draft-ietf-dane-srv-04.txt   draft-ietf-dane-srv-05.txt 
DNS-Based Authentication of Named Entities (DANE) T. Finch DNS-Based Authentication of Named Entities (DANE) T. Finch
Internet-Draft University of Cambridge Internet-Draft University of Cambridge
Intended status: Standards Track M. Miller Intended status: Standards Track M. Miller
Expires: August 15, 2014 Cisco Systems, Inc. Expires: August 17, 2014 Cisco Systems, Inc.
P. Saint-Andre P. Saint-Andre
&yet &yet
February 11, 2014 February 13, 2014
Using DNS-Based Authentication of Named Entities (DANE) TLSA records Using DNS-Based Authentication of Named Entities (DANE) TLSA records
with SRV and MX records. with SRV and MX records.
draft-ietf-dane-srv-04 draft-ietf-dane-srv-05
Abstract Abstract
The DANE specification (RFC 6698) describes how to use TLSA resource The DANE specification (RFC 6698) describes how to use TLSA resource
records in the DNS to associate a server's host name with its TLS records in the DNS to associate a server's host name with its TLS
certificate. The association is secured with DNSSEC. Some certificate. The association is secured with DNSSEC. Some
application protocols use SRV records (RFC 2782) to indirectly name application protocols use SRV records (RFC 2782) to indirectly name
the server hosts for a service domain (SMTP uses MX records for the the server hosts for a service domain (SMTP uses MX records for the
same purpose). This specification gives generic instructions for how same purpose). This specification gives generic instructions for how
these application protocols locate and use TLSA records when these application protocols locate and use TLSA records when
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 15, 2014. This Internet-Draft will expire on August 17, 2014.
Copyright Notice Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Relation between SRV and MX records . . . . . . . . . . . . . 3 3. Relation between SRV and MX records . . . . . . . . . . . . . 3
4. DNS Checks for TLSA and SRV Records . . . . . . . . . . . . . 4 4. DNS Checks for TLSA and SRV Records . . . . . . . . . . . . . 4
4.1. SRV Query . . . . . . . . . . . . . . . . . . . . . . . . 4 4.1. SRV Query . . . . . . . . . . . . . . . . . . . . . . . . 4
4.2. TLSA Queries . . . . . . . . . . . . . . . . . . . . . . 5 4.2. TLSA Queries . . . . . . . . . . . . . . . . . . . . . . 5
5. TLS Checks for TLSA and SRV Records . . . . . . . . . . . . . 6 5. TLS Checks for TLSA and SRV Records . . . . . . . . . . . . . 6
6. Guidance for Application Protocols . . . . . . . . . . . . . 6 6. Guidance for Application Protocols . . . . . . . . . . . . . 7
7. Guidance for Server Operators . . . . . . . . . . . . . . . . 7 7. Guidance for Server Operators . . . . . . . . . . . . . . . . 7
8. Internationalization Considerations . . . . . . . . . . . . . 7 8. Internationalization Considerations . . . . . . . . . . . . . 8
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
10. Security Considerations . . . . . . . . . . . . . . . . . . . 8 10. Security Considerations . . . . . . . . . . . . . . . . . . . 8
10.1. Mixed Security Status . . . . . . . . . . . . . . . . . 8 10.1. Mixed Security Status . . . . . . . . . . . . . . . . . 8
10.2. A Service Domain Trusts its Servers . . . . . . . . . . 8 10.2. A Service Domain Trusts its Servers . . . . . . . . . . 8
10.3. Certificate Subject Name Matching . . . . . . . . . . . 8 10.3. Certificate Subject Name Matching . . . . . . . . . . . 9
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
12.1. Normative References . . . . . . . . . . . . . . . . . . 9 12.1. Normative References . . . . . . . . . . . . . . . . . . 9
12.2. Informative References . . . . . . . . . . . . . . . . . 10 12.2. Informative References . . . . . . . . . . . . . . . . . 10
Appendix A. Mail Example . . . . . . . . . . . . . . . . . . . . 10 Appendix A. Mail Example . . . . . . . . . . . . . . . . . . . . 11
Appendix B. XMPP Example . . . . . . . . . . . . . . . . . . . . 10 Appendix B. XMPP Example . . . . . . . . . . . . . . . . . . . . 11
Appendix C. Rationale . . . . . . . . . . . . . . . . . . . . . 11 Appendix C. Rationale . . . . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction 1. Introduction
The base DANE specification [RFC6698] describes how to use TLSA The base DANE specification [RFC6698] describes how to use TLSA
resource records in the DNS to associate a server's host name with resource records in the DNS to associate a server's host name with
its TLS certificate. The association is secured using DNSSEC. That its TLS certificate. The association is secured using DNSSEC. That
document "only relates to securely associating certificates for TLS document "only relates to securely associating certificates for TLS
and DTLS with host names" (see the last paragraph of section 1.2 of and DTLS with host names" (see the last paragraph of section 1.2 of
[RFC6698]). [RFC6698]).
