XEP-xxxx: OMEMO Encrypted Jingle File Transfer

Abstract:This specification defines a Jingle application for transfering encrypted files from one entity to another. The protocol is based on the regular Jingle File Transfer specification and diverges from that only in the description of the file.
Author:Daniel Gultsch
Copyright:© 1999 – 2018 XMPP Standards Foundation. SEE LEGAL NOTICES.
Status:ProtoXEP
Type:Standards Track
Version:0.0.1
Last Updated:2015-09-02

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.


Table of Contents


1. Introduction
2. Requirements
3. Use Cases
4. Communicating the Checksum or Hashing Algorithm
5. Business Rules
6. Determining Support
7. Implementation Notes
8. Security Considerations
9. IANA Considerations
10. XMPP Registrar Considerations
    10.1. Protocol Namespaces
11. XML Schema

Appendices
    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

Jingle File Transfer (XEP-0234) [1] describes a very flexible and powerful method for peer-to-peer file transfer with interchangable transports. Unfortunatly only some of those transports can by encrypted (e.g. Jingle In-Band Bytestreams Transport Method (XEP-0261) [2]) and none integrate into existing end-to-end encryption schemes. This specification defines an approach to encrypt the actual file before transferring it by using the OMEMO encryption. Note that the encryption can and should happen on the fly.

2. Requirements

3. Use Cases

Remeo and Juliet are already engaged in a private, OMEMO encrypted conversation and want to negotiate a file transfer. The session-initiate stanza of an OMEMO encrypted file tranfer differs from the session-initiate of a regular Jingle File Transfer in that the 'file' element is wrapped in an 'encrypted' element. This reuses the KeyTransportElement from the OMEMO specification.

Example 1. Initiator sends session-initiate

<iq from='romeo@montague.lit/orchard'
    id='nzu25s8'
    to='juliet@capulet.lit/balcony'
    type='set'>
  <jingle xmlns='urn:xmpp:jingle:1'
          action='session-initiate'
          initiator='romeo@montague.lit/orchard'
          sid='851ba2'>
    <content creator='initiator' name='a-file-offer'>
      <description xmlns='urn:xmpp:jingle:apps:encrypted:file-transfer:0'>
        <encrypted xmlns='urn:xmpp:omemo:0'>
          <header sid='27183'>
            <key rid='31415'>BASE64ENCODED...</key>
            <key rid='12321'>BASE64ENCODED...</key>
            <iv>BASE64ENCODED...</iv>
          </header>
          <file>
            <date>2015-08-30T23:24:05Z</date>
            <desc>This is a test. If this were a real file...</desc>
            <media-type>image/png</media-type>
            <name>omemo.png</name>
            <range/>
            <size>51158</size>
            <hash xmlns='urn:xmpp:hashes:1' algo='sha-1'/>
        </file>
        </encrypted>
      </description>
      <transport xmlns='urn:xmpp:jingle:transports:s5b:1'
        	 mode='tcp'
                 sid='vj3hs98y'>
        <candidate cid='hft54dqy'
                   host='192.168.4.1'
                   jid='romeo@montague.lit/orchard'
                   port='5086'
                   priority='8257636'
                   type='direct'/>
        <candidate cid='hutr46fe'
                   host='24.24.24.1'
                   jid='romeo@montague.lit/orchard'
                   port='5087'
                   priority='8258636'
                   type='direct'/>
      </transport>
    </content>
  </jingle>
</iq>
  

The rest of the negotiation is analogous to a regular file transfer. The file is then encrypted and decrypted respectively using the key/IV pair extracted from the encryption header in AES-GCM. The crypto operation SHOULD happen on the fly.

4. Communicating the Checksum or Hashing Algorithm

Even though AES-GCM comes with build-in integrity protection the hosting entity can—at any time during the lifetime of the session—communicate the checksum of the encrypted file.

