draft-ietf-dane-srv-02.txt   draft-ietf-dane-srv-03.txt 
DNS-Based Authentication of Named T. Finch DNS-Based Authentication of Named Entities (DANE) T. Finch
Entities (DANE) University of Cambridge Internet-Draft University of Cambridge
Internet-Draft February 25, 2013 Intended status: Standards Track M. Miller
Intended status: Standards Track Expires: June 16, 2014 P. Saint-Andre
Expires: August 29, 2013 Cisco Systems, Inc.
December 13, 2013
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-02 draft-ietf-dane-srv-03
Abstract Abstract
The DANE specification [RFC6698] 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 can use SRV records [RFC2782] to indirectly application protocols use SRV records (RFC 2782) to indirectly name
name the server hosts for a service domain. (SMTP uses MX records the server hosts for a service domain (SMTP uses MX records for the
for the same purpose.) This specification gives generic instructions same purpose). This specification gives generic instructions for how
for how these application protocols locate and use TLSA records. these application protocols locate and use TLSA records when
Separate documents give the details that are specific to particular technologies such as SRV records are used. Separate documents give
application protocols. the details that are specific to particular application protocols.
Status of this Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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 29, 2013. This Internet-Draft will expire on June 16, 2014.
Copyright Notice Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the Copyright (c) 2013 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
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Relation between SRV and MX records . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. DNS checks for TLSA and SRV records . . . . . . . . . . . . . 4 3. Relation between SRV and MX records . . . . . . . . . . . . . 3
3.1. SRV query . . . . . . . . . . . . . . . . . . . . . . . . 4 4. DNS Checks for TLSA and SRV Records . . . . . . . . . . . . . 4
3.2. TLSA queries . . . . . . . . . . . . . . . . . . . . . . . 5 4.1. SRV Query . . . . . . . . . . . . . . . . . . . . . . . . 4
4. TLS checks for TLSA and SRV records . . . . . . . . . . . . . 5 4.2. TLSA Queries . . . . . . . . . . . . . . . . . . . . . . 5
5. Guidance for application protocols . . . . . . . . . . . . . . 6 5. TLS Checks for TLSA and SRV Records . . . . . . . . . . . . . 5
6. Guidance for server operators . . . . . . . . . . . . . . . . 6 6. Guidance for Application Protocols . . . . . . . . . . . . . 6
7. Security considerations . . . . . . . . . . . . . . . . . . . 7 7. Guidance for Server Operators . . . . . . . . . . . . . . . . 6
7.1. Mixed security status . . . . . . . . . . . . . . . . . . 7 8. Internationalization Considerations . . . . . . . . . . . . . 7
7.2. A service domain trusts its servers . . . . . . . . . . . 7 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
7.3. Certificate subject name matching . . . . . . . . . . . . 8 10. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7.4. Deliberate omissions . . . . . . . . . . . . . . . . . . . 8 10.1. Mixed Security Status . . . . . . . . . . . . . . . . . 7
8. Internationalization Considerations . . . . . . . . . . . . . 8 10.2. A Service Domain Trusts its Servers . . . . . . . . . . 7
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 10.3. Certificate Subject Name Matching . . . . . . . . . . . 8
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8 10.4. Deliberate Omissions . . . . . . . . . . . . . . . . . . 8
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
11.1. Normative References . . . . . . . . . . . . . . . . . . . 9 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
11.2. Informative References . . . . . . . . . . . . . . . . . . 10 12.1. Normative References . . . . . . . . . . . . . . . . . . 9
Appendix A. Example . . . . . . . . . . . . . . . . . . . . . . . 10 12.2. Informative References . . . . . . . . . . . . . . . . . 10
Appendix B. Rationale . . . . . . . . . . . . . . . . . . . . . . 10 Appendix A. Example . . . . . . . . . . . . . . . . . . . . . . 10
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 11 Appendix B. Rationale . . . . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
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, but Some application protocols do not use host names directly; instead,
instead use a service domain. The domain's servers 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]). When they do not use host names [RFC6698] does not SMTP [RFC5321]. (Note: in the "CertID" specification [RFC6125], the
direcly apply to these protocols. source domain and host name are referred to as the "source domain"
and the "derived domain".) Because of this intermediate resolution
step, the normal DANE rules specified in [RFC6698] do not directly
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 result of the domain and the target server host names (i.e., the host names that
SRV or MX query. are discovered by the SRV or MX query).
