Network Working Group P. Saint-Andre
Internet-Draft Jabber Software Foundation
Expires: November 18, 2003 May 20, 2003
End-to-End Object Encryption in XMPP
draft-ietf-xmpp-e2e-03
Status of this Memo
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This Internet-Draft will expire on November 18, 2003.
Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
This document defines a method for end-to-end object signing and
encryption in the Extensible Messaging and Presence Protocol (XMPP).
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2 Discussion Venue . . . . . . . . . . . . . . . . . . . . . . . 3
1.3 Intellectual Property Notice . . . . . . . . . . . . . . . . . 3
2. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Securing Messages . . . . . . . . . . . . . . . . . . . . . . 6
4. Securing Presence . . . . . . . . . . . . . . . . . . . . . . 8
5. Secure Communications Through a Gateway . . . . . . . . . . . 10
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
7. Security Considerations . . . . . . . . . . . . . . . . . . . 12
Normative References . . . . . . . . . . . . . . . . . . . . . 13
Author's Address . . . . . . . . . . . . . . . . . . . . . . . 14
A. Schema for urn:ietf:params:xml:ns:xmpp-e2e . . . . . . . . . . 15
B. Revision History . . . . . . . . . . . . . . . . . . . . . . . 16
B.1 Changes from draft-ietf-xmpp-e2e-02 . . . . . . . . . . . . . 16
B.2 Changes from draft-ietf-xmpp-e2e-01 . . . . . . . . . . . . . 16
B.3 Changes from draft-ietf-xmpp-e2e-00 . . . . . . . . . . . . . 16
Intellectual Property and Copyright Statements . . . . . . . . 17
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1. Introduction
This document define a method for end-to-end signing and encryption
in the Extensible Messaging and Presence Protocol (XMPP). (For
information about XMPP, see XMPP Core [1] and XMPP IM [2].) The
method defined herein enables a sender to encrypt and/or sign an
instant message sent to a specific recipient, encrypt and/or sign
presence information that is directed to a specific user, and sign
presence information that is broadcasted to a specific user. This
document thereby helps the XMPP specifications meet the requirements
defined in RFC 2779 [3].
1.1 Terminology
This document inherits terminology defined in XMPP Core [1] and RFC
2778 [4].
The capitalized key words "MUST", "MUST NOT", "REQUIRED", "SHALL",
"SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in RFC
2119 [5].
1.2 Discussion Venue
The authors welcome discussion and comments related to the topics
presented in this document. The preferred forum is the
<xmppwg@jabber.org> mailing list, for which archives and subscription
information are available at <http://www.jabber.org/cgi-bin/mailman/
listinfo/xmppwg/>.
1.3 Intellectual Property Notice
This document is in full compliance with all provisions of Section 10
of RFC 2026. Parts of this specification use the term "jabber" for
identifying namespaces and other protocol syntax. Jabber[tm] is a
registered trademark of Jabber, Inc. Jabber, Inc. grants permission
to the IETF for use of the Jabber trademark in association with this
specification and its successors, if any.
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2. Requirements
For the purposes of this document, we stipulate the following
requirements:
1. The method defined MUST address encryption and signing
requirements for minimal instant messaging and presence only, as
those are defined in RFC 2779 [3]. The method is NOT REQUIRED to
support non-IM applications of XMPP, nor to support advanced
instant messaging and presence functionality that is outside the
scope of RFC 2799. In particular, the method MUST address the
following requirements defined in RFC 2779:
* The protocol MUST provide means to ensure confidence that a
received message (NOTIFICATION or INSTANT MESSAGE) has not
been corrupted or tampered with. (Section 2.5.1)
* The protocol MUST provide means to ensure confidence that a
received message (NOTIFICATION or INSTANT MESSAGE) has not
been recorded and played back by an adversary. (Section 2.5.2)
* The protocol MUST provide means to ensure that a sent message
(NOTIFICATION or INSTANT MESSAGE) is only readable by ENTITIES
that the sender allows. (Section 2.5.3)
* The protocol MUST allow any client to use the means to ensure
non-corruption, non-playback, and privacy, but the protocol
MUST NOT require that all clients use these means at all
times. (Section 2.5.4)
* When A establishes a SUBSCRIPTION to B's PRESENCE INFORMATION,
the protocol MUST provide A means of verifying the accurate
receipt of the content B chooses to disclose to A. (Section
5.1.4)
* The protocol MUST provide A means of verifying that the
presence information is accurate, as sent by B. (Section
5.3.1)
* The protocol MUST provide A means of ensuring that no other
PRINCIPAL C can see the content of M. (Section 5.4.6)
* The protocol MUST provide A means of ensuring that no other
PRINCIPAL C can tamper with M, and B means to verify that no
tampering has occurred. (Section 5.4.7)
2. The method defined MUST enable interoperability with non-XMPP
messaging systems that support Common Presence and Instant
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Messaging (CPIM) as defined by the Instant Messaging and Presence
(IMPP) Working Group. Therefore:
* Prior to encrypting or signing, the format of an instant
message must conform to the CPIM Message Format defined in
MSGFMT [6].
