idnits 2.17.1 draft-ietf-dmarc-psd-09.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (September 22, 2020) is 1309 days in the past. Is this intentional? 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 September 22, 2020 5 Expires: March 26, 2021 7 DMARC (Domain-based Message Authentication, Reporting, and Conformance) 8 Extension For PSDs (Public Suffix Domains) 9 draft-ietf-dmarc-psd-09 11 Abstract 13 DMARC (Domain-based Message Authentication, Reporting, and 14 Conformance) is a scalable mechanism by which a mail-originating 15 organization can express domain-level policies and preferences for 16 message validation, disposition, and reporting, that a mail-receiving 17 organization can use to improve mail handling. The design of DMARC 18 presumes that domain names represent either nodes in the tree below 19 which registrations occur, or nodes where registrations have 20 occurred; it does not permit a domain name to have both of these 21 properties simultaneously. Since its deployment in 2015, use of 22 DMARC has shown a clear need for the ability to express policy for 23 these domains as well. 25 Domains at which registrations can occur are referred to as Public 26 Suffix Domains (PSDs). This document describes an extension to DMARC 27 to enable DMARC functionality for PSDs. 29 This document also seeks to address implementations that consider a 30 domain on a public Suffix list to be ineligible for DMARC 31 enforcement. 33 Status of This Memo 35 This Internet-Draft is submitted in full conformance with the 36 provisions of BCP 78 and BCP 79. 38 Internet-Drafts are working documents of the Internet Engineering 39 Task Force (IETF). Note that other groups may also distribute 40 working documents as Internet-Drafts. The list of current Internet- 41 Drafts is at https://datatracker.ietf.org/drafts/current/. 43 Internet-Drafts are draft documents valid for a maximum of six months 44 and may be updated, replaced, or obsoleted by other documents at any 45 time. It is inappropriate to use Internet-Drafts as reference 46 material or to cite them other than as "work in progress." 48 This Internet-Draft will expire on March 26, 2021. 50 Copyright Notice 52 Copyright (c) 2020 IETF Trust and the persons identified as the 53 document authors. All rights reserved. 55 This document is subject to BCP 78 and the IETF Trust's Legal 56 Provisions Relating to IETF Documents 57 (https://trustee.ietf.org/license-info) in effect on the date of 58 publication of this document. Please review these documents 59 carefully, as they describe your rights and restrictions with respect 60 to this document. Code Components extracted from this document must 61 include Simplified BSD License text as described in Section 4.e of 62 the Trust Legal Provisions and are provided without warranty as 63 described in the Simplified BSD License. 65 Table of Contents 67 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 68 2. Terminology and Definitions . . . . . . . . . . . . . . . . . 5 69 2.1. Conventions Used in This Document . . . . . . . . . . . . 5 70 2.2. Public Suffix Domain (PSD) . . . . . . . . . . . . . . . 5 71 2.3. Organizational Domain . . . . . . . . . . . . . . . . . . 5 72 2.4. Longest PSD . . . . . . . . . . . . . . . . . . . . . . . 5 73 2.5. Public Suffix Operator (PSO) . . . . . . . . . . . . . . 6 74 2.6. PSO Controlled Domain Names . . . . . . . . . . . . . . . 6 75 2.7. Non-existent Domains . . . . . . . . . . . . . . . . . . 6 76 3. PSD DMARC Updates to DMARC Requirements . . . . . . . . . . . 6 77 3.1. General Updates . . . . . . . . . . . . . . . . . . . . . 6 78 3.2. Changes in Section 6.3 "General Record Format" . . . . . 6 79 3.3. Changes in Section 6.5 "Domain Owner Actions" . . . . . . 7 80 3.4. Changes in Section 6.6.1 "Extract Author Domain" . . . . 7 81 3.5. Changes in Section 6.6.3 "Policy Discovery" . . . . . . . 7 82 3.6. Changes in Section 7 "DMARC Feedback" . . . . . . . . . . 8 83 4. Privacy Considerations . . . . . . . . . . . . . . . . . . . 8 84 4.1. Feedback leakage . . . . . . . . . . . . . . . . . . . . 8 85 5. Security Considerations . . . . . . . . . . . . . . . . . . . 9 86 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 87 6.1. Subdomain Policy Tag . . . . . . . . . . . . . . . . . . 10 88 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 89 7.1. Normative References . . . . . . . . . . . . . . . . . . 10 90 7.2. Informative References . . . . . . . . . . . . . . . . . 10 91 Appendix A. PSD DMARC Privacy Concern Mitigation Experiment . . 11 92 Appendix B. DMARC PSD Registry Examples . . . . . . . . . . . . 12 93 B.1. DMARC PSD DNS Query Service . . . . . . . . . . . . . . . 12 94 B.2. DMARC Public Suffix Domain (PSD) Registry . . . . . . . . 