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Wicinski, Ed. 5 Expires: October 3, 2021 April 1, 2021 7 Experimental DMARC Extension For Public Suffix Domains 8 draft-ietf-dmarc-psd-13 10 Abstract 12 Domain-based Message Authentication, Reporting, and Conformance 13 (DMARC) permits a domain-controlling organization to express domain- 14 level policies and preferences for message validation, disposition, 15 and reporting, which a mail-receiving organization can use to improve 16 mail handling. 18 DMARC distinguishes the portion of a name that is a Public Suffix 19 Domain (PSD), below which organizational domain names are created. 20 The basic DMARC capability allows organizational domains to specify 21 policies that apply to their subdomains, but it does not give that 22 capability to PSDs. This document describes an extension to DMARC to 23 fully enable DMARC functionality for PSDs. 25 Some implementations of DMARC consider a PSD to be ineligible for 26 DMARC enforcement. This specification addresses that case. 28 Status of This Memo 30 This Internet-Draft is submitted in full conformance with the 31 provisions of BCP 78 and BCP 79. 33 Internet-Drafts are working documents of the Internet Engineering 34 Task Force (IETF). Note that other groups may also distribute 35 working documents as Internet-Drafts. The list of current Internet- 36 Drafts is at https://datatracker.ietf.org/drafts/current/. 38 Internet-Drafts are draft documents valid for a maximum of six months 39 and may be updated, replaced, or obsoleted by other documents at any 40 time. It is inappropriate to use Internet-Drafts as reference 41 material or to cite them other than as "work in progress." 43 This Internet-Draft will expire on October 3, 2021. 45 Copyright Notice 47 Copyright (c) 2021 IETF Trust and the persons identified as the 48 document authors. All rights reserved. 50 This document is subject to BCP 78 and the IETF Trust's Legal 51 Provisions Relating to IETF Documents 52 (https://trustee.ietf.org/license-info) in effect on the date of 53 publication of this document. Please review these documents 54 carefully, as they describe your rights and restrictions with respect 55 to this document. Code Components extracted from this document must 56 include Simplified BSD License text as described in Section 4.e of 57 the Trust Legal Provisions and are provided without warranty as 58 described in the Simplified BSD License. 60 Table of Contents 62 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 63 1.1. Example . . . . . . . . . . . . . . . . . . . . . . . . . 3 64 1.2. Discussion . . . . . . . . . . . . . . . . . . . . . . . 4 65 2. Terminology and Definitions . . . . . . . . . . . . . . . . . 5 66 2.1. Conventions Used in This Document . . . . . . . . . . . . 5 67 2.2. Public Suffix Domain (PSD) . . . . . . . . . . . . . . . 5 68 2.3. Organizational Domain . . . . . . . . . . . . . . . . . . 6 69 2.4. Longest PSD . . . . . . . . . . . . . . . . . . . . . . . 6 70 2.5. Public Suffix Operator (PSO) . . . . . . . . . . . . . . 6 71 2.6. PSO Controlled Domain Names . . . . . . . . . . . . . . . 6 72 2.7. Non-existent Domains . . . . . . . . . . . . . . . . . . 6 73 3. PSD DMARC Updates to DMARC Requirements . . . . . . . . . . . 6 74 3.1. General Updates . . . . . . . . . . . . . . . . . . . . . 7 75 3.2. Changes in Section 6.3 "General Record Format" . . . . . 7 76 3.3. Changes in Section 6.5 "Domain Owner Actions" . . . . . . 7 77 3.4. Changes in Section 6.6.1 "Extract Author Domain" . . . . 8 78 3.5. Changes in Section 6.6.3 "Policy Discovery" . . . . . . . 8 79 3.6. Changes in Section 7 "DMARC Feedback" . . . . . . . . . . 8 80 4. Privacy Considerations . . . . . . . . . . . . . . . . . . . 9 81 5. Security Considerations . . . . . . . . . . . . . . . . . . . 10 82 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 83 6.1. Subdomain Policy Tag . . . . . . . . . . . . . . . . . . 10 84 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 11 85 7.1. Normative References . . . . . . . . . . . . . . . . . . 11 86 7.2. Informative References . . . . . . . . . . . . . . . . . 11 87 7.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 12 88 Appendix A. PSD DMARC Privacy Concern Mitigation Experiment . . 