XEP-0027: Current Jabber OpenPGP Usage

Abstract:This document outlines the current usage of OpenPGP for messaging and presence.
Author:Thomas Muldowney
Copyright:© 1999 - 2014 XMPP Standards Foundation. SEE LEGAL NOTICES.
Status:Active
Type:Historical
Version:1.3
Last Updated:2006-11-29

NOTICE: This Historical specification provides canonical documentation of a protocol that is in use within the Jabber/XMPP community. This document is not a standards-track specification within the XMPP Standards Foundation's standards process; however, it might be converted to standards-track in the future or might be obsoleted by a more modern protocol.

Table of Contents


1. Introduction
2. Signing
3. Encrypting
4. Security Considerations
5. Other Known Issues
6. IANA Considerations
7. XMPP Registrar Considerations
8. XML Schemas
    8.1. jabber:x:encrypted
    8.2. jabber:x:signed

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

The Jabber community has long acknowledged the need for privacy and security features in a well-rounded instant messaging system. Unfortunately, finding a consensus solution to the problem of end-to-end encryption during the community's younger days was not easy. Eventually, early contributors created a quick solution using OpenPGP (RFC 4880 [1]). This specification documents the OpenPGP solution as it is used today, so that others may interoperate with clients that support it. This document is not intended to present a standard, because more complete solutions are being investigated.

All operations described here are done with standard OpenPGP software such as GnuPG. All program output is US-ASCII armored output with the headers removed. This allows for easy transportation of the program output directly in the XML. All keys are exchanged using OpenPGP key servers, and usually are retrieved when a signed <presence/> stanza is received (key retrieval does not happen in-band).

2. Signing

Signing enables a sender to verify that they sent a certain block of text. In Jabber, signing uses the 'jabber:x:signed' namespace, and is primarily used with <presence/>, but may also be used with <message/>. The text that is signed MAY be the empty string. When signing presence, the sender SHOULD sign the XML character data of the <status> element. The sender SHOULD sign presence using the private key whose KeyID corresponds to the public key to be used in encrypting messages (see below).

Example 1. A signed presence stanza

<presence from='pgmillard@jabber.org/wj_dev2' to='jer@jabber.org'>
  <status>Online</status>
  <x xmlns='jabber:x:signed'>
    iQA/AwUBOjU5dnol3d88qZ77EQI2JACfRngLJ045brNnaCX78ykKNUZaTIoAoPHI
    2uJxPMGR73EBIvEpcv0LRSy+
    =45f8
  </x>
</presence>

3. Encrypting

Encryption enables the sender to encrypt a message to a specific recipient. This is accomplished using the 'jabber:x:encrypted' namespace in conjunction with <message/> stanzas. Because a block of text is necessary in order to have something to encrypt, <message/> stanzas intended to be encrypted have the same restrictions as signing (see above). The data encrypted MUST be the XML character data of the <body> element. The sender SHOULD encrypt the message body using the public key whose KeyID corresponds to the private key used in signing presence (see above).

Example 2. An encrypted message stanza

<message to='reatmon@jabber.org/jarl' from='pgmillard@jabber.org/wj_dev2'>
  <body>This message is encrypted.</body>
  <x xmlns='jabber:x:encrypted'>
    qANQR1DBwU4DX7jmYZnncmUQB/9KuKBddzQH+tZ1ZywKK0yHKnq57kWq+RFtQdCJ
    WpdWpR0uQsuJe7+vh3NWn59/gTc5MDlX8dS9p0ovStmNcyLhxVgmqS8ZKhsblVeu
    IpQ0JgavABqibJolc3BKrVtVV1igKiX/N7Pi8RtY1K18toaMDhdEfhBRzO/XB0+P
    AQhYlRjNacGcslkhXqNjK5Va4tuOAPy2n1Q8UUrHbUd0g+xJ9Bm0G0LZXyvCWyKH
    kuNEHFQiLuCY6Iv0myq6iX6tjuHehZlFSh80b5BVV9tNLwNR5Eqz1klxMhoghJOA
    w7R61cCPt8KSd8Vcl8K+StqOMZ5wkhosVjUqvEu8uJ9RupdpB/4m9E3gOQZCBsmq
    OsX4/jJhn2wIsfYYWdqkbNKnuYoKCnwrlmn6I+wX72p0R8tTv8peNCwK9bEtL/XS
    mhn4bCxoUkCITv3k8a+Jdvbov9ucduKSFuCBq4/l0fpHmPhHQjkFofxmaWJveFfF
    619NXyYyCfoLTmWk2AaTHVCjtKdf1WmwcTa0vFfk8BuFHkdah6kJJiJ7w/yNwa/E
    O6CMymuZTr/LpcKKWrWCt+SErxqmq8ekPI8h7oNwMxZBYAa7OJ1rXWKNgL9pDtNI
    824Mf0mXj7q5N1eMHvX1QEoKLAda/Ae3TTEevOyeUK1DEgvxfM2KRZ11RzU+XtIE
    My/bJk7EycAw8P/QKyeNlO1fxP58VEd6Gb8NCPqKOYn/LKh1O+c20ZNVEPFM4bNV
    XA4hB4UtFF7Ao8kpdlrUqdKyw4lEtnmdemYQ6+iIIVPEarWl9PxOMY90KAnZrSAq
    bt9uRY/1rPgelRaWblMKvxgpRO8++Y8VjdEyGgMOXxOiE851Ve72ftGzkSxDH8mW
    TgY3pf2aATmBp3lagQ1COkGS/xupovT5AQPA3RzbCxDvc6s6eGYKmVVQVj5vmSj1
    WULad5MB9KT1DzCm6FOSy063nWGBYYMWiejRvGLpo1j4eAnj0qOt7rTWmgv3RkYF
    Oin0vDOhW7aC
    =CvnG</x>
</message>

