draft-ietf-acme-caa-08.txt		draft-ietf-acme-caa-09.txt
	ACME Working Group H. Landau		ACME Working Group H. Landau
	Internet-Draft May 31, 2019		Internet-Draft June 16, 2019
	Intended status: Standards Track		Intended status: Standards Track
	Expires: December 2, 2019		Expires: December 18, 2019
	CAA Record Extensions for Account URI and ACME Method Binding		CAA Record Extensions for Account URI and ACME Method Binding
	draft-ietf-acme-caa-08		draft-ietf-acme-caa-09
	Abstract		Abstract
	The Certification Authority Authorization (CAA) DNS record allows a		The Certification Authority Authorization (CAA) DNS record allows a
	domain to communicate issuance policy to Certification Authorities		domain to communicate issuance policy to Certification Authorities
	(CAs), but only allows a domain to define policy with CA-level		(CAs), but only allows a domain to define policy with CA-level
	granularity. However, the CAA specification also provides facilities		granularity. However, the CAA specification also provides facilities
	for extension to admit more granular, CA-specific policy. This		for extension to admit more granular, CA-specific policy. This
	specification defines two such parameters, one allowing specific		specification defines two such parameters, one allowing specific
	accounts of a CA to be identified by URI and one allowing specific		accounts of a CA to be identified by URI and one allowing specific
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	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF). Note that other groups may also distribute		Task Force (IETF). Note that other groups may also distribute
	working documents as Internet-Drafts. The list of current Internet-		working documents as Internet-Drafts. The list of current Internet-
	Drafts is at https://datatracker.ietf.org/drafts/current/.		Drafts is at https://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 December 2, 2019.		This Internet-Draft will expire on December 18, 2019.
	Copyright Notice		Copyright Notice
	Copyright (c) 2019 IETF Trust and the persons identified as the		Copyright (c) 2019 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
	(https://trustee.ietf.org/license-info) in effect on the date of		(https://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 18 ¶		skipping to change at page 2, line 18 ¶
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
	2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2		2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
	3. Extensions to the CAA Record: accounturi Parameter . . . . . 3		3. Extensions to the CAA Record: accounturi Parameter . . . . . 3
	3.1. Use with ACME . . . . . . . . . . . . . . . . . . . . . . 3		3.1. Use with ACME . . . . . . . . . . . . . . . . . . . . . . 3
	3.2. Use without ACME . . . . . . . . . . . . . . . . . . . . 3		3.2. Use without ACME . . . . . . . . . . . . . . . . . . . . 3
	4. Extensions to the CAA Record: validationmethods Parameter . . 4		4. Extensions to the CAA Record: validationmethods Parameter . . 4
	5. Security Considerations . . . . . . . . . . . . . . . . . . . 4		5. Security Considerations . . . . . . . . . . . . . . . . . . . 4
	5.1. Limited to CAs Processing CAA Records . . . . . . . . . . 4		5.1. Limited to CAs Processing CAA Records . . . . . . . . . . 5
	5.2. Restrictions Ineffective without CA Recognition . . . . . 5		5.2. Restrictions Ineffective without CA Recognition . . . . . 5
	5.3. Mandatory Consistency in CA Recognition . . . . . . . . . 5		5.3. Mandatory Consistency in CA Recognition . . . . . . . . . 5
	5.4. URI Ambiguity . . . . . . . . . . . . . . . . . . . . . . 6		5.4. URI Ambiguity . . . . . . . . . . . . . . . . . . . . . . 6
	5.5. Authorization Freshness . . . . . . . . . . . . . . . . . 6		5.5. Authorization Freshness . . . . . . . . . . . . . . . . . 7
	5.6. Use with and without DNSSEC . . . . . . . . . . . . . . . 6		5.6. Use with and without DNSSEC . . . . . . . . . . . . . . . 7
	5.7. Restrictions Supercedable by DNS Delegation . . . . . . . 8		5.7. Restrictions Supercedable by DNS Delegation . . . . . . . 8
	5.8. Misconfiguration Hazards . . . . . . . . . . . . . . . . 8		5.8. Misconfiguration Hazards . . . . . . . . . . . . . . . . 9
	6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8		5.9. Revelation of Account URIs . . . . . . . . . . . . . . . 9
	7. Normative References . . . . . . . . . . . . . . . . . . . . 8		6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
	Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 9		7. Normative References . . . . . . . . . . . . . . . . . . . . 9
	Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 10		Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 10
			Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 11
	1. Introduction		1. Introduction
	This specification defines two parameters for the "issue" and		This specification defines two parameters for the "issue" and
	"issuewild" properties of the Certification Authority Authorization		"issuewild" properties of the Certification Authority Authorization
	(CAA) DNS resource record [RFC6844]. The first, "accounturi", allows		(CAA) DNS resource record [I-D.ietf-lamps-rfc6844bis]. The first,
	authorization conferred by a CAA policy to be restricted to specific		"accounturi", allows authorization conferred by a CAA policy to be
	accounts of a CA, which are identified by URIs. The second,		restricted to specific accounts of a CA, which are identified by
	"validationmethods", allows the set of validation methods supported		URIs. The second, "validationmethods", allows the set of validation
	by a CA to validate domain control to be limited to a subset of the		methods supported by a CA to validate domain control to be limited to
	full set of methods which it supports.		a subset of the full set of methods which it supports.