12 89 Appendix B. DMARC PSD Registry Examples . . . . . . . . . . . . 12 90 B.1. DMARC PSD DNS Query Service . . . . . . . . . . . . . . . 13 91 B.2. DMARC Public Suffix Domain (PSD) Registry . . . . . . . . 13 92 B.3. DMARC PSD PSL Extension . . . . . . . . . . . . . . . . . 13 94 Appendix C. Implementations . . . . . . . . . . . . . . . . . . 14 95 C.1. Authheaders Module . . . . . . . . . . . . . . . . . . . 14 96 C.2. Zdkimfilter Module . . . . . . . . . . . . . . . . . . . 14 97 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 14 98 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14 100 1. Introduction 102 DMARC [RFC7489] provides a mechanism for publishing organizational 103 policy information to email receivers. DMARC allows policy to be 104 specified for both individual domains and for organizational domains 105 and their sub-domains within a single organization. 107 To determine the organizational domain for a message under 108 evaluation, and thus where to look for a policy statement, DMARC 109 makes use of a public suffix list. The process for doing this can be 110 found in Section 3.2 of the DMARC specification. Currently, the 111 public suffix list being used is the most common one that is 112 maintained by the Mozilla Foundation and made public at 113 http://publicsuffix.org [1]. 115 In the basic DMARC model, Public Suffix Domains (PSDs) are not 116 organizational domains and are thus not subject to DMARC processing. 117 In DMARC, domains fall into one of three categories: organizational 118 domains, sub-domains of organizational domains, or PSDs. A PSD can 119 only publish DMARC policy for itself, and not for any sub-domains 120 under it. In some cases, this limitation allows for the abuse of 121 non-existent organizational-level domains and hampers identification 122 of domain abuse in email. 124 This document specifies experimental updates to the DMARC 125 specification cited above, in an attempt to mitigate this abuse. 127 1.1. Example 129 As an example, imagine a Top-Level Domain (TLD), ".example", that has 130 public subdomains for government and commercial use (".gov.example" 131 and ".com.example"). The maintainer of a list of such a PSD 132 structure would include entries for both of these sub-domains, 133 thereby indicating that they are PSDs, below which organizational 134 domains can be registered. Suppose further that there exists a 135 legitimate domain called "tax.gov.example", registered within 136 ".gov.example". 138 However, by exploiting the typically unauthenticated nature of email, 139 there are regular malicious campaigns to impersonate this 140 organization that use similar-looking ("cousin") domains such as 141 "t4x.gov.example". Such domains are not registered. 143 Within the ".gov.example" public suffix, use of DMARC has been 144 mandated, so "gov.example" publishes the following DMARC DNS record: 146 _dmarc.gov.example. IN TXT ( "v=DMARC1; p=reject;" 147 "rua=mailto:dmc@dmarc.svc.gov.example" ) 149 This DMARC record provides policy and a reporting destination for 150 mail sent from @gov.example. Similarly, "tax.gov.example" will have 151 a DMARC record that specifies policy for mail sent from addresses 152 @tax.gov.example. However, due to DMARC's current method of 153 discovering and applying policy at the organizational domain level, 154 the non-existent organizational domain of @t4x.gov.example does not 155 and cannot fall under a DMARC policy. 157 Defensively registering all variants of "tax" is not a scalable 158 strategy. The intent of this specification, therefore, is to enhance 159 the DMARC discovery method by enabling an agent receiving such a 160 message to be able to determine that a relevant policy is present at 161 "gov.example", which is precluded by the current DMARC specification. 