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Checking references for intended status: Experimental ---------------------------------------------------------------------------- -- Obsolete informational reference (is this intentional?): RFC 5226 (Obsoleted by RFC 8126) Summary: 0 errors (**), 0 flaws (~~), 1 warning (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group S. Kitterman 3 Internet-Draft fTLD Registry Services 4 Intended status: Experimental T. Wicinski, Ed. 5 Expires: September 20, 2021 March 19, 2021 7 Experimental DMARC Extension For Public Suffix Domains 8 draft-ietf-dmarc-psd-11 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 September 20, 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 . . . . . . . . . . . . . . . . . . . . . 6 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" . . . . 7 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 . . . . . . . . . . . . . . . . . . . 8 81 4.1. Feedback leakage . . . . . . . . . . . . . . . . . . . . 8 82 5. Security Considerations . . . . . . . . . . . . . . . . . . . 10 83 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 84 6.1. Subdomain Policy Tag . . . . . . . . . . . . . . . . . . 10 85 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 86 7.1. Normative References . . . . . . . . . . . . . . . . . . 10 87 7.2. Informative References . . . . . . . . . . . . . . . . . 11 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 . . . . . . . . . . . . . . . 12 91 B.2. DMARC Public Suffix Domain (PSD) Registry . . . . . . . . 12 92 B.3. DMARC PSD PSL Extension . . . . . . . . . . . . . . . . . 13 94 Appendix C. Implementations . . . . . . . . . . . . . . . . . . 13 95 C.1. Authheaders Module . . . . . . . . . . . . . . . . . . . 13 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. 112 In the basic DMARC model, PSDs are not organizational domains and are 113 thus not subject to DMARC processing. In DMARC, domains fall into 114 one of three categories: organizational domains, sub-domains of 115 organizational domains, or PSDs. A PSD can only publish DMARC policy 116 for itself, and not for any sub-domains under it. In some cases, 117 this limitation allows for the abuse of non-existent organizational- 118 level domains and hampers identification of domain abuse in email. 120 This document specifies experimental updates to the DMARC and PSL 121 algorithm cited above, in an attempt to mitigate this abuse. 123 1.1. Example 125 As an example, imagine a Top-Level Domain (TLD), ".example", that has 126 public subdomains for government and commercial use (".gov.example" 127 and ".com.example"). The maintainer of a list of such a PSD 128 structure would include entries for both of these sub-domains, 129 thereby indicating that they are PSDs, below which organizational 130 domains can be registered. Suppose further that there exists a 131 legitimate domain called "tax.gov.example", registered within 132 ".gov.example". 134 However, by exploiting the typically unauthenticated nature of email, 135 there are regular malicious campaigns to impersonate this 136 organization that use similar-looking ("cousin") domains such as 137 "t4x.gov.example". Such domains are not registered. 139 Within the ".gov.example" public suffix, use of DMARC has been 140 mandated, so "gov.example" publishes the following DMARC DNS record: 142 _dmarc.gov.example. IN TXT ( "v=DMARC1; p=reject; " 143 "rua=mailto:dmc@dmarc.svc.gov.example" ) 145 This DMARC record provides policy and a reporting destination for 146 mail sent from @gov.example. Similarly, "tax.gov.example" will have 147 a DMARC record that specifies policy for mail sent from addresses 148 @tax.gov.example. However, due to DMARC's current method of 149 discovering and applying policy at the organizational domain level, 150 the non-existent organizational domain of @t4x.gov.example does not 151 and cannot fall under a DMARC policy. 153 Defensively registering all variants of "tax" is obviously not a 154 scalable strategy. The intent of this specification, therefore, is 155 to enhance the DMARC algorithm by enabling an agent receiving such a 156 message to be able to determine that a relevant policy is present at 157 "gov.example", which is precluded by the current DMARC algorithm. 