* Prior to encrypting or signing, the format of presence
information must conform to the CPIM Presence Information Data
Format defined in PIDF [7].
3. The method MUST follow the procedures (including the specific
algorithms) defined in Common Profile for Instant Messaging [8]
and Common Profile for Presence [9]. In particular, these
documents specify:
* Encryption MUST use S/MIME [10] encryption with CMS [11]
EnvelopeData.
* Signing MUST use S/MIME [10] signatures with CMS [11]
SignedData.
* The S/MIME algorithm SHOULD be AES [12].
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3. Securing Messages
In order to encrypt a message, a sending entity MUST use the
following procedure:
1. Generate a "Message/CPIM" object as defined in MSGFMT [6].
2. Encrypt and/or sign both the headers and content of the "Message/
CPIM" object as specified in Requirement 3 of Section 2 above.
3. Provide the resulting multipart S/MIME object (see RFC 1847 [13])
as the CDATA of an <e2e/> child of a <message/> stanza, with the
<e2e/> element scoped by the 'urn:ietf:params:xml:ns:xmpp-e2e'
namespace (note that this namespace name adheres to the format
defined in The IANA XML Registry [14]).
Example 1: Sender generates "Message/CPIM" object:
Content-type: Message/CPIM
From: Juliet Capulet <im:juliet@capulet.com>
To: Romeo Montague <im:romeo@montague.net>
DateTime: 2003-05-14T11:45:36Z
Subject: Imploring
Content-type: text/xml; charset=utf-8
Content-ID: <1234567890@capulet.com>
<body>
Wherefore art thou, Romeo?
</body>
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Example 2: Sender generates signed message (the 'from' address on the
XMPP message stanza is stamped by sender's server):
<message to='romeo@montague.net/orchard' type='chat'>
<e2e xmlns='urn:ietf:params:xml:ns:xmpp-e2e'>
Content-Type: multipart/signed; boundary=next;
micalg=sha1;
protocol=application/pkcs7-signature
--next
Content-type: Message/CPIM
From: Juliet Capulet <im:juliet@capulet.com>
To: Romeo Montague <im:romeo@montague.net>
DateTime: 2003-05-14T23:45:36Z
Subject: Imploring
Content-type: text/xml; charset=utf-8
Content-ID: <1234567890@capulet.com>
<body>
Wherefore art thou, Romeo?
</body>
--next
Content-Type: application/pkcs7-signature
[signed body part]
--next--
</e2e>
</message>
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4. Securing Presence
In order to encrypt presence information, a sending entity MUST use
the following procedure:
1. Generate an "application/cpim-pidf+xml" object defined in PIDF
[7].
2. Encrypt and/or sign the "application/cpim-pidf+xml" object as
specified in Requirement 3 of Section 2 above.
3. Provide the resulting S/MIME object as the CDATA of an <e2e/>
child of a <presence/> stanza, with the <e2e/> element scoped by
the 'urn:ietf:params:xml:ns:xmpp-e2e' namespace (note that this
namespace name adheres to the format defined in The IANA XML
Registry [14]). The <presence/> stanza MUST include a 'to'
attribute, i.e., it must be an instance of directed presence as
defined in XMPP IM [2].
