Network Working Group P. Saint-Andre
Internet-Draft J. Miller
Expires: November 2, 2003 Jabber Software Foundation
May 04, 2003
XMPP Core
draft-ietf-xmpp-core-12
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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This Internet-Draft will expire on November 2, 2003.
Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
This document describes the core features of the Extensible Messaging
and Presence Protocol (XMPP), a protocol for streaming XML elements
in order to exchange messages and presence information in close to
real time. XMPP is used mainly for the purpose of building instant
messaging (IM) and presence applications, such as the servers and
clients that comprise the Jabber network.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 5
1.3 Discussion Venue . . . . . . . . . . . . . . . . . . . . . . 5
1.4 Intellectual Property Notice . . . . . . . . . . . . . . . . 5
2. Generalized Architecture . . . . . . . . . . . . . . . . . . 6
2.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2 Server . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.3 Client . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.4 Gateway . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.5 Network . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3. Addressing Scheme . . . . . . . . . . . . . . . . . . . . . 8
3.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.2 Domain Identifier . . . . . . . . . . . . . . . . . . . . . 8
3.3 Node Identifier . . . . . . . . . . . . . . . . . . . . . . 8
3.4 Resource Identifier . . . . . . . . . . . . . . . . . . . . 9
4. XML Streams . . . . . . . . . . . . . . . . . . . . . . . . 10
4.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.2 Stream Attributes . . . . . . . . . . . . . . . . . . . . . 11
4.3 Namespace Declarations . . . . . . . . . . . . . . . . . . . 12
4.3.1 Stream Namespace Declaration . . . . . . . . . . . . . . . . 12
4.3.2 Default Namespace Declaration . . . . . . . . . . . . . . . 13
4.4 Stream Features . . . . . . . . . . . . . . . . . . . . . . 13
4.5 Stream Errors . . . . . . . . . . . . . . . . . . . . . . . 14
4.5.1 Rules . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4.5.2 Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4.5.3 Conditions . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.5.4 Extensibility . . . . . . . . . . . . . . . . . . . . . . . 16
4.6 Simple Streams Example . . . . . . . . . . . . . . . . . . . 16
5. Stream Encryption . . . . . . . . . . . . . . . . . . . . . 19
5.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 19
5.2 Narrative . . . . . . . . . . . . . . . . . . . . . . . . . 20
5.3 Client-to-Server Example . . . . . . . . . . . . . . . . . . 21
5.4 Server-to-Server Example . . . . . . . . . . . . . . . . . . 23
6. Stream Authentication . . . . . . . . . . . . . . . . . . . 26
6.1 SASL Authentication . . . . . . . . . . . . . . . . . . . . 26
6.1.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 26
6.1.2 Narrative . . . . . . . . . . . . . . . . . . . . . . . . . 27
6.1.3 SASL Definition . . . . . . . . . . . . . . . . . . . . . . 29
6.1.4 Client-to-Server Example . . . . . . . . . . . . . . . . . . 30
6.1.5 Server-to-Server Example . . . . . . . . . . . . . . . . . . 32
6.2 Dialback Authentication . . . . . . . . . . . . . . . . . . 35
6.2.1 Dialback Protocol . . . . . . . . . . . . . . . . . . . . . 37
7. XML Stanzas . . . . . . . . . . . . . . . . . . . . . . . . 42
7.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 42
7.2 Common Attributes . . . . . . . . . . . . . . . . . . . . . 42
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7.2.1 to . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
7.2.2 from . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
7.2.3 id . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
7.2.4 type . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
7.2.5 xml:lang . . . . . . . . . . . . . . . . . . . . . . . . . . 43
7.3 Message Stanzas . . . . . . . . . . . . . . . . . . . . . . 44
7.3.1 Types of Message . . . . . . . . . . . . . . . . . . . . . . 44
