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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: August 16, 2012 Comodo CA Ltd. 6 February 13, 2012 8 DNS Certification Authority Authorization (CAA) Resource Record 9 draft-ietf-pkix-caa-04 11 Abstract 13 The Certification Authority Authorization (CAA) DNS Resource Record 14 allows a DNS domain name holder to specify the certificate signing 15 certificate(s) authorized to issue certificates for that domain. CAA 16 resource records allow a public Certification Authority to implement 17 additional controls to reduce the risk of unintended certificate mis- 18 issue. 20 Status of this Memo 22 This Internet-Draft is submitted in full conformance with the 23 provisions of BCP 78 and BCP 79. 25 Internet-Drafts are working documents of the Internet Engineering 26 Task Force (IETF). Note that other groups may also distribute 27 working documents as Internet-Drafts. The list of current Internet- 28 Drafts is at http://datatracker.ietf.org/drafts/current/. 30 Internet-Drafts are draft documents valid for a maximum of six months 31 and may be updated, replaced, or obsoleted by other documents at any 32 time. It is inappropriate to use Internet-Drafts as reference 33 material or to cite them other than as "work in progress." 35 This Internet-Draft will expire on August 16, 2012. 37 Copyright Notice 39 Copyright (c) 2012 IETF Trust and the persons identified as the 40 document authors. All rights reserved. 42 This document is subject to BCP 78 and the IETF Trust's Legal 43 Provisions Relating to IETF Documents 44 (http://trustee.ietf.org/license-info) in effect on the date of 45 publication of this document. Please review these documents 46 carefully, as they describe your rights and restrictions with respect 47 to this document. Code Components extracted from this document must 48 include Simplified BSD License text as described in Section 4.e of 49 the Trust Legal Provisions and are provided without warranty as 50 described in the Simplified BSD License. 52 Table of Contents 54 1. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 3 55 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 56 1.2. Defined Terms . . . . . . . . . . . . . . . . . . . . . . 3 57 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 58 2.1. The CAA RR type . . . . . . . . . . . . . . . . . . . . . 5 59 3. Certification Authority Processing . . . . . . . . . . . . . . 7 60 3.1. Canonical Domain Name . . . . . . . . . . . . . . . . . . 7 61 3.2. Use of DNS Security . . . . . . . . . . . . . . . . . . . 8 62 3.3. Archive . . . . . . . . . . . . . . . . . . . . . . . . . 8 63 4. Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . 8 64 4.1. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . 8 65 4.1.1. Canonical Presentation Format . . . . . . . . . . . . 10 66 4.2. CAA issue Property . . . . . . . . . . . . . . . . . . . . 10 67 4.3. CAA iodef Property . . . . . . . . . . . . . . . . . . . . 11 68 5. Security Considerations . . . . . . . . . . . . . . . . . . . 12 69 5.1. Mis-Issue by Authorized Certification Authority . . . . . 12 70 5.2. Suppression or spoofing of CAA records . . . . . . . . . . 13 71 5.2.1. Certification Authorities . . . . . . . . . . . . . . 13 72 5.3. Denial of Service . . . . . . . . . . . . . . . . . . . . 13 73 5.4. Abuse of the Critical Flag . . . . . . . . . . . . . . . . 13 74 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 75 6.1. Registration of the CAA Resource Record Type . . . . . . . 14 76 6.2. Certification Authority Authorization Properties . . . . . 14 77 7. Normative References . . . . . . . . . . . . . . . . . . . . . 14 78 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15 80 1. Definitions 82 1.1. Requirements Language 84 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 85 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 86 document are to be interpreted as described in RFC 2119 [RFC2119]. 88 1.2. Defined Terms 90 The following terms are used in this document: 92 Authorization Entry An authorization assertion that grants or denies 93 a specific set of permissions to a specific group of entities. 95 Canonical Domain Name A Domain Name that is not an alias. 97 Canonical Domain Name Value The value of a Canonical Domain Name. 98 The value resulting from applying alias transformations to a 99 Domain Name that is not canonical. 101 Certificate An X.509 Certificate, as specified in RFC 5280 102 [RFC5280]. 104 Certificate Evaluator A party other than a Relying Party that 105 evaluates the trustworthiness of certificates issued by 106 Certification Authorities. 108 Certification Authority (CA) An Issuer that issues Certificates in 109 accordance with a specified Certification Policy. 111 Certification Policy (CP) Specifies the criteria that a 112 Certification Authority undertakes to meet in its issue of 113 certificates. 