Example 3: Sender generates "application/cpim-pidf+xml" object:
Content-type: application/cpim-pidf+xml
From: Juliet Capulet <pres:juliet@capulet.com>
To: Romeo Montague <pres:romeo@montague.net>
DateTime: 2003-05-14T23:53:11Z
Content-type: text/xml; charset=utf-8
Content-ID: <2345678901@capulet.com>
<?xml version="1.0" encoding="UTF-8"?>
<presence xmlns="urn:ietf:params:xml:ns:pidf"
xmlns:im="urn:ietf:params:xml:ns:pidf:im"
entity="pres:juliet@capulet.com">
<tuple id="h40zny"
<status>
<basic>open</basic>
<im:im>away</im:im>
</status>
<note xml:lang="en">retired to the chamber</note>
<timestamp>2003-05-14T23:53:11Z</timestamp>
</tuple>
</presence>
Example 4: Sender generates signed presence (the 'from' address on
the XMPP presence stanza is stamped by sender's server):
<presence to='romeo@montague.net/orchard'>
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<e2e xmlns='urn:ietf:params:xml:ns:xmpp-e2e'>
Content-Type: multipart/signed; boundary=next;
micalg=sha1;
protocol=application/pkcs7-signature
--next
Content-type: application/cpim-pid+xml
From: Juliet Capulet <pres:juliet@capulet.com>
To: Romeo Montague <pres:romeo@montague.net>
DateTime: 2003-05-14T23:53:11Z
Content-type: text/xml; charset=utf-8
Content-ID: <2345678901@capulet.com>
<?xml version="1.0" encoding="UTF-8"?>
<presence xmlns="urn:ietf:params:xml:ns:pidf"
xmlns:im="urn:ietf:params:xml:ns:pidf:im"
entity="pres:juliet@capulet.com">
<tuple id="h40zny"
<status>
<basic>open</basic>
<im:im>away</im:im>
</status>
<note xml:lang="en">retired to the chamber</note>
<timestamp>2003-05-14T23:53:11Z</timestamp>
</tuple>
</presence>
--next
Content-Type: application/pkcs7-signature
[signed body part]
--next--
</e2e>
</presence>
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5. Secure Communications Through a Gateway
A common method for achieving interoperability between two disparate
services is through the use of a "gateway" that interprets the
protocols of each service and translates them into the protocols of
the other. CPIM [8] and CPP [9] define the common profiles to be used
for interoperability between instant messaging and presence services
that comply with RFC 2779 [3]. In the case of communications between
an XMPP service and a non-XMPP service, we can visualize this
relationship as follows:
+-------------+ +-------------+ +-------------+
| | | | | |
| XMPP | | CPIM/CPP | | Non-XMPP |
| Service | <----> | Gateway | <----> | Service |
| | | | | |
+-------------+ +-------------+ +-------------+
The end-to-end encryption method defined herein enables the exchange
of encrypted and/or signed instant messages and presence through
CPIM/CPP gateways. In particular:
o When a gateway receives a secured XMPP message or presence stanza
from the XMPP service that addressed to a user on the non-XMPP
service, it MUST remove the XMPP "wrapper" (everything down to and
including the <e2e> and </e2e> tags) in order to reveal the
multipart S/MIME object, then route the object to the non-XMPP
service (first wrapping it in the protocol used by the non-XMPP
service if necessary).
o When a gateway receives a secured non-XMPP instant message or
presence document from the non-XMPP service that is addressed to a
user on the XMPP service, it MUST remove the non-XMPP "wrapper"
(if any) in order to reveal the multipart S/MIME object, wrap the
object in an XMPP message or presence "wrapper" (including the
<e2e> and </e2e> tags), and then route the XMPP stanza to the XMPP
service.
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6. IANA Considerations
A URN sub-namespace for signed and encrypted content in the
Extensible Messaging and Presence Protocol (XMPP) is defined as
follows.
URI: urn:ietf:params:xml:ns:xmpp-e2e
Specification: [RFCXXXX]
Description: This is the XML namespace name for signed and encrypted
content in the Extensible Messaging and Presence Protocol as
defined by [RFCXXXX].
Registrant Contact: IETF, XMPP Working Group, <xmppwg@jabber.org>
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7. Security Considerations
Detailed security considerations for instant messaging and presence
protocols are given in RFC 2779 [3], specifically in Sections 5.1
through 5.4.
The end-to-end security method defined here MAY result in exchanging
secured instant messages and presence information through a gateway
that implements CPIM [8] and CPP [9]. Such a gateway MUST be
compliant with the minimum security requirements of the instant
messaging and presence protocols with which it interfaces. The
introduction of gateways to the security model of instant messaging
and presence in RFC 2779 also introduces some new risks. End-to-end
security properties (especially confidentiality and integrity)
between instant messaging and presence user agents that interface
through a CPIM/CPP gateway can be provided only if common formats are
supported. The need for end-to-end security is thus met by this
specification through the use of common formats, specifically MSGFMT
[6] for instant messages and PIDF [7] for presence information.
