Internet DRAFT - draft-ivov-grouptextchat-purpose
draft-ivov-grouptextchat-purpose
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
draft-ivov-grouptextchat-purpose-04
Abstract
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.
Copyright Notice
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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:
<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 a "URI purposes" sub-
registry under the existing registry: http://www.iana.org/assignments
/sip-parameters.
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:
<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
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
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. 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
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. 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 http://www.iana.org/
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
Jitsi
Strasbourg 67000
France
Phone: +33-177-624-330
Email: emcho@jitsi.org
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