12 95 B.3. DMARC PSD PSL Extension . . . . . . . . . . . . . . . . . 13 96 Appendix C. Implementations . . . . . . . . . . . . . . . . . . 13 97 C.1. Authheaders Module . . . . . . . . . . . . . . . . . . . 13 98 C.2. Zdkimfilter Module . . . . . . . . . . . . . . . . . . . 13 99 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 13 100 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 14 102 1. Introduction 104 DMARC [RFC7489] provides a mechanism for publishing organizational 105 policy information to email receivers. DMARC allows policy to be 106 specified for both individual domains and for organizational domains 107 and their sub-domains within a single organization. DMARC leverages 108 public suffix lists to determine which domains are organizational 109 domains. It presumes that public suffix list listed domains are not 110 organizational domains and not subject to DMARC processing; domains 111 are either organizational domains, sub-domains of organizational 112 domains, or listed on a public suffix list. For domains listed in a 113 public suffix list, i.e. TLDs and domains that exist between TLDs and 114 organization level domains, policy can only be published for the 115 exact domain. No method is available for these domains to express 116 policy or receive feedback reporting for sub-domains. This missing 117 method allows for the abuse of non-existent organizational-level 118 domains and prevents identification of domain abuse in email. 120 As an example, imagine a country code TLD (ccTLD) which has public 121 subdomains for government and commercial use (.gov.example and 122 .com.example). Suppose there exists a registered domain 123 "tax.gov.example" that is responsible for taxation in this imagined 124 country. However, by exploiting the typically unauthenticated nature 125 of email, there are regular malicious campaigns to impersonate this 126 organization that use similar-looking ("cousin") domains such as 127 "t4x.gov.example". These domains are not registered. Within the 128 ".gov.example" public suffix, use of DMARC has been mandated, so 129 "gov.example" publishes the following DMARC DNS record: 131 _dmarc.gov.example. IN TXT ( "v=DMARC1; p=reject; " 132 "rua=mailto:dmc@dmarc.svc.gov.example" ) 134 This DMARC record provides policy and a reporting destination for 135 mail sent from @gov.example. However, due to DMARC's current method 136 of discovering and applying policy at the organizational domain 137 level, the non-existent organizational domain of @t4x.gov.example 138 does not and cannot fall under a DMARC policy. 140 Defensively registering all variants of "tax" is obviously not a 141 scalable strategy. The intent of this specification, therefore, is 142 to enhance the DMARC algorithm by enabling an agent receiving such a 143 message to be able to determine that a relevant policy is present at 144 "gov.example", which is precluded by the current DMARC algorithm. 146 This document provides a simple extension to DMARC [RFC7489] to allow 147 operators of Public Suffix Domains (PSDs) to: 149 o Express policy at the level of the PSD that covers all 150 organizational domains that do not explicitly publish DMARC 151 records 153 o Extends the DMARC policy query functionality to detect and process 154 such a policy 156 o Describes receiver feedback for such policies 158 o Provides controls to mitigate potential privacy considerations 159 associated with this extension 161 This document also provides a new DMARC [RFC7489] tag to indicate 162 requested handling policy for non-existent subdommains. This is 163 provided specifically to support phased deployment of PSD DMARC, but 164 is expected to be useful more generally. Undesired rejection risks 165 for mail purporting to be from domains that do not exist are 166 substantially lower than for those that do, so the operational risk 167 of requesting harsh policy treatment (e.g. reject) is lower. 169 As an additional benefit, the PSD DMARC extension clarifies existing 170 requirements. Based on the requirements of DMARC [RFC7489], DMARC 171 should function above the organizational level for exact domain 172 matches (i.e. if a DMARC record were published for 'example', then 173 mail from example@example should be subject to DMARC processing). 174 Testing had revealed that this is not consistently applied in 175 different implementations. 177 There are two types of Public Suffix Operators (PSOs) for which this 178 extension would be useful and appropriate: 180 o Branded PSDs (e.g., ".google"): These domains are effectively 181 Organizational Domains as discussed in DMARC [RFC7489]. They 182 control all subdomains of the tree. These are effectively private 183 domains, but listed in the Public Suffix List. They are treated 184 as Public for DMARC purposes. They require the same protections 185 as DMARC Organizational Domains, but are currently unable to 186 benefit from DMARC. 