<?xml version='1.0' encoding='utf-8'?> <?xml-stylesheet type="text/xsl" href="rfc2629.xslt" ?><!-- generated by https://github.com/cabo/kramdown-rfc2629 version 1.2.9 --><!DOCTYPE rfc SYSTEM "rfc2629-xhtml.ent"><?rfc toc="yes"?> <?rfc sortrefs="yes"?> <?rfc symrefs="yes"?><rfc xmlns:xi="http://www.w3.org/2001/XInclude"docName="draft-ietf-lamps-rfc6844bis-07"submissionType="IETF" category="std" consensus="true" number="9999" ipr="trust200902" obsoletes="6844" updates=""submissionType="IETF"xml:lang="en" tocInclude="true" symRefs="true" sortRefs="true" version="3"> <!-- xml2rfc v2v3 conversion2.23.12.23.0 --> <front> <title abbrev="CAA">DNS Certification Authority Authorization (CAA) Resource Record</title> <seriesInfoname="Internet-Draft" value="draft-ietf-lamps-rfc6844bis-07"/>name="RFC" value="9999"/> <author initials="P." surname="Hallam-Baker" fullname="Phillip Hallam-Baker"> <organization/> <address> <email>phill@hallambaker.com</email> </address> </author> <author initials="R." surname="Stradling" fullname="Rob Stradling"> <organization abbrev="Sectigo">Sectigo Ltd.</organization> <address> <email>rob@sectigo.com</email> </address> </author> <author initials="J." surname="Hoffman-Andrews" fullname="Jacob Hoffman-Andrews"> <organization>Let's Encrypt</organization> <address> <email>jsha@letsencrypt.org</email> </address> </author> <date year="2019"month="May" day="30"/>month="June"/> <!-- [rfced] Please insert any keywords (beyond those that appear in the title) for use on https://www.rfc-editor.org/search. --> <keyword>example</keyword> <abstract> <t>The Certification Authority Authorization (CAA) DNS Resource Record allows a DNS domain name holder to specify one or more Certification Authorities (CAs) authorized to issue certificates for that domain name. CAA Resource Records allow a public Certification Authority to implement additional controls to reduce the risk of unintended certificate mis-issue. This document defines the syntax of the CAA record and rules for processing CAA records by certificate issuers.</t> <t>This document obsoletes RFC 6844.</t> </abstract> </front> <middle> <section anchor="introduction" numbered="true" toc="default"> <name>Introduction</name> <t>The Certification Authority Authorization (CAA) DNS Resource Record allows a DNS domain name holder to specify the Certification Authorities (CAs) authorized to issue certificates for that domain name. Publication of CAA Resource Records allows a public Certification Authority to implement additional controls to reduce the risk of unintended certificate mis-issue.</t> <t>Like the TLSA record defined in DNS-Based Authentication of Named Entities (DANE) <xref target="RFC6698" format="default"/>, CAA records are used as a part of a mechanism for checking PKIX <xref target="RFC6698" format="default"/> certificate data. The distinction between the two specifications is that CAA records specify an authorization control to be performed by a certificate issuer before issue of a certificate and TLSA records specify a verification control to be performed by a relying party after the certificate is issued.</t> <t>Conformance with a published CAA record is a necessary but not sufficient condition for issuance of a certificate.</t> <t>Criteria for inclusion of embedded trust anchor certificates in applications are outside the scope of this document. Typically, such criteria require the CA to publish a Certification Practices Statement (CPS) that specifies how the requirements of the Certificate Policy (CP) are achieved. It is also common for a CA to engage an independent third-party auditor to prepare an annual audit statement of its performance against its CPS.</t> <t>A set of CAA records describes only current grants of authority to issue certificates for the corresponding DNS domain name. Since certificates are valid for a period of time, it is possible that a certificate that is not conformant with the CAA records currently published was conformant with the CAA records published at the time that the certificate was issued. Relying partiesMUST NOT<bcp14>MUST NOT</bcp14> use CAA records as part of certificate validation.</t> <t>CAA recordsMAY<bcp14>MAY</bcp14> be used by Certificate Evaluators as a possible indicator of a security policy violation. Such useSHOULD<bcp14>SHOULD</bcp14> take account of the possibility that published CAA records changed between the time a certificate was issued and the time at which the certificate was observed by the Certificate Evaluator.</t> </section> <section anchor="definitions" numbered="true" toc="default"> <name>Definitions</name> <section anchor="requirements-language" numbered="true" toc="default"> <name>Requirements Language</name> <t>The key words"MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY","<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>", "<bcp14>REQUIRED</bcp14>", "<bcp14>SHALL</bcp14>", "<bcp14>SHALL NOT</bcp14>", "<bcp14>SHOULD</bcp14>", "<bcp14>SHOULD NOT</bcp14>", "<bcp14>RECOMMENDED</bcp14>", "<bcp14>NOT RECOMMENDED</bcp14>", "<bcp14>MAY</bcp14>", and"OPTIONAL""<bcp14>OPTIONAL</bcp14>" in this document are to be interpreted as described in BCP 14 <xref target="RFC2119" format="default"/> <xref target="RFC8174" format="default"/> when, and only when, they appear in all capitals, as shown here.</t> </section> <section anchor="defined-terms" numbered="true" toc="default"> <name>Defined Terms</name> <t>The following terms are used in this document:</t><t>Certificate: An<!--Converted plain v2 paragraphs to a v3 definition list: --> <dl newline="true"> <dt>Certificate:</dt> <dd>An X.509 Certificate, as specified in <xref target="RFC5280"format="default"/>.</t> <t>Certificate Evaluator: Aformat="default"/>.</dd> <dt>Certificate Evaluator:</dt> <dd>A party other than a Relying Party that evaluates the trustworthiness of certificates issued by CertificationAuthorities.</t> <t>CertificationAuthorities.</dd> <dt>Certification Authority(CA): An(CA):</dt> <dd>An Issuer that issues certificates in accordance with a specified CertificatePolicy.</t> <t>CertificatePolicy.</dd> <dt>Certificate Policy(CP): Specifies(CP):</dt> <dd>Specifies the criteria that a Certification Authority undertakes to meet in its issue of certificates. See <xref target="RFC3647"format="default"/>.</t> <t>Certificationformat="default"/>.</dd> <dt>Certification Practices Statement(CPS): Specifies(CPS):</dt> <dd>Specifies the means by which the criteria of the Certificate Policy are met. In most cases, this will be the document against which the operations of the Certification Authority are audited. See <xref target="RFC3647"format="default"/>.</t> <t>Domain Name: Theformat="default"/>.</dd> <dt>Domain Name:</dt> <dd>The label assigned to a node in the Domain NameSystem.</t> <t>DomainSystem.</dd> <dt>Domain Name System(DNS): The(DNS):</dt> <dd>The Internet naming system specified in <xref target="RFC1034" format="default"/> and <xref target="RFC1035"format="default"/>.