Network Working Group J. Miller
Internet-Draft P. Saint-Andre
Expires: May 4, 2003 Jabber Software Foundation
November 03, 2002
XMPP Core
draft-miller-xmpp-core-02
Status of this Memo
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Copyright Notice
Copyright (C) The Internet Society (2002). All Rights Reserved.
Abstract
This document describes the core features of the eXtensible Messaging
and Presence Protocol (XMPP), which is used by the servers, clients,
and other applications that comprise the Jabber network.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2 Conventions Used in this Document . . . . . . . . . . . . . 4
1.3 Discussion Venue . . . . . . . . . . . . . . . . . . . . . . 4
1.4 Intellectual Property Notice . . . . . . . . . . . . . . . . 4
2. Generalized Architecture . . . . . . . . . . . . . . . . . . 5
2.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2 Host . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.3 Node . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.4 Service . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.4.1 Gateway . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.5 Network . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Addressing Scheme . . . . . . . . . . . . . . . . . . . . . 8
3.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.2 Domain Identifier . . . . . . . . . . . . . . . . . . . . . 8
3.3 Node Identifier . . . . . . . . . . . . . . . . . . . . . . 8
3.4 Resource Identifier . . . . . . . . . . . . . . . . . . . . 9
3.5 URIs . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
4. XML Streams . . . . . . . . . . . . . . . . . . . . . . . . 11
4.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 11
4.2 Restrictions . . . . . . . . . . . . . . . . . . . . . . . . 12
4.3 Stream Attributes . . . . . . . . . . . . . . . . . . . . . 12
4.4 Namespace Declarations . . . . . . . . . . . . . . . . . . . 13
4.5 Stream Errors . . . . . . . . . . . . . . . . . . . . . . . 14
4.6 Example . . . . . . . . . . . . . . . . . . . . . . . . . . 14
5. Stream Authentication . . . . . . . . . . . . . . . . . . . 17
5.1 SASL Authentication . . . . . . . . . . . . . . . . . . . . 17
5.1.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 17
5.1.2 Example . . . . . . . . . . . . . . . . . . . . . . . . . . 18
5.2 Dialback Authentication . . . . . . . . . . . . . . . . . . 20
5.2.1 Dialback Protocol . . . . . . . . . . . . . . . . . . . . . 22
6. Core Data Elements . . . . . . . . . . . . . . . . . . . . . 26
6.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 26
6.2 Common Attributes . . . . . . . . . . . . . . . . . . . . . 26
6.2.1 to . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
6.2.2 from . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
6.2.3 id . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
6.2.4 type . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
6.3 Message Chunks . . . . . . . . . . . . . . . . . . . . . . . 27
6.3.1 Types of Message . . . . . . . . . . . . . . . . . . . . . . 27
6.3.2 Children . . . . . . . . . . . . . . . . . . . . . . . . . . 27
6.4 Presence Chunks . . . . . . . . . . . . . . . . . . . . . . 28
6.4.1 Types of Presence . . . . . . . . . . . . . . . . . . . . . 28
6.4.2 Children . . . . . . . . . . . . . . . . . . . . . . . . . . 29
6.5 IQ Chunks . . . . . . . . . . . . . . . . . . . . . . . . . 30
6.5.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 30
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6.5.2 Types of IQ . . . . . . . . . . . . . . . . . . . . . . . . 30
6.5.3 Children . . . . . . . . . . . . . . . . . . . . . . . . . . 31
6.6 Extended Namespaces . . . . . . . . . . . . . . . . . . . . 31
7. XML Usage within XMPP . . . . . . . . . . . . . . . . . . . 33
7.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 33
7.2 Namespaces . . . . . . . . . . . . . . . . . . . . . . . . . 33
7.3 Validation . . . . . . . . . . . . . . . . . . . . . . . . . 33
7.4 Character Encodings . . . . . . . . . . . . . . . . . . . . 34
7.5 Inclusion of Text Declaration . . . . . . . . . . . . . . . 34
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . 35
9. Internationalization Considerations . . . . . . . . . . . . 36
10. Security Considerations . . . . . . . . . . . . . . . . . . 37
10.1 Node-to-Host Communications . . . . . . . . . . . . . . . . 37
10.2 Host-to-Host Communications . . . . . . . . . . . . . . . . 37
10.3 Use of SASL . . . . . . . . . . . . . . . . . . . . . . . . 37
References . . . . . . . . . . . . . . . . . . . . . . . . . 38
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 39
A. Standard Error Codes . . . . . . . . . . . . . . . . . . . . 40
B. Formal Definitions . . . . . . . . . . . . . . . . . . . . . 42
B.1 streams namespace . . . . . . . . . . . . . . . . . . . . . 42
B.1.1 DTD . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
B.1.2 Schema . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
B.2 sasl namespace . . . . . . . . . . . . . . . . . . . . . . . 43
B.2.1 DTD . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
B.2.2 Schema . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
B.3 jabber:client namespace . . . . . . . . . . . . . . . . . . 45
B.3.1 DTD . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
B.3.2 Schema . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
C. OpenPGP Usage . . . . . . . . . . . . . . . . . . . . . . . 50
C.1 Signing Presence . . . . . . . . . . . . . . . . . . . . . . 50
C.2 Encrypting Messages . . . . . . . . . . . . . . . . . . . . 51
Full Copyright Statement . . . . . . . . . . . . . . . . . . 53
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1. Introduction
1.1 Overview
The eXtensible Messaging and Presence Protocol (XMPP) is an open, XML
[1] protocol for near-real-time messaging and presence. Currently,
there exist multiple implementations of the protocol, mostly offered
under the name of Jabber. In addition, there are countless
deployments of these implementations, which provide instant messaging
(IM) and presence services at and among thousands of domains to a
user base that is estimated at over one million end users. The
current document defines the core constituents of XMPP; XMPP IM [2]
defines the extensions necessary to provide basic instant messaging
and presence functionality that addresses the requirements defined in
RFC 2779 [3].
1.2 Conventions Used in this Document
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 [4].
1.3 Discussion Venue
The authors welcome discussion and comments related to the topics
presented in this document, preferably on the "xmppwg@jabber.org"
mailing list (archives and subscription information are available at
http://www.jabber.org/cgi-bin/mailman/listinfo/xmppwg/).
1.4 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. Generalized Architecture
2.1 Overview
Although XMPP is not wedded to any specific network architecture, to
this point it has usually been implemented via a typical client-
server architecture, wherein a client utilizing XMPP accesses a
server over a TCP [5] socket. While it can be helpful to keep that
specific architecture in mind when seeking to understand XMPP, we
have herein abstracted from any specific architecture and have
described the architecture in a more generalized fashion.
The following diagram provides a high-level overview of this
generalized architecture (where "-" represents communications that
use XMPP and "=" represents communications that use any other
protocol).
Connection Map
S1 S2
\ /
N1 - H1 - H2 - N3
/ \
N2 - G1 = F1 = C1
The symbols are as follows:
o N1, N2, N3 -- Nodes on the Jabber network
o H1, H2 -- Hosts on the Jabber network
o S1, S2 -- Services that add functionality to a primary host
o G1 -- A gateway that translates between XMPP and the protocol(s)
used on a foreign messaging network
o F1 -- A foreign messaging network
o C1 -- A client on a foreign messaging network
2.2 Host
A host acts as an intelligent abstraction layer for XMPP
communications. Its primary responsibilities are to manage
connections from or sessions for other entities (in the form of XML
streams to and from authorized nodes, trusted services, and other
hosts) and to route appropriately-addressed XML data "chunks" among
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such entities over XML streams. Most XMPP-compliant hosts also
assume responsibility for the storage of data that is used by nodes
or services (e.g., the contact list for each IM user); in this case,
the XML data is processed directly by the host itself on behalf of
the node or service and is not routed to another entity.
