Internet DRAFT - draft-rebs-dnsop-svcb-dane
draft-rebs-dnsop-svcb-dane
dnsop B. M. Schwartz
Internet-Draft R. Evans
Updates: rfc6698 (if approved) Google LLC
Intended status: Standards Track 22 June 2022
Expires: 24 December 2022
Using Service Bindings with DANE
draft-rebs-dnsop-svcb-dane-01
Abstract
Service Binding records introduce a new form of name indirection in
DNS. This document specifies DNS-Based Authentication of Named
Entities (DANE) interaction with Service Bindings to secure endpoints
including use of ports and transports discovered via Service
Parameters.
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/bemasc/svcb-dane.
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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Internet-Drafts are draft documents valid for a maximum of six months
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This Internet-Draft will expire on 24 December 2022.
Copyright Notice
Copyright (c) 2022 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 . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3
3. Using DANE with Service Bindings . . . . . . . . . . . . . . 3
4. Updating the TLSA protocol prefixes . . . . . . . . . . . . . 4
5. Operational considerations . . . . . . . . . . . . . . . . . 4
5.1. Recommended configurations . . . . . . . . . . . . . . . 4
5.2. Accidental pinning . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . 5
7. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 5
7.1. HTTPS ServiceMode . . . . . . . . . . . . . . . . . . . . 6
7.2. HTTPS AliasMode . . . . . . . . . . . . . . . . . . . . . 6
7.3. QUIC and CNAME . . . . . . . . . . . . . . . . . . . . . 6
7.4. New scheme ServiceMode . . . . . . . . . . . . . . . . . 6
7.5. New scheme AliasMode . . . . . . . . . . . . . . . . . . 7
7.6. New protocols . . . . . . . . . . . . . . . . . . . . . . 7
7.7. DNS ServiceMode . . . . . . . . . . . . . . . . . . . . . 7
7.8. DNS AliasMode . . . . . . . . . . . . . . . . . . . . . . 7
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
9.1. Normative References . . . . . . . . . . . . . . . . . . 8
9.2. Informative References . . . . . . . . . . . . . . . . . 9
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
The DNS-Based Authentication of Named Entities specification
[RFC7671] explains how clients locate the TLSA record for a service
of interest, starting with knowledge of the service's hostname,
transport, and port number. These are concatenated, forming a name
like _8080._tcp.example.com. It also specifies how clients should
locate the TLSA record when one or more CNAME records are present,
aliasing either the hostname or the TLSA record's name, and the
resulting server names used in TLS.
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There are various DNS records other than CNAME that add indirection
to the host resolution process, requiring similar specifications.
Thus, [RFC7672] describes how DANE interacts with MX records, and
[RFC7673] describes its interaction with SRV records.
This draft describes the interaction of DANE with indirection via
Service Bindings [SVCB], i.e. SVCB-compatible records such as SVCB
and HTTPS. It also explains how to use DANE with new TLS-based
transports such as QUIC.
2. Conventions and Definitions
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. Using DANE with Service Bindings
Section 6 of [RFC7671] says:
With protocols that support explicit transport redirection via DNS
MX records, SRV records, or other similar records, the TLSA base
domain is based on the redirected transport endpoint rather than
the origin domain.
This draft applies the same logic to SVCB-compatible records.
Specifically, if SVCB resolution was entirely secure (including any
AliasMode records and/or CNAMEs), then for each connection attempt
derived from a SVCB-compatible record,
* The initial TLSA base domain MUST be the final SVCB TargetName
used for this connection attempt. (Names appearing earlier in a
resolution chain are not used.)
* The transport prefix MUST be the transport of this connection
attempt (possibly influenced by the "alpn" SvcParam).
* The port prefix MUST be the port number of this connection attempt
(possibly influenced by the "port" SvcParam).
If the initial TLSA base domain is the start of a secure CNAME chain,
clients MUST first try to use the end of the chain as the TLSA base
domain, with fallback to the initial base domain, as described in
Section 7 of [RFC7671].
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If any TLSA QNAME is aliased by a CNAME, clients MUST follow the TLSA
CNAME to complete the resolution of the TLSA record. (This does not
alter the TLSA base domain.)
If a TLSA RRSet is securely resolved, the client MUST set the SNI to
the TLSA base domain of the RRSet. In usage modes other than DANE-
EE(3), the client MUST validate that the certificate covers this base
domain, and MUST NOT require it to cover any other domain.