159 1.2. Discussion 161 This document provides a simple extension to [RFC7489] to allow 162 operators of Public Suffix Domains (PSDs) to: 164 o Express policy at the level of the PSD that covers all 165 organizational domains that do not explicitly publish DMARC 166 records 168 o Extends the DMARC policy query functionality to detect and process 169 such a policy 171 o Describes receiver feedback for such policies 173 o Provides controls to mitigate potential privacy considerations 174 associated with this extension 176 This document also provides a new DMARC tag to indicate requested 177 handling policy for non-existent subdommains. This is provided 178 specifically to support phased deployment of PSD DMARC, but is 179 expected to be useful more generally. Undesired rejection risks for 180 mail purporting to be from domains that do not exist are 181 substantially lower than for those that do, so the operational risk 182 of requesting harsh policy treatment (e.g. reject) is lower. 184 As an additional benefit, the PSD DMARC extension clarifies existing 185 requirements. Based on the requirements of [RFC7489], DMARC should 186 function above the organizational level for exact domain matches 187 (i.e. if a DMARC record were published for 'example', then mail from 188 example@example should be subject to DMARC processing). Testing had 189 revealed that this is not consistently applied in different 190 implementations. 192 There are two types of Public Suffix Operators (PSOs) for which this 193 extension would be useful and appropriate: 195 o Branded PSDs (e.g., ".google"): These domains are effectively 196 Organizational Domains as discussed in [RFC7489]. They control 197 all subdomains of the tree. These are effectively private 198 domains, but listed in the Public Suffix List. They are treated 199 as Public for DMARC purposes. They require the same protections 200 as DMARC Organizational Domains, but are currently unable to 201 benefit from DMARC. 203 o Multi-organization PSDs that require DMARC usage (e.g., ".bank"): 204 Because existing Organizational Domains using this PSD have their 205 own DMARC policy, the applicability of this extension is for non- 206 existent domains. The extension allows the brand protection 207 benefits of DMARC to extend to the entire PSD, including cousin 208 domains of registered organizations. 210 Due to the design of DMARC and the nature of the Internet email 211 architecture [RFC5598], there are interoperability issues associated 212 with DMARC deployment. These are discussed in Interoperability 213 Issues between DMARC and Indirect Email Flows [RFC7960]. These 214 issues are not typically applicable to PSDs, since they (e.g., the 215 ".gov.example" used above) do not typically send mail. 217 2. Terminology and Definitions 219 This section defines terms used in the rest of the document. 221 2.1. Conventions Used in This Document 223 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 224 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 225 "OPTIONAL" in this document are to be interpreted as described in 226 BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all 227 capitals, as shown here. 229 2.2. Public Suffix Domain (PSD) 231 The global Internet Domain Name System (DNS) is documented in 232 numerous Requests for Comment (RFC). It defines a tree of names 233 starting with root, ".", immediately below which are Top Level Domain 234 names such as ".com" and ".us". The domain name structure consists 235 of a tree of names, each of which is made of a sequence of words 236 ("labels") separated by period characters. The root of the tree is 237 simply called ".". The Internet community at large, through 238 processes and policies external to this work, selects points in this 239 tree at which to register domain names "owned" by independent 240 organizations. Real-world examples are ".com", ".org", ".us", and 241 ".gov.uk". Names at which such registrations occur are called Public 242 Suffix Domains (PSDs), and a registration consists of a label 243 selected by the registrant to which a desirable PSD is appended. For 244 example, "ietf.org" is a registered domain name, and ".org" is its 245 PSD. 247 2.3. Organizational Domain 249 The term Organizational Domains is defined in [RFC7489] Section 3.2. 