115 Certification Practices Statement (CPS) Specifies the means by which 116 the criteria of the Certification Policy are met. In most cases 117 this will be the document against which the operations of the 118 Certification Authority are audited. 120 Domain The set of resources associated with a DNS Domain Name. 122 Domain Name A DNS Domain name as specified in RFC 1035 [RFC1035] and 123 revisions. 125 Domain Name System (DNS) The Internet naming system specified in RFC 126 1035 [RFC1035] and revisions. 128 DNS Security (DNSSEC) Extensions to the DNS that provide 129 authentication services as specified in RFC 4033 [RFC4033] and 130 revisions. 132 Issuer An entity that issues Certificates. 134 Extended Issuer Authorization Set The most specific Issuer 135 Authorization Set that is active for a domain. This is either the 136 Issuer Authorization Set for the domain itself, or if that is 137 empty, the Issuer Authorization Set for the corresponding Public 138 Delegation Point. 140 Issuer Authorization Set The set of Authorization Entries for a 141 domain name that are flagged for use by Issuers. Analogous to an 142 Access Control List but with no ordering specified. 144 Public Delegation Point A Domain Name that is obtained from a public 145 DNS registry. 147 Public Key Infrastructure X.509 (PKIX) Standards and specifications 148 issued by the IETF that apply the X.509 [X.509] certificate 149 standards specified by the ITU to Internet applications as 150 specified in RFC 5280 [RFC5280] and related documents. 152 Resource Record (RR) A set of attributes bound to a Domain Name. 154 Relying Party A party that makes use of an application whose 155 operation depends on use of a Certificate for making a security 156 decision. 158 Relying Application An application whose operation depends on use of 159 a Certificate for making a security decision. 161 2. Introduction 163 The Certification Authority Authorization (CAA) DNS Resource Record 164 allows a DNS domain name holder to specify the Certification 165 Authorities authorized to issue certificates for that domain. 166 Publication of CAA resource records allow a public Certification 167 Authority (CA) to implement additional controls to reduce the risk of 168 unintended certificate mis-issue. 170 Conformance with a published CAA record is a necessary but not 171 sufficient condition for issue of a certificate. Before issuing a 172 certificate, a PKIX CA is required to validate the request according 173 to the policies set out in its Certificate Policy Statement. In the 174 case of a public CA that validates certificate requests as a third 175 party, the certificate will be typically issued under a public root 176 certificate embedded in one or more relevant Relying Applications. 178 Criteria for inclusion of embedded root certificates in applications 179 are outside the scope of this document but typically require the CA 180 to publish a Certificate Practices Statement (CPS) that specifies how 181 the requirements of the Certificate Policy (CP) are achieved and 182 provide an annual audit statement of their performance against their 183 CPS performed by an independent third party auditor. 185 Verification of certificate requests against CAA records published in 186 the corresponding domain is currently under consideration by the CA- 187 Browser Forum as a required element of the Basic Requirements for 188 Certificate issue. 190 CAA records only describe the current state of Certification 191 Authority certificate issue authority. Since a certificate is 192 typically valid for at least a year, it is possible that a 193 certificate that is not conformant with the CAA records currently 194 published was conformant with the CAA records published at the time 195 that it was issued. Thus Relying Applications MUST NOT use failure 196 to conform to currently published CAA records specifying issue 197 authorization as a certificate validity criteria. 199 CAA Records MAY be used by Certificate Evaluators as a possible 200 indicator of a security policy violation. Such use SHOULD take 201 account of the possibility that the published CAA records changed 202 between the time the certificate was issued and the time that they 203 were observed by the Certificate Evaluator. 205 2.1. The CAA RR type 207 A CAA RR publishes a CAA property entry that corresponds to the 208 specified domain name. Multiple property entries MAY be associated 209 with the same domain name by publishing multiple CAA RRs at that 210 domain name. Each property entry MAY be tagged with one or more of 211 the following flag values: 213 Critical If set, indicates that the corresponding property entry tag 214 MUST be understood if the semantics of the CAA record are to be 215 correctly understood by the specified audience. 