [RFC9462] and [RFC9463] specify options to discover DNS
resolvers that allow for encrypted DNS resolution, using either DNS
or, in a local network, Router Advertisements or DHCP. These
specifications use Service Binding (SVCB) resource records or Service
Parameters (SvcParams) to carry information required for
configuration of such resolvers. So far, however, only DNS transfer
protocols based on Transport Layer Security (TLS) are supported,
namely DNS over TLS (DoT) [RFC7858], DNS over HTTPS (DoH) [RFC8484],
and DNS over Dedicated QUIC (DoQ) [RFC9250]. This document discusses
and specifies options to discover DNS resolvers in constrained
environments, mainly based on DNS over CoAP (DoC)
[I-D.ietf-core-dns-over-coap].
DoC provides a solution for encrypted DNS in constrained
environments. In such scenarios, the usage of DoT, DoH, DoQ, or
similar TLS-based solutions is often not possible. The Constrained
Application Protocol (CoAP) [RFC7252], the transfer protocol for DoC,
is mostly agnostic to the transport layer, i.e., CoAP can be
transported over UDP, TCP, or WebSockets [RFC8323], and even less
common transports such as Bluetooth GATT
[I-D.amsuess-core-coap-over-gatt] or SMS [lwm2m] are discussed.
CoAP offers three security modes, which would need to be covered by
the SvcParams:
* *No Security:* This plain CoAP mode does not support any
encryption. It is not recommended when using
[I-D.ietf-core-dns-over-coap] but inherits core CoAP features such
as block-wise transfer [RFC7959] for datagram-based segmentation.
Such features are beneficial in constrained settings even without
encryption.
* *Transport Security:* CoAP may use DTLS when transferred over UDP
[RFC7252] and TLS when transferred over TCP [RFC8323].
* *Object Security:* Securing content objects can be achieved using
OSCORE [RFC8613]. OSCORE can be used either as an alternative or
in addition to transport security.
OSCORE keys have a limited lifetime and need to be set up, for
example through an EDHOC key exchange
[I-D.ietf-core-oscore-edhoc], which may use credentials from
trusted ACE Authorization Server (AS) as described in the ACE
EDHOC profile [I-D.ietf-ace-edhoc-oscore-profile]. As an
alternative to EDHOC, keys can be set up by such an AS as
described in the ACE OSCORE profile [RFC9203].
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To discover a DoC server via Discovery of Designated Resolvers (DDR)
[RFC9462] and Discovery of Network-designated Resolvers (DNR)
[RFC9463], the SvcParams field needs to convey both transfer protocol
and type and parameters of the security parameters. We will specify
extensions of SvcParams in this document.
2. Terminology
The terms “DoC server” and “DoC client” are used as defined in
[I-D.ietf-core-dns-over-coap].
The terms “constrained node” and "constrained network" are used as
defined in [RFC7228].
SvcParams denotes the field in either DNS SVCB/HTTPS records as
defined in [RFC9460], or DHCP and RA messages as defined in
[RFC9463]. SvcParamKeys are used as defined in [RFC9460].
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.
3. Problem Space
The first and most important question to ask for the discoverability
of DoC resolvers is if and what new SvcParamKeys need to be defined.
[RFC9460] defines the “alpn” key, which is used to identify the
protocol suite of a service binding using its Application-Layer
Protocol Negotiation (ALPN) ID [RFC7301]. While this is useful to
identify classic transport layer security, the question is raised if
this is needed or even helpful for when there is only object
security. There is an ALPN ID for CoAP over TLS that was defined in
[RFC8323]. As using the same ALPN ID for different transport layers
is not recommended, an ALPN for CoAP over UDP is being requested in
Section 6. Object security may be selected in addition to transport
layer security, so defining an ALPN ID for each combination might not
be viable or scalable. For some ways of setting up object security,
additional information is needed for the establishment of an
encryption context and for authentication with an authentication
server (AS). Orthogonally to the security mechanism, the transfer
protocol needs to be established.
