XEP-0378: OTR Discovery

Abstract: This document provides a mechanism by which OTR encryption support can be discovered in XMPP, without relying on OTRs protocol agnostic discovery mechanism.
Author:Sam Whited
Copyright:© 1999 – 2017 XMPP Standards Foundation. SEE LEGAL NOTICES.
Type:Standards Track
Last Updated:2016-07-15

WARNING: This Standards-Track document is Experimental. Publication as an XMPP Extension Protocol does not imply approval of this proposal by the XMPP Standards Foundation. Implementation of the protocol described herein is encouraged in exploratory implementations, but production systems are advised to carefully consider whether it is appropriate to deploy implementations of this protocol before it advances to a status of Draft.

Table of Contents

1. Introduction
2. Discovering support
3. Security Considerations
4. IANA Considerations
5. XMPP Registrar Considerations

    A: Document Information
    B: Author Information
    C: Legal Notices
    D: Relation to XMPP
    E: Discussion Venue
    F: Requirements Conformance
    G: Notes
    H: Revision History

1. Introduction

The Off-the-Record messaging protocol (OTR) is widely layered on top of XMPP to provide end-to-end encryption. Current use of the protocol is described in Current Off-the-Record Messaging Usage (XEP-0364) [1]. OTR provides its own discovery mechanism in which it sends messages with special whitespace characters to indicate support. While this works when initializing a session, there is no way to query a client for support and to know in advance that a particular version of OTR is supported. This specification aims to solve that by providing an in-band mechanism for discovering OTR support in XMPP.

It should be noted that newer, more secure encryption protocols exist for XMPP, and that new implementations of OTR are discouraged. This protocol is primarily intended to solve issues with existing implementations of OTR.

2. Discovering support

If an entity supports OTR it MUST advertise the fact by returning a feature of 'urn:xmpp:otr:0' (see Namespace Versioning regarding the possibility of incrementing the version number) in response to a Service Discovery (XEP-0030) [2] information request. This indicates support for OTRv3 as defined by Off-the-Record Messaging Protocol version 3 [3].

Example 1. Disco response

<feature var='urn:xmpp:otr:0' />

If older versions of OTR are required, they may be discovered out of band using OTRs built in mechanism which is beyond the scope of this document.

3. Security Considerations

Because OTR support is advertised outside of any end-to-end encrypted stream, it may be subject to downgrade attacks (eg. the server operator may remove OTR from the features list).

4. IANA Considerations

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

5. XMPP Registrar Considerations

This specification defines the following XML namespaces:

The XMPP Registrar [4] shall include the foregoing namespaces in its disco features registry as defined in Service Discovery (XEP-0030) [2].

Registry Submission

	<desc>Indicates support for Off-the-Record Messaging (OTR) version 3</desc>


Appendix A: Document Information

Series: XEP
Number: 0378
Publisher: XMPP Standards Foundation
Status: Experimental
Type: Standards Track
Version: 0.0.1
Last Updated: 2016-07-15
Approving Body: XMPP Council
Dependencies: XMPP Core, XEP-0030
Supersedes: None
Superseded By: None
Short Name: OTR-DISCO
Source Control: HTML
This document in other formats: XML  PDF

Appendix B: Author Information

Sam Whited

Email: sam@samwhited.com
JabberID: sam@samwhited.com
URI: https://blog.samwhited.com/

Appendix C: Legal Notices


This XMPP Extension Protocol is copyright © 1999 – 2017 by the XMPP Standards Foundation (XSF).


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).

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

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-0364: Current Off-the-Record Messaging Usage <https://xmpp.org/extensions/xep-0364.html>.

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

3. Off-the-Record Messaging Protocol (OTR) version 3 <https://otr.cypherpunks.ca/Protocol-v3-4.0.0.html> (Accessed 2015-08-30).

4. The XMPP Registrar maintains a list of reserved protocol namespaces as well as registries of parameters used in the context of XMPP extension protocols approved by the XMPP Standards Foundation. For further information, see <https://xmpp.org/registrar/>.

Appendix H: Revision History

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

Version 0.0.1 (2016-07-15)

Initial version approved by the Council.