Network Working Group J. Miller
Internet-Draft P. Saint-Andre
Expires: June 6, 2003 Jabber Software Foundation
December 06, 2002
XMPP Core
draft-ietf-xmpp-core-00
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 Server . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.3 Client . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.4 Gateway . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.5 Network . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Addressing Scheme . . . . . . . . . . . . . . . . . . . . . 7
3.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.2 Domain Identifier . . . . . . . . . . . . . . . . . . . . . 7
3.3 Node Identifier . . . . . . . . . . . . . . . . . . . . . . 7
3.4 Resource Identifier . . . . . . . . . . . . . . . . . . . . 8
4. XML Streams . . . . . . . . . . . . . . . . . . . . . . . . 9
4.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 9
4.2 Restrictions . . . . . . . . . . . . . . . . . . . . . . . . 10
4.3 Stream Attributes . . . . . . . . . . . . . . . . . . . . . 10
4.4 Namespace Declarations . . . . . . . . . . . . . . . . . . . 11
4.5 Stream Features . . . . . . . . . . . . . . . . . . . . . . 12
4.6 Stream Errors . . . . . . . . . . . . . . . . . . . . . . . 13
4.7 Simple Streams Example . . . . . . . . . . . . . . . . . . . 13
5. Stream Authentication . . . . . . . . . . . . . . . . . . . 16
5.1 SASL Authentication . . . . . . . . . . . . . . . . . . . . 16
5.1.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 16
5.1.2 Example . . . . . . . . . . . . . . . . . . . . . . . . . . 17
5.2 Dialback Authentication . . . . . . . . . . . . . . . . . . 19
5.2.1 Dialback Protocol . . . . . . . . . . . . . . . . . . . . . 21
6. XML Stanzas . . . . . . . . . . . . . . . . . . . . . . . . 25
6.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 25
6.2 Common Attributes . . . . . . . . . . . . . . . . . . . . . 25
6.2.1 to . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
6.2.2 from . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
6.2.3 id . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
6.2.4 type . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
6.2.5 xml:lang . . . . . . . . . . . . . . . . . . . . . . . . . . 26
6.3 Message Stanzas . . . . . . . . . . . . . . . . . . . . . . 26
6.3.1 Types of Message . . . . . . . . . . . . . . . . . . . . . . 26
6.3.2 Children . . . . . . . . . . . . . . . . . . . . . . . . . . 27
6.4 Presence Stanzas . . . . . . . . . . . . . . . . . . . . . . 28
6.4.1 Types of Presence . . . . . . . . . . . . . . . . . . . . . 28
6.4.2 Children . . . . . . . . . . . . . . . . . . . . . . . . . . 29
6.5 IQ Stanzas . . . . . . . . . . . . . . . . . . . . . . . . . 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 Client-to-Server Communications . . . . . . . . . . . . . . 37
10.2 Server-to-Server Communications . . . . . . . . . . . . . . 37
10.3 Minimum Security Mechanisms . . . . . . . . . . . . . . . . 37
10.4 Firewalls . . . . . . . . . . . . . . . . . . . . . . . . . 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 . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
B.2 SASL namespace . . . . . . . . . . . . . . . . . . . . . . . 43
B.2.1 DTD . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
B.2.2 Schema . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
B.3 jabber:client namespace . . . . . . . . . . . . . . . . . . 45
B.3.1 DTD . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
B.3.2 Schema . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
B.4 jabber:server namespace . . . . . . . . . . . . . . . . . . 49
B.4.1 DTD . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
B.4.2 Schema . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
C. Revision History . . . . . . . . . . . . . . . . . . . . . . 54
C.1 Changes from draft-miller-xmpp-core-02 . . . . . . . . . . . 54
Full Copyright Statement . . . . . . . . . . . . . . . . . . 56
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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. The protocol
was developed originally within the Jabber community starting in
1998, and since 2001 has continued to evolve under the auspices of
the Jabber Software Foundation and now the XMPP WG. 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.
The following diagram provides a high-level overview of this
architecture (where "-" represents communications that use XMPP and
"=" represents communications that use any other protocol).
C1 - S1 - S2 - C3
/ \
C2 - G1 = FN1 = FC1
The symbols are as follows:
o C1, C2, C3 -- XMPP clients
o S1, S2 -- XMPP servers
o G1 -- A gateway that translates between XMPP and the protocol(s)
used on a foreign messaging network
o FN1 -- A foreign messaging network
o FC1 -- A client on a foreign messaging network
2.2 Server
A server 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 clients and other servers) and to
route appropriately-addressed XML data "stanzas" among such entities
over XML streams. Most XMPP-compliant servers also assume
responsibility for the storage of data that is used by clients (e.g.,
the contact list for each IM user); in this case, the XML data is
processed directly by the server itself on behalf of the client and
is not routed to another entity. Compliant server implementations
MUST ensure in-order processing of XML stanzas received from
connected clients, servers, and services.
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2.3 Client
Most clients connect directly to a server over a TCP socket and use
XMPP to take full advantage of the functionality provided by a server
and any 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 server on behalf of each authorized
client, with each resource connecting over a discrete TCP socket and
differentiated by the resource identifier of a Jabber ID (Section 3)
(e.g., user@domain/home vs. user@domain/work). The port assigned by
the IANA [6] for connections between a Jabber client and a Jabber
server is 5222. For further details about client-to-server
communications for the purpose of instant messaging and presence,
refer to XMPP IM [2].
2.4 Gateway
A gateway is a special-purpose server-side 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 servers, and between gateways and the foreign messaging system,
are not defined in this document.
