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<rfc docName="draft-ietf-lamps-rfc6844bis-07" xmlns:xi="http://www.w3.org/2001/XInclude" submissionType="IETF"
     category="std" obsoletes="6844"> consensus="true" docName="draft-ietf-lamps-rfc6844bis-07" number="8659" ipr="trust200902" obsoletes="6844" updates="" xml:lang="en" tocInclude="true" sortRefs="true" symRefs="true" version="3">
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  <front>
    <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">
      <organization></organization>
      <organization>Venture Cryptography</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="November"/>
    <keyword>certificate</keyword>
    <keyword>ca</keyword>
    <keyword>pki</keyword>
    <keyword>issue</keyword>
    <keyword>issuance</keyword>
    <keyword>wildcard</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 CA 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> CAs.</t>
      <t>This document obsoletes RFC 6844.</t>
    </abstract>
  </front>
  <middle>
    <section anchor="introduction" title="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 CA 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"/>, target="RFC6698" format="default"/>, CAA records are used as a part of a
mechanism for checking PKIX <xref target="RFC6698"/> target="RFC6698" format="default"/> certificate data.  The distinction
between the two specifications CAA and TLSA is that CAA records specify an
authorization control to be performed by a certificate issuer CA before
issue of
issuing a certificate and TLSA records specify a verification
control to be performed by a relying party Relying Party after the certificate is
issued.</t>
issued.

</t>
      <t>Conformance with a published CAA record is a necessary necessary, but not
sufficient
sufficient, condition for the issuance of a certificate.</t>
      <t>Criteria for the 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 parties MUST
NOT Parties <bcp14>MUST
NOT</bcp14> use CAA records as part of certificate validation.</t>
      <t>CAA records MAY <bcp14>MAY</bcp14> be used by Certificate Evaluators as a possible
indicator of a security policy violation.  Such use SHOULD <bcp14>SHOULD</bcp14> take into
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" title="Definitions"> numbered="true" toc="default">
      <name>Definitions</name>
      <section anchor="requirements-language" title="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 BCP&nbsp;14
<xref target="RFC2119"/> target="RFC2119" format="default"/> <xref target="RFC8174"/> target="RFC8174" format="default"/> when,
and only when, they appear in all capitals, as shown here.</t>
      </section>
      <section anchor="defined-terms" title="Defined Terms"> numbered="true" toc="default">
        <name>Defined Terms</name>
        <t>The following terms are used in this document:</t>

<t>Certificate:  An
<dl>
          <dt>Certificate:</dt><dd>An X.509 Certificate, as specified in <xref target="RFC5280"/>.</t>

<t>Certificate Evaluator:  A target="RFC5280" format="default"/>.</dd>
          <dt>Certificate Evaluator:</dt><dd>A party other than a Relying Party that
   evaluates the trustworthiness of certificates issued by
   Certification Authorities.</t>

<t>Certification Authorities.</dd>
          <dt>Certification Authority (CA):  An (CA):</dt><dd>An Issuer that issues certificates in
   accordance with a specified Certificate Policy.</t>

<t>Certificate Policy.</dd>
          <dt>Certificate Policy (CP):  Specifies (CP):</dt><dd>Specifies the criteria that a Certification
   Authority CA
   undertakes to meet in its issue of certificates.  See
   <xref target="RFC3647"/>.</t>

<t>Certification target="RFC3647" format="default"/>.</dd>
          <dt>Certification Practices Statement (CPS):  Specifies (CPS):</dt><dd>Specifies the means by
   which the criteria of the Certificate Policy CP are met.  In most
   cases, this will be the document against which the operations of
   the Certification Authority CA are audited.  See <xref target="RFC3647"/>.</t>

<t>Domain Name: The target="RFC3647" format="default"/>.</dd>
          <dt>Domain Name:</dt><dd>The label assigned to a node in the Domain Name System.</t>

<t>Domain System.</dd>
          <dt>Domain Name System (DNS):  The (DNS):</dt><dd>The Internet naming system specified in
   <xref target="RFC1034"/> target="RFC1034" format="default"/> and <xref target="RFC1035"/>.</t>