217 Issuers MUST NOT issue certificates for a domain if the Extended 218 Issuer Authorization Set contains unknown property entry tags that 219 have both the Issuer and Critical bits set. 221 The following properties are defined: 223 issue [; ]* The issue property entry 224 declares an authorization entry granting authorization to issue to 225 the holder of the specified domain name or a party acting under 226 the express written authority of the holder of the domain name. 228 iodef Specifies a URL to which an issuer MAY report 229 certificate issue requests that are inconsistent with the issuer's 230 Certification Practices or Certification Policy or that a 231 certificate evaluator may use to report observation of a possible 232 policy violation. The IODEF format is used. [RFC5070] 234 The following example informs CAs that certificates MUST NOT be 235 issued except by the holder of the domain name 'ca.example.net' or an 236 authorized agent thereof. Since the policy is published at the 237 Public Delegation Point, the policy applies to all subordinate 238 domains under example.com. 240 $ORIGIN example.com 241 . CAA 0 issue "ca.example.net" 243 If the domain name holder specifies one or more iodef properties, a 244 certificate issuer MAY report invalid certificate requests to that 245 address. In the following example the domain name holder specifies 246 that reports MAY be made by means of email with the IODEF data as an 247 attachment or a Web service or both: 249 $ORIGIN example.com 250 . CAA 0 issue "ca.example.net" 251 . CAA 0 iodef "mailto:security@example.com" 252 . CAA 0 iodef "http://iodef.example.com/" 254 A certificate issuer MAY specify additional parameters that allow 255 customers to specify additional parameters governing certificate 256 issue. For example, the Certification Policy under which the 257 certificate is to be issued or the authentication process to be used. 259 $ORIGIN example.com 260 . CAA 0 issue "ca.example.net; account=230123" 262 The syntax and semantics of such parameters is left to site policy 263 and is outside the scope of this document. 265 Future versions of this specification MAY use the critical flag to 266 introduce new semantics that MUST be understood for correct 267 processing of the record, preventing Certification Authorities that 268 do not recognize the record from issuing certificates. 270 In the following example, the property 'tbs' is flagged as critical. 271 Neither the example.net CA, nor any other issuer is authorized to 272 issue under either policy unless the processing rules for the 'tbs' 273 property tag are understood. 275 $ORIGIN example.com 276 . CAA 0 issue "ca.example.net; policy=ev" 277 . CAA 128 tbs "Unknown" 279 Note that the above restrictions only apply to issue of certificates. 280 Since the validity of an end entity certificate is typically a year 281 or more it is quite possible that the CAA records published at a 282 domain will change between the issue of the certificate and 283 verification by a relying party. 285 3. Certification Authority Processing 287 Before issue of a certificate, a compliant CA MUST check for 288 publication of a relevant CAA Resource Record(s) and if such 289 record(s) are published, that the certificate requested is consistent 290 with them. If the certificate requested is not consistent with the 291 relevant CAA RRs, the CA MUST NOT issue the certificate. 293 The Issuer Authorization Set for a domain name consists of the set of 294 all CAA Authorization Entries declared for the canonical form of the 295 specified domain. 297 The Extended Issuer Authorization Set for a domain name consists of 298 the Issuer Authorization Set for that domain name if it is non-empty. 299 Otherwise the Extended Issuer Authorization Set for a domain name 300 consists of the Issuer Authorization Set for the corresponding Public 301 Delegation Point for that domain name. 303 If the Extended Issuer Authorization Set for a domain name is not 304 empty, a Certification Authority MUST NOT issue a certificate unless 305 it conforms to at least one authorization entry in the Extended 306 Issuer Authorization Set. 308 3.1. Canonical Domain Name 310 The DNS defines the CNAME and DNAME mechanisms for specifying domain 311 name aliases. The canonical name of a DNS name is the name that 312 results from performing all DNS alias operations. 314 An issuer MUST perform CNAME and DNAME processing as defined in the 315 DNS specifications 1035 [RFC1035] to resolve CAA records. 317 3.2. Use of DNS Security 319 Use of DNSSEC to authenticate CAA RRs is strongly recommended but not 320 required. An issuer MUST NOT issue certificates if doing so would 321 conflict with the corresponding extended issuer authorization set 322 whether the corresponding DNS records are signed or not. 324 Use of DNSSEC allows an issuer to acquire and archive a non- 325 repudiable proof that they were authorized to issue certificates for 326 the domain. 