2.3 Node
Most nodes connect directly to a host over a TCP socket and use XMPP
to take full advantage of the functionality provided by a host and
its associated services. (Clients on foreign messaging networks may
also be part of the architecture, made accessable via a gateway to
that network.) Multiple resources (e.g., devices or locations) MAY
connect simultaneously to a host on behalf of each authorized node,
with each resource connecting over a discrete TCP socket and
differentiated by the resource identifier of a JID (Section 3) (e.g.,
node@host/home vs. node@host/work). The port assigned by the IANA
[6] for connections between a Jabber node and a Jabber host is 5222.
For further details about node-to-host communications for the purpose
of instant messaging and presence, refer to XMPP IM [2].
2.4 Service
In addition to the basic functionality provided by a host, additional
functionality is made possible by connecting trusted services to a
host. Examples include multi-user chat (a.k.a. conferencing), real-
time alert systems, custom authentication modules, database
connectivity, and translation to foreign messaging protocols. There
is no set port on which services communicate with hosts; this is left
up to the administrator of the service or host. Communications
between services and hosts are not defined in this document.
2.4.1 Gateway
A gateway is a special-purpose service whose primary function is to
translate XMPP into the protocol(s) of another messaging system, as
well as to translate the return data back into XMPP. Examples are
gateways to Internet Relay Chat (IRC), Short Message Service (SMS),
SMTP, and foreign instant messaging networks such as Yahoo!, MSN,
ICQ, and AIM. Communications between gateways and hosts, and between
gateways and the foreign messaging system, are not defined in this
document.
2.5 Network
Because each host is identified by a network address (typically a DNS
hostname) and because host-to-host communications are a simple
extension of the node-to-host protocol, in practice the system
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consists of a network of hosts that inter-communicate. Thus node-
a@host1 is able to exchange messages, presence, and other information
with node-b@host2. This pattern is familiar from messaging protocols
(such as SMTP) that make use of network addressing standards. The
usual method for providing a connection between two hosts is to open
a TCP socket on the IANA-assigned port 5269 and to negotiate a
connection using the Dialback Protocol (Section 5.2) as defined in
this document.
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3. Addressing Scheme
3.1 Overview
Any entity that can be considered a network endpoint (i.e., an ID on
the network) and that can communicate using XMPP is considered a
Jabber Entity. All such entities are uniquely addressable in a form
that is consistent with RFC 2396 [7]. In particular, a valid Jabber
Identifier (JID) contains a set of ordered elements formed of a
domain identifier, node identifier, and resource identifier in the
following format: [node@]domain[/resource].
All JIDs are based on the foregoing structure. The most common use
of this structure is to identify an IM user, the host to which the
user connects, and the user's active session or connection in the
form of user@host/resource. However, other nodes are possible; for
example, a specific conference room is offered by a multi-user chat
service is addressed as room@service, where "room" is the name of the
room and "service" is the hostname of the chat service.
3.2 Domain Identifier
The domain identifier is the primary identifier and is the only
required element of a JID (a simple domain identifier is a valid
JID). It usually represents the network gateway or "primary" host to
which other entities connect for XML routing and data management
capabilities. However, the entity referenced by a domain identifier
is not always a host, and may be a service that is addressed as a
subdomain of a host and that provides functionality above and beyond
the capabilities of a host (a multi-user chat service, a user
directory, a gateway to a foreign messaging system, etc.).
The domain identifier for every host or service that will communicate
over a network SHOULD resolve to a Fully Qualified Domain Name, and a
domain identifier SHOULD conform to RRC 952 [8] and REF 1123 [9].
Specifically, a domain identifier is case-insensitive 7-bit ASCII and
is limited to 255 bytes.
3.3 Node Identifier
The node identifier is an optional secondary identifier. It usually
represents the entity requesting and using network access provided by
the host (e.g., a client), although it can also represent other kinds
of entities (e.g., a multi-user chat room associated with a
conference service). The entity represented by a node identifier is
addressed within the context of a specific domain (e.g., user@host).
Node identifiers are restricted to 256 bytes. A node identifier may
contain any Unicode character higher than #x20 with the exception of
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the following:
o #x22 (")
o #x26 (&)
o #x27 (')
o #x3A (:)
o #x3C (<)
o #x3E (>)
o #x40 (@)
o #x7F (del)
o #xFFFE (BOM)
o #xFFFF (BOM)
Case is preserved, but comparisons are made in case-normalized
canonical form.
3.4 Resource Identifier
The resource identifer is an optional third identifier. It
represents a specific session, connection (e.g., a device or
location), or object (e.g., a participant in a multi-user chat room)
belonging to a node. A node may maintain multiple resources
simultaneously. A resource identifier is restricted to 256 bytes in
length. A resource identifier MAY include any Unicode character
greater than #x20, except #xFFFE and #xFFFF; if the Unicode character
is a valid XML character as defined in Section 2.2 of [1], it MUST be
suitably escaped for inclusion within an XML stream. Resource
identifiers are case sensitive.
3.5 URIs
Full conformance with [7] would be valuable. This would most likely
be effected through use of an 'xmpp:' URI scheme of the following
form:
<xmpp>:[<node-identifier>@]<domain-identifier>[?<query>]
At a minimum, the 'message' and 'presence' query types would be
defined, with the likely addition of query types for 'subscribe' (to
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manage a subscription to teh presence of another entity) and 'roster'
(to manage the representation of another entity in one's contact
list). However, the use of such URIs has not yet been standardized.
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4. XML Streams
4.1 Overview
Two fundamental concepts make possible the rapid, asynchronous
exchange of relatively small payloads of structured information
between presence-aware entities: XML streams and, as a result,
discrete units of structured information that are referred to as "XML
chunks". (Note: in this overview we use the example of
communications between a node and host; however XML streams are more
generalized and may be used for communications among hosts and
services as well.)
In order to connect to a host, a node must initiate an XML stream by
sending a <stream> tag to the host, optionally preceded by a text
declaration specifying the XML version supported and the character
encoding. A compliant entity must accept any namespace prefix on the
<stream/> element; however, for historical reasons some entities may
accept only a 'stream' prefix, resulting in use of a <stream:stream/>
element. The host should then reply with a second XML stream back to
the node, again optionally preceded by a text declaration.
Within the context of an XML stream, a sender may send a discrete
semantic unit of structured information to any recipient. This unit
of structured information is a well-balanced XML chunk, such as a
message, presence, or IQ chunk (a chunk of an XML document is said to
be well-balanced if it matches production [43] content of [1]).
These chunks exist at the direct child level (depth=1) of the root
<stream/> element. The start of any XML chunk is unambiguously
denoted by the element start tag at depth=1 (e.g., <presence>), and
the end of any XML chunk is unambiguously denoted by the
corresponding close tag at depth=1 (e.g., </presence>). Each XML
chunk may contain child elements or CDATA sections as necessary in
order to convey the desired information from the sender to the
recipient. The session is closed at the node's request by sending a
closing </stream> tag to the host.
Thus a node's session with a host can be seen as two open-ended XML
documents that are built up through the accumulation of the XML
chunks that are sent over the course of the session (one from the
node to the host and one from the host to the node), and the root
<stream/> element may be considered the document entity for those
streams. In essence, then, an XML stream acts as an envelope for all
the XML chunks sent during a session. We can represent this
graphically as follows:
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|-------------------|
| <stream> |
|-------------------|
| <message to=''> |
| <body/> |
| </message> |
|-------------------|
| <presence to=''> |
| <show/> |
| </presence> |
|-------------------|
| <iq to=''> |
| <query/> |
| </iq> |
|-------------------|
| </stream> |
|-------------------|
4.2 Restrictions
XML streams are used to transport a subset of XML. Specifically, XML
streams SHOULD NOT contain processing instructions, non-predefined
entities (as defined in Section 4.6 of [1]), comments, or DTDs. Any
such XML data SHOULD be ignored.