<t>DNS target="RFC1035" format="default"/>.</dd>
          <dt>DNS Security (DNSSEC):  Extensions (DNSSEC):</dt><dd>Extensions to the DNS that provide
   authentication services as specified in <xref target="RFC4033"/>, target="RFC4033" format="default"/>, <xref target="RFC4034"/>, target="RFC4034" format="default"/>,
   <xref target="RFC4035"/>, target="RFC4035" format="default"/>, <xref target="RFC5155"/>, target="RFC5155" format="default"/>, and revisions.</t>

<t>Fully-Qualified Domain Name (FQDN): A
   any revisions to these specifications.</dd>
          <dt>Fully Qualified Domain Name (FQDN):</dt><dd>A domain name that includes the labels of all
  superior nodes in the Domain Name System.</t>

<t>Issuer:  An DNS.</dd>
          <dt>Issuer:</dt><dd>An entity that issues certificates.  See <xref target="RFC5280"/>.</t>

<t>Property:  The target="RFC5280" format="default"/>.</dd>
          <dt>Property:</dt><dd>The tag-value portion of a CAA Resource Record.</t>

<t>Property Tag:  The Record.</dd>
          <dt>Property Tag:</dt><dd>The tag portion of a CAA Resource Record.</t>

<t>Property Value:  The Record.</dd>
          <dt>Property Value:</dt><dd>The value portion of a CAA Resource Record.</t>

<t>Resource Record.</dd>
          <dt>Relevant Resource Record (RR):  A Set (Relevant RRset):</dt><dd>A set of CAA
   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 whose
   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 DNS, including the
   owner name, class, type, time to live, and data, as defined in
   <xref target="RFC1034"/> target="RFC1034" format="default"/> and <xref target="RFC2181"/>.</t>

<t>Resource target="RFC2181" format="default"/>.</dd>
          <dt>Resource Record Set (RRSet):  A (RRset):</dt><dd>A set of Resource Records RRs of a
   particular owner name, class, and type.  The time to live on all
   RRs within an RRSet RRset is always the same, but the data may be
   different among RRs in the RRSet.</t>

<t>Relevant Resource Record Set (Relevant RRSet):  A set of CAA Resource Records resulting
   from applying the algorithm in Section 3 to a specific Fully-Qualified Domain Name or
   Wildcard Domain Name.</t>

<t>Relying Party:  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"/>.</t>

<t>Wildcard Domain Name: A RRset.</dd>
          <dt>Wildcard Domain Name Name:</dt><dd>A domain name consisting of a single asterisk
   character followed by a single full stop "full stop" character (“*.”) ("*.") followed
   by a Fully-Qualified Domain Name.</t> an FQDN.</dd>
        </dl>
      </section>
    </section>
    <section anchor="relevant-resource-record-set" title="Relevant numbered="true" toc="default">
      <name>Relevant Resource Record Set"> Set</name>
      <t>Before issuing a certificate, a compliant CA MUST <bcp14>MUST</bcp14> check for
publication of a Relevant RRSet. RRset.  If such an RRSet RRset
exists, a CA MUST NOT <bcp14>MUST&nbsp;NOT</bcp14> issue a certificate unless the CA
determines that either (1) the (1)&nbsp;the certificate request is consistent with
the applicable CAA Resource Record set RRset or (2) an (2)&nbsp;an exception specified
in the relevant Certificate Policy CP or Certification Practices
Statement CPS applies. If the Relevant RRSet RRset for a Fully-Qualified Domain Name an FQDN
or Wildcard Domain Name contains no Property Tags that restrict issuance
(for instance, if it contains only iodef Property Tags, Tags or only Property
Tags unrecognized by the CA), CAA does not restrict issuance.</t>
      <t>A certificate request MAY <bcp14>MAY</bcp14> specify more than one Fully-Qualified Domain Name FQDN and MAY <bcp14>MAY</bcp14>
specify Wildcard Domain Names.  Issuers MUST <bcp14>MUST</bcp14> verify authorization for all
the Fully-Qualified Domain Names FQDNs and Wildcard Domain Names specified in the request.</t>
      <t>The search for a CAA RRSet RRset climbs the DNS name tree from the
specified label up to to, but not including including, the DNS root ‘.’ "."
until a CAA RRSet RRset is found.</t>
      <t>Given a request for a specific Fully-Qualified Domain Name X, FQDN X or a request for a Wildcard Domain
Name *.X, the Relevant Resource Record Set RRset RelevantCAASet(X) is determined as follows (in pseudocode):</t>