Some application protocols do not use host names directly; instead, Some application protocols do not use host names directly; instead,
they use a service domain and the relevant host names are located they use a service domain and the relevant host names are located
indirectly via SRV records [RFC2782], or MX records in the case of indirectly via SRV records [RFC2782], or MX records in the case of
SMTP [RFC5321]. (Note: in the "CertID" specification [RFC6125], the SMTP [RFC5321] (Note: in the "CertID" specification [RFC6125], the
source domain and host name are referred to as the "source domain" source domain and host name are referred to as the "source domain"
and the "derived domain".) Because of this intermediate resolution and the "derived domain"). Because of this intermediate resolution
step, the normal DANE rules specified in [RFC6698] do not directly step, the normal DANE rules specified in [RFC6698] do not directly
apply to protocols that use SRV or MX records. apply to protocols that use SRV or MX records.
This document describes how to use DANE TLSA records with SRV and MX This document describes how to use DANE TLSA records with SRV and MX
records. To summarize: records. To summarize:
o We rely on DNSSEC to secure the association between the service o We rely on DNSSEC to secure the association between the service
domain and the target server host names (i.e., the host names that domain and the target server host names (i.e., the host names that
are discovered by the SRV or MX query). are discovered by the SRV or MX query).
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application protocols, such as SMTP [I-D.ietf-dane-smtp-with-dane] application protocols, such as SMTP [I-D.ietf-dane-smtp-with-dane]
and XMPP [I-D.ietf-xmpp-dna]. and XMPP [I-D.ietf-xmpp-dna].
2. Terminology 2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this memo are to be interpreted as described in "OPTIONAL" in this memo are to be interpreted as described in
[RFC2119]. [RFC2119].
This draft uses the definitions for "secure", "insecure", "bogus",
and "indeterminate" from [RFC4035]. This draft uses the acronyms
from [I-D.ietf-dane-registry-acronyms] for the values of TLSA fields
where appropriate.
3. Relation between SRV and MX records 3. Relation between SRV and MX records
For the purpose of this specification (to avoid cluttering the For the purpose of this specification (to avoid cluttering the
description with special cases) we treat each MX record ([RFC5321] description with special cases) we treat each MX record ([RFC5321]
section 5) as being equivalent to an SRV record [RFC2782] with section 5) as being equivalent to an SRV record [RFC2782] with
corresponding fields copied from the MX record and the remaining corresponding fields copied from the MX record and the remaining
fields having fixed values as follows: fields having fixed values as follows:
Table 1: SRV Fields and MX Equivalents Table 1: SRV Fields and MX Equivalents
+---------------+-----------------------------+ +---------------+-----------------------------+
| DNS SRV Field | Equivalent MX Value | | DNS SRV Field | Equivalent MX Value |
+---------------+-----------------------------+ +---------------+-----------------------------+
| Service | smtp | | Service | smtp |
+---------------+-----------------------------+ +---------------+-----------------------------+
| Proto | tcp | | Proto | tcp |
+---------------+-----------------------------+ +---------------+-----------------------------+
| Name | MX owner name (mail domain) | | Name | MX owner name (mail domain) |
+---------------+-----------------------------+ +---------------+-----------------------------+
| TTL | MX TTL | | TTL | MX TTL |
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4. DNS Checks for TLSA and SRV Records 4. DNS Checks for TLSA and SRV Records
4.1. SRV Query 4.1. SRV Query
When the client makes an SRV query, a successful result will be a When the client makes an SRV query, a successful result will be a
list of one or more SRV records (or possibly a chain of CNAME / DNAME list of one or more SRV records (or possibly a chain of CNAME / DNAME
aliases referring to such a list). aliases referring to such a list).
