doc: Add RFC documents

1 files changed, 1011 insertions, 0 deletions

diff --git a/doc/rfc/rfc6844.txt b/doc/rfc/rfc6844.txt
new file mode 100644
index 0000000..d923649
--- /dev/null
+++ b/doc/rfc/rfc6844.txt
@@ -0,0 +1,1011 @@
+
+
+
+
+
+
+Internet Engineering Task Force (IETF)                   P. Hallam-Baker
+Request for Comments: 6844                            Comodo Group, Inc.
+Category: Standards Track                                   R. Stradling
+ISSN: 2070-1721                                          Comodo CA, Ltd.
+                                                            January 2013
+
+
+    DNS Certification Authority Authorization (CAA) Resource Record
+
+Abstract
+
+   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.
+
+Status of This Memo
+
+   This is an Internet Standards Track document.
+
+   This document is a product of the Internet Engineering Task Force
+   (IETF).  It represents the consensus of the IETF community.  It has
+   received public review and has been approved for publication by the
+   Internet Engineering Steering Group (IESG).  Further information on
+   Internet Standards is available in Section 2 of RFC 5741.
+
+   Information about the current status of this document, any errata,
+   and how to provide feedback on it may be obtained at
+   http://www.rfc-editor.org/info/rfc6844.
+
+Copyright Notice
+
+   Copyright (c) 2013 IETF Trust and the persons identified as the
+   document authors.  All rights reserved.
+
+   This document is subject to BCP 78 and the IETF Trust's Legal
+   Provisions Relating to IETF Documents
+   (http://trustee.ietf.org/license-info) in effect on the date of
+   publication of this document.  Please review these documents
+   carefully, as they describe your rights and restrictions with respect
+   to this document.  Code Components extracted from this document must
+   include Simplified BSD License text as described in Section 4.e of
+   the Trust Legal Provisions and are provided without warranty as
+   described in the Simplified BSD License.
+
+
+
+
+Hallam-Baker & Stradling     Standards Track                    [Page 1]
+
+RFC 6844          Certification Authority Authorization     January 2013
+
+
+Table of Contents
+
+   1. Introduction ....................................................2
+   2. Definitions .....................................................3
+      2.1. Requirements Language ......................................3
+      2.2. Defined Terms ..............................................3
+   3. The CAA RR Type .................................................5
+   4. Certification Authority Processing ..............................7
+      4.1. Use of DNS Security ........................................8
+   5. Mechanism .......................................................8
+      5.1. Syntax .....................................................8
+           5.1.1. Canonical Presentation Format ......................10
+      5.2. CAA issue Property ........................................10
+      5.3. CAA issuewild Property ....................................12
+      5.4. CAA iodef Property ........................................12
+   6. Security Considerations ........................................13
+      6.1. Non-Compliance by Certification Authority .................13
+      6.2. Mis-Issue by Authorized Certification Authority ...........13
+      6.3. Suppression or Spoofing of CAA Records ....................13
+      6.4. Denial of Service .........................................14
+      6.5. Abuse of the Critical Flag ................................14
+   7. IANA Considerations ............................................14
+      7.1. Registration of the CAA Resource Record Type ..............14
+      7.2. Certification Authority Restriction Properties ............15
+      7.3. Certification Authority Restriction Flags .................15
+   8. Acknowledgements ...............................................16
+   9. References .....................................................16
+      9.1. Normative References ......................................16
+      9.2. Informative References ....................................17
+
+1.  Introduction
+
+   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.
+   Publication of CAA Resource Records allows a public Certification
+   Authority to implement additional controls to reduce the risk of
+   unintended certificate mis-issue.
+
+   Like the TLSA record defined in DNS-Based Authentication of Named
+   Entities (DANE) [RFC6698], CAA records are used as a part of a
+   mechanism for checking PKIX certificate data.  The distinction
+   between the two specifications is that CAA records specify an
+   authorization control to be performed by a certificate issuer before
+   issue of a certificate and TLSA records specify a verification
+   control to be performed by a relying party after the certificate is
+   issued.
