Network Working Group                                            E. Ivov
Internet-Draft                                                     Jitsi
Intended status: Informational                         November 04, 2013
Expires: May 08, 2014

A Group Text Chat Purpose for Conference and Service URIs in the Session
      Initiation Protocol (SIP) Event Package for Conference State


   This document defines and registers a value of "grouptextchat"
   ("Group Text Chat") value for the URI <purpose> element of SIP's
   Conference Event Package [RFC4575].

Status of This Memo

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   This Internet-Draft will expire on May 08, 2014.

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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 . . . . . . . . . . . . . . . . . .   5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   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 such as a web
   page, availability of recordings and others.

   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
   also have a <purpose> element that specifies their nature as
   illustrated in the following example:

   <subject>Agenda: This sprint's goals</subject>

   In addition to the "web-page" purpose mentioned above, [RFC4575] also
   defines several other possible values in a "URI purposes" sub-
   registry under the existing registry:

   This specification adds the "grouptextchat" value in this "URI
   purposes" sub-registry.  The new value allows conference mixers or

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   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 would
   allow for instant text communication between participants of the
   conference.  Suitable URI schemes include sip: and sips: [RFC3261]
   for SIP signalled 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:

   <subject>Agenda: The goals for this development sprint.</subject>

   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
   and banning participants, etc.  A conference mixer or focus agent,
   can mimic these settings within the conference call, actually muting,
   kicking, or banning participants in 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 also provides a SIP
   signalled 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 present the user
   with a choice or join multiple chats simultaneously.  Either way
   there is to be no expectation about any content synchronization
   between chat rooms.  If it exists such behaviour would be entirely
   implementation specific.

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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 the above are possible, clients will need to clearly
   display the address of the destination chat room (before and after it
   has been joined) so that users could notice possible discrepancies.

   As an example, let's consider a situation where an attacker would
   trick participants into joining a conference chat at rather than the chat at xmpp:dev-, 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.  Client developers are hence encouraged to
   implement additional checks that would allow users to request via
   configuration that target chat room satisfy some basic criteria, such

   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.  Hence the suggestion to have them
   as configuration options.

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

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   where such a constraint could be considered to have negative impact
   on usability and where automatic joins are seen as important, clients
   may still perform them 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 the auxiliary chatroom might be easier (or
   harder) than an attack on the main conference 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

   The IANA is requested to add a new predefined value "grouptextchat"
   in the "URI purposes" sub-registry of the
   assignments/sip-parameters registry 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

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   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
   Strasbourg  67000

   Phone: +33-177-624-330

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