TOC 
XMPP Working GroupP. Saint-Andre
Internet-DraftJabber Software Foundation
Expires: January 10, 2005July 12, 2004

End-to-End Signing and Object Encryption for the Extensible Messaging and Presence Protocol (XMPP)

draft-ietf-xmpp-e2e-09

Status of this Memo

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Copyright Notice

Copyright (C) The Internet Society (2004). All Rights Reserved.

Abstract

This memo defines a methods of end-to-end signing and object encryption for the Extensible Messaging and Presence Protocol (XMPP).



Table of Contents

1.  Introduction
2.  Requirements
3.  Securing Messages
4.  Securing Presence
5.  Securing Arbitrary XMPP Data
6.  Rules for S/MIME Generation and Handling
7.  Recipient Error Handling
8.  Secure Communications Through a Gateway
9.  urn:ietf:params:xml:xmpp-e2e Namespace
10.  application/xmpp+xml Media Type
11.  Security Considerations
12.  IANA Considerations
§.  Normative References
§.  Informative References
§  Author's Address
A.  Schema for urn:ietf:params:xml:ns:xmpp-e2e
B.  Revision History
§  Intellectual Property and Copyright Statements




 TOC 

1. Introduction

This memo define methods of end-to-end signing and object encryption for the Extensible Messaging and Presence Protocol (XMPP). (For information about XMPP, see [XMPP-CORE]Saint-Andre, P., XMPP Core, May 2004. and [XMPP-IM]Saint-Andre, P., XMPP Instant Messaging, April 2004..) The method specified herein enables a sender to sign and/or encrypt an instant message sent to a specific recipient, sign and/or encrypt presence information that is directed to a specific user, and sign and/or encrypt any arbitrary XMPP stanza directed to a specific user. This memo thereby helps the XMPP specifications meet the requirements specified in [IMP-REQS]Day, M., Aggarwal, S. and J. Vincent, Instant Messaging / Presence Protocol Requirements, February 2000..

1.1 Terminology

This document inherits terminology defined in [CMS]Housley, R., Cryptographic Message Syntax (CMS), July 2004., [IMP-MODEL]Day, M., Rosenberg, J. and H. Sugano, A Model for Presence and Instant Messaging, February 2000., [SMIME]Ramsdell, B., Secure/Multipurpose Internet Mail Extensions (S/MIME) Version 3.1 Message Specification, July 2004., and [XMPP-CORE]Saint-Andre, P., XMPP Core, May 2004..

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 [TERMS]Bradner, S., Key words for use in RFCs to Indicate Requirement Levels, March 1997..



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2. Requirements

For the purposes of this memo, we stipulate the following requirements:

  1. The method defined MUST address signing and encryption requirements for minimal instant messaging and presence, as those are defined in [IMP-REQS]Day, M., Aggarwal, S. and J. Vincent, Instant Messaging / Presence Protocol Requirements, February 2000.. In particular, the method MUST address the following requirements, which are copied here verbatim from [IMP-REQS]Day, M., Aggarwal, S. and J. Vincent, Instant Messaging / Presence Protocol Requirements, February 2000.:
  2. The method defined MUST enable interoperability with non-XMPP messaging systems that support the Common Presence and Instant Messaging (CPIM) specifications published by the Instant Messaging and Presence (IMPP) Working Group. Two corollaries of this requirement are:
  3. The method MUST follow the required procedures (including the specific algorithms) defined in [CPIM]Peterson, J., Common Profile for Instant Messaging (CPIM), August 2004. and [CPP]Peterson, J., Common Profile for Presence (CPP), August 2004.. In particular, these documents specify:
  4. In order to enable interoperable implementations, sending and receiving applications MUST implement the algorithms specified under Mandatory-to-Implement Cryptographic AlgorithmsMandatory-to-Implement Cryptographic Algorithms.

We further stipulate that the following functionality is out of scope for this memo:



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3. Securing Messages

3.1 Process for Securing Messages

In order to sign and/or encrypt a message, a sending agent MUST use the following procedure:

  1. Generate a "Message/CPIM" object as defined in [MSGFMT]Klyne, G. and D. Atkins, Common Presence and Instant Messaging (CPIM): Message Format, August 2004..
  2. Sign and/or encrypt both the headers and content of the "Message/CPIM" object as specified in Requirement 3 of Section 2Requirements above.
  3. Provide the resulting signed and/or encrypted object within an XML CDATA section (see Section 2.7 of [XML]Bray, T., Paoli, J., Sperberg-McQueen, C. and E. Maler, Extensible Markup Language (XML) 1.0 (3rd ed), February 2004.) contained in an <e2e/> child of a <message/> stanza, where the <e2e/> element is qualified by the 'urn:ietf:params:xml:ns:xmpp-e2e' namespace as specified more fully in Section 9urn:ietf:params:xml:xmpp-e2e Namespace below.

3.2 Example of a Signed Message

The following example illustrates the defined steps for signing a message.

First, the sending agent generates a "Message/CPIM" object in accordance with the rules and formats specified in [MSGFMT]Klyne, G. and D. Atkins, Common Presence and Instant Messaging (CPIM): Message Format, August 2004..

Example 1: Sender generates "Message/CPIM" object:

|   Content-type: Message/CPIM
|   
|   From: Juliet Capulet <im:juliet@example.com>
|   To: Romeo Montague <im:romeo@example.net>
|   DateTime: 2003-12-09T11:45:36.66Z
|   Subject: Imploring
|   
|   Content-type: text/plain; charset=utf-8
|   Content-ID: <1234567890@example.com>
|   
|   Wherefore art thou, Romeo?
          

