< 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
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	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 12 ¶		skipping to change at page 4, line 4 ¶
	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
	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
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