163 1.2. Discussion 165 This document provides a simple extension to [RFC7489] to allow 166 operators of Public Suffix Domains (PSDs) to: 168 o Express policy at the level of the PSD that covers all 169 organizational domains that do not explicitly publish DMARC 170 records 172 o Extends the DMARC policy query functionality to detect and process 173 such a policy 175 o Describes receiver feedback for such policies 177 o Provides controls to mitigate potential privacy considerations 178 associated with this extension 180 This document also provides a new DMARC tag to indicate requested 181 handling policy for non-existent subdomains. This is provided 182 specifically to support phased deployment of PSD DMARC, but is 183 expected to be useful more generally. Undesired rejection risks for 184 mail purporting to be from domains that do not exist are 185 substantially lower than for those that do, so the operational risk 186 of requesting harsh policy treatment (e.g., reject) is lower. 188 As an additional benefit, the PSD DMARC extension clarifies existing 189 requirements. Based on the requirements of [RFC7489], DMARC should 190 function above the organizational level for exact domain matches 191 (i.e., if a DMARC record were published for "example", then mail from 192 example@example should be subject to DMARC processing). Testing had 193 revealed that this is not consistently applied in different 194 implementations. 196 There are two types of Public Suffix Operators (PSOs) for which this 197 extension would be useful and appropriate: 199 o Branded PSDs (e.g., ".google"): These domains are effectively 200 Organizational Domains as discussed in [RFC7489]. They control 201 all subdomains of the tree. These are effectively private 202 domains, but listed in the current public suffix list. They are 203 treated as Public for DMARC purposes. They require the same 204 protections as DMARC Organizational Domains, but are currently 205 unable to benefit from DMARC. 207 o Multi-organization PSDs that require DMARC usage (e.g., ".bank"): 208 Because existing Organizational Domains using this PSD have their 209 own DMARC policy, the applicability of this extension is for non- 210 existent domains. The extension allows the brand protection 211 benefits of DMARC to extend to the entire PSD, including cousin 212 domains of registered organizations. 214 Due to the design of DMARC and the nature of the Internet email 215 architecture [RFC5598], there are interoperability issues associated 216 with DMARC deployment. These are discussed in Interoperability 217 Issues between DMARC and Indirect Email Flows [RFC7960]. These 218 issues are not typically applicable to PSDs, since they (e.g., the 219 ".gov.example" used above) do not typically send mail. 221 2. Terminology and Definitions 223 This section defines terms used in the rest of the document. 225 2.1. Conventions Used in This Document 227 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 228 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 229 "OPTIONAL" in this document are to be interpreted as described in 230 BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all 231 capitals, as shown here. 233 2.2. Public Suffix Domain (PSD) 235 The global Internet Domain Name System (DNS) is documented in 236 numerous RFCs. It defines a tree of names starting with root, ".", 237 immediately below which are Top Level Domain names such as ".com" and 238 ".us". The domain name structure consists of a tree of names, each 239 of which is made of a sequence of words ("labels") separated by 240 period characters. The root of the tree is simply called ".". The 241 Internet community at large, through processes and policies external 242 to this work, selects points in this tree at which to register domain 243 names "owned" by independent organizations. Real-world examples are 244 ".com", ".org", ".us", and ".gov.uk". Names at which such 245 registrations occur are called Public Suffix Domains (PSDs), and a 246 registration consists of a label selected by the registrant to which 247 a desirable PSD is appended. For example, "ietf.org" is a registered 248 domain name, and ".org" is its PSD. 250 2.3. Organizational Domain 252 The term Organizational Domains is defined in [RFC7489] Section 3.2. 254 2.4. Longest PSD 256 The longest PSD is the Organizational Domain with one label removed. 