188 o Multi-organization PSDs that require DMARC usage (e.g., ".bank"): 189 Because existing Organizational Domains using this PSD have their 190 own DMARC policy, the applicability of this extension is for non- 191 existent domains. The extension allows the brand protection 192 benefits of DMARC to extend to the entire PSD, including cousin 193 domains of registered organizations. 195 Due to the design of DMARC [RFC7489] and the nature of the Internet 196 email architecture [RFC5598], there are interoperability issues 197 associated with DMARC [RFC7489] deployment. These are discussed in 198 Interoperability Issues between DMARC and Indirect Email Flows 199 [RFC7960]. These issues are not typically applicable to PSDs, since 200 they (e.g., the ".gov.example" used above) do not typically send 201 mail. 203 2. Terminology and Definitions 205 This section defines terms used in the rest of the document. 207 2.1. Conventions Used in This Document 209 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 210 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 211 "OPTIONAL" in this document are to be interpreted as described in 212 BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all 213 capitals, as shown here. 215 2.2. Public Suffix Domain (PSD) 217 The global Internet Domain Name System (DNS) is documented in 218 numerous Requests for Comment (RFC). It defines a tree of names 219 starting with root, ".", immediately below which are Top Level Domain 220 names such as ".com" and ".us". The domain name structure consists 221 of a tree of names, each of which is made of a sequence of words 222 ("labels") separated by period characters. The root of the tree is 223 simply called ".". The Internet community at large, through 224 processes and policies external to this work, selects points in this 225 tree at which to register domain names "owned" by independent 226 organizations. Real-world examples are ".com", ".org", ".us", and 227 ".gov.uk". Names at which such registrations occur are called Public 228 Suffix Domains (PSDs), and a registration consists of a label 229 selected by the registrant to which a desirable PSD is appended. For 230 example, "ietf.org" is a registered domain name, and ".org" is its 231 PSD. 233 2.3. Organizational Domain 235 The term Organizational Domains is defined in DMARC [RFC7489] 236 Section 3.2. 238 2.4. Longest PSD 240 The longest PSD is the Organizational Domain with one label removed. 242 2.5. Public Suffix Operator (PSO) 244 A Public Suffix Operator is an organization which manages operations 245 within a PSD, particularly the DNS records published for names at and 246 under that domain name. 248 2.6. PSO Controlled Domain Names 250 PSO Controlled Domain Names are names in the DNS that are managed by 251 a PSO and are not available for use as Organizational Domains. PSO 252 Controlled Domain Names may have one (e.g., ".com") or more (e.g., 253 ".co.uk") name components, depending on PSD policy. 255 2.7. Non-existent Domains 257 For DMARC purposes, a non-existent domain is a domain for which there 258 is an NXDOMAIN or NODATA response for A, AAAA, and MX records. This 259 is a broader definition than that in NXDOMAIN [RFC8020]. 261 3. PSD DMARC Updates to DMARC Requirements 263 This document updates DMARC [RFC7489] as follows: 265 3.1. General Updates 267 References to "Domain Owners" also apply to PSOs. 269 3.2. Changes in Section 6.3 "General Record Format" 271 A new tag is added after "fo": 273 np: Requested Mail Receiver policy for non-existent subdomains 274 (plain-text; OPTIONAL). Indicates the policy to be enacted by the 275 Receiver at the request of the Domain Owner. It applies only to 276 non-existent subdomains of the domain queried and not to either 277 existing subdomains or the domain itself. Its syntax is identical 278 to that of the "p" tag defined below. If the 'np' tag is absent, 279 the policy specified by the "sp" tag (if the 'sp' tag is present) 280 or the policy specified by the "p" tag, if the 'sp' tag is not 281 present, MUST be applied for non-existent subdomains. Note that 282 "np" will be ignored for DMARC records published on subdomains of 283 Organizational Domains and PSDs due to the effect of the DMARC 284 policy discovery mechanism described in DMARC [RFC7489] 285 Section 6.6.3. 