o The TLSA records are located using the SRV port, protocol, and o The TLSA records are located using the port, protocol, and target
target host name fields. host name fields (not the service domain).
o Clients always use TLS when connecting to servers with TLSA o Clients always use TLS when connecting to servers with TLSA
records. records.
o The server's certificate is expected to authenticate the server o Assuming that the association is secure, the server's certificate
host name, rather than the service domain. is expected to authenticate the target server host name, rather
than the service domain.
Separate documents give the details that are specific to particular Separate documents give the details that are specific to particular
application protocols. For examples, see [I-D.ietf-dane-smtp] and application protocols, such as SMTP [I-D.ietf-dane-smtp-with-dane]
[I-D.ietf-dane-mua]. and XMPP [I-D.ietf-xmpp-dna].
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", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
memo are to be interpreted as described in [RFC2119]. "OPTIONAL" in this memo are to be interpreted as described in
[RFC2119].
2. 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 a 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:
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
skipping to change at page 4, line 23 skipping to change at page 4, line 14
Class - MX Class Class - MX Class
Priority - MX Priority Priority - MX Priority
Weight - 0 Weight - 0
Port - 25 Port - 25
Target - MX Target Target - MX Target
For example this MX record is treated as if it were the following SRV Thus we can treat the following MX record as if it were the SRV
record: record shown below:
example.com. 86400 IN MX 10 mx.example.net. example.com. 86400 IN MX 10 mx.example.net.
_smtp._tcp.example.com. 86400 IN SRV 10 0 25 mx.example.net. _smtp._tcp.example.com. 86400 IN SRV 10 0 25 mx.example.net.
Other details that are specific to SMTP are described in Other details that are specific to SMTP are described in
[I-D.ietf-dane-smtp]. [I-D.ietf-dane-smtp-with-dane].
3. DNS checks for TLSA and SRV records 4. DNS Checks for TLSA and SRV Records
3.1. SRV query 4.1. SRV Query
When the client makes a SRV query, a successful result will be (a When the client makes an SRV query, a successful result will be a
possible chain of CNAME / DNAME aliases referring to) a list of one list of one or more SRV records (or possibly a chain of CNAME / DNAME
or more SRV records. aliases referring to such a list).
For this specification to take effect, all of these DNS RRsets MUST For this specification to apply, all of these DNS RRsets MUST be
be "secure" according to DNSSSEC validation ([RFC4033] section 5). "secure" according to DNSSSEC validation ([RFC4033] section 5). In
In the case of aliases, the whole chain MUST be secure as well as the the case of aliases, the whole chain MUST be secure as well as the
ultimate target. (This corresponds to the AD bit being set in the ultimate target. (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 fully
deployed. The client SHOULD fall back to its non-DNSSEC non-DANE deployed. The client SHOULD fall back to its non-DNSSEC non-DANE
behaviour. (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 the If any of the responses is "bogus" according to DNSSEC validation,
client MUST abort. (This usually corresponds to a "server failure" the client MUST abort. (This usually corresponds to a "server
response.) 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 Section 4). use when checking certificate names (see Section 5).
3.2. TLSA queries 4.2. TLSA Queries
This sub-section applies to each server host name individually, This sub-section applies to each server host name individually,
provided the SRV response was secure according to DNSSEC validation. provided the SRV response was secure according to DNSSEC validation.
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: port from [RFC6698] section 3, based on fields from the SRV record: the port
the SRV RDATA, protocol from the SRV query name, and the TLSA base from the SRV RDATA, the protocol from the SRV query name, and the
domain is the SRV target host name. TLSA base domain set to the SRV target host name.