</t> <t>DNSformat="default"/>.</dd> <dt>DNS Security(DNSSEC): Extensions(DNSSEC):</dt> <dd>Extensions to the DNS that provide authentication services as specified in <xref target="RFC4033" format="default"/>, <xref target="RFC4034" format="default"/>, <xref target="RFC4035" format="default"/>, <xref target="RFC5155" format="default"/>, andrevisions.</t> <t>Fully-Qualifiedrevisions.</dd> <dt>Fully Qualified Domain Name(FQDN): A(FQDN):</dt> <dd>A Domain Name that includes the labels of all superior nodes in the Domain NameSystem.</t> <t>Issuer: AnSystem.</dd> <dt>Issuer:</dt> <dd>An entity that issues certificates. See <xref target="RFC5280"format="default"/>.</t> <t>Property: Theformat="default"/>.</dd> <dt>Property:</dt> <dd>The tag-value portion of a CAA ResourceRecord.</t> <t>Property Tag: TheRecord.</dd> <dt>Property Tag:</dt> <dd>The tag portion of a CAA ResourceRecord.</t> <t>Property Value: TheRecord.</dd> <dt>Property Value:</dt> <dd>The value portion of a CAA ResourceRecord.</t> <t>ResourceRecord.</dd> <dt>Resource Record(RR): A(RR):</dt> <dd>A particular entry in the DNS including the owner name, class, type, time to live, and data, as defined in <xref target="RFC1034" format="default"/> and <xref target="RFC2181"format="default"/>.</t> <t>Resourceformat="default"/>.</dd> <dt>Resource Record Set(RRSet): A(RRSet):</dt> <dd>A set of Resource Records of a particular owner name, class, and type. The time to live on all RRs within an RRSet is always the same, but the data may be different among RRs in theRRSet.</t> <t>RelevantRRSet.</dd> <dt>Relevant Resource Record Set (RelevantRRSet): ARRSet):</dt> <dd>A set of CAA Resource Records resulting from applying the algorithm inSection 3<xref target="relevant-resource-record-set" format="default"/> to a specificFully-QualifiedFully Qualified Domain Name or Wildcard DomainName.</t> <t>Relying Party: AName.</dd> <dt>Relying Party:</dt> <dd>A party that makes use of an application whose operation depends on use of a certificate for making a security decision. See <xref target="RFC5280"format="default"/>.</t> <t>Wildcardformat="default"/>.</dd> <dt>Wildcard DomainName: AName:</dt> <dd>A Domain Name consisting of a single asterisk character followed by a single full stop character ("*.") followed by aFully-QualifiedFully Qualified DomainName.</t>Name.</dd> </dl> </section> </section> <section anchor="relevant-resource-record-set" numbered="true" toc="default"> <name>Relevant Resource Record Set</name> <t>Before issuing a certificate, a compliant CAMUST<bcp14>MUST</bcp14> check for publication of a Relevant RRSet. If such an RRSet exists, a CAMUST NOT<bcp14>MUST NOT</bcp14> issue a certificate unless the CA determines that either (1) the certificate request is consistent with the applicable CAA Resource Record set or (2) an exception specified in the relevant Certificate Policy or Certification Practices Statement applies. If the Relevant RRSet for aFully-QualifiedFully Qualified Domain Name or Wildcard Domain Name contains no Property Tags that restrict issuance (for instance, if it contains only iodef Property Tags, or only Property Tags unrecognized by the CA), CAA does not restrict issuance.</t> <t>A certificate requestMAY<bcp14>MAY</bcp14> specify more than oneFully-QualifiedFully Qualified Domain Name andMAY<bcp14>MAY</bcp14> specify Wildcard Domain Names. IssuersMUST<bcp14>MUST</bcp14> verify authorization for all theFully-QualifiedFully Qualified Domain Names and Wildcard Domain Names specified in the request.</t> <t>The search for a CAA RRSet climbs the DNS name tree from the specified label up to but not including the DNS root '.' until a CAA RRSet is found.</t> <t>Given a request for a specificFully-QualifiedFully Qualified Domain Name X, or a request for a Wildcard Domain Name *.X, the Relevant Resource Record Set RelevantCAASet(X) is determined as follows (inpseudocode):</t> <t>Letthe pseudocode below):</t> <!-- Single-level bullet list --> <ul> <li>Let CAA(X) be the RRSet returned by performing a CAA record query for theFully-QualifiedFully Qualified DomainName X,Name X, according to the lookup algorithm specified inRFC 1034 section 4.3.2<xref target="RFC1034" sectionFormat="comma" section="4.3.2"/> (inparticularparticular, chasingaliases). Letaliases).</li> <li>Let Parent(X) be theFully-QualifiedFully Qualified Domain Name produced by removing the leftmost label ofX.</t> <artwork name="" type="" align="left" alt=""><![CDATA[X.</li> </ul> <sourcecode name="Pseudocode" type="pseudocode"><![CDATA[ RelevantCAASet(domain): while domain is not ".": if CAA(domain) is not Empty: return CAA(domain) domain = Parent(domain) return Empty]]></artwork>]]></sourcecode> <t>For example, processing CAA for theFully-QualifiedFully Qualified Domain Name "X.Y.Z" where there are no CAA records at any level in the tree RelevantCAASet would have the following steps:</t> <artwork name="" type="" align="left" alt=""><![CDATA[ CAA("X.Y.Z.") = Empty; domain = Parent("X.Y.Z.") = "Y.Z." CAA("Y.Z.") = Empty; domain = Parent("Y.Z.") = "Z." CAA("Z.") = Empty; domain = Parent("Z.") = "." return Empty ]]></artwork> <t>Processing CAA for theFully-QualifiedFully Qualified Domain Name "A.B.C" where there is a CAA record "issue example.com" at "B.C" would terminate early upon finding the CAA record:</t> <artwork name="" type="" align="left" alt=""><![CDATA[ CAA("A.B.C.") = Empty; domain = Parent("A.B.C.") = "B.C." CAA("B.C.") = "issue example.com" return "issue example.com" ]]></artwork> </section> <section anchor="mechanism" numbered="true" toc="default"> <name>Mechanism</name> <section anchor="syntax" numbered="true" toc="default"> <name>Syntax</name> <t>A CAA Resource Record contains a single Property consisting of a tag-value pair. AFully-QualifiedFully Qualified Domain NameMAY<bcp14>MAY</bcp14> have multiple CAA RRs associated with it and a given Property TagMAY<bcp14>MAY</bcp14> be specified morethan oncethan once across those RRs.</t> <t>The RDATA section for a CAA Resource Record contains one Property. A Property consists of the following:</t> <artwork name="" type="" align="left" alt=""><![CDATA[ +0-1-2-3-4-5-6-7-|0-1-2-3-4-5-6-7-| | Flags | Tag Length = n | +----------------|----------------+...+---------------+ | Tag char 0 | Tag char 1 |...| Tag char n-1 | +----------------|----------------+...+---------------+ +----------------|----------------+.....+----------------+ | Value byte 0 | Value byte 1 |.....| Value byte m-1 | +----------------|----------------+.....+----------------+ ]]></artwork> <t>Where n is the length specified in the Tag length field and m is the remaining octets in the Value field. They are related by (m = d - n - 2) where d is the length of the RDATA section.