+
+
+
+
+Hallam-Baker & Stradling     Standards Track                    [Page 2]
+
+RFC 6844          Certification Authority Authorization     January 2013
+
+
+   Conformance with a published CAA record is a necessary but not
+   sufficient condition for issuance of a certificate.  Before issuing a
+   certificate, a PKIX CA is required to validate the request according
+   to the policies set out in its Certificate Policy.  In the case of a
+   public CA that validates certificate requests as a third party, the
+   certificate will typically be issued under a public trust anchor
+   certificate embedded in one or more relevant Relying Applications.
+
+   Criteria for inclusion of embedded trust anchor certificates in
+   applications are outside the scope of this document.  Typically, such
+   criteria require the CA to publish a Certificate 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.
+
+   A set of CAA records describes only current grants of authority to
+   issue certificates for the corresponding DNS domain.  Since a
+   certificate is typically valid for at least a year, 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 Applications MUST
+   NOT use CAA records as part of certificate validation.
+
+   CAA records MAY be used by Certificate Evaluators as a possible
+   indicator of a security policy violation.  Such use SHOULD take
+   account of the possibility that published CAA records changed between
+   the time a certificate was issued and the time at which the
+   certificate was observed by the Certificate Evaluator.
+
+2.  Definitions
+
+2.1.  Requirements Language
+
+   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
+   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
+   document are to be interpreted as described in [RFC2119].
+
+2.2.  Defined Terms
+
+   The following terms are used in this document:
+
+   Authorization Entry:  An authorization assertion that grants or
+      denies a specific set of permissions to a specific group of
+      entities.
+
+   Certificate:  An X.509 Certificate, as specified in [RFC5280].
+
+
+
+
+Hallam-Baker & Stradling     Standards Track                    [Page 3]
+
+RFC 6844          Certification Authority Authorization     January 2013
+
+
+   Certificate Evaluator:  A party other than a relying party that
+      evaluates the trustworthiness of certificates issued by
+      Certification Authorities.
+
+   Certification Authority (CA):  An issuer that issues certificates in
+      accordance with a specified Certificate Policy.
+
+   Certificate Policy (CP):  Specifies the criteria that a Certification
+      Authority undertakes to meet in its issue of certificates.  See
+      [RFC3647].
+
+   Certification Practices Statement (CPS):  Specifies the means by
+      which the criteria of the Certificate Policy are met.  In most
+      cases, this will be the document against which the operations of
+      the Certification Authority are audited.  See [RFC3647].
+
+   Domain:  A DNS Domain Name.
+
+   Domain Name:  A DNS Domain Name as specified in [STD13].
+
+   Domain Name System (DNS):  The Internet naming system specified in
+      [STD13].
+
+   DNS Security (DNSSEC):  Extensions to the DNS that provide
+      authentication services as specified in [RFC4033], [RFC4034],
+      [RFC4035], [RFC5155], and revisions.
+
+   Issuer:  An entity that issues certificates.  See [RFC5280].
+
+   Property:  The tag-value portion of a CAA Resource Record.
+
+   Property Tag:  The tag portion of a CAA Resource Record.
+
+   Property Value:  The value portion of a CAA Resource Record.
+
+   Public Key Infrastructure X.509 (PKIX):  Standards and specifications
+      issued by the IETF that apply the [X.509] certificate standards
+      specified by the ITU to Internet applications as specified in
+      [RFC5280] and related documents.
+
+   Resource Record (RR):  A particular entry in the DNS including the
+      owner name, class, type, time to live, and data, as defined in
+      [STD13] and [RFC2181].
+
+   Resource Record Set (RRSet):  A set of Resource Records or a
+      particular owner name, class, and type.  The time to live on all
+      RRs with an RRSet is always the same, but the data may be
+      different among RRs in the RRSet.
+
+
+
+Hallam-Baker & Stradling     Standards Track                    [Page 4]
+
+RFC 6844          Certification Authority Authorization     January 2013
+
+
+   Relying Party:  A party that makes use of an application whose
+      operation depends on use of a certificate for making a security
+      decision.  See [RFC5280].