4.3 Stream Attributes
The attributes of the stream element are as follows (we now
generalize the endpoints by using the terms "initiating entity" and
"receiving entity"):
o to -- The 'to' attribute should be used only in the XML stream
from the initiating entity to the receiving entity, and must be
set to the JID of the receiving entity. There should be no 'to'
attribute set in the XML stream by which the receiving entity
replies to the initiating entity; however, if a 'to' attribute is
included, it SHOULD be ignored by the receiving entity.
o from -- The 'from' attribute should be used only in the XML stream
from the receiving entity to the initiating entity, and must be
set to the JID of the receiving entity granting access to the
initiating entity. There should be no 'from' attribute on the XML
stream sent from the initiating entity to the receiving entity;
however, if a 'from' attribute is included, it SHOULD be ignored
by the receiving entity.
o id -- The 'id' attribute should be used only in the XML stream
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from the receiving entity to the initiating entity. This
attribute is a unique identifier created by the receiving entity
to function as a session key for the initiating entity's session
with the receiving entity. There should be no 'id' attribute on
the XML stream sent from the initiating entity to the receiving
entity; however, if an 'id' attribute is included, it SHOULD be
ignored by the receiving entity.
We can summarize these values as follows:
| initiating to receiving | receiving to initiating
------------------------------------------------------------
to | JID of receiver | ignored
from | ignored | JID of receiver
id | ignored | session key
4.4 Namespace Declarations
The stream element may also contain namespace declarations as defined
in [11].
A stream namespace declaration is REQUIRED in both XML streams. A
compliant entity must accept any namespace prefix on the <stream/>
element; however, for historical reasons some entities may accept
only a 'stream' prefix, resulting in use of a <stream:stream/>
element as the stream root. The value of the stream namespace MUST
be "http://etherx.jabber.org/streams".
A default namespace declaration ('xmlns') is REQUIRED and is used in
both XML streams in order to scope the allowable first-level children
of the root stream element for both streams. This namespace
declaration must be the same for the initiating stream and the
responding stream so that both streams are scoped consistently.
XML streams function as containers for any XML chunks sent
asynchronously between network endpoints. It should be possible to
scope an XML stream with any default namespace declaration, i.e., it
should be possible to send any properly-namespaced XML chunk over an
XML stream. However, for historical reasons existing implementations
will support only the following default namespaces:
o jabber:client -- this default namespace is declared when the
stream is used for communications between a node and a host
o jabber:server -- this default namespace is declared when the
stream is used for communications between two hosts
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o jabber:component:accept or jabber:component:connect -- one of
these default namespaces is declared when the stream is used for
communications between a host and a trusted service
This document addresses the jabber:client and jabber:server
namespaces only (indeed these two namespaces have identical schemas).
The jabber:component:* namespaces are outside the scope of this
document.
4.5 Stream Errors
The root stream element MAY contain an error child element (e.g.,
<stream:error/> if the stream namespace prefix is 'stream'). The
error child is used to signify that a stream-level error has
occurred. Examples include the sending of invalid XML, the shutdown
of a host, an internal server error such as the shutdown of a session
manager, and an attempt by a node to authenticate as the same
resource that is currently connected. If an error occurs at the
level of the stream, the entity (initiating entity or receiving
entity) that detects the error should send a stream error to the
other entity specifying why the streams are being closed and then
send a closing </stream> tag. XML of the following form is sent
within the context of an existing stream:
<stream:stream ...>
...
<stream:error>
Error message (e.g., "Invalid XML")
</stream:error>
</stream:stream>
4.6 Example
The following is a simple stream-based session of a node on a host
(where the NODE lines are sent from the node to the host, and the
HOST lines are sent from the host to the node):
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A simple session:
NODE: <?xml version='1.0'?>
<stream:stream
to='host'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'>
HOST: <?xml version='1.0'?>
<stream:stream
from='host'
id='id_123456789'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'>
NODE: <message from='node@host' to='receiving-ID'>
NODE: <body>Watson come here, I need you!</body>
NODE: </message>
HOST: <message from='receiving-ID' to='node@host'>
HOST: <body>I'm on my way!</body>
HOST: </message>
NODE: </stream:stream>
HOST: </stream:stream>
These are in actuality a sending stream and a receiving stream, which
can be viewed a-chronologically as two XML documents:
NODE: <?xml version='1.0'?>
<stream:stream
to='host'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'>
NODE: <message from='node@host' to='receiving-ID'>
NODE: <body>Watson come here, I need you!</body>
NODE: </message>
NODE: </stream:stream>
HOST: <?xml version='1.0'?>
<stream:stream
from='host'
id='id_123456789'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'>
HOST: <message from='receiving-ID' to='node@host'>
HOST: <body>I'm on my way!</body>
HOST: </message>
HOST: </stream:stream>
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A session gone bad:
NODE: <?xml version='1.0'?>
<stream:stream
to='host'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'>
HOST: <?xml version='1.0'?>
<stream:stream
from='host'
id='id_123456789'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'>
NODE: <message><body>Bad XML, no closing body tag!</message>
HOST: <stream:error>Invalid XML</stream:error>
HOST: </stream:stream>
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5. Stream Authentication
XMPP includes two methods for enforcing authentication at the level
of XML streams. When one entity is already known to another (i.e.,
there is an existing trust relationship between the entities such as
that established when a node registers with a host or an
administrator configures a host to trust a service), the preferred
method for authenticating streams between the two entities uses an
XMPP adaptation of the Simple Authentication and Security Layer
(SASL) [10]. When there is no existing trust relationship between
the two entities, such trust MAY be established based on existing
trust in DNS; the authentication method used when two such entities
are hosts is the server dialback protocol that is native to XMPP.
Both of these methods are described in this section.
5.1 SASL Authentication
5.1.1 Overview
The Simple Authentication and Security Layer (SASL) provides a
generalized method for adding authentication support to connection-
based protocols. XMPP uses a generic XML namespace profile for SASL
that conforms to section 4 ("Profiling Requirements") of [10] (the
namespace identifier for this protocol is http://www.iana.org/
assignments/sasl-mechanisms). If an entity (node, host, or service)
is capable of authenticating by means of SASL, it MUST include the
agreed-upon SASL namespace within the opening root stream tag it uses
to initiate communications.
The following example shows the use of SASL in node authentication
with a host, for which the steps involved are as follows:
1. The node requests SASL authentication by including the
appropriate namespace declaration (xmlns:sasl='http://
www.iana.org/assignments/sasl-mechanisms') in the opening XML
stream header sent to the host.
2. The host includes the xmlns:sasl namespace declaration in the XML
stream header sent in reply to the node.
3. The host responds with a list of available SASL authentication
mechanisms, each of which is a <mechanism/> element included as a
child within a <mechanisms/> container element that is sent as a
first-level child of the root <stream/> element.
4. The node selects a mechanism by sending a <sasl:auth/> element to
the host; this element MAY optionally contain character data.
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5. If necessary, the host challenges the node by sending a
<sasl:challenge/> element to the node; this element MAY
optionally contain character data.
6. The node responds to challenge by sending a <sasl:response/>
element to the host; this element MAY optionally contain
character data.
7. If necessary, the host sends more challenges and the node sends
more responses.
This series of challenge/response pairs continues until one of three
things happens:
o The node aborts the handshake by sending a <sasl:abort/> element
to the host.
o The host reports failure by sending a <sasl:failure/> element to
the node.
o The host reports success by sending a <sasl:success/> element to
the node; this element MAY optionally contain character data.
Any character data contained within these elements MUST be encoded
using base64.
5.1.2 Example
The following example shows the data flow for a node authenticating
with a host using SASL.