7.3.2 Children . . . . . . . . . . . . . . . . . . . . . . . . . . 44
7.4 Presence Stanzas . . . . . . . . . . . . . . . . . . . . . . 46
7.4.1 Types of Presence . . . . . . . . . . . . . . . . . . . . . 46
7.4.2 Children . . . . . . . . . . . . . . . . . . . . . . . . . . 46
7.5 IQ Stanzas . . . . . . . . . . . . . . . . . . . . . . . . . 48
7.5.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 48
7.5.2 Types of IQ . . . . . . . . . . . . . . . . . . . . . . . . 48
7.5.3 Children . . . . . . . . . . . . . . . . . . . . . . . . . . 49
7.6 Extended Namespaces . . . . . . . . . . . . . . . . . . . . 49
7.7 Stanza Errors . . . . . . . . . . . . . . . . . . . . . . . 50
7.7.1 Rules . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
7.7.2 Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
7.7.3 Conditions . . . . . . . . . . . . . . . . . . . . . . . . . 51
7.7.4 Extensibility . . . . . . . . . . . . . . . . . . . . . . . 52
8. XML Usage within XMPP . . . . . . . . . . . . . . . . . . . 54
8.1 Restrictions . . . . . . . . . . . . . . . . . . . . . . . . 54
8.2 Namespaces . . . . . . . . . . . . . . . . . . . . . . . . . 54
8.3 Validation . . . . . . . . . . . . . . . . . . . . . . . . . 54
8.4 Character Encodings . . . . . . . . . . . . . . . . . . . . 55
8.5 Inclusion of Text Declaration . . . . . . . . . . . . . . . 55
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . 56
9.1 XML Namespace Name for TLS Data . . . . . . . . . . . . . . 56
9.2 XML Namespace Name for SASL Data . . . . . . . . . . . . . . 56
9.3 XML Namespace Name for Stream Errors . . . . . . . . . . . . 56
9.4 XML Namespace Name for Stanza Errors . . . . . . . . . . . . 57
9.5 Existing Registrations . . . . . . . . . . . . . . . . . . . 57
10. Internationalization Considerations . . . . . . . . . . . . 58
11. Security Considerations . . . . . . . . . . . . . . . . . . 59
11.1 High Security . . . . . . . . . . . . . . . . . . . . . . . 59
11.2 Client-to-Server Communications . . . . . . . . . . . . . . 59
11.3 Server-to-Server Communications . . . . . . . . . . . . . . 60
11.4 Firewalls . . . . . . . . . . . . . . . . . . . . . . . . . 60
11.5 Mandatory to Implement Technologies . . . . . . . . . . . . 60
Normative References . . . . . . . . . . . . . . . . . . . . 61
Informative References . . . . . . . . . . . . . . . . . . . 63
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 63
A. XML Schemas . . . . . . . . . . . . . . . . . . . . . . . . 65
A.1 Streams namespace . . . . . . . . . . . . . . . . . . . . . 65
A.2 TLS namespace . . . . . . . . . . . . . . . . . . . . . . . 66
A.3 SASL namespace . . . . . . . . . . . . . . . . . . . . . . . 66
A.4 Dialback namespace . . . . . . . . . . . . . . . . . . . . . 67
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A.5 Client namespace . . . . . . . . . . . . . . . . . . . . . . 68
A.6 Server namespace . . . . . . . . . . . . . . . . . . . . . . 72
A.7 Stream error namespace . . . . . . . . . . . . . . . . . . . 76
A.8 Stanza error namespace . . . . . . . . . . . . . . . . . . . 77
B. Revision History . . . . . . . . . . . . . . . . . . . . . . 79
B.1 Changes from draft-ietf-xmpp-core-09 . . . . . . . . . . . . 79
B.2 Changes from draft-ietf-xmpp-core-09 . . . . . . . . . . . . 79
B.3 Changes from draft-ietf-xmpp-core-08 . . . . . . . . . . . . 79
B.4 Changes from draft-ietf-xmpp-core-07 . . . . . . . . . . . . 80
B.5 Changes from draft-ietf-xmpp-core-06 . . . . . . . . . . . . 80
B.6 Changes from draft-ietf-xmpp-core-05 . . . . . . . . . . . . 80
B.7 Changes from draft-ietf-xmpp-core-04 . . . . . . . . . . . . 80
B.8 Changes from draft-ietf-xmpp-core-03 . . . . . . . . . . . . 80
B.9 Changes from draft-ietf-xmpp-core-02 . . . . . . . . . . . . 81
B.10 Changes from draft-ietf-xmpp-core-01 . . . . . . . . . . . . 81
B.11 Changes from draft-ietf-xmpp-core-00 . . . . . . . . . . . . 81
B.12 Changes from draft-miller-xmpp-core-02 . . . . . . . . . . . 81
Intellectual Property and Copyright Statements . . . . . . . 83
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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, presence, and