Once the sending agent has generated the "Message/CPIM" object, the sending agent may sign it. The result is a multipart [SMIME]Ramsdell, B., Secure/Multipurpose Internet Mail Extensions (S/MIME) Version 3.1 Message Specification, July 2004. object (see [MULTI]Galvin, J., Murphy, S., Crocker, S. and N. Freed, Security Multiparts for MIME: Multipart/Signed and Multipart/Encrypted, October 1995.) that has a Content-Type of "multipart/signed" and includes two parts: one whose Content-Type is "Message/CPIM" and another whose Content-Type is "application/pkcs7-signature".

Example 2: Sender generates multipart/signed object:

|   Content-Type: multipart/signed; boundary=next;
|                 micalg=sha1;
|                 protocol=application/pkcs7-signature
|   
|   --next
|   Content-type: Message/CPIM
|   
|   From: Juliet Capulet <im:juliet@example.com>
|   To: Romeo Montague <im:romeo@example.net>
|   DateTime: 2003-12-09T23:45:36.66Z
|   Subject: Imploring
|   
|   Content-type: text/plain; charset=utf-8
|   Content-ID: <1234567890@example.com>
|   
|   Wherefore art thou, Romeo?
|   --next
|   Content-Type: application/pkcs7-signature
|   Content-Disposition: attachment;handling=required;\
|                                   filename=smime.p7s
|   
|   [signed body part]
|   
|   --next--
        

The sending agent now wraps the "mulipart/signed" object in an XML CDATA section, which is contained in an <e2e/> element that is included as a child element of the XMPP message stanza and that is qualified by the 'urn:ietf:params:xml:ns:xmpp-e2e' namespace.

Example 3: Sender generates XMPP message stanza:

|   <message to='romeo@example.net/orchard' type='chat'>
|     <e2e xmlns='urn:ietf:params:xml:ns:xmpp-e2e'>
|   <![CDATA[
|   Content-Type: multipart/signed; boundary=next;
|                 micalg=sha1;
|                 protocol=application/pkcs7-signature
|   
|   --next
|   Content-type: Message/CPIM
|   
|   From: Juliet Capulet <im:juliet@example.com>
|   To: Romeo Montague <im:romeo@example.net>
|   DateTime: 2003-12-09T23:45:36.66Z
|   Subject: Imploring
|   
|   Content-type: text/plain; charset=utf-8
|   Content-ID: <1234567890@example.com>
|   
|   Wherefore art thou, Romeo?
|   --next
|   Content-Type: application/pkcs7-signature
|   Content-Disposition: attachment;handling=required;\
|                                   filename=smime.p7s
|   
|   [signed body part]
|   
|   --next--
|   ]]>
|     </e2e>
|   </message>
          

3.3 Example of an Encrypted Message

The following example illustrates the defined steps for encrypting a message.

First, the sending agent generates a "Message/CPIM" object in accordance with the rules and formats specified in [MSGFMT]Klyne, G. and D. Atkins, Common Presence and Instant Messaging (CPIM): Message Format, August 2004..

Example 4: Sender generates "Message/CPIM" object:

|   Content-type: Message/CPIM
|   
|   From: Juliet Capulet <im:juliet@example.com>
|   To: Romeo Montague <im:romeo@example.net>
|   DateTime: 2003-12-09T11:45:36.66Z
|   Subject: Imploring
|   
|   Content-type: text/plain; charset=utf-8
|   Content-ID: <1234567890@example.com>
|   
|   Wherefore art thou, Romeo?
          

Once the sending agent has generated the "Message/CPIM" object, the sending agent may encrypt it.

Example 5: Sender generates encrypted object:

|   U2FsdGVkX19okeKTlLxa/1n1FE/upwn1D20GhPWqhDWlexKMUKYJInTWzERP+vcQ
|   /OxFs40uc9Fx81a5/62p/yPb/UWnuG6SR6o3Ed2zwcusDImyyz125HFERdDUMBC9
|   Pt6Z4cTGKBmJzZBGyuc3Y+TMBTxqFFUAxeWaoxnZrrl+LP72vwbriYc3KCMxDbQL
|   Igc1Vzs5/5JecegMieNY24SlNyX9HMFRNFpbI64vLxYEk55A+3IYbZsluCFT31+a
|   +GeAvJkvH64LRV4mPbUhENTQ2wbAwnOTvbLIaQEQrii78xNEh+MK8Bx7TBTvi4yH
|   Ddzf9Sim6mtWsXaCAvWSyp0X91d7xRJ4JIgKfPzkxNsWJFCLthQS1p734eDxXVd3
|   i08lEHzyll6htuEr59ZDAw==
          

The sending agent now wraps the encrypted object in an XML CDATA section, which is contained in an <e2e/> element that is included as a child element of the XMPP message stanza and that is qualified by the 'urn:ietf:params:xml:ns:xmpp-e2e' namespace.