	2. Terminology		2. Terminology
	In this document, the key words "MUST", "MUST NOT", "REQUIRED",		In this document, the key words "MUST", "MUST NOT", "REQUIRED",
	"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT		"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT
	RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as		RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as
	described in BCP 14 [RFC2119] [RFC8174] when, and only when, they		described in BCP 14 [RFC2119] [RFC8174] when, and only when, they
	appear in all capitals, as shown here.		appear in all capitals, as shown here.
	3. Extensions to the CAA Record: accounturi Parameter		3. Extensions to the CAA Record: accounturi Parameter
	A CAA parameter "accounturi" is defined for the "issue" and		A CAA parameter "accounturi" is defined for the "issue" and
	"issuewild" properties defined by [RFC6844]. The value of this		"issuewild" properties defined by [I-D.ietf-lamps-rfc6844bis]. The
	parameter, if specified, MUST be a URI [RFC3986] identifying a		value of this parameter, if specified, MUST be a URI [RFC3986]
	specific CA account.		identifying a specific CA account.
	"CA account" means an object, maintained by a specific CA and which		"CA account" means an object, maintained by a specific CA and which
	may request the issuance of certificates, which represents a specific		may request the issuance of certificates, which represents a specific
	entity or group of related entities.		entity or group of related entities.
	The presence of this parameter constrains the property to which it is		The presence of this parameter constrains the property to which it is
	attached. Where a CAA property has an "accounturi" parameter, a CA		attached. Where a CAA property has an "accounturi" parameter, a CA
	MUST only consider that property to authorize issuance in the context		MUST only consider that property to authorize issuance in the context
	of a given certificate issuance request if the CA recognises the URI		of a given certificate issuance request if the CA recognises the URI
	specified as identifying the account making that request.		specified in the value portion of that parameter as identifying the
			account making that request.
	A property without an "accounturi" parameter matches any account. A		A property without an "accounturi" parameter matches any account. A
	property with an invalid or unrecognised "accounturi" parameter is		property with an invalid or unrecognised "accounturi" parameter is
	unsatisfiable. A property with multiple "accounturi" parameters is		unsatisfiable. A property with multiple "accounturi" parameters is
	unsatisfiable.		unsatisfiable.
	The presence of an "accounturi" parameter does not replace or		The presence of an "accounturi" parameter does not replace or
	supercede the need to validate the domain name specified in an		supercede the need to validate the domain name specified in an
	"issue" or "issuewild" record in the manner described in the CAA		"issue" or "issuewild" record in the manner described in the CAA
	specification. CAs MUST still perform such validation. For example,		specification. CAs MUST still perform such validation. For example,
	a CAA "issue" property which specifies a domain name belonging to CA		a CAA "issue" property which specifies a domain name belonging to CA
	A and an "accounturi" parameter identifying an account at CA B is		A and an "accounturi" parameter identifying an account at CA B is
	unsatisfiable.		unsatisfiable.
	3.1. Use with ACME		3.1. Use with ACME
	An ACME [I-D.ietf-acme-acme] account object MAY be identified by		An ACME [RFC8555] account object MAY be identified by setting the
	setting the "accounturi" parameter to the URI of the ACME account		"accounturi" parameter to the URI of the ACME account object.
	object.
	Implementations of this specification which also implement ACME MUST		Implementations of this specification which also implement ACME MUST
	recognise such URIs.		recognise such URIs.
	3.2. Use without ACME		3.2. Use without ACME
	The "accounturi" specification provides a general mechanism to		The "accounturi" specification provides a general mechanism to
	identify entities which may request certificate issuance via URIs.		identify entities which may request certificate issuance via URIs.
	The use of specific kinds of URI may be specified in future RFCs, and		The use of specific kinds of URI may be specified in future RFCs, and
	CAs not implementing ACME MAY assign and recognise their own URIs		CAs not implementing ACME MAY assign and recognise their own URIs
	arbitrarily.		arbitrarily.
	4. Extensions to the CAA Record: validationmethods Parameter		4. Extensions to the CAA Record: validationmethods Parameter
	A CAA parameter "validationmethods" is also defined for the "issue"		A CAA parameter "validationmethods" is also defined for the "issue"
	and "issuewild" properties. The value of this parameter, if		and "issuewild" properties. The value of this parameter, if
	specified, MUST be a comma-separated string of challenge method		specified, MUST be a comma-separated string of validation method
	names. Each challenge method name MUST be either an ACME challenge		labels.
	method name or a CA-assigned non-ACME challenge method name.
