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Network Working Group                                        A. Melnikov
Internet-Draft                                                 Isode Ltd
Intended status: Informational                              B. Hoeneisen
Expires: May 7, 2020                                      pEp Foundation
                                                       November 04, 2019


  IANA Registration of Content-Type Header Field Parameter 'forwarded'
                  draft-melnikov-iana-reg-forwarded-00

Abstract

   This document defines a new Content-Type header field parameter named
   "forwarded" for "message/rfc822" and "message/global" media types,
   and its registration with IANA.

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
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   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 May 7, 2020.

Copyright Notice

   Copyright (c) 2019 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
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.




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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Use Cases . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.2.  Implementations . . . . . . . . . . . . . . . . . . . . .   3
     1.3.  Requirements Language . . . . . . . . . . . . . . . . . .   3
     1.4.  Terms . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Specification . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Example . . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   5.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .   5
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   5
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Appendix A.  Additional Example (pEp) . . . . . . . . . . . . . .   6
   Appendix B.  Document Changelog . . . . . . . . . . . . . . . . .   8
   Appendix C.  Open Issues  . . . . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   This document defines a new Content-Type header field parameter
   [RFC2045] for "message/rfc822" and "message/global" [RFC6532] media
   types with name "forwarded".  The parameter value is case-
   insensitive and can be either "yes" or "no".  Setting the value to
   "no" is meaningful when used within S/MIME or PGP/MIME signed or
   encrypted body parts (cf.
   [I-D.ietf-lamps-header-protection-requirements].  The value "yes"
   means that the message nested inside "message/rfc822" (or "message/
   global") is a simple forwarded message.  If the parameter is missing,
   the default assumption is the message has been forwarded.

1.1.  Use Cases

   Two use cases have been discovered so far:

   1.  This parameter indicates whether a nested message is signed and/
       or encrypted (S/MIME or PGP/MIME), which tells the receiving side
       how to display the message to the user.  Currently, many email
       clients display "weird artefacts" to users due to this missing
       information.

   2.  This parameter indicates to mailing lists which email messages
       are forwarded, and which are signed and/or encrypted (S/MIME or
       PGP/MIME), and how to handle these respective messages.




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1.2.  Implementations

   At this time, there are two known email systems which use this
   Content-Type header field parameter:

   1.  Isode with S/MIME [RFC8551]

   2.  pEp with PGP/MIME [I-D.birk-pep]

1.3.  Requirements Language

   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].

1.4.  Terms

   The following terms are defined for the scope of this document:

   o  Header Field (HF): cf. [RFC5322]

   o  Header Section (HS): cf. [RFC5322]

2.  Specification

   This section defines the new "forwarded" Content-Type header field
   parameter.

   The Content-Type header field parameter "forwarded" may assume three
   values:

   o  "yes": The email message contained in the MIME part is a forwarded
      message.  A MUA (Mail User Agent) that is forwarding a message
      should add a Content-Type header field parameter "forwarded=yes".

   o  "no": The email message contained in the MIME part is a
      encapsulated email message that has been signed and/or encrypted
      for header protection.  MUAs SHOULD add a Content-Type header
      field parameter "forwarded=no" to indicate the message is not
      forwarded, but encapsulated for header protection (cf.
      [I-D.ietf-lamps-header-protection-requirements]).

   o  absent: If the MUA has no information to determine whether an
      email message is forwarded or encapsulated, it omits the
      "forwarded" Content-Type header field parameter.  A receiving MUAs
      default behavior is to assume the email message contained in the
      MIME part is a forwarded message.




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3.  Example

   The following example shows the usage of the Content-Type header
   field parameter "forwarded" for an email message that is not
   forwarded, but encapsulated in another email message.

     Date: Mon, 25 Sep 2017 17:31:42 +0100 (GMT Daylight Time)
     Message-ID: <e4a483cb-1dfb-481d-903b-298c92c21f5e@matt.example.net>
     Subject: Meeting at my place
     From: "Alexey Melnikov" <alexey.melnikov@example.net>
     MIME-Version: 1.0
     Content-Type: multipart/signed; charset=us-ascii; micalg=sha1;
      protocol="application/pkcs7-signature";
      boundary=.cbe16d2a-e1a3-4220-b821-38348fc97237

     This is a multipart message in MIME format.
     --.cbe16d2a-e1a3-4220-b821-38348fc97237
     Content-Type: message/rfc822; forwarded=no

     Date: Mon, 25 Sep 2017 17:31:42 +0100 (GMT Daylight Time)
     From: "Alexey Melnikov" <alexey.melnikov@example.net>
     Message-ID: <e4a483cb-1dfb-481d-903b-298c92c21f5e@matt.example.net>
     MIME-Version: 1.0
     MMHS-Primary-Precedence: 3
     Subject: Meeting at my place
     To: somebody@example.net
     X-Mailer: Example Mailer
     Content-Type: text/plain; charset=us-ascii

     This is an important message that I don't want to be modified.

     --.cbe16d2a-e1a3-4220-b821-38348fc97237
     Content-Transfer-Encoding: base64
     Content-Type: application/pkcs7-signature

     [[base-64 encoded signature]]

     --.cbe16d2a-e1a3-4220-b821-38348fc97237--


   Appendix A contains an additional example on the usage of the
   Content-Type header field parameter "forwarded" as used by pEp
   [I-D.birk-pep].








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4.  Security Considerations

   This document does not define a new protocol, and thus does not
   create new security concerns in and of itself.