request-response services. The basic syntax and semantics were
developed originally within the Jabber open-source community, mainly
in 1999. In 2002, the XMPP WG was chartered with developing an
adaptation of the Jabber protocol that would be suitable as an IETF
instant messaging and presence technology. As a result of work by the
XMPP WG, the current document defines the core features of XMPP; XMPP
IM [23] defines the extensions required to provide the instant
messaging (IM) and presence functionality defined in RFC 2779 [2].
1.2 Terminology
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 [3].
1.3 Discussion Venue
The authors welcome discussion and comments related to the topics
presented in this document. The preferred forum is the
<xmppwg@jabber.org> mailing list, for which archives and subscription
information are available at <http://www.jabber.org/cgi-bin/mailman/
listinfo/xmppwg/>.
1.4 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 usually has been implemented via a typical
client-server architecture, wherein a client utilizing XMPP accesses
a server over a TCP [4] 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 (non-XMPP) 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, servers, and other entities)
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.,
contact lists for users of XMPP-based IM applications); 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
between any two entities.
2.3 Client
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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. Although there is no necessary coupling
of an XML stream to a TCP socket (e.g., a client COULD connect via
HTTP polling or some other mechanism), this specification defines a
binding for XMPP to TCP only. 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
Identifier (e.g., user@domain/home vs. user@domain/work) as defined
under Section 3. The port registered with the IANA [5] for
connections between a Jabber client and a Jabber server is 5222.
2.4 Gateway
A gateway is a special-purpose server-side service whose primary
function is to translate XMPP into the protocol used by a foreign
(non-XMPP) 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 legacy instant messaging
networks such as AIM, ICQ, MSN Messenger, and Yahoo! Instant
Messenger. 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 and because
server-to-server communications are a straightforward 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. There
are two methods for negotiating a connection between any two servers:
primarily SASL authentication (Section 6.1) and secondarily server
dialback (Section 6.2).
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3. Addressing Scheme
3.1 Overview
An entity is anything that can be considered a network endpoint
(i.e., an ID on the network) and that can communicate using XMPP. All
such entities are uniquely addressable in a form that is consistent
with RFC 2396 [24]. 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 offered by a multi-user chat service could be addressed as
<room@service> (where "room" is the name of the chat room and
"service" is the hostname of the multi-user chat service) and a
specific occupant of such a room could be addressed as <room@service/
nick> (where "nick" is the occupant's room nickname). Many other JID
types are possible (e.g., <domain/resource> could be a server-side
script or service).
3.2 Domain Identifier
The domain identifier is the primary identifier and is the only
REQUIRED element of a JID (a mere 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. A domain identifier MUST conform to RFC 952 [6] and RFC 1123
[7]. A domain identifier MUST be no more than 1023 bytes in length
and MUST conform to the nameprep [8] profile of stringprep [9].
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 (i.e., a client), although it can also
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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; within IM applications of XMPP this address is called a "bare
JID" and is of the form <user@domain>.
