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<front> <front>
<title abbrev="CAA">DNS Certification Authority Authorization (CAA) Resource Record</title> <title abbrev="CAA">DNS Certification Authority Authorization (CAA) Resource Record</title>
<seriesInfo name="RFC" value="8659"/>
<author initials="P." surname="Hallam-Baker" fullname="Phillip Hallam-Baker" > <author initials="P." surname="Hallam-Baker" fullname="Phillip Hallam-Baker" >
<organization></organization> <organization>Venture Cryptography</organization>
<address> <address>
<email>phill@hallambaker.com</email> <email>phill@hallambaker.com</email>
</address> </address>
</author> </author>
<author initials="R." surname="Stradling" fullname="Rob Stradling"> <author initials="R." surname="Stradling" fullname="Rob Stradling">
<organization abbrev="Sectigo">Sectigo Ltd.</organization> <organization abbrev="Sectigo">Sectigo Ltd.</organization>
<address> <address>
<email>rob@sectigo.com</email> <email>rob@sectigo.com</email>
</address> </address>
</author> </author>
<author initials="J." surname="Hoffman-Andrews" fullname="Jacob Hoffman-Andr ews"> <author initials="J." surname="Hoffman-Andrews" fullname="Jacob Hoffman-Andr ews">
<organization>Let's Encrypt</organization> <organization>Let's Encrypt</organization>
<address> <address>
<email>jsha@letsencrypt.org</email> <email>jsha@letsencrypt.org</email>
</address> </address>
</author> </author>
<date year="2019" month="November"/>
<keyword>certificate</keyword>
<keyword>ca</keyword>
<keyword>pki</keyword>
<keyword>issue</keyword>
<keyword>issuance</keyword>
<keyword>wildcard</keyword>
<date year="2019" month="May" day="30"/> <abstract>
<t>The Certification Authority Authorization (CAA) DNS Resource Record
<abstract>
<t>The Certification Authority Authorization (CAA) DNS Resource Record
allows a DNS domain name holder to specify one or more Certification allows a DNS domain name holder to specify one or more Certification
Authorities (CAs) authorized to issue certificates for that domain name. Authorities (CAs) authorized to issue certificates for that domain name.
CAA Resource Records allow a public Certification Authority to CAA Resource Records allow a public CA to
implement additional controls to reduce the risk of unintended implement additional controls to reduce the risk of unintended
certificate mis-issue. This document defines the syntax of the CAA certificate mis-issue. This document defines the syntax of the CAA
record and rules for processing CAA records by certificate issuers.</t> record and rules for processing CAA records by CAs.</t>
<t>This document obsoletes RFC 6844.</t>
<t>This document obsoletes RFC 6844.</t>
</abstract> </abstract>
</front> </front>
<middle> <middle>
<section anchor="introduction" numbered="true" toc="default">
<section anchor="introduction" title="Introduction"> <name>Introduction</name>
<t>The Certification Authority Authorization (CAA) DNS Resource Record
<t>The Certification Authority Authorization (CAA) DNS Resource Record
allows a DNS domain name holder to specify the Certification allows a DNS domain name holder to specify the Certification
Authorities (CAs) authorized to issue certificates for that domain name. Authorities (CAs) authorized to issue certificates for that domain name.
Publication of CAA Resource Records allows a public Certification Publication of CAA Resource Records allows a public CA to implement additional c
Authority to implement additional controls to reduce the risk of ontrols to reduce the risk of
unintended certificate mis-issue.</t> 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"/> certificat
e data. The distinction
between CAA and TLSA is that CAA records specify an
authorization control to be performed by a CA before
issuing a certificate and TLSA records specify a verification
control to be performed by a Relying Party after the certificate is
issued.
<t>Like the TLSA record defined in DNS-Based Authentication of Named </t>
Entities (DANE) <xref target="RFC6698"/>, CAA records are used as a part of a <t>Conformance with a published CAA record is a necessary, but not
mechanism for checking PKIX <xref target="RFC6698"/> certificate data. The dist sufficient, condition for the issuance of a certificate.</t>
inction <t>Criteria for the inclusion of embedded trust anchor certificates in
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 applications are outside the scope of this document. Typically, such
criteria require the CA to publish a Certification Practices Statement criteria require the CA to publish a Certification Practices Statement
(CPS) that specifies how the requirements of the Certificate Policy (CPS) that specifies how the requirements of the Certificate Policy
(CP) are achieved. It is also common for a CA to engage an (CP) are achieved. It is also common for a CA to engage an
independent third-party auditor to prepare an annual audit statement independent third-party auditor to prepare an annual audit statement
of its performance against its CPS.</t> of its performance against its CPS.</t>
<t>A set of CAA records describes only current grants of authority to
<t>A set of CAA records describes only current grants of authority to
issue certificates for the corresponding DNS domain name. Since issue certificates for the corresponding DNS domain name. Since
certificates are valid for a period of time, it is possible certificates are valid for a period of time, it is possible
that a certificate that is not conformant with the CAA records that a certificate that is not conformant with the CAA records
currently published was conformant with the CAA records published at currently published was conformant with the CAA records published at
the time that the certificate was issued. Relying parties MUST the time that the certificate was issued. Relying Parties <bcp14>MUST
NOT use CAA records as part of certificate validation.</t> NOT</bcp14> use CAA records as part of certificate validation.</t>
<t>CAA records <bcp14>MAY</bcp14> be used by Certificate Evaluators as a p
<t>CAA records MAY be used by Certificate Evaluators as a possible ossible
indicator of a security policy violation. Such use SHOULD take indicator of a security policy violation. Such use <bcp14>SHOULD</bcp14> take i
account of the possibility that published CAA records changed between nto
account the possibility that published CAA records changed between
the time a certificate was issued and the time at which the the time a certificate was issued and the time at which the
certificate was observed by the Certificate Evaluator.</t> certificate was observed by the Certificate Evaluator.</t>
</section>
</section> <section anchor="definitions" numbered="true" toc="default">
<section anchor="definitions" title="Definitions"> <name>Definitions</name>
<section anchor="requirements-language" numbered="true" toc="default">
<section anchor="requirements-language" title="Requirements Language"> <name>Requirements Language</name>
<t>The key words "<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>", "<bcp
<t>The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, 14>REQUIRED</bcp14>", "<bcp14>SHALL</bcp14>",
“SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “NOT RECOMMENDED”, “MAY”, and "<bcp14>SHALL NOT</bcp14>", "<bcp14>SHOULD</bcp14>", "<bcp14>SHOULD NOT</bcp14>"
“OPTIONAL” in this document are to be interpreted as described in , "<bcp14>RECOMMENDED</bcp14>",
BCP 14 <xref target="RFC2119"/> <xref target="RFC8174"/> when, and only when, th "<bcp14>NOT RECOMMENDED</bcp14>", "<bcp14>MAY</bcp14>", and "<bcp14>OPTIONAL</bc
ey appear in all p14>" in this document
capitals, as shown here.</t> are to be interpreted as described in BCP&nbsp;14
<xref target="RFC2119" format="default"/> <xref target="RFC8174" format="default
</section> "/> when,
<section anchor="defined-terms" title="Defined Terms"> and only when, they appear in all capitals, as shown here.</t>
</section>
<t>The following terms are used in this document:</t> <section anchor="defined-terms" numbered="true" toc="default">
<name>Defined Terms</name>
<t>Certificate: An X.509 Certificate, as specified in <xref target="RFC5280"/>. <t>The following terms are used in this document:</t>
</t> <dl>
<dt>Certificate:</dt><dd>An X.509 Certificate, as specified in <xref t
<t>Certificate Evaluator: A party other than a Relying Party that arget="RFC5280" format="default"/>.</dd>
<dt>Certificate Evaluator:</dt><dd>A party other than a Relying Party
that
evaluates the trustworthiness of certificates issued by evaluates the trustworthiness of certificates issued by
Certification Authorities.</t> Certification Authorities.</dd>
<dt>Certification Authority (CA):</dt><dd>An Issuer that issues certif
<t>Certification Authority (CA): An Issuer that issues certificates in icates in
accordance with a specified Certificate Policy.</t> accordance with a specified Certificate Policy.</dd>
<dt>Certificate Policy (CP):</dt><dd>Specifies the criteria that a CA
<t>Certificate Policy (CP): Specifies the criteria that a Certification undertakes to meet in its issue of certificates. See