Example 6: Sender generates XMPP message stanza:

|   <message to='romeo@example.net/orchard' type='chat'>
|     <e2e xmlns='urn:ietf:params:xml:ns:xmpp-e2e'>
|   <![CDATA[
|   U2FsdGVkX19okeKTlLxa/1n1FE/upwn1D20GhPWqhDWlexKMUKYJInTWzERP+vcQ
|   /OxFs40uc9Fx81a5/62p/yPb/UWnuG6SR6o3Ed2zwcusDImyyz125HFERdDUMBC9
|   Pt6Z4cTGKBmJzZBGyuc3Y+TMBTxqFFUAxeWaoxnZrrl+LP72vwbriYc3KCMxDbQL
|   Igc1Vzs5/5JecegMieNY24SlNyX9HMFRNFpbI64vLxYEk55A+3IYbZsluCFT31+a
|   +GeAvJkvH64LRV4mPbUhENTQ2wbAwnOTvbLIaQEQrii78xNEh+MK8Bx7TBTvi4yH
|   Ddzf9Sim6mtWsXaCAvWSyp0X91d7xRJ4JIgKfPzkxNsWJFCLthQS1p734eDxXVd3
|   i08lEHzyll6htuEr59ZDAw==
|   ]]>
|     </e2e>
|   </message>
          


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4. Securing Presence

4.1 Process for Securing Presence Information

In order to sign and/or encrypt presence information, a sending agent MUST use the following procedure:

  1. Generate an "application/pidf+xml" object as defined in [PIDF]Sugano, H., Fujimoto, S., Klyne, G., Bateman, A., Carr, W. and J. Peterson, Presence Information Data Format (PIDF), August 2004..
  2. Sign and/or encrypt the "application/pidf+xml" object as specified in Requirement 3 of Section 2Requirements above.
  3. Provide the resulting signed and/or encrypted object within an XML CDATA section (see Section 2.7 of [XML]Bray, T., Paoli, J., Sperberg-McQueen, C. and E. Maler, Extensible Markup Language (XML) 1.0 (3rd ed), February 2004.) contained in an <e2e/> child of a <presence/> stanza, where the <e2e/> element is qualified by the 'urn:ietf:params:xml:ns:xmpp-e2e' namespace. The <presence/> stanza MUST include a 'to' attribute, i.e., it must be an instance of directed presence as defined in [XMPP-IM]Saint-Andre, P., XMPP Instant Messaging, April 2004..

4.2 Example of Signed Presence Information

The following example illustrates the defined steps for signing presence information.

First, the sending agent generates an "application/pidf+xml" object in accordance with the rules and formats specified in [PIDF]Sugano, H., Fujimoto, S., Klyne, G., Bateman, A., Carr, W. and J. Peterson, Presence Information Data Format (PIDF), August 2004..

Example 7: Sender generates "application/pidf+xml" object:

|   <?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@example.com">
|     <tuple id="hr0zny"
|       <status>
|         <basic>open</basic>
|         <im:im>away</im:im>
|       </status>
|       <note xml:lang="en">retired to the chamber</note>
|       <timestamp>2003-12-09T23:53:11.31</timestamp>
|     </tuple>
|   </presence>
          

Once the sending agent has generated the "application/pidf+xml" object, the sending agent may sign it. The result is a multipart [SMIME]Ramsdell, B., Secure/Multipurpose Internet Mail Extensions (S/MIME) Version 3.1 Message Specification, July 2004. object (see [MULTI]Galvin, J., Murphy, S., Crocker, S. and N. Freed, Security Multiparts for MIME: Multipart/Signed and Multipart/Encrypted, October 1995.) that has a Content-Type of "multipart/signed" and includes two parts: one whose Content-Type is "application/pidf+xml" and another whose Content-Type is "application/pkcs7-signature".

Example 8: Sender generates multipart/signed object:

|   Content-Type: multipart/signed; boundary=next;
|                 micalg=sha1;
|                 protocol=application/pkcs7-signature
|   
|   --next
|   Content-type: application/pidf+xml
|   Content-ID: <2345678901@example.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@example.com">
|     <tuple id="hr0zny">
|       <status&gt;
|         <basic>open</basic>
|         <im:im>away</im:im>
|       </status>
|       <note xml:lang="en">retired to the chamber</note>
|       <timestamp>2003-12-09T23:53:11.31Z</timestamp>
|     </tuple>
|   </presence>
|   --next
|   Content-Type: application/pkcs7-signature
|   Content-Disposition: attachment;handling=required;\
|                                   filename=smime.p7s
|   
|   [signed body part]
|   
|   --next--
          

The sending agent now wraps the "mulipart/signed" object in an XML CDATA section, which is contained in an <e2e/> element that is included as a child element of the XMPP message stanza and that is qualified by the 'urn:ietf:params:xml:ns:xmpp-e2e' namespace.

Example 9: Sender generates XMPP presence stanza:

|   <presence to='romeo@example.net/orchard'>
|     <e2e xmlns='urn:ietf:params:xml:ns:xmpp-e2e'>
|   <![CDATA[
|   Content-Type: multipart/signed; boundary=next;
|                 micalg=sha1;
|                 protocol=application/pkcs7-signature
|   
|   --next
|   Content-type: application/pidf+xml
|   Content-ID: <2345678901@example.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@example.com">
|     <tuple id="hr0zny">
|       <status>
|         <basic>open</basic>
|         <im:im>away</im:im>
|       </status>
|       <note xml:lang="en">retired to the chamber</note>
|       <timestamp>2003-12-09T23:53:11.31Z</timestamp>
|     </tuple>
|   </presence>
|   --next
|   Content-Type: application/pkcs7-signature
|   Content-Disposition: attachment;handling=required;\
|                                   filename=smime.p7s
|   
|   [signed body part]
|   
|   --next--
|   ]]>
|     </e2e>
|   </presence>
          

4.3 Example of Encrypted Presence Information

The following example illustrates the defined steps for encrypting presence information.