2.5 Network
Because each server is identified by a network address (typically a
DNS hostname) and because server-to-server communications are a
simple extension of the client-to-server protocol, in practice the
system consists of a network of servers that inter-communicate. Thus
user-a@domain1 is able to exchange messages, presence, and other
information with user-b@domain2. 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 servers 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 server to which the
user connects, and the user's active session or connection (e.g., a
specific client) in the form of user@domain/resource. However, node
types other than clients are possible; for example, a specific chat
room is offered by a multi-user chat service is addressed as
room@service, where "room" is the name of the chat room and "service"
is the hostname of the multi-user 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" server
to which other entities connect for XML routing and data management
capabilities. However, the entity referenced by a domain identifier
is not always a server, and may be a service that is addressed as a
subdomain of a server and that provides functionality above and
beyond the capabilities of a server (a multi-user chat service, a
user directory, a gateway to a foreign messaging system, etc.).
The domain identifier for every server 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 server or gateway (e.g., a client), although it can also
represent other kinds of entities (e.g., a multi-user chat room
associated with a multi-user chat service). The entity represented
by a node identifier is addressed within the context of a specific
domain (e.g., user@domain). Node identifiers are restricted to 256
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bytes. A node identifier MAY contain any Unicode character higher
than #x20 with the exception of 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 the entity associated with a node identifier. An entity
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 the XML specification [1], it
MUST be suitably escaped for inclusion within an XML stream.
Resource identifiers are case sensitive.
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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
stanzas". (Note: in this overview we use the example of
communications between a client and server; however XML streams are
more generalized and may be used for communications from server to
server and from service to server as well.)
In order to connect to a server, a client must initiate an XML stream
by sending a <stream> tag to the server, 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 server SHOULD then reply with a second
XML stream back to the client, again optionally preceded by a text
declaration.
Within the context of an XML stream, a sender is able to send a
discrete semantic unit of structured information to any recipient.
This unit of structured information is a well-balanced XML stanza,
such as a message, presence, or IQ stanza (a stanza of an XML
document is said to be well-balanced if it matches production [43]
content of the XML specification [1]). These stanzas exist at the
direct child level (depth=1) of the root <stream/> element. The
start of any XML stanza is unambiguously denoted by the element start
tag at depth=1 (e.g., <presence>), and the end of any XML stanza is
unambiguously denoted by the corresponding close tag at depth=1
(e.g., </presence>). Each XML stanza 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 client's request by sending a closing </stream> tag to the
server.
Thus a client's session with a server can be seen as two open-ended
XML documents that are built up through the accumulation of the XML
stanzas that are sent over the course of the session (one from the
client to the server and one from the server to the client), and the
root <stream/> element can be considered the document entity for
those streams. In essence, then, an XML stream acts as an envelope
for all the XML stanzas 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 the XML specification [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. The 'id' attribute is of type ID
as defined in section 3.3.1 of the XML specification [1] and
therefore MUST match the Name production as defined in section 2.3
of the XML specification [1]. Validity contraints on names within
XML documents (but not XML streams) are defined in the XML
specification [1]; however, because the stream in one direction
can be seen as a document that is built up over the length of a
session, at a minimum the value of an 'id' attribute MUST be
unique within that stream.
o version -- The 'version' attribute MAY be used in the XML stream
from the initiating entity to the receiving entity in order signal
compliance with the protocol defined herein; this is done by
setting the value of the attribute to "1.0". If the initiating
entity includes the version attribute, the receiving entity MUST
reciprocate by including the attribute in its response (if the
receiving entity supports XMPP 1.0).
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
version | signals XMPP 1.0 support | signals XMPP 1.0 support
4.4 Namespace Declarations
The stream element MAY also contain namespace declarations as defined
in the XML namespaces specification [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
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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. The
default namespace declaration applies to the stream and all stanzas
sent within a stream.
XML streams function as containers for any XML stanzas 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 stanza over an
XML stream. A compliant implementation MUST support the following
two namespaces (for historical reasons, existing implementations MAY
support only these two default namespaces):
o jabber:client -- this default namespace is declared when the
stream is used for communications between a client and a server
o jabber:server -- this default namespace is declared when the
stream is used for communications between two servers
The jabber:client and jabber:server namespaces are nearly identical
but are used in different contexts (client-to-server communications
for jabber:client and server-to-server communications for
jabber:server). The only difference between the two is that the 'to'
and 'from' attributes are OPTIONAL on stanzas sent within
jabber:client, whereas they are REQUIRED on stanzas sent within
jabber:server. If a compliant implementation accepts a stream that
is scoped by the 'jabber:client' or 'jabber:server' namespace, it
MUST support all three core stanza types (message, presence, and IQ)
as described herein and defined in the DTD and schema.
4.5 Stream Features
The root stream element MAY contain a features child element (e.g.,
<stream:features/> if the stream namespace prefix is 'stream'). This
is used to communicate generic stream-level capabilities including
stream-level features that can be negotiated as the streams are set
up. If the initiating entity sends a "version='1.0'" attribute in
its initiating stream element, the receiving entity MUST send a
features child element to the initiating entity if there are any
capabilities that need to be advertised or features that can be
negotiated for the stream. Currently this is used for SASL and TLS
negotiation only, but it could be used for other negotiable features
in the future. Examples are shown under Stream Authentication
(Section 5) below.