Authority undertakes to meet in its issue of certificates. See <xref target="RFC3647" format="default"/>.</dd>
<xref target="RFC3647"/>.</t> <dt>Certification Practices Statement (CPS):</dt><dd>Specifies the mea
ns by
<t>Certification Practices Statement (CPS): Specifies the means by which the criteria of the CP are met. In most
which the criteria of the Certificate Policy are met. In most
cases, this will be the document against which the operations of cases, this will be the document against which the operations of
the Certification Authority are audited. See <xref target="RFC3647"/>.</t> the CA are audited. See <xref target="RFC3647" format="default"/>.</dd>
<dt>Domain Name:</dt><dd>The label assigned to a node in the Domain Na
<t>Domain Name: The label assigned to a node in the Domain Name System.</t> me System.</dd>
<dt>Domain Name System (DNS):</dt><dd>The Internet naming system speci
<t>Domain Name System (DNS): The Internet naming system specified in fied in
<xref target="RFC1034"/> and <xref target="RFC1035"/>.</t> <xref target="RFC1034" format="default"/> and <xref target="RFC1035" format="
default"/>.</dd>
<t>DNS Security (DNSSEC): Extensions to the DNS that provide <dt>DNS Security (DNSSEC):</dt><dd>Extensions to the DNS that provide
authentication services as specified in <xref target="RFC4033"/>, <xref targe authentication services as specified in <xref target="RFC4033" format="defaul
t="RFC4034"/>, t"/>, <xref target="RFC4034" format="default"/>,
<xref target="RFC4035"/>, <xref target="RFC5155"/>, and revisions.</t> <xref target="RFC4035" format="default"/>, <xref target="RFC5155" format="def
ault"/>, and
<t>Fully-Qualified Domain Name (FQDN): A Domain Name that includes the labels of any revisions to these specifications.</dd>
all <dt>Fully Qualified Domain Name (FQDN):</dt><dd>A domain name that inc
superior nodes in the Domain Name System.</t> ludes the labels of all
superior nodes in the DNS.</dd>
<t>Issuer: An entity that issues certificates. See <xref target="RFC5280"/>.</ <dt>Issuer:</dt><dd>An entity that issues certificates. See <xref tar
t> get="RFC5280" format="default"/>.</dd>
<dt>Property:</dt><dd>The tag-value portion of a CAA Resource Record.<
<t>Property: The tag-value portion of a CAA Resource Record.</t> /dd>
<dt>Property Tag:</dt><dd>The tag portion of a CAA Resource Record.</d
<t>Property Tag: The tag portion of a CAA Resource Record.</t> d>
<dt>Property Value:</dt><dd>The value portion of a CAA Resource Record
<t>Property Value: The value portion of a CAA Resource Record.</t> .</dd>
<dt>Relevant Resource Record Set (Relevant RRset):</dt><dd>A set of CA
<t>Resource Record (RR): A particular entry in the DNS including the A
Resource Records resulting
from applying the algorithm in <xref target="relevant-resource-record-set"
format="default"/> to a specific FQDN or Wildcard Domain Name.</dd>
<dt>Relying Party:</dt><dd>A party that makes use of an application wh
ose
operation depends on the use of a certificate for making a security
decision. See <xref target="RFC5280" format="default"/>.</dd>
<dt>Resource Record (RR):</dt><dd>A particular entry in the DNS, inclu
ding the
owner name, class, type, time to live, and data, as defined in owner name, class, type, time to live, and data, as defined in
<xref target="RFC1034"/> and <xref target="RFC2181"/>.</t> <xref target="RFC1034" format="default"/> and <xref target="RFC2181" format="
default"/>.</dd>
<t>Resource Record Set (RRSet): A set of Resource Records of a <dt>Resource Record Set (RRset):</dt><dd>A set of RRs of a
particular owner name, class, and type. The time to live on all 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 RRs within an RRset is always the same, but the data may be
different among RRs in the RRSet.</t> different among RRs in the RRset.</dd>
<dt>Wildcard Domain Name:</dt><dd>A domain name consisting of a single
<t>Relevant Resource Record Set (Relevant RRSet): A set of CAA Resource Records asterisk
resulting character followed by a single "full stop" character ("*.") followed
from applying the algorithm in Section 3 to a specific Fully-Qualified Domain by an FQDN.</dd>
Name or </dl>
Wildcard Domain Name.</t> </section>
</section>
<t>Relying Party: A party that makes use of an application whose <section anchor="relevant-resource-record-set" numbered="true" toc="default"
operation depends on use of a certificate for making a security >
decision. See <xref target="RFC5280"/>.</t> <name>Relevant Resource Record Set</name>
<t>Before issuing a certificate, a compliant CA <bcp14>MUST</bcp14> check
<t>Wildcard Domain Name: A Domain Name consisting of a single asterisk for
character followed by a single full stop character (“*.”) followed publication of a Relevant RRset. If such an RRset
by a Fully-Qualified Domain Name.</t> exists, a CA <bcp14>MUST&nbsp;NOT</bcp14> issue a certificate unless the CA
determines that either (1)&nbsp;the certificate request is consistent with
</section> the applicable CAA RRset or (2)&nbsp;an exception specified
</section> in the relevant CP or CPS applies. If the Relevant RRset for an FQDN
<section anchor="relevant-resource-record-set" title="Relevant Resource Record S
et">
<t>Before issuing a certificate, a compliant CA MUST check for
publication of a Relevant RRSet. If such an RRSet
exists, a CA MUST NOT 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 a Fully-Qualified Domain Name
or Wildcard Domain Name contains no Property Tags that restrict issuance or Wildcard Domain Name contains no Property Tags that restrict issuance
(for instance, if it contains only iodef Property Tags, or only Property (for instance, if it contains only iodef Property Tags or only Property
Tags unrecognized by the CA), CAA does not restrict issuance.</t> Tags unrecognized by the CA), CAA does not restrict issuance.</t>
<t>A certificate request <bcp14>MAY</bcp14> specify more than one FQDN and
<bcp14>MAY</bcp14>
specify Wildcard Domain Names. Issuers <bcp14>MUST</bcp14> verify authorization
for all
the FQDNs 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 specific FQDN X or a request for a Wildcard Domai
n
Name *.X, the Relevant RRset RelevantCAASet(X) is determined as follows (in pseu
docode):</t>
<ul empty="true" spacing="normal">
<li>Let CAA(X) be the RRset returned by performing a CAA record query fo
r the
FQDN X, according to the lookup algorithm
specified in <xref target="RFC1034" sectionFormat="of" section="4.3.2" /> (in pa
rticular, chasing
aliases). Let Parent(X) be the FQDN produced by
removing the leftmost label of X.</li>
</ul>
<sourcecode name="pseudocode-1" type="pseudocode"><![CDATA[
RelevantCAASet(domain):
while domain is not ".":
if CAA(domain) is not Empty:
return CAA(domain)
domain = Parent(domain)
return Empty ]]></sourcecode>
<t>A certificate request MAY specify more than one Fully-Qualified Domain Name a <ul empty="true" spacing="normal">
nd MAY <li>For example, processing CAA for the FQDN "X.Y.Z" where there are
specify Wildcard Domain Names. Issuers MUST verify authorization for all
the Fully-Qualified Domain Names and Wildcard Domain Names specified in the requ
est.</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 specific Fully-Qualified Domain Name X, or a request fo
r a Wildcard Domain
Name *.X, the Relevant Resource Record Set RelevantCAASet(X) is determined as fo
llows (in pseudocode):</t>
<t>Let CAA(X) be the RRSet returned by performing a CAA record query for the
Fully-Qualified Domain Name X, according to the lookup algorithm specified in RF
C 1034 section
4.3.2 (in particular chasing aliases). Let Parent(X) be the Fully-Qualified Doma
in Name
produced by removing the leftmost label of X.</t>
<figure><artwork><![CDATA[
RelevantCAASet(domain):
while domain is not ".":
if CAA(domain) is not Empty:
return CAA(domain)
domain = Parent(domain)
return Empty
]]></artwork></figure>
<t>For example, processing CAA for the Fully-Qualified Domain Name “X.Y.Z” where
there are
no CAA records at any level in the tree RelevantCAASet would have the no CAA records at any level in the tree RelevantCAASet would have the
following steps:</t> following steps:</li>
</ul>
<figure><artwork><![CDATA[ <artwork name="" type="" align="left" alt=""><![CDATA[
CAA("X.Y.Z.") = Empty; domain = Parent("X.Y.Z.") = "Y.Z." CAA("X.Y.Z.") = Empty; domain = Parent("X.Y.Z.") = "Y.Z."
CAA("Y.Z.") = Empty; domain = Parent("Y.Z.") = "Z." CAA("Y.Z.") = Empty; domain = Parent("Y.Z.") = "Z."
CAA("Z.") = Empty; domain = Parent("Z.") = "." CAA("Z.") = Empty; domain = Parent("Z.") = "."
return Empty return Empty ]]></artwork>
]]></artwork></figure> <ul empty="true" spacing="normal">
<li>Processing CAA for the FQDN "A.B.C" where there is a CAA record
<t>Processing CAA for the Fully-Qualified Domain Name “A.B.C” where there is a C "issue example.com" at "B.C" would terminate early upon finding the CAA
AA record record:</li>
“issue example.com” at “B.C” would terminate early upon finding the CAA </ul>
record:</t> <artwork name="" type="" align="left" alt=""><![CDATA[
CAA("A.B.C.") = Empty; domain = Parent("A.B.C.") = "B.C."
