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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Internet Engineering Task Force P. Hallam-Baker 3 Internet-Draft Comodo Group Inc. 4 Intended status: Standards Track R. Stradling 5 Expires: February 24, 2013 Comodo CA Ltd. 6 August 23, 2012 8 DNS Certification Authority Authorization (CAA) Resource Record 9 draft-ietf-pkix-caa-12 11 Abstract 13 The Certification Authority Authorization (CAA) DNS Resource Record 14 allows a DNS domain name holder to specify one or more Certification 15 Authorities (CAs) authorized to issue certificates for that domain. 16 CAA resource records allow a public Certification Authority to 17 implement additional controls to reduce the risk of unintended 18 certificate mis-issue. This document defines the syntax of the CAA 19 record and rules for processing CAA records by certificate issuers. 21 Status of this Memo 23 This Internet-Draft is submitted in full conformance with the 24 provisions of BCP 78 and BCP 79. 26 Internet-Drafts are working documents of the Internet Engineering 27 Task Force (IETF). Note that other groups may also distribute 28 working documents as Internet-Drafts. The list of current Internet- 29 Drafts is at http://datatracker.ietf.org/drafts/current/. 31 Internet-Drafts are draft documents valid for a maximum of six months 32 and may be updated, replaced, or obsoleted by other documents at any 33 time. It is inappropriate to use Internet-Drafts as reference 34 material or to cite them other than as "work in progress." 36 This Internet-Draft will expire on February 24, 2013. 38 Copyright Notice 40 Copyright (c) 2012 IETF Trust and the persons identified as the 41 document authors. All rights reserved. 43 This document is subject to BCP 78 and the IETF Trust's Legal 44 Provisions Relating to IETF Documents 45 (http://trustee.ietf.org/license-info) in effect on the date of 46 publication of this document. Please review these documents 47 carefully, as they describe your rights and restrictions with respect 48 to this document. Code Components extracted from this document must 49 include Simplified BSD License text as described in Section 4.e of 50 the Trust Legal Provisions and are provided without warranty as 51 described in the Simplified BSD License. 53 Table of Contents 55 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 56 2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 4 57 2.1. Requirements Language . . . . . . . . . . . . . . . . . . 4 58 2.2. Defined Terms . . . . . . . . . . . . . . . . . . . . . . 4 59 3. The CAA RR type . . . . . . . . . . . . . . . . . . . . . . . 5 60 4. Certification Authority Processing . . . . . . . . . . . . . . 7 61 4.1. Use of DNS Security . . . . . . . . . . . . . . . . . . . 8 62 5. Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . 8 63 5.1. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . 8 64 5.1.1. Canonical Presentation Format . . . . . . . . . . . . 10 65 5.2. CAA issue Property . . . . . . . . . . . . . . . . . . . . 10 66 5.3. CAA issuewild Property . . . . . . . . . . . . . . . . . . 12 67 5.4. CAA iodef Property . . . . . . . . . . . . . . . . . . . . 12 68 6. Security Considerations . . . . . . . . . . . . . . . . . . . 13 69 6.1. Non-Compliance by Certification Authority . . . . . . . . 13 70 6.2. Mis-Issue by Authorized Certification Authority . . . . . 13 71 6.3. Suppression or spoofing of CAA records . . . . . . . . . . 13 72 6.4. Denial of Service . . . . . . . . . . . . . . . . . . . . 14 73 6.5. Abuse of the Critical Flag . . . . . . . . . . . . . . . . 14 74 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 75 7.1. Registration of the CAA Resource Record Type . . . . . . . 14 76 7.2. Certification Authority Authorization Properties . . . . . 15 77 7.3. Acknowledgements . . . . . . . . . . . . . . . . . . . . . 15 78 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15 79 8.1. Normative References . . . . . . . . . . . . . . . . . . . 15 80 8.2. Informative References . . . . . . . . . . . . . . . . . 17 81 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17 83 1. Introduction 85 The Certification Authority Authorization (CAA) DNS Resource Record 86 allows a DNS domain name holder to specify the Certification 87 Authorities authorized to issue certificates for that domain. 88 Publication of CAA resource records allow a public Certification 89 Authority (CA) to implement additional controls to reduce the risk of 90 unintended certificate mis-issue. 