</t> <t>The fields are defined as follows:</t> <t>Flags: One octet containing the following field:</t> <t>Bit 0, Issuer Critical Flag: If the value is set to '1', the Property is critical. A Certification AuthorityMUST NOT<bcp14>MUST NOT</bcp14> issue certificates for any FQDN the Relevant RRSet for that FQDN contains a CAA critical Property for an unknown or unsupported Property Tag.</t> <t>Note that according to the conventions set out in <xref target="RFC1035" format="default"/>, bit 0 is the Most Significant Bit and bit 7 is the Least Significant Bit. Thus, the Flags value 1 means that bit 7 is set while a value of 128 means that bit 0 is set according to this convention.</t> <t>All other bit positions are reserved for future use.</t> <t>To ensure compatibility with future extensions to CAA, DNS records compliant with this version of the CAA specificationMUST<bcp14>MUST</bcp14> clear (set to "0") all reserved flags bits. Applications that interpret CAA recordsMUST<bcp14>MUST</bcp14> ignore the value of all reserved flag bits.</t> <t>Tag Length: A single octet containing an unsigned integer specifying the tag length in octets. The tag lengthMUST<bcp14>MUST</bcp14> be at least 1.</t> <t>Tag: The Property identifier, a sequence of US-ASCII characters.</t> <t>TagsMAY<bcp14>MAY</bcp14> contain US-ASCII characters 'a' through 'z', 'A' through 'Z', and the numbers 0 through 9. TagsMUST NOT<bcp14>MUST NOT</bcp14> contain any other characters. Matching of tags is case insensitive.</t> <t>Tags submitted for registration by IANAMUST NOT<bcp14>MUST NOT</bcp14> contain any characters other than the (lowercase) US-ASCII characters 'a' through 'z' and the numbers 0 through 9.</t> <t>Value: A sequence of octets representing the Property Value. Property Values are encoded as binary values andMAY<bcp14>MAY</bcp14> employ sub-formats.</t> <t>The length of the value field is specified implicitly as the remaining length of the enclosing RDATA section.</t> <section anchor="canonical-presentation-format" numbered="true" toc="default"> <name>Canonical Presentation Format</name> <t>The canonical presentation format of the CAA record is:</t><t>CAA <flags> <tag> <value></t><artwork name="" type="" align="left" alt=""><![CDATA[ CAA <flags> <tag> <value> ]]></artwork> <t>Where:</t> <t>Flags: Is an unsigned integer between 0 and 255.</t> <t>Tag: Is a non-zero-length sequence of US-ASCII letters and numbers in lower case.</t> <t>Value: The value field, expressed as a contiguous set of characters without interior spaces, or as a quoted string. See the <character-string> format specified in <xref target="RFC1035"format="default"/>, Section 5.1,sectionFormat="comma" section="5.1"/>, but note that the value field contains no length byte and is not limited to 255 characters.</t> </section> </section> <section anchor="caa-issue-property" numbered="true" toc="default"> <name>CAA issue Property</name> <t>If the issue Property Tag is present in the Relevant RRSet for aFully-QualifiedFully Qualified Domain Name, it is a request that Issuers</t> <ol spacing="normal" type="1"> <li>Perform CAA issue restriction processing for the FQDN, and</li> <li>Grant authorization to issue certificates containing that FQDN to the holder of the issuer-domain-name or a party acting under the explicit authority of the holder of the issuer-domain-name.</li> </ol> <t>The CAA issue Property Value has the following sub-syntax (specified in ABNF as per <xref target="RFC5234" format="default"/>).</t><artwork name="" type="" align="left" alt=""><![CDATA[<sourcecode name="CAA Issue Property Value Sub-syntax" type="abnf"><![CDATA[ issue-value = *WSP [issuer-domain-name *WSP] [";" *WSP [parameters *WSP]] issuer-domain-name = label *("." label) label = (ALPHA / DIGIT) *( *("-") (ALPHA / DIGIT)) parameters = (parameter *WSP ";" *WSP parameters) / parameter parameter = tag *WSP "=" *WSP value tag = (ALPHA / DIGIT) *( *("-") (ALPHA / DIGIT)) value = *(%x21-3A / %x3C-7E)]]></artwork>]]></sourcecode> <t>For consistency with other aspects of DNS administration, FQDN values are specified in letter-digit-hyphen Label (LDH-Label) form.</t> <t>The following CAA record set requests that no certificates be issued for the FQDN 'certs.example.com' by any Issuer other than ca1.example.net or ca2.example.org.</t> <artwork name="" type="" align="left" alt=""><![CDATA[ certs.example.com CAA 0 issue "ca1.example.net" certs.example.com CAA 0 issue "ca2.example.org" ]]></artwork> <t>Because the presence of an issue Property Tag in the Relevant RRSet for an FQDN restricts issuance, FQDN owners can use an issue Property Tag with no issuer-domain-name to request no issuance.</t> <t>For example, the following RRSet requests that no certificates be issued for the FQDN 'nocerts.example.com' by any Issuer.</t> <artwork name="" type="" align="left" alt=""><![CDATA[ nocerts.example.com CAA 0 issue ";" ]]></artwork> <t>An issue Property Tag where the issue-value does not match the ABNF grammarMUST<bcp14>MUST</bcp14> be treated the same as one specifying an empty issuer-domain-name. For example, the following malformed CAA RRSet forbids issuance:</t> <artwork name="" type="" align="left" alt=""><![CDATA[ malformed.example.com CAA 0 issue "%%%%%" ]]></artwork> <t>CAA authorizations are additive; thus, the result of specifying both an empty issuer-domain-name and a non-empty issuer-domain-name is the same as specifying just the non-empty issuer-domain-name.</t> <t>An IssuerMAY<bcp14>MAY</bcp14> choose to specify parameters that further constrain the issue of certificates by that Issuer, for example, specifying that certificates are to be subject to specific validation polices, billed to certain accounts, or issued under specific trust anchors.</t> <t>For example, if ca1.example.net has requested its customer accountable.example.com to specify their account number "230123" in each of the customer's CAA records using the (CA-defined) "account" parameter, it would look like this:</t> <artwork name="" type="" align="left" alt=""><![CDATA[ accountable.example.com CAA 0 issue "ca1.example.net; account=230123" ]]></artwork> <t>The semantics of parameters to the issue Property Tag are determined by the Issuer alone.</t> </section> <section anchor="caa-issuewild-property" numbered="true" toc="default"> <name>CAA issuewild Property</name> <t>The issuewild Property Tag has the same syntax and semantics as the issue Property Tag except that it only grants authorization to issue certificates that specify a Wildcard Domain Name and issuewild properties take precedence over issue properties when specified. Specifically:</t> <t>issuewild propertiesMUST<bcp14>MUST</bcp14> be ignored when processing a request for aFully-QualifiedFully Qualified Domain Name that is not a Wildcard Domain Name.</t> <t>If at least one issuewild Property is specified in the Relevant RRSet for a Wildcard Domain Name, all issue propertiesMUST<bcp14>MUST</bcp14> be ignored when processing a request for that Wildcard Domain Name.