<figure><artwork><![CDATA[ CAA("B.C.") = "issue example.com"
CAA("A.B.C.") = Empty; domain = Parent("A.B.C.") = "B.C." return "issue example.com" ]]></artwork>
CAA("B.C.") = "issue example.com" </section>
return "issue example.com" <section anchor="mechanism" numbered="true" toc="default">
]]></artwork></figure> <name>Mechanism</name>
<section anchor="syntax" numbered="true" toc="default">
</section> <name>Syntax</name>
<section anchor="mechanism" title="Mechanism"> <t>A CAA RR contains a single Property consisting of a tag&#8209;value
pair. An FQDN <bcp14>MAY</bcp14> have multiple CAA RRs associated with it, and a
<section anchor="syntax" title="Syntax"> given Property Tag <bcp14>MAY</bcp14> be specified more than once across those R
Rs.</t>
<t>A CAA Resource Record contains a single Property consisting of a tag-value <t>The RDATA section for a CAA RR contains one Property. A Property
pair. A Fully-Qualified Domain Name MAY have multiple CAA RRs associated with it
and a
given Property Tag MAY be specified more than once across those RRs.</t>
<t>The RDATA section for a CAA Resource Record contains one Property. A Property
consists of the following:</t> consists of the following:</t>
<artwork name="" type="" align="left" alt=""><![CDATA[
<figure><artwork><![CDATA[
+0-1-2-3-4-5-6-7-|0-1-2-3-4-5-6-7-| +0-1-2-3-4-5-6-7-|0-1-2-3-4-5-6-7-|
| Flags | Tag Length = n | | Flags | Tag Length = n |
+----------------|----------------+...+---------------+ +----------------|----------------+...+---------------+
| Tag char 0 | Tag char 1 |...| Tag char n-1 | | Tag char 0 | Tag char 1 |...| Tag char n-1 |
+----------------|----------------+...+---------------+ +----------------|----------------+...+---------------+
+----------------|----------------+.....+----------------+ +----------------|----------------+.....+----------------+
| Value byte 0 | Value byte 1 |.....| Value byte m-1 | | Value byte 0 | Value byte 1 |.....| Value byte m-1 |
+----------------|----------------+.....+----------------+ +----------------|----------------+.....+----------------+
]]></artwork></figure> ]]></artwork>
<t>Where n is the length specified in the Tag Length field and m is the
<t>Where n is the length specified in the Tag length field and m is the number of remaining octets in the Value field. They are related by
remaining octets in the Value field. They are related by (m = d - n - 2) (m&nbsp;=&nbsp;d&nbsp;-&nbsp;n&nbsp;-&nbsp;2)
where d is the length of the RDATA section.</t> where d is the length of the RDATA section.</t>
<t>The fields are defined as follows:</t>
<dl newline="false" spacing="normal">
<dt>Flags:</dt>
<dd>
<t>One octet containing the following field:
<t>The fields are defined as follows:</t> </t>
<dl newline="false" spacing="normal">
<t>Flags: One octet containing the following field:</t> <dt>Bit 0, Issuer Critical Flag:</dt>
<dd>If the value is set to "1", the
<t>Bit 0, Issuer Critical Flag: If the value is set to ‘1’, the Property is critical. A CA <bcp14>MUST NOT</bcp14> issue
Property is critical. A Certification Authority MUST NOT issue certificates for any FQDN if the Relevant RRset for
certificates for any FQDN the Relevant RRSet for that FQDN contains a CAA critical
that FQDN contains a CAA critical Property for an unknown or unsupported Property Tag.
Property for an unknown or unsupported Property Tag.</t>
<t>Note that according to the conventions set out in <xref target="RFC1035"/>, b </dd>
it 0 </dl>
</dd>
</dl>
<t>Note that according to the conventions set out in <xref target="RFC10
35" format="default"/>, bit 0
is the Most Significant Bit and bit 7 is the Least Significant 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 Bit. Thus, according to those conventions, the Flags value 1 means that bit 7 is
of 128 means that bit 0 is set according to this convention.</t> set, while a value of 128 means that bit 0 is set.</t>
<t>All other bit positions are reserved for future use.</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 specification <bcp14>MUST</bcp14> clear
<t>To ensure compatibility with future extensions to CAA, DNS records (set to "0") all reserved flag bits.
compliant with this version of the CAA specification MUST clear
(set to “0”) all reserved flags bits. Applications that interpret
CAA records MUST 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 length MUST be at least 1.</t>
<t>Tag: The Property identifier, a sequence of US-ASCII characters.</t>
<t>Tags MAY contain US-ASCII characters ‘a’ through ‘z’, ‘A’ Applications that interpret
through ‘Z’, and the numbers 0 through 9. Tags MUST NOT CAA records <bcp14>MUST</bcp14> ignore the value of all reserved flag bits.</t>
<dl newline="false" spacing="normal">
<dt>Tag Length:</dt>
<dd>A single octet containing an unsigned integer specifying
the tag length in octets. The tag length <bcp14>MUST</bcp14> be at least 1.</dd
>
<dt>Tag:</dt>
<dd>The Property identifier -- a sequence of ASCII characters.</dd>
</dl>
<t>Tags <bcp14>MAY</bcp14> contain ASCII characters "a" through "z", "A"
through "Z", and the numbers 0 through 9. Tags <bcp14>MUST NOT</bcp14>
contain any other characters. Matching of tags is case contain any other characters. Matching of tags is case
insensitive.</t> insensitive.</t>
<t>Tags submitted for registration by IANA <bcp14>MUST NOT</bcp14> conta
<t>Tags submitted for registration by IANA MUST NOT contain any in any
characters other than the (lowercase) US-ASCII characters ‘a’ characters other than the (lowercase) ASCII characters "a"
through ‘z’ and the numbers 0 through 9.</t> through "z" and the numbers 0 through 9.</t>
<dl newline="false" spacing="normal">
<t>Value: A sequence of octets representing the Property Value. <dt>Value:</dt>
Property Values are encoded as binary values and MAY employ <dd>A sequence of octets representing the Property Value.
sub-formats.</t> Property Values are encoded as binary values and <bcp14>MAY</bcp14> employ
sub&#8209;formats.</dd>
<t>The length of the value field is specified implicitly as the </dl>
<t>The length of the Value field is specified implicitly as the
remaining length of the enclosing RDATA section.</t> remaining length of the enclosing RDATA section.</t>
<section anchor="canonical-presentation-format" numbered="true" toc="def
<section anchor="canonical-presentation-format" title="Canonical Presentation Fo ault">
rmat"> <name>Canonical Presentation Format</name>
<t>The canonical presentation format of the CAA record is:</t>
<t>The canonical presentation format of the CAA record is:</t> <artwork name="" type="" align="left" alt=""><![CDATA[
CAA <flags> <tag> <value>
<t>CAA &lt;flags&gt; &lt;tag&gt; &lt;value&gt;</t> ]]></artwork>
<t>Where:</t>
<t>Where:</t> <dl newline="false" spacing="normal">
<dt>Flags:</dt>
<t>Flags: Is an unsigned integer between 0 and 255.</t> <dd>An unsigned integer between 0 and 255.</dd>
<dt>Tag:</dt>
<t>Tag: Is a non-zero-length sequence of US-ASCII letters and numbers in lower <dd>A non-zero-length sequence of ASCII letters and numbers in lower
case.</t> case.</dd>
<dt>Value:</dt>
<t>Value: The value field, expressed as a contiguous set of characters <dd>The Value field, expressed as either (1)&nbsp;a contiguous set o
without interior spaces, or as a quoted string. See the f characters
&lt;character-string&gt; format specified in <xref target="RFC1035"></xref>, without interior spaces or (2)&nbsp;a quoted string. See the
Section 5.1, &lt;character-string&gt; format specified in <xref target="RFC1035" sectionFo
but note that the value field contains no length byte and is not rmat="comma" section="5.1"/>,
limited to 255 characters.</t> but note that the Value field contains no length byte and is not
limited to 255 characters.</dd>
</section> </dl>
</section> </section>
<section anchor="caa-issue-property" title="CAA issue Property"> </section>
<section anchor="caa-issue-property" numbered="true" toc="default">
<t>If the issue Property Tag is present in the Relevant RRSet for a <name>CAA issue Property</name>
Fully-Qualified Domain Name, it is a request that Issuers</t> <t>If the issue Property Tag is present in the Relevant RRset for an
FQDN, it is a request that Issuers:</t>
<t><list style="numbers"> <ol spacing="normal" type="1">
<t>Perform CAA issue restriction processing for the FQDN, and</t> <li>Perform CAA issue restriction processing for the FQDN, and</li>
<t>Grant authorization to issue certificates containing that FQDN <li>Grant authorization to issue certificates containing that FQDN
to the holder of the issuer-domain-name to the holder of the issuer-domain-name