For example this SRV record leads to the following TLSA query: For example, the following SRV record leads to the TLSA query shown
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 in section Section 4. 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" or "indeterminate", the client
SHALL proceed as if this server has no TLSA records. It MAY connect SHALL proceed as if this server has no TLSA records. It MAY connect
to the server with or without TLS. to the server with or without TLS.
If the TLSA response is "bogus" then the client MUST NOT connect to If the TLSA response is "bogus", then the client MUST NOT connect to
the corresponding server. (The client can still use other SRV the corresponding server. (The client can still use other SRV
targets.) targets.)
4. 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] without further input from the TLSA records. If the client without further input from the TLSA records. If the client received
received one or more usable TLSA certificate associations, it SHALL one or more usable TLSA certificate associations, it SHALL process
process them as described in [RFC6698] section 2.1. them as described in [RFC6698] section 2.1.
The client uses the DNSSEC validation status of the SRV query in its The client uses the DNSSEC validation status of the SRV query in its
server certificate identity checks. (The TLSA validation status does server certificate identity checks. (The TLSA validation status does
not affect the server certificate identity checks.) It SHALL use the not affect the server certificate identity checks.) It SHALL use the
Server Name Indication extension (TLS SNI) [RFC6066] with the Server Name Indication extension (TLS SNI) [RFC6066] or its
preferred name chosen as follows. It SHALL verify the identity functional equivalent in the relevant application protocol (e.g., in
asserted by the server's certificate according to [RFC6125] section XMPP [RFC6120] this is the the 'to' address of the initial stream
6, using a list of reference identifiers constructed as follows. header). The preferred name SHALL be chosen as follows, and the
client SHALL verify the identity asserted by the server's certificate
according to [RFC6125] section 6, using a list of reference
identifiers constructed as follows. (Note again that in RFC 6125 the
terms "source domain" and "derived domain" refer to the same things
as "service domain" and "target host name" in this document.)
SRV is insecure or indeterminate: The reference identifiers SHALL SRV is insecure or indeterminate: The reference identifiers SHALL
include the service domain and MUST NOT include the SRV target include the service domain and MUST NOT include the SRV target
host name. The service domain is the preferred name for TLS SNI. host name. The service domain is the preferred name for TLS SNI
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. 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 is compatible with servers that do and do not support this it is compatible with servers that do and do not support this
specification.) specification.)
5. 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. If you are writing such as
document the following points ought to be covered: (This section is document the following points ought to be covered:
currently sketchy.)
o SRV fallback logic? In the event of bogus replies etc. o Fallback logic in the event of bogus replies and the like.
o Compatibility with non-SRV clients. o Compatibility with clients that do not support SRV lookups.
6. Guidance for server operators 7. Guidance for Server Operators
In order to support this specification, server software MUST In order to support this specification, server software MUST
implement the TLS Server Name Indication extension (TLS SNI) implement the TLS Server Name Indication extension (TLS SNI)
[RFC6066] for selecting the appropriate certificate. [RFC6066] (or its functional equivalent in the relevant application
protocol) for selecting the appropriate certificate.
A server that supports TLS and is the target of a SRV record MUST A server that supports TLS and is the target of an SRV record MUST
have a TLS certificate that authenticates the SRV query domain (i.e. have a TLS certificate that authenticates the SRV query domain (i.e.
the service domain, or "source domain" in [RFC6125] terms). This is the service domain, or "source domain" in [RFC6125] terms). This is
necessary for clients that cannot perform DNSSEC validation. This necessary for clients that cannot perform DNSSEC validation. This
certificate MUST be the default that is presented if the client does certificate MUST be the default that is presented if the client does
not use TLS SNI. not use TLS SNI or its functional equivalent.
In order to support this specification, the server SHOULD also have a In order to support this specification, the server SHOULD also have a
certificate that authenticates the SRV target domain (the mail server certificate that authenticates the SRV target domain (e.g., the mail
hostname). This can be done using a multi-name certificate or by server hostname). This can be done using a multi-name certificate or
using the client's TLS SNI to select the appropriate certificate. by using the client's TLS SNI or its functional equivalent to select
The server's TLSA record SHOULD correspond to this certificate. the appropriate certificate. The server's TLSA record SHOULD
correspond to this certificate.