+
+   Relying Application:  An application whose operation depends on use
+      of a certificate for making a security decision.
+
+3.  The CAA RR Type
+
+   A CAA RR consists of a flags byte and a tag-value pair referred to as
+   a property.  Multiple properties MAY be associated with the same
+   domain name by publishing multiple CAA RRs at that domain name.  The
+   following flag is defined:
+
+   Issuer Critical:  If set to '1', indicates that the corresponding
+      property tag MUST be understood if the semantics of the CAA record
+      are to be correctly interpreted by an issuer.
+
+      Issuers MUST NOT issue certificates for a domain if the relevant
+      CAA Resource Record set contains unknown property tags that have
+      the Critical bit set.
+
+   The following property tags are defined:
+
+   issue <Issuer Domain Name> [; <name>=<value> ]* :  The issue property
+      entry authorizes the holder of the domain name <Issuer Domain
+      Name> or a party acting under the explicit authority of the holder
+      of that domain name to issue certificates for the domain in which
+      the property is published.
+
+   issuewild <Issuer Domain Name> [; <name>=<value> ]* :  The issuewild
+      property entry authorizes the holder of the domain name <Issuer
+      Domain Name> or a party acting under the explicit authority of the
+      holder of that domain name to issue wildcard certificates for the
+      domain in which the property is published.
+
+   iodef <URL> :  Specifies a URL to which an issuer MAY report
+      certificate issue requests that are inconsistent with the issuer's
+      Certification Practices or Certificate Policy, or that a
+      Certificate Evaluator may use to report observation of a possible
+      policy violation.  The Incident Object Description Exchange Format
+      (IODEF) format is used [RFC5070].
+
+   The following example is a DNS zone file (see [RFC1035]) that informs
+   CAs that certificates are not to be issued except by the holder of
+   the domain name 'ca.example.net' or an authorized agent thereof.
+   This policy applies to all subordinate domains under example.com.
+
+
+
+
+Hallam-Baker & Stradling     Standards Track                    [Page 5]
+
+RFC 6844          Certification Authority Authorization     January 2013
+
+
+   $ORIGIN example.com
+   .       CAA 0 issue "ca.example.net"
+
+   If the domain name holder specifies one or more iodef properties, a
+   certificate issuer MAY report invalid certificate requests to that
+   address.  In the following example, the domain name holder specifies
+   that reports may be made by means of email with the IODEF data as an
+   attachment, a Web service [RFC6546], or both:
+
+   $ORIGIN example.com
+   .       CAA 0 issue "ca.example.net"
+   .       CAA 0 iodef "mailto:security@example.com"
+   .       CAA 0 iodef "http://iodef.example.com/"
+
+   A certificate issuer MAY specify additional parameters that allow
+   customers to specify additional parameters governing certificate
+   issuance.  This might be the Certificate Policy under which the
+   certificate is to be issued, the authentication process to be used
+   might be specified, or an account number specified by the CA to
+   enable these parameters to be retrieved.
+
+   For example, the CA 'ca.example.net' has requested its customer
+   'example.com' to specify the CA's account number '230123' in each of
+   the customer's CAA records.
+
+   $ORIGIN example.com
+   .       CAA 0 issue "ca.example.net; account=230123"
+
+   The syntax of additional parameters is a sequence of name-value pairs
+   as defined in Section 5.2.  The semantics of such parameters is left
+   to site policy and is outside the scope of this document.
+
+   The critical flag is intended to permit future versions CAA to
+   introduce new semantics that MUST be understood for correct
+   processing of the record, preventing conforming CAs that do not
+   recognize the new semantics from issuing certificates for the
+   indicated domains.
+
+   In the following example, the property 'tbs' is flagged as critical.
+   Neither the example.net CA nor any other issuer is authorized to
+   issue under either policy unless the processing rules for the 'tbs'
+   property tag are understood.
+
+   $ORIGIN example.com
+   .       CAA 0 issue "ca.example.net; policy=ev"
+   .       CAA 128 tbs "Unknown"
+
+
+
+
+
+Hallam-Baker & Stradling     Standards Track                    [Page 6]
+
+RFC 6844          Certification Authority Authorization     January 2013
+
+
+   Note that the above restrictions only apply at certificate issue.