or a party acting under the explicit authority of the holder of the or a party acting under the explicit authority of the holder of the
issuer-domain-name.</t> issuer-domain-name.</li>
</list></t> </ol>
<t>The CAA issue Property Value has the following sub&#8209;syntax (spec
<t>The CAA issue Property Value has the following sub-syntax (specified ified
in ABNF as per <xref target="RFC5234"/>).</t> in ABNF as per <xref target="RFC5234" format="default"/>).</t>
<sourcecode name="caa-issue-prop-value-abnf" type="abnf"><![CDATA[
<figure><artwork><![CDATA[ issue-value = *WSP [issuer-domain-name *WSP]
issue-value = *WSP [issuer-domain-name *WSP] [";" *WSP [parameters *WSP]] [";" *WSP [parameters *WSP]]
issuer-domain-name = label *("." label) issuer-domain-name = label *("." label)
label = (ALPHA / DIGIT) *( *("-") (ALPHA / DIGIT)) label = (ALPHA / DIGIT) *( *("-") (ALPHA / DIGIT))
parameters = (parameter *WSP ";" *WSP parameters) / parameter parameters = (parameter *WSP ";" *WSP parameters) / parameter
parameter = tag *WSP "=" *WSP value parameter = tag *WSP "=" *WSP value
tag = (ALPHA / DIGIT) *( *("-") (ALPHA / DIGIT)) tag = (ALPHA / DIGIT) *( *("-") (ALPHA / DIGIT))
value = *(%x21-3A / %x3C-7E) value = *(%x21-3A / %x3C-7E)
]]></artwork></figure> ]]></sourcecode>
<t>For consistency with other aspects of DNS administration, FQDN
<t>For consistency with other aspects of DNS administration, FQDN
values are specified in letter-digit-hyphen Label (LDH-Label) form.</t> values are specified in letter-digit-hyphen Label (LDH-Label) form.</t>
<t>The following CAA RRset requests that no
<t>The following CAA record set requests that no certificates be issued for the FQDN "certs.example.com" by any
certificates be issued for the FQDN ‘certs.example.com’ by any
Issuer other than ca1.example.net or ca2.example.org.</t> Issuer other than ca1.example.net or ca2.example.org.</t>
<artwork name="" type="" align="left" alt=""><![CDATA[
<figure><artwork><![CDATA[
certs.example.com CAA 0 issue "ca1.example.net" certs.example.com CAA 0 issue "ca1.example.net"
certs.example.com CAA 0 issue "ca2.example.org" certs.example.com CAA 0 issue "ca2.example.org"
]]></artwork></figure> ]]></artwork>
<t>Because the presence of an issue Property Tag in the Relevant RRset
<t>Because the presence of an issue Property Tag in the Relevant RRSet
for an FQDN restricts issuance, FQDN owners can use an issue for an FQDN restricts issuance, FQDN owners can use an issue
Property Tag with no issuer-domain-name to request no issuance.</t> Property Tag with no issuer-domain-name to request no issuance.</t>
<t>For example, the following RRset requests that no
<t>For example, the following RRSet requests that no certificates be issued for the FQDN "nocerts.example.com" by any
certificates be issued for the FQDN ‘nocerts.example.com’ by any
Issuer.</t> Issuer.</t>
<artwork name="" type="" align="left" alt=""><![CDATA[
<figure><artwork><![CDATA[
nocerts.example.com CAA 0 issue ";" nocerts.example.com CAA 0 issue ";"
]]></artwork></figure> ]]></artwork>
<t>An issue Property Tag where the issue-value does not match the ABNF
<t>An issue Property Tag where the issue-value does not match the ABNF grammar <bcp14>MUST</bcp14> be treated the same as one specifying an empty issue
grammar MUST be treated the same as one specifying an empty issuer-domain-name. r&#8209;domain-name. For
For example, the following malformed CAA RRset forbids issuance:</t>
example, the following malformed CAA RRSet forbids issuance:</t> <artwork name="" type="" align="left" alt=""><![CDATA[
<figure><artwork><![CDATA[
malformed.example.com CAA 0 issue "%%%%%" malformed.example.com CAA 0 issue "%%%%%"
]]></artwork></figure> ]]></artwork>
<t>CAA authorizations are additive; thus, the result of specifying both
<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 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> same as specifying just the non-empty issuer-domain-name.</t>
<t>An Issuer <bcp14>MAY</bcp14> choose to specify parameters that furthe
<t>An Issuer MAY choose to specify parameters that further r
constrain the issue of certificates by that Issuer, for example, constrain the issue of certificates by that Issuer -- for example,
specifying that certificates are to be subject to specific validation specifying that certificates are to be subject to specific validation
polices, billed to certain accounts, or issued under specific trust policies, billed to certain accounts, or issued under specific trust
anchors.</t> anchors.</t>
<t>For example, if ca1.example.net has requested that its customer
<t>For example, if ca1.example.net has requested its customer account.example.com specify their account number "230123" in each
accountable.example.com to specify their account number “230123” in each of the customer's CAA records using the (CA-defined) "account" parameter,
of the customer’s CAA records using the (CA-defined) “account” parameter,
it would look like this:</t> it would look like this:</t>
<artwork name="" type="" align="left" alt=""><![CDATA[
<figure><artwork><![CDATA[ account.example.com CAA 0 issue "ca1.example.net; account=230123"
accountable.example.com CAA 0 issue "ca1.example.net; account=230123" ]]></artwork>
]]></artwork></figure> <t>The semantics of parameters to the issue Property Tag are determined
by
<t>The semantics of parameters to the issue Property Tag are determined by
the Issuer alone.</t> the Issuer alone.</t>
</section>
</section> <section anchor="caa-issuewild-property" numbered="true" toc="default">
<section anchor="caa-issuewild-property" title="CAA issuewild Property"> <name>CAA issuewild Property</name>
<t>The issuewild Property Tag has the same syntax and semantics as the i
<t>The issuewild Property Tag has the same syntax and semantics as the issue ssue
Property Tag except that it only grants authorization to Property Tag except that it only grants authorization to
issue certificates that specify a Wildcard Domain Name and issuewild issue certificates that specify a Wildcard Domain Name and each issuewild
properties take precedence over issue properties when specified. Property takes precedence over each issue Property when specified.
Specifically:</t> Specifically:</t>
<t>Each issuewild Property <bcp14>MUST</bcp14> be ignored when processin
<t>issuewild properties MUST be ignored when processing a request for g a request for
a Fully-Qualified Domain Name that is not a Wildcard Domain Name.</t> an FQDN that is not a Wildcard Domain Name.</t>
<t>If at least one issuewild Property is specified in the Relevant
<t>If at least one issuewild Property is specified in the Relevant RRset for a Wildcard Domain Name, each issue Property <bcp14>MUST</bcp14>
RRSet for a Wildcard Domain Name, all issue properties MUST
be ignored when processing a request for that Wildcard Domain Name.</t> be ignored when processing a request for that Wildcard Domain Name.</t>
<t>For example, the following RRset requests that <em>only</em>
<t>For example, the following RRSet requests that <spanx style="emph">only</span ca1.example.net issue certificates for "wild.example.com" or
x> "sub.wild.example.com", and that <em>only</em> ca2.example.org issue certificate
ca1.example.net issue certificates for “wild.example.com” or s for
“sub.wild.example.com”, and that <spanx style="emph">only</spanx> ca2.example.or "*.wild.example.com" or "*.sub.wild.example.com". Note that this presumes
g issue certificates for that there are no CAA RRs for sub.wild.example.com.</t>
“*.wild.example.com” or “*.sub.wild.example.com). Note that this presumes <artwork name="" type="" align="left" alt=""><![CDATA[
there are no CAA RRs for sub.wild.example.com.</t>
<figure><artwork><![CDATA[
wild.example.com CAA 0 issue "ca1.example.net" wild.example.com CAA 0 issue "ca1.example.net"
wild.example.com CAA 0 issuewild "ca2.example.org" wild.example.com CAA 0 issuewild "ca2.example.org"
]]></artwork></figure> ]]></artwork>
<t>The following RRset requests that <em>only</em> ca1.example.net issue
<t>The following RRSet requests that <spanx style="emph">only</spanx> ca1.exampl certificates for "wild2.example.com", "*.wild2.example.com", or
e.net issue "*.sub.wild2.example.com".</t>
certificates for “wild2.example.com”, “*.wild2.example.com” or <artwork name="" type="" align="left" alt=""><![CDATA[
“*.sub.wild2.example.com”.</t>
<figure><artwork><![CDATA[
wild2.example.com CAA 0 issue "ca1.example.net" wild2.example.com CAA 0 issue "ca1.example.net"
]]></artwork></figure> ]]></artwork>
<t>The following RRset requests that <em>only</em> ca2.example.org issue