Example 2. Initiator sends checksum in session-info

<iq from='romeo@montague.lit/orchard'
    id='kqh401b5'
    to='juliet@capulet.lit/balcony'
    type='set'>
  <jingle xmlns='urn:xmpp:jingle:1'
          action='session-info'
          initiator='romeo@montague.lit/orchard'
          sid='a73sjjvkla37jfea'>
    <checksum xmlns='urn:xmpp:jingle:apps:encrypted:file-transfer:0'>
      <file>
        <hash xmlns='urn:xmpp:hashes:1' algo='sha-1'>552da749930852c69ae5d2141d3766b1</hash>
      </file>
    </checksum>
  </jingle>
</iq>
  

5. Business Rules

6. Determining Support

To advertise its support for the OMEMO Encrypted Jingle File Transfer, when replying to service discovery information ("disco#info") requests an entity MUST return URNs for any version of this protocol that the entity supports -- e.g., 'urn:xmpp:jingle:apps:encrypted:file-transfer:0' for this version (see Namespace Versioning regarding the possibility of incrementing the version number).

Example 3. Service discovery information request

<iq from='romeo@montague.lit/orchard'
    id='uw72g176'
    to='juliet@capulet.lit/balcony'
    type='get'>
  <query xmlns='http://jabber.org/protocol/disco#info'/>
</iq>
  

Example 4. Service discovery information response

<iq from='juliet@capulet.lit/balcony'
    id='uw72g176'
    to='romeo@montague.lit/orchard'
    type='result'>
  <query xmlns='http://jabber.org/protocol/disco#info'>
    <feature var='urn:xmpp:jingle:1'/>
    <feature var='urn:xmpp:jingle:apps:encrypted:file-transfer:0'/>
    <feature var='urn:xmpp:jingle:apps:file-transfer:4'/>
    <feature var='urn:xmpp:jingle:transports:s5b:1'/>
    <feature var='urn:xmpp:jingle:transports:ibb:1'/>
  </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) [3]. However, if an application has not received entity capabilities information from an entity, it SHOULD use explicit service discovery instead.

7. Implementation Notes

Since the OMEMO Encryption does not provide a direct relation between resources and Device ID’s the initiating entity might not the Device ID of the resource it is creating a session with. Thus it MAY include a key for every trusted device of the foreign entity. However it SHOULD omit the keys for its own devices.

8. Security Considerations

9. IANA Considerations

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

10. XMPP Registrar Considerations

10.1 Protocol Namespaces

This specification defines the following XML namespace:

Upon advancement of this specification from a status of Experimental to a status of Draft, the XMPP Registrar [4] shall add the foregoing namespace to the registry located at <https://xmpp.org/registrar/namespaces.html>, as described in Section 4 of XMPP Registrar Function (XEP-0053) [5].

11. XML Schema

tbd


Appendices


Appendix A: Document Information

Series: XEP
Number: xxxx
Publisher: XMPP Standards Foundation
Status: ProtoXEP
Type: Standards Track
Version: 0.0.1
Last Updated: 2015-09-02
Approving Body: XMPP Council
Dependencies: XMPP Core, XEP-0001, Etc.
Supersedes: None
Superseded By: None
Short Name: NOT_YET_ASSIGNED
This document in other formats: XML  PDF


Appendix B: Author Information

Daniel Gultsch

Email: daniel@gultsch.de
JabberID: daniel@gultsch.de


Appendix C: Legal Notices

Copyright

This XMPP Extension Protocol is copyright (c) 1999 - 2014 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. In no event shall the XMPP Standards Foundation or the authors of this Specification be liable for any claim, damages, or other liability, whether in an action of contract, tort, or otherwise, arising from, out of, or in connection with the Specification or the implementation, deployment, or other use of the Specification. ##

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 out of the use or inability to use 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 may be found at <http://xmpp.org/extensions/ipr-policy.shtml> or obtained by writing to XSF, P.O. Box 1641, Denver, CO 80201 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-0234: Jingle File Transfer <https://xmpp.org/extensions/xep-0234.html>.

2. XEP-0261: Jingle In-Band Bytestreams Transport Method <https://xmpp.org/extensions/xep-0261.html>.

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

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/>.

5. XEP-0053: XMPP Registrar Function <https://xmpp.org/extensions/xep-0053.html>.


Appendix H: Revision History

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

Version 0.0.1 (2015-09-02)

First draft.

(dg)

END