Note: In some application protocols, there are old non-SRV clients Note: In some application protocols, there are old non-SRV clients
that expect a server's TLS certificate to authenticate its host name; that expect a server's TLS certificate to authenticate its host name;
they are also unlikely to support SNI. This means that servers for they are also unlikely to support SNI. This means that servers for
old clients need a different default certificate from servers that old clients need a different default certificate from servers that
are the targets of SRV records. If the server does not have a are the targets of SRV records. If the server does not have a
certificate that authenticates all relevant names, it is necessary to certificate that authenticates all relevant names, it is necessary to
segregate old and new clients. This can be done by using different segregate old and new clients. This can be done by using different
target hosts or non-standard ports in the SRV targets. (The latter target hosts or non-standard ports in the SRV targets. (The latter
avoids the need for additional certificates.) avoids the need for additional certificates.)
7. Security considerations 8. Internationalization Considerations
7.1. Mixed security status If any of the DNS queries are for an internationalized domain name,
then they need to use the A-label form [RFC5890].
We do not specify that clients check that all of a service domain's 9. IANA Considerations
No IANA action is required.
10. Security Considerations
10.1. Mixed Security Status
We do not specify that clients checking all of a service domain's
server host names are consistent in whether they have or do not have server host names are consistent in whether they have or do not have
TLSA records. This is so that partial or incremental deployment does TLSA records. This is so that partial or incremental deployment does
not break the service. Different levels of deployment are likely if not break the service. Different levels of deployment are likely if
a service domain has a third-party fall-back server, for example. a service domain has a third-party fallback server, for example.
The SRV and MX sorting rules are unchanged; in particular they have The SRV and MX sorting rules are unchanged; in particular they have
not been altered in order to prioritize secure servers over insecure not been altered in order to prioritize secure servers over insecure
servers. If a site wants to be secure it needs to deploy this servers. If a site wants to be secure it needs to deploy this
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.
7.2. 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, and publishing a
TLSA record under that name. If these are not correct then TLSA record under that name. If these are not correct then
connections from TLSA-aware clients might fail. connections from TLSA-aware clients might fail.
7.3. 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 checking might appear to be unnecessary, since DNSSEC provides a Name checking might appear to be unnecessary, since DNSSEC provides a
secure binding between the server name and the TLSA record, which in secure binding between the server name and the TLSA record, which in
turn authenticates the certificate. However this latter step can be turn authenticates the certificate. However this latter step can be
indirect, via a chain of certificates. A usage=0 TLSA record only indirect, via a chain of certificates. A usage=0 TLSA record only
authenticates the CA that issued the certificate, and third parties authenticates the CA that issued the certificate, and third parties
can obtain certificates from the same CA. can obtain certificates from the same CA.
So this specification says that clients check that the server's Therefore this specification says that a client needs to check
certificate matches the server host name, to ensure that the whether the server's certificate matches the server host name, to
certificate was issued by the CA to the server that the client is ensure that the certificate was issued by the CA to the server that
connecting to. The client always performs this check regardless of the client is connecting to. The client always performs this check
the TLSA usage, to simplify implementation and so that this regardless of the TLSA usage, to simplify implementation and so that
specification is less likely to need updating when new TLSA usages this specification is less likely to need updating when new TLSA
are added. usages are added.
7.4. Deliberate omissions 10.4. Deliberate Omissions
We do not specify that clients check the DNSSEC state of the server We do not specify that clients check the DNSSEC state of the server
address records. This is not necessary since the certificate checks address records. This is not necessary since the certificate checks
ensure that the client has connected to the correct server. (The ensure that the client has connected to the correct server. (The
address records will normally have the same security state as the address records will normally have the same security state as the
TLSA records, but they can differ if there are CNAME or DNAME TLSA records, but they can differ if there are CNAME or DNAME
indirections.) indirections.)
