Network Working Group                                        A. Melnikov
Internet-Draft                                                 Isode Ltd
Intended status: Informational                              B. Hoeneisen
Expires: 17 August 2023                                   pEp Foundation
                                                        13 February 2023


      IANA Registration of Content-Disposition Header Field value
                             'encapsulated'
               draft-melnikov-iana-reg-cd-encapsulated-00

Abstract

   This document defines a new Content-Disposition header field value
   "encapsulated" to be used with "message/rfc822" and "message/global"
   media types.  Content-Disposition "encapsulated" signals that
   enclosed message should be presented inline, instead of being
   presented as a forwarded message.  One use case for this is for S/
   MIME header protection.

About This Document

   This note is to be removed before publishing as an RFC.

   Status information for this document may be found at
   https://datatracker.ietf.org/doc/draft-melnikov-iana-reg-cd-
   encapsulated/.

   Discussion of this document takes place on the dispatch non-WG
   mailing list (mailto:dispatch@ietf.org), which is archived at
   https://mailarchive.ietf.org/arch/browse/dispatch/.

   Source for this draft and an issue tracker can be found at
   https://gitea.pep.foundation/pEp.foundation/internet-drafts.

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/.







Melnikov & Hoeneisen     Expires 17 August 2023                 [Page 1]


Internet-Draft     Content-Disposition 'encapsulated'      February 2023


   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 17 August 2023.

Copyright Notice

   Copyright (c) 2023 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 (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 Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

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











Melnikov & Hoeneisen     Expires 17 August 2023                 [Page 2]


Internet-Draft     Content-Disposition 'encapsulated'      February 2023


1.  Introduction

   This document defines a new Content-Disposition header field
   [RFC2183] value "encapsulated" to be used with "message/rfc822"
   [RFC2046] and "message/global" [RFC6532] media types.  The value
   "encapsulated" is meaningful when used within S/MIME or PGP/MIME
   signed or encrypted body parts (e.g., as specified in
   [I-D.ietf-lamps-header-protection] for S/MIME).  Absence of Content-
   Disposition header field (or presence of any value other than
   "encapsulated") when Content-Type is "message/rfc822" or "message/
   global" means that the message nested inside "message/rfc822" (or
   "message/global") is a simple forwarded message.  Presence of
   "Content-Disposition: encapsulated" means that encapsulation is used
   for header protection, but otherwise the message should be displayed
   inline.

1.1.  Use Cases

   Two use cases have been discovered so far:

   1.  This Content-Disposition value 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 Content-Disposition values indicates to mailing lists which
       signed and/or encrypted (S/MIME or PGP/MIME) email messages are
       forwarded, and which are just encapsulated for the purpose of
       header protection, and how to handle these respective messages.

1.2.  Implementations

   At this time, the following email systems are known to use this
   Content-Disposition header field value:

   1.  Isode Harrier Web Server with S/MIME [RFC8551] support

1.3.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.






Melnikov & Hoeneisen     Expires 17 August 2023                 [Page 3]


Internet-Draft     Content-Disposition 'encapsulated'      February 2023


1.4.  Terms

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

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

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

2.  Specification

   This section defines the new "encapsulated" Content-Disposition
   header field value.

   An implementation that supports Content-Disposition header field as
   defined in [RFC2183], but doesn't support this specification will
   interpret "encapsulated" in the same way as the value "attachment"
   (as per requirements in [RFC2183]).

   An implementation that supports this specification uses the Content-
   Disposition value "encapsulated" with Content-Type "message/rfc822"
   or "message/global" to signal that the message is encapsulated for
   header protection (cf.  [I-D.ietf-lamps-header-protection]).
   Presence of Content-Disposition "encapsulated" with any other
   Content-Type should be treated in the same way as the Content-
   Disposition value "inline".

3.  Example

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




















Melnikov & Hoeneisen     Expires 17 August 2023                 [Page 4]


Internet-Draft     Content-Disposition 'encapsulated'      February 2023


     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
     Content-Disposition: encapsulated

     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--

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-Disposition
   header field value [RFC2183] "encapsulated" with the reference [RFC
   THIS].



Melnikov & Hoeneisen     Expires 17 August 2023                 [Page 5]


Internet-Draft     Content-Disposition 'encapsulated'      February 2023


   [[ RFC Editor: Replace [RFC THIS] with the number of this RFC before
   publication. ]]

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.

8.  References

8.1.  Normative References

   [RFC2046]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part Two: Media Types", RFC 2046,
              DOI 10.17487/RFC2046, November 1996,
              <https://www.rfc-editor.org/info/rfc2046>.

   [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>.

   [RFC2183]  Troost, R., Dorner, S., and K. Moore, Ed., "Communicating
              Presentation Information in Internet Messages: The
              Content-Disposition Header Field", RFC 2183,
              DOI 10.17487/RFC2183, August 1997,
              <https://www.rfc-editor.org/info/rfc2183>.

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

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [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.ietf-lamps-header-protection]
              Gillmor, D. K., Hoeneisen, B., and A. Melnikov, "Header
              Protection for S/MIME", Work in Progress, Internet-Draft,



Melnikov & Hoeneisen     Expires 17 August 2023                 [Page 6]


Internet-Draft     Content-Disposition 'encapsulated'      February 2023


              draft-ietf-lamps-header-protection-11, 24 January 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-lamps-
              header-protection-11>.

   [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.  Document Changelog

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

   *  draft-melnikov-iana-reg-cd-encapsulated-00

      -  Renamed document

      -  Replaced Content-Type forwarded parameter with Content-
         Disposition "encapsulated"

   *  draft-melnikov-iana-reg-forwarded-00

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

Appendix B.  Open Issues

   [[ 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
   United Kingdom
   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/




Melnikov & Hoeneisen     Expires 17 August 2023                 [Page 7]