+   Since the validity of an end entity certificate is typically a year
+   or more, it is quite possible that the CAA records published at a
+   domain will change between the time a certificate was issued and
+   validation by a relying party.
+
+4.  Certification Authority Processing
+
+   Before issuing a certificate, a compliant CA MUST check for
+   publication of a relevant CAA Resource Record set.  If such a record
+   set 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.
+
+   A certificate request MAY specify more than one domain name and MAY
+   specify wildcard domains.  Issuers MUST verify authorization for all
+   the domains and wildcard domains specified in the request.
+
+   The search for a CAA record climbs the DNS name tree from the
+   specified label up to but not including the DNS root '.'.
+
+   Given a request for a specific domain X, or a request for a wildcard
+   domain *.X, the relevant record set R(X) is determined as follows:
+
+   Let CAA(X) be the record set returned in response to performing a CAA
+   record query on the label X, P(X) be the DNS label immediately above
+   X in the DNS hierarchy, and A(X) be the target of a CNAME or DNAME
+   alias record specified at the label X.
+
+   o  If CAA(X) is not empty, R(X) = CAA (X), otherwise
+
+   o  If A(X) is not null, and R(A(X)) is not empty, then R(X) =
+      R(A(X)), otherwise
+
+   o  If X is not a top-level domain, then R(X) = R(P(X)), otherwise
+
+   o  R(X) is empty.
+
+   For example, if a certificate is requested for X.Y.Z the issuer will
+   search for the relevant CAA record set in the following order:
+
+      X.Y.Z
+
+      Alias (X.Y.Z)
+
+      Y.Z
+
+
+
+Hallam-Baker & Stradling     Standards Track                    [Page 7]
+
+RFC 6844          Certification Authority Authorization     January 2013
+
+
+      Alias (Y.Z)
+
+      Z
+
+      Alias (Z)
+
+      Return Empty
+
+4.1.  Use of DNS Security
+
+   Use of DNSSEC to authenticate CAA RRs is strongly RECOMMENDED but not
+   required.  An issuer MUST NOT issue certificates if doing so would
+   conflict with the relevant CAA Resource Record set, irrespective of
+   whether the corresponding DNS records are signed.
+
+   DNSSEC provides a proof of non-existence for both DNS domains and RR
+   set within domains.  DNSSEC verification thus enables an issuer to
+   determine if the answer to a CAA record query is empty because the RR
+   set is empty or if it is non-empty but the response has been
+   suppressed.
+
+   Use of DNSSEC allows an issuer to acquire and archive a proof that
+   they were authorized to issue certificates for the domain.
+   Verification of such archives MAY be an audit requirement to verify
+   CAA record processing compliance.  Publication of such archives MAY
+   be a transparency requirement to verify CAA record processing
+   compliance.
+
+5.  Mechanism
+
+5.1.  Syntax
+
+   A CAA RR contains a single property entry consisting of a tag-value
+   pair.  Each tag represents a property of the CAA record.  The value
+   of a CAA property is that specified in the corresponding value field.
+
+   A domain name MAY have multiple CAA RRs associated with it and a
+   given property MAY be specified more than once.
+
+   The CAA data field contains one property entry.  A property entry
+   consists of the following data fields:
+
+
+
+
+
+
+
+
+
+
+Hallam-Baker & Stradling     Standards Track                    [Page 8]
+
+RFC 6844          Certification Authority Authorization     January 2013
+
+
+   +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 |
+   +----------------+----------------+.....+----------------+
+
+   Where n is the length specified in the Tag length field and m is the
+   remaining octets in the Value field (m = d - n - 2) where d is the
+   length of the RDATA section.
+
+   The data fields are defined as follows:
+
+   Flags:  One octet containing the following fields:
+
+      Bit 0, Issuer Critical Flag:  If the value is set to '1', the
+         critical flag is asserted and the property MUST be understood
+         if the CAA record is to be correctly processed by a certificate
+         issuer.
