XEP-0246: End-to-End XML Streams

This specification defines methods for communicating via end-to-end XML streams over a logical or physical connection that provides a reliable transport between two endpoints.

WARNING: This Standards-Track document is Experimental. Publication as an XMPP Extension Protocol does not imply approval of this proposal by the XMPP Standards Foundation. Implementation of the protocol described herein is encouraged in exploratory implementations, but production systems should not deploy implementations of this protocol until it advances to a status of Draft.

Document Information

Series: XEP
Number: 0246
Publisher: XMPP Standards Foundation
Status: Experimental
Type: Standards Track
Version: 0.1
Last Updated: 2008-06-18
Approving Body: XMPP Council
Dependencies: XMPP Core
Supersedes: None
Superseded By: None
Short Name: NOT_YET_ASSIGNED
Registry: <http://www.xmpp.org/registrar/NOT_YET_ASSIGNED.html>
Wiki Page: <http://wiki.jabber.org/index.php/End-to-End XML Streams (XEP-0246)>

Author Information

Legal Notices

Discussion Venue

The preferred venue for discussion of this document is the Standards discussion list: <http://mail.jabber.org/mailman/listinfo/standards>.

Errata may be sent to <editor@xmpp.org>.

Relation to XMPP

The Extensible Messaging and Presence Protocol (XMPP) is defined in the XMPP Core (RFC 3920) and XMPP IM (RFC 3921) 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.

Conformance Terms

The following 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".

Table of Contents

1. Introduction

XMPP as defined in RFC 3920 [1] does not support direct interaction between endpoints, since it requires a client to authenticate an XML stream with a "home" server and send of all of its outbound XML stanzas through that server (which potentially can route those stanzas through a peer server for delivery to the intended recipient). However, in some scenarios it is desirable to establish end-to-end XML streams between two endpoints instead of relying on the standard client-server architecture. These scenarios include:

• Two endpoints cannot access an XMPP server
• Two endpoints want to enforce end-to-end encryption
• Two endpoints want to send a high volume of XMPP traffic but the intermediate servers enforce rate limits

The first scenario is addressed by Link-Local Messaging [2]. The second and third scenarios are addressed by Jingle XML Streams [3]. Both of those technologies result in the establishment of a direct or mediated connection between two endpoints, such as a direct TCP connection, a bytestream through SOCKS5 (SOCKS5 Bytestreams [4]) or XMPP itself (In-Band Bytestreams [5]), or other future transport methods such as TCP Candidates with Interactive Connectivity Establishment (ICE) [6].

Once two endpoints have opened a direct or mediated connection, they can establish an XML stream over that connection for end-to-end "("e2e") communication. We call this an "e2e stream".

2. Initiating an e2e Stream

The initiator and recipient essentially follow the process defined in RFC 3920 to establish XML streams between themselves.

First, the initiator opens an XML stream to the recipient over the negotiated transport.

Example 1. Opening a Stream

<stream:stream 
        xmlns='jabber:client' 
        xmlns:stream='http://etherx.jabber.org/streams'
        from='romeo@forza'
        to='juliet@pronto'
        version='1.0'>
  

In accordance with rfc3921bis [7], the initial stream header SHOULD include the 'to' and 'from' attributes. In the case of XEP-0174, these SHOULD be the username@machine-name advertised in the PTR record. In the case of Jingle XML Streams, these SHOULD be the bare JIDs (<localpart@domain.tld> or <domain.tld>) of the entities as communicated via XMPP.

If the initiator supports stream features and the other stream-related aspects of XMPP 1.0 as specified in RFC 3920, then it SHOULD include the version='1.0' flag as shown in the previous example.

The recipient then responds with a stream header as well:

Example 2. Stream Header Response

<stream:stream 
        xmlns='jabber:client' 
        xmlns:stream='http://etherx.jabber.org/streams'
        from='juliet@pronto'
        to='romeo@forza'
        version='1.0'>
  

If both the initiator and recipient included the version='1.0' flag, the recipient SHOULD also send stream features as specified in RFC 3920:

Example 3. Recipient Sends Stream Features

<stream:features>
  <starttls xmlns='urn:ietf:params:xml:ns:xmpp-tls'/>
</stream:features>
  

3. Stream Encryption

The mere exchange of stream headers results in an unencrypted and unauthenticated channel between the two entities. The entities SHOULD upgrade the channel to an encrypted stream using the XMPP STARTTLS command defined in XMPP Core [8] using RFC 4346 [9], optionally followed by SASL negotiation for mutual authentication (see RFC 4422 [10]).

End-to-end XML streams can be negotiated between two XMPP clients, between an XMPP client and a remote XMPP service (i.e., a service with which a client does not have a direct XML stream, such as a remote Multi-User Chat [11] room), or between two remote XMPP services. Therefore, if standard X.509 certificates are used then a party to an e2e XML stream will present either a client certificate or a server certificate as appropriate. If X.509 certificates are used, they MUST at a minimum be generated and validated in accordance with the certificate guidelines guidelines provided in rfc3920bis [12]; however, applications of end-to-end XML streams MAY define supplemental guidelines for certificate validation in the context of particular architectures, such as XEP-0174 for link-local streams and XEP-0247 for direct or mediated streams negotiated through XMPP servers.

To ease the transition from the PGP-based object encryption method specified in Current Jabber OpenPGP Usage [13], clients using TLS for e2e streams MAY use the OpenPGP TLS extension defined in RFC 5081 [14] (if available).

Use of other TLS extensions MAY be appropriate as well, including those defined in RFC 4346 [15] and RFC 5054 [16].

4. Exchanging Stanzas

Once the streams are established, either entity then can send XMPP message, presence, and IQ stanzas, with or without 'to' and 'from' addresses.

Example 4. Sending a Message

<message from='romeo@forza' to='juliet@pronto'>
  <body>M'lady, I would be pleased to make your acquaintance.</body>
</message>
  

Example 5. A Reply

<message from='juliet@pronto' to='romeo@forza'>
  <body>Art thou not Romeo, and a Montague?</body>
</message>
  

5. Ending an e2e Stream

To end the stream, either party closes the XML stream:

Example 6. Closing the Stream

</stream:stream>
  

The other party then closes the stream in the other direction as well:

Example 7. Closing the Stream

</stream:stream>
  

Both parties then SHOULD close the logical or physical connection between them.

6. Security Considerations

End-to-end streams SHOULD be encrypted; see the Stream Encryption section of this document.

7. IANA Considerations

This document requires no interaction with the Internet Assigned Numbers Authority (IANA) [17].

8. XMPP Registrar Considerations

This document requires no interaction with the XMPP Registrar [18].

Notes

Revision History

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