For this specification to apply, all of these DNS RRsets MUST be For this specification to apply, all of these DNS RRsets MUST be
"secure" according to DNSSSEC validation ([RFC4033] section 5). In "secure" according to DNSSSEC validation ([RFC4033] section 5). In
the case of aliases, the whole chain MUST be secure as well as the the case of aliases, the whole chain of CNAME and DNAME RRsets MUST
ultimate target. (This corresponds to the AD bit being set in the be secure as well. This corresponds to the AD bit being set in the
response(s) - see [RFC4035] section 3.2.3.) response(s); see [RFC4035] section 3.2.3.
If they are not all secure, this protocol has not been fully
If they are not all secure, this protocol has not been correctly
deployed. The client SHOULD fall back to its non-DNSSEC non-DANE deployed. The client SHOULD fall back to its non-DNSSEC non-DANE
behavior. (This corresponds to the AD bit being unset.) behavior (this corresponds to the AD bit being unset).
If any of the responses is "bogus" according to DNSSEC validation, If any of the responses are "bogus" or "indeterminate" according to
the client MUST abort. (This usually corresponds to a "server DNSSEC validation, the client MUST abort (This usually corresponds to
failure" response.) a "server failure" response).
In the successful case, the client now has an authentic list of In the successful case, the client now has an authentic list of
server host names with weight and priority values. It performs server host names with weight and priority values. It performs
server ordering and selection using the weight and priority values server ordering and selection using the weight and priority values
without regard to the presence or absence of DNSSEC or TLSA records. without regard to the presence or absence of DNSSEC or TLSA records.
It takes note of the DNSSEC validation status of the SRV response for It takes note of the DNSSEC validation status of the SRV response for
use when checking certificate names (see Section 5). use when checking certificate names (see Section 5).
4.2. TLSA Queries 4.2. TLSA Queries
If the SRV response was insecure or indeterminate, the client MUST If the SRV response was insecure, the client MUST NOT perform any
NOT perform any TLSA queries. If the SRV response is secure TLSA queries. If the SRV response is "secure" according to DNSSEC
according to DNSSEC validation, the client performs a TLSA query for validation, the client performs a TLSA query for each SRV target as
each SRV target as describes in this section. described in this section.
For each SRV target host name, if the response to the address (A or For each SRV target host name, the client performs DNSSEC validation
AAAA) query is insecure or indeterminate, the client MUST NOT perform on the address (A, AAAA) response and continues based on the results:
a TLSA query for that target; the TLSA a query will most likely fail.
o if the response is "insecure", the client MUST NOT perform a TLSA
query for that target; the TLSA query will most likely fail.
o If the response is "bogus" or "indeterminate", the client MUST NOT
connect to this host name; instead it uses the next most
appropriate SRV target.
The client SHALL construct the TLSA query name as described in The client SHALL construct the TLSA query name as described in
[RFC6698] section 3, based on fields from the SRV record: the port [RFC6698] section 3, based on fields from the SRV record: the port
from the SRV RDATA, the protocol from the SRV query name, and the from the SRV RDATA, the protocol from the SRV query name, and the
TLSA base domain set to the SRV target host name. TLSA base domain set to the SRV target host name.
For example, the following SRV record leads to the TLSA query shown For example, the following SRV record leads to the TLSA query shown
below: below:
_imap._tcp.example.com. 86400 IN SRV 10 0 143 imap.example.net. _imap._tcp.example.com. 86400 IN SRV 10 0 143 imap.example.net.
_143._tcp.imap.example.net. IN TLSA ? _143._tcp.imap.example.net. IN TLSA ?
The client SHALL determine if the TLSA record(s) are usable according The client SHALL determine if the TLSA record(s) are usable according
to section 4.1 of [RFC6698]. This affects SRV handling as follows: to section 4.1 of [RFC6698]. This affects SRV handling as follows:
If the TLSA response is "secure", the client MUST use TLS when If the TLSA response is "secure", the client MUST use TLS when
connecting to the server. The TLSA records are used when validating connecting to the server. The TLSA records are used when validating
the server's certificate as described under Section 5. the server's certificate as described under Section 5.
If the TLSA response is "insecure" or "indeterminate", the client If the TLSA response is "insecure", the client SHALL proceed as if
SHALL proceed as if this server has no TLSA records. It MAY connect this server has no TLSA records. It MAY connect to the server with
to the server with or without TLS. or without TLS.
If the TLSA response is "bogus", then the client MUST NOT connect to If the TLSA response is "bogus" or "indeterminate", then the client
the corresponding server. (The client can still use other SRV MUST NOT connect to this server (the client can still use other SRV
targets.) targets).