<t>Let
      <ul empty="true" spacing="normal">
        <li>Let CAA(X) be the RRSet RRset returned by performing a CAA record query for the
Fully-Qualified Domain Name
FQDN X, according to the lookup algorithm
specified in RFC 1034 section
4.3.2 <xref target="RFC1034" sectionFormat="of" section="4.3.2" /> (in particular particular, chasing
aliases). Let Parent(X) be the Fully-Qualified Domain Name FQDN produced by
removing the leftmost label of X.</t>

<figure><artwork><![CDATA[ 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
]]></artwork></figure>

<t>For ]]></sourcecode>

      <ul empty="true" spacing="normal">
        <li>For example, processing CAA for the Fully-Qualified Domain Name “X.Y.Z” FQDN "X.Y.Z" where there are
no CAA records at any level in the tree RelevantCAASet would have the
following steps:</t>

<figure><artwork><![CDATA[ steps:</li>
      </ul>
      <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></figure>

<t>Processing ]]></artwork>
      <ul empty="true" spacing="normal">
        <li>Processing CAA for the Fully-Qualified Domain Name “A.B.C” FQDN "A.B.C" where there is a CAA record
“issue example.com”
"issue example.com" at “B.C” "B.C" would terminate early upon finding the CAA
record:</t>

<figure><artwork><![CDATA[
record:</li>
      </ul>
      <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></figure> ]]></artwork>
    </section>
    <section anchor="mechanism" title="Mechanism"> numbered="true" toc="default">
      <name>Mechanism</name>
      <section anchor="syntax" title="Syntax"> numbered="true" toc="default">
        <name>Syntax</name>
        <t>A CAA Resource Record RR contains a single Property consisting of a tag-value tag&#8209;value
pair. A Fully-Qualified Domain Name MAY An FQDN <bcp14>MAY</bcp14> have multiple CAA RRs associated with it it, and a
given Property Tag MAY <bcp14>MAY</bcp14> be specified more than once across those RRs.</t>
        <t>The RDATA section for a CAA Resource Record RR contains one Property. A Property
consists of the following:</t>

<figure><artwork><![CDATA[
        <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></figure>
]]></artwork>
        <t>Where n is the length specified in the Tag length Length field and m is the
number of 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>
        <t>The fields are defined as follows:</t>

<t>Flags:  One
        <dl newline="false" spacing="normal">
          <dt>Flags:</dt>
          <dd>
            <t>One octet containing the following field:</t>

<t>Bit field:

            </t>
            <dl newline="false" spacing="normal">
              <dt>Bit 0, Issuer Critical Flag:  If Flag:</dt>
              <dd>If the value is set to ‘1’, "1", the
 Property is critical. A Certification Authority MUST NOT CA <bcp14>MUST NOT</bcp14> issue
 certificates for any FQDN if the Relevant RRSet RRset for
 that FQDN contains a CAA critical
 Property for an unknown or unsupported Property Tag.</t> Tag.

 </dd>
            </dl>
          </dd>
        </dl>
        <t>Note that according to the conventions set out in <xref target="RFC1035"/>, target="RFC1035" format="default"/>, bit 0
is the Most Significant Bit and bit 7 is the Least Significant
Bit. Thus, according to those conventions, the Flags value 1 means that bit 7 is set
set, while a value of 128 means that bit 0 is set according to this convention.</t> set.</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 MUST <bcp14>MUST</bcp14> clear
(set to “0”) "0") all reserved flags flag bits.

  Applications that interpret
CAA records MUST <bcp14>MUST</bcp14> ignore the value of all reserved flag bits.</t>

<t>Tag Length:  A
        <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 MUST <bcp14>MUST</bcp14> be at least 1.</t>

<t>Tag:  The 1.</dd>
          <dt>Tag:</dt>
          <dd>The Property identifier, identifier -- a sequence of US-ASCII characters.</t> ASCII characters.</dd>
        </dl>
        <t>Tags MAY <bcp14>MAY</bcp14> contain US-ASCII ASCII characters ‘a’ "a" through ‘z’, ‘A’ "z", "A"
through ‘Z’, "Z", and the numbers 0 through 9.  Tags MUST NOT <bcp14>MUST NOT</bcp14>
contain any other characters.  Matching of tags is case
insensitive.</t>
        <t>Tags submitted for registration by IANA MUST NOT <bcp14>MUST NOT</bcp14> contain any
characters other than the (lowercase) US-ASCII ASCII characters ‘a’ "a"
through ‘z’ "z" and the numbers 0 through 9.</t>

