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
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This Internet-Draft will expire on May 7, 2020.
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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.
[]
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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