First, the sending agent generates an "application/pidf+xml" object in accordance with the rules and formats specified in [PIDF]Sugano, H., Fujimoto, S., Klyne, G., Bateman, A., Carr, W. and J. Peterson, Presence Information Data Format (PIDF), August 2004..

Example 10: Sender generates "application/pidf+xml" object:

|   <?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@example.com">
|     <tuple id="hr0zny"
|       <status>
|         <basic>open</basic>
|         <im:im>away</im:im>
|       </status>
|       <note xml:lang="en">retired to the chamber</note>
|       <timestamp>2003-12-09T23:53:11.31</timestamp>
|     </tuple>
|   </presence>
          

Once the sending agent has generated the "application/pidf+xml" object, the sending agent may encrypt it.

Example 11: Sender generates encrypted object:

|   U2FsdGVkX18VJPbx5GMdFPTPZrHLC9QGiVP+ziczu6zWZLFQxae6O5PP6iqpr2No
|   zOvBVMWvYeRAT0zd18hr6qsqKiGl/GZpAAbTvPtaBxeIykxsd1+CX+U+iw0nEGCr
|   bjiQrk0qUKJ79bNxwRnqdidjhyTpKSbOJC0XZ8CTe7AE9KDM3Q+uk+O3jrqX4byL
|   GBlKThbzKidxz32ObojPEEwfFiM/yUeqYUP1OcJpUmeQ8lcXhD6tcx+m2MAyYYLP
|   boKQxpLknxRnbM8T/voedlnFLbbDu69mOlxDPbr1mHZd3hDsyFudb1fb4rI3Kw0K
|   Nq+3udr2IkysviJDgQo+xGIQUG/5sED/mAaPRlj4f/JtTzvT4EaQTawv69ntXfKV
|   MCr9KdIMMdjdJzOJkYLoAhNVrcZn5tw8WsJGwuKuhYb/SShy7InzOapPaPAl7/Mm
|   PHj7zj3NZ6EEIweDOuAwWlIG/dT506tci27+EW7JnXwMPnFMkF+6a7tr/0Y+iiej
|   woJxUIBqCOgX+U7srHpK2NYtNTZ7UQp2V0yEx1JV8+Y=
          

The sending agent now wraps the encrypted object in an XML CDATA section, which is contained in an <e2e/> element that is included as a child element of the XMPP message stanza and that is qualified by the 'urn:ietf:params:xml:ns:xmpp-e2e' namespace.

Example 12: Sender generates XMPP presence stanza:

|   <presence to='romeo@example.net/orchard'>
|     <e2e xmlns='urn:ietf:params:xml:ns:xmpp-e2e'>
|   <![CDATA[
|   U2FsdGVkX18VJPbx5GMdFPTPZrHLC9QGiVP+ziczu6zWZLFQxae6O5PP6iqpr2No
|   zOvBVMWvYeRAT0zd18hr6qsqKiGl/GZpAAbTvPtaBxeIykxsd1+CX+U+iw0nEGCr
|   bjiQrk0qUKJ79bNxwRnqdidjhyTpKSbOJC0XZ8CTe7AE9KDM3Q+uk+O3jrqX4byL
|   GBlKThbzKidxz32ObojPEEwfFiM/yUeqYUP1OcJpUmeQ8lcXhD6tcx+m2MAyYYLP
|   boKQxpLknxRnbM8T/voedlnFLbbDu69mOlxDPbr1mHZd3hDsyFudb1fb4rI3Kw0K
|   Nq+3udr2IkysviJDgQo+xGIQUG/5sED/mAaPRlj4f/JtTzvT4EaQTawv69ntXfKV
|   MCr9KdIMMdjdJzOJkYLoAhNVrcZn5tw8WsJGwuKuhYb/SShy7InzOapPaPAl7/Mm
|   PHj7zj3NZ6EEIweDOuAwWlIG/dT506tci27+EW7JnXwMPnFMkF+6a7tr/0Y+iiej
|   woJxUIBqCOgX+U7srHpK2NYtNTZ7UQp2V0yEx1JV8+Y=
|   ]]>
|     </e2e>
|   </presence>
          


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5. Securing Arbitrary XMPP Data

The foregoing sections of this memo describe how to secure "least common denominator" messaging and presence data of the kind that can be directly translated into the MSGFMT or PIDF formats. However, XMPP possesses a third base-level stanza type (<iq/>) in addition to <message/> and <presence/>, as well as the ability to include extended XML data within arbitrary child elements of the three core stanza types. Therefore it would be desirable to secure such data if possible.

Because [MSGFMT]Klyne, G. and D. Atkins, Common Presence and Instant Messaging (CPIM): Message Format, August 2004. specifies the ability to encapsulate any MIME type, the approach taken in this memo is to include arbitrary XMPP data in an XML media type named "application/xmpp+xml" as specified more fully in Section 10application/xmpp+xml Media Type below.

The following examples illustrate the structure of the "application/xmpp+xml" MIME type. (Note: The 'http://jabber.org/protocol/evil' namespace used in these examples is associated with an April Fool's protocol written to be the instant messaging equivalent of RFC 3514; it is included only as an instance of extended information included in an XML stanza and should not be taken seriously as a functional XMPP extension.)