It is considered polite to include an unencrypted message <body/> explaining that the actual message body is encrypted. This helps if the client experiences an error while decrypting the message, or if the user's a client that does not support encryption (although generally this should not happen, since the signed presence can be used to indicate that a client accepts encrypted messages).

4. Security Considerations

The method defined herein has the following security issues:

5. Other Known Issues

In addition to the security considerations listed above, there are several other known issues with this method:

6. IANA Considerations

This document requires no interaction with the Internet Assigned Numbers Authority (IANA) [2].

7. XMPP Registrar Considerations

The XMPP Registrar [3] shall register the 'jabber:x:encrypted' and 'jabber:x:signed' namespaces as a result of this document.

8. XML Schemas

8.1 jabber:x:encrypted

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

<xs:schema
    xmlns:xs='http://www.w3.org/2001/XMLSchema'
    targetNamespace='jabber:x:encrypted'
    xmlns='jabber:x:encrypted'
    elementFormDefault='qualified'>

  <xs:annotation>
    <xs:documentation>
      The protocol documented by this schema is defined in
      XEP-0027: http://www.xmpp.org/extensions/xep-0027.html
    </xs:documentation>
  </xs:annotation>

  <xs:element name='x' type='xs:string'/>

</xs:schema>

8.2 jabber:x:signed

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

<xs:schema
    xmlns:xs='http://www.w3.org/2001/XMLSchema'
    targetNamespace='jabber:x:signed'
    xmlns='jabber:x:signed'
    elementFormDefault='qualified'>

  <xs:annotation>
    <xs:documentation>
      The protocol documented by this schema is defined in
      XEP-0027: http://www.xmpp.org/extensions/xep-0027.html
    </xs:documentation>
  </xs:annotation>

  <xs:element name='x' type='xs:string'/>

</xs:schema>

Appendices

Appendix A: Document Information

Series: XEP
Number: 0027
Publisher: XMPP Standards Foundation
Status: Active
Type: Historical
Version: 1.3
Last Updated: 2006-11-29
Approving Body: XMPP Council
Dependencies: XMPP Core, RFC 4880
Supersedes: None
Superseded By: None
Short Name: openpgp
XML Schema for jabber:x:encrypted namespace: <http://www.xmpp.org/schemas/x-encrypted.xsd>
XML Schema for jabber:x:signed namespace: <http://www.xmpp.org/schemas/x-signed.xsd>
Source Control: HTML
This document in other formats: XML  PDF

Appendix B: Author Information

Thomas Muldowney

Email: temas@jabber.org
JabberID: temas@jabber.org

Appendix C: Legal Notices

Copyright

This XMPP Extension Protocol is copyright © 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. ##

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 <http://xmpp.org/about-xmpp/xsf/xsf-ipr-policy/> or obtained by writing to XMPP Standards Foundation, 1899 Wynkoop Street, Suite 600, Denver, CO 80202 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.

Given that this XMPP Extension Protocol normatively references IETF technologies, discussion on the <xsf-ietf@xmpp.org> list might also be appropriate.

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. RFC 4880: OpenPGP Message Format <http://tools.ietf.org/html/rfc4880>.

2. 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/>.

3. 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 <http://xmpp.org/registrar/>.

Appendix H: Revision History

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

Version 1.3 (2006-11-29)

Removed the unnecessary requirement that the presence status or message body must contain XML character data, since an empty string can be signed. (psa)

Version 1.2 (2004-03-08)

Clarified the text in several places; added several more security considerations and known issues. (psa)

Version 1.1 (2004-01-06)

Added XML schemas; added security, IANA, and XMPP Registrar considerations. (psa)

Version 1.0 (2002-04-23)

Changed status to Active. (psa)

Version 0.2 (2002-04-11)

Merged DW's comments on key usage as well as more known issues. (tjm)

Version 0.1 (2002-03-12)

First draft. (tjm)

END