Common formats are further ensured by requiring the use of multipart
S/MIME [10] objects, as well as CMS [11] EnvelopeData for encryption
and CMS [11] SignedData for signing. Finally, the algorithm used
SHOULD be AES [12], since it is expected that AES best suits the
capabilities of many platforms. However, an IETF specification for
the use of AES is still incomplete at the time of writing.
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Normative References
[1] Saint-Andre, P. and J. Miller, "XMPP Core",
draft-ietf-xmpp-core-12 (work in progress), May 2003.
[2] Saint-Andre, P. and J. Miller, "XMPP Instant Messaging",
draft-ietf-xmpp-im-11 (work in progress), May 2003.
[3] Day, M., Aggarwal, S. and J. Vincent, "Instant Messaging /
Presence Protocol Requirements", RFC 2779, February 2000.
[4] Day, M., Rosenberg, J. and H. Sugano, "A Model for Presence and
Instant Messaging", RFC 2778, February 2000, <http://
www.ietf.org/rfc/rfc2778.txt>.
[5] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[6] Atkins, D. and G. Klyne, "Common Presence and Instant Messaging
Message Format", draft-ietf-impp-cpim-msgfmt-08 (work in
progress), January 2003.
[7] Fujimoto, S., Sugano, H., Klyne, G., Bateman, A., Carr, W. and
J. Peterson, "CPIM Presence Information Data Format",
draft-ietf-impp-cpim-pidf-08 (work in progress), May 2003.
[8] Crocker, D. and J. Peterson, "Common Profile for Instant
Messaging (CPIM)", draft-ietf-impp-im-02 (work in progress),
March 2003.
[9] Crocker, D. and J. Peterson, "Common Profile for Presence
(CPP)", draft-ietf-impp-pres-02 (work in progress), March 2003.
[10] Ramsdell, B., "S/MIME Version 3 Message Specification", RFC
2633, June 1999.
[11] Housley, R., "Cryptographic Message Syntax (CMS)", RFC 3369,
August 2002.
[12] Housley, R. and J. Schaad, "Use of the AES Encryption Algorithm
and RSA-OAEP Key Transport in CMS", draft-ietf-smime-aes-alg-06
(work in progress), January 2003.
[13] Galvin, J., Murphy, S., Crocker, S. and N. Freed, "Security
Multiparts for MIME: Multipart/Signed and Multipart/Encrypted",
RFC 1847, October 1995.
[14] Mealling, M., "The IANA XML Registry",
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draft-mealling-iana-xmlns-registry-04 (work in progress), June
2002.
Author's Address
Peter Saint-Andre
Jabber Software Foundation
EMail: stpeter@jabber.org
URI: http://www.jabber.org/people/stpeter.php
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Appendix A. Schema for urn:ietf:params:xml:ns:xmpp-e2e
The following XML schema is descriptive, not normative.
<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
xmlns:xs='http://www.w3.org/2001/XMLSchema'
targetNamespace='urn:ietf:params:xml:ns:xmpp-e2e'
xmlns='urn:ietf:params:xml:ns:xmpp-e2e'
elementFormDefault='qualified'>
<xs:element name='e2e' type='xs:string'/>
</xs:schema>
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Appendix B. Revision History
Note to RFC Editor: please remove this entire appendix, and the
corresponding entries in the table of contents, prior to publication.
B.1 Changes from draft-ietf-xmpp-e2e-02
o Completely revised to use CPIM/CPP.
B.2 Changes from draft-ietf-xmpp-e2e-01
o Removed old Section 6 (Signalling Support via Presence) -- the
ability to sign broadcasted presence made it redundant.
o Made small editorial changes to address RFC Editor requirements.
B.3 Changes from draft-ietf-xmpp-e2e-00
o Added support for all stanza types.
o Specified that the full stanza is encrypted.
o Added support for S/MIME in addition to OpenPGP.
o Specified that encrypted presence must be directed to a specific
recipient.
o Specified order of encrypting and signing.
o Added support for signing broadcasted presence.
o Added IANA considerations.
o Changed namespace to 'urn:ietf:params:xml:ns:xmpp-e2e'.
o Added XML schema.
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Intellectual Property Statement
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intellectual property or other rights that might be claimed to
pertain to the implementation or use of the technology described in
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might or might not be available; neither does it represent that it
has made any effort to identify any such rights. Information on the
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licenses to be made available, or the result of an attempt made to
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proprietary rights by implementors or users of this specification can
be obtained from the IETF Secretariat.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF Executive
Director.
Full Copyright Statement
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This document and translations of it may be copied and furnished to
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HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
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