5. TLS Checks for TLSA and SRV Records 5. TLS Checks for TLSA and SRV Records
When connecting to a server, the client MUST use TLS if the responses When connecting to a server, the client MUST use TLS if the responses
to the SRV and TLSA queries were "secure" as described above. If the to the SRV and TLSA queries were "secure" as described above. If the
client received zero usable TLSA certificate associations, it SHALL client received zero usable TLSA certificate associations, it SHALL
validate the server's TLS certificate using the normal PKIX rules validate the server's TLS certificate using the normal PKIX rules
[RFC5280] or protocol-specific rules (e.g., following [RFC6125]) [RFC5280] or protocol-specific rules (e.g., following [RFC6125])
without further input from the TLSA records. If the client received without further input from the TLSA records. If the client received
one or more usable TLSA certificate associations, it SHALL process one or more usable TLSA certificate associations, it SHALL process
them as described in [RFC6698] section 2.1. them as described in [RFC6698] section 2.1.
If a usable TLSA record with Certificate Usage "3" matches the TLS If the TLS server's certificate -- or the public key of the server's
server's certificate, or public key for the certificate, all other certificate -- matches a usable TLSA record with Certificate Usage
validation and verification checks MAY be ignored (e.g., reference "DANE-EE", the client MUST consider the server to be authenticated.
identifier, key usage, expiration, issuance, etc.). Because the information in such a TLSA record supersedes the non-key
information in the certificate, all other [RFC5280] and [RFC6125]
authentication checks (e.g., reference identifier, key usage,
expiration, issuance, etc.) MUST be ignored or omitted.
Otherwise, the client uses the DNSSEC validation status of the SRV Otherwise, the client uses the information in the server certificate
query in its server certificate identity checks. It SHOULD use the and DNSSEC validation status of the SRV query in its authentication
Server Name Indication extension (TLS SNI) [RFC6066] or its checks. It SHOULD use the Server Name Indication extension (TLS SNI)
functional equivalent in the relevant application protocol (e.g., in [RFC6066] or its functional equivalent in the relevant application
XMPP [RFC6120] this is the the 'to' address of the initial stream protocol (e.g., in XMPP [RFC6120] this is the 'to' address of the
header). The preferred name SHALL be chosen as follows, and the initial stream header). The preferred name SHALL be chosen as
client SHALL verify the identity asserted by the server's certificate follows, and the client SHALL verify the identity asserted by the
according to [RFC6125] section 6, using a list of reference server's certificate according to [RFC6125] section 6, using a list
identifiers constructed as follows. (Note again that in RFC 6125 the of reference identifiers constructed as follows (note again that in
terms "source domain" and "derived domain" refer to the same things RFC 6125 the terms "source domain" and "derived domain" refer to the
as "service domain" and "target host name" in this document.) same things as "service domain" and "target host name" in this
document).
SRV is insecure or indeterminate: The reference identifiers SHALL SRV is insecure: The reference identifiers SHALL include the service
include the service domain and MUST NOT include the SRV target domain and MUST NOT include the SRV target host name. The service
host name. The service domain is the preferred name for TLS SNI domain is the preferred name for TLS SNI or its equivalent.
or its equivalent.
SRV is secure: The reference identifiers SHALL include both the SRV is secure: The reference identifiers SHALL include both the
service domain and the SRV target host name. The target host name service domain and the SRV target host name. The target host name
is the preferred name for TLS SNI or its equivalent. is the preferred name for TLS SNI or its equivalent.
(In the latter case, the client will accept either identity so that In the latter case, the client will accept either identity so that it
it is compatible with servers that do and do not support this is compatible with servers that do and do not support this
specification.) specification.
6. Guidance for Application Protocols 6. Guidance for Application Protocols
Separate documents describe how to apply this specification to Separate documents describe how to apply this specification to
particular application protocols. If you are writing such as particular application protocols. Such documents ought to cover the
document the following points ought to be covered: following points:
o Fallback logic in the event of bogus replies and the like. o Fallback logic in the event of bogus replies and the like.
o The use of TLS SNI or its functional equivalent.
o Appropriate mappings for non-SRV technologies such as MX.
o Compatibility with clients that do not support SRV lookups. o Compatibility with clients that do not support SRV lookups.
7. Guidance for Server Operators 7. Guidance for Server Operators
To conform to this specification, the published SRV records and To conform to this specification, the published SRV records and
subsequent address (A, AAAA) records MUST be secured with DNSSEC. subsequent address (A, AAAA) records MUST be secured with DNSSEC.