328 3.3. Archive 330 A compliant issuer SHOULD maintain an archive of the DNS transactions 331 used to verify CAA eligibility. 333 In particular an issuer SHOULD ensure that where DNSSEC data is 334 available that the corresponding signature and NSEC/NSEC3 records are 335 preserved so as to enable later compliance audits. 337 4. Mechanism 339 4.1. Syntax 341 A CAA RR contains a single property entry consisting of a tag value 342 pair. Each tag represents a property of the CAA record. The value 343 of a CAA property is that specified in the corresponding value field. 345 A domain name MAY have multiple CAA RRs associated with it and a 346 given property MAY be specified more than once. 348 The CAA data field contains one property entry. A property entry 349 consists of the following data fields: 351 +0-1-2-3-4-5-6-7-|0-1-2-3-4-5-6-7-| 352 | Flags | Tag Length = n | 353 +----------------+----------------+...+---------------+ 354 | Tag char 0 | Tag Char 1 |...| Tag Char n-1 | 355 +----------------+----------------+...+---------------+ 356 +----------------+----------------+.....+---------------+ 357 | Data byte 0 | Data byte 1 |.....| Data byte m-1 | 358 +----------------+----------------+.....+---------------+ 359 Where n is the length specified in the tag length field and m is the 360 remaining octets in the data field (m = d - n - 2) where d is the 361 length of the data section. 363 The data fields are defined as follows: 365 Flags One octet containing the following fields: 367 Bit 0: Issuer Critical Flag If the value is set (1), the critical 368 flag is asserted and the property MUST be understood if the CAA 369 record is to be correctly processed by a certificate issuer. 371 A Certification Authority MUST NOT issue certificates for any 372 Domain that contains a CAA critical property for an unknown or 373 unsupported property type that has the issuer bit set. 375 Note that according to the conventions set out in RFC 1035 376 [RFC1035] Bit 0 is the Most Significant Bit and Bit 7 is the Least 377 Significant. Thus the flags value 1 means that bit 7 is set while 378 a value of 128 means that bit 0 is set according to this 379 convention. 381 All other bit positions are reserved for future use. 383 To ensure compatibility with futuree extensions to CAA, DNS 384 records compliant with this version of the CAA specification MUST 385 clear (0) all reserved flags bits. Applications that interpret 386 CAA records MUST ignore the value of all reserved flag bits. 388 Tag Length A single octet containing an unsigned integer specifying 389 the tag length in octets. The tag length MUST be at least 1 and 390 SHOULD be no more than 15. 392 Tag The property identifier, a sequence of ASCII characters. 394 Tag values MAY contain ASCII characters a through z and the 395 numbers 0 through 9. Tag values MUST NOT contain any other 396 characters. Matching of tag values is case insensitive. 398 Value A sequence of octets representing the property value. 399 Property values are encoded as binary values and MAY employ sub- 400 formats. 402 The length of the value field is specified implicitly as the 403 remaining length of the enclosing Resource Record data field. 405 4.1.1. Canonical Presentation Format 407 The canonical presentation format of the CAA record is as follows: 409 CAA 411 Where: 413 flags Is an unsigned integer between 0 and 255. 415 tag Is a non-zero sequence of ASCII letter and numbers in lower 416 case. 418 data Is the ascii text Encoding of the value field 420 4.2. CAA issue Property 422 The issue property is used to request that certificate issuers 423 perform CAA issue restriction processing for the domain and to grant 424 authorization to specific certificate issuers. 426 The CAA issue property value has the following sub-syntax (specified 427 in ABNF as per [RFC4234]). 429 Property = space [domain] * (space ";" parameter) space 431 domain = label *("." label) 432 label = 1* (ALPHA / DIGIT / "_" / "-" ) 434 space = *(SP / HTAB) 436 parameter = / space tag "=" value 438 tag = 1* (ALPHA / DIGIT) 440 value = *VCHAR | DQUOTE *(%x20-21 / %x23-7E) DQUOTE 442 A CAA record with an issue parameter tag that does not specify a 443 domain name is a request that certificate issuers perform CAA issue 444 restriction processing for the corresponding domain without granting 445 authorization to any certificate issuer. 447 This form of issue restriction would be appropriate for use with a 448 domain that the domain name owner does not intend to be used. 450 For example, the following CAA record set requests that no 451 certificates be issued for the domain 'nocerts.example.com' by any 452 certificate issuer. 