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4.6 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 SHOULD be sent by a Jabber entity (usually a server
rather than a client) if it perceives that a stream-level error has
occurred. Examples include the sending of invalid XML, the shutdown
of a server, an internal server error such as the shutdown of a
session manager, and an attempt by a client 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>
4.7 Simple Streams Example
The following is a simple stream-based session of a client on a
server (where the "C" lines are sent from the client to the server,
and the "S" lines are sent from the server to the client):
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A simple session:
C: <?xml version='1.0'?>
<stream:stream
to='server'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
version='1.0'>
S: <?xml version='1.0'?>
<stream:stream
from='server'
id='id_123456789'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
version='1.0'>
... authentication ...
C: <message from='me@mydomain' to='you@yourdomain'>
C: <body>Watson come here, I need you!</body>
C: </message>
S: <message from='you@yourdomain' to='me@mydomain'>
S: <body>I'm on my way!</body>
S: </message>
C: </stream:stream>
S: </stream:stream>
These are in actuality a sending stream and a receiving stream, which
can be viewed a-chronologically as two XML documents:
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C: <?xml version='1.0'?>
<stream:stream
to='server'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
version='1.0'>
C: <message from='me@mydomain' to='you@yourdomain'>
C: <body>Watson come here, I need you!</body>
C: </message>
C: </stream:stream>
S: <?xml version='1.0'?>
<stream:stream
from='server'
id='id_123456789'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
version='1.0'>
S: <message from='you@yourdomain' to='me@mydomain'>
S: <body>I'm on my way!</body>
S: </message>
S: </stream:stream>
A session gone bad:
C: <?xml version='1.0'?>
<stream:stream
to='server'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
version='1.0'>
S: <?xml version='1.0'?>
<stream:stream
from='server'
id='id_123456789'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
version='1.0'>
C: <message><body>Bad XML, no closing body tag!</message>
S: <stream:error>Invalid XML</stream:error>
S: </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 user registers with a server or an
administrator configures a server 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 servers 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 RFC 2222
[10] (the namespace identifier for this protocol is http://
www.iana.org/assignments/sasl-mechanisms). If an entity (client,
server, 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 client authentication
with a server, for which the steps involved are as follows:
1. The client 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 server.
2. The server includes the xmlns:sasl namespace declaration in the
XML stream header sent in reply to the client.
3. The server 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 client selects a mechanism by sending a <sasl:auth/> element
to the server; this element MAY optionally contain character
data.
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5. If necessary, the server challenges the client by sending a
<sasl:challenge/> element to the client; this element MAY
optionally contain character data.
6. The client responds to challenge by sending a <sasl:response/>
element to the server; this element MAY optionally contain
character data.
7. If necessary, the server sends more challenges and the client
sends more responses.
This series of challenge/response pairs continues until one of three
things happens:
o The client aborts the handshake by sending a <sasl:abort/> element
to the server.
o The server reports failure by sending a <sasl:failure/> element to
the client.
o The server reports success by sending a <sasl:success/> element to
the client; 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 client authenticating
with a server using SASL.
Step 1: Client initiates stream to server:
<stream:stream
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
to='capulet.com'
version='1.0'>
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Step 2: Server responds with a stream tag sent to the client:
<stream:stream
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
id='12345678'
version='1.0'>
Step 3: Server informs client of available authentication mechanisms:
<stream:features>
<mechanisms xmlns='http://www.iana.org/assignments/sasl-mechanisms'>
<mechanism>DIGEST-MD5</mechanism>
<mechanism>PLAIN</mechanism>
</mechanisms>
</stream:features>
Step 4: Client selects an authentication mechanism:
<auth
xmlns='http://www.iana.org/assignments/sasl-mechanisms'
mechanism='DIGEST-MD5'/>
Step 5: Server sends a challenge to the client:
<challenge xmlns='http://www.iana.org/assignments/sasl-mechanisms'>
cmVhbG09ImNhdGFjbHlzbS5jeCIsbm9uY2U9Ik9BNk1HOXRFUUdtMmhoIi
xxb3A9ImF1dGgiLGNoYXJzZXQ9dXRmLTgsYWxnb3JpdGhtPW1kNS1zZXNz
</challenge>
Step 6: Client responds to the challenge:
<response xmlns='http://www.iana.org/assignments/sasl-mechanisms'>
dXNlcm5hbWU9InJvYiIscmVhbG09ImNhdGFjbHlzbS5jeCIsbm9uY2U9Ik
9BNk1HOXRFUUdtMmhoIixjbm9uY2U9Ik9BNk1IWGg2VnFUclJrIixuYz0w
MDAwMDAwMSxxb3A9YXV0aCxkaWdlc3QtdXJpPSJqYWJiZXIvY2F0YWNseX
NtLmN4IixyZXNwb25zZT1kMzg4ZGFkOTBkNGJiZDc2MGExNTIzMjFmMjE0
M2FmNyxjaGFyc2V0PXV0Zi04
</response>
Step 7: Server sends another challenge to the client:
<challenge xmlns='http://www.iana.org/assignments/sasl-mechanisms'>
cnNwYXV0aD1lYTQwZjYwMzM1YzQyN2I1NTI3Yjg0ZGJhYmNkZmZmZA==
</challenge>
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Step 8: Client responds to the challenge:
<response xmlns='http://www.iana.org/assignments/sasl-mechanisms'/>
Step 9: Server informs client of successful authentication:
<success xmlns='http://www.iana.org/assignments/sasl-mechanisms'/>
Step 9 (alt): Server informs client of failed authentication:
<failure xmlns='http://www.iana.org/assignments/sasl-mechanisms'/>
5.2 Dialback Authentication
XMPP includes a protocol-level method for verifying that a connection
between two servers can be trusted to some degree. 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 stanzas.