A node identifier MUST be no more than 1023 bytes in length and MUST
conform to the nodeprep [10] profile of stringprep [9].
3.4 Resource Identifier
The resource identifier is an optional tertiary identifier, which may
modify either a <user@domain> or mere <domain> address. It usually
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. A resource
identifier is opaque to both servers and other clients, and is
typically defined by a client implementation as the authzid value
provided during stream authentication. An entity may maintain
multiple resources simultaneously.
A resource identifier MUST be no more than 1023 bytes in length and
MUST conform to the resourceprep [11] profile of stringprep [9].
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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 XML stanzas. These
terms may be defined as follows:
Definition of XML Stream: An XML stream is a container for the
exchange of XML elements between any two entities over a network.
An XML stream is negotiated from an initiating entity (usually a
client or server) to a receiving entity (usually a server),
normally over a TCP socket, and corresponds to the initiating
entity's "session" with the receiving entity. The start of the XML
stream is denoted unambiguously by an opening XML <stream> tag
with appropriate attributes and namespace declarations, and the
end of the XML stream is denoted unambiguously by a closing XML </
stream> tag. An XML stream is unidirectional; in order to enable
bidirectional information exchange, the initiating entity and
receiving entity must negotiate one stream in each direction,
normally over the same TCP connection.
Definition of XML Stanza: An XML stanza is a discrete semantic unit
of structured information that is sent from one entity to another
over an XML stream. An XML stanza exists at the direct child level
of the root <stream/> element and is said to be well-balanced if
it matches production [43] content of the XML specification [1]).
The start of any XML stanza is denoted unambiguously by the
element start tag at depth=1 of the XML stream (e.g., <presence>),
and the end of any XML stanza is denoted unambiguously by the
corresponding close tag at depth=1 (e.g., </presence>). An XML
stanza MAY contain child elements (with accompanying attributes,
elements, and CDATA) as necessary in order to convey the desired
information.
Consider the example of a client's session with a server. In order to
connect to a server, a client must initiate an XML stream by sending
an opening <stream> tag to the server, optionally preceded by a text
declaration specifying the XML version supported and the character
encoding (see also Section 8.4). The server SHOULD then reply with a
second XML stream back to the client, again optionally preceded by a
text declaration. Once the client has authenticated with the server
(see Section 6), the client MAY send an unlimited number of XML
stanzas over the stream to any recipient on the network. When the
client desires to close the stream, it simply sends a closing </
stream> tag to the server (alternatively, the stream may be closed by
the server), after which both the client and server SHOULD close the
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underlying TCP connection as well.
Those who are accustomed to thinking of XML in a document-centric
manner may wish to view a client's session with a server as
consisting of two open-ended XML documents: one from the client to
the server and one from the server to the client. From this
perspective, the root <stream/> element can be considered the
document entity for each "document", and the two "documents" are
built up through the accumulation of XML stanzas sent over the two
XML streams. However, this perspective is a convenience only, and
XMPP does not deal in documents but in XML streams and XML stanzas.
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:
|--------------------|
| <stream> |
|--------------------|
| <presence> |
| <show/> |
| </presence> |
|--------------------|
| <message to='foo'> |
| <body/> |
| </message> |
|--------------------|
| <iq to='bar'> |
| <query/> |
| </iq> |
|--------------------|
| ... |
|--------------------|
| </stream> |
|--------------------|
4.2 Stream Attributes
The attributes of the stream element are as follows:
o to -- The 'to' attribute SHOULD be used only in the XML stream
header from the initiating entity to the receiving entity, and
MUST be set to the XMPP address of the receiving entity. There
SHOULD be no 'to' attribute set in the XML stream header by which
the receiving entity replies to the initiating entity; however, if
a 'to' attribute is included, it SHOULD be silently ignored by the
initiating entity.