</t> <t>For example, the following RRSet requests that <em>only</em> ca1.example.net issue certificates for "wild.example.com" or "sub.wild.example.com", and that <em>only</em> ca2.example.org issue certificates for "*.wild.example.com" or "*.sub.wild.example.com). Note that this presumes there are no CAA RRs for sub.wild.example.com.</t> <artwork name="" type="" align="left" alt=""><![CDATA[ wild.example.com CAA 0 issue "ca1.example.net" wild.example.com CAA 0 issuewild "ca2.example.org" ]]></artwork> <t>The following RRSet requests that <em>only</em> ca1.example.net issue certificates for "wild2.example.com", "*.wild2.example.com" or "*.sub.wild2.example.com".</t> <artwork name="" type="" align="left" alt=""><![CDATA[ wild2.example.com CAA 0 issue "ca1.example.net" ]]></artwork> <t>The following RRSet requests that <em>only</em> ca2.example.org issue certificates for "*.wild3.example.com" or "*.sub.wild3.example.com". It does not permit any Issuer to issue for "wild3.example.com" or "sub.wild3.example.com".</t> <artwork name="" type="" align="left" alt=""><![CDATA[ wild3.example.com CAA 0 issuewild "ca2.example.org" wild3.example.com CAA 0 issue ";" ]]></artwork> <t>The following RRSet requests that <em>only</em> ca2.example.org issue certificates for "*.wild3.example.com" or "*.sub.wild3.example.com". It permits any Issuer to issue for "wild3.example.com" or "sub.wild3.example.com".</t> <artwork name="" type="" align="left" alt=""><![CDATA[ wild3.example.com CAA 0 issuewild "ca2.example.org" ]]></artwork> </section> <section anchor="caa-iodef-property" numbered="true" toc="default"> <name>CAA iodef Property</name> <t>The iodef Property specifies a means of reporting certificate issue requests or cases of certificate issue for domains for which the Property appears in the Relevant RRSet, when those requests or issuances violate the security policy of the Issuer or the FQDN holder.</t> <t>The Incident Object Description Exchange Format (IODEF) <xref target="RFC7970" format="default"/> is used to present the incident report in machine-readable form.</t> <t>The iodef Property Tag takes a URL as its Property Value. The URL scheme type determines the method used for reporting:</t><t>mailto:<ul> <li>mailto: The IODEF incident report is reported as a MIME email attachment to an SMTP email that is submitted to the mail address specified. The mail message sentSHOULD<bcp14>SHOULD</bcp14> contain a brief text message to alert the recipient to the nature of theattachment.</t> <t>httpattachment.</li> <li>http or https: The IODEF report is submitted as a Web service request to the HTTP address specified using the protocol specified in <xref target="RFC6546"format="default"/>.</t>format="default"/>.</li> </ul> <t>These are the only supported URL schemes.</t> <t>The following RRSet specifies that reports may be made by means of email with the IODEF data as an attachment, a Web service <xref target="RFC6546" format="default"/>, or both:</t> <artwork name="" type="" align="left" alt=""><![CDATA[ report.example.com CAA 0 issue "ca1.example.net" report.example.com CAA 0 iodef "mailto:security@example.com" report.example.com CAA 0 iodef "http://iodef.example.com/" ]]></artwork> </section> <section anchor="critical-flag" numbered="true" toc="default"> <name>Critical Flag</name> <t>The critical flag is intended to permit future versions of CAA to introduce new semantics thatMUST<bcp14>MUST</bcp14> be understood for correct processing of the record, preventing conforming CAs that do not recognize the new semantics from issuing certificates for the indicated FQDNs.</t> <t>In the following example, the Property with a Property Tag of 'tbs' is flagged as critical. Neither the ca1.example.net CA nor any other Issuer is authorized to issue for "new.example.com" (or any other domains for which this is the Relevant RRSet) unless the Issuer has implemented the processing rules for the 'tbs' Property Tag.</t> <artwork name="" type="" align="left" alt=""><![CDATA[ new.example.com CAA 0 issue "ca1.example.net" new.example.com CAA 128 tbs "Unknown" ]]></artwork> </section> </section> <section anchor="security-considerations" numbered="true" toc="default"> <name>Security Considerations</name> <t>CAA records assert a security policy that the holder of an FDQN wishes to be observed by Issuers. The effectiveness of CAA records as an access control mechanism is thus dependent on observance of CAA constraints by Issuers.</t> <t>The objective of the CAA record properties described in this document is to reduce the risk of certificate mis-issue rather than avoid reliance on a certificate that has been mis-issued. DANE <xref target="RFC6698" format="default"/> describes a mechanism for avoiding reliance on mis-issued certificates.</t> <section anchor="use-of-dns-security" numbered="true" toc="default"> <name>Use of DNS Security</name> <t>Use of DNSSEC to authenticate CAA RRs is stronglyRECOMMENDED<bcp14>RECOMMENDED</bcp14> but not required. An IssuerMUST NOT<bcp14>MUST NOT</bcp14> issue certificates if doing so would conflict with the Relevant RRSet, irrespective of whether the corresponding DNS records are signed.</t> <t>DNSSEC provides a proof of non-existence for both DNSFully-QualifiedFully Qualified Domain Names and RRSets within FQDNs. DNSSEC verification thus enables an Issuer to determine if the answer to a CAA record query is empty because the RRSet is empty or if it is non-empty but the response has been suppressed.</t> <t>Use of DNSSEC allows an Issuer to acquire and archive a proof that they were authorized to issue certificates for the FQDN. Verification of such archives may be an audit requirement to verify CAA record processing compliance. Publication of such archives may be a transparency requirement to verify CAA record processing compliance.</t> </section> <section anchor="non-compliance-by-certification-authority" numbered="true" toc="default"> <name>Non-Compliance by Certification Authority</name> <t>CAA records offer CAs a cost-effective means of mitigating the risk of certificate mis-issue: the cost of implementing CAA checks is very small and the potential costs of a mis-issue event include the removal of an embedded trust anchor.</t> </section> <section anchor="mis-issue-by-authorized-certification-authority" numbered="true" toc="default"> <name>Mis-Issue by Authorized Certification Authority</name> <t>Use of CAA records does not prevent mis-issue by an authorized Certification Authority, i.e., a CA that is authorized to issue certificates for the FQDN in question by CAA records.</t> <t>FQDN holdersSHOULD<bcp14>SHOULD</bcp14> verify that the CAs they authorize to issue certificates for their FQDNs employ appropriate controls to ensure that certificates are issued only to authorized parties within their organization.