<t>Value:  A
        <dl newline="false" spacing="normal">
          <dt>Value:</dt>
          <dd>A sequence of octets representing the Property Value.
Property Values are encoded as binary values and MAY <bcp14>MAY</bcp14> employ
sub-formats.</t>
sub&#8209;formats.</dd>
        </dl>
        <t>The length of the value Value field is specified implicitly as the
remaining length of the enclosing RDATA section.</t>
        <section anchor="canonical-presentation-format" title="Canonical numbered="true" toc="default">
          <name>Canonical Presentation Format"> Format</name>
          <t>The canonical presentation format of the CAA record is:</t>

<t>CAA &lt;flags&gt; &lt;tag&gt; &lt;value&gt;</t>
          <artwork name="" type="" align="left" alt=""><![CDATA[
   CAA <flags> <tag> <value>
]]></artwork>
          <t>Where:</t>

<t>Flags:  Is an
          <dl newline="false" spacing="normal">
            <dt>Flags:</dt>
            <dd>An unsigned integer between 0 and 255.</t>

<t>Tag:  Is a 255.</dd>
            <dt>Tag:</dt>
            <dd>A non-zero-length sequence of US-ASCII ASCII letters and numbers in lower
   case.</t>

<t>Value:  The value lowercase.</dd>
            <dt>Value:</dt>
            <dd>The Value field, expressed as a either (1)&nbsp;a contiguous set of characters
   without interior spaces, spaces or as a (2)&nbsp;a quoted string.  See the
   &lt;character-string&gt; format specified in <xref target="RFC1035"></xref>, Section 5.1, target="RFC1035" sectionFormat="comma" section="5.1"/>,
   but note that the value Value field contains no length byte and is not
   limited to 255 characters.</t> characters.</dd>
          </dl>
        </section>
      </section>
      <section anchor="caa-issue-property" title="CAA numbered="true" toc="default">
        <name>CAA issue Property"> Property</name>
        <t>If the issue Property Tag is present in the Relevant RRSet RRset for a
Fully-Qualified Domain Name, an
FQDN, it is a request that Issuers</t>

<t><list style="numbers">
  <t>Perform Issuers:</t>
        <ol spacing="normal" type="1">
          <li>Perform CAA issue restriction processing for the FQDN, and</t>
  <t>Grant 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.</t>
</list></t>
 issuer-domain-name.</li>
        </ol>
        <t>The CAA issue Property Value has the following sub-syntax sub&#8209;syntax (specified
in ABNF as per <xref target="RFC5234"/>).</t>

<figure><artwork><![CDATA[ target="RFC5234" format="default"/>).</t>
        <sourcecode name="caa-issue-prop-value-abnf" 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></figure>
]]></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 RRset requests that no
certificates be issued for the FQDN ‘certs.example.com’ "certs.example.com" by any
Issuer other than ca1.example.net or ca2.example.org.</t>

<figure><artwork><![CDATA[
        <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></figure>
]]></artwork>
        <t>Because the presence of an issue Property Tag in the Relevant RRSet 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 RRset requests that no
certificates be issued for the FQDN ‘nocerts.example.com’ "nocerts.example.com" by any
Issuer.</t>

<figure><artwork><![CDATA[
        <artwork name="" type="" align="left" alt=""><![CDATA[
nocerts.example.com       CAA 0 issue ";"
]]></artwork></figure>
]]></artwork>
        <t>An issue Property Tag where the issue-value does not match the ABNF
grammar MUST <bcp14>MUST</bcp14> be treated the same as one specifying an empty issuer-domain-name. issuer&#8209;domain-name. For
example, the following malformed CAA RRSet RRset forbids issuance:</t>

<figure><artwork><![CDATA[
        <artwork name="" type="" align="left" alt=""><![CDATA[
malformed.example.com     CAA 0 issue "%%%%%"
]]></artwork></figure>
]]></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 Issuer MAY <bcp14>MAY</bcp14> choose to specify parameters that further
constrain the issue of certificates by that Issuer, Issuer -- for example,
specifying that certificates are to be subject to specific validation
polices,
policies, billed to certain accounts, or issued under specific trust
anchors.</t>
        <t>For example, if ca1.example.net has requested that its customer
accountable.example.com to
account.example.com specify their account number “230123” "230123" in each
of the customer’s customer's CAA records using the (CA-defined) “account” "account" parameter,
it would look like this:</t>

