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Keywords: SIP, Conference Event Package, service-uris, conference-uris, URI purpose
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.
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
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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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.
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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.
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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 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
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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.
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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
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