</t> <t>Such controls are most appropriately determined by the FQDN holder and the authorized CA(s) directly and are thus out of scope of this document.</t> </section> <section anchor="suppression-or-spoofing-of-caa-records" numbered="true" toc="default"> <name>Suppression or Spoofing of CAA Records</name> <t>Suppression of the CAA record or insertion of a bogus CAA record could enable an attacker to obtain a certificate from an Issuer that was not authorized to issue for an affected FQDN.</t> <t>Where possible, IssuersSHOULD<bcp14>SHOULD</bcp14> perform DNSSEC validation to detect missing or modified CAA record sets.</t> <t>In cases where DNSSEC is not deployed for a corresponding FQDN, an IssuerSHOULD<bcp14>SHOULD</bcp14> attempt to mitigate this risk by employing appropriate DNS security controls. For example, all portions of the DNS lookup processSHOULD<bcp14>SHOULD</bcp14> be performed against the authoritative name server. Data cached by third partiesMUST NOT<bcp14>MUST NOT</bcp14> be relied on as the sole source of DNS CAA information butMAY<bcp14>MAY</bcp14> be used to support additional anti-spoofing or anti-suppression controls.</t> </section> <section anchor="denial-of-service" numbered="true" toc="default"> <name>Denial of Service</name> <t>Introduction of a malformed or malicious CAA RR could in theory enable a Denial-of-Service (DoS) attack. This could happen by modification of authoritative DNS records or by spoofing inflight DNS responses.</t> <t>This specific threat is not considered to add significantly to the risk of running an insecure DNS service.</t> <t>An attacker could, in principle, perform a DoS attack against an Issuer by requesting a certificate with a maliciously long DNS name. In practice, the DNS protocol imposes a maximum name length and CAA processing does not exacerbate the existing need to mitigate DoS attacks to any meaningful degree.</t> </section> <section anchor="abuse-of-the-critical-flag" numbered="true" toc="default"> <name>Abuse of the Critical Flag</name> <t>A Certification Authority could make use of the critical flag to trick customers into publishing records that prevent competing Certification Authorities from issuing certificates even though the customer intends to authorize multiple providers. This could happen if the customers were setting CAA records based on data provided by the CA rather than generating those records themselves.</t> <t>In practice, such an attack would be of minimal effect since any competent competitor that found itself unable to issue certificates due to lack of support for a Property marked critical should investigate the cause and report the reason to the customer. The customer will thus discover that they had been deceived.</t> </section> </section> <section anchor="deployment-considerations" numbered="true" toc="default"> <name>Deployment Considerations</name> <t>A CA implementing CAA may find that they receive errors looking up CAA records. The following are some common causes of such errors, so that CAs may provide guidance to their subscribers on fixing the underlying problems.</t> <section anchor="blocked-queries-or-responses" numbered="true" toc="default"> <name>Blocked Queries or Responses</name> <t>Some middleboxes, in particular anti-DDoS appliances, may be configured to drop DNS packets of unknown types, or may start dropping such packets when they consider themselves under attack. This generally manifests as a timed-out DNS query, or a SERVFAIL at a local recursive resolver.</t> </section> <section anchor="rejected-queries-and-malformed-responses" numbered="true" toc="default"> <name>Rejected Queries and Malformed Responses</name> <t>Some authoritative nameservers respond with REJECTED or NOTIMP when queried for a Resource Record type they do not recognize. At least one authoritative resolver produces a malformed response (with the QR bit set to 0) when queried for unknown Resource Record types. Per RFC 1034, the correct response for unknown Resource Record types is NOERROR.</t> </section> <section anchor="delegation-to-private-nameservers" numbered="true" toc="default"> <name>Delegation to Private Nameservers</name> <t>Some FQDN administrators make the contents of a subdomain unresolvable on the public Internet by delegating that subdomain to a nameserver whose IP address is private. A CA processing CAA records for such subdomains will receive SERVFAIL from its recursive resolver. The CAMAY<bcp14>MAY</bcp14> interpret that as preventing issuance. FQDN administrators wishing to issue certificates for private FQDNsSHOULD<bcp14>SHOULD</bcp14> use split-horizon DNS with a publicly available nameserver, so that CAs can receive a valid, empty CAA response for those FQDNs.</t> </section> <section anchor="bogus-dnssec-responses" numbered="true" toc="default"> <name>Bogus DNSSEC Responses</name> <t>Queries for CAA Resource Records are different from most DNS RR types, because a signed, empty response to a query for CAA RRs is meaningfully different from a bogus response. A signed, empty response indicates that there is definitely no CAA policy set at a given label. A bogus response may mean either a misconfigured zone, or an attacker tampering with records. DNSSEC implementations may have bugs with signatures on empty responses that go unnoticed, because for more common Resource Record types like A and AAAA, the difference to an end user between empty and bogus is irrelevant; they both mean a site is unavailable.</t> <t>In particular, at least two authoritative resolvers that implement live signing had bugs when returning empty Resource Record sets for DNSSEC-signed zones, in combination with mixed-case queries. Mixed-case queries, also known as DNS 0x20, are used by some recursive resolvers to increase resilience against DNS poisoning attacks. DNSSEC-signing authoritative resolvers are expected to copy the same capitalization from the query into their ANSWER section, but sign the response as if they had used all lowercase. In particular, PowerDNS versions prior to 4.0.4 had this bug.</t> </section> </section> <section anchor="differences-versus-rfc6844" numbered="true" toc="default"> <name>Differences versusRFC6844</name>RFC 6844</name> <t>This document obsoletesRFC6844.RFC 6844. The most important change is to the Certification Authority Processing section.RFC6844RFC 6844 specified an algorithm that performed DNS tree-climbing not only on the FQDN being processed, but also on all CNAMEs and DNAMEs encountered along the way. This made the processing algorithm very inefficient when used on FQDNs that utilize many CNAMEs, and would have made it difficult for hosting providers to set CAA policies on their own FQDNs without setting potentially unwanted CAA policies on their customers' FQDNs. This document specifies a simplified processing algorithm that only performs tree climbing on the FQDN being processed, and leaves processing of CNAMEs and DNAMEs up to the CA's recursive resolver.