Example 13: Message stanza with extended data contained in "application/xmpp+xml" MIME type:

|   <?xml version='1.0' encoding='UTF-8'?>
|   <xmpp xmlns='jabber:client'>
|     <message 
|         from='iago@example.com/pda' 
|         to='emilia@example.com/cell'>
|       <body> 
|         I told him what I thought, and told no more 
|         Than what he found himself was apt and true.  
|       </body>
|       <evil xmlns='http://jabber.org/protocol/evil'/>
|     </message>
|   </xmpp>
        

Example 14: Presence stanza with extended data contained in "application/xmpp+xml" MIME type:

|   <?xml version='1.0' encoding='UTF-8'?>
|   <xmpp xmlns='jabber:client'>
|     <presence from='iago@example.com/pda'>
|       <show>dnd</show>
|       <status>Fomenting dissension</status>
|       <evil xmlns='http://jabber.org/protocol/evil'/>
|     </presence>
|   </xmpp>
        

Example 15: IQ stanza with extended data contained in "application/xmpp+xml" MIME type:

|   <?xml version='1.0' encoding='UTF-8'?>
|   <xmpp xmlns='jabber:client'>
|     <iq type='result'
|         from='iago@example.com/pda'
|         to='emilia@example.com/cell'
|         id='evil1'>
|       <query xmlns='jabber:iq:version'>
|         <name>Stabber</name>
|         <version>666</version>
|         <os>FiendOS</os>
|       </query>
|       <evil xmlns='http://jabber.org/protocol/evil'/>
|     </iq>
|   </xmpp>
        

Just as with the "Message/CPIM" and "application/pidf+xml" objects, the "application/xmpp+xml" object would be signed and/or encrypted, then encapsulated within an XML CDATA section (see Section 2.7 of [XML]Bray, T., Paoli, J., Sperberg-McQueen, C. and E. Maler, Extensible Markup Language (XML) 1.0 (3rd ed), February 2004.) contained in an <e2e/> child of a <presence/> stanza, where the <e2e/> element is qualified by the 'urn:ietf:params:xml:ns:xmpp-e2e' namespace.



 TOC 

6. Rules for S/MIME Generation and Handling

6.1 Certificate Enrollment

[SMIME]Ramsdell, B., Secure/Multipurpose Internet Mail Extensions (S/MIME) Version 3.1 Message Specification, July 2004. does not specify how to obtain a certificate from a certificate authority, but instead mandates that every sending agent must already have a certificate. The PKIX Working Group has, at the time of this writing, produced two separate standards for certificate enrollment: [CMP]Adams, C. and S. Farrell, Internet X.509 Public Key Infrastructure Certificate Management Protocols, March 1999. and [CMC]Myers, M., Liu, X., Schaad, J. and J. Weinstein, Certificate Management Messages over CMS, April 2000.. Which method to use for certificate enrollment is outside the scope of this memo.

6.2 Certificate Retrieval

A receiving agent MUST provide some certificate retrieval mechanism in order to gain access to certificates for recipients of digital envelopes. This memo does not address how S/MIME agents handle certificates, only what they do after a certificate has been validated or rejected. S/MIME certification issues are covered in [CERT]Ramsdell, B., Secure/Multipurpose Internet Mail Extensions (S/MIME) Version 3.1 Certificate Handling, July 2004..

However, at a minimum, for initial S/MIME deployment, a user agent SHOULD automatically generate a message to an intended recipient requesting that recipient's certificate in a signed return message. Receiving and sending agents SHOULD also provide a mechanism to allow a user to "store and protect" certificates for correspondents in such a way so as to guarantee their later retrieval.

6.3 Certificate Names

End-entity certificates used by XMPP entities in the context of this memo SHOULD contain a valid instant messaging and presence address. The address SHOULD be specified as both an 'im:' URI (for instant messaging, as defined in [CPIM]Peterson, J., Common Profile for Instant Messaging (CPIM), August 2004.) and a 'pres:' URI (for presence, as defined in [CPP]Peterson, J., Common Profile for Presence (CPP), August 2004.); each of these URIs SHOULD be specified in a separate GeneralName entry of type uniformResourceIdentifier inside the subjectAltName (i.e., two separate entries). Information in the subject distinguished name SHOULD be ignored.

Each URI MUST be of the form <im:address> or <pres:address>, where the "address" portion is an XMPP address (also referred to as a Jabber Identifier or JID) as defined in [XMPP-CORE]Saint-Andre, P., XMPP Core, May 2004., prepended with the 'im:' or 'pres:' URI scheme. The address SHOULD be of the form <node@domain> (i.e., a "bare JID"), although any valid JID form MAY be used.

The value of the JID contained in the XMPP 'from' attribute MUST match a JID provided in the signer's certificate, with the exception that the resource identifier portion of the JID contained in the 'from' attribute SHOULD be ignored for matching purposes.

Receiving agents MUST check that the sending JID matches a JID provided in the signer's certificate, with the exception that the resource identifier portion of the JID contained in the 'from' attribute SHOULD be ignored for matching purposes. A receiving agent SHOULD provide some explicit alternate processing of the stanza if this comparison fails, which may be to display a message informing the recipient of the addresses in the certificate or other certificate details.

The subject alternative name extension is used in S/MIME as the preferred means to convey the instant messaging and presence address that corresponds to the entity for this certificate. Any XMPP address present in the certificate MUST be encoded using the ASN.1 Object Identifier "id-on-xmppAddr" as specified in Section 5.1.1 of [XMPP-CORE]Saint-Andre, P., XMPP Core, May 2004..

6.4 Transfer Encoding

Because it is expected that XMPP applications will not interface with older 7-bit systems, the transfer encoding (as defined in Section 3.1.2 of [SMIME]Ramsdell, B., Secure/Multipurpose Internet Mail Extensions (S/MIME) Version 3.1 Message Specification, July 2004.) MUST be "binary".