There SHOULD also be at least one TLSA record published that There SHOULD also be at least one TLSA record published that
authenticates the server's certificate. Except for Certificate Usage authenticates the server's certificate.
"3", the certificate authenticated by the TLSA record(s) MUST contain
a reference identifier that matches: When using TLSA records with Certificate Usage "DANE-EE", the
deployed certificate does not need to contain any of the possible
reference identifiers discussed below. Indeed, none of the
certificate's information is necessary for such certificates.
However, servers that rely solely on validation using Certificate
Usage "DANE-EE" TLSA records might prevent clients that do not
support this specification from successfully connecting with TLS.
For TLSA records with Certificate Usage types other than "DANE-EE",
the certificate(s) MUST contain a reference identifier that matches:
o the service domain name (the "source domain" in [RFC6125] terms, o the service domain name (the "source domain" in [RFC6125] terms,
which is the SRV query domain); and/or which is the SRV query domain); and/or
o the server host name (the "derived domain" in [RFC6125] terms, o the server host name (the "derived domain" in [RFC6125] terms,
which is the SRV target). which is the SRV target).
Servers that support multiple service domains (i.e., multi-tenant) Servers that support multiple service domains (i.e., multi-tenant)
can implement Server Name Identifier (TLS SNI) [RFC6066] or its can implement Server Name Indicator (TLS SNI) [RFC6066] or its
functional equivalent to determine which certificate to offer. functional equivalent to determine which certificate to offer.
Clients that do not support this specification will indicate a Clients that do not support this specification will indicate a
preference for the service domain name, while clients that support preference for the service domain name, while clients that support
this specification will indicate the server host name. However, the this specification will indicate the server host name. However, the
server determines what certificate to present in the TLS handshake; server determines what certificate to present in the TLS handshake;
e.g., the presented certificate might only authenticate the server e.g., the presented certificate might only authenticate the server
host name. host name.
8. Internationalization Considerations 8. Internationalization Considerations
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protocol completely; a partial deployment is not secure and we make protocol completely; a partial deployment is not secure and we make
no special effort to support it. no special effort to support it.
10.2. A Service Domain Trusts its Servers 10.2. A Service Domain Trusts its Servers
By signing their zone with DNSSEC, service domain operators By signing their zone with DNSSEC, service domain operators
implicitly instruct their clients to check their server TLSA records. implicitly instruct their clients to check their server TLSA records.
This implies another point in the trust relationship between service This implies another point in the trust relationship between service
domain holders and their server operators. Most of the setup domain holders and their server operators. Most of the setup
requirements for this protocol fall on the server operator: requirements for this protocol fall on the server operator:
installing a TLS certificate with the correct name, and publishing a installing a TLS certificate with the correct name (where necessary),
TLSA record under that name. If these are not correct then and publishing a TLSA record for that certificate. If these are not
connections from TLSA-aware clients might fail. correct then connections from TLSA-aware clients might fail.
10.3. Certificate Subject Name Matching 10.3. Certificate Subject Name Matching
Section 4 of the TLSA specification [RFC6698] leaves the details of Section 4 of the TLSA specification [RFC6698] leaves the details of
checking names in certificates to higher level application protocols, checking names in certificates to higher level application protocols,
though it suggests the use of [RFC6125]. though it suggests the use of [RFC6125].
Name checks are not necessary if the matching TLSA record is of Name checks are not necessary if the matching TLSA record is of
Certificate Usage "3". Because such a record identifies the specific Certificate Usage "DANE-EE". Because such a record identifies the
certificate (or public key of the certificate), additional checks are specific certificate (or public key of the certificate), additional
superfluous and potentially conflicting. checks are superfluous and potentially conflicting.
Otherwise, while DNSSEC provides a secure binding between the server Otherwise, while DNSSEC provides a secure binding between the server
name and the TLSA record, and the TLSA record provides a binding to a name and the TLSA record, and the TLSA record provides a binding to a
certificate, this latter step can be indirect via a chain of certificate, this latter step can be indirect via a chain of
certificates. For example, a Certificate Usage "0" TLSA record only certificates. For example, a Certificate Usage "PKIX-TA" TLSA record
authenticates the CA that issued the certificate, and third parties only authenticates the CA that issued the certificate, and third
can obtain certificates from the same CA. Therefore, clients need to parties can obtain certificates from the same CA. Therefore, clients
check whether the server's certificate matches one of the expected need to check whether the server's certificate matches one of the
reference identifiers to ensure the certificate was issued by the CA expected reference identifiers to ensure the certificate was issued
to the server the client expects. by the CA to the server the client expects.