+
+         A Certification Authority MUST NOT issue certificates for any
+         Domain that contains a CAA critical property for an unknown or
+         unsupported property tag that for which the issuer critical
+         flag is set.
+
+      Note that according to the conventions set out in [RFC1035], bit 0
+      is the Most Significant Bit and bit 7 is the Least Significant
+      Bit. Thus, the Flags value 1 means that bit 7 is set while a value
+      of 128 means that bit 0 is set according to this convention.
+
+      All other bit positions are reserved for future use.
+
+      To ensure compatibility with future extensions to CAA, DNS records
+      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.
+
+   Tag Length:  A single octet containing an unsigned integer specifying
+      the tag length in octets.  The tag length MUST be at least 1 and
+      SHOULD be no more than 15.
+
+
+
+
+
+
+
+
+
+Hallam-Baker & Stradling     Standards Track                    [Page 9]
+
+RFC 6844          Certification Authority Authorization     January 2013
+
+
+   Tag:  The property identifier, a sequence of US-ASCII characters.
+
+      Tag values MAY contain US-ASCII characters 'a' through 'z', 'A'
+      through 'Z', and the numbers 0 through 9.  Tag values SHOULD NOT
+      contain any other characters.  Matching of tag values is case
+      insensitive.
+
+      Tag values submitted for registration by IANA MUST NOT contain any
+      characters other than the (lowercase) US-ASCII characters 'a'
+      through 'z' and the numbers 0 through 9.
+
+   Value:  A sequence of octets representing the property value.
+      Property values are encoded as binary values and MAY employ sub-
+      formats.
+
+      The length of the value field is specified implicitly as the
+      remaining length of the enclosing Resource Record data field.
+
+5.1.1.  Canonical Presentation Format
+
+   The canonical presentation format of the CAA record is:
+
+   CAA <flags> <tag> <value>
+
+   Where:
+
+   Flags:  Is an unsigned integer between 0 and 255.
+
+   Tag:  Is a non-zero sequence of US-ASCII letters and numbers in lower
+      case.
+
+   Value:  Is the <character-string> encoding of the value field as
+      specified in [RFC1035], Section 5.1.
+
+5.2.  CAA issue Property
+
+   The issue property tag is used to request that certificate issuers
+   perform CAA issue restriction processing for the domain and to grant
+   authorization to specific certificate issuers.
+
+   The CAA issue property value has the following sub-syntax (specified
+   in ABNF as per [RFC5234]).
+
+
+
+
+
+
+
+
+
+Hallam-Baker & Stradling     Standards Track                   [Page 10]
+
+RFC 6844          Certification Authority Authorization     January 2013
+
+
+   issuevalue  = space [domain] space [";" *(space parameter) space]
+
+   domain = label *("." label)
+   label = (ALPHA / DIGIT) *( *("-") (ALPHA / DIGIT))
+
+   space = *(SP / HTAB)
+
+   parameter =  tag "=" value
+
+   tag = 1*(ALPHA / DIGIT)
+
+   value = *VCHAR
+
+   For consistency with other aspects of DNS administration, domain name
+   values are specified in letter-digit-hyphen Label (LDH-Label) form.
+
+   A CAA record with an issue parameter tag that does not specify a
+   domain name is a request that certificate issuers perform CAA issue
+   restriction processing for the corresponding domain without granting
+   authorization to any certificate issuer.
+
+   This form of issue restriction would be appropriate to specify that
+   no certificates are to be issued for the domain in question.
+
+   For example, the following CAA record set requests that no
+   certificates be issued for the domain 'nocerts.example.com' by any
+   certificate issuer.
+
+   nocerts.example.com       CAA 0 issue ";"
+
+   A CAA record with an issue parameter tag that specifies a domain name
+   is a request that certificate issuers perform CAA issue restriction
+   processing for the corresponding domain and grants authorization to
+   the certificate issuer specified by the domain name.
+
+   For example, the following CAA record set requests that no
+   certificates be issued for the domain 'certs.example.com' by any
+   certificate issuer other than the example.net certificate issuer.