287 The following tag definitions from DMARC [RFC7489] are updated: 289 p: The sentence 'Policy applies to the domain queried and to 290 subdomains, unless subdomain policy is explicitly described using 291 the "sp" tag' is updated to read 'Policy applies to the domain 292 queried and to subdomains, unless subdomain policy is explicitly 293 described using the "sp" or "np" tags.' 295 sp: The sentence 'If absent, the policy specified by the "p" tag 296 MUST be applied for subdomains' is updated to read 'If both the 297 'sp' tag is absent and the 'np' tag is either absent or not 298 applicable, the policy specified by the "p" tag MUST be applied 299 for subdomains. 301 3.3. Changes in Section 6.5 "Domain Owner Actions" 303 In addition to the DMARC domain owner actions, PSOs that require use 304 of DMARC and participate in PSD DMARC ought to make that information 305 available to receivers. This document is an experimental mechanism 306 for doing so. See the [this document] experiment description 307 (Appendix A). 309 3.4. Changes in Section 6.6.1 "Extract Author Domain" 311 Experience with DMARC has shown that some implementations short- 312 circuit messages, bypassing DMARC policy application, when the domain 313 name extracted by the receiver (from the RFC5322.From) is on the 314 public suffix list used by the receiver. This negates the capability 315 being created by this specification. Therefore, the following 316 paragraph is appended to Section 6.6.1 of DMARC [RFC7489]: 318 Note that domain names that appear on a public suffix list are not 319 exempt from DMARC policy application and reporting. 321 3.5. Changes in Section 6.6.3 "Policy Discovery" 323 A new step between step 3 and 4 is added: 325 3A. If the set is now empty and the longest PSD (Section 2.4) of the 326 Organizational Domain is one that the receiver has determined is 327 acceptable for PSD DMARC (discussed in the [this document] 328 experiment description (Appendix A)), the Mail Receiver MUST query 329 the DNS for a DMARC TXT record at the DNS domain matching the 330 [this document] longest PSD (Section 2.4) in place of the 331 RFC5322.From domain in the message (if different). A possibly 332 empty set of records is returned. 334 As an example, for a message with the Organizational Domain of 335 "example.compute.cloudcompany.com.example", the query for PSD DMARC 336 would use "compute.cloudcompany.com.example" as the [this document] 337 longest PSD (Section 2.4). The receiver would check to see if that 338 PSD is listed in the DMARC PSD Registry, and if so, perform the 339 policy lookup at "_dmarc.compute.cloudcompany.com.example". 341 Note: Because the PSD policy query comes after the Organizational 342 Domain policy query, PSD policy is not used for Organizational 343 domains that have published a DMARC policy. Specifically, this is 344 not a mechanism to provide feedback addresses (RUA/RUF) when an 345 Organizational Domain has declined to do so. 347 3.6. Changes in Section 7 "DMARC Feedback" 349 Operational note for PSD DMARC: For PSOs, feedback for non-existent 350 domains is desirable and useful, just as it is for org-level DMARC 351 operators. See Section 4 of [this document] for discussion of 352 Privacy Considerations for PSD DMARC. 354 4. Privacy Considerations 356 These privacy considerations are developed based on the requirements 357 of [RFC6973]. Additionally, the Privacy Considerations of [RFC7489] 358 apply to the mechanisms described by this document. 360 4.1. Feedback leakage 362 Providing feedback reporting to PSOs can, in some cases, cause 363 information to leak out of an organization to the PSO. This leakage 364 could potentially be utilized as part of a program of pervasive 365 surveillance (See [RFC7624]). There are roughly three cases to 366 consider: 368 o Single Organization PSDs (e.g., ".google"), RUA and RUF reports 369 based on PSD DMARC have the potential to contain information about 370 emails related to entities managed by the organization. Since 371 both the PSO and the Organizational Domain owners are common, 372 there is no additional privacy risk for either normal or non- 373 existent Domain reporting due to PSD DMARC. 375 o Multi-organization PSDs that require DMARC usage (e.g., ".bank"): 376 PSD DMARC based reports will only be generated for domains that do 377 not publish a DMARC policy at the organizational or host level. 378 For domains that do publish the required DMARC policy records, the 379 feedback reporting addresses (RUA and RUF) of the organization (or 380 hosts) will be used. The only direct feedback leakage risk for 381 these PSDs are for Organizational Domains that are out of 382 compliance with PSD policy. Data on non-existent cousin domains 383 would be sent to the PSO. 385 o Multi-organization PSDs (e.g., ".com") that do not mandate DMARC 386 usage: Privacy risks for Organizational Domains that have not 387 deployed DMARC within such PSDs are significant. For non-DMARC 388 Organizational Domains, all DMARC feedback will be directed to the 389 PSO. PSD DMARC is opt-out (by publishing a DMARC record at the 390 Organizational Domain level) vice opt-in, which would be the more 391 desirable characteristic. This means that any non-DMARC 392 organizational domain would have its feedback reports redirected 393 to the PSO. The content of such reports, particularly for 394 existing domains, is privacy sensitive. 