< 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
	skipping to change at page 1, line 42 ¶		skipping to change at page 1, line 42 ¶
	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
	skipping to change at page 2, line 24 ¶		skipping to change at page 2, line 24 ¶
	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).
	skipping to change at page 3, line 38 ¶		skipping to change at page 3, line 38 ¶
	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 |
	skipping to change at page 4, line 46 ¶		skipping to change at page 4, line 49 ¶
	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
	skipping to change at page 8, line 28 ¶		skipping to change at page 8, line 50 ¶
	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.
	skipping to change at page 11, line 4 ¶		skipping to change at page 11, line 31 ¶
	; 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:
End of changes. 36 change blocks.
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