92 Like the TLSA record defined in DNS-Based Authentication of Named 93 Entities (DANE) [DANE], CAA records are used as a part of a mechanism 94 for checking PKIX certificate data. The distinction between the two 95 specifications is that CAA records specify a authorization control to 96 be performed by a certificate issuer before issue of a certificate 97 and TLSA records specify a verification control to be performed by a 98 Relying Party after the certificate is issued. 100 Conformance with a published CAA record is a necessary but not 101 sufficient condition for issueance of a certificate. Before issuing 102 a certificate, a PKIX CA is required to validate the request 103 according to the policies set out in its Certificate Policy. In the 104 case of a public CA that validates certificate requests as a third 105 party, the certificate will be typically issued under a public trust 106 anchor certificate embedded in one or more relevant Relying 107 Applications. 109 Criteria for inclusion of embedded trust anchor certificates in 110 applications are outside the scope of this document. Typically such 111 criteria require the CA to publish a Certificate Practices Statement 112 (CPS) that specifies how the requirements of the Certificate Policy 113 (CP) are achieved. It is also common for a CA to engage an 114 independent third party auditor to prepare an annual audit statement 115 of its performance against its CPS. 117 A set of CAA records describes only current grants of authority to 118 issue certificates for the corresponding DNS domain. Since a 119 certificate is typically valid for at least a year, it is possible 120 that a certificate that is not conformant with the CAA records 121 currently published was conformant with the CAA records published at 122 the time that the certificate was issued. Relying Applications MUST 123 NOT use CAA records as part of certificate validation. 125 CAA Records MAY be used by Certificate Evaluators as a possible 126 indicator of a security policy violation. Such use SHOULD take 127 account of the possibility that published CAA records changed between 128 the time a certificate was issued and the time at which the 129 certificate was observed by the Certificate Evaluator. 131 2. Definitions 133 2.1. Requirements Language 135 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 136 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 137 document are to be interpreted as described in [RFC2119]. 139 2.2. Defined Terms 141 The following terms are used in this document: 143 Authorization Entry: An authorization assertion that grants or 144 denies a specific set of permissions to a specific group of 145 entities. 147 Certificate: An X.509 Certificate, as specified in [RFC5280]. 149 Certificate Evaluator: A party other than a Relying Party that 150 evaluates the trustworthiness of certificates issued by 151 Certification Authorities. 153 Certification Authority (CA): An Issuer that issues Certificates in 154 accordance with a specified Certificate Policy. 156 Certificate Policy (CP): Specifies the criteria that a Certification 157 Authority undertakes to meet in its issue of certificates. See 158 [RFC3647]. 160 Certification Practices Statement (CPS): Specifies the means by 161 which the criteria of the Certificate Policy are met. In most 162 cases this will be the document against which the operations of 163 the Certification Authority are audited. See [RFC3647]. 165 Domain: The set of resources associated with a DNS Domain Name. 167 Domain Name: A DNS Domain name as specified in [STD13]. 169 Domain Name System (DNS): The Internet naming system specified in 170 [STD13]. 172 DNS Security (DNSSEC): Extensions to the DNS that provide 173 authentication services as specified in [RFC4033], [RFC4034], 174 [RFC4035], [RFC5155] and revisions. 176 Issuer: An entity that issues Certificates. See [RFC5280]. 178 Property: The tag-value portion of a CAA Resource Record. 180 Property Tag: The tag portion of a CAA Resource Record. 182 Property Value: The value portion of a CAA Resource Record. 184 Public Key Infrastructure X.509 (PKIX): Standards and specifications 185 issued by the IETF that apply the [X.509] certificate standards 186 specified by the ITU to Internet applications as specified in 187 [RFC5280] and related documents. 189 Resource Record (RR): A set of attributes bound to a Domain Name as 190 defined in [RFC1035]. 192 Relying Party: A party that makes use of an application whose 193 operation depends on use of a Certificate for making a security 194 decision. See [RFC5280]. 