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DMARC Working Group                                          K. Andersen
Internet-Draft                                                  LinkedIn
Intended status: Experimental                              S. Blank, Ed.
Expires: March 14, 2019                                         ValiMail
                                                          J. Levine, Ed.
                                                    Taughannock Networks
                                                      September 10, 2018


 Using Multiple Signing Algorithms with the ARC (Authenticated Received
                            Chain) Protocol
                     draft-ietf-dmarc-arc-multi-02

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 RFC 8463 has expanded 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 March 14, 2019.

Copyright Notice

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





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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Definitions and Terminology . . . . . . . . . . . . . . . . .   3
   4.  Supporting Alternate Signing Algorithms . . . . . . . . . . .   3
   5.  General Approach  . . . . . . . . . . . . . . . . . . . . . .   3
     5.1.  Signers . . . . . . . . . . . . . . . . . . . . . . . . .   3
     5.2.  Validators  . . . . . . . . . . . . . . . . . . . . . . .   4
   6.  Phases of Algorithm Evolution . . . . . . . . . . . . . . . .   4
     6.1.  Introductory Period . . . . . . . . . . . . . . . . . . .   4
     6.2.  Co-Existence Period . . . . . . . . . . . . . . . . . . .   4
     6.3.  Deprecation Period  . . . . . . . . . . . . . . . . . . .   4
     6.4.  Obsolescence Period . . . . . . . . . . . . . . . . . . .   4
   7.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .   4
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   5
     10.2.  Informative References . . . . . . . . . . . . . . . . .   5
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .   6
   Appendix B.  Comments and Feedback  . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

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 RFC 8463 expanded the supported algorithms.
   This specification defines how to extend ARC for multiple signing
   algorithms.







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2.  Overview

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

3.  Definitions and Terminology

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

   The capitalized 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 and the problems [RFC7960] created by the
   initial DMARC [RFC7489] .

4.  Supporting Alternate Signing Algorithms

   To enable multiple algorithms, 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

   There is a separate independent signing chain for each signing
   algorithm.  Hence, when creating an ARC signature, a signer MUST
   include only other signatures that use the same algorithm as the
   signature being created.

   Wnen signing a message with no previous ARC signatures, signers MUST
   sign using all supported algorithms.

   A signer MUST continue the longest ARC chain(s) in a message with all
   algorithms that it supports.  That is, if at least one of the longest
   chains uses an algorithm that a signer supports, the signer continues
   the chain(s).  If none of the longest chains in a message use an
   algorithm supported by a signer, the signer MUST NOT extend any
   chains, even if a shorter chain does use a supported algorithm.





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5.2.  Validators

   A validator MUST use the longest ARC chain(s) on the message.  If a
   validator cannot interpret the signing algorithm on any of the
   longest chains, validation fails, evven if a shorter chain does use a
   supported algorithm.

   If there is more than one longest chain, the overall result reported
   can be that of of any of the validations.  The result used when
   extending an ARC chain MUST be the result from validating that chain.

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] protocol.







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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] protocol.

10.  References

10.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC5598]  Crocker, D., "Internet Mail Architecture", RFC 5598,
              DOI 10.17487/RFC5598, July 2009,
              <https://www.rfc-editor.org/info/rfc5598>.

10.2.  Informative References

   [ARC-DRAFT]
              Andersen, K., Long, B., and S. Jones, "Authenticated
              Received Chain (ARC) Protocol (I-D-16)", n.d.,
              <https://tools.ietf.org/html/
              draft-ietf-dmarc-arc-protocol-16>.

   [RFC7489]  Kucherawy, M., Ed. and E. Zwicky, Ed., "Domain-based
              Message Authentication, Reporting, and Conformance
              (DMARC)", RFC 7489, DOI 10.17487/RFC7489, March 2015,
              <https://www.rfc-editor.org/info/rfc7489>.

   [RFC7960]  Martin, F., Ed., Lear, E., Ed., Draegen. Ed., T., Zwicky,
              E., Ed., and K. Andersen, Ed., "Interoperability Issues
              between Domain-based Message Authentication, Reporting,
              and Conformance (DMARC) and Indirect Email Flows",
              RFC 7960, DOI 10.17487/RFC7960, September 2016,
              <https://www.rfc-editor.org/info/rfc7960>.

10.3.  URIs

   [1] mailto:dmarc@ietf.org






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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 [1].

Authors' Addresses

   Kurt Andersen
   LinkedIn
   1000 West Maude Ave
   Sunnyvale, California  94085
   US

   Email: kurta@linkedin.com


   Seth Blank (editor)
   ValiMail
   Montgomery
   San Francisco, California
   US

   Email: seth@valimail.com


   John Levine (editor)
   Taughannock Networks
   PO Box 727
   Trumansburg, New York
   US

   Email: standards@taugh.com












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