251 2.4. Longest PSD 253 The longest PSD is the Organizational Domain with one label removed. 254 It names the immediate parent node of the Organizational Domain in 255 the DNS namespace tree. 257 2.5. Public Suffix Operator (PSO) 259 A Public Suffix Operator is an organization which manages operations 260 within a PSD, particularly the DNS records published for names at and 261 under that domain name. 263 2.6. PSO Controlled Domain Names 265 PSO Controlled Domain Names are names in the DNS that are managed by 266 a PSO and are not available for use as Organizational Domains. PSO 267 Controlled Domain Names may have one (e.g., ".com") or more (e.g., 268 ".co.uk") name components, depending on PSD policy. 270 2.7. Non-existent Domains 272 For DMARC purposes, a non-existent domain is a domain for which there 273 is an NXDOMAIN or NODATA response for A, AAAA, and MX records. This 274 is a broader definition than that in NXDOMAIN [RFC8020]. 276 3. PSD DMARC Updates to DMARC Requirements 278 This document updates DMARC as follows: 280 3.1. General Updates 282 References to "Domain Owners" also apply to PSOs. 284 3.2. Changes in Section 6.3 "General Record Format" 286 A new tag is added after "fo": 288 np: Requested Mail Receiver policy for non-existent subdomains 289 (plain-text; OPTIONAL). Indicates the policy to be enacted by the 290 Receiver at the request of the Domain Owner. It applies only to 291 non-existent subdomains of the domain queried and not to either 292 existing subdomains or the domain itself. Its syntax is identical 293 to that of the "p" tag defined below. If the 'np' tag is absent, 294 the policy specified by the "sp" tag (if the 'sp' tag is present) 295 or the policy specified by the "p" tag, if the 'sp' tag is not 296 present, MUST be applied for non-existent subdomains. Note that 297 "np" will be ignored for DMARC records published on subdomains of 298 Organizational Domains and PSDs due to the effect of the DMARC 299 policy discovery mechanism described in DMARC Section 6.6.3. 301 The following tag definitions from DMARC are updated: 303 p: The sentence 'Policy applies to the domain queried and to 304 subdomains, unless subdomain policy is explicitly described using 305 the "sp" tag' is updated to read 'Policy applies to the domain 306 queried and to subdomains, unless subdomain policy is explicitly 307 described using the "sp" or "np" tags.' 309 sp: The sentence 'If absent, the policy specified by the "p" tag 310 MUST be applied for subdomains' is updated to read 'If both the 311 'sp' tag is absent and the 'np' tag is either absent or not 312 applicable, the policy specified by the "p" tag MUST be applied 313 for subdomains. 315 3.3. Changes in Section 6.5 "Domain Owner Actions" 317 In addition to the DMARC domain owner actions, PSOs that require use 318 of DMARC and participate in PSD DMARC ought to make that information 319 available to receivers. This document is an experimental mechanism 320 for doing so. See the [this document] experiment description 321 (Appendix A). 323 3.4. Changes in Section 6.6.1 "Extract Author Domain" 325 Experience with DMARC has shown that some implementations short- 326 circuit messages, bypassing DMARC policy application, when the domain 327 name extracted by the receiver (from the RFC5322.From) is on the 328 public suffix list used by the receiver. This negates the capability 329 being created by this specification. Therefore, the following 330 paragraph is appended to Section 6.6.1 of DMARC: 332 Note that domain names that appear on a public suffix list are not 333 exempt from DMARC policy application and reporting. 335 3.5. Changes in Section 6.6.3 "Policy Discovery" 337 A new step between step 3 and 4 is added: 339 3A. If the set is now empty and the longest PSD (Section 2.4) of the 340 Organizational Domain is one that the receiver has determined is 341 acceptable for PSD DMARC (discussed in the [this document] 342 experiment description (Appendix A)), the Mail Receiver MUST query 343 the DNS for a DMARC TXT record at the DNS domain matching the 344 [this document] longest PSD (Section 2.4) in place of the 345 RFC5322.From domain in the message (if different). A possibly 346 empty set of records is returned. 