Step 1: Node initiates stream to host:
<stream:stream
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
xmlns:sasl='http://www.iana.org/assignments/sasl-mechanisms'
to='capulet.com'
version='1.0'>
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Step 2: Host responds with a stream tag sent to the node:
<stream:stream
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
xmlns:sasl='http://www.iana.org/assignments/sasl-mechanisms'
id='12345678'
version='1.0'>
Step 3: Host informs node of available authentication mechanisms:
<sasl:features>
<mechanisms xmlns='http://www.iana.org/assignments/sasl-mechanisms'>
<mechanism>DIGEST-MD5</mechanism>
<mechanism>PLAIN</mechanism>
</mechanisms>
<starttls xmlns='http://www.ietf.org/rfc/rfc2246.txt'/>
</sasl:features>
Step 4: Node selects an authentication mechanism:
<sasl:auth mechanism='DIGEST-MD5'/>
Step 5: Host sends a challenge to the node:
<sasl:challenge>
cmVhbG09ImNhdGFjbHlzbS5jeCIsbm9uY2U9Ik9BNk1HOXRFUUdtMmhoIi
xxb3A9ImF1dGgiLGNoYXJzZXQ9dXRmLTgsYWxnb3JpdGhtPW1kNS1zZXNz
</sasl:challenge>
Step 6: Node responds to the challenge:
<sasl:response>
dXNlcm5hbWU9InJvYiIscmVhbG09ImNhdGFjbHlzbS5jeCIsbm9uY2U9Ik
9BNk1HOXRFUUdtMmhoIixjbm9uY2U9Ik9BNk1IWGg2VnFUclJrIixuYz0w
MDAwMDAwMSxxb3A9YXV0aCxkaWdlc3QtdXJpPSJqYWJiZXIvY2F0YWNseX
NtLmN4IixyZXNwb25zZT1kMzg4ZGFkOTBkNGJiZDc2MGExNTIzMjFmMjE0
M2FmNyxjaGFyc2V0PXV0Zi04
</sasl:response>
Step 7: Host sends another challenge to the node:
<sasl:challenge>
cnNwYXV0aD1lYTQwZjYwMzM1YzQyN2I1NTI3Yjg0ZGJhYmNkZmZmZA==
</sasl:challenge>
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Step 8: Node responds to the challenge:
<sasl:response/>
Step 9: Host informs node of successful authentication:
<sasl:success/>
Step 9 (alt): Host informs node of failed authentication:
<sasl:failure/>
5.2 Dialback Authentication
XMPP includes a protocol-level method for verifying that a connection
between two hosts may be trusted. The method is called dialback and
is used only within XML streams that are declared under the
"jabber:server" namespace.
The purpose of the dialback protocol is to make server spoofing more
difficult, and thus to make it more difficult to forge XML chunks.
Dialback is not intended as a mechanism for securing or encrypting
the streams between servers, only for helping to prevent the spoofing
of a hostname and the sending of false data from it. Dialback is
made possible by the existence of DNS, since one host can verify that
another host which is connecting to it is authorized to represent a
given host on the Jabber network. All DNS host resolutions must
first resolve the host using an SRV [12] record of _jabber._tcp.host.
If the SRV lookup fails, the fallback is a normal A lookup to
determine the IP address, using the jabber-server port of 5269
assigned by the Internet Assigned Numbers Authority [6].
Note that the method used to generate and verify the keys used in the
dialback protocol must take into account the hostnames being used,
along with a secret known only by the receiving host and the random
id per stream. Generating unique but verifiable keys is important to
prevent common man-in-the-middle attacks and host spoofing.
In the description that follows we use the following terminology:
o Originating Host -- the host that is attempting to establish a
connection between the two hosts
o Receiving Host -- the host that is trying to authenticate that the
Originating Host represents the Jabber host which it claims to be
o Authoritative Host -- the host which is given when a DNS lookup is
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performed on the name that the Originating Host initially gave;
for simple environments this will be the Originating Host, but it
could be a separate machine in the Originating Host's network
The following is a brief summary of the order of events in dialback:
1. Originating Host establishes a connection to Receiving Host.
2. Originating Host sends a 'key' value over the connection to
Receiving Host.
3. Receiving Host establishes a connection to Authoritative Host.
4. Receiving Host sends the same 'key' value to Authoritative Host.
5. Authoritative Host replies that key is valid or invalid.
6. Receiving Host tells Originating Host whether it is authenticated
or not.
We can represent this flow of events graphically as follows:
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Originating Receiving
Host Host
----------- ---------
| |
| establish connection |
| ----------------------> |
| |
| send stream header |
| ----------------------> |
| |
| establish connection |
| <---------------------- |
| |
| send stream header |
| <---------------------- |
| | Authoritative
| send dialback key | Host
| ----------------------> | -------------
| | |
| establish connection |
| ----------------------> |
| |
| send stream header |
| ----------------------> |
| |
| send stream header |
| <---------------------- |
| |
| send dialback key |
| ----------------------> |
| |
| validate dialback key |
| <---------------------- |
|
| report dialback result |
| <---------------------- |
| |
5.2.1 Dialback Protocol
The traffic sent between the hosts is as follows:
1. Originating Host establishes connection to Receiving Host
2. Originating Host sends a stream header to Receiving Host (the
'to' and 'from' attributes are not required):
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<stream:stream
xmlns:stream='http://etherx.jabber.org/streams'
xmlns='jabber:server'
xmlns:db='jabber:server:dialback'>
Note: the value of the xmlns:db namespace declaration indicates
to Receiving Host that the Originating Host supports dialback.
3. Receiving Host sends a stream header back to Originating Host
(the 'to' and 'from' attributes are not required):
<stream:stream
xmlns:stream='http://etherx.jabber.org/streams'
xmlns='jabber:server'
xmlns:db='jabber:server:dialback'
id='457F9224A0...'>
4. Originating Host sends a dialback key to Receiving Host:
<db:result
to='Receiving Host'
from='Originating Host'>
98AF014EDC0...
</db:result>
Note: this key is not examined by Receiving Host, since the
Receiving Host does not keep information about Originating Host
between sessions.
5. Receiving Host now establishes a connection back to Originating
Host, getting the Authoritative Host.
6. Receiving Host sends Authoritative Host a stream header (the
'to' and 'from' attributes are not required):
<stream:stream
xmlns:stream='http://etherx.jabber.org/streams'
xmlns='jabber:server'
xmlns:db='jabber:server:dialback'>
7. Authoritative Host sends Receiving Host a stream header:
<stream:stream
xmlns:stream='http://etherx.jabber.org/streams'
xmlns='jabber:server'
xmlns:db='jabber:server:dialback'
id='1251A342B...'>
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8. Receiving Host sends Authoritative Host a chunk indicating it
wants Authoritative Host to verify a key:
<db:verify
from='Receiving Host'
to='Originating Host'
id='457F9224A0...'>
98AF014EDC0...
</db:verify>
Note: passed here are the hostnames, the original identifier
from Receiving Host's stream header to Originating Host in step
2, and the key Originating Host gave Receiving Host in step 3.
Based on this information and shared secret information within
the 'Originating Host' network, the key is verified. Any
verifiable method can be used to generate the key.
9. Authoritative Host sends a chunk back to Receiving Host
indicating whether the key was valid or invalid:
<db:result
from='Originating Host'
to='Receiving Host'
type='valid'
id='457F9224A0...'/>
or
<db:result
from='Originating Host'
to='Receiving Host'
type='invalid'
id='457F9224A0...'/>
10. Receiving Host informs Originating Host of the result:
<db:result
from='Receiving Host'
to='Originating Host'
type='valid'/>
Note: At this point the connection has either been validated via
a type='valid', or reported as invalid. Once the connection is
validated, data can be sent by the Originating Host and read by
the Receiving Host; before that, all data chunks sent to
Receiving Host SHOULD be dropped. As a final guard against
domain spoofing, the Receiving Host MUST verify that all XML
chunks received from the Originating Host include a 'from'
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attribute and that from address of each chunk includes the
validated domain. In addition, all XML chunks of type message,
presence, and IQ MUST include a 'to' attribute.