<figure><artwork><![CDATA[
accountable.example.com
        <artwork name="" type="" align="left" alt=""><![CDATA[
account.example.com   CAA 0 issue "ca1.example.net; account=230123"
]]></artwork></figure>
]]></artwork>
        <t>The semantics of parameters to the issue Property Tag are determined by
the Issuer alone.</t>
      </section>
      <section anchor="caa-issuewild-property" title="CAA numbered="true" toc="default">
        <name>CAA issuewild Property"> 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 each issuewild
properties take
Property takes precedence over each issue properties Property when specified.
Specifically:</t>

<t>issuewild properties MUST
        <t>Each issuewild Property <bcp14>MUST</bcp14> be ignored when processing a request for
a Fully-Qualified Domain Name
an FQDN that is not a Wildcard Domain Name.</t>
        <t>If at least one issuewild Property is specified in the Relevant
RRSet
RRset for a Wildcard Domain Name, all each issue properties MUST Property <bcp14>MUST</bcp14>
be ignored when processing a request for that Wildcard Domain Name.</t>
        <t>For example, the following RRSet RRset requests that <spanx style="emph">only</spanx> <em>only</em>
ca1.example.net issue certificates for “wild.example.com” "wild.example.com" or
“sub.wild.example.com”,
"sub.wild.example.com", and that <spanx style="emph">only</spanx> <em>only</em> ca2.example.org issue certificates for
“*.wild.example.com”
"*.wild.example.com" or “*.sub.wild.example.com). "*.sub.wild.example.com". Note that this presumes
that there are no CAA RRs for sub.wild.example.com.</t>

<figure><artwork><![CDATA[
        <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></figure>
]]></artwork>
        <t>The following RRSet RRset requests that <spanx style="emph">only</spanx> <em>only</em> ca1.example.net issue
certificates for “wild2.example.com”, “*.wild2.example.com” "wild2.example.com", "*.wild2.example.com", or
“*.sub.wild2.example.com”.</t>

<figure><artwork><![CDATA[
"*.sub.wild2.example.com".</t>
        <artwork name="" type="" align="left" alt=""><![CDATA[
wild2.example.com         CAA 0 issue "ca1.example.net"
]]></artwork></figure>
]]></artwork>
        <t>The following RRSet RRset requests that <spanx style="emph">only</spanx> <em>only</em> ca2.example.org issue
certificates for “*.wild3.example.com” "*.wild3.example.com" or “*.sub.wild3.example.com”. "*.sub.wild3.example.com". It
does not permit any Issuer to issue for “wild3.example.com” "wild3.example.com" or
“sub.wild3.example.com”.</t>

<figure><artwork><![CDATA[
"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></figure>
]]></artwork>
        <t>The following RRSet RRset requests that <spanx style="emph">only</spanx> <em>only</em> ca2.example.org issue
certificates for “*.wild3.example.com” "*.wild3.example.com" or “*.sub.wild3.example.com”. "*.sub.wild3.example.com". It
permits any Issuer to issue for “wild3.example.com” "wild3.example.com" or “sub.wild3.example.com”.</t>

<figure><artwork><![CDATA[ "sub.wild3.example.com".</t>
        <artwork name="" type="" align="left" alt=""><![CDATA[
wild3.example.com         CAA 0 issuewild "ca2.example.org"
]]></artwork></figure>
]]></artwork>
      </section>
      <section anchor="caa-iodef-property" title="CAA numbered="true" toc="default">
        <name>CAA iodef Property"> 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, 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"/> 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:  The
        <dl newline="false" spacing="normal">
          <dt>mailto:</dt>
          <dd>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 sent SHOULD <bcp14>SHOULD</bcp14> contain a brief text
   message to alert the recipient to the nature of the attachment.</t>