Dialback is not intended as a mechanism for securing or encrypting
the streams between servers, only for helping to prevent the spoofing
of a server and the sending of false data from it. Dialback is made
possible by the existence of DNS, since one server can verify that
another server which is connecting to it is authorized to represent a
given server on the Jabber network. All DNS hostname resolutions
MUST first resolve the hostname using an SRV [13] record of
_jabber._tcp.server. 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 server and the random
id per stream. Generating unique but verifiable keys is important to
prevent common man-in-the-middle attacks and server spoofing.
In the description that follows we use the following terminology:
o Originating Server -- the server that is attempting to establish a
connection between the two servers
o Receiving Server -- the server that is trying to authenticate that
the Originating Server represents the Jabber server which it
claims to be
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o Authoritative Server -- the server which is given when a DNS
lookup is performed on the name that the Originating Server
initially gave; for simple environments this will be the
Originating Server, but it could be a separate machine in the
Originating Server's network
The following is a brief summary of the order of events in dialback:
1. Originating Server establishes a connection to Receiving Server.
2. Originating Server sends a 'key' value over the connection to
Receiving Server.
3. Receiving Server establishes a connection to Authoritative
Server.
4. Receiving Server sends the same 'key' value to Authoritative
Server.
5. Authoritative Server replies that key is valid or invalid.
6. Receiving Server tells Originating Server whether it is
authenticated or not.
We can represent this flow of events graphically as follows:
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Originating Receiving
Server Server
----------- ---------
| |
| establish connection |
| ----------------------> |
| |
| send stream header |
| ----------------------> |
| |
| establish connection |
| <---------------------- |
| |
| send stream header |
| <---------------------- |
| | Authoritative
| send dialback key | Server
| ----------------------> | -------------
| | |
| 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 servers is as follows:
1. Originating Server establishes connection to Receiving Server
2. Originating Server sends a stream header to Receiving Server
(the 'to' and 'from' attributes are NOT REQUIRED on the root
stream element):
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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 Server that the Originating Server supports
dialback.
3. Receiving Server sends a stream header back to Originating
Server (the 'to' and 'from' attributes are NOT REQUIRED on the
root stream element):
<stream:stream
xmlns:stream='http://etherx.jabber.org/streams'
xmlns='jabber:server'
xmlns:db='jabber:server:dialback'
id='457F9224A0...'>
4. Originating Server sends a dialback key to Receiving Server:
<db:result
to='Receiving Server'
from='Originating Server'>
98AF014EDC0...
</db:result>
Note: this key is not examined by Receiving Server, since the
Receiving Server does not keep information about Originating
Server between sessions.
5. Receiving Server now establishes a connection back to
Originating Server, getting the Authoritative Server.
6. Receiving Server sends Authoritative Server a stream header (the
'to' and 'from' attributes are NOT REQUIRED on the root stream
element):
<stream:stream
xmlns:stream='http://etherx.jabber.org/streams'
xmlns='jabber:server'
xmlns:db='jabber:server:dialback'>
7. Authoritative Server sends Receiving Server a stream header:
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<stream:stream
xmlns:stream='http://etherx.jabber.org/streams'
xmlns='jabber:server'
xmlns:db='jabber:server:dialback'
id='1251A342B...'>
8. Receiving Server sends Authoritative Server a stanza indicating
it wants Authoritative Server to verify a key:
<db:verify
from='Receiving Server'
to='Originating Server'
id='457F9224A0...'>
98AF014EDC0...
</db:verify>
Note: passed here are the hostnames, the original identifier
from Receiving Server's stream header to Originating Server in
step 2, and the key Originating Server gave Receiving Server in
step 3. Based on this information and shared secret information
within the 'Originating Server' network, the key is verified.
Any verifiable method can be used to generate the key.
9. Authoritative Server sends a stanza back to Receiving Server
verifying whether the key was valid or invalid:
<db:verify
from='Originating Server'
to='Receiving Server'
type='valid'
id='457F9224A0...'/>
or
<db:verify
from='Originating Server'
to='Receiving Server'
type='invalid'
id='457F9224A0...'/>
10. Receiving Server informs Originating Server of the result:
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<db:result
from='Receiving Server'
to='Originating Server'
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 Server and read
by the Receiving Server; before that, all data stanzas sent to
Receiving Server SHOULD be dropped. As a final guard against
domain spoofing, the Receiving Server MUST verify that all XML
stanzas received from the Originating Server include a 'from'
attribute and that the value of that attribute includes the
validated domain. In addition, all XML stanzas MUST include a
'to' attribute.
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6. XML Stanzas
6.1 Overview
There are three core data elements for XMPP communications: <message/
>, <presence/>, and <iq/>. These 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. Any such
direct child element of the root stream element is called an "XML
stanza".
6.2 Common Attributes
Four attributes are common to message, presence, and IQ stanzas.
These are defined below.
6.2.1 to
The 'to' attribute specifies the JID of the intended recipient for
the stanza. In the 'jabber:client' namespace, a stanza SHOULD
possess a 'to' attribute, although a stanza sent from a client to a
server for handling by that server (e.g., presence sent to the server
for broadcasting to other entities) MAY legitimately lack a 'to'
attribute. In the 'jabber:server' namespace, a stanza MUST possess a
'to' attribute.
6.2.2 from
The 'from' attribute specifies the JID of the sender.
In the 'jabber:client' namespace, a client MUST NOT include a 'from'
attribute on the stanzas it sends to a server; if a server receives a
stanza from a client and the stanza possesses a 'from' attribute, it
MUST ignore the value of the 'from' attribute. In addition, a server
MUST stamp stanzas received from a client with the user@domain/
resource (full JID) of the connected resource that generated the
stanza. In the 'jabber:server' namespace, a stanza MUST possess a
'from' attribute.