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o from -- The 'from' attribute SHOULD be used only in the XML stream
header from the receiving entity to the initiating entity, and
MUST be set to the XMPP address of the receiving entity granting
access to the initiating entity. There SHOULD be no 'from'
attribute on the XML stream header sent from the initiating entity
to the receiving entity; however, if a 'from' attribute is
included, it SHOULD be silently ignored by the receiving entity.
o id -- The 'id' attribute SHOULD be used only in the XML stream
header 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 streams
with the receiving entity. There SHOULD be no 'id' attribute on
the XML stream header sent from the initiating entity to the
receiving entity; however, if an 'id' attribute is included, it
SHOULD be silently ignored by the receiving entity.
o version -- If the initiating entity complies with the protocol
defined herein, it MUST include a 'version' attribute in the XML
stream header it sends to the receiving entity, and it MUST set
the value of the 'version' attribute to "1.0". If the initiating
entity includes the version attribute and the receiving entity
supports XMPP 1.0, the receiving entity MUST reciprocate by
including the attribute in its response.
We can summarize these values as follows:
| initiating to receiving | receiving to initiating
------------------------------------------------------------
to | hostname of receiver | silently ignored
from | silently ignored | hostname of receiver
id | silently ignored | session key
version | signals XMPP 1.0 support | signals XMPP 1.0 support
4.3 Namespace Declarations
The stream element MUST possess both a stream namespace declaration
and a default namespace declaration (as "namespace declaration" is
defined in the XML namespaces specification [12]).
4.3.1 Stream Namespace Declaration
A stream namespace declaration (e.g., 'xmlns:stream') is REQUIRED in
both XML streams. A compliant entity SHOULD accept any namespace
prefix on the <stream/> element; however, for historical reasons some
entities MAY accept only a 'stream' prefix, resulting in the use of a
<stream:stream/> element as the stream root. The name of the stream
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namespace MUST be "http://etherx.jabber.org/streams".
4.3.2 Default Namespace Declaration
A default namespace declaration ('xmlns') is REQUIRED and is used in
both XML streams in order to define 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. The
default namespace declaration applies to the stream and all stanzas
sent within a stream (unless explicitly scoped by another namespace).
Since 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. At a
minimum, a compliant implementation MUST support the following two
namespaces (for historical reasons, some 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 schema.
4.4 Stream Features
If the initiating entity sends a "version='1.0'" flag in its
initiating stream element, the receiving entity MUST send a features
child element to the initiating entity in order to announce any
stream-level features that can be negotiated (or capabilities that
otherwise need to be advertised). Currently this is used for SASL and
TLS negotiation only, but it could be used for other negotiable
features in the future (usage is defined under Stream Encryption
(Section 5) and Stream Authentication (Section 6) below). If an
entity does not understand or support some features, it SHOULD
silently ignore them.
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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 MUST be sent by a compliant entity (usually a server
rather than a client) if it perceives that a stream-level error has
occurred.
4.5.1 Rules
The following rules apply to stream-level errors:
o It is assumed that all stream-level errors are unrecoverable;
therefore, if an error occurs at the level of the stream, the
entity that detects the error MUST send a stream error to the
other entity, send a closing </stream> tag, and close the
underlying TCP connection.
o If the error occurs while the stream is being set up, the
receiving entity MUST still send the opening and closing stream
tags and include the error element as a child of the stream
element. In this case, if the initiating entity provides an
unknown host in the 'to' attribute (or provides no 'to' attribute
at all), the server SHOULD provide the server's authoritative
hostname in the 'from' attribute of the stream header sent before
termination.