348 As an example, for a message with the Organizational Domain of 349 "example.compute.cloudcompany.com.example", the query for PSD DMARC 350 would use "compute.cloudcompany.com.example" as the [this document] 351 longest PSD (Section 2.4). The receiver would check to see if that 352 PSD is listed in the DMARC PSD Registry, and if so, perform the 353 policy lookup at "_dmarc.compute.cloudcompany.com.example". 355 Note: Because the PSD policy query comes after the Organizational 356 Domain policy query, PSD policy is not used for Organizational 357 domains that have published a DMARC policy. Specifically, this is 358 not a mechanism to provide feedback addresses (RUA/RUF) when an 359 Organizational Domain has declined to do so. 361 3.6. Changes in Section 7 "DMARC Feedback" 363 Operational note for PSD DMARC: For PSOs, feedback for non-existent 364 domains is desirable and useful, just as it is for org-level DMARC 365 operators. See Section 4 of [this document] for discussion of 366 Privacy Considerations for PSD DMARC. 368 4. Privacy Considerations 370 These privacy considerations are developed based on the requirements 371 of [RFC6973]. Additionally, the Privacy Considerations of [RFC7489] 372 apply to the mechanisms described by this document. 374 4.1. Feedback leakage 376 Providing feedback reporting to PSOs can, in some cases, cause 377 information to leak out of an organization to the PSO. This leakage 378 could potentially be utilized as part of a program of pervasive 379 surveillance (See [RFC7624]). There are roughly three cases to 380 consider: 382 o Single Organization PSDs (e.g., ".google"), RUA and RUF reports 383 based on PSD DMARC have the potential to contain information about 384 emails related to entities managed by the organization. Since 385 both the PSO and the Organizational Domain owners are common, 386 there is no additional privacy risk for either normal or non- 387 existent Domain reporting due to PSD DMARC. 389 o Multi-organization PSDs that require DMARC usage (e.g., ".bank"): 390 PSD DMARC based reports will only be generated for domains that do 391 not publish a DMARC policy at the organizational or host level. 392 For domains that do publish the required DMARC policy records, the 393 feedback reporting addresses (RUA and RUF) of the organization (or 394 hosts) will be used. The only direct feedback leakage risk for 395 these PSDs are for Organizational Domains that are out of 396 compliance with PSD policy. Data on non-existent cousin domains 397 would be sent to the PSO. 399 o Multi-organization PSDs (e.g., ".com") that do not mandate DMARC 400 usage: Privacy risks for Organizational Domains that have not 401 deployed DMARC within such PSDs are significant. For non-DMARC 402 Organizational Domains, all DMARC feedback will be directed to the 403 PSO. PSD DMARC is opt-out (by publishing a DMARC record at the 404 Organizational Domain level) vice opt-in, which would be the more 405 desirable characteristic. This means that any non-DMARC 406 organizational domain would have its feedback reports redirected 407 to the PSO. The content of such reports, particularly for 408 existing domains, is privacy sensitive. 410 PSOs will receive feedback on non-existent domains, which may be 411 similar to existing Organizational Domains. Feedback related to such 412 cousin domains have a small risk of carrying information related to 413 an actual Organizational Domain. To minimize this potential concern, 414 PSD DMARC feedback MUST be limited to Aggregate Reports. Feedback 415 Reports carry more detailed information and present a greater risk. 417 Due to the inherent Privacy and Security risks associated with PSD 418 DMARC for Organizational Domains in multi-organization PSDs that do 419 not particpate in DMARC, any Feedback Reporting related to multi- 420 organizational PSDs MUST be limited to non-existent domains except in 421 cases where the reporter knows that PSO requires use of DMARC. 