A server MUST include a 'from' attribute on stanzas it routes to
other servers. The domain identifier of the JID contained in the
'from' attribute MUST match the hostname of the server as
communicated in the dialback negotiation (or a subdomain thereof).
6.2.3 id
The optional 'id' attribute MAY be used to track stanzas sent and
received. The 'id' attribute is generated by the sender. An 'id'
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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 stanza MAY return that 'id' in any replies, but is NOT
REQUIRED to do so.
The 'id' attribute is of type ID as defined in section 3.3.1 of the
XML specification [1] and therefore MUST match the Name production as
defined in section 2.3 of the XML specification [1]. Validity
contraints on names within XML documents (but not XML streams) are
defined in the XML specification [1]; however, because the stream in
one direction can be seen as a document that is built up over the
length of a session, at a minimum the value of an 'id' attribute MUST
be unique within that stream.
6.2.4 type
The 'type' attribute specifies detailed information about the purpose
or context of the message, presence, or IQ stanza. The particular
allowable values for the 'type' attribute vary depending on whether
the stanza is a message, presence, or IQ, and thus are specified in
the following sections.
6.2.5 xml:lang
Any message or presence stanza MAY possess an 'xml:lang' attribute
specifying the default language of any CDATA sections of the stanza
or its child elements. An IQ stanza SHOULD NOT possess an 'xml:lang'
attribute, since it is merely a vessel for data in other namespaces
and does not itself contain children that have CDATA. The value of
the 'xml:lang' attribute MUST be a NMTOKEN and MUST conform to the
format defined in RFC 3066 [12].
6.3 Message Stanzas
Message stanzas 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 stanza is optional and specifies
the conversational context of the message. The sending of a message
stanza without a 'type' attribute signals that the message stanza is
a single message. However, the 'type' attribute MAY also have one of
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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 stanza 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 any of
the following child elements (which MUST NOT contain mixed content):
o body -- The textual contents of the message; normally included but
NOT REQUIRED. The <body/> element MUST NOT possess any
attributes, with the exception of the 'xml:lang' attribute.
Multiple instances of the <body/> element MAY be included but only
if each instance possesses an 'xml:lang' attribute with a distinct
language value.
o subject -- The subject of the message. The <subject/> element
MUST NOT possess any attributes, with the exception of the
'xml:lang' attribute. Multiple instances of the <subject/>
element MAY be included but only if each instance possesses an
'xml:lang' attribute with a distinct language value.
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 between two entities. If used, it MUST be
unique to that conversation thread within the stream and MUST be
consistent throughout that conversation. Only one <thread/>
element MAY be included in a message stanza, and it MUST NOT
possess any attributes.
If the message stanza is of type "error", it MUST include an <error/>
child, which in turn MUST possess a 'code' attribute corresponding to
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one of the standard error codes (Appendix A), MAY possess an
'xml:lang' attribute, and MAY also contain PCDATA corresponding to a
natural-language description of the error. An <error/> child MUST
NOT be included if the stanza type is anything other than "error".
As described under extended namespaces (Section 6.6), a message
stanza MAY also contain any properly-namespaced child element (other
than the core data elements, stream elements, or defined children
thereof).
6.4 Presence Stanzas
Presence stanzas 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 stanza is optional. A presence
stanza 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 stanza. 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.
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 stanza.
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Information about the subscription model used within XMPP can be
found in XMPP IM [2].
6.4.2 Children
If a presence stanza possesses no 'type' attribute, it MAY contain
any of the following child elements (note that the <status/> child
MAY be sent in a presence stanza of type "unavailable" or, for
historical reasons, "subscribe"):
o show -- Describes the availability status of an entity or specific
resource. Only one <show/> element MAY be included in a presence
stanza, and it MUST NOT possess any attributes. The value SHOULD
be one of the following (values other than these four MAY be
ignored; additional availability types could be defined through a
properly-namespaced child element of the presence stanza):
* 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"). The <status/> element MUST NOT possess any
attributes, with the exception of the 'xml:lang' attribute.
Multiple instances of the <status/> element MAY be included but
only if each instance possesses an 'xml:lang' attribute with a
distinct language value.
o priority -- A non-negative integer representing the priority level
of the connected resource, with zero as the lowest priority. Only
one <priority/> element MAY be included in a presence stanza, and
it MUST NOT possess any attributes.
If the presence stanza 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 contain
PCDATA corresponding to a natural-language description of the error.
An <error/> child MUST NOT be included if the stanza type is anything
other than "error".
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As described under extended namespaces (Section 6.6), a presence
stanza MAY also contain any properly-namespaced child element (other
than the core data elements, stream elements, or defined children
thereof).
6.5 IQ Stanzas
6.5.1 Overview
Info/Query, or IQ, is a simple request-response mechanism. Just as
HTTP is a request-response medium, IQ stanzas 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"> |
| <--------------------- |
| |
An entity that receives a request of type 'get' or 'set' MUST reply
with a response of type 'result' or 'error'.
6.5.2 Types of IQ
The 'type' attribute of an IQ stanza is REQUIRED. The 'type'
attribute specifies a distinct step within a request-response
interaction. The value SHOULD be one of the following (all other
values MAY be ignored):
o get -- The stanza is a request for information.
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o set -- The stanza provides required data, sets new values, or
replaces existing values.
o result -- The stanza 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 stanza 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 stanza MAY contain any properly-namespaced child element (other
than the core data elements, stream elements, or defined children
thereof).