4.5.2 Syntax
The syntax for stream errors is as follows:
<stream:error class='error-class'>
<condition xmlns='urn:ietf:params:xml:ns:xmpp-streams'>
<descriptive-element-name/>
</condition>
</stream:error>
The value of the 'class' attribute must be one of the following:
o address -- the condition relates to the JID or domain to which the
stream was addressed
o format -- the condition relates to XML format or structure
o redirect -- the condition relates to a host redirection
o server -- the condition relates to the internal state of the
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server
The <condition/> element MUST contain a child element that specifies
a particular stream-level error condition, as defined in the next
section. (Note: the XML namespace name
'urn:ietf:params:xml:ns:xmpp-streams' that scopes the <condition/>
element adheres to the format defined in The IETF XML Registry [25].)
4.5.3 Conditions
The following stream-level error conditions are defined:
o <host-gone/> -- the value of the 'to' attribute provided by the
initiating entity in the stream header corresponds to a hostname
that is no longer hosted by the server; the associated class is
"address".
o <host-unknown/> -- the value of the 'to' attribute provided by the
initiating entity in the stream header does not correspond to a
hostname that is hosted by the server; the associated class is
"address".
o <internal-server-error/> -- the server has experienced a
misconfiguration or an otherwise-undefined internal error that
prevents it from servicing the stream; the associated class is
"server".
o <invalid-id/> -- the stream ID or dialback ID is invalid or does
not match an ID previously provided; the associated class is
"format".
o <invalid-namespace/> -- the stream namespace name is something
other than "http://etherx.jabber.org/streams" or the dialback
namespace name is something other than "jabber:server:dialback";
the associated class is "format".
o <nonmatching-hosts/> -- the hostname provided in a 'from' address
does not match the hostname (or any validated domain) negotiated
via SASL or dialback; the associated class is "address".
o <not-authorized/> -- the entity does not possess sufficient
privileges to perform the desired action; the associated class is
"access".
o <remote-connection-failed/> -- the server is unable to properly
connect to a remote resource that is required for authentication
or authorization; the associated class is "server".
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o <resource-constraint/> -- the server is resource-contrained and is
unable to service the stream; the associated class is "server".
o <see-other-host/> -- the server will not provide service to the
initiating entity but is redirecting traffic to another host; this
element SHOULD contain CDATA specifying the alternate hostname or
IP address to which the initiating entity MAY attempt to connect;
the associated class is "redirect".
o <system-shutdown/> -- the server is being shut down and all active
streams are being closed; the associated class is "server".
o <unsupported-stanza-type/> -- the initiating entity has sent a
first-level child of the stream that is not supported by the
server; the associated class is "format".
o <unsupported-version/> -- the value of the 'version' attribute
provided by the initiating entity in the stream header specifies a
version of XMPP that is not supported by the server; this element
MAY contain CDATA specifying the XMPP version(s) supported by the
server; the associated class is "format".
o <xml-not-well-formed/> -- the initiating entity has sent XML that
is not well-formed as defined by the XML specification [1]; the
associated class is "format".
4.5.4 Extensibility
If desired, an XMPP application MAY provide custom error information;
this MUST be contained in a properly-namespaced child of the
<condition/> element (i.e., the namespace name MUST NOT be one of the
namespace names defined herein).
4.6 Simple Streams Example
The following is a 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 basic session:
C: <?xml version='1.0'?>
<stream:stream
to='shakespeare.lit'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
version='1.0'>
S: <?xml version='1.0'?>
<stream:stream
from='shakespeare.lit'
id='id_123456789'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
version='1.0'>
... authentication ...
C: <message from='juliet@shakespeare.lit'
to='romeo@shakespeare.lit'>
C: <body>Art thou not Romeo, and a Montague?</body>
C: </message>
S: <message from='romeo@shakespeare.lit'
to='juliet@shakespeare.lit'>
S: <body>Neither, fair saint, if either thee dislike.</body>
S: </message>
C: </stream:stream>
S: </stream:stream>
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A session gone bad:
C: <?xml version='1.0'?>
<stream:stream
to='shakespeare.lit'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
version='1.0'>
S: <?xml version='1.0'?>
<stream:stream
from='shakespeare.lit'
id='id_123456789'
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
version='1.0'>
... authentication ...