423 5. Security Considerations 425 This document does not change the Security Considerations of 426 [RFC7489] and [RFC7960]. 428 The risks of the issues identified in [RFC7489], Section 12.3, DNS 429 Security, are amplified by PSD DMARC. In particular, DNS cache 430 poisoning (or Name Chaining), see [RFC3833] for details, consequences 431 are increased because a successful attack would potentially have a 432 much wider scope. 434 The risks of the issues identified in [RFC7489], Section 12.5, 435 External Reporting Addresses, are amplified by PSD DMARC. By design, 436 PSD DMARC causes unrequested reporting of feedback to entities 437 external to the Organizational Domain. This is discussed in more 438 detail in Section 4. 440 6. IANA Considerations 442 This section describes actions requested to be completed by IANA. 444 6.1. Subdomain Policy Tag 446 IANA is requested to add a new tag to DMARC Tag Registry in the 447 Domain-based Message Authentication, Reporting, and Conformance 448 (DMARC) Parameters Registry. 450 The entry is as follows: 452 +----------+-----------+---------+-------------------------------+ 453 | Tag Name | Reference | Status | Description | 454 +----------+-----------+---------+-------------------------------+ 455 | np | this | current | Requested handling policy for | 456 | | document | | non-existent subdomains | 457 +----------+-----------+---------+-------------------------------+ 459 7. References 461 7.1. Normative References 463 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 464 Requirement Levels", BCP 14, RFC 2119, 465 DOI 10.17487/RFC2119, March 1997, 466 . 468 [RFC7489] Kucherawy, M., Ed. and E. Zwicky, Ed., "Domain-based 469 Message Authentication, Reporting, and Conformance 470 (DMARC)", RFC 7489, DOI 10.17487/RFC7489, March 2015, 471 . 473 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 474 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 475 May 2017, . 477 7.2. Informative References 479 [psddmarc.org] 480 multiple, "PSD DMARC Web Site", April 2019, 481 . 483 [RFC3833] Atkins, D. and R. Austein, "Threat Analysis of the Domain 484 Name System (DNS)", RFC 3833, DOI 10.17487/RFC3833, August 485 2004, . 487 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 488 IANA Considerations Section in RFCs", RFC 5226, 489 DOI 10.17487/RFC5226, May 2008, 490 . 492 [RFC5598] Crocker, D., "Internet Mail Architecture", RFC 5598, 493 DOI 10.17487/RFC5598, July 2009, 494 . 496 [RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., 497 Morris, J., Hansen, M., and R. Smith, "Privacy 498 Considerations for Internet Protocols", RFC 6973, 499 DOI 10.17487/RFC6973, July 2013, 500 . 502 [RFC7624] Barnes, R., Schneier, B., Jennings, C., Hardie, T., 503 Trammell, B., Huitema, C., and D. Borkmann, 504 "Confidentiality in the Face of Pervasive Surveillance: A 505 Threat Model and Problem Statement", RFC 7624, 506 DOI 10.17487/RFC7624, August 2015, 507 . 509 [RFC7960] Martin, F., Ed., Lear, E., Ed., Draegen, T., Ed., Zwicky, 510 E., Ed., and K. Andersen, Ed., "Interoperability Issues 511 between Domain-based Message Authentication, Reporting, 512 and Conformance (DMARC) and Indirect Email Flows", 513 RFC 7960, DOI 10.17487/RFC7960, September 2016, 514 . 516 [RFC8020] Bortzmeyer, S. and S. Huque, "NXDOMAIN: There Really Is 517 Nothing Underneath", RFC 8020, DOI 10.17487/RFC8020, 518 November 2016, . 520 Appendix A. PSD DMARC Privacy Concern Mitigation Experiment 522 The experiment being performed has three different questions which 523 are looking to be addressed in this document. 525 o Section 3.2 modifies policy discovery to add an additional DNS 526 lookup. To determine if this lookup is useful, PSDs will add 527 additional DMARC records in place, and will analyze the DMARC 528 reports. Success will be determined if a consensus of PSDs that 529 publish DMARC records are able to collect useful data. 531 o Section 3.2 adds the "np" tag for non-existent subdomains (DNS 532 NXDOMAIN). PSOs wishing to test this will add this flag to their 533 DMARC record, and will analyze DMARC reports for deployment. 