<t>The following RRSet requests that <spanx style="emph">only</spanx> ca2.exampl certificates for "*.wild3.example.com" or "*.sub.wild3.example.com". It
e.org issue does not permit any Issuer to issue for "wild3.example.com" or
certificates for “*.wild3.example.com” or “*.sub.wild3.example.com”. It "sub.wild3.example.com".</t>
does not permit any Issuer to issue for “wild3.example.com” or <artwork name="" type="" align="left" alt=""><![CDATA[
“sub.wild3.example.com”.</t>
<figure><artwork><![CDATA[
wild3.example.com CAA 0 issuewild "ca2.example.org" wild3.example.com CAA 0 issuewild "ca2.example.org"
wild3.example.com CAA 0 issue ";" wild3.example.com CAA 0 issue ";"
]]></artwork></figure> ]]></artwork>
<t>The following RRset requests that <em>only</em> ca2.example.org issue
<t>The following RRSet requests that <spanx style="emph">only</spanx> ca2.exampl certificates for "*.wild3.example.com" or "*.sub.wild3.example.com". It
e.org issue permits any Issuer to issue for "wild3.example.com" or "sub.wild3.example.com".<
certificates for “*.wild3.example.com” or “*.sub.wild3.example.com”. It /t>
permits any Issuer to issue for “wild3.example.com” or “sub.wild3.example.com”.< <artwork name="" type="" align="left" alt=""><![CDATA[
/t>
<figure><artwork><![CDATA[
wild3.example.com CAA 0 issuewild "ca2.example.org" wild3.example.com CAA 0 issuewild "ca2.example.org"
]]></artwork></figure> ]]></artwork>
</section>
</section> <section anchor="caa-iodef-property" numbered="true" toc="default">
<section anchor="caa-iodef-property" title="CAA iodef Property"> <name>CAA iodef Property</name>
<t>The iodef Property specifies a means of reporting certificate issue
<t>The iodef Property specifies a means of reporting certificate issue
requests or cases of certificate issue for domains for which the Property requests or cases of certificate issue for domains for which the Property
appears in the Relevant RRSet, when those requests or issuances appears in the Relevant RRset, when those requests or issuances
violate the security policy of the Issuer or the FQDN holder.</t> violate the security policy of the Issuer or the FQDN holder.</t>
<t>The Incident Object Description Exchange Format (IODEF) <xref target=
<t>The Incident Object Description Exchange Format (IODEF) <xref target="RFC7970 "RFC7970" format="default"/> is
"/> is
used to present the incident report in machine-readable form.</t> 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 sc
<t>The iodef Property Tag takes a URL as its Property Value. The URL scheme typ heme type
e
determines the method used for reporting:</t> determines the method used for reporting:</t>
<dl newline="false" spacing="normal">
<t>mailto: The IODEF incident report is reported as a MIME email <dt>mailto:</dt>
<dd>The IODEF report is reported as a MIME email
attachment to an SMTP email that is submitted to the mail address attachment to an SMTP email that is submitted to the mail address
specified. The mail message sent SHOULD contain a brief text specified. The mail message sent <bcp14>SHOULD</bcp14> contain a brief text
message to alert the recipient to the nature of the attachment.</t> message to alert the recipient to the nature of the attachment.</dd>
<dt>http or https:</dt>
<t>http or https: The IODEF report is submitted as a Web service <dd>The IODEF report is submitted as a web service
request to the HTTP address specified using the protocol specified request to the HTTP address specified using the protocol specified
in <xref target="RFC6546"/>.</t> in <xref target="RFC6546" format="default"/>.</dd>
</dl>
<t>These are the only supported URL schemes.</t> <t>These are the only supported URL schemes.</t>
<t>The following RRset specifies
<t>The following RRSet specifies
that reports may be made by means of email with the IODEF data as an that reports may be made by means of email with the IODEF data as an
attachment, a Web service <xref target="RFC6546"></xref>, or both:</t> attachment, a web service <xref target="RFC6546" format="default"/>, or both:</t
>
<figure><artwork><![CDATA[ <artwork name="" type="" align="left" alt=""><![CDATA[
report.example.com CAA 0 issue "ca1.example.net" 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 "mailto:security@example.com"
report.example.com CAA 0 iodef "http://iodef.example.com/" report.example.com CAA 0 iodef "https://iodef.example.com/"
]]></artwork></figure> ]]></artwork>
</section>
</section> <section anchor="critical-flag" numbered="true" toc="default">
<section anchor="critical-flag" title="Critical Flag"> <name>Critical Flag</name>
<t>The critical flag is intended to permit future versions of CAA to
<t>The critical flag is intended to permit future versions of CAA to introduce new semantics that <bcp14>MUST</bcp14> be understood for correct
introduce new semantics that MUST be understood for correct
processing of the record, preventing conforming CAs that do not processing of the record, preventing conforming CAs that do not
recognize the new semantics from issuing certificates for the recognize the new semantics from issuing certificates for the
indicated FQDNs.</t> indicated FQDNs.</t>
<t>In the following example, the Property with a Property Tag of
<t>In the following example, the Property with a Property Tag of "tbs" is flagged as critical.
‘tbs’ is flagged as critical.
Neither the ca1.example.net CA nor any other Issuer is authorized to 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 issue for "new.example.com" (or any other domains for which this is
the Relevant RRSet) unless the Issuer has implemented the the Relevant RRset) unless the Issuer has implemented the
processing rules for the ‘tbs’ Property Tag.</t> processing rules for the "tbs" Property Tag.</t>
<artwork name="" type="" align="left" alt=""><![CDATA[
<figure><artwork><![CDATA[
new.example.com CAA 0 issue "ca1.example.net" new.example.com CAA 0 issue "ca1.example.net"
new.example.com CAA 128 tbs "Unknown" new.example.com CAA 128 tbs "Unknown"
]]></artwork></figure> ]]></artwork>
</section>
</section> </section>
</section> <section anchor="security-considerations" numbered="true" toc="default">
<section anchor="security-considerations" title="Security Considerations"> <name>Security Considerations</name>
<t>CAA records assert a security policy that the holder of an FQDN
<t>CAA records assert a security policy that the holder of an FDQN
wishes to be observed by Issuers. The effectiveness of wishes to be observed by Issuers. The effectiveness of
CAA records as an access control mechanism is thus dependent on CAA records as an access control mechanism is thus dependent on
observance of CAA constraints by Issuers.</t> observance of CAA constraints by Issuers.</t>
<t>The objective of the CAA record properties described in this document
<t>The objective of the CAA record properties described in this document
is to reduce the risk of certificate mis-issue rather than avoid 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" /> reliance on a certificate that has been mis-issued. DANE <xref target="RFC6698" format="default"/>
describes a mechanism for avoiding reliance on mis-issued describes a mechanism for avoiding reliance on mis-issued
certificates.</t> certificates.</t>
<section anchor="use-of-dns-security" numbered="true" toc="default">
<section anchor="use-of-dns-security" title="Use of DNS Security"> <name>Use of DNS Security</name>
<t>The use of DNSSEC to authenticate CAA RRs is strongly <bcp14>RECOMMEN
<t>Use of DNSSEC to authenticate CAA RRs is strongly RECOMMENDED but not DED</bcp14> but not
required. An Issuer MUST NOT issue certificates if doing so would required. An Issuer <bcp14>MUST NOT</bcp14> issue certificates if doing so woul
conflict with the Relevant RRSet, irrespective of d
conflict with the Relevant RRset, irrespective of
whether the corresponding DNS records are signed.</t> whether the corresponding DNS records are signed.</t>
<t>DNSSEC provides a proof of non-existence for both DNS FQDNs and
<t>DNSSEC provides a proof of non-existence for both DNS Fully-Qualified Domain RRsets within FQDNs. DNSSEC verification thus enables an Issuer to
Names and determine whether the answer to a CAA record query (1)&nbsp;is empty because
RRSets within FQDNs. DNSSEC verification thus enables an Issuer to the RRset is empty or (2)&nbsp;is non-empty but the response has been
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> suppressed.</t>
<t>The use of DNSSEC allows an Issuer to acquire and archive a proof tha
<t>Use of DNSSEC allows an Issuer to acquire and archive a proof that t
they were authorized to issue certificates for the FQDN. they were authorized to issue certificates for the FQDN.
