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 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 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 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. Melnikov & Hoeneisen Expires May 7, 2020 [Page 1] Internet-Draft Content-Type HF Parameter 'forwarded' November 2019 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. Melnikov & Hoeneisen Expires May 7, 2020 [Page 2] Internet-Draft Content-Type HF Parameter 'forwarded' November 2019 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. Melnikov & Hoeneisen Expires May 7, 2020 [Page 3] Internet-Draft Content-Type HF Parameter 'forwarded' November 2019 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: Subject: Meeting at my place From: "Alexey Melnikov" 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" Message-ID: 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]. Melnikov & Hoeneisen Expires May 7, 2020 [Page 4] Internet-Draft Content-Type HF Parameter 'forwarded' November 2019 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, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC5322] Resnick, P., Ed., "Internet Message Format", RFC 5322, DOI 10.17487/RFC5322, October 2008, . Melnikov & Hoeneisen Expires May 7, 2020 [Page 5] Internet-Draft Content-Type HF Parameter 'forwarded' November 2019 [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, . 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, . 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. Melnikov & Hoeneisen Expires May 7, 2020 [Page 6] Internet-Draft Content-Type HF Parameter 'forwarded' November 2019 Message-ID: From: Alice Spivak Hyatt To: Carol Burnett 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: From: Alice Spivak Hyatt To: Carol Burnett 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-- Melnikov & Hoeneisen Expires May 7, 2020 [Page 7] Internet-Draft Content-Type HF Parameter 'forwarded' November 2019 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/ Melnikov & Hoeneisen Expires May 7, 2020 [Page 8]