534 Success will be determined if organizations find explicitly 535 blocking non-existent subdomains domains desirable and provide 536 added value. 538 o Section 4.1 discusses three cases where providing feedback could 539 cause information to leak out of an organization. This experiment 540 will analyze the feedback reports generated for each case to 541 determine if there is information leakage. 543 Appendix B. DMARC PSD Registry Examples 545 To facilitate experimentation around data leakage mitigation, samples 546 of the DNS based and IANA like registries are available at 547 [psddmarc.org]. 549 B.1. DMARC PSD DNS Query Service 551 A sample stand-alone DNS query service is available at 552 [psddmarc.org]. It was developed based on the contents suggested for 553 an IANA registry in an earlier revision of this draft. Usage of the 554 service is described on the web site. 556 B.2. DMARC Public Suffix Domain (PSD) Registry 558 [psddmarc.org] provides an IANA like DMARC Public Suffix Domain (PSD) 559 Registry as a stand-alone DNS query service. It follows the contents 560 and structure described below. There is a Comma Separated Value 561 (CSV) version of the listed PSD domains which is suitable for use in 562 build updates for PSD DMARC capable software. 564 Names of PSDs participating in PSD DMARC must be registered this new 565 registry. New entries are assigned only for PSDs that require use of 566 DMARC. The requirement has to be documented in a manner that 567 satisfies the terms of Expert Review,per [RFC5226]. The Designated 568 Expert needs to confirm that provided documentation adequately 569 describes PSD policy to require domain owners to use DMARC or that 570 all domain owners are part of a single organization with the PSO. 572 The initial set of entries in this registry is as follows: 574 +-------------+---------------+ 575 | PSD | Status | 576 +-------------+---------------+ 577 | .bank | current | 578 +-------------+---------------+ 579 | .insurance | current | 580 +-------------+---------------+ 581 | .gov.uk | current | 582 +-------------+---------------+ 583 | .mil | current | 584 +-------------+---------------+ 586 B.3. DMARC PSD PSL Extension 588 [psddmarc.org] provides a PSL like file to enable to facilitate 589 identification of PSD DMARC participants. Contents are functionally 590 identical to the IANA like registry, but presented in a different 591 format. 593 When using this approach, the input domain of the extension lookup is 594 supposed to be the output domain of the regular PSL lookup, i.e. the 595 organizational domain. This alternative data approach is potentially 596 useful since DMARC implementations already need to be able to parse 597 the data format, so it should be easier to implement. 599 Appendix C. Implementations 601 There are two known implementations of PSD DMARC available for 602 testing. 604 C.1. Authheaders Module 606 The authheaders Python module and command line tool is available for 607 download or installation from Pypi (Python Packaging Index). 609 It supports both use of the DNS based query service and download of 610 the CSV registry file from [psddmarc.org]. 612 C.2. Zdkimfilter Module 614 The zdkimfilter module is a separately available add-on to Courier- 615 MTA. 617 Mostly used for DKIM signing, it can be configured to also verify, 618 apply DMARC policies, and send aggregate reports. For PSD DMARC it 619 uses the PSL extension list approach, which is available from from 620 [psddmarc.org] 622 Acknowledgements 624 Thanks to the following individuals for their contributions (both 625 public and private) to improving this document. Special shout out to 626 Dave Crocker for naming the beast. 628 Kurt Andersen, Seth Blank, Dave Crocker, Heather Diaz, Tim Draegen, 629 Zeke Hendrickson, Andrew Kennedy, John Levine, Dr Ian Levy, Craig 630 Schwartz, Alessandro Vesely, and Tim Wicinski 632 Authors' Addresses 634 Scott Kitterman 635 fTLD Registry Services 636 600 13th Street, NW, Suite 400 637 Washington, DC 20005 638 United States of America 640 Phone: +1 301 325-5475 641 Email: scott@kitterman.com 643 Tim Wicinski (editor) 644 Elkins, WV 26241 645 USA 647 Email: tjw.ietf@gmail.com