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6. Core Data Elements
6.1 Overview
The core data elements for XMPP communications are <message/>,
<presence/>, and <iq/>. These data elements are sent as direct
(depth=1) children of the root <stream/> element and are scoped by
one of the default namespaces identified in Section 4.4.
6.2 Common Attributes
Four attributes are common to message, presence, and IQ chunks.
These are defined below.
6.2.1 to
The 'to' attribute specifies the JID of the intended recipient for
the chunk. A chunk SHOULD possess a 'to' attribute. A chunk sent
from a node to a host for handling by that host (e.g., presence sent
to the host for broadcasting to other entities) MAY legitimately lack
a 'to' attribute.
6.2.2 from
The 'from' attribute specifies the JID of the sender.
A node MUST NOT include a 'from' attribute on the chunks it sends to
a host; if a host receives a chunk from a node and the chunk
possesses a 'from' attribute, it must ignore the value of the 'from'
attribute. A host MUST stamp chunks received from a node with the
user@host/resource (full JID) of the connected resource that
generated the chunk.
A host MUST include a 'from' attribute on chunks it routes to other
hosts. The domain identifier of the JID contained in the 'from'
attribute MUST match the hostname of the host as communicated in the
dialback negotiation (or a subdomain thereof).
6.2.3 id
The optional 'id' attribute may be used to track chunks sent and
received. The 'id' attribute is generated by the sender. An 'id'
attribute included in an IQ request of type "get" or "set" SHOULD be
returned to the sender in any IQ response of type "result" or "error"
generated by the recipient of the request. A recipient of a message
or presence chunk MAY return that 'id' in any replies, but is not
required to do so.
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6.2.4 type
The 'type' attribute specifies detailed information about the purpose
or context of the message, presence, or IQ chunk. The particular
allowable values for the 'type' attribute vary depending on whether
the chunk is a message, presence, or IQ, and thus are specified in
the following sections.
6.3 Message Chunks
Message chunks in the 'jabber:client' or 'jabber:server' namespace
are used to "push" information to another entity. Common uses in the
context of instant messaging include single messages, messages sent
in the context of a chat conversation, messages sent in the context
of a multi-user chat room, headlines, and errors. These messages
types are identified more fully below.
6.3.1 Types of Message
The 'type' attribute of a message chunk is optional and specifies the
conversational context of the message. The sending of a message
chunk without a 'type' attribute signals that the message chunk is a
single message. However, the 'type' attribute may also have one of
the following values:
o chat -- The message is sent in the context of a one-to-one chat
conversation.
o groupchat -- The message is sent in the context of a multi-user
chat environment.
o headline -- The message is generated by an automated service that
delivers content (news, sports, market information, etc.).
o error - A message returned to a sender specifying an error
associated with a previous message sent by the sender (for a full
list of error messages, see error codes (Appendix A))
For detailed information about these message types, refer to XMPP IM
[2].
6.3.2 Children
If a message chunk in the 'jabber:client' or 'jabber:server'
namespace has no 'type' attribute or has a 'type' attribute with a
value of "chat", "groupchat", or "headline", it MAY contain zero or
one of each of the following child elements (which MUST NOT contain
mixed content):
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o body -- The textual contents of the message; normally included but
not required. The <body/> element MUST NOT have any attributes.
o subject -- The subject of the message. The <subject/> element
MUST NOT have any attributes.
o thread -- A random string that is generated by the sender and that
MAY be copied back in replies; it is used for tracking a
conversation thread. The <thread/> element MUST NOT have any
attributes.
If the message chunk is of type "error", it MUST include an <error/>
child, which in turn MUST possess a 'code' attribute corresponding to
one of the standard error codes (Appendix A) and MAY also contain
PCDATA corresponding to a natural-language description of the error.
An <error/> child MUST NOT be included if the chunk type is anything
other than "error".
As described under extended namespaces (Section 6.6), a message chunk
MAY also contain any properly-namespaced child element (other than
the core data elements, stream elements, or defined children
thereof).
6.4 Presence Chunks
Presence chunks are used in the 'jabber:client' or 'jabber:server'
namespace to express an entity's current availability status (offline
or online, along with various sub-states of the latter) and to
communicate that status to other entities. They are also used to
negotiate and manage subscriptions to the presence of other entities.
6.4.1 Types of Presence
The 'type' attribute of a presence chunk is optional. A presence
chunk that does not have a 'type' attribute is used to signal that
the sender is online and available for communication. If included,
the 'type' attribute specifies the availability state of the sender,
a request to manage a subscription to another entity's presence, a
request for another entity's current presence, or an error related to
a previously-sent presence chunk. The 'type' attribute may have one
of the following values:
o unavailable -- Signals that the entity is no longer available for
communication.
o subscribe -- The sender wishes to subscribe to the recipient's
presence.
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o subscribed -- The sender has allowed the recipient to receive
their presence.
o unsubscribe -- A notification that an entity is unsubscribing from
another entity's presence.
o unsubscribed -- The subscription request has been denied or a
previously-granted subscription has been cancelled.
o probe -- A request for an entity's current presence.
o error -- An error has occurred regarding processing or delivery of
a previously-sent presence chunk.
Information about the subscription model used within XMPP may be
found in [2].
6.4.2 Children
If a presence chunk possesses no 'type' attribute, it MAY contain
zero or one of each of the following child elements (for historical
reasons the <status/> child MAY be sent in a presence chunk of type
"subscribe"):
o show -- Describes the availability status of an entity or specific
resource. The value SHOULD be one of the following (values other
than these four MAY be ignored; additional availability types
should be defined through a properly-namespaced child element of
the presence chunk):
* away -- The entity or resource is temporarily away.
* chat -- The entity or resource is actively interested in
chatting.
* xa -- The entity or resource is away for an extended period (xa
= "eXtended Away").
* dnd -- The entity or resource is busy (dnd = "Do Not Disturb").
o status -- An optional natural-language description of availability
status. Normally used in conjunction with the show element to
provide a detailed description of an availability state (e.g., "In
a meeting").
o priority -- A non-negative integer representing the priority level
of the connected resource, with zero as the lowest priority.
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If the presence chunk is of type "error", it MUST include an <error/>
child, which in turn MUST possess a 'code' attribute corresponding to
one of the standard error codes (Appendix A) and MAY also contain
PCDATA corresponding to a natural-language description of the error.
An <error/> child MUST NOT be included if the chunk type is anything
other than "error".
As described under extended namespaces (Section 6.6), a presence
chunk MAY also contain any properly-namespaced child element (other
than the core data elements, stream elements, or defined children
thereof).
6.5 IQ Chunks
6.5.1 Overview
Info/Query, or IQ, is a simple request-response mechanism. Just as
HTTP is a request-response medium, IQ chunks in the 'jabber:client'
or 'jabber:server' namespace enable an entity to make a request of,
and receive a response from, another entity. The data content of the
request and response is defined by the namespace declaration of a
direct child element of the iq element.
Most IQ interactions follow a common pattern of structured data
exchange such as get/result or set/result:
Requesting Responding
Entity Entity
---------- ----------
| |
| <iq type="get"> |
| ---------------------> |
| |
| <iq type="result"> |
| <--------------------- |
| |
| <iq type="set"> |
| ---------------------> |
| |
| <iq type="result"> |
| <--------------------- |
| |
6.5.2 Types of IQ
The 'type' attribute of an IQ chunk is REQUIRED. The 'type'
attribute specifies a distinct step within a request-response
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interaction. The value SHOULD be one of the following (all other
values MAY be ignored):
o get -- The chunk is a request for information.
o set -- The chunk provides required data, sets new values, or
replaces existing values.
o result -- The chunk is a response to a successful get or set
request.
o error -- An error has occurred regarding processing or delivery of
a previously-sent get or set.