</t> <t>This document also includes a "Deployment Considerations" section (<xref target="deployment-considerations"/>) detailing experience gained with practical deployment of CAA enforcement among CAs in the WebPKI.</t> <t>This document clarifies the ABNF grammar for the issue and issuewild tags and resolves some inconsistencies with the document text. In particular, it specifies that parameters are separated with semicolons. It also allows hyphens in Property Tags.</t> <t>This document also clarifies processing of a CAA RRset that is not empty, but contains no issue orissuewild tags.</t>issuewild tags.</t> <t>This document removes the section titled "The CAA RR Type," merging it with "Mechanism" because the definitions were mainly duplicates. It moves the "Use of DNS Security" section (now <xref target="use-of-dns-security"/>) into the SecurityConsiderations.Considerations section (<xref target="security-considerations"/>). It renames "Certification Authority Processing" to "Relevant Resource RecordSet,"Set" (<xref target="relevant-resource-record-set"/>) and emphasizes the use of that term to more clearly define which domains are affected by a given RRset.</t> </section> <section anchor="iana-considerations" numbered="true" toc="default"> <name>IANA Considerations</name> <t>IANA is requested to add[[[ RFC Editor: Please replace withthisRFC ]]]document as a reference for the Certification Authority Restriction Flags and Certification Authority Restriction Properties registries, and update references to <xref target="RFC6844" format="default"/> within those registries to refer to[[[ RFC Editor: Please replace withthisRFC ]]].document. IANA is also requested to update the CAA TYPE in the DNS Parameters registry with a reference to[[[ RFC Editor: Please replace with this RFC ]]].</t> </section> <section anchor="acknowledgements" numbered="true" toc="default"> <name>Acknowledgements</name> <t>The authors would like to thank the following people who contributed to the design and documentation ofthiswork item: Corey Bonnell, Chris Evans, Stephen Farrell, Jeff Hodges, Paul Hoffman, Tim Hollebeek, Stephen Kent, Adam Langley, Ben Laurie, James Manger, Chris Palmer, Scott Schmit, Sean Turner, and Ben Wilson.</t>document.</t> </section> </middle> <back> <references> <name>References</name> <references> <name>Normative References</name> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6698.xml"/> <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.2119.xml"/> <referenceanchor="RFC6698" target="https://www.rfc-editor.org/info/rfc6698">anchor="RFC8174" target="https://www.rfc-editor.org/info/rfc8174"> <front><title>The DNS-Based Authentication<title>Ambiguity ofNamed Entities (DANE) Transport Layer Security (TLS) Protocol: TLSA</title>Uppercase vs Lowercase in RFC 2119 Key Words</title> <seriesInfo name="DOI"value="10.17487/RFC6698"/>value="10.17487/RFC8174"/> <seriesInfo name="RFC"value="6698"/> <author initials="P." surname="Hoffman" fullname="P. Hoffman"> <organization/> </author>value="8174"/> <seriesInfo name="BCP" value="14"/> <authorinitials="J." surname="Schlyter" fullname="J. Schlyter">initials="B." surname="Leiba" fullname="B. Leiba"> <organization/> </author> <dateyear="2012" month="August"/> <abstract> <t>Encrypted communication on the Internet often uses Transport Layer Security (TLS), which depends on third parties to certify the keys used. This document improves on that situation by enabling the administrators of domain names to specify the keys used in that domain's TLS servers. This requires matching improvements in TLS client software, but no change in TLS server software. [STANDARDS-TRACK]</t> </abstract>year="2017" month="May"/> </front> </reference> <referenceanchor="RFC2119" target="https://www.rfc-editor.org/info/rfc2119">anchor="RFC5280" target="https://www.rfc-editor.org/info/rfc5280"> <front><title>Key words for use in RFCs to Indicate Requirement Levels</title><title>Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile</title> <seriesInfo name="DOI"value="10.17487/RFC2119"/>value="10.17487/RFC5280"/> <seriesInfo name="RFC"value="2119"/> <seriesInfo name="BCP" value="14"/>value="5280"/> <authorinitials="S." surname="Bradner" fullname="S. Bradner"> <organization/> </author> <date year="1997" month="March"/> <abstract> <t>In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.</t> </abstract> </front> </reference> <reference anchor="RFC8174" target="https://www.rfc-editor.org/info/rfc8174"> <front> <title>Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words</title> <seriesInfo name="DOI" value="10.17487/RFC8174"/> <seriesInfo name="RFC" value="8174"/> <seriesInfo name="BCP" value="14"/> <author initials="B." surname="Leiba" fullname="B. Leiba"> <organization/> </author> <date year="2017" month="May"/> <abstract> <t>RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings.</t> </abstract> </front> </reference> <reference anchor="RFC5280" target="https://www.rfc-editor.org/info/rfc5280"> <front> <title>Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile</title> <seriesInfo name="DOI" value="10.17487/RFC5280"/> <seriesInfo name="RFC" value="5280"/> <author initials="D." surname="Cooper" fullname="D. Cooper">initials="D." surname="Cooper" fullname="D. Cooper"> <organization/> </author> <author initials="S." surname="Santesson" fullname="S. Santesson"> <organization/> </author> <author initials="S." surname="Farrell" fullname="S. Farrell"> <organization/> </author> <author initials="S." surname="Boeyen" fullname="S. Boeyen"> <organization/> </author> <author initials="R." surname="Housley" fullname="R. Housley"> <organization/> </author> <author initials="W." surname="Polk" fullname="W. Polk"> <organization/> </author> <date year="2008" month="May"/><abstract> <t>This memo profiles the X.509 v3 certificate and X.509 v2 certificate revocation list (CRL) for use in the Internet. An overview of this approach and model is provided as an introduction. The X.509 v3 certificate format is described in detail, with additional information regarding the format and semantics of Internet name forms. Standard certificate extensions are described and two Internet-specific extensions are defined. A set of required certificate extensions is specified. The X.509 v2 CRL format is described in detail along with standard and Internet-specific extensions. An algorithm for X.509 certification path validation is described. An ASN.1 module and examples are provided in the appendices. [STANDARDS-TRACK]</t> </abstract></front> </reference> <reference anchor="RFC1034" target="https://www.rfc-editor.org/info/rfc1034"> <front> <title>Domain names - concepts and facilities</title> <seriesInfo name="DOI" value="10.17487/RFC1034"/> <seriesInfo name="RFC" value="1034"/> <seriesInfo name="STD" value="13"/> <author initials="P.V." surname="Mockapetris" fullname="P.V. Mockapetris"> <organization/> </author> <date year="1987" month="November"/><abstract> <t>This RFC is the revised basic definition of The Domain Name System. It obsoletes RFC-882. This memo describes the domain style names and their used for host address look up and electronic mail forwarding. It discusses the clients and servers in the domain name system and the protocol used between them.