8. Internationalization Considerations 11. Acknowledgements
If any of the DNS queries are for an internationalized domain name,
then they need to use the A-label form [RFC5890].
9. IANA Considerations
No IANA action is required.
10. 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, Ned Freed, Olafur secure the SRV / MX lookup. Thanks to James Cloos, Ned Freed, Olafur
Gudmundsson, Paul Hoffman, Phil Pennock, Hector Santos, Jonas Gudmundsson, Paul Hoffman, Phil Pennock, Hector Santos, Jonas
Schneider, and Alessandro Vesely for helpful suggestions. Schneider, and Alessandro Vesely for helpful suggestions.
11. References 12. References
11.1. Normative References 12.1. Normative References
[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", Rose, "DNS Security Introduction and Requirements", RFC
RFC 4033, March 2005. 4033, March 2005.
[RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S. [RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Protocol Modifications for the DNS Security Rose, "Protocol Modifications for the DNS Security
Extensions", RFC 4035, March 2005. Extensions", RFC 4035, March 2005.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, May 2008. (CRL) Profile", RFC 5280, May 2008.
[RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321, [RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
October 2008. October 2008.
[RFC5890] Klensin, J., "Internationalized Domain Names for [RFC5890] Klensin, J., "Internationalized Domain Names for
Applications (IDNA): Definitions and Document Framework", Applications (IDNA): Definitions and Document Framework",
RFC 5890, August 2010. RFC 5890, August 2010.
[RFC6066] Eastlake, D., "Transport Layer Security (TLS) Extensions: [RFC6066] Eastlake, D., "Transport Layer Security (TLS) Extensions:
Extension Definitions", RFC 6066, January 2011. Extension Definitions", RFC 6066, January 2011.
[RFC6120] Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Core", RFC 6120, March 2011.
[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and [RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
Verification of Domain-Based Application Service Identity Verification of Domain-Based Application Service Identity
within Internet Public Key Infrastructure Using X.509 within Internet Public Key Infrastructure Using X.509
(PKIX) Certificates in the Context of Transport Layer (PKIX) Certificates in the Context of Transport Layer
Security (TLS)", RFC 6125, March 2011. Security (TLS)", RFC 6125, March 2011.
[RFC6698] Hoffman, P. and J. Schlyter, "The DNS-Based Authentication [RFC6698] Hoffman, P. and J. Schlyter, "The DNS-Based Authentication
of Named Entities (DANE) Transport Layer Security (TLS) of Named Entities (DANE) Transport Layer Security (TLS)
Protocol: TLSA", RFC 6698, August 2012. Protocol: TLSA", RFC 6698, August 2012.
11.2. Informative References 12.2. Informative References
[I-D.ietf-dane-smtp] [I-D.ietf-dane-smtp-with-dane]
Finch, T., "Secure SMTP using DNS-Based Authentication of Dukhovni, V. and W. Hardaker, "(DANE) TLSA records.",
Named Entities (DANE) TLSA records.", draft-ietf-dane-smtp draft-ietf-dane-smtp-with-dane (work in progress),
(work in progress), March 2013. November 2013.
[I-D.ietf-dane-mua] [I-D.ietf-xmpp-dna]
Finch, T., "Using DNS-Based Authentication of Named Saint-Andre, P. and M. Miller, "Domain Name Associations
Entities (DANE) with POP, IMAP, and message submission.", (DNA) in the Extensible Messaging and Presence Protocol
draft-ietf-dane-mua (work in progress), March 2013. (XMPP)", draft-ietf-xmpp-dna-04 (work in progress),
October 2013.
Appendix A. Example Appendix A. 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.