6.5.3 Children
An IQ chunk contains no children in the 'jabber:client' or
'jabber:server' namespace since it is a vessel for XML in another
namespace. As described under extended namespaces (Section 6.6), an
IQ chunk MAY contain any properly-namespaced child element (other
than the core data elements, stream elements, or defined children
thereof).
If the IQ chunk is of type "error", it MUST include an <error/>
child, which in turn MUST possess a 'code' attribute corresponding to
one of the standard error codes (Appendix A) and MAY also contain
PCDATA corresponding to a natural-language description of the error.
An <error/> child MUST NOT be included if the chunk type is anything
other than "error".
6.6 Extended Namespaces
While the core data elements defined in this document provide a basic
level of functionality for messaging and presence, XMPP uses XML
namespaces to extend the core data elements for the purpose of
providing additional functionality. Thus a message, presence, or IQ
chunk may house one or more optional child elements containing
content that extends the meaning of the message (e.g., an encrypted
form of the message body as described in Appendix C). This child
element MAY be any element (other than the core data elements, stream
elements, or defined children thereof). The child element MUST
possess an 'xmlns' namespace declaration (other than the stream
namespace and the default namespace) that defines all data contained
within the child element.
Support for any given extended namespace is OPTIONAL on the part of
any implementation. If an entity does not understand such a
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namespace, it must ignore the associated XML data. If an entity
receives an IQ chunk in a namespace it does not understand, the
entity SHOULD return an IQ chunk of type "error" with an error
element of code 400 (bad request). If an entity receives a message
or presence chunk that contains XML data in an extended namespace it
does not understand, the portion of the chunk that is in the unknown
namespace SHOULD be ignored. If an entity receives a message chunk
without a <body/> element but containing only a child element bound
by a namespace it does not understand, it MUST ignore that chunk.
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7. XML Usage within XMPP
7.1 Overview
In essence, XMPP core consists of three interrelated parts:
1. XML streams (Section 4), which provide a stateful means for
transporting data in an asynchronous manner from one entity to
another
2. stream authentication using SASL authentication (Section 5.1) or
the dialback protocol (Section 5.2)
3. core data elements (Section 6) (message, presence, and iq), which
provide a framework for communications between entities
XML [1] is used to define each of these protocols, as described in
detail in the following sections.
In addition, XMPP contains protocol extensions (such as extended
namespaces) that address the specific functionality required to
create a basic instant messaging and presence application; these non-
core protocol extensions are defined in XMPP IM [2].
7.2 Namespaces
XML Namespaces [11] are used within all XMPP-compliant XML to create
strict boundaries of data ownership. The basic function of
namespaces is to separate different vocabularies of XML elements that
are structurally mixed together. Ensuring that XMPP-compliant XML is
namespace-aware enables any XML to be structurally mixed with any
data element within XMPP. This feature is relied upon frequently
within XMPP to separate the XML that is processed by different
services. Mainly for historical reasons, the default namespace for
XMPP data chunks MUST be one of the namespaces identified in Section
4.4.
Additionally, XMPP is more strict about namespace prefixes than the
XML namespace specification requires.
7.3 Validation
A host is not responsible for validating the XML elements forwarded
to a node; an implementation MAY choose to provide only validated
data elements but is NOT REQUIRED to do so. Nodes and services
SHOULD NOT rely on the ability to send data which does not conform to
the schemas, and SHOULD ignore any non-conformant elements or
attributes on the incoming XML stream.
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7.4 Character Encodings
Software implementing XML streams MUST support the UTF-8 and UTF-16
encodings for received data. Software MUST NOT attempt to use any
other encoding for transmitted data. The encodings of the transmit
and receive streams are independent. Software may select either UTF-
8 or UTF-16 for the transmitted stream, and should deduce the
encoding of the received stream as described in [1].
7.5 Inclusion of Text Declaration
An application MAY send a text declaration. Applications MUST follow
the rules in [1] concerning the circumstances in which a text
declaration is included.
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8. IANA Considerations
The IANA registers "jabber-client" and "jabber-server" as GSS-API
[14] service names, as specified in Section 6.1.1.
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9. Internationalization Considerations
o A node SHOULD include an xml:lang declaration on the stream:stream
it initiates to a host, denoting the node's default (preferred)
language.
o If the host detects an xml:lang declaration on the stream:stream
from a node, it SHOULD remember that value.
o If a host does not receive an xml:lang from a node, it SHOULD have
a configurable default locale that it remembers instead.
o For all chunks, if the node does not send an xml:lang attribute on
the root tag of the packet, the server SHOULD apply its remembered
value.
o If a node does send an xml:lang attribute on a chunk, the server
MUST NOT modify or delete it.
o A host SHOULD include an xml:lang declaration on the stream:stream
with which it replies to a node, denoting the host's default
(preferred) language.
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10. Security Considerations
10.1 Node-to-Host Communications
The SASL protocol for authenticating XML streams negotiated between a
node and a host (defined under Section 5.1 above) provides a reliable
mechanism for validating that a node connecting to a host is who it
claims to be.
The IP address and method of access of nodes MUST NOT be made
available by a host, nor are any connections other than the original
host connection required. This helps protect the node's host from
direct attack or identification by third parties.
End-to-end encryption of message bodies and presence status
information MAY be effected through use of OpenPGP [13]; for details,
see Appendix C.
10.2 Host-to-Host Communications
It is OPTIONAL for any given host to communicate with other hosts,
and host-to-host communications MAY be disabled by the administrator
of any given deployment.
If two hosts would like to enable communications between themselves,
they MUST form a relationship of trust at some level, either based on
trust in DNS or based on a pre-existing trust relationship (e.g.,
through exchange of certificates). If two hosts have a pre-existing
trust relationship, they MAY use SASL Authentication (Section 5.1)
for the purpose of authenticating each other. If they do not have a
pre-existing relationship, they MUST use the Dialback Protocol
(Section 5.2), which provides a reliable mechanism for preventing the
spoofing of hosts.
10.3 Use of SASL
Although service provisioning is a policy matter, at a minimum, all
implementations MUST provide the SASL DIGEST-MD5 mechanism for
authentication.
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References
[1] World Wide Web Consortium, "Extensible Markup Language (XML)
1.0 (Second Edition)", W3C xml, October 2000, <http://
www.w3.org/TR/2000/REC-xml-20001006>.
[2] Miller, J. and P. Saint-Andre, "XMPP Instant Messaging (draft-
miller-xmpp-im-02, work in progress)", November 2002.
[3] Day, M., Aggarwal, S., Mohr, G. and J. Vincent, "A Model for
Presence and Instant Messaging", RFC 2779, February 2000,
<http://www.ietf.org/rfc/rfc2779.txt>.
[4] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[5] University of Southern California, "Transmission Control
Protocol", RFC 793, September 1981, <http://www.ietf.org/rfc/
rfc0793.txt>.
[6] Internet Assigned Numbers Authority, "Internet Assigned Numbers
Authority", January 1998, <http://www.iana.org/>.
[7] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
Resource Identifiers (URI): Generic Syntax", RFC 2396, August
1998, <http://www.ietf.org/rfc/rfc2396.txt>.
[8] Harrenstien, K., Stahl, M. and E. Feinler, "DoD Internet host
table specification", RFC 952, October 1985.
[9] Braden, R., "Requirements for Internet Hosts - Application and
Support", STD 3, RFC 1123, October 1989.
[10] Myers, J., "Simple Authentication and Security Layer (SASL)",
RFC 2222, October 1997.
[11] World Wide Web Consortium, "Namespaces in XML", W3C xml-names,
January 1999, <http://www.w3.org/TR/1999/REC-xml-names-
19990114/>.
[12] Gulbrandsen, A. and P. Vixie, "A DNS RR for specifying the
location of services (DNS SRV)", RFC 2052, October 1996.
[13] Elkins, M., Del Torto, D., Levien, R. and T. Roessler, "MIME
Security with OpenPGP", RFC 3156, August 2001.