396 PSOs will receive feedback on non-existent domains, which may be 397 similar to existing Organizational Domains. Feedback related to such 398 cousin domains have a small risk of carrying information related to 399 an actual Organizational Domain. To minimize this potential concern, 400 PSD DMARC feedback MUST be limited to Aggregate Reports. Feedback 401 Reports carry more detailed information and present a greater risk. 403 Due to the inherent Privacy and Security risks associated with PSD 404 DMARC for Organizational Domains in multi-organization PSDs that do 405 not particpate in DMARC, any Feedback Reporting related to multi- 406 organizational PSDs MUST be limited to non-existent domains except in 407 cases where the reporter knows that PSO requires use of DMARC. 409 5. Security Considerations 411 This document does not change the Security Considerations of 412 [RFC7489] and [RFC7960]. 414 The risks of the issues identified in [RFC7489], Section 12.3, DNS 415 Security, are amplified by PSD DMARC. In particular, DNS cache 416 poisoning (or Name Chaining), see [RFC3833] for details, consequences 417 are increased because a successful attack would potentially have a 418 much wider scope. 420 The risks of the issues identified in [RFC7489], Section 12.5, 421 External Reporting Addresses, are amplified by PSD DMARC. By design, 422 PSD DMARC causes unrequested reporting of feedback to entities 423 external to the Organizational Domain. This is discussed in more 424 detail in Section 4. 426 6. IANA Considerations 428 This section describes actions requested to be completed by IANA. 430 6.1. Subdomain Policy Tag 432 IANA is requested to add a new tag to DMARC Tag Registry in the 433 Domain-based Message Authentication, Reporting, and Conformance 434 (DMARC) Parameters Registry. 436 The entry is as follows: 438 +----------+-----------+---------+-------------------------------+ 439 | Tag Name | Reference | Status | Description | 440 +----------+-----------+---------+-------------------------------+ 441 | np | this | current | Requested handling policy for | 442 | | document | | non-existent subdomains | 443 +----------+-----------+---------+-------------------------------+ 445 7. References 447 7.1. Normative References 449 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 450 Requirement Levels", BCP 14, RFC 2119, 451 DOI 10.17487/RFC2119, March 1997, 452 . 454 [RFC7489] Kucherawy, M., Ed. and E. Zwicky, Ed., "Domain-based 455 Message Authentication, Reporting, and Conformance 456 (DMARC)", RFC 7489, DOI 10.17487/RFC7489, March 2015, 457 . 459 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 460 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 461 May 2017, . 463 7.2. Informative References 465 [psddmarc.org] 466 multiple, "PSD DMARC Web Site", April 2019, 467 . 469 [RFC3833] Atkins, D. and R. Austein, "Threat Analysis of the Domain 470 Name System (DNS)", RFC 3833, DOI 10.17487/RFC3833, August 471 2004, . 473 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 474 IANA Considerations Section in RFCs", RFC 5226, 475 DOI 10.17487/RFC5226, May 2008, 476 . 478 [RFC5598] Crocker, D., "Internet Mail Architecture", RFC 5598, 479 DOI 10.17487/RFC5598, July 2009, 480 . 482 [RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., 483 Morris, J., Hansen, M., and R. Smith, "Privacy 484 Considerations for Internet Protocols", RFC 6973, 485 DOI 10.17487/RFC6973, July 2013, 486 . 488 [RFC7624] Barnes, R., Schneier, B., Jennings, C., Hardie, T., 489 Trammell, B., Huitema, C., and D. Borkmann, 490 "Confidentiality in the Face of Pervasive Surveillance: A 491 Threat Model and Problem Statement", RFC 7624, 492 DOI 10.17487/RFC7624, August 2015, 493 . 495 [RFC7960] Martin, F., Ed., Lear, E., Ed., Draegen. Ed., T., Zwicky, 496 E., Ed., and K. Andersen, Ed., "Interoperability Issues 497 between Domain-based Message Authentication, Reporting, 498 and Conformance (DMARC) and Indirect Email Flows", 499 RFC 7960, DOI 10.17487/RFC7960, September 2016, 500 . 502 [RFC8020] Bortzmeyer, S. and S. Huque, "NXDOMAIN: There Really Is 503 Nothing Underneath", RFC 8020, DOI 10.17487/RFC8020, 504 November 2016, . 