257 It names the immediate parent node of the Organizational Domain in 258 the DNS namespace tree. 260 2.5. Public Suffix Operator (PSO) 262 A Public Suffix Operator is an organization which manages operations 263 within a PSD, particularly the DNS records published for names at and 264 under that domain name. 266 2.6. PSO Controlled Domain Names 268 PSO Controlled Domain Names are names in the DNS that are managed by 269 a PSO and are not available for use as Organizational Domains. PSO 270 Controlled Domain Names may have one (e.g., ".com") or more (e.g., 271 ".co.uk") name components, depending on PSD policy. 273 2.7. Non-existent Domains 275 For DMARC purposes, a non-existent domain is a domain for which there 276 is an NXDOMAIN or NODATA response for A, AAAA, and MX records. This 277 is a broader definition than that in [RFC8020]. 279 3. PSD DMARC Updates to DMARC Requirements 281 To participate in this experiment, implementations should interept 282 RFC7489 as follows: 284 3.1. General Updates 286 References to "Domain Owners" also apply to PSOs. 288 3.2. Changes in Section 6.3 "General Record Format" 290 If this experiment is successful, this paragraph is added to this 291 setion. A new tag is added after "fo": 293 np: Requested Mail Receiver policy for non-existent subdomains 294 (plain-text; OPTIONAL). Indicates the policy to be enacted by the 295 Receiver at the request of the Domain Owner. It applies only to 296 non-existent subdomains of the domain queried and not to either 297 existing subdomains or the domain itself. Its syntax is identical 298 to that of the "p" tag defined below. If the "np" tag is absent, 299 the policy specified by the "sp" tag (if the "sp" tag is present) 300 or the policy specified by the "p" tag, if the "sp" tag is not 301 present, MUST be applied for non-existent subdomains. Note that 302 "np" will be ignored for DMARC records published on subdomains of 303 Organizational Domains and PSDs due to the effect of the DMARC 304 policy discovery mechanism described in DMARC Section 6.6.3. 306 The following tag definitions from DMARC are updated: 308 p: The sentence 'Policy applies to the domain queried and to 309 subdomains, unless subdomain policy is explicitly described using 310 the "sp" tag' is updated to read 'Policy applies to the domain 311 queried and to subdomains, unless subdomain policy is explicitly 312 described using the "sp" or "np" tags.' 314 sp: The sentence 'If absent, the policy specified by the "p" tag 315 MUST be applied for subdomains' is updated to read 'If both the 316 "sp" tag is absent and the "np" tag is either absent or not 317 applicable, the policy specified by the "p" tag MUST be applied 318 for subdomains. 320 3.3. Changes in Section 6.5 "Domain Owner Actions" 322 In addition to the DMARC domain owner actions, PSOs that require use 323 of DMARC and participate in PSD DMARC ought to make that information 324 available to receivers. This document is an experimental mechanism 325 for doing so. See the [this document] experiment description 326 (Appendix A). 328 3.4. Changes in Section 6.6.1 "Extract Author Domain" 330 Experience with DMARC has shown that some implementations short- 331 circuit messages, bypassing DMARC policy application, when the domain 332 name extracted by the receiver (from the RFC5322.From) is on the 333 public suffix list used by the receiver. This negates the capability 334 being created by this specification. Therefore, the following 335 paragraph is appended to Section 6.6.1 of DMARC: 337 Note that domain names that appear on a public suffix list are not 338 exempt from DMARC policy application and reporting. 340 3.5. Changes in Section 6.6.3 "Policy Discovery" 342 A new step between step 3 and 4 is added: 344 3A. If the set is now empty and the longest PSD (Section 2.4) of the 345 Organizational Domain is one that the receiver has determined is 346 acceptable for PSD DMARC (discussed in the [this document] 347 experiment description (Appendix A)), the Mail Receiver MUST query 348 the DNS for a DMARC TXT record at the DNS domain matching the 349 [this document] longest PSD (Section 2.4) in place of the 350 RFC5322.From domain in the message (if different). A possibly 351 empty set of records is returned. 