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 element of SIP's Conference Event Package [RFC4575]. 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 Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on May 08, 2014. Copyright Notice Copyright (c) 2013 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. Ivov Expires May 08, 2014 [Page 1] Internet-Draft Entry Purpose: GroupTextChat November 2013 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 child element of the element. Such details are presented as a set of child elements each containing the URI allowing access the corresponding auxiliary service. In addition to the URI, entries can also contain a descriptive element and are expected to also have a element that specifies their nature as illustrated in the following example: Agenda: This sprint's goals http://conference.example.com/dev-group/ web-page 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 Ivov Expires May 08, 2014 [Page 2] Internet-Draft Entry Purpose: GroupTextChat November 2013 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: Agenda: The goals for this development sprint. xmpp:dev-sprint@conference.example.com grouptextchat 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. Ivov Expires May 08, 2014 [Page 3] Internet-Draft Entry Purpose: GroupTextChat November 2013 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" 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 Ivov Expires May 08, 2014 [Page 4] Internet-Draft Entry Purpose: GroupTextChat November 2013 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 Ivov Expires May 08, 2014 [Page 5] Internet-Draft Entry Purpose: GroupTextChat November 2013 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 Ivov Expires May 08, 2014 [Page 6]