If the IQ stanza 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 contain PCDATA
corresponding to a natural-language description of the error. An
<error/> child MUST NOT be included if the stanza 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
stanza 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). 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
namespace, it MUST ignore the associated XML data. If an entity
receives an IQ stanza in a namespace it does not understand, the
entity SHOULD return an IQ stanza of type "error" with an error
element of code 400 (bad request). If an entity receives a message
or presence stanza that contains XML data in an extended namespace it
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does not understand, the portion of the stanza that is in the unknown
namespace SHOULD be ignored. If an entity receives a message stanza
without a <body/> element but containing only a child element bound
by a namespace it does not understand, it MUST ignore that stanza.
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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. Mainly for historical reasons, the default
namespace for XMPP data stanzas 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 server is not responsible for validating the XML elements forwarded
to a client; an implementation MAY choose to provide only validated
data elements but is NOT REQUIRED to do so. Clients 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. Validation of XML streams and stanzas is NOT
REQUIRED or recommended, and DTDs and schemas are included herein for
descriptive purposes only.
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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 the XML specification
[1].
7.5 Inclusion of Text Declaration
An application MAY send a text declaration. Applications MUST follow
the rules in the XML specification [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
[15] service names, as specified in Section 6.1.1; these service
names are associated with TCP ports 5222 and 5269 respectively.
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9. Internationalization Considerations
o If a client sends an xml:lang attribute on a stanza, the server
MUST NOT modify or delete it.
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10. Security Considerations
10.1 Client-to-Server Communications
The SASL protocol for authenticating XML streams negotiated between a
client and a server (defined under Section 5.1 above) provides a
reliable mechanism for validating that a client connecting to a
server is who it claims to be.
The IP address and method of access of clients MUST NOT be made
available by a server, nor are any connections other than the
original server connection required. This helps protect the client's
server 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 [14].
10.2 Server-to-Server Communications
It is OPTIONAL for any given server to communicate with other
servers, and server-to-server communications MAY be disabled by the
administrator of any given deployment.
If two servers 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
servers 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 servers.
10.3 Minimum Security Mechanisms
Although service provisioning is a policy matter, at a minimum, all
implementations MUST support the SASL DIGEST-MD5 mechanism for
authentication.
10.4 Firewalls
Communications using XMPP occur over TCP sockets on port 5222
(client-to-server) or port 5269 (server-to-server), as registered
with the IANA [6]. Use of these well-known ports allows
administrators to easily enable or disable XMPP activity through
existing and commonly-deployed firewalls.
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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-
ietf-xmpp-im-00, work in progress)", December 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] Alvestrand, H., "Tags for the Identification of Languages", BCP
47, RFC 3066, January 2001.
[13] Gulbrandsen, A. and P. Vixie, "A DNS RR for specifying the
location of services (DNS SRV)", RFC 2052, October 1996.
[14] Elkins, M., Del Torto, D., Levien, R. and T. Roessler, "MIME
Security with OpenPGP", RFC 3156, August 2001.
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[15] Linn, J., "Generic Security Service Application Program
Interface, Version 2", RFC 2078, January 1997.
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
stanzas. This element is a child of the failed stanza 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 clients that they
have provided incorrect authorization information, e.g., an
incorrect password or unknown username when attempting to
authenticate with a server.
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 user attempts to set information associated
with another user.
o 404 (Not Found) - Code 404 is used to inform a sender that no
recipient was found matching the JID to which an XML stanza was
sent, e.g., if a sender has attempted to send a message to a JID
that does not exist. (Note: if the server 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 client attempts to set the time or version of a server.
o 406 (Not Acceptable) - Code 406 is used when an XML stanza is for
some reason not acceptable to a server or other entity. This
might be generated when, for example, a user attempts to register
with a server 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,
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e.g., if a user attempts to send a message through a gateway to a
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 server or
service encounters an unexpected condition which prevents it from
handling an XML stanza from a sender, e.g., if an authentication
request is not handled by a server 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 user attempts to register with a server that does not allow
registration.
o 502 (Remote Server Error) - Code 502 is used when delivery of an
XML stanza fails because of an inability to reach the intended
remote server or service, e.g., because a remote server'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 server timeout, e.g., if an incorrect hostname is
specified.
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Appendix B. Formal Definitions
B.1 streams namespace
The namespace declaration for the root stream element is 'http://
etherx.jabber.org/streams'.
B.1.1 DTD
<?xml version='1.0' encoding='UTF-8'?>
<!ELEMENT stream (#PCDATA | error?)*>
<!ATTLIST stream
to CDATA #IMPLIED
from CDATA #IMPLIED
id ID #IMPLIED
version CDATA #IMPLIED
>
<!ELEMENT error (#PCDATA)>
<!ELEMENT features (#PCDATA)>
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B.1.2 Schema
<?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:server'
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:ID' use='optional'/>
<xsd:attribute name='version' type='xsd:decimal' use='optional'/>
</xsd:complexType>
</xsd:element>
<xsd:element name='error' type='xsd:string'/>
</xsd:schema>
B.2 SASL namespace
The namespace declaration for SASL-related elements is 'http://
www.iana.org/assignments/sasl-mechanisms'.
