Independent Submission                                    P. Saint-Andre
Request for Comments: 7259                                          &yet
Category: Informational                                         May 2014
ISSN: 2070-1721


                       The Jabber-ID Header Field

Abstract

   This document defines a header field that enables the author of an
   email or netnews message to include a Jabber ID in the message header
   block for the purpose of associating the author with a particular
   Extensible Messaging and Presence Protocol (XMPP) address.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This is a contribution to the RFC Series, independently of any other
   RFC stream.  The RFC Editor has chosen to publish this document at
   its discretion and makes no statement about its value for
   implementation or deployment.  Documents approved for publication by
   the RFC Editor are not a candidate for any level of Internet
   Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7259.

Copyright Notice

   Copyright (c) 2014 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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   to this document.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Syntax  . . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Usage . . . . . . . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Inclusion . . . . . . . . . . . . . . . . . . . . . . . .   3
     3.2.  Generation  . . . . . . . . . . . . . . . . . . . . . . .   3
     3.3.  Processing  . . . . . . . . . . . . . . . . . . . . . . .   4
     3.4.  Disposition . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   5.  Security and Privacy Considerations . . . . . . . . . . . . .   5
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   The Extensible Messaging and Presence Protocol (XMPP), documented in
   [RFC6120], is a streaming XML technology that enables any two
   entities on a network to exchange well-defined but extensible XML
   elements (called "XML stanzas") in close to real time.  Given XMPP's
   heritage in the Jabber open-source community, one of the primary uses
   for XMPP is instant messaging and presence as documented in
   [RFC6121], and XMPP addresses are still referred to as Jabber IDs.

   Because almost all human users of Jabber/XMPP instant messaging and
   presence systems also use email systems [RFC5322] and because many
   also use netnews systems [RFC5536], it can be helpful for them to
   associate their Jabber IDs with the messages they author.  The
   Jabber-ID header field provides a standard location for that
   information.

   Members of the XMPP instant messaging and presence community have
   been experimenting with the Jabber-ID header field for many years.
   This document defines the syntax and usage of the Jabber-ID header
   field, including the information necessary to register the field in
   the Provisional Message Header Field Names registry maintained by the
   IANA.

2.  Syntax

   The syntax of the Jabber-ID header field is defined below using
   Augmented Backus-Naur Form [RFC5234], where the "pathxmpp" rule is
   defined in the XMPP URI specification [RFC5122] and the remaining
   rules are defined in the Internet Message Format specification
   [RFC5322]:

      Jabber-ID = SP *WSP pathxmpp *WSP CRLF

   Although a native XMPP address can contain virtually any Unicode
   character [UNICODE], the header of an email or netnews message is
   allowed to contain only printable ASCII characters (see Section 2 of
   [RFC5322]).  Therefore, any characters outside the ASCII range
   [RFC20] in an XMPP address need to be converted to ASCII before
   inclusion in a Jabber-ID header field, in accordance with the rules
   defined in the XMPP URI specification [RFC5122].  In addition,
   characters allowed in XMPP localparts and XMPP resourceparts but
   disallowed by the relevant URI rules need to be percent-encoded in
   accordance with the rules defined in the URI specification [RFC3986].

3.  Usage

3.1.  Inclusion

   The Jabber-ID header field is associated with the author of the
   message; see [RFC5322].  If the "From:" header field of an email
   message contains more than one mailbox, it is best not to add the
   Jabber-ID header field to the message.  To reduce the possibility of
   confusion, it is best to include only one instance of the Jabber-ID
   header field in a given message.

3.2.  Generation

   For a user whose XMPP address is "juliet@example.com", the
   corresponding Jabber-ID header field would be:

      Jabber-ID: juliet@example.com

   As noted, non-ASCII characters in XMPP addresses need to be converted
   into ASCII before inclusion in a Jabber-ID header field.  Consider
   the following XMPP address:

      jiři@čechy.example

   In the foregoing example, the string "ř" stands for the Unicode
   character LATIN SMALL LETTER R WITH CARON and the string "č"
   stands for the Unicode character LATIN SMALL LETTER C WITH CARON,

   following the "XML Notation" used in [RFC3987] to represent
   characters that cannot be rendered in ASCII-only documents.  For
   those who do not read Czech, this example could be anglicized as
   "george@czech-lands.example".