196 Relying Application: An application whose operation depends on use 197 of a Certificate for making a security decision. 199 3. The CAA RR type 201 A CAA RR consists of a flags byte and a tag-value pair referred to as 202 a property. Multiple properties MAY be associated with the same 203 domain name by publishing multiple CAA RRs at that domain name. The 204 following flag is defined: 206 Issuer Critical: If set (=1), indicates that the corresponding 207 property entry tag MUST be understood if the semantics of the CAA 208 record are to be correctly interpreted by an issuer. 210 Issuers MUST NOT issue certificates for a domain if the relevant 211 CAA Resource Record set contains unknown property entry tags that 212 have the Critical bit set. 214 The following property tags are defined: 216 issue [; ]* : The issue property 217 entry authorizes the holder of the domain name or a party acting under the explicit authority of the holder 219 of that domain name to issue certificates for the domain in which 220 the property is published. 222 iodef : Specifies a URL to which an issuer MAY report 223 certificate issue requests that are inconsistent with the issuer's 224 Certification Practices or Certificate Policy, or that a 225 certificate evaluator may use to report observation of a possible 226 policy violation. The IODEF format is used [RFC5070]. 228 The following example is a DNS zone file (see [RFC1035]) that informs 229 CAs that certificates are not to be issued except by the holder of 230 the domain name 'ca.example.net' or an authorized agent thereof. 231 This policy applies to all subordinate domains under example.com. 233 $ORIGIN example.com 234 . CAA 0 issue "ca.example.net" 236 If the domain name holder specifies one or more iodef properties, a 237 certificate issuer MAY report invalid certificate requests to that 238 address. In the following example the domain name holder specifies 239 that reports may be made by means of email with the IODEF data as an 240 attachment, a Web service [RFC6546] or both: 242 $ORIGIN example.com 243 . CAA 0 issue "ca.example.net" 244 . CAA 0 iodef "mailto:security@example.com" 245 . CAA 0 iodef "http://iodef.example.com/" 247 A certificate issuer MAY specify additional parameters that allow 248 customers to specify additional parameters governing certificate 249 issuance. This might be the Certificate Policy under which the 250 certificate is to be issued, the authentication process to be used 251 might be specified or an account number specified by the CA to enable 252 these parameters to be retrieved. 254 For example, the CA 'ca.example.net' has requested its customer 255 'example.com' to specify the CA's account number '230123' in each of 256 the customer's CAA records. 258 $ORIGIN example.com 259 . CAA 0 issue "ca.example.net; account=230123" 261 The syntax of additional parameters is a sequence of tag-value pairs 262 as defined in section [RFC5234]. The semantics of such parameters is 263 left to site policy and is outside the scope of this document. 265 The critical flag is intended to permit future versions CAA to 266 introduce new semantics that MUST be understood for correct 267 processing of the record, preventing conforming CAs that do not 268 recognize the new semantics from issuing certificates for the 269 indicated domains. 271 In the following example, the property 'tbs' is flagged as critical. 272 Neither the example.net CA, nor any other issuer is authorized to 273 issue under either policy unless the processing rules for the 'tbs' 274 property tag are understood. 276 $ORIGIN example.com 277 . CAA 0 issue "ca.example.net; policy=ev" 278 . CAA 128 tbs "Unknown" 280 Note that the above restrictions only apply to issue of certificates. 281 Since the validity of an end entity certificate is typically a year 282 or more, it is quite possible that the CAA records published at a 283 domain will change between the time a certificate was issued and 284 validation by a relying party. 286 4. Certification Authority Processing 288 Before issuing a certificate, a compliant CA MUST check for 289 publication of an relevant CAA Resource Record set. If such a record 290 set exists, a CA MUST NOT issue a certificate unless the CA 291 determines that either (1) the certificate request is consistent with 292 the applicable CAA Resource Record set or (2) that an exception 293 specified in the relevant Certificate Policy or Certification 294 Practices Statement Applies. 