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Beyond the SvcParamKeys, there is the question of what the field
values of the Encrypted DNS Options defined in [RFC9463] might be
with EDHOC or ACE EDHOC. While most fields map, “authentication-
domain-name” (ADN) and its corresponding ADN length field may not
matter in ACE driven cases.
Out of scope of this document are related issues adjacent to its
problem space. they are listed both for conceptual delimitation, and
to aid in discussion of more comprehensive solutions:
* There is ongoing work in addressing the trouble created by CoAP
using a diverse set of URI schemes in the shape of coap+..., such
as coap+tcp [I-D.ietf-core-transport-indication]. The creation of
URI authority values that express the content of SVCB records
together with IP literals is part of the solution space that will
be explored there.
* Route Advertisements (RAs) as used in [RFC9463] can easily exceed
the link layer fragmentation threshold of constrained networks.
The presence of DNR information in an RA can contribute to that
issue.
4. Solution Sketches
To answer the raised questions, we first look at the general case
then 4 base scenarios, from which other scenarios might be a
combination of:
* Unencrypted DoC,
* DoC over TLS/DTLS,
* DoC over OSCORE using EDHOC, and
* DoC over OSCORE using ACE-EDHOC.
In the general case, we mostly need to answer the question for
additional SvcParamKeys. [RFC9460] defines the keys “mandatory”,
“alpn”, “no-default-alpn”, “port”, “ipv4hint”, and “ipv6hint” were
defined. Additionally, [RFC9461] defines “dohpath” which carries the
URI template for the DNS resource at the DoH server in relative form.
For DoC, the DNS resource needs to be identified as, so a
corresponding “docpath” key should be provided that provides either a
relative URI or CRI [I-D.ietf-core-href]. Since the URI-Path option
in CoAP may be omitted (defaulting to the root path), this could also
be done for the “docpath”.
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4.1. Unencrypted DoC
While unencrypted DoC is not recommended by
[I-D.ietf-core-dns-over-coap] and might not even be viable using DDR/
DNR, it provides additional benefits not provided by classic
unencrypted DNS over UDP, such as segmentation block-wise transfer
[RFC7959]. However, it provides the simplest DoC configuration and
thus is here discussed.
At minimum for a DoC server a way to identify the following keys are
required. “docpath” (see above), an optional “port” (see [RFC9460]),
the IP address (either with an optional “ipv6hint”/“ipv4hint” or the
respective IP address field in [RFC9463]), and a yet to be defined
SvcParamKey for the CoAP transfer protocol, e.g., “coaptransfer”. The
latter can be used to identify the service binding as a CoAP service
binding.
The “authenticator-domain-name” field should remain empty as it does
not serve a purpose without encryption.
See this example for the possible values of a DNR option:
authenticator-domain-name: ""
ipv6-address: <DoC server address>
svc-params:
- coaptransfer="tcp"
- docpath="/dns"
- port=61616
4.2. DoC over TLS/DTLS
In addition to the SvcParamKeys proposed in Section 4.1, this
scenario needs the “alpn” key. While there is a “coap” ALPN ID
defined, it only identifies CoAP over TLS [RFC8323]. As such, a new
ALPN ID for CoAP over DTLS is required.
See this example for the possible values of a DNR option:
authenticator-domain-name: "dns.example.com"
ipv6-address: <DoC server address>
svc-params:
- alpn="co"
- docpath="/dns"
Note that “coaptransfer” is not needed, as it is implied by the ALPN
ID; thus, no values for it would be allocated for transfer protocols
that use transport security.
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4.3. DoC over OSCORE using EDHOC
While the “alpn” SvcParamKey is needed for the transport layer
security (see Section 4.2), we can implement a CA-style
authentication with EDHOC when using object security with OSCORE
using the authenticator-domain-name field.
A new key SvcParamKey “objectsecurity” identifies the type of object
security, using the value "edhoc" in this scenario.
