XEP-xxxx: Use of ZRTP in Jingle RTP Sessions

Abstract
This specification defines a Jingle application type for negotiating one or more sessions that use the Real-time Transport Protocol (RTP) to exchange media such as voice or video. The application type includes a straightforward mapping to Session Description Protocol (SDP) for interworking with SIP media endpoints.
Author
Peter Saint-Andre
Copyright
© 1999 – 2020 XMPP Standards Foundation. SEE LEGAL NOTICES.
Status

ProtoXEP

WARNING: This document has not yet been accepted for consideration or approved in any official manner by the XMPP Standards Foundation, and this document is not yet an XMPP Extension Protocol (XEP). If this document is accepted as a XEP by the XMPP Council, it will be published at <http://xmpp.org/extensions/> and announced on the <standards@xmpp.org> mailing list.
Type
Standards Track
Version
0.0.2 (2009-02-24)
Document Lifecycle
  1. Experimental
  2. Proposed
  3. Draft
  4. Final

1. Protocol

Jingle RTP Sessions (XEP-0167) [1] recommends the use of the Secure Real-time Transport Protocol (SRTP) for end-to-end encryption of RTP sessions negotiated using Jingle (XEP-0166) [2]. An alternative approach to end-to-end encryption of RTP traffic is provided by RFC 6189 [3]. Although negotiation of ZRTP mainly occurs in the media channel rather than the signalling channel, the ZRTP specification defines one SDP attribute called "zrtp-hash" (this communicates the ZRTP version supported as well as a hash of the Hello message).

The SDP format is shown below.

a=zrtp-hash:zrtp-version zrtp-hash-value
  

An example follows.

a=zrtp-hash:1.10 fe30efd02423cb054e50efd0248742ac7a52c8f91bc2df881ae642c371ba46df
  

This SDP attribute can be translated into Jingle as a <zrtp-hash/> element, as shown below.

<zrtp-hash version='zrtp-version'>zrtp-hash-value</zrtp-hash>
  

An example follows.

<zrtp-hash version='1.10'>fe30efd02423cb054e50efd0248742ac7a52c8f91bc2df881ae642c371ba46df</zrtp-hash>
  

If either party to a Jingle RTP session wishes to use ZRTP, the party SHOULD send a Jingle session-info message that includes a <zrtp-hash/> element qualified by the 'urn:xmpp:jingle:apps:rtp:zrtp:0' namespace, as shown in the following example.

Example 1. Initiator sends session-info message with zrtp-hash
<iq from='romeo@montague.lit/orchard'
    id='vna13b9a'
    from='juliet@capulet.lit/balcony'
    type='set'>
  <jingle xmlns='urn:xmpp:jingle:0'
          action='session-info'
          initiator='romeo@montague.lit/orchard'
          sid='a73sjjvkla37jfea'>
    <zrtp-hash xmlns='urn:xmpp:jingle:apps:rtp:zrtp:0'
               version='1.10'>fe30efd02423cb054e50efd0248742ac7a52c8f91bc2df881ae642c371ba46df</zrtp-hash>
  </jingle>
</iq>
    

In accordance with XEP-0166, if the receiving party does not understand the payload of the session-info message then it MUST return a <feature-not-implemented/> error.

Example 2. Receiver returns feature-not-implemented error
<iq from='juliet@capulet.lit/balcony'
    id='ringing1'
    to='romeo@montague.lit/orchard'
    type='error'>
  <error type='modify'>
    <feature-not-implemented xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
    <unsupported-info xmlns='urn:xmpp:jingle:errors:0'/>
  </error>
</iq>
    

However, if the receiving party also supports and wishes to use ZRTP, it too SHOULD send a session-info message containing a zrtp-hash element.

2. Determining Support

If an entity supports the zrtp-hash session-info message, it MUST advertise that fact in its responses to Service Discovery (XEP-0030) [4] information ("disco#info") requests by returning a feature of "urn:xmpp:jingle:apps:rtp:zrtp:0":

Example 3. A disco#info query
<iq type='get'
    from='calvin@usrobots.lit/lab'
    to='herbie@usrobots.lit/home'
    id='disco1'>
  <query xmlns='http://jabber.org/protocol/disco#info'/>
</iq>
  
Example 4. A disco#info response
<iq type='result'
    from='herbie@usrobots.lit/home'
    to='calvin@usrobots.lit/lab'
    id='disco1'>
  <query xmlns='http://jabber.org/protocol/disco#info'>
    <feature var='urn:xmpp:jingle:apps:rtp:zrtp:0'/>
  </query>
</iq>
  

In order for an application to determine whether an entity supports this protocol, where possible it SHOULD use the dynamic, presence-based profile of service discovery defined in Entity Capabilities (XEP-0115) [5]. However, if an application has not received entity capabilities information from an entity, it SHOULD use explicit service discovery instead.

3. Security Considerations

Security considerations for ZRTP itself are provided in draft-zimmermann-avt-zrtp.

XMPP stanzas such as Jingle session-info messages and service discovery exchanges are not encrypted or signed. As a result, it is possible for an attacker to intercept these stanzas and modify them, thus convincing one party that the other party does not support ZRTP and therefore denying the parties an opportunity to use ZRTP. However, because the zrtp-hash is mostly advisory, the parties could still use ZRTP even if the signalling channel is compromised.

4. IANA Considerations

This document requires no interaction with the Internet Assigned Numbers Authority (IANA) [6].

5. XMPP Registrar Considerations

See the XML Schemas section of this document.

