XEP-0477: Pubsub Targeted Encryption

Abstract: Specifies a way to encrypt pubsub items for a restricted set of entities
Author: Jérôme Poisson
Copyright: © 2022 – 2022 XMPP Standards Foundation. SEE LEGAL NOTICES.
Status: Experimental
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.
Type: Standards Track
Version: 0.1.0 (2022-12-20)

Document Lifecycle

Experimental
Proposed
Stable
Final

1. Introduction¶

While it is nowadays possible to encrypt pubsub items with OpenPGP for XMPP Pubsub, this specification is designed for pubsub nodes were all items are end-to-end encrypted, and it is using symmetric encryption with a system of key sharing, meaning that if a key is available, it can decrypt all items encrypted with it.

This is fine for most use cases, however it may be desirable to only encrypt a few items with properties such as Perfect Forward Secrecy. This specification describes a way on how to do that by adapting existing end-to-end encryption algorithms used in instant messaging to pubsub items. This may be used to implement restricted items (a feature known is some other software such as "aspects" or "circles") or for transient nodes.

2. Requirements¶

The design goal of this specification is do adapt simply existing e2e encryption algorithms used for messages to pubsub items.

3. Use Cases¶

3.1 Encrypting a Pubsub Item¶

Juliet holds a public blog using Microblogging Over XMPP (XEP-0277) [1]. However, she wants to publish a new items that should be visible only to some well targeted users. To do so she encrypt the payload in the same way as she encrypt messages with algorithm such as OMEMO Encryption (XEP-0384) [2]. She wrap the encrypted payload in an <encrypted/> element qualified by the 'urn:xmpp:pte:0' namespace which MUST have a 'by' attribute with its own bare jid as value, and which MUST have a 'type' attribute whose value is the namespace of the algorithm used.

She decides to use OMEMO Encryption (XEP-0384) [2] to encrypt her items, her client publish an item like this:

Example 1. Juliet Publish a Targeted Encrypted Item¶

<iq xmlns="jabber:client" id="pte_1" type="set" from="juliet@capulet.lit/chamber" to="juliet@capulet.lit">
  <pubsub xmlns="http://jabber.org/protocol/pubsub">
    <items node="urn:xmpp:microblog:0">
      <item id="secret_blog_post" publisher="juliet@capulet.lit/chamber">
        <encrypted xmlns="urn:xmpp:pte:0" by="juliet@capulet.lit" type="urn:xmpp:omemo:2">
          <encrypted xmlns="urn:xmpp:omemo:2">
            <header sid="878841001">
              <keys jid="juliet@capulet.lit">
                <key rid="673880319">ChDRqSBLTR+RtRIH8io7kf22EmgIARACGiCasIYfB6Zfe5SNyT8twIa+mEYA8h7uEQIjQ64dJx4vXiJAZSpXPRW+sVVSC7gc4lDEiTA4DT7AIh/woa82PFjgFdL0A8HTyBe7yh3UWThZGuTp5A3zmjXH7pAwKX85oxQ8XA==</key>
              </keys>
            </header>
            <payload>DWmAVvrKlPPh23OmvmIrJmQXj5hVtgAnY8IOGZNqJc59T93hzsTen7tw7Kea5KfM3btfS25xd6RRWe0ZrqdvdGtKfHJFc77k5pQ052br4Qxw9kLWCVGqpNkrpwoBUshqs5mwA1WRLGdUfEsMaePwZv4m9xvXZSrxNIf9vQNX/GJM2GAT55exZSRU0Px8/E8j0XMtHCuZ4j3z0EBk1NZin0suQv8rVy1liWACPNuVrnU7h8LpdWmUggYztqL9l1yoxzEOFRrpdFkDqcZDLbO8bWAcYQNpWYoefaYvnvLV4zkW4dELQydSC2KkGMN/LmdYspVUPzPpQt7OmAKAndFWXTsAV5wmbtVsr15TzxI4NVDZyp7G70TYyTHlhG2gAq7StVj09bJi6IHa59L1BgNrNKT/ZG8pbe/GXUoPg4q9ZfuDiOYBHUugUxNsVFactRp6UocaQT/RogrqKY3o6NlTvnqVYpMJsi72cp8uQWTPtqwBpxyhAY0jKp1D+y7m2wzbeD2SZCw5+FryXulQhCKJ0dLI00PJr4dELWdu+uQLdyHl5FxG4D8mLQVOnY/TMa0vXUxsMAQI8g8LEHdJIhKU4GyVt125WhrbMrbcBu8iKCYmiz820siZeD8i5iZa1eQ69hnA9iCqMRS2DsqieUeI1Y4I7+0pHcyzpNC8408B7LhkgwxOEopExdOfv1NFwamsN5zXhCqj386oGRl9Ry0Gw+QSv9jlW4FB0rM8r+GF5gB66p0nYU/U5W8efXgNI/W1yAdUxgXc9FiQMmzIauTmR4m5WUxPjBggVYz1q3TkeZHQJpWy47EWZPnM9leWKNqC</payload>
          </encrypted>
        </encrypted>
      </item>
    </items>
  </pubsub>
</iq>

4. Business Rules¶

The properties of the encryption algorithm applies. For instance in the case of OMEMO Encryption (XEP-0384) [2], there Perfect Forward Secrecy, meaning that once an item has been decrypted once by a targeted entity, it can't be decrypted anymore. Client shoud then handle pubsub caching of the decrypted item when necessary.

5. Discovering Support¶

If a client supports the protocol specified in this XEP, it MUST advertise it by including the "urn:xmpp:pte:0" discovery feature in response to a Service Discovery (XEP-0030) [3] information request, Then the supported encryption algorithms are announced as explained in their respective XEPs.

6. Security Considerations¶

7. IANA Considerations¶

8. XMPP Registrar Considerations¶

9. XML Schema¶

10. Acknowledgements¶

Appendices

Appendix A: Document Information¶

Appendix B: Author Information¶

Jérôme Poisson

Appendix C: Legal Notices¶

Copyright

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¶

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 <https://xmpp.org/community/> for a complete list.

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".