353 As an example, for a message with the Organizational Domain of 354 "example.compute.cloudcompany.com.example", the query for PSD DMARC 355 would use "compute.cloudcompany.com.example" as the [this document] 356 longest PSD (Section 2.4). The receiver would check to see if that 357 PSD is listed in the DMARC PSD Registry, and if so, perform the 358 policy lookup at "_dmarc.compute.cloudcompany.com.example". 360 Note: Because the PSD policy query comes after the Organizational 361 Domain policy query, PSD policy is not used for Organizational 362 domains that have published a DMARC policy. Specifically, this is 363 not a mechanism to provide feedback addresses (RUA/RUF) when an 364 Organizational Domain has declined to do so. 366 3.6. Changes in Section 7 "DMARC Feedback" 368 If this experiment is successful, this paragraph is added to this 369 setion. 371 Operational note for PSD DMARC: For PSOs, feedback for non-existent 372 domains is desirable and useful, just as it is for org-level DMARC 373 operators. See Section 4 of [this document] for discussion of 374 Privacy Considerations for PSD DMARC. 376 4. Privacy Considerations 378 These privacy considerations are developed based on the requirements 379 of [RFC6973]. Additionally, the Privacy Considerations of [RFC7489] 380 apply to the mechanisms described by this document. If this 381 experiment is successful, this section should be incorporated into 382 the Privacy Considerations section as "Feedback leakage". 384 Providing feedback reporting to PSOs can, in some cases, cause 385 information to leak out of an organization to the PSO. This leakage 386 could potentially be utilized as part of a program of pervasive 387 surveillance (See [RFC7624]). There are roughly three cases to 388 consider: 390 o Single Organization PSDs (e.g., ".google"), RUA and RUF reports 391 based on PSD DMARC have the potential to contain information about 392 emails related to entities managed by the organization. Since 393 both the PSO and the Organizational Domain owners are common, 394 there is no additional privacy risk for either normal or non- 395 existent Domain reporting due to PSD DMARC. 397 o Multi-organization PSDs that require DMARC usage (e.g., ".bank"): 398 PSD DMARC based reports will only be generated for domains that do 399 not publish a DMARC policy at the organizational or host level. 400 For domains that do publish the required DMARC policy records, the 401 feedback reporting addresses (RUA and RUF) of the organization (or 402 hosts) will be used. The only direct feedback leakage risk for 403 these PSDs are for Organizational Domains that are out of 404 compliance with PSD policy. Data on non-existent cousin domains 405 would be sent to the PSO. 407 o Multi-organization PSDs (e.g., ".com") that do not mandate DMARC 408 usage: Privacy risks for Organizational Domains that have not 409 deployed DMARC within such PSDs are significant. For non-DMARC 410 Organizational Domains, all DMARC feedback will be directed to the 411 PSO. PSD DMARC is opt-out (by publishing a DMARC record at the 412 Organizational Domain level) instead of opt-in, which would be the 413 more desirable characteristic. This means that any non-DMARC 414 organizational domain would have its feedback reports redirected 415 to the PSO. The content of such reports, particularly for 416 existing domains, is privacy sensitive. 418 PSOs will receive feedback on non-existent domains, which may be 419 similar to existing Organizational Domains. Feedback related to such 420 cousin domains have a small risk of carrying information related to 421 an actual Organizational Domain. To minimize this potential concern, 422 PSD DMARC feedback MUST be limited to Aggregate Reports. Feedback 423 Reports carry more detailed information and present a greater risk. 425 Due to the inherent Privacy and Security risks associated with PSD 426 DMARC for Organizational Domains in multi-organization PSDs that do 427 not participate in DMARC, any Feedback Reporting related to multi- 428 organizational PSDs MUST be limited to non-existent domains except in 429 cases where the reporter knows that PSO requires use of DMARC (by 430 checking the DMARC PSD Registry). 432 5. Security Considerations 434 This document does not change the Security Considerations of 435 [RFC7489] and [RFC7960]. 