6. XML Schemas

If this specification is advanced to a status of Draft, the XMPP Registrar shall add the following element definition to the schema for the 'urn:xmpp:jingle:apps:rtp:info:1' namespace defined in XEP-0167:

<?xml version='1.0' encoding='UTF-8'?>

<xs:schema
    xmlns:xs='http://www.w3.org/2001/XMLSchema'
    targetNamespace='urn:xmpp:jingle:apps:rtp:zrtp:0'
    xmlns='urn:xmpp:jingle:apps:rtp:zrtp:0'
    elementFormDefault='qualified'>

  <xs:element name='zrtp-hash'>
    <xs:complexType>
      <xs:simpleContent>
        <xs:extension base='xs:string'>
          <xs:attribute name='version' type='xs:string' use='required'/>
        </xs:extension>
      </xs:simpleContent>
    </xs:complexType>
  </xs:element>

</xs:schema>
  

Appendices

Appendix A: Document Information

Series
XEP
Number
xxxx
Publisher
XMPP Standards Foundation
Status
ProtoXEP
Type
Standards Track
Version
0.0.2
Last Updated
2009-02-24
Approving Body
XMPP Council
Dependencies
XMPP Core, XEP-0166, XEP-0167, draft-zimmermann-avt-zrtp
Supersedes
None
Superseded By
None
Short Name
N/A

This document in other formats: XML  PDF

Appendix B: Author Information

Peter Saint-Andre
Email
xsf@stpeter.im
JabberID
peter@jabber.org
URI
http://stpeter.im/

Copyright

This XMPP Extension Protocol is copyright © 1999 – 2020 by the XMPP Standards Foundation (XSF).

Permissions

Permission is hereby granted, free of charge, to any person obtaining a copy of this specification (the "Specification"), to make use of the Specification without restriction, including without limitation the rights to implement the Specification in a software program, deploy the Specification in a network service, and copy, modify, merge, publish, translate, distribute, sublicense, or sell copies of the Specification, and to permit persons to whom the Specification is furnished to do so, subject to the condition that the foregoing copyright notice and this permission notice shall be included in all copies or substantial portions of the Specification. Unless separate permission is granted, modified works that are redistributed shall not contain misleading information regarding the authors, title, number, or publisher of the Specification, and shall not claim endorsement of the modified works by the authors, any organization or project to which the authors belong, or the XMPP Standards Foundation.

Disclaimer of Warranty

## NOTE WELL: This Specification is provided on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, express or implied, including, without limitation, any warranties or conditions of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A PARTICULAR PURPOSE. ##

Limitation of Liability

In no event and under no legal theory, whether in tort (including negligence), contract, or otherwise, unless required by applicable law (such as deliberate and grossly negligent acts) or agreed to in writing, shall the XMPP Standards Foundation or any author of this Specification be liable for damages, including any direct, indirect, special, incidental, or consequential damages of any character arising from, out of, or in connection with the Specification or the implementation, deployment, or other use of the Specification (including but not limited to damages for loss of goodwill, work stoppage, computer failure or malfunction, or any and all other commercial damages or losses), even if the XMPP Standards Foundation or such author has been advised of the possibility of such damages.

IPR Conformance

This XMPP Extension Protocol has been contributed in full conformance with the XSF's Intellectual Property Rights Policy (a copy of which can be found at <https://xmpp.org/about/xsf/ipr-policy> or obtained by writing to XMPP Standards Foundation, P.O. Box 787, Parker, CO 80134 USA).

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Appendix D: Relation to XMPP

The Extensible Messaging and Presence Protocol (XMPP) is defined in the XMPP Core (RFC 6120) and XMPP IM (RFC 6121) specifications contributed by the XMPP Standards Foundation to the Internet Standards Process, which is managed by the Internet Engineering Task Force in accordance with RFC 2026. Any protocol defined in this document has been developed outside the Internet Standards Process and is to be understood as an extension to XMPP rather than as an evolution, development, or modification of XMPP itself.

Appendix E: Discussion Venue

There exists a special venue for discussion related to the technology described in this document: the <jingle@xmpp.org> mailing list.

The primary venue for discussion of XMPP Extension Protocols is the <standards@xmpp.org> discussion list.

Discussion on other xmpp.org discussion lists might also be appropriate; see <http://xmpp.org/about/discuss.shtml> for a complete list.

Errata can be sent to <editor@xmpp.org>.

Appendix F: Requirements Conformance

The following requirements keywords as used in this document are to be interpreted as described in RFC 2119: "MUST", "SHALL", "REQUIRED"; "MUST NOT", "SHALL NOT"; "SHOULD", "RECOMMENDED"; "SHOULD NOT", "NOT RECOMMENDED"; "MAY", "OPTIONAL".

Appendix G: Notes

1. XEP-0167: Jingle RTP Sessions <https://xmpp.org/extensions/xep-0167.html>.

2. XEP-0166: Jingle <https://xmpp.org/extensions/xep-0166.html>.

3. RFC 6189: ZRTP: Media Path Key Agreement for Unicast Secure RTP <http://tools.ietf.org/html/rfc6189>.

4. XEP-0030: Service Discovery <https://xmpp.org/extensions/xep-0030.html>.

5. XEP-0115: Entity Capabilities <https://xmpp.org/extensions/xep-0115.html>.

6. The Internet Assigned Numbers Authority (IANA) is the central coordinator for the assignment of unique parameter values for Internet protocols, such as port numbers and URI schemes. For further information, see <http://www.iana.org/>.

Appendix H: Revision History

Note: Older versions of this specification might be available at http://xmpp.org/extensions/attic/

  1. Version 0.0.2 (2009-02-24)

    Defined dedicated namespace for the zrtp-hash element to improve service discovery and handling of session-info message; clarified protocol flow and security considerations.

    psa
  2. Version 0.0.1 (2009-02-17)

    First draft, copied from XEP-0167.

    psa

END