Verification of such archives may be an audit requirement to verify Verification of such archives may be an audit requirement to verify
CAA record processing compliance. Publication of such archives may CAA record-processing compliance. Publication of such archives may
be a transparency requirement to verify CAA record processing be a transparency requirement to verify CAA record-processing
compliance.</t> compliance.</t>
</section>
</section> <section anchor="non-compliance-by-certification-authority" numbered="true
<section anchor="non-compliance-by-certification-authority" title="Non-Complianc " toc="default">
e by Certification Authority"> <name>Non-compliance by Certification Authority</name>
<t>CAA records offer CAs a cost-effective means of mitigating the risk
<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 of certificate mis-issue: the cost of implementing CAA checks is very
small and the potential costs of a mis-issue event include the small, and the potential costs of a mis-issue event include the
removal of an embedded trust anchor.</t> removal of an embedded trust anchor.</t>
</section>
</section> <section anchor="mis-issue-by-authorized-certification-authority" numbered
<section anchor="mis-issue-by-authorized-certification-authority" title="Mis-Iss ="true" toc="default">
ue by Authorized Certification Authority"> <name>Mis-Issue by Authorized Certification Authority</name>
<t>The use of CAA records does not prevent mis-issue by an authorized
<t>Use of CAA records does not prevent mis-issue by an authorized CA, i.e., a CA that is authorized to issue
Certification Authority, i.e., a CA that is authorized to issue
certificates for the FQDN in question by CAA records.</t> certificates for the FQDN in question by CAA records.</t>
<t>FQDN holders <bcp14>SHOULD</bcp14> verify that the CAs they authorize
<t>FQDN holders SHOULD verify that the CAs they authorize to to
issue certificates for their FQDNs employ appropriate controls to issue certificates for their FQDNs employ appropriate controls to
ensure that certificates are issued only to authorized parties within ensure that certificates are issued only to authorized parties within
their organization.</t> their organization.</t>
<t>Such controls are most appropriately determined by the FQDN
<t>Such controls are most appropriately determined by the FQDN holder and the authorized CA(s) directly and are thus outside the scope of
holder and the authorized CA(s) directly and are thus out of scope of
this document.</t> this document.</t>
</section>
</section> <section anchor="suppression-or-spoofing-of-caa-records" numbered="true" t
<section anchor="suppression-or-spoofing-of-caa-records" title="Suppression or S oc="default">
poofing of CAA Records"> <name>Suppression or Spoofing of CAA Records</name>
<t>Suppression of a CAA record or insertion of a bogus CAA record
<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 could enable an attacker to obtain a certificate from an Issuer that
was not authorized to issue for an affected FQDN.</t> was not authorized to issue for an affected FQDN.</t>
<t>Where possible, Issuers <bcp14>SHOULD</bcp14> perform DNSSEC validati
<t>Where possible, Issuers SHOULD perform DNSSEC validation to detect on to detect
missing or modified CAA record sets.</t> missing or modified CAA RRsets.</t>
<t>In cases where DNSSEC is not deployed for a corresponding FQDN, an
<t>In cases where DNSSEC is not deployed for a corresponding FQDN, an Issuer <bcp14>SHOULD</bcp14> attempt to mitigate this risk by employing appropri
Issuer SHOULD attempt to mitigate this risk by employing appropriate ate
DNS security controls. For example, all portions of the DNS lookup DNS security controls. For example, all portions of the DNS lookup
process SHOULD be performed against the authoritative name server. process <bcp14>SHOULD</bcp14> be performed against the authoritative nameserver.
Data cached by third parties MUST NOT be relied on as the sole source of DNS CAA Data cached by third parties <bcp14>MUST NOT</bcp14> be relied on as the sole so
information but MAY be used to urce of DNS CAA
support additional anti-spoofing or anti-suppression controls.</t> information but <bcp14>MAY</bcp14> be used to
support additional anti&#8209;spoofing or anti-suppression controls.</t>
</section> </section>
<section anchor="denial-of-service" title="Denial of Service"> <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 <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 enable a Denial-of-Service (DoS) attack. This could happen by modification of
authoritative DNS records or by spoofing inflight DNS responses.</t> authoritative DNS records or by spoofing inflight DNS responses.</t>
<t>This specific threat is not considered to add significantly to the
<t>This specific threat is not considered to add significantly to the
risk of running an insecure DNS service.</t> risk of running an insecure DNS service.</t>
<t>An attacker could, in principle, perform a DoS attack against an
<t>An attacker could, in principle, perform a DoS attack against an
Issuer by requesting a certificate with a maliciously long DNS name. Issuer by requesting a certificate with a maliciously long DNS name.
In practice, the DNS protocol imposes a maximum name length and CAA In practice, the DNS protocol imposes a maximum name length, and CAA
processing does not exacerbate the existing need to mitigate DoS processing does not exacerbate the existing need to mitigate DoS
attacks to any meaningful degree.</t> attacks to any meaningful degree.</t>
</section>
</section> <section anchor="abuse-of-the-critical-flag" numbered="true" toc="default"
<section anchor="abuse-of-the-critical-flag" title="Abuse of the Critical Flag"> >
<name>Abuse of the Critical Flag</name>
<t>A Certification Authority could make use of the critical flag to <t>A CA could make use of the critical flag to
trick customers into publishing records that prevent competing trick customers into publishing records that prevent competing CAs
Certification Authorities from issuing certificates even though the from issuing certificates even though the
customer intends to authorize multiple providers. This could happen if 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 customers were setting CAA records based on data provided by the CA rather than
generating those records themselves.</t> generating those records themselves.</t>
<t>In practice, such an attack would be of minimal effect, since any
<t>In practice, such an attack would be of minimal effect since any
competent competitor that found itself unable to issue certificates competent competitor that found itself unable to issue certificates
due to lack of support for a Property marked critical should due to lack of support for a Property marked critical should
investigate the cause and report the reason to the customer. The investigate the cause and report the reason to the customer. The
customer will thus discover that they had been deceived.</t> customer will thus discover that they had been deceived.</t>
</section>
</section> </section>
</section> <section anchor="deployment-considerations" numbered="true" toc="default">
<section anchor="deployment-considerations" title="Deployment Considerations"> <name>Deployment Considerations</name>
<t>A CA implementing CAA may find that they receive errors looking up CAA
<t>A CA implementing CAA may find that they receive errors looking up CAA record records.
s.
The following are some common causes of such errors, so that CAs may provide The following are some common causes of such errors, so that CAs may provide
guidance to their subscribers on fixing the underlying problems.</t> guidance to their subscribers on fixing the underlying problems.</t>
<section anchor="blocked-queries-or-responses" numbered="true" toc="defaul
<section anchor="blocked-queries-or-responses" title="Blocked Queries or Respons t">
es"> <name>Blocked Queries or Responses</name>
<t>Some middleboxes -- in particular, anti-DDoS appliances -- may be con
<t>Some middleboxes, in particular anti-DDoS appliances, may be configured to figured to
drop DNS packets of unknown types, or may start dropping such packets when drop DNS packets of unknown types, or they may start dropping such packets when
they consider themselves under attack. This generally manifests as a timed-out they consider themselves under attack. This generally manifests as a timed-out
DNS query, or a SERVFAIL at a local recursive resolver.</t> DNS query or as a SERVFAIL at a local recursive resolver.</t>
</section>
</section> <section anchor="rejected-queries-and-malformed-responses" numbered="true"
<section anchor="rejected-queries-and-malformed-responses" title="Rejected Queri toc="default">
es and Malformed Responses"> <name>Rejected Queries and Malformed Responses</name>
<t>Some authoritative nameservers respond with REJECTED or NOTIMP when q
<t>Some authoritative nameservers respond with REJECTED or NOTIMP when queried ueried
for a Resource Record type they do not recognize. At least one authoritative for an RR type they do not recognize. At least one authoritative
resolver produces a malformed response (with the QR bit set to 0) when queried resolver produces a malformed response (with the QR (Query/Response) bit set to
for unknown Resource Record types. Per RFC 1034, the correct response for "0") when queried
unknown Resource Record types is NOERROR.</t> for unknown RR types. Per <xref target="RFC1034"/>, the correct response RCODE
for
</section> unknown RR types is 0 ("No error condition").
