DMARC Working Group K. Andersen
Internet-Draft LinkedIn
Intended status: Experimental S. Blank, Ed.
Expires: July 26, 2018 ValiMail
J. Levine, Ed.
Taughannock Networks
January 22, 2018

Using Multiple Signing Algorithms with the ARC (Authenticated Received Chain) Protocol
draft-ietf-dmarc-arc-multi-00

Abstract

The Authenticated Received Chain (ARC) protocol creates a mechanism whereby a series of handlers of an email message can conduct authentication of the email message as it passes among them on the way to its destination.

Initial development of ARC has been done with a single allowed signing algorithm, but parallel work in the DCRUP working group (https://datatracker.ietf.org/wg/dcrup/about/) is expanding the supported algorithms. This specification defines how to extend ARC for multiple signing algorithms.

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 https://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 July 26, 2018.

Copyright Notice

Copyright (c) 2018 IETF Trust and the persons identified as the document authors. All rights reserved.

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Table of Contents

1. Introduction

The Authenticated Received Chain (ARC) protocol adds a traceable chain of signatures that cover the handling of an email message through a chain of intermediary handlers.

Initial development of ARC has been done with a single allowed signing algorithm, but parallel work in the DCRUP working group (https://datatracker.ietf.org/wg/dcrup/about/) is expanding the supported algorithms. This specification defines how to extend ARC for multiple signing algorithms.

2. Overview

In order to phase in new signing algorithms, this specification identifies how signers and validators MUST process ARC sets found in email messages.

3. Definitions and Terminology

This section defines terms used in the rest of the document.

The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in this document are to be interpreted as described in [RFC2119].

Because many of the core concepts and definitions are found in [RFC5598], readers SHOULD to be familiar with the contents of [RFC5598], and in particular, the potential roles of intermediaries in the delivery of email.

4. Supporting Alternate Signing Algorithms

During a period where multiple algorithms are allowed, all of the statements in the ARC spec which refer to “exactly one set of ARC headers per instance” need to be understood as “at least one set per instance and no more than one set per instance per algorithm”.

5. General Approach

5.1. Signers

Signers MUST initiate ARC signing of messages with all supported algorithms that they are capable of using.

Signers MUST continue ARC chains with all supported algorithms that they are capable of using.

5.2. Validators

Validators MUST use the longest ARC chain on the message for which they can interpret the signing algorithm.

6. Phases of Algorithm Evolution

6.1. Introductory Period

Intermediaries MUST be able to validate ARC chains built with either algorithm but MAY create ARC sets with either (or both) algorithm.

The introductory period should be at least six (6) months.

6.2. Co-Existence Period

Intermediaries MUST be able to validate ARC chains build with either algorithm and MUST create ARC sets with both algorithms. Chains ending with either algorithm may be used for the result.

6.3. Deprecation Period

ARC sets built with algorithms that are being deprecated MAY be considered valid within an ARC chain, however, intermediaries MUST NOT create additional sets with the deprecated algorithm.

The deprecation period should be at least two (2) years.

6.4. Obsolescence Period

ARC sets built with algorithms that are obsolete MUST NOT be considered valid within an ARC chain. Intermediaries MUST NOT create any sets with any obsoleted algorithm.

7. Privacy Considerations

No unique privacy considerations are introduced by this specification beyond those of the base [ARC-DRAFT-11] protocol.

8. IANA Considerations

No new IANA considerations are introduced by this specification.

9. Security Considerations

No new security considerations are introduced by this specification beyond those of the base [ARC-DRAFT-11] protocol.