</t> </abstract></front> </reference> <reference anchor="RFC1035" target="https://www.rfc-editor.org/info/rfc1035"> <front> <title>Domain names - implementation and specification</title> <seriesInfo name="DOI" value="10.17487/RFC1035"/> <seriesInfo name="RFC" value="1035"/> <seriesInfo name="STD" value="13"/> <author initials="P.V." surname="Mockapetris" fullname="P.V. Mockapetris"> <organization/> </author> <date year="1987" month="November"/><abstract> <t>This RFC is the revised specification of the protocol and format used in the implementation of the Domain Name System. It obsoletes RFC-883. This memo documents the details of the domain name client - server communication.</t> </abstract></front> </reference> <reference anchor="RFC4033" target="https://www.rfc-editor.org/info/rfc4033"> <front> <title>DNS Security Introduction and Requirements</title> <seriesInfo name="DOI" value="10.17487/RFC4033"/> <seriesInfo name="RFC" value="4033"/> <author initials="R." surname="Arends" fullname="R. Arends"> <organization/></author> <author initials="R." surname="Austein" fullname="R. Austein"> <organization/> </author> <author initials="M." surname="Larson" fullname="M. Larson"> <organization/> </author> <author initials="D." surname="Massey" fullname="D. Massey"> <organization/> </author> <author initials="S." surname="Rose" fullname="S. Rose"> <organization/> </author> <date year="2005" month="March"/> <abstract> <t>The Domain Name System Security Extensions (DNSSEC) add data origin authentication and data integrity to the Domain Name System. This document introduces these extensions and describes their capabilities and limitations. This document also discusses the services that the DNS security extensions do and do not provide. Last, this document describes the interrelationships between the documents that collectively describe DNSSEC. [STANDARDS-TRACK]</t> </abstract></author> <author initials="R." surname="Austein" fullname="R. Austein"> <organization/> </author> <author initials="M." surname="Larson" fullname="M. Larson"> <organization/> </author> <author initials="D." surname="Massey" fullname="D. Massey"> <organization/> </author> <author initials="S." surname="Rose" fullname="S. Rose"> <organization/> </author> <date year="2005" month="March"/> </front> </reference> <reference anchor="RFC4034" target="https://www.rfc-editor.org/info/rfc4034"> <front> <title>Resource Records for the DNS Security Extensions</title> <seriesInfo name="DOI" value="10.17487/RFC4034"/> <seriesInfo name="RFC" value="4034"/> <author initials="R." surname="Arends" fullname="R. Arends"> <organization/> </author> <author initials="R." surname="Austein" fullname="R. Austein"> <organization/> </author> <author initials="M." surname="Larson" fullname="M. Larson"> <organization/> </author> <author initials="D." surname="Massey" fullname="D. Massey"> <organization/> </author> <author initials="S." surname="Rose" fullname="S. Rose"> <organization/> </author> <date year="2005" month="March"/><abstract> <t>This document is part of a family of documents that describe the DNS Security Extensions (DNSSEC). The DNS Security Extensions are a collection of resource records and protocol modifications that provide source authentication for the DNS. This document defines the public key (DNSKEY), delegation signer (DS), resource record digital signature (RRSIG), and authenticated denial of existence (NSEC) resource records. The purpose and format of each resource record is described in detail, and an example of each resource record is given. </t> <t> This document obsoletes RFC 2535 and incorporates changes from all updates to RFC 2535. [STANDARDS-TRACK]</t> </abstract></front> </reference> <reference anchor="RFC4035" target="https://www.rfc-editor.org/info/rfc4035"> <front> <title>Protocol Modifications for the DNS Security Extensions</title> <seriesInfo name="DOI" value="10.17487/RFC4035"/> <seriesInfo name="RFC" value="4035"/> <author initials="R." surname="Arends" fullname="R. Arends"> <organization/> </author> <author initials="R." surname="Austein" fullname="R. Austein"> <organization/> </author> <author initials="M." surname="Larson" fullname="M. Larson"> <organization/> </author> <author initials="D." surname="Massey" fullname="D. Massey"> <organization/> </author> <author initials="S." surname="Rose" fullname="S. Rose"> <organization/> </author> <date year="2005" month="March"/><abstract> <t>This document is part of a family of documents that describe the DNS Security Extensions (DNSSEC). The DNS Security Extensions are a collection of new resource records and protocol modifications that add data origin authentication and data integrity to the DNS. This document describes the DNSSEC protocol modifications. This document defines the concept of a signed zone, along with the requirements for serving and resolving by using DNSSEC. These techniques allow a security-aware resolver to authenticate both DNS resource records and authoritative DNS error indications. </t> <t> This document obsoletes RFC 2535 and incorporates changes from all updates to RFC 2535. [STANDARDS-TRACK]</t> </abstract></front> </reference> <reference anchor="RFC5155" target="https://www.rfc-editor.org/info/rfc5155"> <front> <title>DNS Security (DNSSEC) Hashed Authenticated Denial of Existence</title> <seriesInfo name="DOI" value="10.17487/RFC5155"/> <seriesInfo name="RFC" value="5155"/> <author initials="B." surname="Laurie" fullname="B. Laurie"> <organization/> </author> <author initials="G." surname="Sisson" fullname="G. Sisson"> <organization/> </author> <author initials="R." surname="Arends" fullname="R. Arends"> <organization/> </author> <author initials="D." surname="Blacka" fullname="D. Blacka"> <organization/> </author> <date year="2008" month="March"/><abstract> <t>The Domain Name System Security (DNSSEC) Extensions introduced the NSEC resource record (RR) for authenticated denial of existence. This document introduces an alternative resource record, NSEC3, which similarly provides authenticated denial of existence. However, it also provides measures against zone enumeration and permits gradual expansion of delegation-centric zones. [STANDARDS-TRACK]</t> </abstract></front> </reference> <reference anchor="RFC2181" target="https://www.rfc-editor.org/info/rfc2181"> <front> <title>Clarifications to the DNS Specification</title> <seriesInfo name="DOI" value="10.17487/RFC2181"/> <seriesInfo name="RFC" value="2181"/> <author