296 A certificate request MAY specify more than one domain name and MAY 297 specify wildcard domains. Issuers MUST verify authorization for all 298 the domains and wildcard domains specified in the request. 300 Given a request for a specific domain X, or a request for a wildcard 301 domain *.X, the relevant record set R(X) is determined as follows: 303 Let CAA(X) be the record set returned in response to performing a CAA 304 record query on the label X, P(X) be the DNS label immediately above 305 X in the DNS hierarchy and A(X) be the target of a CNAME or DNAME 306 alias record specified at the label X. 308 o If CAA(X) is not empty, R(X) = CAA (X), otherwise 310 o If A(X) is not null, and R(A(X)) is not empty, then R(X) = 311 R(A(X)), otherwise 313 o If X is not a top level domain then R(X) = R(P(X), otherwise 315 o R(X) is empty. 317 For example, if a certificate is requested for X.Y.Z the issuer will 318 search for the relevant CAA record set in the following order: 320 X.Y.Z 322 Alias (X.Y.Z) 324 Y.Z 326 Alias (Y.Z) 328 Z 330 Alias (Z) 332 Return Empty 334 4.1. Use of DNS Security 336 Use of DNSSEC to authenticate CAA RRs is strongly RECOMMENDED but not 337 required. An issuer MUST NOT issue certificates if doing so would 338 conflict with the relevant CAA Resource Record set, irrespective of 339 whether the corresponding DNS records are signed. 341 DNSSEC provides a proof of non-existence for both DNS domains and RR 342 set within domains. DNSSEC verification thus enables an issuer to 343 determine if the answer to a CAA record query is empty because the RR 344 set is empty or if it is non-empty but the response has been 345 supressed. 347 Use of DNSSEC allows an issuer to acquire and archive a proof that 348 they were authorized to issue certificates for the domain. 349 Verification of such archives MAY be an audit requirement to verify 350 CAA record processing compliance. Publication of such archives MAY 351 be a transparency requirement to verify CAA record processing 352 compliance. 354 5. Mechanism 356 5.1. Syntax 358 A CAA RR contains a single property entry consisting of a tag value 359 pair. Each tag represents a property of the CAA record. The value 360 of a CAA property is that specified in the corresponding value field. 362 A domain name MAY have multiple CAA RRs associated with it and a 363 given property MAY be specified more than once. 365 The CAA data field contains one property entry. A property entry 366 consists of the following data fields: 368 +0-1-2-3-4-5-6-7-|0-1-2-3-4-5-6-7-| 369 | Flags | Tag Length = n | 370 +----------------+----------------+...+---------------+ 371 | Tag char 0 | Tag Char 1 |...| Tag Char n-1 | 372 +----------------+----------------+...+---------------+ 373 +----------------+----------------+.....+----------------+ 374 | Value byte 0 | Value byte 1 |.....| Value byte m-1 | 375 +----------------+----------------+.....+----------------+ 377 Where n is the length specified in the Tag length field and m is the 378 remaining octets in the Value field (m = d - n - 2) where d is the 379 length of the RDATA section. 381 The data fields are defined as follows: 383 Flags: One octet containing the following fields: 385 Bit 0: Issuer Critical Flag If the value is set (1), the critical 386 flag is asserted and the property MUST be understood if the CAA 387 record is to be correctly processed by a certificate issuer. 389 A Certification Authority MUST NOT issue certificates for any 390 Domain that contains a CAA critical property for an unknown or 391 unsupported property tag that for which the issuer critical 392 flag is set. 394 Note that according to the conventions set out in [RFC1035], Bit 0 395 is the Most Significant Bit and Bit 7 is the Least Significant 396 Bit. Thus the Flags value 1 means that bit 7 is set while a value 397 of 128 means that bit 0 is set according to this convention. 399 All other bit positions are reserved for future use. 401 To ensure compatibility with future extensions to CAA, DNS records 402 compliant with this version of the CAA specification MUST clear 403 (set to "0") all reserved flags bits. Applications that interpret 404 CAA records MUST ignore the value of all reserved flag bits. 406 Tag Length: A single octet containing an unsigned integer specifying 407 the tag length in octets. The tag length MUST be at least 1 and 408 SHOULD be no more than 15. 410 Tag: The property identifier, a sequence of ASCII characters. 412 Tag values MAY contain ASCII characters 'a' through 'z', 'A' 413 through 'Z' and the numbers 0 through 9. Tag values SHOULD NOT 414 contain any other characters. Matching of tag values is case 415 insensitive. 