[14] Linn, J., "Generic Security Service Application Program
Interface, Version 2", RFC 2078, January 1997.
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Authors' Addresses
Jeremie Miller
Jabber Software Foundation
1899 Wynkoop Street, Suite 600
Denver, CO 80202
US
EMail: jeremie@jabber.org
URI: http://www.jabber.org/people/jer.php
Peter Saint-Andre
Jabber Software Foundation
1899 Wynkoop Street, Suite 600
Denver, CO 80202
US
EMail: stpeter@jabber.org
URI: http://www.jabber.org/people/stpeter.php
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Appendix A. Standard Error Codes
A standard error element is used for failed processing of XML chunks.
This element is a child of the failed chunk and MUST include a 'code'
attribute corresponding to one of the following error codes.
o 302 (Redirect) - Whereas HTTP contains eight different codes for
redirection, XMPP contains only one (which is intended to stand
for any redirection error). However, code 302 is being reserved
for future functionality and is not implemented at this time.
o 400 (Bad Request) - Code 400 is used to inform a sender that a
request could not be understood by the recipient. This might be
generated when, for example, an entity sends a message that does
not have a 'to' attribute.
o 401 (Unauthorized) - Code 401 is used to inform nodes that they
have provided incorrect authorization information, e.g., an
incorrect password or unknown username when attempting to
authenticate with a host.
o 402 (Payment Required) - Code 402 is being reserved for future
use.
o 403 (Forbidden) - Code 403 is used to inform an entity that the
its request was understood but that the recipient is refusing to
fulfill it, e.g., if a node attempts to set information associated
with another node.
o 404 (Not Found) - Code 404 is used to inform a sender that no
recipient was found matching the JID to which an XML chunk was
sent, e.g., if a sender has attempted to send a message to a JID
that does not exist. (Note: if the host of the intended recipient
cannot be reached, an error code from the 500 series must be
sent).
o 405 (Not Allowed) - Code 405 is used when the action requested is
not allowed for the JID identified by the 'from' address, e.g., if
a node attempts to set the time or version of a host.
o 406 (Not Acceptable) - Code 406 is used when an XML chunk is for
some reason not acceptable to a host or other entity. This might
be generated when, for example, a node attempts to register with a
host using an empty password.
o 407 (Registration Required) - Code 407 is used when a message or
request is sent to a service that requires prior registration,
e.g., if a node attempts to send a message through a gateway to a
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foreign messaging system without having first registered with that
gateway.
o 408 (Request Timeout) - Code 408 is returned when a recipient does
not produce a response within the time that the sender was
prepared to wait.
o 500 (Internal Server Error) - Code 500 is used when a host or
service encounters an unexpected condition which prevents it from
handling an XML chunk from a sender, e.g., if an authentication
request is not handled by a host because the password could not be
retrieved.
o 501 (Not Implemented) - Code 501 is used when the recipient does
not support the functionality being requested by a sender, e.g.,
if a node attempts to register with a host that does not allow
registration.
o 502 (Remote Server Error) - Code 502 is used when delivery of an
XML chunk fails because of an inability to reach the intended
remote host or service, e.g., because a remote host's hostname
could not be resolved.
o 503 (Service Unavailable) - Code 503 is used when a sender
requests a service that a recipient is temporarily unable to
offer.
o 504 (Remote Server Timeout) - Code 504 is used when attempts to
contact a remote host timeout, e.g., if an incorrect hostname is
specified.
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Appendix B. Formal Definitions
B.1 streams namespace
B.1.1 DTD
<?xml version='1.0' encoding='UTF-8'?>
<!ELEMENT stream (#PCDATA | error?)*>
<!ATTLIST stream
to CDATA #REQUIRED
from CDATA #IMPLIED
id CDATA #IMPLIED>
<!ELEMENT error (#PCDATA)>
B.1.2 Schema
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<?xml version='1.0' encoding='UTF-8'?>
<xsd:schema
xmlns:xsd='http://www.w3.org/2001/XMLSchema'
targetNamespace='http://etherx.jabber.org/streams'
xmlns='http://etherx.jabber.org/streams'
elementFormDefault='qualified'>
<xsd:element name='stream'>
<xsd:complexType mixed='true'>
<xsd:element ref='error' minOccurs='0' maxOccurs='1'/>
<xsd:choice>
<xsd:any
namespace='jabber:client'
maxOccurs='1'/>
<xsd:any
namespace='jabber:component:accept'
maxOccurs='1'/>
<xsd:any
namespace='jabber:component:connect'
maxOccurs='1'/>
<xsd:any
namespace='jabber:server'
maxOccurs='1'/>
<xsd:any
namespace='http://www.iana.org/assignments/sasl-mechanisms'
maxOccurs='1'/>
</xsd:choice>
<xsd:attribute name='to' type='xsd:string' use='optional'/>
<xsd:attribute name='from' type='xsd:string' use='optional'/>
<xsd:attribute name='id' type='xsd:string' use='optional'/>
</xsd:complexType>
</xsd:element>
<xsd:element name='error' type='xsd:string'/>
</xsd:schema>
B.2 sasl namespace
B.2.1 DTD
The DTD for the sasl: namespace is as follows:
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<?xml version='1.0' encoding='UTF-8'?>
<!ELEMENT mechanisms (mechanism)*>
<!ELEMENT mechanism (#PCDATA)>
<!ATTLIST mechanism name CDATA #REQUIRED>
<!ELEMENT auth (#PCDATA)>
<!ATTLIST auth name CDATA #REQUIRED>
<!ELEMENT challenge (#PCDATA)>
<!ELEMENT response (#PCDATA)>
<!ELEMENT abort (#PCDATA)>
<!ELEMENT success (#PCDATA)>
<!ELEMENT failure (#PCDATA)>
B.2.2 Schema
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<?xml version='1.0' encoding='UTF-8'?>
<xsd:schema
xmlns:xsd='http://www.w3.org/2001/XMLSchema'
targetNamespace='http://www.iana.org/assignments/sasl-mechanisms'
xmlns='http://www.iana.org/assignments/sasl-mechanisms'
elementFormDefault='qualified'>
<xsd:element name='mechanisms'>
<xsd:complexType>
<xsd:sequence minOccurs='0' maxOccurs='unbounded'>
<xsd:element ref='mechanism'/>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
<xsd:element name='mechanism'>
<xsd:complexType mixed='true'>
<xsd:attribute name='name' type='xsd:string' use='optional'/>
</xsd:complexType>
</xsd:element>
<xsd:element name='auth'>
<xsd:complexType mixed='true'>
<xsd:attribute name='name' type='xsd:string' use='optional'/>
</xsd:complexType>
</xsd:element>
<xsd:element name='challenge' type='xsd:string'/>
<xsd:element name='response' type='xsd:string'/>
<xsd:element name='abort' type='xsd:string'/>
<xsd:element name='success' type='xsd:string'/>
<xsd:element name='failure' type='xsd:string'/>
</xsd:schema>
B.3 jabber:client namespace
Note: the formal definition for the 'jabber:server' namespace is
identical to that for the 'jabber:client' namespace.