5.  Privacy Considerations

   This document does not introduce any new issues regarding Privacy.

6.  IANA Considerations

   This document requests IANA to register the Content-Type header field
   parameter [RFC2045] with name "forwarded" for "message/rfc822" and
   "message/global" media types as specified in Section 2 of this
   document.

7.  Acknowledgments

   The authors would like to thank the following people who have
   provided helpful comments and suggestions for this document: David
   Wilson, Kelly Bristol, Krista Bennett, Robert Williams, Steve Kille,
   and Wei Chuang.

   David Wilson came up with the idea of defining a new Content-Type
   header field parameter to distinguish forwarded messages from inner
   header field protection constructs.

8.  References

8.1.  Normative References

   [RFC2045]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part One: Format of Internet Message
              Bodies", RFC 2045, DOI 10.17487/RFC2045, November 1996,
              <https://www.rfc-editor.org/info/rfc2045>.

   [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>.

   [RFC5322]  Resnick, P., Ed., "Internet Message Format", RFC 5322,
              DOI 10.17487/RFC5322, October 2008,
              <https://www.rfc-editor.org/info/rfc5322>.







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   [RFC8551]  Schaad, J., Ramsdell, B., and S. Turner, "Secure/
              Multipurpose Internet Mail Extensions (S/MIME) Version 4.0
              Message Specification", RFC 8551, DOI 10.17487/RFC8551,
              April 2019, <https://www.rfc-editor.org/info/rfc8551>.

8.2.  Informative References

   [I-D.birk-pep]
              Marques, H., Luck, C., and B. Hoeneisen, "pretty Easy
              privacy (pEp): Privacy by Default", draft-birk-pep-04
              (work in progress), July 2019.

   [I-D.ietf-lamps-header-protection-requirements]
              Melnikov, A. and B. Hoeneisen, "Problem Statement and
              Requirements for Header Protection", draft-ietf-lamps-
              header-protection-requirements-01 (work in progress),
              October 2019.

   [RFC6532]  Yang, A., Steele, S., and N. Freed, "Internationalized
              Email Headers", RFC 6532, DOI 10.17487/RFC6532, February
              2012, <https://www.rfc-editor.org/info/rfc6532>.

Appendix A.  Additional Example (pEp)

   The following example shows the usage of the Content-Type header
   field parameter "forwarded" as used by pEp [I-D.birk-pep] in an email
   message (after decryption).  The inner email message was not
   forwarded, but encapsulated in another email message.























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     Message-ID: <pEp.PVUYXR.CEB1A-47AC-4B4D-AC1B-F8F02D49D@example.org>
     From: Alice Spivak Hyatt <alice@example.org>
     To: Carol Burnett <carol@example.net>
     Subject: pEp
     [...]
     MIME-Version: 1.0
     Content-Type: multipart/mixed;
      boundary="238e1f2946e87ccd3d1b58ba507ed7ab"

     --238e1f2946e87ccd3d1b58ba507ed7ab
     Content-Type: text/plain; charset="utf-8"
     Content-Disposition: inline; filename="msg.txt"

     [[ User-Information, e.g. "If you are seeing this message, your
     client does not support raising message attachments. Please click
     on the message attachment to view it!" ]]

     --238e1f2946e87ccd3d1b58ba507ed7ab
     Content-Type: message/rfc822; forwarded="no"

     Message-ID: <pEp.PVUYXR.CEB1A-47AC-4B4D-AC1B-F8F02D49D@example.org>
     From: Alice Spivak Hyatt <alice@example.org>
     To: Carol Burnett <carol@example.net>
     Subject: Boom shaka laka
     [...]
     MIME-Version: 1.0
     Content-Type: text/plain; charset="utf-8"
     Content-Transfer-Encoding: quoted-printable
     Content-Disposition: inline; filename="msg.txt"

     Don't you get sick of these=3F
     --238e1f2946e87ccd3d1b58ba507ed7ab
     Content-Type: application/pgp-keys
     Content-Disposition: attachment; filename="pEpkey.asc"

     -----BEGIN PGP PUBLIC KEY BLOCK-----

     xsBNBFV4PbEBCADTmjGDsoti/VPoZ3w2oCjLBNq1jWIGMkbiUgCGUQjVsNrSZ80U
     [...]
     q46bEcclS/gTGHtFweVOiqRnR4H5YEjurCd84h8zF8MAArhxBhAtbg1nYgeHjkKX
     =t2WB
     -----END PGP PUBLIC KEY BLOCK-----

     --238e1f2946e87ccd3d1b58ba507ed7ab--







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Appendix B.  Document Changelog

   [[ RFC Editor: This section is to be removed before publication ]]

   o  draft-melnikov-iana-reg-forwarded-00

   o  Initial version derived from draft-ietf-lamps-header-protection-
      requirements-01

Appendix C.  Open Issues

   o  Determine whether to add an option for "forwarded=unknown" to
      indicate support for this Content-Type header field parameter.

   [[ RFC Editor: This section should be empty and is to be removed
   before publication. ]]

Authors' Addresses

   Alexey Melnikov
   Isode Ltd
   14 Castle Mews
   Hampton, Middlesex  TW12 2NP
   UK

   Email: alexey.melnikov@isode.com


   Bernie Hoeneisen
   pEp Foundation
   Oberer Graben 4
   CH-8400 Winterthur
   Switzerland

   Email: bernie.hoeneisen@pep.foundation
   URI:   https://pep.foundation/















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