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).
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).
<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>
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).
<message to='reatmon@jabber.org/jarl' from='pgmillard@jabber.org/wj_dev2'>
<body>This message is encrypted.</body>
<x xmlns='jabber:x:encrypted'>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=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).
The method defined herein has the following security issues:
In addition to the security considerations listed above, there are several other known issues with this method:
This document requires no interaction with the Internet Assigned Numbers Authority (IANA) [2].
The XMPP Registrar [3] shall register the 'jabber:x:encrypted' and 'jabber:x:signed' namespaces as a result of this document.
<?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>
<?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>
This document in other formats: XML PDF
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Discussion on other xmpp.org discussion lists might also be appropriate; see <https://xmpp.org/community/> 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>.
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".
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 <https://xmpp.org/registrar/>.
Note: Older versions of this specification might be available at https://xmpp.org/extensions/attic/
@report{muldowney2002openpgp,
title = {Current Jabber OpenPGP Usage},
author = {Muldowney, Thomas},
type = {XEP},
number = {0027},
version = {1.4},
institution = {XMPP Standards Foundation},
url = {https://xmpp.org/extensions/xep-0027.html},
date = {2002-03-12/2014-03-14},
}END