437 The risks of the issues identified in [RFC7489], Section 12.3, DNS 438 Security, are amplified by PSD DMARC. In particular, DNS cache 439 poisoning (or Name Chaining), see [RFC3833] for details, consequences 440 are increased because a successful attack would potentially have a 441 much wider scope. 443 The risks of the issues identified in [RFC7489], Section 12.5, 444 External Reporting Addresses, are amplified by PSD DMARC. By design, 445 PSD DMARC causes unrequested reporting of feedback to entities 446 external to the Organizational Domain. This is discussed in more 447 detail in Section 4. 449 6. IANA Considerations 451 This section describes actions requested to be completed by IANA. 453 6.1. Subdomain Policy Tag 455 IANA is requested to add a new tag to DMARC Tag Registry in the 456 Domain-based Message Authentication, Reporting, and Conformance 457 (DMARC) Parameters Registry. The "Status" column is defined in 458 [RFC7489]Section 11.4. 460 The entry is as follows: 462 +----------+-----------+---------+-------------------------------+ 463 | Tag Name | Reference | Status | Description | 464 +----------+-----------+---------+-------------------------------+ 465 | np | this | current | Requested handling policy for | 466 | | document | | non-existent subdomains | 467 +----------+-----------+---------+-------------------------------+ 469 [RFC EDITOR: Please replace "This document" with the RFC number of 470 this document.] 472 7. References 474 7.1. Normative References 476 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 477 Requirement Levels", BCP 14, RFC 2119, 478 DOI 10.17487/RFC2119, March 1997, 479 . 481 [RFC7489] Kucherawy, M., Ed. and E. Zwicky, Ed., "Domain-based 482 Message Authentication, Reporting, and Conformance 483 (DMARC)", RFC 7489, DOI 10.17487/RFC7489, March 2015, 484 . 486 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 487 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 488 May 2017, . 490 7.2. Informative References 492 [psddmarc.org] 493 multiple, "PSD DMARC Web Site", April 2019, 494 . 496 [RFC3833] Atkins, D. and R. Austein, "Threat Analysis of the Domain 497 Name System (DNS)", RFC 3833, DOI 10.17487/RFC3833, August 498 2004, . 500 [RFC5598] Crocker, D., "Internet Mail Architecture", RFC 5598, 501 DOI 10.17487/RFC5598, July 2009, 502 . 504 [RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., 505 Morris, J., Hansen, M., and R. Smith, "Privacy 506 Considerations for Internet Protocols", RFC 6973, 507 DOI 10.17487/RFC6973, July 2013, 508 . 510 [RFC7624] Barnes, R., Schneier, B., Jennings, C., Hardie, T., 511 Trammell, B., Huitema, C., and D. Borkmann, 512 "Confidentiality in the Face of Pervasive Surveillance: A 513 Threat Model and Problem Statement", RFC 7624, 514 DOI 10.17487/RFC7624, August 2015, 515 . 517 [RFC7960] Martin, F., Ed., Lear, E., Ed., Draegen, T., Ed., Zwicky, 518 E., Ed., and K. Andersen, Ed., "Interoperability Issues 519 between Domain-based Message Authentication, Reporting, 520 and Conformance (DMARC) and Indirect Email Flows", 521 RFC 7960, DOI 10.17487/RFC7960, September 2016, 522 . 524 [RFC8020] Bortzmeyer, S. and S. Huque, "NXDOMAIN: There Really Is 525 Nothing Underneath", RFC 8020, DOI 10.17487/RFC8020, 526 November 2016, . 528 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 529 Writing an IANA Considerations Section in RFCs", BCP 26, 530 RFC 8126, DOI 10.17487/RFC8126, June 2017, 531 . 533 7.3. URIs 535 [1] http://publicsuffix.org 537 Appendix A. PSD DMARC Privacy Concern Mitigation Experiment 539 The experiment being performed has three different questions which 540 are looking to be addressed in this document. 542 o Section 3.2 modifies policy discovery to add an additional DNS 543 lookup. To determine if this lookup is useful, PSDs will add 544 additional DMARC records in place, and will analyze the DMARC 545 reports. Success will be determined if a consensus of PSDs that 546 publish DMARC records are able to collect useful data. 548 o Section 3.2 adds the "np" tag for non-existent subdomains (DNS 549 NXDOMAIN). PSOs wishing to test this will add this flag to their 550 DMARC record, and will analyze DMARC reports for deployment. 