<t>http attachment.</dd>
          <dt>http or https:  The https:</dt>
          <dd>The IODEF report is submitted as a Web web service
   request to the HTTP address specified using the protocol specified
   in <xref target="RFC6546"/>.</t> target="RFC6546" format="default"/>.</dd>
        </dl>
        <t>These are the only supported URL schemes.</t>
        <t>The following RRSet RRset specifies
that reports may be made by means of email with the IODEF data as an
attachment, a Web web service <xref target="RFC6546"></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 iodef "mailto:security@example.com"
report.example.com         CAA 0 iodef "http://iodef.example.com/"
]]></artwork></figure> "https://iodef.example.com/"
]]></artwork>
      </section>
      <section anchor="critical-flag" title="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 that MUST <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’
"tbs" is flagged as critical.
Neither the ca1.example.net CA nor any other Issuer is authorized to
issue for “new.example.com” "new.example.com" (or any other domains for which this is
the Relevant RRSet) RRset) unless the Issuer has implemented the
processing rules for the ‘tbs’ "tbs" Property Tag.</t>

<figure><artwork><![CDATA[
        <artwork name="" type="" align="left" alt=""><![CDATA[
new.example.com       CAA 0 issue "ca1.example.net"
new.example.com       CAA 128 tbs "Unknown"
]]></artwork></figure>
]]></artwork>
      </section>
    </section>
    <section anchor="security-considerations" title="Security Considerations"> numbered="true" toc="default">
      <name>Security Considerations</name>
      <t>CAA records assert a security policy that the holder of an FDQN FQDN
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"/> target="RFC6698" format="default"/>
describes a mechanism for avoiding reliance on mis-issued
certificates.</t>
      <section anchor="use-of-dns-security" title="Use numbered="true" toc="default">
        <name>Use of DNS Security">

<t>Use Security</name>
        <t>The use of DNSSEC to authenticate CAA RRs is strongly RECOMMENDED <bcp14>RECOMMENDED</bcp14> but not
required.  An Issuer MUST NOT <bcp14>MUST NOT</bcp14> issue certificates if doing so would
conflict with the Relevant RRSet, RRset, irrespective of
whether the corresponding DNS records are signed.</t>
        <t>DNSSEC provides a proof of non-existence for both DNS Fully-Qualified Domain Names FQDNs and
RRSets
RRsets within FQDNs.  DNSSEC verification thus enables an Issuer to
determine if whether the answer to a CAA record query is (1)&nbsp;is empty because
the RRSet RRset is empty or if it is (2)&nbsp;is non-empty but the response has been
suppressed.</t>

<t>Use
        <t>The 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 record-processing compliance.  Publication of such archives may
be a transparency requirement to verify CAA record processing record-processing
compliance.</t>
      </section>
      <section anchor="non-compliance-by-certification-authority" title="Non-Compliance numbered="true" toc="default">
        <name>Non-compliance by Certification Authority"> 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
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" title="Mis-Issue numbered="true" toc="default">
        <name>Mis-Issue by Authorized Certification Authority">

<t>Use Authority</name>
        <t>The use of CAA records does not prevent mis-issue by an authorized
Certification Authority,
CA, i.e., a CA that is authorized to issue
certificates for the FQDN in question by CAA records.</t>
        <t>FQDN holders SHOULD <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 outside the scope of
this document.</t>
      </section>
      <section anchor="suppression-or-spoofing-of-caa-records" title="Suppression numbered="true" toc="default">
        <name>Suppression or Spoofing of CAA Records"> Records</name>
        <t>Suppression of the a 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, Issuers SHOULD <bcp14>SHOULD</bcp14> perform DNSSEC validation to detect
missing or modified CAA record sets.</t> RRsets.</t>
        <t>In cases where DNSSEC is not deployed for a corresponding FQDN, an
Issuer SHOULD <bcp14>SHOULD</bcp14> attempt to mitigate this risk by employing appropriate
DNS security controls.  For example, all portions of the DNS lookup
process SHOULD <bcp14>SHOULD</bcp14> be performed against the authoritative name server. nameserver.
Data cached by third parties MUST NOT <bcp14>MUST NOT</bcp14> be relied on as the sole source of DNS CAA
information but MAY <bcp14>MAY</bcp14> be used to
support additional anti-spoofing anti&#8209;spoofing or anti-suppression controls.</t>
      </section>
      <section anchor="denial-of-service" title="Denial numbered="true" toc="default">
        <name>Denial of Service"> Service</name>
        <t>Introduction of a malformed or malicious CAA RR could could, in theory 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 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" title="Abuse numbered="true" toc="default">
        <name>Abuse of the Critical Flag"> Flag</name>
        <t>A Certification Authority CA could make use of the critical flag to
trick customers into publishing records that prevent competing
Certification Authorities CAs
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 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" title="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" title="Blocked numbered="true" toc="default">
        <name>Blocked Queries or Responses"> Responses</name>
        <t>Some middleboxes, middleboxes -- in particular particular, anti-DDoS appliances, appliances -- may be configured to
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
DNS query, query or as a SERVFAIL at a local recursive resolver.</t>
      </section>
      <section anchor="rejected-queries-and-malformed-responses" title="Rejected numbered="true" toc="default">
        <name>Rejected Queries and Malformed Responses"> Responses</name>
        <t>Some authoritative nameservers respond with REJECTED or NOTIMP when queried
for a Resource Record an RR type they do not recognize. At least one authoritative
resolver produces a malformed response (with the QR (Query/Response) bit set to 0) "0") when queried
for unknown Resource Record RR types.  Per RFC 1034, <xref target="RFC1034"/>, the correct response RCODE for
unknown Resource Record RR types is NOERROR.</t> 0 ("No error condition").