+
+   certs.example.com       CAA 0 issue "example.net"
+
+   CAA authorizations are additive; thus, the result of specifying both
+   the empty issuer and a specified issuer is the same as specifying
+   just the specified issuer alone.
+
+
+
+
+
+
+
+Hallam-Baker & Stradling     Standards Track                   [Page 11]
+
+RFC 6844          Certification Authority Authorization     January 2013
+
+
+   An issuer MAY choose to specify issuer-parameters that further
+   constrain the issue of certificates by that issuer, for example,
+   specifying that certificates are to be subject to specific validation
+   polices, billed to certain accounts, or issued under specific trust
+   anchors.
+
+   The semantics of issuer-parameters are determined by the issuer
+   alone.
+
+5.3.  CAA issuewild Property
+
+   The issuewild property has the same syntax and semantics as the issue
+   property except that issuewild properties only grant authorization to
+   issue certificates that specify a wildcard domain and issuewild
+   properties take precedence over issue properties when specified.
+   Specifically:
+
+      issuewild properties MUST be ignored when processing a request for
+      a domain that is not a wildcard domain.
+
+      If at least one issuewild property is specified in the relevant
+      CAA record set, all issue properties MUST be ignored when
+      processing a request for a domain that is a wildcard domain.
+
+5.4.  CAA iodef Property
+
+   The iodef property specifies a means of reporting certificate issue
+   requests or cases of certificate issue for the corresponding domain
+   that violate the security policy of the issuer or the domain name
+   holder.
+
+   The Incident Object Description Exchange Format (IODEF) [RFC5070] is
+   used to present the incident report in machine-readable form.
+
+   The iodef property takes a URL as its parameter.  The URL scheme type
+   determines the method used for reporting:
+
+   mailto:  The IODEF incident report is reported as a MIME email
+      attachment to an SMTP email that is submitted to the mail address
+      specified.  The mail message sent SHOULD contain a brief text
+      message to alert the recipient to the nature of the attachment.
+
+   http or https:  The IODEF report is submitted as a Web service
+      request to the HTTP address specified using the protocol specified
+      in [RFC6546].
+
+
+
+
+
+
+Hallam-Baker & Stradling     Standards Track                   [Page 12]
+
+RFC 6844          Certification Authority Authorization     January 2013
+
+
+6.  Security Considerations
+
+   CAA records assert a security policy that the holder of a domain name
+   wishes to be observed by certificate issuers.  The effectiveness of
+   CAA records as an access control mechanism is thus dependent on
+   observance of CAA constraints by issuers.
+
+   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 [RFC6698]
+   describes a mechanism for avoiding reliance on mis-issued
+   certificates.
+
+6.1.  Non-Compliance by Certification Authority
+
+   CAA records offer CAs a cost-effective means of mitigating the risk
+   of certificate mis-issue: the cost of implementing CAA checks is very
+   small and the potential costs of a mis-issue event include the
+   removal of an embedded trust anchor.
+
+6.2.  Mis-Issue by Authorized Certification Authority
+
+   Use of CAA records does not prevent mis-issue by an authorized
+   Certification Authority, i.e., a CA that is authorized to issue
+   certificates for the domain in question by CAA records.
+
+   Domain name holders SHOULD verify that the CAs they authorize to
+   issue certificates for their domains employ appropriate controls to
+   ensure that certificates are issued only to authorized parties within
+   their organization.
+
+   Such controls are most appropriately determined by the domain name
+   holder and the authorized CA(s) directly and are thus out of scope of
+   this document.
+
+6.3.  Suppression or Spoofing of CAA Records
+
+   Suppression of the CAA record or insertion of a bogus CAA record
+   could enable an attacker to obtain a certificate from an issuer that
+   was not authorized to issue for that domain name.
+
+   Where possible, issuers SHOULD perform DNSSEC validation to detect
+   missing or modified CAA record sets.
+
+   In cases where DNSSEC is not deployed in a corresponding domain, an
+   issuer SHOULD attempt to mitigate this risk by employing appropriate
+   DNS security controls.  For example, all portions of the DNS lookup
+
+
+
+
+Hallam-Baker & Stradling     Standards Track                   [Page 13]
+
+RFC 6844          Certification Authority Authorization     January 2013
+
+
+   process SHOULD be performed against the authoritative name server.