See this example for the possible values of a DNR option:
authenticator-domain-name: "dns.example.com"
ipv6-address: <DoC server address>
svc-params:
- coaptransfer="udp",
- objectsecurity="edhoc",
- docpath="/dns",
- port=61616
The use of objectsecurity="edhoc" with an authenticator-domain-name
and no further ACE details indicates that the client can use CA based
authentication of the server.
4.4. DoC over ACE-OSCORE
Using ACE, we require an OAuth context to authenticate the server in
addition to the “objectsecurity” key. We propose three keys “oauth-
aud” for the audience, “oauth-scope” for the OAuth scope, and “auth-
as” for the authentication server. “oauth-aud” should be the valid
domain name of the DoC server, “oauth-scope” a list of identifiers
for the scope, and “oauth-as” a valid URI or CRI.
TBD: should oauth-scope be expressed at all?
Since authentication is done over OAuth and not CA-style, the
“authenticator-domain-name” is not needed. There might be merit,
however, to use it instead of the “oauth-aud” SvcParamKey.
See this example for the possible values of a DNR option:
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authenticator-domain-name: ""
ipv6-address: <DoC server address>
svc-params:
- coaptransfer="tcp"
- objectsecurity="edhoc" /* TBD: or ace-edhoc? */
- docpath="/dns",
- port=61616,
- oauth-aud="dns.example.com",
- oauth-scope="resolve DNS"
- oauth-as="coap://as.example.com"
5. Security Considerations
TODO Security
6. IANA Considerations
6.1. TLS ALPN for CoAP
The following entry is being requested for addition into the "TLS
Application-Layer Protocol Negotiation (ALPN) Protocol IDs" registry,
which is part of the "Transport Layer Security (TLS) Extensions"
group.
* Protocol: CoAP (over DTLS)
* Identification sequence: 0x63 0x6f ("co")
* Reference: [RFC7252] and [this document]
Note that [RFC7252] does not prescribe the use of the ALPN TLS
extension during connection the DTLS handshake. This document does
not change that, and thus does not establish any rules like those in
Section 8.2 of [RFC8323].
7. References
7.1. Normative References
[I-D.ietf-core-dns-over-coap]
Lenders, M. S., Amsüss, C., Gündoğan, C., Schmidt, T. C.,
and M. Wählisch, "DNS over CoAP (DoC)", Work in Progress,
Internet-Draft, draft-ietf-core-dns-over-coap-05, 17
November 2023, <https://datatracker.ietf.org/doc/html/
draft-ietf-core-dns-over-coap-05>.
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[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>.
[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/rfc/rfc2119>.
[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/rfc/rfc7252>.
[RFC7301] Friedl, S., Popov, A., Langley, A., and E. Stephan,
"Transport Layer Security (TLS) Application-Layer Protocol
Negotiation Extension", RFC 7301, DOI 10.17487/RFC7301,
July 2014, <https://www.rfc-editor.org/rfc/rfc7301>.
[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/rfc/rfc8174>.
[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/rfc/rfc8613>.
[RFC9460] Schwartz, B., Bishop, M., and E. Nygren, "Service Binding
and Parameter Specification via the DNS (SVCB and HTTPS
Resource Records)", RFC 9460, DOI 10.17487/RFC9460,
November 2023, <https://www.rfc-editor.org/rfc/rfc9460>.
[RFC9461] Schwartz, B., "Service Binding Mapping for DNS Servers",
RFC 9461, DOI 10.17487/RFC9461, November 2023,
<https://www.rfc-editor.org/rfc/rfc9461>.
[RFC9462] Pauly, T., Kinnear, E., Wood, C. A., McManus, P., and T.
Jensen, "Discovery of Designated Resolvers", RFC 9462,
DOI 10.17487/RFC9462, November 2023,
<https://www.rfc-editor.org/rfc/rfc9462>.