<section anchor="delegation-to-private-nameservers" title="Delegation to Private
Nameservers">
<t>Some FQDN administrators make the contents of a subdomain unresolvable on the </t>
</section>
<section anchor="delegation-to-private-nameservers" numbered="true" toc="d
efault">
<name>Delegation to Private Nameservers</name>
<t>Some FQDN administrators make the contents of a subdomain unresolvabl
e on the
public Internet by delegating that subdomain to a nameserver whose IP address is public Internet by delegating that subdomain to a nameserver whose IP address is
private. A CA processing CAA records for such subdomains will receive private. A CA processing CAA records for such subdomains will receive
SERVFAIL from its recursive resolver. The CA MAY interpret that as preventing SERVFAIL from its recursive resolver. The CA <bcp14>MAY</bcp14> interpret that a s preventing
issuance. FQDN administrators wishing to issue certificates for private issuance. FQDN administrators wishing to issue certificates for private
FQDNs SHOULD use split-horizon DNS with a publicly available nameserver, so FQDNs <bcp14>SHOULD</bcp14> use split-horizon DNS with a publicly available name server, so
that CAs can receive a valid, empty CAA response for those FQDNs.</t> that CAs can receive a valid, empty CAA response for those FQDNs.</t>
</section>
</section> <section anchor="bogus-dnssec-responses" numbered="true" toc="default">
<section anchor="bogus-dnssec-responses" title="Bogus DNSSEC Responses"> <name>Bogus DNSSEC Responses</name>
<t>Queries for CAA RRs are different from most DNS RR&nbsp;types, becaus
<t>Queries for CAA Resource Records are different from most DNS RR types, becaus e
e
a signed, empty response to a query for CAA RRs is meaningfully different 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 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 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 either a misconfigured zone or an attacker tampering with records. DNSSEC
implementations may have bugs with signatures on empty responses that go implementations may have bugs with signatures on empty responses that go
unnoticed, because for more common Resource Record types like A and AAAA, unnoticed, because for more common RR types like A and AAAA,
the difference to an end user between empty and bogus is irrelevant; they the difference to an end user between empty and bogus is irrelevant; they
both mean a site is unavailable.</t> both mean a site is unavailable.</t>
<t>In particular, at least two authoritative resolvers that implement li
<t>In particular, at least two authoritative resolvers that implement live signi ve signing
ng had bugs when returning empty RRsets for DNSSEC-signed zones, in
had bugs when returning empty Resource Record sets for DNSSEC-signed zones, in combination with mixed-case queries. Mixed&#8209;case queries, also known as DNS
combination with mixed-case queries. Mixed-case queries, also known as DNS 0x20, 0x20,
are used by some recursive resolvers to increase resilience against DNS are used by some recursive resolvers to increase resilience against DNS
poisoning attacks. DNSSEC-signing authoritative resolvers are expected to copy poisoning attacks. DNSSEC-signing authoritative resolvers are expected to copy
the same capitalization from the query into their ANSWER section, but sign the the same capitalization from the query into their ANSWER section but also to sig n the
response as if they had used all lowercase. In particular, PowerDNS versions response as if they had used all lowercase. In particular, PowerDNS versions
prior to 4.0.4 had this bug.</t> prior to 4.0.4 had this bug.</t>
</section>
</section> </section>
</section> <section anchor="differences-versus-rfc6844" numbered="true" toc="default">
<section anchor="differences-versus-rfc6844" title="Differences versus RFC6844"> <name>Differences from RFC 6844</name>
<t>This document obsoletes <xref target="RFC6844"/>. The most important ch
<t>This document obsoletes RFC6844. The most important change is to ange is to
the Certification Authority Processing section. RFC6844 specified an the "Certification Authority Processing" section (now called
"Relevant Resource Record Set" (<xref target="relevant-resource-record-set"/>),
as noted below). <xref target="RFC6844"/> specified an
algorithm that performed DNS tree-climbing not only on the FQDN algorithm that performed DNS tree-climbing not only on the FQDN
being processed, but also on all CNAMEs and DNAMEs encountered along being processed but also on all CNAMEs and DNAMEs encountered along
the way. This made the processing algorithm very inefficient when used the way. This made the processing algorithm very inefficient when used
on FQDNs that utilize many CNAMEs, and would have made it difficult on FQDNs that utilize many CNAMEs and would have made it difficult
for hosting providers to set CAA policies on their own FQDNs without for hosting providers to set CAA policies on their own FQDNs without
setting potentially unwanted CAA policies on their customers’ FQDNs. setting potentially unwanted CAA policies on their customers' FQDNs.
This document specifies a simplified processing algorithm that only This document specifies a simplified processing algorithm that only
performs tree climbing on the FQDN being processed, and leaves performs tree-climbing on the FQDN being processed, and it leaves the
processing of CNAMEs and DNAMEs up to the CA’s recursive resolver.</t> processing of CNAMEs and DNAMEs up to the CA's recursive resolver.</t>
<t>This document also includes a "Deployment Considerations" section
<t>This document also includes a “Deployment Considerations” section (<xref target="deployment-considerations"/>) detailing experience gained with pr
detailing experience gained with practical deployment of CAA enforcement actical deployment of CAA enforcement
among CAs in the WebPKI.</t> among CAs in the WebPKI.</t>
<t>This document clarifies the ABNF grammar for the issue and issuewild ta
<t>This document clarifies the ABNF grammar for the issue and issuewild tags gs
and resolves some inconsistencies with the document text. In particular, and resolves some inconsistencies with the document text. In particular,
it specifies that parameters are separated with semicolons. It also allows it specifies that parameters are separated with semicolons. It also allows
hyphens in Property Tags.</t> hyphens in Property Tags.</t>
<t>This document also clarifies the processing of a CAA RRset that is not
<t>This document also clarifies processing of a CAA RRset that is not empty, empty
but contains no issue or issuewild tags.</t> but that does not contain any issue or issuewild tags.</t>
<t>This document removes the section titled "The CAA RR Type," merging it
<t>This document removes the section titled “The CAA RR Type,” merging it with with
“Mechanism” because the definitions were mainly duplicates. It moves the “Use of "Mechanism" (<xref target="mechanism"/>) because the definitions were mainly dup
DNS Security” section into Security Considerations. It renames “Certification licates. It moves the "Use of
Authority Processing” to “Relevant Resource Record Set,” and emphasizes the use DNS Security" section into Security Considerations (<xref target="security-consi
derations"/>). It renames "Certification
Authority Processing" to "Relevant Resource Record 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> of that term to more clearly define which domains are affected by a given RRset. </t>
</section>
</section> <section anchor="iana-considerations" numbered="true" toc="default">
<section anchor="iana-considerations" title="IANA Considerations"> <name>IANA Considerations</name>
<t>IANA has added this document as
<t>IANA is requested to add [[[ RFC Editor: Please replace with this RFC ]]] as a reference for the "Certification Authority Restriction Flags" and
a reference for the Certification Authority Restriction Flags and "Certification Authority Restriction Properties" registries and updated
Certification Authority Restriction Properties registries, and update references references to <xref target="RFC6844" format="default"/> within those registries
to <xref target="RFC6844"/> within those registries to refer to [[[ RFC Editor: to refer instead to
Please this document. IANA has also updated the CAA TYPE in the
replace with this RFC ]]]. IANA is also "Resource Record (RR) TYPEs" subregistry of the "Domain Name System (DNS) Parame
requested to update the CAA TYPE in the DNS Parameters registry with a reference ters" registry with a reference
to [[[ RFC Editor: Please replace with this RFC ]]].</t> to this document.</t>
</section>
</section> </middle>
<section anchor="acknowledgements" title="Acknowledgements"> <back>
<references>
<t>The authors would like to thank the following people who contributed <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"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8174.
xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5280.
xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.1034.
xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.1035.
xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.4033.
xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.4034.
xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.4035.
xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5155.
xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.2181.
xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5234.
xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7970.
xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6546.
xml"/>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6844.
xml"/>
</references>
<references>
<name>Informative References</name>
<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.3647.
xml"/>
</references>
</references>
<section anchor="acknowledgements" numbered="false" toc="default">
<name>Acknowledgements</name>
<t>The authors would like to thank the following people who contributed
to the design and documentation of this work item: Corey Bonnell, Chris Evans, to the design and documentation of this work item: Corey Bonnell, Chris Evans,
Stephen Farrell, Jeff Hodges, Paul Hoffman, Tim Hollebeek, Stephen Kent, Adam Stephen Farrell, Jeff Hodges, Paul Hoffman, Tim Hollebeek, Stephen Kent, Adam
Langley, Ben Laurie, James Manger, Chris Palmer, Scott Schmit, Sean Turner, and Langley, Ben Laurie, James Manger, Chris Palmer, Scott Schmit, Sean Turner, and
Ben Wilson.</t> Ben Wilson.</t>
</section>
</section>
</middle>
<back>
<references title='Normative References'>
<reference anchor="RFC6698" target='https://www.rfc-editor.org/info/rfc6698'>
<front>
<title>The DNS-Based Authentication of Named Entities (DANE) Transport Layer Sec
urity (TLS) Protocol: TLSA</title>
<author initials='P.' surname='Hoffman' fullname='P. Hoffman'><organization /></
author>
<author initials='J.' surname='Schlyter' fullname='J. Schlyter'><organization />
</author>
<date year='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 d
ocument improves on that situation by enabling the administrators of domain name
s 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. [ST