; mail domain ; mail domain
example.com. MX 1 mx.example.net. example.com. MX 1 mx.example.net.
example.com. RRSIG MX ... example.com. RRSIG MX ...
skipping to change at page 10, line 44 skipping to change at page 10, line 45
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. Rationale Appendix B. 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 and scales up more easily to larger numbers of service domains (so-called "multi-tenanted environments") and scales up more
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:
o The certificate is part of the server configuration, so it makes o The certificate is part of the server configuration, so it makes
sense to associate it with the server name rather than the service sense to associate it with the server host name rather than the
domain. service domain.
o In the absence of TLS SNI, if the certificate identifies the host o In the absence of TLS SNI, if the certificate identifies the host
name then it does not need to list all the possible service name then it does not need to list all the possible service
domains. domains.
o When the server certificate is replaced it is much easier if there o When the server certificate is replaced it is much easier if there
is one part of the DNS that needs updating to match, instead of an is one part of the DNS that needs updating to match, instead of an
unbounded number of hosted service domains. unbounded number of hosted service domains.
o The same TLSA records work with this specification, and with o The same TLSA records work with this specification, and with
direct connections to the host name in the style of [RFC6698]. direct connections to the host name in the style of [RFC6698].
o Some application protocols, such as SMTP, allow a client to o Some application protocols, such as SMTP, allow a client to
perform transactions with multiple service domains in the same perform transactions with multiple service domains in the same
connection. It is not in general feasible for the client to connection. It is not in general feasible for the client to
specify the service domain using TLS SNI when the connection is specify the service domain using TLS SNI when the connection is
established, and the server might not be able to present a established, and the server might not be able to present a
certificate that authenticates all possible service domains. certificate that authenticates all possible service domains.
o It is common for SMTP servers to act in multiple roles, as o It is common for SMTP servers to act in multiple roles, for
outgoing relays or as incoming MX servers, depending on the client example as outgoing relays or as incoming MX servers, depending on
identity. It is simpler if the server can present the same the client identity. It is simpler if the server can present the
certificate regardless of the role in which it is to act. same certificate regardless of the role in which it is to act.
Sometimes the server does not know its role until the client has Sometimes the server does not know its role until the client has
authenticated, which usually occurs after TLS has been authenticated, which usually occurs after TLS has been
established. established.
This specification does not provide an option to put TLSA records This specification does not provide an option to put TLSA records
under the service domain because that would add complexity without under the service domain because that would add complexity without
providing any benefit, and security protocols are best kept simple. providing any benefit, and security protocols are best kept simple.
As described above, there are real-world cases where authenticating As described above, there are real-world cases where authenticating
the service domain cannot be made to work, so there would be the service domain cannot be made to work, so there would be
complicated criteria for when service domain TLSA records might be complicated criteria for when service domain TLSA records might be
used and when they cannot. This is all avoided by putting the TLSA used and when they cannot. This is all avoided by putting the TLSA
records under the server host name. records under the server host name.
The disadvantage is that clients which do not do DNSSEC validation The disadvantage is that clients which do not do DNSSEC validation
must, according to [RFC6125] rules, check the server certificate must, according to [RFC6125] rules, check the server certificate
against the service domain, since they have no other way to against the service domain, since they have no other way to
authenticate the server. This means that Server Name Indication authenticate the server. This means that SNI support or its
support is necessary for backwards compatibility. functional equivalent is necessary for backward compatibility.
Author's Address
Authors' Addresses
Tony Finch Tony Finch
University of Cambridge Computing Service University of Cambridge Computing Service
New Museums Site New Museums Site
Pembroke Street Pembroke Street
Cambridge CB2 3QH Cambridge CB2 3QH
ENGLAND ENGLAND
Phone: +44 797 040 1426 Phone: +44 797 040 1426
Email: dot@dotat.at Email: dot@dotat.at
URI: http://dotat.at/ URI: http://dotat.at/
Matthew Miller
Cisco Systems, Inc.
1899 Wynkoop Street, Suite 600
Denver, CO 80202
USA
Email: mamille2@cisco.com
Peter Saint-Andre
Cisco Systems, Inc.
1899 Wynkoop Street, Suite 600
Denver, CO 80202
USA
Email: psaintan@cisco.com
 End of changes. 69 change blocks. 
155 lines changed or deleted 174 lines changed or added

This html diff was produced by rfcdiff 1.41. The latest version is available from http://tools.ietf.org/tools/rfcdiff/