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[RFC9463] Boucadair, M., Ed., Reddy.K, T., Ed., Wing, D., Cook, N.,
and T. Jensen, "DHCP and Router Advertisement Options for
the Discovery of Network-designated Resolvers (DNR)",
RFC 9463, DOI 10.17487/RFC9463, November 2023,
<https://www.rfc-editor.org/rfc/rfc9463>.
7.2. Informative References
[I-D.amsuess-core-coap-over-gatt]
Amsüss, C., "CoAP over GATT (Bluetooth Low Energy Generic
Attributes)", Work in Progress, Internet-Draft, draft-
amsuess-core-coap-over-gatt-05, 23 October 2023,
<https://datatracker.ietf.org/doc/html/draft-amsuess-core-
coap-over-gatt-05>.
[I-D.ietf-ace-edhoc-oscore-profile]
Selander, G., Mattsson, J. P., Tiloca, M., and R. Höglund,
"Ephemeral Diffie-Hellman Over COSE (EDHOC) and Object
Security for Constrained Environments (OSCORE) Profile for
Authentication and Authorization for Constrained
Environments (ACE)", Work in Progress, Internet-Draft,
draft-ietf-ace-edhoc-oscore-profile-03, 23 October 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-ace-
edhoc-oscore-profile-03>.
[I-D.ietf-core-href]
Bormann, C. and H. Birkholz, "Constrained Resource
Identifiers", Work in Progress, Internet-Draft, draft-
ietf-core-href-14, 9 January 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-core-
href-14>.
[I-D.ietf-core-transport-indication]
Amsüss, C., "CoAP Protocol Indication", Work in Progress,
Internet-Draft, draft-ietf-core-transport-indication-03,
23 October 2023, <https://datatracker.ietf.org/doc/html/
draft-ietf-core-transport-indication-03>.
[lwm2m] OMA SpecWorks, "White Paper – Lightweight M2M 1.1",
October 2018, <https://omaspecworks.org/white-paper-
lightweight-m2m-1-1/>.
[RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for
Constrained-Node Networks", RFC 7228,
DOI 10.17487/RFC7228, May 2014,
<https://www.rfc-editor.org/rfc/rfc7228>.
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[RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
and P. Hoffman, "Specification for DNS over Transport
Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May
2016, <https://www.rfc-editor.org/rfc/rfc7858>.
[RFC7959] Bormann, C. and Z. Shelby, Ed., "Block-Wise Transfers in
the Constrained Application Protocol (CoAP)", RFC 7959,
DOI 10.17487/RFC7959, August 2016,
<https://www.rfc-editor.org/rfc/rfc7959>.
[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/rfc/rfc8323>.
[RFC8484] Hoffman, P. and P. McManus, "DNS Queries over HTTPS
(DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018,
<https://www.rfc-editor.org/rfc/rfc8484>.
[RFC9203] Palombini, F., Seitz, L., Selander, G., and M. Gunnarsson,
"The Object Security for Constrained RESTful Environments
(OSCORE) Profile of the Authentication and Authorization
for Constrained Environments (ACE) Framework", RFC 9203,
DOI 10.17487/RFC9203, August 2022,
<https://www.rfc-editor.org/rfc/rfc9203>.
[RFC9250] Huitema, C., Dickinson, S., and A. Mankin, "DNS over
Dedicated QUIC Connections", RFC 9250,
DOI 10.17487/RFC9250, May 2022,
<https://www.rfc-editor.org/rfc/rfc9250>.
Acknowledgments
TODO acknowledge.
Authors' Addresses
Martine Sophie Lenders
TUD Dresden University of Technology
Helmholtzstr. 10
D-01069 Dresden
Germany
Email: martine.lenders@tu-dresden.de
Christian Amsüss
Email: christian@amsuess.com
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Thomas C. Schmidt
HAW Hamburg
Email: t.schmidt@haw-hamburg.de
Matthias Wählisch
TUD Dresden University of Technology & Barkhausen Institut
Helmholtzstr. 10
D-01069 Dresden
Germany
Email: m.waehlisch@tu-dresden.de
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