			A validation method label identifies a validation method. A
			validation method is a particular way in which a CA can validate
			control over a domain.
	The presence of this parameter constrains the property to which it is		The presence of this parameter constrains the property to which it is
	attached. A CA MUST only consider a property with the		attached. A CA MUST only consider a property with the
	"validationmethods" parameter to authorize issuance where the name of		"validationmethods" parameter to authorize issuance where the
	the challenge method being used is one of the names listed in the		validation method being used is identified by one of the validation
	comma-separated list.		method labels listed in the comma-separated list.
			Each validation method label MUST be either the label of a method
			defined in the ACME Validation Methods IANA registry, or a CA-
			specific non-ACME validation method label as defined below.
	Where a CA supports both the "validationmethods" parameter and one or		Where a CA supports both the "validationmethods" parameter and one or
	more non-ACME challenge methods, it MUST assign identifiers to those		more non-ACME validation methods, it MUST assign labels to those
	methods. If appropriate non-ACME identifiers are not present in the		methods. If appropriate non-ACME labels are not present in the ACME
	ACME Validation Methods IANA registry, the CA MUST use identifiers		Validation Methods IANA registry, the CA MUST use labels beginning
	beginning with the string "ca-", which are defined to have CA-		with the string "ca-", which are defined to have CA-specific meaning.
	specific meaning.
			The value of the "validationmethods" parameter MUST comply with the
			following ABNF [RFC5234]:
			value = [*(label ",") label]
			label = 1*(ALPHA / DIGIT / "-")
	5. Security Considerations		5. Security Considerations
	This specification describes an extension to the CAA record		This specification describes an extension to the CAA record
	specification increasing the granularity at which CAA policy can be		specification increasing the granularity at which CAA policy can be
	expressed. This allows the set of entities capable of successfully		expressed. This allows the set of entities capable of successfully
	requesting issuance of certificates for a given domain to be		requesting issuance of certificates for a given domain to be
	restricted beyond that which would otherwise be possible, while still		restricted beyond that which would otherwise be possible, while still
	allowing issuance for specific accounts of a CA. This improves the		allowing issuance for specific accounts of a CA. This improves the
	security of issuance for domains which choose to employ it, when		security of issuance for domains which choose to employ it, when
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	As such, a domain which via CAA records authorizes only CAs adopting		As such, a domain which via CAA records authorizes only CAs adopting
	this specification, and which constrains its policy by means of this		this specification, and which constrains its policy by means of this
	specification, remains vulnerable to unauthorized issuance by CAs		specification, remains vulnerable to unauthorized issuance by CAs
	which do not honour CAA records, or which honour them only on an		which do not honour CAA records, or which honour them only on an
	advisory basis. Where a domain uses DNSSEC, it also remains		advisory basis. Where a domain uses DNSSEC, it also remains
	vulnerable to CAs which honour CAA records but which do not validate		vulnerable to CAs which honour CAA records but which do not validate
	CAA records by means of a trusted DNSSEC-validating resolver.		CAA records by means of a trusted DNSSEC-validating resolver.
	5.2. Restrictions Ineffective without CA Recognition		5.2. Restrictions Ineffective without CA Recognition
	The CAA parameters specified in this specification rely on their		Because the parameters of "issue" or "issuewild" CAA properties
	being recognised by the CA named by an "issue" or "issuewild" CAA		constitute a CA-specific namespace, the CA identified by an "issue"
	property. As such, the parameters are not an effective means of		or "issuewild" property decides what parameters to recognise and
	control over issuance unless a CA's support for the parameters is		their semantics. Accordingly, the CAA parameters defined in this
			specification rely on their being recognised by the CA named by an
			"issue" or "issuewild" CAA property, and are not an effective means
			of control over issuance unless a CA's support for the parameters is
	established beforehand.		established beforehand.
	CAs which implement this specification SHOULD make available		CAs which implement this specification SHOULD make available
	documentation indicating as such, including explicit statements as to		documentation indicating as such, including explicit statements as to
	which parameters are supported. Domains configuring CAA records for		which parameters are supported. Domains configuring CAA records for
	a CA MUST NOT assume that the restrictions implied by the		a CA MUST NOT assume that the restrictions implied by the
	"accounturi" and "validationmethods" parameters are effective in the		"accounturi" and "validationmethods" parameters are effective in the
	absence of explicit indication as such from that CA.		absence of explicit indication as such from that CA.