454 nocerts.example.com CAA 0 issue ";" 456 A CAA record with an issue parameter tag that specifies a domain name 457 is a request that certificate issuers perform CAA issue restriction 458 processing for the corresponding domain and grants authorization to 459 the certificate issuer specified by the domain name. 461 For example, the following CAA record set requests that no 462 certificates be issued for the domain 'certs.example.com' by any 463 certificate issuer other than the example.net certificate issuer. 465 certs.example.com CAA 0 issue "example.net" 467 CAA authorizations are additive. thus the result of specifying both 468 the empty issuer and a specified issuer is the same as specifying 469 just the specified issuer alone. 471 An issuer MAY choose to specify issuer-parameters that further 472 constrain the issue of certificates by that issuer. For example 473 specifying that certificates are to be subject to specific validation 474 polices, billed to certain accounts or issued off specific roots. 476 The syntax and semantics of issuer-parameters are determined by the 477 issuer alone. 479 4.3. CAA iodef Property 481 The iodef property specifies a means of reporting certificate issue 482 requests or cases of certificate issue for the corresponding domain 483 that violate the security policy of the issuer or the domain name 484 holder. 486 The Incident Object Description Exchange Format (IODEF) [RFC5070] is 487 used to present the incident report in machine readable form. 489 The iodef property takes a URL as its parameter. The URL scheme type 490 determines the method used for reporting: 492 mailto The IODEF incident report is reported as a MIME email 493 attachment to an SMTP email that is submitted to the mail address 494 specified. The mail message sent SHOULD contain a brief text 495 message to alert the recipient to the nature of the attachment. 497 http or https The IODEF report is submitted as a Web Service request 498 to the HTTP address specified using the protocol specified in 499 [RFC6046]. 501 5. Security Considerations 503 CAA Records assert a security policy that the holder of a domain name 504 wishes to be observed by certificate issuers. The effectiveness of 505 CAA records as an access control is thus dependent on observance of 506 CAA constraints by issuers. 508 Observance of CAA records by issuers is subject to accountability 509 controls and proposed industry requirements. 511 While a Certification Authority can choose to ignore published CAA 512 records, doing so increases the both the probability that they will 513 mis-issue a certificate and the consequences of doing so. Once it is 514 known that a CA observes CAA records, malicious registration requests 515 will disproportionately target the negligent CAs that do not, and so 516 the mis-issue rate amongst the negligent CAs will increase. Since 517 the CA could clearly have avoided the mis-issue by performing CAA 518 processing, the likelihood of sanctions against the negligent CA is 519 increased. Failure to observe CAA issue restrictions provides an 520 objective criteria for excluding issuers from embedded roots of 521 trust. 523 In contrast, a Certification Authority that processes CAA records 524 correctly can reasonably claim that any residual mis-issue event 525 could have been avoided had the Domain Name holder published 526 appropriate CAA records. 528 5.1. Mis-Issue by Authorized Certification Authority 530 Use of CAA records does not provide protection against mis-issue by 531 an authorized Certification Authority. 533 Domain name holders SHOULD ensure that the CAs they authorize to 534 issue certificates for their domains employ appropriate controls to 535 ensure that certificates are only issued to authorized parties within 536 their organization. 538 Such controls are most appropriately determined by the domain name 539 holder and the authorized CA(s) directly and are thus out of scope of 540 this document. 542 5.2. Suppression or spoofing of CAA records 544 Suppression of the CAA record or insertion of a bogus CAA record 545 could enable an attacker to obtain a certificate from a CA that was 546 not authorized to issue for that domain name. 548 5.2.1. Certification Authorities 550 Since a certificate issued by a CA can be valid for several years, 551 the consequences of a spoofing or suppression attack are much greater 552 for Certification Authorities and so additional countermeasures are 553 justified. 555 A CA MUST mitigate this risk by employing DNSSEC verification 556 whenever possible and rejecting certificate requests in any case 557 where it is not possible to verify the non-existence or contents of a 558 relevant CAA record. 