10. References

10.1. Normative References

[RFC1345] Simonsen, K., "Character Mnemonics and Character Sets", RFC 1345, DOI 10.17487/RFC1345, June 1992.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.
[RFC2142] Crocker, D., "Mailbox Names for Common Services, Roles and Functions", RFC 2142, DOI 10.17487/RFC2142, May 1997.
[RFC2606] Eastlake 3rd, D. and A. Panitz, "Reserved Top Level DNS Names", BCP 32, RFC 2606, DOI 10.17487/RFC2606, June 1999.
[RFC3463] Vaudreuil, G., "Enhanced Mail System Status Codes", RFC 3463, DOI 10.17487/RFC3463, January 2003.
[RFC4686] Fenton, J., "Analysis of Threats Motivating DomainKeys Identified Mail (DKIM)", RFC 4686, DOI 10.17487/RFC4686, September 2006.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", RFC 5226, DOI 10.17487/RFC5226, May 2008.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, DOI 10.17487/RFC5234, January 2008.
[RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321, DOI 10.17487/RFC5321, October 2008.
[RFC5322] Resnick, P., "Internet Message Format", RFC 5322, DOI 10.17487/RFC5322, October 2008.
[RFC5585] Hansen, T., Crocker, D. and P. Hallam-Baker, "DomainKeys Identified Mail (DKIM) Service Overview", RFC 5585, DOI 10.17487/RFC5585, July 2009.
[RFC5598] Crocker, D., "Internet Mail Architecture", RFC 5598, DOI 10.17487/RFC5598, July 2009.
[RFC5863] Hansen, T., Siegel, E., Hallam-Baker, P. and D. Crocker, "DomainKeys Identified Mail (DKIM) Development, Deployment, and Operations", RFC 5863, DOI 10.17487/RFC5863, May 2010.
[RFC6376] Crocker, D., Hansen, T. and M. Kucherawy, "DomainKeys Identified Mail (DKIM) Signatures", STD 76, RFC 6376, DOI 10.17487/RFC6376, September 2011.
[RFC6377] Kucherawy, M., "DomainKeys Identified Mail (DKIM) and Mailing Lists", BCP 167, RFC 6377, DOI 10.17487/RFC6377, September 2011.
[RFC6651] Kucherawy, M., "Extensions to DomainKeys Identified Mail (DKIM) for Failure Reporting", RFC 6651, DOI 10.17487/RFC6651, June 2012.
[RFC7208] Kitterman, S., "Sender Policy Framework (SPF) for Authorizing Use of Domains in Email, Version 1", RFC 7208, DOI 10.17487/RFC7208, April 2014.
[RFC7601] Kucherawy, M., "Message Header Field for Indicating Message Authentication Status", RFC 7601, DOI 10.17487/RFC7601, August 2015.

10.2. Informative References

[ARC-DRAFT-11] Andersen, K., Long, B. and S. Jones, "Authenticated Received Chain (ARC) Protocol (I-D-11)", n.d..
[ENHANCED-STATUS] "IANA SMTP Enhanced Status Codes", n.d..
[RFC6982] Sheffer, Y. and A. Farrel, "Improving Awareness of Running Code: The Implementation Status Section", RFC 6982, DOI 10.17487/RFC6982, July 2013.
[RFC7489] Kucherawy, M. and E. Zwicky, "Domain-based Message Authentication, Reporting, and Conformance (DMARC)", RFC 7489, DOI 10.17487/RFC7489, March 2015.
[RFC7960] Martin, F., Lear, E., Draegen. Ed., T., Zwicky, E. and K. Andersen, "Interoperability Issues between Domain-based Message Authentication, Reporting, and Conformance (DMARC) and Indirect Email Flows", RFC 7960, DOI 10.17487/RFC7960, September 2016.

Appendix A. Acknowledgements

This draft is the work of DMARC Working Group.

Grateful appreciation is extended to the people who provided feedback through the discuss mailing list.

Appendix B. Comments and Feedback

Please address all comments, discussions, and questions to dmarc@ietf.org.

Authors' Addresses

Kurt Andersen LinkedIn 1000 West Maude Ave Sunnyvale, California 94085 US EMail: kurta@linkedin.com
Seth Blank (editor) ValiMail Montgomery San Francisco, US EMail: seth@valimail.com
John Levine (editor) Taughannock Networks PO Box 727 Trumansburg, US EMail: standards@taugh.com