initials="R." surname="Elz" fullname="R. Elz"> <organization/> </author> <author initials="R." surname="Bush" fullname="R. Bush"> <organization/> </author> <date year="1997" month="July"/><abstract> <t>This document considers some areas that have been identified as problems with the specification of the Domain Name System, and proposes remedies for the defects identified. [STANDARDS-TRACK]</t> </abstract></front> </reference> <reference anchor="RFC5234" target="https://www.rfc-editor.org/info/rfc5234"> <front> <title>Augmented BNF for Syntax Specifications: ABNF</title> <seriesInfo name="DOI" value="10.17487/RFC5234"/> <seriesInfo name="RFC" value="5234"/> <seriesInfo name="STD" value="68"/> <author initials="D." surname="Crocker" fullname="D. Crocker" role="editor"> <organization/> </author> <author initials="P." surname="Overell" fullname="P. Overell"> <organization/> </author> <date year="2008"month="January"/> <abstract> <t>Internet technical specifications often need to define a formal syntax. Over the years, a modified version of Backus-Naur Form (BNF), called Augmented BNF (ABNF), has been popular among many Internet specifications. The current specification documents ABNF. It balances compactness and simplicity with reasonable representational power. The differences between standard BNF and ABNF involve naming rules, repetition, alternatives, order-independence, and value ranges. This specification also supplies additional rule definitions and encoding for a core lexical analyzer of the type common to several Internet specifications. [STANDARDS-TRACK]</t> </abstract>month="January"/> </front> </reference> <reference anchor="RFC7970" target="https://www.rfc-editor.org/info/rfc7970"> <front> <title>The Incident Object Description Exchange Format Version 2</title> <seriesInfo name="DOI" value="10.17487/RFC7970"/> <seriesInfo name="RFC" value="7970"/> <author initials="R." surname="Danyliw" fullname="R. Danyliw"> <organization/> </author> <date year="2016" month="November"/><abstract> <t>The Incident Object Description Exchange Format (IODEF) defines a data representation for security incident reports and indicators commonly exchanged by operational security teams for mitigation and watch and warning. This document describes an updated information model for the IODEF and provides an associated data model specified with the XML schema. This new information and data model obsoletes RFCs 5070 and 6685.</t> </abstract></front> </reference> <reference anchor="RFC6546" target="https://www.rfc-editor.org/info/rfc6546"> <front> <title>Transport of Real-time Inter-network Defense (RID) Messages over HTTP/TLS</title> <seriesInfo name="DOI" value="10.17487/RFC6546"/> <seriesInfo name="RFC" value="6546"/> <author initials="B." surname="Trammell" fullname="B. Trammell"> <organization/> </author> <date year="2012" month="April"/><abstract> <t>The Incident Object Description Exchange Format (IODEF) defines a common XML format for document exchange, and Real-time Inter-network Defense (RID) defines extensions to IODEF intended for the cooperative handling of security incidents within consortia of network operators and enterprises. This document specifies an application-layer protocol for RID based upon the passing of RID messages over HTTP/TLS. [STANDARDS-TRACK]</t> </abstract></front> </reference> <reference anchor="RFC6844" target="https://www.rfc-editor.org/info/rfc6844"> <front> <title>DNS Certification Authority Authorization (CAA) Resource Record</title> <seriesInfo name="DOI" value="10.17487/RFC6844"/> <seriesInfo name="RFC" value="6844"/> <author initials="P." surname="Hallam-Baker" fullname="P. Hallam-Baker"> <organization/> </author> <author initials="R." surname="Stradling" fullname="R. Stradling"> <organization/> </author> <date year="2013" month="January"/><abstract> <t>The Certification Authority Authorization (CAA) DNS Resource Record allows a DNS domain name holder to specify one or more Certification Authorities (CAs) authorized to issue certificates for that domain. CAA Resource Records allow a public Certification Authority to implement additional controls to reduce the risk of unintended certificate mis-issue. This document defines the syntax of the CAA record and rules for processing CAA records by certificate issuers. [STANDARDS-TRACK]</t> </abstract></front> </reference> </references> <references> <name>Informative References</name> <reference anchor="RFC3647" target="https://www.rfc-editor.org/info/rfc3647"> <front> <title>Internet X.509 Public Key Infrastructure Certificate Policy and Certification Practices Framework</title> <seriesInfo name="DOI" value="10.17487/RFC3647"/> <seriesInfo name="RFC" value="3647"/> <author initials="S." surname="Chokhani" fullname="S. Chokhani"> <organization/> </author> <author initials="W." surname="Ford" fullname="W. Ford"> <organization/> </author> <author initials="R." surname="Sabett" fullname="R. Sabett"> <organization/> </author> <author initials="C." surname="Merrill" fullname="C. Merrill"> <organization/> </author> <author initials="S." surname="Wu" fullname="S. Wu"> <organization/> </author> <date year="2003" month="November"/><abstract> <t>This document presents a framework</front> </reference> </references> </references> <section anchor="acknowledgements" numbered="false" toc="default"> <name>Acknowledgements</name> <t>The authors would like toassistthank thewriters of certificate policies or certification practice statements for participants within public key infrastructures, such as certification authorities, policy authorities, and communities of interest that wishfollowing people who contributed torely on certificates. In particular,theframework provides a comprehensive listdesign and documentation oftopics that potentially (at the writer's discretion) need to be covered in a certificate policy or a certification practice statement. This document supersedes RFC 2527.</t> </abstract> </front> </reference> </references> </references>this work item: Corey Bonnell, Chris Evans, Stephen Farrell, Jeff Hodges, Paul Hoffman, Tim Hollebeek, Stephen Kent, Adam Langley, Ben Laurie, James Manger, Chris Palmer, Scott Schmit, Sean Turner, and Ben Wilson.</t> </section> </back><!-- ##markdown-source: H4sIAGdw8FwAA8096XLjxpn/+yl66cpKckha0sz4kMtZcyRNLEejkSU5duJ1 bYFAk4QFAgwa1OFjKw+y+3J5kv2ubnSDoDzjPWqnUrEENPr4+rsvjUYj1eRN YY704OTiWh+buslneZo0eVXqybpZVHXePLqffuTnu8eTyZ6+MrZa16mBH9Kq zgYqmU5rc3ek4a3KqrRMljBtViezZpSbZjYqkuXKjupZ+uHHz59Pc6tgGTOv 6scjbZtMVVNbFaYx9kjjAKVsk5TZvyVFVcI8j8aqVX6kv2uqdKhtVTe1mVn4 6XGJP3yvVEJ7PFJ6pDT8y0uY6HKsv0gKWHj0Mrk1Nb3gfV0u8qLIV5uvzTLJ iyO9wvefL+jtFF+O02oZzX011tdNnWRFXs6Dia+qaed5Vc+P9LVJm3xe6fMm G9NTBy15Ea5dV9PPLT/eWPVLOFE1my2TcjQps9rc22DtL5MUVu97T3s4N82O 1adlWj+umnDBH+wi+Rxgbw2/G8NwpdRoNIJtWjhM2ih1szDvhB+ITx0cUQDO 6t7qhF5mFaxe0tb1oioyU+um0nZl0nz2qOHWYdd6WdWdZZVbNjcWl7J7OpHl 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