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Versions: 00 01 02                                                      
Network Working Group                                     P. Saint-Andre
Internet-Draft                                                      &yet
Intended status: Standards Track                             T. Alkemade
Expires: August 17, 2014
                                                       February 13, 2014

 STRINT Workshop Position Paper: Strengthening the Extensible Messaging
                      and Presence Protocol (XMPP)


   This document describes existing and potential future efforts at
   strengthening the Extensible Messaging and Presence Protocol (XMPP),
   for discussion at the W3C/IAB workshop on Strengthening the Internet
   Against Pervasive Monitoring (STRINT).

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
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   This Internet-Draft will expire on August 17, 2014.

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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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Per-Hop Encryption  . . . . . . . . . . . . . . . . . . . . .   3
   4.  End-to-End Encryption . . . . . . . . . . . . . . . . . . . .   4
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   5
     7.3.  URIs  . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   The Extensible Messaging and Presence Protocol (XMPP) [RFC6120]
   (along with its precursor, the so-called "Jabber protocol") has been
   used since 1999 for instant messaging(IM), presence, and other forms
   of near-real-time communication.

   XMPP has a distributed client-server architecture, with one hop from
   a client to a server and one hop between any two servers, for a total
   of at most three hops on the communication path from a given client
   to another client.  Although XMPP has supported per-hop channel
   encryption using Transport Layer Security (TLS) [RFC5246] since 2004
   through a STARTTLS upgrade mechanism on the standard XMPP ports (with
   a hardcoded TLS-only port for the client-to-server hop since 1999),
   in practice TLS has not been universally deployed for operational
   reasons.  In the last few months, operators of XMPP services have
   been working to deploy TLS more widely, and those efforts are
   summarized in this document.

   Given the client-server architecture of XMPP, per-hop encryption
   using TLS does not protect messages inside the application servers
   that are used for routing.  Therefore, various efforts have been made
   to provide end-to-end object encryption for the payloads of XMPP
   "stanzas".  To put it mildly, these efforts have been less than
   completely successful.  This document also summarizes the state of
   end-to-end encryption for XMPP.

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2.  Terminology

   Various security-related terms are to be understood in the sense
   defined in [RFC4949].

3.  Per-Hop Encryption

   As mentioned, XMPP includes the ability to protect each hop in a
   communication path using Transport Layer Security (TLS).  Although
   per-hop encryption does not protect XMPP payloads from attacks
   against XMPP servers (since absent end-to-end encryption the payloads
   would still be cleartext within the servers), it does protect against
   eavesdropping on the relevant XML streams.  Because eavesdropping on
   unprotected XML streams would reveal personally identifying
   information such as a user's contact list (which in XMPP is stored on
   the server) and the intended recipients of a user's messages,
   protecting all the hops in a communication path is critically
   important for maintaining the privacy and security of XMPP-based

   Until recently, client-to-server streams were widely protected on the
   XMPP network, but server-to-server streams were not.  This state of
   affairs has had many causes:

   o  The lack of TLS protection was not as visible to end users or
      server administrators.

   o  Several major XMPP services did not offer or negotiate TLS over
      server-to-server streams.

   o  Deployment of proper certificates for authenticated encryption is
      operationally impossible in multi-tenanted environments.

   The last item deserves some explanation.  Many instant messaging
   clients "hardcode" the connection hosts for multi-tenanted domains.
   For example, if the XMPP service for example.com is serviced by
   hosting.example.net (and example.net is a large enough service
   provider), many IM clients will provide a "wizard" interface that
   enables the end user to choose "example.net" as a service type or
   provider when configuring an account.  As a result, the client
   software will hide the security details of the connection to
   example.com and override identity mismatches of the kind otherwise
   forbidden by the security considerations of the core XMPP
   specification [RFC6120] and the "CertID" specification [RFC6125].
   However, because these overrides are not applied on server-to-server
   streams, many existing implementations and deployments do not even
   attempt TLS negotiation for server-to-server streams.

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   Although a technology like DANE/DNSSEC (see [I-D.ietf-dane-srv]) or
   POSH/HTTPS (see [I-D.ietf-xmpp-posh] and [I-D.ietf-xmpp-dna]) would
   provide means to overcome the operational limitations of
   authenticated encryption, neither is yet widely deployed.  Thus, in
   practice, when server-to-server streams are being protected often the
   technology used is unauthenticated encryption via TLS and the XMPP
   Server Dialback extension [XEP-0220].