6.5 Order of Signing and Encrypting

If a stanza is both signed and encrypted, it SHOULD be signed first, then encrypted.

6.6 Inclusion of Certificates

If the sender and recipient are involved in an active messaging session over a period of time, the sending agent SHOULD include the sender's certificate along with at least one encrypted message stanza every five minutes. Outside the context of an active messaging session, the sending agent SHOULD include the sender's certificate along with each encrypted message stanza. A sending agent MAY include the sender's certificate along with each encrypted presence stanza. However, a sending agent SHOULD NOT include a certificate more than once every five minutes.

6.7 Attachment and Checking of Signatures

Sending agents SHOULD attach a signature to each encrypted XML stanza. If a signature is attached, a Content-Disposition header field (as defined in [DISP]Troost, R., Dorner, S. and K. Moore, Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field, August 1997.) SHOULD be included to specify how the signature is to be handled by the receiving application.

If the receiving agent determines that the signature attached to an encrypted XML stanza is invalid, it SHOULD NOT present the stanza to the intended recipient (human or application), SHOULD provide some explicit alternate processing of the stanza (which may be to display a message informing the recipient that the attached signature is invalid), and MAY return a stanza error to the sender as described under Recipient Error HandlingRecipient Error Handling.

6.8 Decryption

If the receiving agent is unable to decrypt the encrypted XML stanza, it SHOULD NOT present the stanza to the intended recipient (human or application), SHOULD provide some explicit alternate processing of the stanza (which may be to display a message informing the recipient that it has received a stanza that cannot be decrypted), and MAY return a stanza error to the sender as described under Recipient Error HandlingRecipient Error Handling.

6.9 Inclusion and Checking of Timestamps

Timestamps are included in "Message/CPIM" and "application/pidf+xml" objects to help prevent replay attacks. All timestamps MUST conform to [DATETIME]Klyne, G. and C. Newman, Date and Time on the Internet: Timestamps, July 2002. and be presented as UTC with no offset, including fractions of a second as appropriate. Absent a local adjustment to the sending agent's perceived time or the underlying clock time, the sending agent MUST ensure that the timestamps it sends to the receiver increase monotonically (if necessary by incrementing the seconds fraction in the timestamp if the clock returns the same time for multiple requests). The following rules apply to the receiving application:

6.10 Mandatory-to-Implement Cryptographic Algorithms

All implementations MUST support the following algorithms. Implementations MAY support other algorithms as well.

For CMS SignedData:

For CMS EnvelopedData:



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7. Recipient Error Handling

When an XMPP entity receives an XML stanza containing data that is signed and/or encrypted using the protocol described herein, several scenarios are possible:

Case #1:
The receiving application does not understand the protocol.
Case #2:
The receiving application understands the protocol and is able to decrypt the payload and verify the sender's signature.
Case #3:
The receiving application understands the protocol and is able to decrypt the payload and verify the sender's signature, but the timestamps fail the checks specified above under Checking of TimestampsInclusion and Checking of Timestamps.
Case #4:
The receiving application understands the protocol and is able to decrypt the payload but is unable to verify the sender's signature.
Case #5:
The receiving application understands the protocol but is unable to decrypt the payload.

In Case #1, the receiving application MUST do one and only one of the following: (1) ignore the <e2e/> extension, (2) ignore the entire stanza, or (3) return a <service-unavailable/> error to the sender, as described in [XMPP-CORE]Saint-Andre, P., XMPP Core, May 2004..

In Case #2, the receiving application MUST NOT return a stanza error to the sender, since this is the success case.

In Case #3, the receiving application MAY return a <not-acceptable/> error to the sender (as described in [XMPP-CORE]Saint-Andre, P., XMPP Core, May 2004.), optionally supplemented by an application-specific error condition element <bad-timestamp/> as shown below:

Example 16: Recipient returns <not-acceptable/> error:

<message from='romeo@example.net/orchard' type='chat'>
  <e2e xmlns='urn:ietf:params:xml:ns:xmpp-e2e'>
  [CDATA section here]
  </e2e>
  <error type='modify'>
    <not-acceptable xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
    <bad-timestamp xmlns='urn:ietf:params:xml:xmpp-e2e'/>
  </error>
</message>
        

In Case #4, the receiving application SHOULD return a <not-acceptable/> error to the sender (as described in [XMPP-CORE]Saint-Andre, P., XMPP Core, May 2004.), optionally supplemented by an application-specific error condition element <unverified-signature/> as shown below:

Example 17: Recipient returns <not-acceptable/> error:

<message from='romeo@example.net/orchard' type='chat'>
  <e2e xmlns='urn:ietf:params:xml:ns:xmpp-e2e'>
  [CDATA section here]
  </e2e>
  <error type='modify'>
    <not-acceptable xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
    <unverified-signature xmlns='urn:ietf:params:xml:xmpp-e2e'/>
  </error>
</message>
        

In Case #5, the receiving application SHOULD return a <bad-request/> error to the sender (as described in [XMPP-CORE]Saint-Andre, P., XMPP Core, May 2004.), optionally supplemented by an application-specific error condition element <decryption-failed/> as shown below:

Example 18: Recipient returns <bad-request/> error:

<message from='romeo@example.net/orchard' type='chat'>
  <e2e xmlns='urn:ietf:params:xml:ns:xmpp-e2e'>
  [CDATA section here]
  </e2e>
  <error type='modify'>
    <bad-request xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
    <decryption-failed xmlns='urn:ietf:params:xml:xmpp-e2e'/>
  </error>
</message>
        