ANDARDS-TRACK]</t></abstract>
</front>
<seriesInfo name='RFC' value='6698'/>
<seriesInfo name='DOI' value='10.17487/RFC6698'/>
</reference>
<reference anchor="RFC2119" target='https://www.rfc-editor.org/info/rfc2119'>
<front>
<title>Key words for use in RFCs to Indicate Requirement Levels</title>
<author initials='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 Comm
unity, and requests discussion and suggestions for improvements.</t></abstract>
</front>
<seriesInfo name='BCP' value='14'/>
<seriesInfo name='RFC' value='2119'/>
<seriesInfo name='DOI' value='10.17487/RFC2119'/>
</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>
<author initials='B.' surname='Leiba' fullname='B. Leiba'><organization /></auth
or>
<date year='2017' month='May' />
<abstract><t>RFC 2119 specifies common key words that may be used in protocol s
pecifications. This document aims to reduce the ambiguity by clarifying that on
ly UPPERCASE usage of the key words have the defined special meanings.</t></abs
tract>
</front>
<seriesInfo name='BCP' value='14'/>
<seriesInfo name='RFC' value='8174'/>
<seriesInfo name='DOI' value='10.17487/RFC8174'/>
</reference>
<reference anchor="RFC5280" target='https://www.rfc-editor.org/info/rfc5280'>
<front>
<title>Internet X.509 Public Key Infrastructure Certificate and Certificate Revo
cation List (CRL) Profile</title>
<author initials='D.' surname='Cooper' fullname='D. Cooper'><organization /></au
thor>
<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 /></au
thor>
<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 certificat
e revocation list (CRL) for use in the Internet. An overview of this approach a
nd model is provided as an introduction. The X.509 v3 certificate format is des
cribed 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 extensi
ons is specified. The X.509 v2 CRL format is described in detail along with sta
ndard and Internet-specific extensions. An algorithm for X.509 certification pa
th validation is described. An ASN.1 module and examples are provided in the ap
pendices. [STANDARDS-TRACK]</t></abstract>
</front>
<seriesInfo name='RFC' value='5280'/>
<seriesInfo name='DOI' value='10.17487/RFC5280'/>
</reference>
<reference anchor="RFC1034" target='https://www.rfc-editor.org/info/rfc1034'>
<front>
<title>Domain names - concepts and facilities</title>
<author initials='P.V.' surname='Mockapetris' fullname='P.V. Mockapetris'><organ
ization /></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 us
ed for host address look up and electronic mail forwarding. It discusses the cl
ients and servers in the domain name system and the protocol used between them.<
/t></abstract>
</front>
<seriesInfo name='STD' value='13'/>
<seriesInfo name='RFC' value='1034'/>
<seriesInfo name='DOI' value='10.17487/RFC1034'/>
</reference>
<reference anchor="RFC1035" target='https://www.rfc-editor.org/info/rfc1035'>
<front>
<title>Domain names - implementation and specification</title>
<author initials='P.V.' surname='Mockapetris' fullname='P.V. Mockapetris'><organ
ization /></author>
<date year='1987' month='November' />
<abstract><t>This RFC is the revised specification of the protocol and format us
ed 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>
<seriesInfo name='STD' value='13'/>
<seriesInfo name='RFC' value='1035'/>
<seriesInfo name='DOI' value='10.17487/RFC1035'/>
</reference>
<reference anchor="RFC4033" target='https://www.rfc-editor.org/info/rfc4033'>
<front>
<title>DNS Security Introduction and Requirements</title>
<author initials='R.' surname='Arends' fullname='R. Arends'><organization /></au
thor>
<author initials='R.' surname='Austein' fullname='R. Austein'><organization /></
author>
<author initials='M.' surname='Larson' fullname='M. Larson'><organization /></au
thor>
<author initials='D.' surname='Massey' fullname='D. Massey'><organization /></au
thor>
<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 int
roduces 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>
</front>
<seriesInfo name='RFC' value='4033'/>
<seriesInfo name='DOI' value='10.17487/RFC4033'/>
</reference>
<reference anchor="RFC4034" target='https://www.rfc-editor.org/info/rfc4034'>
<front>
<title>Resource Records for the DNS Security Extensions</title>
<author initials='R.' surname='Arends' fullname='R. Arends'><organization /></au
thor>
<author initials='R.' surname='Austein' fullname='R. Austein'><organization /></
author>
<author initials='M.' surname='Larson' fullname='M. Larson'><organization /></au
thor>
<author initials='D.' surname='Massey' fullname='D. Massey'><organization /></au
thor>
<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 DN
S 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 exis
tence (NSEC) resource records. The purpose and format of each resource record i
s 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 RF
C 2535. [STANDARDS-TRACK]</t></abstract>
</front>
<seriesInfo name='RFC' value='4034'/>
<seriesInfo name='DOI' value='10.17487/RFC4034'/>
</reference>
<reference anchor="RFC4035" target='https://www.rfc-editor.org/info/rfc4035'>
<front>
<title>Protocol Modifications for the DNS Security Extensions</title>
<author initials='R.' surname='Arends' fullname='R. Arends'><organization /></au
thor>
<author initials='R.' surname='Austein' fullname='R. Austein'><organization /></
author>
<author initials='M.' surname='Larson' fullname='M. Larson'><organization /></au
thor>
<author initials='D.' surname='Massey' fullname='D. Massey'><organization /></au
thor>
<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 DN
S Security Extensions (DNSSEC). The DNS Security Extensions are a collection of
new resource records and protocol modifications that add data origin authentica
tion 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 al
low a security-aware resolver to authenticate both DNS resource records and auth
oritative DNS error indications. </t><t> This document obsoletes RFC 2535 and in
corporates changes from all updates to RFC 2535. [STANDARDS-TRACK]</t></abstrac
t>
</front>
<seriesInfo name='RFC' value='4035'/>
<seriesInfo name='DOI' value='10.17487/RFC4035'/>
</reference>
<reference anchor="RFC5155" target='https://www.rfc-editor.org/info/rfc5155'>
<front>
<title>DNS Security (DNSSEC) Hashed Authenticated Denial of Existence</title>
<author initials='B.' surname='Laurie' fullname='B. Laurie'><organization /></au
thor>
<author initials='G.' surname='Sisson' fullname='G. Sisson'><organization /></au
thor>
<author initials='R.' surname='Arends' fullname='R. Arends'><organization /></au
thor>
<author initials='D.' surname='Blacka' fullname='D. Blacka'><organization /></au
thor>
<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 i
ntroduces an alternative resource record, NSEC3, which similarly provides authen
ticated denial of existence. However, it also provides measures against zone en
umeration and permits gradual expansion of delegation-centric zones. [STANDARDS
-TRACK]</t></abstract>
</front>
<seriesInfo name='RFC' value='5155'/>
<seriesInfo name='DOI' value='10.17487/RFC5155'/>
</reference>
<reference anchor="RFC2181" target='https://www.rfc-editor.org/info/rfc2181'>
<front>
<title>Clarifications to the DNS Specification</title>
<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 pro
blems with the specification of the Domain Name System, and proposes remedies fo
r the defects identified. [STANDARDS-TRACK]</t></abstract>
</front>
<seriesInfo name='RFC' value='2181'/>
<seriesInfo name='DOI' value='10.17487/RFC2181'/>
</reference>
<reference anchor="RFC5234" target='https://www.rfc-editor.org/info/rfc5234'>
<front>
<title>Augmented BNF for Syntax Specifications: ABNF</title>
<author initials='D.' surname='Crocker' fullname='D. Crocker' role='editor'><org
anization /></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 syn
tax. Over the years, a modified version of Backus-Naur Form (BNF), called Augme
nted BNF (ABNF), has been popular among many Internet specifications. The curre
nt specification documents ABNF. It balances compactness and simplicity with rea
sonable representational power. The differences between standard BNF and ABNF i
nvolve naming rules, repetition, alternatives, order-independence, and value ran
ges. This specification also supplies additional rule definitions and encoding
for a core lexical analyzer of the type common to several Internet specification
s. [STANDARDS-TRACK]</t></abstract>
</front>
<seriesInfo name='STD' value='68'/>
<seriesInfo name='RFC' value='5234'/>
<seriesInfo name='DOI' value='10.17487/RFC5234'/>
</reference>
<reference anchor="RFC7970" target='https://www.rfc-editor.org/info/rfc7970'>
<front>
<title>The Incident Object Description Exchange Format Version 2</title>
<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 d
ata representation for security incident reports and indicators commonly exchang
ed by operational security teams for mitigation and watch and warning. This doc
ument describes an updated information model for the IODEF and provides an assoc
iated data model specified with the XML schema. This new information and data m
odel obsoletes RFCs 5070 and 6685.</t></abstract>
</front>
<seriesInfo name='RFC' value='7970'/>
<seriesInfo name='DOI' value='10.17487/RFC7970'/>
</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>
<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 c
ommon 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 me
ssages over HTTP/TLS. [STANDARDS-TRACK]</t></abstract>
</front>
<seriesInfo name='RFC' value='6546'/>
<seriesInfo name='DOI' value='10.17487/RFC6546'/>
</reference>
<reference anchor="RFC6844" target='https://www.rfc-editor.org/info/rfc6844'>
<front>
<title>DNS Certification Authority Authorization (CAA) Resource Record</title>
<author initials='P.' surname='Hallam-Baker' fullname='P. Hallam-Baker'><organiz
ation /></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 Authoritie
s (CAs) authorized to issue certificates for that domain. CAA Resource Records a
llow 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>
<seriesInfo name='RFC' value='6844'/>
<seriesInfo name='DOI' value='10.17487/RFC6844'/>
</reference>
</references>
<references title='Informative References'>
<reference anchor="RFC3647" target='https://www.rfc-editor.org/info/rfc3647'>
<front>
<title>Internet X.509 Public Key Infrastructure Certificate Policy and Certifica
tion Practices Framework</title>
<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 /></au
thor>
<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 to assist the writers of certifi
cate policies or certification practice statements for participants within publi
c key infrastructures, such as certification authorities, policy authorities, an
d communities of interest that wish to rely on certificates. In particular, the
framework provides a comprehensive list of topics that potentially (at the writ
er's discretion) need to be covered in a certificate policy or a certification p
ractice statement. This document supersedes RFC 2527.</t></abstract>
</front>
<seriesInfo name='RFC' value='3647'/>
<seriesInfo name='DOI' value='10.17487/RFC3647'/>
</reference>
</references>
</back> </back>
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