   In late 2013, a number of service operators in the XMPP community
   committed to mandating encryption on all hops under their control,
   and a number of software developers committed to supporting the
   features needed to make such encryption possible.  The goal is to
   enable such encryption permanently on May 19, 2014.  So far, one test
   day has been held (on January 4, 2014) and another test day will be
   held (on February 22, 2014) before the date of the STRINT workshop.
   The test day revealed bugs in several XMPP software implementations
   and prompted security improvements at a number of deployed services.

   Also helpful has been the "IM Observatory" site at [1].  Most IM
   clients allow end users to inspect their connection to determine
   whether it is encrypted or not.  However, users cannot easily
   determine the status of the other hops on the path to a user on a
   different server.  Thus the IM Observatory has multiple goals: to
   give end users a tool with which they can examine the security of the
   entire end-to-end path, to give service operators information about
   improvements they can make to their servers' security, and to give
   all XMPP developers helpful statistics about the entire network.

4.  End-to-End Encryption

   The XMPP community has experimented with a significant number of end-
   to-end encryption technologies, including OpenPGP [XEP-0027], S/MIME
   [RFC3923], SIGMA [XEP-0116], end-to-end TLS
   [I-D.meyer-xmpp-e2e-encryption], XML encryption (never publicly
   documented), CMS with JOSE formats [I-D.miller-xmpp-e2e], and Off-
   the-Record (OTR) Messaging [2].  Unfortunately, none of these
   technologies has been formalized through a standards development
   organization.  However OTR is the most widely implemented.

5.  IANA Considerations

   This document requests no actions of the IANA.

6.  Security Considerations

   This entire document discusses security.

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7.  References

7.1.  Normative References

   [RFC4949]  Shirey, R., "Internet Security Glossary, Version 2", RFC
              4949, August 2007.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, August 2008.

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

   [RFC6125]  Saint-Andre, P. and J. Hodges, "Representation and
              Verification of Domain-Based Application Service Identity
              within Internet Public Key Infrastructure Using X.509
              (PKIX) Certificates in the Context of Transport Layer
              Security (TLS)", RFC 6125, March 2011.

7.2.  Informative References

              Finch, T., Miller, M., and P. Saint-Andre, "Using DNS-
              Based Authentication of Named Entities (DANE) TLSA records
              with SRV and MX records.", draft-ietf-dane-srv-04 (work in
              progress), February 2014.

              Saint-Andre, P. and M. Miller, "Domain Name Associations
              (DNA) in the Extensible Messaging and Presence Protocol
              (XMPP)", draft-ietf-xmpp-dna-05 (work in progress),
              February 2014.

              Miller, M. and P. Saint-Andre, "PKIX over Secure HTTP
              (POSH)", draft-ietf-xmpp-posh-00 (work in progress),
              February 2014.

              Meyer, D. and P. Saint-Andre, "XTLS: End-to-End Encryption
              for the Extensible Messaging and Presence Protocol (XMPP)
              Using Transport Layer Security (TLS)", draft-meyer-xmpp-
              e2e-encryption-02 (work in progress), June 2009.

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              Miller, M., "End-to-End Object Encryption and Signatures
              for the Extensible Messaging and Presence Protocol
              (XMPP)", draft-miller-xmpp-e2e-06 (work in progress), June

   [RFC3923]  Saint-Andre, P., "End-to-End Signing and Object Encryption
              for the Extensible Messaging and Presence Protocol
              (XMPP)", RFC 3923, October 2004.

              Muldowney, T., "Current Jabber OpenPGP Usage", XSF XEP
              0027, November 2006.

              Paterson, I., Saint-Andre, P., and D. Smith, "Encrypted
              Session Negotiation", XSF XEP 0116, May 2007.

              Miller, J., Saint-Andre, P., and P. Hancke, "Server
              Dialback", XSF XEP 0220, September 2013.

7.3.  URIs

   [1] https://xmpp.net/

   [2] https://otr.cypherpunks.ca/

Authors' Addresses

   Peter Saint-Andre

   Email: ietf@stpeter.im

   Thijs Alkemade

   Email: me@thijsalkema.de

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