If the client has SVCB-optional behavior (as defined in Section 3 of
[SVCB]), it MUST use the standard DANE logic described in Section 4.1
of [RFC6698] when falling back to non-SVCB connection.
4. Updating the TLSA protocol prefixes
Section 3 of [RFC6698] defined the protocol prefix used for
constructing TLSA QNAMEs, and said:
The transport names defined for this protocol are "tcp", "udp",
and "sctp".
At that time, there was exactly one TLS-based protocol defined for
each of these transports. However, with the introduction of QUIC
[RFC9000], there are now multiple TLS-derived protocols that can
operate over UDP, even on the same port. To distinguish the
availability and configuration of DTLS and QUIC, this draft Updates
the above sentence as follows:
The transport names defined for this protocol are "tcp" (TLS over
TCP [RFC8446]), "udp" (DTLS [I-D.draft-ietf-tls-dtls13]), "sctp"
(TLS over SCTP [RFC3436]), and "quic" (QUIC [RFC9000]).
5. Operational considerations
5.1. Recommended configurations
Service consumers are expected to use CNAME or SVCB AliasMode to
point at provider-controlled records, e.g.:
alias.net. HTTPS 0 xyz.provider.com.
www.alias.net. CNAME xyz.provider.com.
xyz.provider.com. HTTPS 1 . alpn=h2 ...
xyz.provider.com. A 192.0.2.1
_443._tcp.xyz.provider.com. TLSA <provider keys>
For ease of management, providers may want to alias various TLSA
QNAMEs to a single RRSet:
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_443._tcp.xyz.provider.com. CNAME dane-central.provider.com.
dane-central.provider.com. TLSA <provider keys>
5.2. Accidental pinning
When a service is used by third-party consumers, DANE allows the
consumer to publish records that make claims about the certificates
used by the service. When the service subsequently rotates its TLS
keys, DANE authentication will fail for these consumers, resulting in
an outage. Accordingly, zone owners MUST NOT publish TLSA records
for public keys that are not under their control unless they have an
explicit arrangement with the key holder.
To prevents the above misconfiguration and ensure that TLS keys can
be rotated freely, service operators MAY reject TLS connections whose
SNI does not correspond to an approved TLSA base domain.
Service Bindings also enable any third party consumer to publish
fixed SvcParams for the service. This can cause an outage or service
degradation if the service makes a backward-incompatible
configuration change. Accordingly, zone owners SHOULD NOT publish
SvcParams for a TargetName that they do not control, and service
operators should take caution when making incompatible configuration
changes.
6. Security Considerations
This document specifies the use of TLSA as a property of each
connection attempt. In environments where DANE is optional, this
means that the fallback procedure might use DANE for some conection
attempts but not others.
This document only specifies the use of TLSA records when the SVCB
records were resolved securely. Use of TLSA records in conjunction
with insecurely resolved SVCB records is not safe in general,
although there may be some configurations where it is appropriate
(e.g. when only opportunistic security is available).
7. Examples
The following examples demonstrate Serving Binding interaction with
TLSA base domain selection.
All of the RRSets below are assumed fully-secure with all related
DNSSEC record types omitted for brevity.
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7.1. HTTPS ServiceMode
Given service URI https://api.example.com and record:
api.example.com. HTTPS 1 .
The TLSA QNAME is _443._tcp.api.example.com.
7.2. HTTPS AliasMode
Given service URI https://api.example.com and records:
api.example.com. HTTPS 0 svc4.example.net.
svc4.example.net. HTTPS 0 xyz.example-cdn.com.
xyz.example-cdn.com. A 192.0.2.1
The TLSA QNAME is _443._tcp.xyz.example-cdn.com.
7.3. QUIC and CNAME
Given service URI https://api.example.com and records:
www.example.com. CNAME api.example.com.
api.example.com. HTTPS 1 svc4.example.net alpn=h2,h3 port=8443
svc4.example.net. CNAME xyz.example-cdn.com.
If the connection attempt is using HTTP/3, the transport label is set
to _quic; otherwise _tcp is used.
The initial TLSA QNAME would be one of:
* _8443._quic.xyz.example-cdn.com
* _8443._tcp.xyz.example-cdn.com
If no TLSA record is found, the fallback TLSA QNAME would be one of:
* _8443._quic.svc4.example.net
* _8443._tcp.svc4.example.net
7.4. New scheme ServiceMode
Given service URI foo://api.example.com:8443 and record:
_8443._foo.api.example.com. SVCB 1 api.example.com.
