Internet Engineering Task Force (IETF)                           E. Ivov
Request for Comments: 7106                                         Jitsi
Category: Informational                                     January 2014
ISSN: 2070-1721


    A Group Text Chat Purpose for Conference and Service URIs in the
                 SIP Event Package for Conference State

Abstract

   This document defines and registers a value of "grouptextchat"
   ("Group Text Chat") for the URI <purpose> element of SIP's Conference
   Event Package.

Status of This Memo

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

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Not all documents
   approved by the IESG are 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/rfc7106.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   4.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     4.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     4.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   The Conference Event Package [RFC4575] defines means for a SIP User
   Agent (UA) to obtain information about the state of the conference,
   the types of media that are being used, the number and state of
   current participants, additional sources of information (e.g., web
   page), availability of recordings, and more.

   Details describing auxiliary services available for a conference are
   included within a <service-uris> child element of the
   <conference-description> element.  Such details are presented as a
   set of <entry> child elements, each containing the URI allowing
   access the corresponding auxiliary service.  In addition to the URI,
   entries can also contain a descriptive <display-text> element and are
   expected to have a <purpose> element that specifies their nature as
   illustrated in the following example:

   <conference-description>
   <subject>Agenda: This sprint's goals</subject>
     <service-uris>
       <entry>
         <uri>http://conference.example.com/dev-group/</uri>
         <purpose>web-page</purpose>
       </entry>
     </service-uris>
   </conference-description>

   In addition to the "web-page" purpose mentioned above, [RFC4575] also
   defines several other possible values in the "URI Purposes" sub-
   registry under the existing "Session Initiation Protocol (SIP)
   Parameters" registry.

   This specification adds the "grouptextchat" value to this "URI
   Purposes" sub-registry.  The new value allows conference mixers or
   focus agents to advertise a multi-user chat location (i.e., a chat
   room) associated with the current conference.

   The actual URI carried by the entry with the "grouptextchat" purpose
   can be of any type as long as the content that it points to allows
   for instant text communication between participants of the
   conference.  Suitable URI schemes include sip: and sips: [RFC3261]
   for SIP-signaled Message Session Relay Protocol (MSRP) conferences,
   xmpp: [RFC5122] for XMPP Multi-User Chat (MUC), irc: for Internet
   Relay Chat, http: or https: for web-based chat, and others.

   The following example shows one possible use case:

   <conference-description>
   <subject>Agenda: The goals for this development sprint.</subject>
     <service-uris>
       <entry>
         <uri>xmpp:dev-sprint@conference.example.com</uri>
         <purpose>grouptextchat</purpose>
       </entry>
     </service-uris>
   </conference-description>

   It is worth pointing out that, in addition to simply adding text
   messaging capabilities to an audio/video conference, group chats can
   also be used for defining roles, giving permissions, muting, kicking
   out and banning participants, etc.  A conference mixer or focus agent
   can mimic these settings within the conference call, actually muting,
   kicking out, or banning participants on the call as these actions
   occur in the chat room.  Such an approach requires no additional
   specification and is purely an implementation decision for the
   conferencing software.

   It is also worth mentioning that it is possible for the grouptextchat
   URI to match the URI of the conference.  This would typically be the
   case in scenarios where the conference focus agent also provides a
   SIP-signaled MSRP chat service at the same URI.

   Also, in some cases, servers could potentially advertise more than a
   single chat room for a specific conference.  When this happens,
   clients supporting the "grouptextchat" purpose could either present
   the user with a choice of joining individual chats or simply opening
   all of them simultaneously.  Either way, there is to be no
   expectation about any content synchronization between chat rooms.  If
   synchronization exists, such behavior would be entirely
   implementation specific.

2.  Security Considerations

   Advertising group text chats over SIP could provide malicious
   entities with the following attack vector: if a malicious entity is
   capable of intercepting and modifying conference package event
   notifications, it could trick participants into joining a third-party
   chat room where the attacker could eavesdrop on the conversation and
   potentially even impersonate some of the participants.

   Similar attacks are already possible with the "participation"
   <conference-uris> defined in [RFC4575], which is why it recommends "a
   strong means for authentication and conference information
   protection" as well as "comprehensive authorization rules".  Clients
   can integrity protect and encrypt notification messages using end-to-
   end mechanisms such as S/MIME or hop-by-hop mechanisms such as TLS.
   When none of these are possible, clients need to clearly display the
   address of the destination chat room (before and after it has been
   joined) so that users can notice possible discrepancies.

   As an example, let's consider a situation in which an attacker tricks
   participants into joining a conference chat at
   xmpp:attack@evil.example.com rather than the chat at
   xmpp:dev-sprint@conference.example.com, which was originally
   advertised for this conference.  In the absence of any SIP-layer
   security, displaying the full URI of the target chat room to the user
   would be the only way of actually detecting the problem.

   Obviously, relying on human-performed string comparison is a rather
   meek form of protection.  Therefore, client developers are encouraged
   to implement additional checks that would allow users to request via
   configuration that a target chat room satisfy some basic criteria,
   such as:

   o  target chat rooms belong to the same domain as the conference
      service that is advertising them.

   o  chat room names (user part of the chat room URI) match the name of
      the conference.

   Once again, these conditions are only satisfied if the corresponding
   deployment conventions have been followed and they cannot be
   universally required by clients.  Therefore, they are suggested
   configuration options.

   An additional security consideration might be the possibility for
   using a large-scale conference as leverage to perform a flooding
   attack on a chat room.  To help prevent this, clients could to
   require an explicit user action before joining chat rooms on behalf

   of users.  In cases where such a constraint could be considered to
   have a negative impact on usability and where automatic joins are
   seen as important, clients may still perform the joins but only when
   they can confirm a relationship between the room and the conference
   (e.g., they both belong to the same administrative domain, or domains
   that the client is provisioned to consider as related).

   Furthermore, an attack on an auxiliary chat room might be easier (or
   harder) than an attack on the main conference chat room depending on
   the security policies in effect.  Once again, clients would have to
   make sure that users are appropriately notified about the security
   levels of each component of the conference and that user-specified
   privacy restrictions are applied to all of them.

3.  IANA Considerations

   IANA has added the value "grouptextchat" to the "URI Purposes" sub-
   registry of the "Session Initiation Protocol (SIP) Parameters"
   registry <http://www.iana.org/assignments/sip-parameters> as follows:

     Value: grouptextchat
     Description: The URI can be used to join a multi-user chat directly
        associated with the conference
     Document: [this document]

4.  References

4.1.  Normative References

   [RFC4575]  Rosenberg, J., Schulzrinne, H., and O. Levin, "A Session
              Initiation Protocol (SIP) Event Package for Conference
              State", RFC 4575, August 2006.

4.2.  Informative References

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              June 2002.

   [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.

Appendix A.  Acknowledgements

   Thanks to Jonathan Lennox, Mary Barnes, Paul Kyzivat, Peter Saint-
   Andre, Rifaat Shekh-Yusef, and Saul Ibarra Corretge for their input.

Author's Address

   Emil Ivov
   Jitsi
   Strasbourg  67000
   France

   Phone: +33-177-624-330
   EMail: emcho@jitsi.org