SPFBIS Working Group M. Kucherawy Internet-Draft Cloudmark Intended status: Informational February 17, 2012 Expires: August 20, 2012 The SPF/Sender-ID Experiment draft-kucherawy-spfbis-experiment-00 Abstract In 2006 the IETF published a suite of protocol documents comprising SPF and Sender-ID, two proposed email authentication protocols. Because of interoperability concerns and the inability of the working group producing them to converge on a single specification, the IESG required them to have Experimental status and invited the community to observe their deployments for a period of time, hoping convergence would be possible later. After six years, sufficient experience and evidence have been collected that the experiment thus created can be considered concluded, and a common path toward can be selected. This memo presents those findings. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on August 20, 2012. Copyright Notice Copyright (c) 2012 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents Kucherawy Expires August 20, 2012 [Page 1] Internet-Draft SPF/Sender-ID Experiment February 2012 (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. The Need For Convergence . . . . . . . . . . . . . . . . . . . 3 3. Evidence of Deployment . . . . . . . . . . . . . . . . . . . . 4 4. Evidence of Differences . . . . . . . . . . . . . . . . . . . . 4 5. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . 4 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4 7. Security Considerations . . . . . . . . . . . . . . . . . . . . 5 8. Informative References . . . . . . . . . . . . . . . . . . . . 5 Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 5 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 6 Kucherawy Expires August 20, 2012 [Page 2] Internet-Draft SPF/Sender-ID Experiment February 2012 1. Introduction In April, 2006, the MARID working group published the [SPF] and [SUBMITTER]/[SENDER-ID]/[PRA] email authentication protocols. Both of these enabled one to publish via the Domain Name System a policy declaring which mail servers were authorized to send email on behalf of a specific domain name. The two protocols made use of this policy statement and some specific (but different) logic to evaluate whether or not the email client sending or relaying a message was authorized to do so. Because Sender-ID could use the same policy statement as SPF, the IESG at the time was concerned that an implementation of Sender-ID might erroneously apply that statement to a message and, depending on selected recipient actions, could improperly interfere with message delivery. As a result, the IESG required the publication of all of these documents as Experimental, and requested that the community observe deployment and operation of the protocols over a period of two years from publication in order to determine a reasonable path forward. This working group has convened to resolve this experiment and propose advancement of a single protocol going forward. This memo presents evidence on both deployment and efficacy of the two protocols, and further discusses the increasing need for convergence. At the end it presents conclusions and recommends a path forward, as the IESG requested. 2. The Need For Convergence These two protocols fall into a family of protocols that provide domain-level email authentication services. Another prominent one is [DKIM]. Various efforts exist that use these as building blocks to increased abuse filtering capabilties, and indeed this sort of work has spawned another working group in the Applications area, with still more of these incubating in associations and trade groups outside of the IETF. There is thus some palpable interest in having a path authorization scheme, as well as a domain-level signing scheme, on the Standards Track so that these newer technologies can develop. This is, in part, why the community has decided to expend the energy to bring this experiment to a conclusion and document the results. Kucherawy Expires August 20, 2012 [Page 3] Internet-Draft SPF/Sender-ID Experiment February 2012 3. Evidence of Deployment A query of approximately 287,000 domains known to be publishing SPF policy records in some way revealed that only 1.63% of them published using the SPF resource record type. This suggests that using SPF records as a way of separating SPF processing from Sender-ID processing is not a reliable heuristic. For sites that published both SPF and TXT RRs, as many as 17% of these actually included separate policies, which suggests that keeping the two synchronized could actually be an operational concern. It is possible, but considered unlikely, that the deviation was deliberate in the observed cases. Further analysis suggests that of that same large set of domains, approximately 1,200, or fewer than 1%, published Sender-ID records (identified by "v=spf2"). It is likely impossible to determine from a survey which MTAs have SPF or Sender-ID checking enabled at message ingress since it does not appear, for example in the reply to the EHLO command from extended [SMTP]. 4. Evidence of Differences Specific data collected by multiple independent working group contributors (see Appendix A) shows that in more than 95% of cases, Sender-ID and SPF reach the same conclusion about a message. Given the data presented in the previous section, this means the domains found in PRA-selected header fields in the message matched the RFC5321.MailFrom domain. [other data TBD] 5. Conclusions Given the evidence above, the working group feels that the experiment allows the following conclusions: 1. [conclusions here] 6. IANA Considerations This memo presents no actions for IANA. [RFC Editor: Please remove this section prior to publication.] Kucherawy Expires August 20, 2012 [Page 4] Internet-Draft SPF/Sender-ID Experiment February 2012 7. Security Considerations This memo contains information for the community only, akin to an implementation report, and does not introduce any new security concerns. Its implications could, in fact, resolve some. 8. Informative References [DKIM] Crocker, D., Ed., Hansen, T., Ed., and M. Kucherawy, Ed., "DomainKeys Identified Mail (DKIM) Signatures", RFC 6376, September 2011. [PRA] Lyon, J., "Purported Responsible Address in E-Mail Messages", RFC 4407, April 2006. [SENDER-ID] Lyon, J. and M. Wong, "Sender ID: Authenticating E-Mail", RFC 4406, April 2006. [SMTP] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321, October 2008. [SPF] Wong, M. and W. Schlitt, "Sender Policy Framework (SPF) for Authorizing Use of Domains in E-Mail, Version 1", RFC 4408, April 2006. [SUBMITTER] Allman, E. and H. Katz, "SMTP Service Extension for Indicating the Responsible Submitter of an E-Mail Message", RFC 4405, April 2006. Appendix A. Acknowledgments The following provided operational data that contributed to the findings presented above: Cisco: contributed data about observed Sender-ID and SPF data in the DNS for a large number of domains Hotmail: contributed data about the difference between Sender-ID and SPF evaluations The Trusted Domain Project: contributed data about the difference between Sender-ID and SPF evaluations The author would also like to thank the following for their Kucherawy Expires August 20, 2012 [Page 5] Internet-Draft SPF/Sender-ID Experiment February 2012 contributions to the development of this memo: (names) Author's Address Murray S. Kucherawy Cloudmark 128 King St., 2nd Floor San Francisco, CA 94107 USA Phone: +1 415 946 3800 Email: msk@cloudmark.com Kucherawy Expires August 20, 2012 [Page 6]