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The TLSA QNAME is _8443._$PROTO.api.example.com, where $PROTO is the
appropriate value for the client-selected transport as discussed in
Section 4 .
7.5. New scheme AliasMode
Given service URI foo://api.example.com:8443 and records:
_8443._foo.api.example.com. SVCB 0 svc4.example.net.
svc4.example.net. SVCB 1 .
svc4.example.net. A 192.0.2.1
The TLSA QNAME is _8443._$PROTO.svc4.example.net (with $PROTO as
above). This is the same if the ServiceMode record is absent.
7.6. New protocols
Given service URI foo://api.example.com:8443 and records:
_8443._foo.api.example.com. SVCB 0 svc4.example.net.
svc4.example.net. SVCB 3 . alpn=foo,bar port=8004
The TLSA QNAME is _8004._$PROTO1.svc4.example.net or
_8004._$PROTO2.svc4.example.net, where $PROTO1 and $PROTO2 are the
transport prefixes appropriate for "foo" and "bar" respectively.
(Note that SVCB requires each ALPN to unambiguously indicate a
transport.)
7.7. DNS ServiceMode
Given a DNS server dns.example.com and record:
_dns.dns.example.com. SVCB 1 dns.example.com. alpn=dot
The TLSA QNAME is _853._tcp.dns.example.com. The TLSA base name is
taken from the SVCB TargetName. The port and protocol are taken from
the "dot" ALPN value.
7.8. DNS AliasMode
Given a DNS server dns.example.com and records:
_dns.dns.example.com. SVCB 0 dns.my-dns-host.net.
dns.my-dns-host.net. SVCB 1 . alpn=dot
The TLSA QNAME is _853._tcp.ns1.my-dns-host.net.
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8. IANA Considerations
IANA is instructed to add the following entry to the "Underscored and
Globally Scoped DNS Node Names" registry:
+=========+============+=================+
| RR Type | _NODE NAME | Reference |
+=========+============+=================+
| TLSA | _quic | (This document) |
+---------+------------+-----------------+
Table 1
9. References
9.1. Normative References
[I-D.draft-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-
dtls13-43, 30 April 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-tls-
dtls13-43>.
[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>.
[RFC3436] Jungmaier, A., Rescorla, E., and M. Tuexen, "Transport
Layer Security over Stream Control Transmission Protocol",
RFC 3436, DOI 10.17487/RFC3436, December 2002,
<https://www.rfc-editor.org/rfc/rfc3436>.
[RFC6698] Hoffman, P. and J. Schlyter, "The DNS-Based Authentication
of Named Entities (DANE) Transport Layer Security (TLS)
Protocol: TLSA", RFC 6698, DOI 10.17487/RFC6698, August
2012, <https://www.rfc-editor.org/rfc/rfc6698>.
[RFC7671] Dukhovni, V. and W. Hardaker, "The DNS-Based
Authentication of Named Entities (DANE) Protocol: Updates
and Operational Guidance", RFC 7671, DOI 10.17487/RFC7671,
October 2015, <https://www.rfc-editor.org/rfc/rfc7671>.
[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>.
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[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/rfc/rfc8446>.
[RFC9000] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", RFC 9000,
DOI 10.17487/RFC9000, May 2021,
<https://www.rfc-editor.org/rfc/rfc9000>.
[SVCB] Schwartz, B., Bishop, M., and E. Nygren, "Service binding
and parameter specification via the DNS (DNS SVCB and
HTTPS RRs)", Work in Progress, Internet-Draft, draft-ietf-
dnsop-svcb-https-10, 24 May 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-dnsop-
svcb-https-10>.
9.2. Informative References
[RFC7672] Dukhovni, V. and W. Hardaker, "SMTP Security via
Opportunistic DNS-Based Authentication of Named Entities
(DANE) Transport Layer Security (TLS)", RFC 7672,
DOI 10.17487/RFC7672, October 2015,
<https://www.rfc-editor.org/rfc/rfc7672>.
[RFC7673] Finch, T., Miller, M., and P. Saint-Andre, "Using DNS-
Based Authentication of Named Entities (DANE) TLSA Records
with SRV Records", RFC 7673, DOI 10.17487/RFC7673, October
2015, <https://www.rfc-editor.org/rfc/rfc7673>.
Acknowledgments
TODO acknowledge.
Authors' Addresses
Benjamin M. Schwartz
Google LLC
Email: bemasc@google.com
Robert Evans
Google LLC
Email: evansr@google.com
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