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8. 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. The CPIM specifications (specifically [MSGFMT]Klyne, G. and D. Atkins, Common Presence and Instant Messaging (CPIM): Message Format, August 2004. and [PIDF]Sugano, H., Fujimoto, S., Klyne, G., Bateman, A., Carr, W. and J. Peterson, Presence Information Data Format (PIDF), August 2004. define the common profiles to be used for interoperability between instant messaging and presence services that comply with [IMP-REQS]Day, M., Aggarwal, S. and J. Vincent, Instant Messaging / Presence Protocol Requirements, February 2000.. In the case of communications between an XMPP service and a non-XMPP service, we can visualize this relationship as follows:

+-------------+        +-------------+        +------------+
|             |        |             |        |            |
|    XMPP     |        |  XMPP-CPIM  |        |  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 an XMPP-CPIM gateway. In particular:

The wrapped S/MIME object MUST be immutable and MUST NOT be modified by an XMPP-CPIM gateway.



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9. urn:ietf:params:xml:xmpp-e2e Namespace

The <e2e xmlns='urn:ietf:params:xml:ns:xmpp-e2e'/> element is a wrapper for an XML CDATA section (see Section 2.7 of [XML]Bray, T., Paoli, J., Sperberg-McQueen, C. and E. Maler, Extensible Markup Language (XML) 1.0 (3rd ed), February 2004.) that contains a "Message/CPIM", "application/pidf+xml", or "application/xmpp+xml" object. Thus the 'urn:ietf:params:xml:xmpp-e2e' namespace has no inherent semantics, and the semantics of the encapsulated object are defined by one of the following specifications:

Although the "application/xmpp+xml" media type is specified in this document, the <xmpp/> element is simply a wrapper for a <message/>, <presence/>, or <iq/> stanza, where the semantics of those stanza types are specified in [XMPP-CORE]Saint-Andre, P., XMPP Core, May 2004..

Given that the 'urn:ietf:params:xml:ns:xmpp-e2e' namespace has no inherent semantics and specifies a using protocol only, versioning is the responsibility of the protocols that define the encapsulated objects ([MSGFMT]Klyne, G. and D. Atkins, Common Presence and Instant Messaging (CPIM): Message Format, August 2004., [PIDF]Sugano, H., Fujimoto, S., Klyne, G., Bateman, A., Carr, W. and J. Peterson, Presence Information Data Format (PIDF), August 2004., and [XMPP-CORE]Saint-Andre, P., XMPP Core, May 2004.).



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10. application/xmpp+xml Media Type

The "application/xmpp+xml" media type adheres to the guidelines specified in [XML-MEDIA]Murata, M., St. Laurent, S. and D. Kohn, XML Media Types, January 2001.. The root element for this MIME type is <xmpp/>, and the root element MUST contain one and only one child element, corresponding to one of the XMPP stanza types (i.e., message, presence, or iq) if the default namespace is 'jabber:client' or 'jabber:server' as defined in [XMPP-CORE]Saint-Andre, P., XMPP Core, May 2004.. The character encoding for this XML media type MUST be UTF-8, in accordance with Section 11.5 of [XMPP-CORE]Saint-Andre, P., XMPP Core, May 2004..



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11. Security Considerations

This entire memo discusses security. Detailed security considerations for instant messaging and presence protocols are given in [IMP-REQS]Day, M., Aggarwal, S. and J. Vincent, Instant Messaging / Presence Protocol Requirements, February 2000. (Sections 5.1 through 5.4), and for XMPP in particular are given in [XMPP-CORE]Saint-Andre, P., XMPP Core, May 2004. (Sections 12.1 through 12.6). In addition, all of the security considerations specified in [XML-MEDIA]Murata, M., St. Laurent, S. and D. Kohn, XML Media Types, January 2001. apply to the "application/xmpp+xml" media type.

The end-to-end security method defined here MAY result in exchanging secured instant messages and presence information through a gateway that implements the CPIM specifications. Such a gateway MUST be compliant with the minimum security requirements of the instant messaging and presence protocols with which it interfaces.



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12. IANA Considerations

12.1 XML Namespace Name for e2e Data in XMPP

A URN sub-namespace of signed and encrypted content for the Extensible Messaging and Presence Protocol (XMPP) is defined as follows. (This namespace name adheres to the format defined in [XML-REG]Mealling, M., The IETF XML Registry, January 2004..)

URI:
urn:ietf:params:xml:ns:xmpp-e2e
Specification:
XXXX
Description:
This is an XML namespace name of signed and encrypted content for the Extensible Messaging and Presence Protocol as defined by XXXX.
Registrant Contact:
IESG, <iesg@ietf.org>

12.2 Content-type Registration for "application/xmpp+xml"

To: ietf-types@iana.org

Subject: Registration of MIME media type application/xmpp+xml

MIME media type name: application
MIME subtype name: xmpp+xml
Required parameters: (none)
Optional parameters: (charset)
Same as charset parameter of application/xml as specified in RFC 3023; per Section 11.5 of [draft-ietf-xmpp-core-24], the charset must be UTF-8.
Encoding considerations:
Same as encoding considerations of application/xml as specified in RFC 3023; per Section 11.5 of [draft-ietf-xmpp-core-24], the encoding must be UTF-8.
Security considerations:
All of the security considerations specified in RFC 3023 and [draft-ietf-xmpp-core-24] apply to this XML media type. Refer to Section 11Security Considerations of XXXX.
Interoperability considerations: (none)
Specification:
XXXX
Applications which use this media type:
XMPP-compliant instant messaging and presence systems.
Additional information: (none)
Person and email address to contact for further information:
IESG, <iesg@ietf.org>
Intended usage:
COMMON
Author/Change controller:
IETF, XMPP Working Group


