XEP-xxxx: E2E Authentication in XMPP: CA Requirements

This specification defines requirements for certificate authorities issuing X.509 certificates for e2e authentication in XMPP.
Evgeny Khramtsov
© 1999 – 2020 XMPP Standards Foundation. SEE LEGAL NOTICES.


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.
0.0.1 (2019-02-08)
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1. Introduction

E2E Authentication in XMPP (XEP-EAX) describes how X.509 certificates can be used for end-to-end (e2e) authentication in XMPP. As in any PKIX based authentication, a certificate authority (CA) plays a major role in e2e authentication. This document specifies requirements for certificate authorities issuing certificates for the purpose of e2e authentication in XMPP. In addition, a special role of the XSF is outlined.

2. Requirements

2.1 CA Requirements

The following rules apply to any CA:

  1. The CA MUST be Sybil resistant, i.e. it MUST NOT allow massive certificate creation by the same human user. To accomplish this the CA SHOULD identify a human user or an organization behind the XMPP address or the associated domain. The methods for such identification are out of scope of this document.
  2. The CA SHOULD issue enough certificates for a human user owning the XMPP address to run all user's devices. In other words, the CA MAY issue multiple certificates with the same XMPP address but different RELOAD URIs.
  3. The CA MUST issue a valid certificate, which means that the certificate MUST comply to the rules defined in Section 3.2 of XEP-EAX.
  4. The CA MUST generate a cryptographically random 128-bit integer each time it issues a leaf certificate for a new user device. This integer MUST be a part of the RELOAD URI and MUST be included in the certificate as specified under Section 3.2 of XEP-EAX.
  5. The CA MUST maintain a Certificate Revocation List (CRL). The CRL URI is encoded in the certificates as specified under Section 3.2 of XEP-EAX.

The following rules apply to domain-associated CAs:

  1. The domain-associated CA MAY issue leaf certificates for users of its domain, i.e. a domain part of an XmppAddr of a leaf certificate matches the domain associated with this CA.
  2. The domain-associated CA MUST NOT issue any other certificates.

The following rules apply to root CAs:

  1. The root CA MUST maintain a RELOAD enrollment server with the Overlay Configuration document (see Section 11.1 of RFC6940). Even if XOR extension (XEP-XOR) is unused, the document can be used to retrieve the list of the root certificates.
  2. All root CAs MUST synchronize the Overlay Configuration between them keeping the same content of the document. This is the minimum required coordination of the root CAs.
  3. The Overlay Configuration MUST be located at HTTP relative path "/.well-known/reload-config" of the enrollment server of each root CA.

Failing to follow the above rules MAY lead to certificate revocation by either appending the intermediate certificate to the parent's Certificate Revocation List or by removing the root certificate from the listing of the XSF.

2.2 XSF Requirements

The XSF acts as an entry point for the Overlay Configuration. In accordance with Section 11.2 of RFC6940, to provide such an entry point, the following requirements are applied to the XSF:

  1. The XSF MUST maintain an HTTP server for domain "xmpp.org".
  2. The XSF MUST serve URL "https://xmpp.org/.well-known/reload-config".
  3. The XSF MUST redirect HTTP requests to the above URL to the URLs provided by representatives of the root CAs. The redirection MUST be performed in a round-robin manner, i.e. no priority should be given to any particular CA URL.

Since the location of the Overlay Configuration document is defined in this specification, the XSF doesn't need to maintain SRV DNS entries for a Service name of "reload-config".

It is expected that modifications of the list of root CA URLs will be rarely needed. Also, maintaining URL redirections is a relatively simple task. Thus operational costs for the XSF are expected to be low.

3. Glossary

Refer to Glossary sections of XEP-EAX and XEP-XOR.

4. Business Rules

TODO: describe interaction between the XMPP Board and representatives of the root CAs.

5. Security Considerations

This specification requires to maintain an HTTP server. A standard practice should be used to protect the HTTP server from security threats.

6. IANA Considerations

None required.

7. XMPP Registrar Considerations

None required.


Appendix A: Document Information

XMPP Standards Foundation
Last Updated
Approving Body
XSF Board of Directors
Superseded By
Short Name

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Appendix B: Author Information

Evgeny Khramtsov


This XMPP Extension Protocol is copyright © 1999 – 2020 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).

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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 by the membership of the XSF might also be appropriate (see <http://mail.jabber.org/mailman/listinfo/members> for details).

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

Appendix H: Revision History

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

  1. Version 0.0.1 (2019-02-08)

    First draft.