560 In cases where DNSSEC is not deployed in a corresponding domain, a CA 561 SHOULD attempt to mitigate this risk by employing appropriate DNS 562 security controls. For example all portions of the DNS lookup 563 process SHOULD be performed against the authoritative name server. 564 Cached data MUST NOT be relied on but MAY be used to support 565 additional anti-spoofing or anti-suppression controls. 567 5.3. Denial of Service 569 Introduction of a malformed or malicious CAA RR could in theory 570 enable a Denial of Service attack. 572 This specific threat is not considered to add significantly to the 573 risk of running an insecure DNS service. 575 5.4. Abuse of the Critical Flag 577 A Certification Authority could make use of the critical flag to 578 trick customers into publishing records which prevent competing 579 Certification Authorities from issuing certificates even though the 580 customer intends to authorize multiple providers. 582 In practice, such an attack would be of minimal effect since any 583 competent competitor that found itself unable to issue certificates 584 due to lack of support for a property marked critical SHOULD 585 investigate the cause and report the reason to the customer who will 586 thus discover the deception. It is thus unlikely that the attack 587 would succeed and the attempt might lay the perpetrator open to civil 588 or criminal sanctions. 590 6. IANA Considerations 592 6.1. Registration of the CAA Resource Record Type 594 [Note to IANA, the CAA resource record has already been assigned. On 595 issue of this draft as an RFC, the record should be updated to 596 reflect this document as the authoritative specificaton and this 597 paragraph (but not the following ones deleted] 599 IANA has assigned Resource Record Type 257 for the CAA Resource 600 Record Type and added the line depicted below to the registry named 601 Resource Record (RR) TYPEs and QTYPEs as defined in BCP 42 RFC 5395 602 [RFC5395] and located at 603 http://www.iana.org/assignments/dns-parameters. 605 Value and meaning Reference 606 ----------- --------------------------------------------- --------- 607 CAA 257 Certification Authority Restriction [RFC-THIS] 609 6.2. Certification Authority Authorization Properties 611 [Note to IANA, this is a new registry that needs to be created and 612 this paragraph but not the following ones deleted.] 614 IANA has created the Certification Authority Authorization Properties 615 registry with the following initial values: 617 Meaning Reference 618 ----------- ----------------------------------------------- --------- 619 issue Authorization Entry by Domain [RFC-THIS] 620 iodef Report incident by means of IODEF format report [RFC-THIS] 621 auth Reserved 622 path Reserved 623 policy Reserved 625 Addition of tag identifiers requires a public specification and 626 expert review as set out in RFC5395 [RFC5395] 628 7. Normative References 630 [RFC1035] Mockapetris, P., "Domain names - implementation and 631 specification", STD 13, RFC 1035, November 1987. 633 [RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail 634 Extensions (MIME) Part One: Format of Internet Message 635 Bodies", RFC 2045, November 1996. 637 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 638 Requirement Levels", BCP 14, RFC 2119, March 1997. 640 [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. 641 Rose, "DNS Security Introduction and Requirements", 642 RFC 4033, March 2005. 644 [RFC4055] Schaad, J., Kaliski, B., and R. Housley, "Additional 645 Algorithms and Identifiers for RSA Cryptography for use in 646 the Internet X.509 Public Key Infrastructure Certificate 647 and Certificate Revocation List (CRL) Profile", RFC 4055, 648 June 2005. 650 [RFC4234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax 651 Specifications: ABNF", RFC 4234, October 2005. 653 [RFC5070] Danyliw, R., Meijer, J., and Y. Demchenko, "The Incident 654 Object Description Exchange Format", RFC 5070, 655 December 2007. 657 [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., 658 Housley, R., and W. Polk, "Internet X.509 Public Key 659 Infrastructure Certificate and Certificate Revocation List 660 (CRL) Profile", RFC 5280, May 2008. 662 [RFC5395] Eastlake, D., "Domain Name System (DNS) IANA 663 Considerations", RFC 5395, November 2008. 665 [RFC6046] Moriarty, K. and B. Trammell, "Transport of Real-time 666 Inter-network Defense (RID) Messages", RFC 6046, 667 November 2010. 669 [X.509] International Telecommunication Union, "ITU-T 670 Recommendation X.509 (11/2008): Information technology - 671 Open systems interconnection - The Directory: Public-key 672 and attribute certificate frameworks", ITU-T 673 Recommendation X.509, November 2008. 675 Authors' Addresses 677 Phillip Hallam-Baker 678 Comodo Group Inc. 680 Email: philliph@comodo.com 681 Rob Stradling 682 Comodo CA Ltd. 684 Email: rob.stradling@comodo.com