551 Success will be determined if organizations find explicitly 552 blocking non-existent subdomains domains desirable and provide 553 added value. 555 o Section 4.1 discusses three cases where providing feedback could 556 cause information to leak out of an organization. This experiment 557 will analyze the feedback reports generated for each case to 558 determine if there is information leakage. 560 Appendix B. DMARC PSD Registry Examples 562 To facilitate experimentation around data leakage mitigation, samples 563 of the DNS based and IANA like registries are available at 564 [psddmarc.org]. 566 B.1. DMARC PSD DNS Query Service 568 A sample stand-alone DNS query service is available at 569 [psddmarc.org]. It was developed based on the contents suggested for 570 an IANA registry in an earlier revision of this draft. Usage of the 571 service is described on the web site. 573 B.2. DMARC Public Suffix Domain (PSD) Registry 575 [psddmarc.org] provides an IANA like DMARC Public Suffix Domain (PSD) 576 Registry as a stand-alone DNS query service. It follows the contents 577 and structure described below. There is a Comma Separated Value 578 (CSV) version of the listed PSD domains which is suitable for use in 579 build updates for PSD DMARC capable software. 581 PSDs that are deploying DMARC and are participating in PSD DMARC must 582 be register their public suffix domain in this new registry. The 583 requirement has to be documented in a manner that satisfies the terms 584 of Expert Review, per [RFC8126]. The Designated Expert needs to 585 confirm that provided documentation adequately describes PSD policy 586 to require domain owners to use DMARC or that all domain owners are 587 part of a single organization with the PSO. 589 The initial set of entries in this registry is as follows: 591 +-------------+---------------+ 592 | PSD | Status | 593 +-------------+---------------+ 594 | .bank | current | 595 +-------------+---------------+ 596 | .insurance | current | 597 +-------------+---------------+ 598 | .gov.uk | current | 599 +-------------+---------------+ 600 | .mil | current | 601 +-------------+---------------+ 603 B.3. DMARC PSD PSL Extension 605 [psddmarc.org] provides a file formatted like the Public Suffix List 606 (PSL) in order to facilitate identification of PSD DMARC 607 participants. Contents are functionally identical to the IANA like 608 registry, but presented in a different format. 610 When using this approach, the input domain of the extension lookup is 611 supposed to be the output domain of the regular PSL lookup, i.e., the 612 organizational domain. This alternative data approach is potentially 613 useful since DMARC implementations already need to be able to parse 614 the data format, so it should be easier to implement. 616 Appendix C. Implementations 618 There are two known implementations of PSD DMARC available for 619 testing. 621 C.1. Authheaders Module 623 The authheaders Python module and command line tool is available for 624 download or installation from Pypi (Python Packaging Index). 626 It supports both use of the DNS based query service and download of 627 the CSV registry file from [psddmarc.org]. 629 C.2. Zdkimfilter Module 631 The zdkimfilter module is a separately available add-on to Courier- 632 MTA. 634 Mostly used for DKIM signing, it can be configured to also verify, 635 apply DMARC policies, and send aggregate reports. For PSD DMARC it 636 uses the PSL extension list approach, which is available from 637 [psddmarc.org] 639 Acknowledgements 641 Thanks to the following individuals for their contributions (both 642 public and private) to improving this document. Special shout out to 643 Dave Crocker for naming the beast. 645 Kurt Andersen, Seth Blank, Dave Crocker, Heather Diaz, Tim Draegen, 646 Zeke Hendrickson, Andrew Kennedy, John Levine, Dr Ian Levy, Craig 647 Schwartz, Alessandro Vesely, and Tim Wicinski 649 Authors' Addresses 651 Scott Kitterman 652 fTLD Registry Services 653 600 13th Street, NW, Suite 400 654 Washington, DC 20005 655 United States of America 657 Phone: +1 301 325-5475 658 Email: scott@kitterman.com 659 Tim Wicinski (editor) 660 Elkins, WV 26241 661 USA 663 Email: tjw.ietf@gmail.com