417 Tag values submitted for registration by IANA MUST NOT contain any 418 characters other than the (lowercase) ASCII characters 'a' through 419 'z' and the numbers 0 through 9. 421 Value: A sequence of octets representing the property value. 422 Property values are encoded as binary values and MAY employ sub- 423 formats. 425 The length of the value field is specified implicitly as the 426 remaining length of the enclosing Resource Record data field. 428 5.1.1. Canonical Presentation Format 430 The canonical presentation format of the CAA record is as follows: 432 CAA 434 Where: 436 Flags: Is an unsigned integer between 0 and 255. 438 Tag: Is a non-zero sequence of ASCII letter and numbers in lower 439 case. 441 Value: Is the US-ASCII text Encoding of the value field 443 5.2. CAA issue Property 445 The issue property tag is used to request that certificate issuers 446 perform CAA issue restriction processing for the domain and to grant 447 authorization to specific certificate issuers. 449 The CAA issue property value has the following sub-syntax (specified 450 in ABNF as per [RFC5234]). 452 Property = space [domain] space [";" space * (parameter space) 454 domain = label *("." label) 455 label = (ALPHA / DIGIT) * ( ["-"] (ALPHA / DIGIT )) 457 space = *(SP / HTAB) 459 parameter = / space tag "=" value 461 tag = 1* (ALPHA / DIGIT) 463 value = *VCHAR | DQUOTE *(%x20-21 / %x23-7E) DQUOTE 465 For consistency with other aspects of DNS administration, Domain name 466 values are specified in Letter-Digit-Hyphen Label (LDH-Label) form. 468 A CAA record with an issue parameter tag that does not specify a 469 domain name is a request that certificate issuers perform CAA issue 470 restriction processing for the corresponding domain without granting 471 authorization to any certificate issuer. 473 This form of issue restriction would be appropriate to specify that 474 no certificates are to be issued for the domain in question. 476 For example, the following CAA record set requests that no 477 certificates be issued for the domain 'nocerts.example.com' by any 478 certificate issuer. 480 nocerts.example.com CAA 0 issue ";" 482 A CAA record with an issue parameter tag that specifies a domain name 483 is a request that certificate issuers perform CAA issue restriction 484 processing for the corresponding domain and grants authorization to 485 the certificate issuer specified by the domain name. 487 For example, the following CAA record set requests that no 488 certificates be issued for the domain 'certs.example.com' by any 489 certificate issuer other than the example.net certificate issuer. 491 certs.example.com CAA 0 issue "example.net" 493 CAA authorizations are additive. thus the result of specifying both 494 the empty issuer and a specified issuer is the same as specifying 495 just the specified issuer alone. 497 An issuer MAY choose to specify issuer-parameters that further 498 constrain the issue of certificates by that issuer. For example 499 specifying that certificates are to be subject to specific validation 500 polices, billed to certain accounts or issued under specific trust 501 anchors. 503 The semantics of issuer-parameters are determined by the issuer 504 alone. 506 5.3. CAA issuewild Property 508 The issuewild property has the same syntax and semantics as the issue 509 property except that issuewild properties only grant authorization to 510 issue certificates that specify a wildcard domain and issuewild 511 properties take precedence over issue properties when specified. 512 Specifically: 514 issuewild properties MUST be ignored when processing a request for 515 a domain that is not a wildcard domain. 517 If at least one issuewild property is specified in the relevant 518 CAA record set, all issue properties MUST be ignored when 519 processing a request for a domain that is a wildcard domain. 521 5.4. CAA iodef Property 523 The iodef property specifies a means of reporting certificate issue 524 requests or cases of certificate issue for the corresponding domain, 525 that violate the security policy of the issuer or the domain name 526 holder. 528 The Incident Object Description Exchange Format (IODEF) [RFC5070] is 529 used to present the incident report in machine readable form. 531 The iodef property takes a URL as its parameter. The URL scheme type 532 determines the method used for reporting: 534 mailto: The IODEF incident report is reported as a MIME email 535 attachment to an SMTP email that is submitted to the mail address 536 specified. The mail message sent SHOULD contain a brief text 537 message to alert the recipient to the nature of the attachment. 