+   Data cached by third parties MUST NOT be relied on but MAY be used to
+   support additional anti-spoofing or anti-suppression controls.
+
+6.4.  Denial of Service
+
+   Introduction of a malformed or malicious CAA RR could in theory
+   enable a Denial-of-Service (DoS) attack.
+
+   This specific threat is not considered to add significantly to the
+   risk of running an insecure DNS service.
+
+   An attacker could, in principle, perform a DoS attack against an
+   issuer by requesting a certificate with a maliciously long DNS name.
+   In practice, the DNS protocol imposes a maximum name length and CAA
+   processing does not exacerbate the existing need to mitigate DoS
+   attacks to any meaningful degree.
+
+6.5.  Abuse of the Critical Flag
+
+   A Certification Authority could make use of the critical flag to
+   trick customers into publishing records that prevent competing
+   Certification Authorities from issuing certificates even though the
+   customer intends to authorize multiple providers.
+
+   In practice, such an attack would be of minimal effect since any
+   competent competitor that found itself unable to issue certificates
+   due to lack of support for a property marked critical SHOULD
+   investigate the cause and report the reason to the customer.  The
+   customer will thus discover that they had been deceived.
+
+7.  IANA Considerations
+
+7.1.  Registration of the CAA Resource Record Type
+
+   IANA has assigned Resource Record Type 257 for the CAA Resource
+   Record Type and added the line depicted below to the registry named
+   "Resource Record (RR) TYPEs" and QTYPEs as defined in BCP 42
+   [RFC6195] and located at
+   http://www.iana.org/assignments/dns-parameters.
+
+ RR Name      Value and meaning                                Reference
+ -----------  ---------------------------------------------    ---------
+ CAA          257 Certification Authority Restriction          [RFC6844]
+
+
+
+
+
+
+
+Hallam-Baker & Stradling     Standards Track                   [Page 14]
+
+RFC 6844          Certification Authority Authorization     January 2013
+
+
+7.2.  Certification Authority Restriction Properties
+
+   IANA has created the "Certification Authority Restriction Properties"
+   registry with the following initial values:
+
+
+   Tag          Meaning                                Reference
+   -----------  -------------------------------------- ---------
+   issue        Authorization Entry by Domain          [RFC6844]
+   issuewild    Authorization Entry by Wildcard Domain [RFC6844]
+   iodef        Report incident by IODEF report        [RFC6844]
+   auth         Reserved                               [HB2011]
+   path         Reserved                               [HB2011]
+   policy       Reserved                               [HB2011]
+
+
+   Although [HB2011] has expired, deployed clients implement the CAA
+   properties specified in the document and reuse of these property tags
+   for a different purpose could cause unexpected behavior.
+
+   Addition of tag identifiers requires a public specification and
+   Expert Review as set out in [RFC6195], Section 3.1.1.
+
+   The tag space is designed to be sufficiently large that exhausting
+   the possible tag space need not be a concern.  The scope of Expert
+   Review SHOULD be limited to the question of whether the specification
+   provided is sufficiently clear to permit implementation and to avoid
+   unnecessary duplication of functionality.
+
+7.3.  Certification Authority Restriction Flags
+
+   IANA has created the "Certification Authority Restriction Flags"
+   registry with the following initial values:
+
+
+             Flag         Meaning                            Reference
+   -----------  ---------------------------------- ---------
+   0            Issuer Critical Flag               [RFC6844]
+   1-7          Reserved>                          [RFC6844]
+
+   Assignment of new flags follows the RFC Required policy set out in
+   [RFC5226], Section 4.1.
+
+
+
+
+
+
+
+
+
+Hallam-Baker & Stradling     Standards Track                   [Page 15]
+
+RFC 6844          Certification Authority Authorization     January 2013
+
+
+8.  Acknowledgements
+
+   The authors would like to thank the following people who contributed
+   to the design and documentation of this work item: Chris Evans,
+   Stephen Farrell, Jeff Hodges, Paul Hoffman, Stephen Kent, Adam
+   Langley, Ben Laurie, James Manager, Chris Palmer, Scott Schmit, Sean
+   Turner, and Ben Wilson.