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B.2.1 DTD
<?xml version='1.0' encoding='UTF-8'?>
<!ELEMENT mechanisms (mechanism)*>
<!ELEMENT mechanism (#PCDATA)>
<!ELEMENT auth (#PCDATA)>
<!ATTLIST auth mechanism CDATA #REQUIRED>
<!ELEMENT challenge (#PCDATA)>
<!ELEMENT response (#PCDATA)>
<!ELEMENT abort (#PCDATA)>
<!ELEMENT success (#PCDATA)>
<!ELEMENT failure (#PCDATA)>
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B.2.2 Schema
<?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:element name='auth'>
<xsd:complexType mixed='true'>
<xsd:attribute name='mechanism' 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
B.3.1 DTD
<?xml version='1.0' encoding='UTF-8'?>
<!ELEMENT message (( body* | subject* | thread? |
error? | (#PCDATA) )*)>
<!ATTLIST message
to CDATA #IMPLIED
from CDATA #IMPLIED
id ID #IMPLIED
xml:lang NMTOKEN #IMPLIED
type ( chat | groupchat | headline | error ) #IMPLIED
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>
<!ELEMENT body (#PCDATA)>
<!ATTLIST body xml:lang NMTOKEN #IMPLIED>
<!ELEMENT subject (#PCDATA)>
<!ATTLIST subject xml:lang NMTOKEN #IMPLIED>
<!ELEMENT thread (#PCDATA)>
<!ELEMENT presence (( show? | status* | priority? | error? )*)>
<!ATTLIST presence
to CDATA #IMPLIED
from CDATA #IMPLIED
id ID #IMPLIED
xml:lang NMTOKEN #IMPLIED
type ( subscribe | subscribed | unsubscribe |
unsubscribed | unavailable | error ) #IMPLIED
>
<!ELEMENT show (#PCDATA)>
<!ELEMENT status (#PCDATA)>
<!ATTLIST status xml:lang NMTOKEN #IMPLIED>
<!ELEMENT priority (#PCDATA)>
<!ELEMENT iq ( error | (#PCDATA) )*>
<!ATTLIST iq
to CDATA #IMPLIED
from CDATA #IMPLIED
id ID #IMPLIED
type ( get | set | result | error ) #REQUIRED
>
<!ELEMENT error (#PCDATA)>
<!ATTLIST error
code CDATA #REQUIRED
xml:lang NMTOKEN #IMPLIED
>
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'>
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<xsd:element name='message'>
<xsd:complexType mixed='true'>
<xsd:choice>
<xsd:element ref='body' minOccurs='0' maxOccurs='unbounded'/>
<xsd:element ref='subject' minOccurs='0' maxOccurs='unbounded'/>
<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:ID' use='optional'/>
<xsd:attribute name='xml:lang' type='xsd:NMTOKEN' use='optional'/>
<xsd:attribute name='type' use='optional'>
<xsd:simpleType>
<xsd:restriction base='xsd:NCName'>
<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:complexType>
<xsd:attribute name='xml:lang' type='xsd:NMTOKEN' use='optional'/>
</xsd:complexType>
</xsd:element>
<xsd:element name='subject' type='xsd:string'>
<xsd:complexType>
<xsd:attribute name='xml:lang' type='xsd:NMTOKEN' use='optional'/>
</xsd:complexType>
</xsd:element>
<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='unbounded'/>
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<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:ID' use='optional'/>
<xsd:attribute name='xml:lang' type='xsd:NMTOKEN' use='optional'/>
<xsd:attribute name='type' use='optional'>
<xsd:simpleType>
<xsd:restriction base='xsd:NCName'>
<xsd:enumeration value='subscribe'/>
<xsd:enumeration value='subscribed'/>
<xsd:enumeration value='unsubscribe'/>
<xsd:enumeration value='unsubscribed'/>
<xsd:enumeration value='unavailable'/>
<xsd:enumeration value='error'/>
</xsd:restriction>
</xsd:simpleType>
</xsd:attribute>
</xsd:complexType>
</xsd:element>
<xsd:element name='show'>
<xsd:simpleType>
<xsd:restriction base='xsd:NCName'>
<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:complexType>
<xsd:attribute name='xml:lang' type='xsd:NMTOKEN' use='optional'/>
</xsd:complexType>
</xsd:element>
<xsd:element name='priority' type='xsd:nonNegativeInteger'/>
<xsd:element name='iq'>
<xsd:complexType mixed='true'>
<xsd:choice>
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<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:ID' use='optional'/>
<xsd:attribute name='type' use='required'>
<xsd:simpleType>
<xsd:restriction base='xsd:NCName'>
<xsd:enumeration value='get'/>
<xsd:enumeration value='set'/>
<xsd:enumeration value='result'/>
<xsd:enumeration value='error'/>
</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:attribute name='xml:lang' type='xsd:NMTOKEN' use='optional'/>
</xsd:complexType>
</xsd:element>
</xsd:schema>
B.4 jabber:server namespace
B.4.1 DTD
<?xml version='1.0' encoding='UTF-8'?>
<!ELEMENT message (( body* | subject* | thread? |
error? | (#PCDATA) )*)>
<!ATTLIST message
to CDATA #REQUIRED
from CDATA #REQUIRED
id ID #IMPLIED
xml:lang NMTOKEN #IMPLIED
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type ( chat | groupchat | headline | error ) #IMPLIED
>
<!ELEMENT body (#PCDATA)>
<!ATTLIST body xml:lang NMTOKEN #IMPLIED>
<!ELEMENT subject (#PCDATA)>
<!ATTLIST subject xml:lang NMTOKEN #IMPLIED>
<!ELEMENT thread (#PCDATA)>
<!ELEMENT presence (( show? | status* | priority? | error? )*)>
<!ATTLIST presence
to CDATA #REQUIRED
from CDATA #REQUIRED
id ID #IMPLIED
xml:lang NMTOKEN #IMPLIED
type ( subscribe | subscribed | unsubscribe |
unsubscribed | unavailable | error ) #IMPLIED
>
<!ELEMENT show (#PCDATA)>
<!ELEMENT status (#PCDATA)>
<!ATTLIST status xml:lang NMTOKEN #IMPLIED>
<!ELEMENT priority (#PCDATA)>
<!ELEMENT iq ( error | (#PCDATA) )*>
<!ATTLIST iq
to CDATA #REQUIRED
from CDATA #REQUIRED
id ID #IMPLIED
type ( get | set | result | error ) #REQUIRED