	CAs SHOULD also document whether they implement DNSSEC validation for		CAs SHOULD also document whether they implement DNSSEC validation for
	skipping to change at page 8, line 30 ¶		skipping to change at page 9, line 11 ¶
	for subdomains of a domain, where control over those subdomains is		for subdomains of a domain, where control over those subdomains is
	delegated to another party (such as via DNS delegation or by		delegated to another party (such as via DNS delegation or by
	providing limited access to manage subdomain DNS records).		providing limited access to manage subdomain DNS records).
	5.8. Misconfiguration Hazards		5.8. Misconfiguration Hazards
	Because the "accounturi" and "validationmethods" parameters express		Because the "accounturi" and "validationmethods" parameters express
	restrictive security policies, misconfiguration of said parameters		restrictive security policies, misconfiguration of said parameters
	may result in legitimate issuance requests being refused.		may result in legitimate issuance requests being refused.
			5.9. Revelation of Account URIs
			Because CAA records are publically accessible, use of the
			"accounturi" parameter enables third parties to observe the
			authorized account URIs for a domain. This may allow third parties
			to identify a correlation between domains if those domains use the
			same account URIs.
			CAs are encouraged to select and process account URIs under the
			assumption that untrusted third parties may learn of them.
	6. IANA Considerations		6. IANA Considerations
	None. As per the CAA specification, the parameter namespace for the		None. As per the CAA specification, the parameter namespace for the
	CAA "issue" and "issuewild" properties has CA-defined semantics and		CAA "issue" and "issuewild" properties has CA-defined semantics and
	the identifiers within that namespace may be freely and arbitrarily		the identifiers within that namespace may be freely and arbitrarily
	assigned by a CA. This document merely specifies recommended		assigned by a CA. This document merely specifies recommended
	semantics for parameters of the names "accounturi" and		semantics for parameters of the names "accounturi" and
	"validationmethods", which CAs may choose to adopt.		"validationmethods", which CAs may choose to adopt.
	7. Normative References		7. Normative References
	[I-D.ietf-acme-acme]		[I-D.ietf-lamps-rfc6844bis]
	Barnes, R., Hoffman-Andrews, J., McCarney, D., and J.		Hallam-Baker, P., Stradling, R., and J. Hoffman-Andrews,
	Kasten, "Automatic Certificate Management Environment		"DNS Certification Authority Authorization (CAA) Resource
	(ACME)", draft-ietf-acme-acme-18 (work in progress),		Record", draft-ietf-lamps-rfc6844bis-07 (work in
	December 2018.		progress), May 2019.
	[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,		Requirement Levels", BCP 14, RFC 2119,
	DOI 10.17487/RFC2119, March 1997,		DOI 10.17487/RFC2119, March 1997,
	<https://www.rfc-editor.org/info/rfc2119>.		<https://www.rfc-editor.org/info/rfc2119>.
	[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform		[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
	Resource Identifier (URI): Generic Syntax", STD 66,		Resource Identifier (URI): Generic Syntax", STD 66,
	RFC 3986, DOI 10.17487/RFC3986, January 2005,		RFC 3986, DOI 10.17487/RFC3986, January 2005,
	<https://www.rfc-editor.org/info/rfc3986>.		<https://www.rfc-editor.org/info/rfc3986>.
	[RFC6844] Hallam-Baker, P. and R. Stradling, "DNS Certification		[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
	Authority Authorization (CAA) Resource Record", RFC 6844,		Specifications: ABNF", STD 68, RFC 5234,
	DOI 10.17487/RFC6844, January 2013,		DOI 10.17487/RFC5234, January 2008,
	<https://www.rfc-editor.org/info/rfc6844>.		<https://www.rfc-editor.org/info/rfc5234>.
	[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC		[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
	2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,		2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
	May 2017, <https://www.rfc-editor.org/info/rfc8174>.		May 2017, <https://www.rfc-editor.org/info/rfc8174>.
			[RFC8555] Barnes, R., Hoffman-Andrews, J., McCarney, D., and J.
			Kasten, "Automatic Certificate Management Environment
			(ACME)", RFC 8555, DOI 10.17487/RFC8555, March 2019,
			<https://www.rfc-editor.org/info/rfc8555>.
	Appendix A. Examples		Appendix A. Examples
	The following shows an example DNS zone file fragment which nominates		The following shows an example DNS zone file fragment which nominates
	two account URIs as authorized to issue certificates for the domain		two account URIs as authorized to issue certificates for the domain
	"example.com". Issuance is restricted to the CA "example.net".		"example.com". Issuance is restricted to the CA "example.net".
	example.com. IN CAA 0 issue "example.net; \		example.com. IN CAA 0 issue "example.net; \
	accounturi=https://example.net/account/1234"		accounturi=https://example.net/account/1234"
	example.com. IN CAA 0 issue "example.net; \		example.com. IN CAA 0 issue "example.net; \
	accounturi=https://example.net/account/2345"		accounturi=https://example.net/account/2345"
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