539 http or https: The IODEF report is submitted as a web service 540 request to the HTTP address specified using the protocol specified 541 in [RFC6546]. 543 6. Security Considerations 545 CAA Records assert a security policy that the holder of a domain name 546 wishes to be observed by certificate issuers. The effectiveness of 547 CAA records as an access control mechanism is thus dependent on 548 observance of CAA constraints by issuers. 550 The objective of the CAA record properties described in this document 551 is to reduce the risk of certificate mis-issue rather than avoid 552 reliance on a certificate that has ben mis-issued. DANE [DANE] 553 describes a mechanism for avoiding reliance on mis-issued 554 certificates. 556 6.1. Non-Compliance by Certification Authority 558 CAA records offer CAs a cost-effective means of mitigating the risk 559 of certificate mis-issue: The cost of implementing CAA checks is very 560 small and the potential costs of a mis-issue event include the 561 removal of an embedded trust anchor. 563 6.2. Mis-Issue by Authorized Certification Authority 565 Use of CAA records does not prevent mis-issue by an authorized 566 Certification Authority. , i.e., a CA that is authorized to issue 567 certificates for the domain in question by CAA records.. 569 Domain name holders SHOULD verify that the CAs they authorize to 570 issue certificates for their domains employ appropriate controls to 571 ensure that certificates are issued only to authorized parties within 572 their organization. 574 Such controls are most appropriately determined by the domain name 575 holder and the authorized CA(s) directly and are thus out of scope of 576 this document. 578 6.3. Suppression or spoofing of CAA records 580 Suppression of the CAA record or insertion of a bogus CAA record 581 could enable an attacker to obtain a certificate from an issuer that 582 was not authorized to issue for that domain name. 584 Where possible, Issuers SHOULD perform DNSSEC validation to detect 585 missing or modified CAA record sets. 587 In cases where DNSSEC is not deployed in a corresponding domain, an 588 issuer SHOULD attempt to mitigate this risk by employing appropriate 589 DNS security controls. For example all portions of the DNS lookup 590 process SHOULD be performed against the authoritative name server. 592 Data cached by third parties MUST NOT be relied on but MAY be used to 593 support additional anti-spoofing or anti-suppression controls. 595 6.4. Denial of Service 597 Introduction of a malformed or malicious CAA RR could in theory 598 enable a Denial of Service attack. 600 This specific threat is not considered to add significantly to the 601 risk of running an insecure DNS service. 603 An attacker could, in principle, perform a Denial of Service attack 604 against an issuer by requesting a certificate with a maliciously long 605 DNS name. In practice, the DNS protocol imposes a maximum name 606 length and CAA processing does not exacerbate the existing need to 607 mitigate Denial of Service attacks to any meaningful degree. 609 6.5. Abuse of the Critical Flag 611 A Certification Authority could make use of the critical flag to 612 trick customers into publishing records which prevent competing 613 Certification Authorities from issuing certificates even though the 614 customer intends to authorize multiple providers. 616 In practice, such an attack would be of minimal effect since any 617 competent competitor that found itself unable to issue certificates 618 due to lack of support for a property marked critical SHOULD 619 investigate the cause and report the reason to the customer who will 620 thus discover that they had been deceived. 622 7. IANA Considerations 624 7.1. Registration of the CAA Resource Record Type 626 [Note to IANA, the CAA resource record has already been assigned. On 627 issue of this draft as an RFC, the record should be updated to 628 reflect this document as the authoritative specification and this 629 paragraph (but not the following ones deleted] 631 IANA has assigned Resource Record Type 257 for the CAA Resource 632 Record Type and added the line depicted below to the registry named 633 Resource Record (RR) TYPEs and QTYPEs as defined in BCP 42 [RFC6195] 634 and located at http://www.iana.org/assignments/dns-parameters. 