B.3.1 DTD
<?xml version='1.0' encoding='UTF-8'?>
<!ELEMENT message (( body? | subject? | thread? |
error? | (#PCDATA) )*)>
<!ATTLIST message
to CDATA #IMPLIED
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from CDATA #IMPLIED
id CDATA #IMPLIED
type ( chat | groupchat | headline | error ) #IMPLIED
>
<!ELEMENT body (#PCDATA)>
<!ELEMENT subject (#PCDATA)>
<!ELEMENT thread (#PCDATA)>
<!ELEMENT presence (( show? | status? | priority? | error? )*)>
<!ATTLIST presence
to CDATA #IMPLIED
from CDATA #IMPLIED
id CDATA #IMPLIED
type ( subscribe | subscribed | unsubscribe |
unsubscribed | unavailable | error ) #IMPLIED
>
<!ELEMENT show (#PCDATA)>
<!ELEMENT status (#PCDATA)>
<!ELEMENT priority (#PCDATA)>
<!ELEMENT iq ( error | (#PCDATA) )*>
<!ATTLIST iq
to CDATA #IMPLIED
from CDATA #IMPLIED
id CDATA #IMPLIED
type ( get | set | result | error ) #REQUIRED
>
<!ELEMENT error (#PCDATA)>
<!ATTLIST error code CDATA #REQUIRED>
B.3.2 Schema
<?xml version='1.0' encoding='UTF-8'?>
<xsd:schema
xmlns:xsd='http://www.w3.org/2001/XMLSchema'
targetNamespace='http://www.jabber.org/protocol'
xmlns='http://www.jabber.org/protocol'
elementFormDefault='qualified'>
<xsd:element name='message'>
<xsd:complexType mixed='true'>
<xsd:choice>
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<xsd:element ref='body' minOccurs='0' maxOccurs='1'/>
<xsd:element ref='subject' minOccurs='0' maxOccurs='1'/>
<xsd:element ref='thread' minOccurs='0' maxOccurs='1'/>
<xsd:element ref='error' minOccurs='0' maxOccurs='1'/>
<xsd:any
namespace='##other'
minOccurs='0'
maxOccurs='unbounded'/>
</xsd:choice>
<xsd:attribute name='to' type='xsd:string' use='optional'/>
<xsd:attribute name='from' type='xsd:string' use='optional'/>
<xsd:attribute name='id' type='xsd:string' use='optional'/>
<xsd:attribute name='type' use='optional' default='normal'>
<xsd:simpleType>
<xsd:restriction base='xsd:NCName'>
<xsd:enumeration value='normal'/>
<xsd:enumeration value='chat'/>
<xsd:enumeration value='groupchat'/>
<xsd:enumeration value='headline'/>
<xsd:enumeration value='error'/>
</xsd:restriction>
</xsd:simpleType>
</xsd:attribute>
</xsd:complexType>
</xsd:element>
<xsd:element name='body' type='xsd:string'/>
<xsd:element name='subject' type='xsd:string'/>
<xsd:element name='thread' type='xsd:string'/>
<xsd:element name='presence'>
<xsd:complexType>
<xsd:choice>
<xsd:element ref='show' minOccurs='0' maxOccurs='1'/>
<xsd:element ref='status' minOccurs='0' maxOccurs='1'/>
<xsd:element ref='priority' minOccurs='0' maxOccurs='1'/>
<xsd:element ref='error' minOccurs='0' maxOccurs='1'/>
<xsd:any
namespace='##other'
minOccurs='0'
maxOccurs='unbounded'/>
</xsd:choice>
<xsd:attribute name='to' type='xsd:string' use='optional'/>
<xsd:attribute name='from' type='xsd:string' use='optional'/>
<xsd:attribute name='id' type='xsd:string' use='optional'/>
<xsd:attribute name='type' use='optional'>
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<xsd:simpleType>
<xsd:restriction base='xsd:string'>
<xsd:enumeration value='unavailable'/>
<xsd:enumeration value='subscribe'/>
<xsd:enumeration value='subscribed'/>
<xsd:enumeration value='unsubscribe'/>
<xsd:enumeration value='unsubscribed'/>
<xsd:enumeration value='error'/>
</xsd:restriction>
</xsd:simpleType>
</xsd:attribute>
</xsd:complexType>
</xsd:element>
<xsd:element name='show'>
<xsd:simpleType>
<xsd:restriction base='xsd:string'>
<xsd:enumeration value='away'/>
<xsd:enumeration value='chat'/>
<xsd:enumeration value='xa'/>
<xsd:enumeration value='dnd'/>
</xsd:restriction>
</xsd:simpleType>
</xsd:element>
<xsd:element name='status' type='xsd:string'/>
<xsd:element name='priority' type='xsd:nonNegativeInteger'/>
<xsd:element name='iq'>
<xsd:complexType mixed='true'>
<xsd:choice>
<xsd:element ref='error' minOccurs='0' maxOccurs='1'/>
<xsd:any
namespace='##other'
minOccurs='0'
maxOccurs='unbounded'/>
</xsd:choice>
<xsd:attribute name='to' type='xsd:string' use='optional'/>
<xsd:attribute name='from' type='xsd:string' use='optional'/>
<xsd:attribute name='id' type='xsd:string' use='optional'/>
<xsd:attribute name='type' use='required'>
<xsd:simpleType>
<xsd:restriction base='xsd:string'>
<xsd:enumeration value='get'/>
<xsd:enumeration value='set'/>
<xsd:enumeration value='result'/>
<xsd:enumeration value='error'/>
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</xsd:restriction>
</xsd:simpleType>
</xsd:attribute>
</xsd:complexType>
</xsd:element>
<xsd:element name='error'>
<xsd:complexType>
<xsd:attribute
name='code'
type='xsd:nonNegativeInteger'
use='required'/>
</xsd:complexType>
</xsd:element>
</xsd:schema>
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Appendix C. OpenPGP Usage
This section is non-normative. It describes an end-to-end encryption
and signing method currently in use within the Jabber community. It
is not recommended as a complete solution for encrypting streams or
for guaranteeing the privacy of messages or presence. When this
method is used, replay attacks are possible on presence chunks and
also on messages for which the recipient is not mentioned in the
message body. Key exchange may rely on the web of trust model used
on the OpenPGP keys network. There is no method to check a
fingerprint or ownership of a key other than checking the user IDs on
a key.
All operations described herein may be completed using standard
OpenPGP software. All program output is US-ASCII armored output with
the headers removed, which allows for straightforward encapsulation
of the program output directly in XML chunks. It is assumed that all
keys are exchanged using OpenPGP key servers; for example, the key of
another user may be retrieved automatically when a signed presence
chunk is received from that user.
C.1 Signing Presence
Signing enables a sender to verify that they sent a certain block of
text. As applied within the Jabber community, the <status/> child of
a presence chunk is signed and sent as extended presence information
in the 'jabber:x:signed' namespace. Because signing requires a block
of text, a signed presence chunk MUST contain a <status/> child
element that is non-empty (i.e., contains text.
When signing presence, the sender MUST use the private key which is
the same KeyID as the one they wish to use for encrypted messages.
This is because there is no feature negotiation related to message
encryption; the only indicator that another user encrypts is or her
messages is that one receives signed presence chunks from that user.
As shown in the following example, the only presence information that
is signed is the CDATA of the <status> element.
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<presence
from='romeo@montague.net/orchard'
to='juliet@capulet.com/balcony'>
<status>Online</status>
<x xmlns='jabber:x:signed'>
iQA/AwUBOjU5dnol3d88qZ77EQI2JACfRngLJ045brNnaCX78ykKNUZaTIoAoPHI
2uJxPMGR73EBIvEpcv0LRSy+
=45f8
</x>
</presence>
C.2 Encrypting Messages
Encryption enables the sender to encrypt a message sent to a specific
recipient. This is accomplished by sending the encrypted form of the
CDATA from the <body/> child in second child that is scoped by the
'jabber:x:encrypted' namespace. Because a block of text is
necessary, the message chunk MUST contain a <body/> child element
that is non-empty (i.e., that contains some CDATA text). It is
considered polite to include a message <body/> informing the
recipient that the message is encrypted. The public key used for
message encryption should match the KeyID used for signing presence.
The actual data that is encrypted is what would be the CDATA of the
<body> element if the message were not encrypted.
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<message
from='juliet@capulet.com/balcony'
to='romeo@montague.net/orchard'>
<body>This message is encrypted.</body>
<x xmlns='jabber:x:encrypted'>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=CvnG
</x>
</message>
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Full Copyright Statement
Copyright (C) The Internet Society (2002). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
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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