</t>
      </section>
      <section anchor="delegation-to-private-nameservers" title="Delegation numbered="true" toc="default">
        <name>Delegation to Private Nameservers"> 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 CA MAY <bcp14>MAY</bcp14> interpret that as preventing
issuance. FQDN administrators wishing to issue certificates for private
FQDNs SHOULD <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" title="Bogus numbered="true" toc="default">
        <name>Bogus DNSSEC Responses"> Responses</name>
        <t>Queries for CAA Resource Records RRs are different from most DNS RR types, RR&nbsp;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, 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 RR 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 RRsets for DNSSEC-signed zones, in
combination with mixed-case queries. Mixed-case Mixed&#8209;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, section but also to 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" title="Differences versus RFC6844"> numbered="true" toc="default">
      <name>Differences from RFC 6844</name>
      <t>This document obsoletes RFC6844. <xref target="RFC6844"/>. The most important change is to
the Certification "Certification Authority Processing section. RFC6844 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
being processed, 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, 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’ customers' FQDNs.
This document specifies a simplified processing algorithm that only
performs tree climbing tree-climbing on the FQDN being processed, and it leaves the
processing of CNAMEs and DNAMEs up to the CA’s CA's recursive resolver.</t>
      <t>This document also includes a “Deployment Considerations” "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 the processing of a CAA RRset that is not empty, empty
but contains no that does not contain any issue or issuewild tags.</t>
      <t>This document removes the section titled “The "The CAA RR Type,” Type," merging it with
“Mechanism”
"Mechanism" (<xref target="mechanism"/>) because the definitions were mainly duplicates. It moves the “Use "Use of
DNS Security” Security" section into Security Considerations. Considerations (<xref target="security-considerations"/>). It renames “Certification "Certification
Authority Processing” Processing" to “Relevant "Relevant Resource Record Set,” 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" title="IANA Considerations"> numbered="true" toc="default">
      <name>IANA Considerations</name>
      <t>IANA is requested to add [[[ RFC Editor: Please replace with has added this RFC ]]] document as
a reference for the Certification "Certification Authority Restriction Flags Flags" and
Certification
"Certification Authority Restriction Properties registries, Properties" registries and update updated
references to <xref target="RFC6844"/> target="RFC6844" format="default"/> within those registries to refer instead to [[[ RFC Editor: Please
replace with
this RFC ]]]. document. IANA is has also
requested to update updated the CAA TYPE in the DNS Parameters
"Resource Record (RR) TYPEs" subregistry of the "Domain Name System (DNS) Parameters" registry with a reference
to [[[ RFC Editor: Please replace with this RFC ]]].</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"/>
<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" title="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,
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>

  </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 Security (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 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>
</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 Community, 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 /></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>
<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 Revocation List (CRL) Profile</title>
<author 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>
<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'><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>
<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'><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>
<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 /></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>
</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 /></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>
<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 /></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>
<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 /></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>
<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 problems with the specification of the Domain Name System, and proposes remedies for 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'><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>
</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 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>
<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 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>
<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'><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>
<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 Certification 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 /></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 to assist the writers of certificate policies or certification practice statements for participants within public key infrastructures, such as certification authorities, policy authorities, and communities of interest that wish to rely on certificates.  In particular, the framework provides a comprehensive list of topics 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>
<seriesInfo name='RFC' value='3647'/>
<seriesInfo name='DOI' value='10.17487/RFC3647'/>
</reference>

    </references>
  </back>

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