+
+9.  References
+
+9.1.  Normative References
+
+   [RFC1035]  Mockapetris, P., "Domain names - implementation and
+              specification", STD 13, RFC 1035, November 1987.
+
+   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
+              Requirement Levels", BCP 14, RFC 2119, March 1997.
+
+   [RFC2181]  Elz, R. and R. Bush, "Clarifications to the DNS
+              Specification", RFC 2181, July 1997.
+
+   [RFC4033]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
+              Rose, "DNS Security Introduction and Requirements",
+              RFC 4033, March 2005.
+
+   [RFC4034]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
+              Rose, "Resource Records for the DNS Security Extensions",
+              RFC 4034, March 2005.
+
+   [RFC4035]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
+              Rose, "Protocol Modifications for the DNS Security
+              Extensions", RFC 4035, March 2005.
+
+   [RFC5070]  Danyliw, R., Meijer, J., and Y. Demchenko, "The Incident
+              Object Description Exchange Format", RFC 5070,
+              December 2007.
+
+   [RFC5155]  Laurie, B., Sisson, G., Arends, R., and D. Blacka, "DNS
+              Security (DNSSEC) Hashed Authenticated Denial of
+              Existence", RFC 5155, March 2008.
+
+   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
+              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
+              May 2008.
+
+   [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
+              Specifications: ABNF", STD 68, RFC 5234, January 2008.
+
+
+
+
+Hallam-Baker & Stradling     Standards Track                   [Page 16]
+
+RFC 6844          Certification Authority Authorization     January 2013
+
+
+   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
+              Housley, R., and W. Polk, "Internet X.509 Public Key
+              Infrastructure Certificate and Certificate Revocation List
+              (CRL) Profile", RFC 5280, May 2008.
+
+   [RFC6195]  Eastlake, D., "Domain Name System (DNS) IANA
+              Considerations", BCP 42, RFC 6195, March 2011.
+
+   [RFC6546]  Trammell, B., "Transport of Real-time Inter-network
+              Defense (RID) Messages over HTTP/TLS", RFC 6546,
+              April 2012.
+
+   [RFC6698]  Hoffman, P. and J. Schlyter, "The DNS-Based Authentication
+              of Named Entities (DANE) Transport Layer Security (TLS)
+              Protocol: TLSA", RFC 6698, August 2012.
+
+   [STD13]    Mockapetris, P., "Domain names - concepts and facilities",
+              STD 13, RFC 1034, November 1987.
+
+              Mockapetris, P., "Domain names - implementation and
+              specification", STD 13, RFC 1035, November 1987.
+
+   [X.509]    International Telecommunication Union, "ITU-T
+              Recommendation X.509 (11/2008): Information technology -
+              Open systems interconnection - The Directory: Public-key
+              and attribute certificate frameworks", ITU-T
+              Recommendation X.509, November 2008.
+
+9.2.  Informative References
+
+   [HB2011]   Hallam-Baker, P., Stradling, R., and B. Laurie, "DNS
+              Certification Authority Authorization (CAA) Resource
+              Record", Work in Progress, May 2011.
+
+   [RFC3647]  Chokhani, S., Ford, W., Sabett, R., Merrill, C., and S.
+              Wu, "Internet X.509 Public Key Infrastructure Certificate
+              Policy and Certification Practices Framework", RFC 3647,
+              November 2003.
+
+
+
+
+
+
+
+
+
+
+
+
+
+Hallam-Baker & Stradling     Standards Track                   [Page 17]
+
+RFC 6844          Certification Authority Authorization     January 2013
+
+
+Authors' Addresses
+
+   Phillip Hallam-Baker
+   Comodo Group, Inc.
+
+   EMail: philliph@comodo.com
+
+
+   Rob Stradling
+   Comodo CA, Ltd.
+
+   EMail: rob.stradling@comodo.com
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Hallam-Baker & Stradling     Standards Track                   [Page 18]
+