   Following the rules in [RFC5122] and the Jabber-ID header field
   syntax, the resulting header field might be as shown below (note that
   this representation includes folding white space, which is allowed in
   accordance with the ABNF):

      Jabber-ID:
             ji%C5%99i@%C4%8Dechy.example

3.3.  Processing

   Upon receiving an email message or netnews message containing a
   Jabber-ID header field, a user agent that supports the field ought to
   process the field by converting any escaped characters to characters
   outside the ASCII range in accordance with the rules defined in
   [RFC5122], thus yielding a Jabber ID that can be used for native
   communication on the XMPP network.

3.4.  Disposition

   A user agent that has processed a Jabber-ID header field can provide
   appropriate interface elements if it has independent information
   linking the author of the email or netnews message with the specified
   Jabber ID (e.g., via a user-controlled address book or automated
   directory lookup).  Such interface elements might include an
   indicator of "presence" (i.e., that the author is online and
   available for communication via XMPP) if the user is subscribed to
   the presence of the author, and an element that enables the user to
   send an instant message or initiate a text chat session with the
   author.

4.  IANA Considerations

   The IANA has added "Jabber-ID" to the Provisional Message Header
   Field Names registry.  The completed registration template follows.

   Header field name:  Jabber-ID

   Applicable protocol:  mail, netnews

   Status:  provisional

   Author/Change controller  Peter Saint-Andre <stpeter@jabber.org>

   Specification document:  RFC 7259

   Related information:  See RFC 6120

5.  Security and Privacy Considerations

   Message headers are an existing standard and are designed to easily
   accommodate new types.  Although the Jabber-ID header field could be
   forged, this problem is inherent in Internet email and netnews.
   However, because a forged Jabber-ID header field might break
   automated processing, applications are discouraged from depending on
   the Jabber-ID header field to indicate the authenticity of an email
   or netnews message, or the identity of its author or sender.
   Including the Jabber-ID header field among the signer header fields
   in DomainKeys Identified Mail (DKIM) can help to mitigate against
   forging of the header (see [RFC6376]).

   Advertising XMPP addresses in email or netnews headers might make it
   easier for malicious users to harvest XMPP addresses and therefore to
   send unsolicited bulk communications to the users or applications
   represented by those addresses.  Providing such a binding between an
   email address and a Jabber ID can also increase the possibility of
   drawing a connection between different kinds of communications
   traffic for purposes of surveillance and other breaches of privacy.
   Care ought to be taken in balancing the benefits of open information
   exchange against the potential costs of security and privacy
   weaknesses.  An email or netnews user agent that is capable of
   including the Jabber-ID header field in outgoing email or netnews
   messages needs to provide an option for its user to disable inclusion
   of the Jabber-ID header field generally, on a per-recipient basis,
   and on a per-message basis.

   The security and privacy considerations discussed in [RFC3986],
   [RFC3987], [RFC5122], [RFC6120], and [RFC6121] also apply to the
   Jabber-ID message header.

6.  References

6.1.  Normative References

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66, RFC
              3986, January 2005.

   [RFC3987]  Duerst, M. and M. Suignard, "Internationalized Resource
              Identifiers (IRIs)", RFC 3987, January 2005.

   [RFC5122]  Saint-Andre, P., "Internationalized Resource Identifiers
              (IRIs) and Uniform Resource Identifiers (URIs) for the
              Extensible Messaging and Presence Protocol (XMPP)", RFC
              5122, February 2008.

   [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008.

   [RFC5322]  Resnick, P., Ed., "Internet Message Format", RFC 5322,
              October 2008.

   [RFC6120]  Saint-Andre, P., "Extensible Messaging and Presence
              Protocol (XMPP): Core", RFC 6120, March 2011.

   [UNICODE]  The Unicode Consortium, "The Unicode Standard, Version
              6.3", (Mountain View, CA: The Unicode Consortium, 2013.
              ISBN 978-1-936213-08-5),
              <http://www.unicode.org/versions/Unicode6.3.0/>.

6.2.  Informative References

   [RFC20]    Cerf, V., "ASCII format for network interchange", RFC 20,
              October 1969.

   [RFC5536]  Murchison, K., Lindsey, C., and D. Kohn, "Netnews Article
              Format", RFC 5536, November 2009.

   [RFC6121]  Saint-Andre, P., "Extensible Messaging and Presence
              Protocol (XMPP): Instant Messaging and Presence", RFC
              6121, March 2011.

   [RFC6376]  Crocker, D., Hansen, T., and M. Kucherawy, "DomainKeys
              Identified Mail (DKIM) Signatures", RFC 6376, September
              2011.

Appendix A.  Acknowledgements

   Thanks to Dave Cridland, Stephen Farrell, Russ Housley, and Alexey
   Melnikov for their feedback.

Author's Address

   Peter Saint-Andre
   &yet

   EMail: ietf@stpeter.im