636 RR Name Value and meaning Reference 637 ----------- --------------------------------------------- --------- 638 CAA 257 Certification Authority Restriction [RFC-THIS] 639 7.2. Certification Authority Authorization Properties 641 [Note to IANA, this is a new registry that needs to be created and 642 this paragraph but not the following ones deleted.] 644 IANA has created the Certification Authority Authorization Properties 645 registry with the following initial values: 647 Tag Meaning Reference 648 ----------- ---------------------------------- --------- 649 issue Authorization Entry by Domain [RFC-THIS] 650 issuewild Authorization Entry by Domain [RFC-THIS] 651 iodef Report incident by IODEF report [RFC-THIS] 652 auth Reserved 653 path Reserved 654 policy Reserved 656 Although [HB2011]" has expired, deployed clients implement the CAA 657 properties specified in the draft and re-use of these property tags 658 for a different purtpose could cause unexpected behavior. 660 Addition of tag identifiers requires a public specification and 661 expert review as set out in [RFC6195]. 663 The tag space is designed to be sufficiently large that exhausting 664 the possible tag space need not be a concern. The scope of expert 665 review SHOULD be limited to the question of whether the specification 666 provided is sufficiently clear to permit implementation and to avoid 667 unnecessary duplication of functionality. 669 7.3. Acknowledgements 671 The authors would like to thank the following people who contributed 672 to the design and documentation of this work item: Chris Evans, 673 Stephen Farrell, Jeff Hodges, Paul Hoffman, Stephen Kent, Adam 674 Langley, Ben Laurie, Chris Palmer, Scott Schmit, Sean Turner and Ben 675 Wilson. 677 8. References 679 8.1. Normative References 681 [DANE] P. Hoffman., J. Schlyter, "draft-ietf-dane-protocol-23: 682 Replace with reference to RFC before issue.", 2012. 684 [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", 685 STD 13, RFC 1034, November 1987. 687 [RFC1035] Mockapetris, P., "Domain names - implementation and 688 specification", STD 13, RFC 1035, November 1987. 690 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 691 Requirement Levels", BCP 14, RFC 2119, March 1997. 693 [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. 694 Rose, "DNS Security Introduction and Requirements", 695 RFC 4033, March 2005. 697 [RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S. 698 Rose, "Resource Records for the DNS Security Extensions", 699 RFC 4034, March 2005. 701 [RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S. 702 Rose, "Protocol Modifications for the DNS Security 703 Extensions", RFC 4035, March 2005. 705 [RFC5070] Danyliw, R., Meijer, J., and Y. Demchenko, "The Incident 706 Object Description Exchange Format", RFC 5070, 707 December 2007. 709 [RFC5155] Laurie, B., Sisson, G., Arends, R., and D. Blacka, "DNS 710 Security (DNSSEC) Hashed Authenticated Denial of 711 Existence", RFC 5155, March 2008. 713 [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax 714 Specifications: ABNF", STD 68, RFC 5234, January 2008. 716 [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., 717 Housley, R., and W. Polk, "Internet X.509 Public Key 718 Infrastructure Certificate and Certificate Revocation List 719 (CRL) Profile", RFC 5280, May 2008. 721 [RFC6195] Eastlake, D., "Domain Name System (DNS) IANA 722 Considerations", BCP 42, RFC 6195, March 2011. 724 [RFC6546] Trammell, B., "Transport of Real-time Inter-network 725 Defense (RID) Messages over HTTP/TLS", RFC 6546, 726 April 2012. 728 [STD13] Mockapetris, P., "Domain names - concepts and facilities", 729 STD 13, RFC 1034, November 1987. 731 Mockapetris, P., "Domain names - implementation and 732 specification", STD 13, RFC 1035, November 1987. 734 [X.509] International Telecommunication Union, "ITU-T 735 Recommendation X.509 (11/2008): Information technology - 736 Open systems interconnection - The Directory: Public-key 737 and attribute certificate frameworks", ITU-T 738 Recommendation X.509, November 2008. 740 8.2. Informative References 742 [HB2011] Hallam-Baker, P., Stradling, R., and B. Laurie, "DNS 743 Certification Authority Authorization (CAA) Resource 744 Record", draft-hallambaker-donotissue-04 (work in 745 progress), May 2011. 747 [RFC3647] Chokhani, S., Ford, W., Sabett, R., Merrill, C., and S. 748 Wu, "Internet X.509 Public Key Infrastructure Certificate 749 Policy and Certification Practices Framework", RFC 3647, 750 November 2003. 752 Authors' Addresses 754 Phillip Hallam-Baker 755 Comodo Group Inc. 757 Email: philliph@comodo.com 759 Rob Stradling 760 Comodo CA Ltd. 762 Email: rob.stradling@comodo.com