506 Appendix A. PSD DMARC Privacy Concern Mitigation Experiment 508 The experiment being performed has three different questions which 509 are looking to be addressed in this document. 511 o Section 3.2 modifies policy discovery to add an additional DNS 512 lookup. To determine if this lookup is useful, PSDs will add 513 additional DMARC records in place, and will analyze the DMARC 514 reports. Success will be determined if a consensus of PSDs that 515 publish DMARC records are able to collect useful data. 517 o Section 3.2 adds the "np" tag for non-existent subdomains (DNS 518 NXDOMAIN). PSOs wishing to test this will add this flag to their 519 DMARC record, and will analyze DMARC reports for deployment. 520 Success will be determined if organizations find explicitly 521 blocking non-existent subdomains domains desirable and provide 522 added value. 524 o Section 4.1 discusses three cases where providing feedback could 525 cause information to leak out of an organization. This experiment 526 will analyze the feedback reports generated for each case to 527 determine if there is information leakage. 529 Appendix B. DMARC PSD Registry Examples 531 To facilitate experimentation around data leakage mitigation, samples 532 of the DNS based and IANA like registries are available at 533 [psddmarc.org]. 535 B.1. DMARC PSD DNS Query Service 537 A sample stand-alone DNS query service is available at 538 [psddmarc.org]. It was developed based on the contents suggested for 539 an IANA registry in an earlier revision of this draft. Usage of the 540 service is described on the web site. 542 B.2. DMARC Public Suffix Domain (PSD) Registry 544 [psddmarc.org] provides an IANA like DMARC Public Suffix Domain (PSD) 545 Registry as a stand-alone DNS query service. It follows the contents 546 and structure described below. There is a Comma Separated Value 547 (CSV) version of the listed PSD domains which is suitable for use in 548 build updates for PSD DMARC capable software. 550 Names of PSDs participating in PSD DMARC must be registered this new 551 registry. New entries are assigned only for PSDs that require use of 552 DMARC. The requirement has to be documented in a manner that 553 satisfies the terms of Expert Review,per [RFC5226]. The Designated 554 Expert needs to confirm that provided documentation adequately 555 describes PSD policy to require domain owners to use DMARC or that 556 all domain owners are part of a single organization with the PSO. 558 The initial set of entries in this registry is as follows: 560 +-------------+---------------+ 561 | PSD | Status | 562 +-------------+---------------+ 563 | .bank | current | 564 +-------------+---------------+ 565 | .insurance | current | 566 +-------------+---------------+ 567 | .gov.uk | current | 568 +-------------+---------------+ 569 | .mil | current | 570 +-------------+---------------+ 572 B.3. DMARC PSD PSL Extension 574 [psddmarc.org] provides a PSL like file to enable to facilitate 575 identification of PSD DMARC participants. Contents are functionally 576 identical to the IANA like registry, but presented in a different 577 format. 579 When using this approach, the input domain of the extension lookup is 580 supposed to be the output domain of the regular PSL lookup, i.e. the 581 organizational domain. This alternative data approach is potentially 582 useful since DMARC implementations already need to be able to parse 583 the data format, so it should be easier to implement. 585 Appendix C. Implementations 587 There are two known implementations of PSD DMARC available for 588 testing. 590 C.1. Authheaders Module 592 The authheaders Python module and command line tool is available for 593 download or installation from Pypi (Python Packaging Index). 595 It supports both use of the DNS based query service and download of 596 the CSV registry file from [psddmarc.org]. 598 C.2. Zdkimfilter Module 600 The zdkimfilter module is a separately available add-on to Courier- 601 MTA. 603 Mostly used for DKIM signing, it can be configured to also verify, 604 apply DMARC policies, and send aggregate reports. For PSD DMARC it 605 uses the PSL extension list approach, which is available from from 606 [psddmarc.org] 608 Acknowledgements 610 Thanks to the following individuals for their contributions (both 611 public and private) to improving this document. Special shout out to 612 Dave Crocker for naming the beast. 614 Kurt Andersen, Seth Blank, Dave Crocker, Heather Diaz, Tim Draegen, 615 Zeke Hendrickson, Andrew Kennedy, John Levine, Dr Ian Levy, Craig 616 Schwartz, Alessandro Vesely, and Tim Wicinski 618 Author's Address 620 Scott Kitterman 621 fTLD Registry Services 622 600 13th Street, NW, Suite 400 623 Washington, DC 20005 624 United States of America 626 Phone: +1 301 325-5475 627 Email: scott@kitterman.com