11. Acknowledgements 11. Acknowledgements
Thanks to Mark Andrews for arguing that authenticating the server Thanks to Mark Andrews for arguing that authenticating the server
host name is the right thing, and that we ought to rely on DNSSEC to host name is the right thing, and that we ought to rely on DNSSEC to
secure the SRV / MX lookup. Thanks to James Cloos, Viktor Dukhovni, secure the SRV / MX lookup. Thanks to James Cloos, Viktor Dukhovni,
Ned Freed, Olafur Gudmundsson, Paul Hoffman, Phil Pennock, Hector Ned Freed, Olafur Gudmundsson, Paul Hoffman, Phil Pennock, Hector
Santos, Jonas Schneider, and Alessandro Vesely for helpful Santos, Jonas Schneider, and Alessandro Vesely for helpful
suggestions. suggestions.
12. References 12. References
12.1. Normative References 12.1. Normative References
[I-D.ietf-dane-registry-acronyms]
Gudmundsson, O., "Adding acronyms to simplify DANE
conversations", draft-ietf-dane-registry-acronyms-03 (work
in progress), January 2014.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for [RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782, specifying the location of services (DNS SRV)", RFC 2782,
February 2000. February 2000.
[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "DNS Security Introduction and Requirements", RFC Rose, "DNS Security Introduction and Requirements", RFC
4033, March 2005. 4033, March 2005.
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; TLSA resource record ; TLSA resource record
_25._tcp.mx.example.net. TLSA ... _25._tcp.mx.example.net. TLSA ...
_25._tcp.mx.example.net. RRSIG TLSA ... _25._tcp.mx.example.net. RRSIG TLSA ...
Mail for addresses at example.com is delivered by SMTP to Mail for addresses at example.com is delivered by SMTP to
mx.example.net. Connections to mx.example.net port 25 that use mx.example.net. Connections to mx.example.net port 25 that use
STARTTLS will get a server certificate that authenticates the name STARTTLS will get a server certificate that authenticates the name
mx.example.net. mx.example.net.
Appendix B. XMPP Example Appendix B. XMPP Example
In the following, most of the DNS resource data is elided for In the following, most of the DNS resource data is elided for
simplicity. simplicity.
; XMPP domain ; XMPP domain
_xmpp-client.example.com. SRV 1 0 5222 im.example.net. _xmpp-client.example.com. SRV 1 0 5222 im.example.net.
_xmpp-clientexample.com. RRSIG SRV ... _xmpp-client.example.com. RRSIG SRV ...
; XMPP server host name ; XMPP server host name
im.example.net. A 192.0.2.3 im.example.net. A 192.0.2.3
im.example.net. RRSIG A ... im.example.net. RRSIG A ...
im.example.net. AAAA 2001:db8:212:8::e:4 im.example.net. AAAA 2001:db8:212:8::e:4
im.example.net. RRSIG AAAA ... im.example.net. RRSIG AAAA ...
; TLSA resource record ; TLSA resource record
_5222._tcp.im.example.net. TLSA ... _5222._tcp.im.example.net. TLSA ...
_5222._tcp.im.example.net. RRSIG TLSA ... _5222._tcp.im.example.net. RRSIG TLSA ...
Mail for addresses at example.com is delivered by SMTP to XMPP sessions for addresses at example.com are established at
mx.example.net. Connections to mx.example.net port 25 that use im.example.net. Connections to im.example.net port 5222 that use
STARTTLS will get a server certificate that authenticates the name STARTTLS will get a server certificate that authenticates the name
mx.example.net. im.example.net.
Appendix C. Rationale Appendix C. Rationale
The long-term goal of this specification is to settle on TLS The long-term goal of this specification is to settle on TLS
certificates that verify the server host name rather than the service certificates that verify the server host name rather than the service
domain, since this is more convenient for servers hosting multiple domain, since this is more convenient for servers hosting multiple
domains (so-called "multi-tenanted environments") and scales up more domains (so-called "multi-tenanted environments") and scales up more
easily to larger numbers of service domains. easily to larger numbers of service domains.
There are a number of other reasons for doing it this way: There are a number of other reasons for doing it this way:
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