>
<!ELEMENT error (#PCDATA)>
<!ATTLIST error
code CDATA #REQUIRED
xml:lang NMTOKEN #IMPLIED
>
B.4.2 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'
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elementFormDefault='qualified'>
<xsd:element name='message'>
<xsd:complexType mixed='true'>
<xsd:choice>
<xsd:element ref='body' minOccurs='0' maxOccurs='unbounded'/>
<xsd:element ref='subject' minOccurs='0' maxOccurs='unbounded'/>
<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='required'/>
<xsd:attribute name='from' type='xsd:string' use='required'/>
<xsd:attribute name='id' type='xsd:ID' use='optional'/>
<xsd:attribute name='xml:lang' type='xsd:NMTOKEN' use='optional'/>
<xsd:attribute name='type' use='optional'>
<xsd:simpleType>
<xsd:restriction base='xsd:NCName'>
<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:complexType>
<xsd:attribute name='xml:lang' type='xsd:NMTOKEN' use='optional'/>
</xsd:complexType>
</xsd:element>
<xsd:element name='subject' type='xsd:string'>
<xsd:complexType>
<xsd:attribute name='xml:lang' type='xsd:NMTOKEN' use='optional'/>
</xsd:complexType>
</xsd:element>
<xsd:element name='thread' type='xsd:string'/>
<xsd:element name='presence'>
<xsd:complexType>
<xsd:choice>
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<xsd:element ref='show' minOccurs='0' maxOccurs='1'/>
<xsd:element ref='status' minOccurs='0' maxOccurs='unbounded'/>
<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='required'/>
<xsd:attribute name='from' type='xsd:string' use='required'/>
<xsd:attribute name='id' type='xsd:ID' use='optional'/>
<xsd:attribute name='xml:lang' type='xsd:NMTOKEN' use='optional'/>
<xsd:attribute name='type' use='optional'>
<xsd:simpleType>
<xsd:restriction base='xsd:NCName'>
<xsd:enumeration value='subscribe'/>
<xsd:enumeration value='subscribed'/>
<xsd:enumeration value='unsubscribe'/>
<xsd:enumeration value='unsubscribed'/>
<xsd:enumeration value='unavailable'/>
<xsd:enumeration value='error'/>
</xsd:restriction>
</xsd:simpleType>
</xsd:attribute>
</xsd:complexType>
</xsd:element>
<xsd:element name='show'>
<xsd:simpleType>
<xsd:restriction base='xsd:NCName'>
<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:complexType>
<xsd:attribute name='xml:lang' type='xsd:NMTOKEN' use='optional'/>
</xsd:complexType>
</xsd:element>
<xsd:element name='priority' type='xsd:nonNegativeInteger'/>
<xsd:element name='iq'>
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<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='required'/>
<xsd:attribute name='from' type='xsd:string' use='required'/>
<xsd:attribute name='id' type='xsd:ID' use='optional'/>
<xsd:attribute name='type' use='required'>
<xsd:simpleType>
<xsd:restriction base='xsd:NCName'>
<xsd:enumeration value='get'/>
<xsd:enumeration value='set'/>
<xsd:enumeration value='result'/>
<xsd:enumeration value='error'/>
</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:attribute name='xml:lang' type='xsd:NMTOKEN' use='optional'/>
</xsd:complexType>
</xsd:element>
</xsd:schema>
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Appendix C. Revision History
Note to RFC editor: please remove this entire appendix, and the
corresponding entries in the table of contents, prior to publication.
C.1 Changes from draft-miller-xmpp-core-02
o Brought Streams Authentication section into line with discussion
on list and at IETF 55 meeting.
o Added information about the optional 'xml:lang' attribute per
discussion on list and at IETF 55 meeting.
o Specified that validation is neither required nor recommended, and
that the formal definitions (DTDs and schemas) are included for
descriptive purposes only.
o Specified that the response to an IQ stanza of type 'get' or 'set'
must be an IQ stanza of type 'result' or 'error'.
o Specified that compliant server implementations must process
stanzas in order.
o Specified that for historical reasons some server implementations
may accept 'stream:' as the only valid namespace prefix on the
root stream element.
o Clarified the difference between 'jabber:client' and
'jabber:server' namespaces, namely, that 'to' and 'from'
attributes are required on all stanzas in the latter but not the
former.
o Fixed typo in Step 9 of the dialback protocol (changed db:result
to db:verify).
o Removed references to TLS pending list discussion.
o Removed the non-normative appendix on OpenPGP usage pending its
inclusion in a separate I-D.
o Simplified the architecture diagram, removed most references to
services, and removed references to the 'jabber:component:*'
namespaces.
o Noted that XMPP activity respects firewall administration
policies.
o Further specified the scope and uniqueness of the 'id' attribute
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in all stanza types and the <thread/> element in message stanzas.
o Nomenclature changes: (1) from "chunks" to "stanzas"; (2) from
"host" to "server" and from "node" to "client" (except with regard
to definition of the addressing scheme).
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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
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Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
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