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13. References



 TOC 

13.1 Normative References

[CERT] Ramsdell, B., "Secure/Multipurpose Internet Mail Extensions (S/MIME) Version 3.1 Certificate Handling", RFC 3850, July 2004.
[CMS] Housley, R., "Cryptographic Message Syntax (CMS)", RFC 3852, July 2004.
[CMS-AES] Schaad, J., "Use of the Advanced Encryption Standard (AES) Encryption Algorithm in Cryptographic Message Syntax (CMS)", RFC 3565, July 2003.
[CMS-ALG] Housley, R., "Cryptographic Message Syntax (CMS) Algorithms", RFC 3370, August 2002.
[CPIM] Peterson, J., "Common Profile for Instant Messaging (CPIM)", RFC 3860, August 2004.
[CPP] Peterson, J., "Common Profile for Presence (CPP)", RFC 3859, August 2004.
[DATETIME] Klyne, G. and C. Newman, "Date and Time on the Internet: Timestamps", RFC 3339, July 2002.
[DISP] Troost, R., Dorner, S. and K. Moore, "Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field", RFC 2183, August 1997 (TXT, HTML, XML).
[IMP-MODEL] Day, M., Rosenberg, J. and H. Sugano, "A Model for Presence and Instant Messaging", RFC 2778, February 2000.
[IMP-REQS] Day, M., Aggarwal, S. and J. Vincent, "Instant Messaging / Presence Protocol Requirements", RFC 2779, February 2000.
[MSGFMT] Klyne, G. and D. Atkins, "Common Presence and Instant Messaging (CPIM): Message Format", RFC 3862, August 2004.
[MULTI] Galvin, J., Murphy, S., Crocker, S. and N. Freed, "Security Multiparts for MIME: Multipart/Signed and Multipart/Encrypted", RFC 1847, October 1995.
[PIDF] Sugano, H., Fujimoto, S., Klyne, G., Bateman, A., Carr, W. and J. Peterson, "Presence Information Data Format (PIDF)", RFC 3863, August 2004.
[SMIME] Ramsdell, B., "Secure/Multipurpose Internet Mail Extensions (S/MIME) Version 3.1 Message Specification", RFC 3851, July 2004.
[TERMS] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[X509] Housley, R., Polk, W., Ford, W. and D. Solo, "Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile", RFC 3280, April 2002.
[XML-MEDIA] Murata, M., St. Laurent, S. and D. Kohn, "XML Media Types", RFC 3023, January 2001.
[XMPP-CORE] Saint-Andre, P., "XMPP Core", draft-ietf-xmpp-core-24 (work in progress), May 2004.
[XMPP-IM] Saint-Andre, P., "XMPP Instant Messaging", draft-ietf-xmpp-im-22 (work in progress), April 2004.


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13.2 Informative References

[CAPS] Hildebrand, J. and P. Saint-Andre, "Entity Capabilities", JSF JEP 0115, August 2004.
[CMC] Myers, M., Liu, X., Schaad, J. and J. Weinstein, "Certificate Management Messages over CMS", RFC 2797, April 2000.
[CMP] Adams, C. and S. Farrell, "Internet X.509 Public Key Infrastructure Certificate Management Protocols", RFC 2510, March 1999.
[DISCO] Hildebrand, J., Millard, P., Eatmon, R. and P. Saint-Andre, "Service Discovery", JSF JEP 0030, July 2004.
[MUC] Saint-Andre, P., "Multi-User Chat", JSF JEP 0045, June 2004.
[XML] Bray, T., Paoli, J., Sperberg-McQueen, C. and E. Maler, "Extensible Markup Language (XML) 1.0 (3rd ed)", W3C REC-xml, February 2004.
[XML-REG] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, January 2004.
[XMPP-CPIM] Saint-Andre, P., "Mapping the Extensible Messaging and Presence Protocol (XMPP) to Common Presence and Instant Messaging (CPIM)", draft-ietf-xmpp-cpim-05 (work in progress), May 2004.


 TOC 

Author's Address

  Peter Saint-Andre
  Jabber Software Foundation
EMail:  stpeter@jabber.org


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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:element name='decryption-failed' type='empty'/>
  <xs:element name='signature-unverified' type='empty'/>
  <xs:element name='bad-timestamp' type='empty'/>

  <xs:simpleType name='empty'>
    <xs:restriction base='xs:string'>
      <xs:enumeration value=''/>
    </xs:restriction>
  </xs:simpleType>

</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-08

B.2 Changes from draft-ietf-xmpp-e2e-07

B.3 Changes from draft-ietf-xmpp-e2e-06

B.4 Changes from draft-ietf-xmpp-e2e-05

B.5 Changes from draft-ietf-xmpp-e2e-04

B.6 Changes from draft-ietf-xmpp-e2e-03

B.7 Changes from draft-ietf-xmpp-e2e-02

B.8 Changes from draft-ietf-xmpp-e2e-01

B.9 Changes from draft-ietf-xmpp-e2e-00



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Intellectual Property Statement

Disclaimer of Validity

Copyright Statement

Acknowledgment