C: <message><body>Bad XML, no closing body tag!</message>
S: <stream:error class='format'>
<condition xmlns='urn:ietf:params:xml:ns:xmpp-streams'>
<xml-not-well-formed/>
</condition>
</stream:error>
S: </stream:stream>
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5. Stream Encryption
5.1 Overview
XMPP includes a method for securing the stream from tampering and
eavesdropping. This channel encryption method makes use of the
Transport Layer Security (TLS) [13] protocol, along with a "STARTTLS"
extension that is modelled after similar extensions for the IMAP
[26], POP3 [27], and ACAP [28] protocols as described in RFC 2595
[29]. The namespace name for the STARTTLS extension is
'urn:ietf:params:xml:ns:xmpp-tls', which adheres to the format
defined in The IETF XML Registry [25].)
TLS SHOULD be used between any initiating entity and any receiving
entity (e.g., a stream from a client to a server or from one server
to another). An administrator of a given domain MAY require use of
TLS for either or both client-to-server communications and
server-to-server communications. Servers SHOULD use TLS betweeen two
domains for the purpose of securing server-to-server communications.
When the remote domain is already known, the server can verify the
credentials of the known domain by comparing known keys or
certificates. When the remote domain is not recognized, it may still
be possible to verify a certificate if it is signed by a common
trusted authority. Even if there is no way to verify certificates
(e.g., an unknown domain with a self-signed certificate, or a
certificate signed by an unrecognized authority), if the servers
choose to communicate despite the lack of verified credentials, TLS
still SHOULD be used to provide channel encryption.
The following business rules apply:
1. An initiating entity that complies with this specification MUST
include the "version='1.0'" flag in the initiating stream header.
2. When a receiving entity that complies with this specification
receives an initiating stream header that includes the
"version='1.0'" flag, after sending a stream header in reply
(including the version flag) it MUST include a <starttls/>
element scoped by the 'urn:ietf:params:xml:ns:xmpp-tls' namespace
with the list of other stream features it supports.
3. If the initiating entity chooses to use TLS for stream
encryption, TLS negotiation MUST be completed before proceeding
to SASL negotiation.
4. The initiating entity MUST validate the certificate presented by
the receiving entity:
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Case 1 -- The initiating entity has been configured with a set of
trusted root certificates: Normal certificate validation
processing is appropriate, and SHOULD follow the rules defined
for HTTP over TLS [14]. The trusted roots may be either a
well-known public set or a manually configured Root CA (e.g.,
an organization's own Certificate Authority or a self-signed
Root CA for the service as described under High Security
(Section 11.1)). This case is RECOMMENDED.
Case 2 -- The initiating entity has been configured with the
receiving entity's self-signed service certificate: Simple
comparison of public keys is appropriate. This case is NOT
RECOMMENDED (see High Security (Section 11.1) for details).
If the above methods fail, the certificate SHOULD be presented to
a user for approval; if presented, the receiver MUST deliver the
entire certificate chain to the user, who SHOULD be given the
option to store the Root CA certificate (not the service or End
Entity certificate) and to not be queried again regarding
acceptance of the certificate for some reasonable period of time.
5. If the TLS negotiation is successful, the receiving entity MUST
discard any knowledge obtained from the initiating entity before
TLS takes effect.
6. If the TLS negotiation is successful, the initiating entity MUST
discard any knowledge obtained from the receiving entity before
TLS takes effect.
7. If the TLS negotiation is successful, the receiving entity MUST
NOT offer the STARTTLS extension to the initiating entity along
with the other stream features that are offered when the stream
is restarted.
8. If the TLS negotiation results in success, the initiating entity
SHOULD continue with SASL negotiation.
9. If the TLS negotiation results in failure, the receiving entity
MUST terminate both the XML stream and the underlying TCP
connection.
5.2 Narrative
When an initiating entity secures a stream with a receiving entity,
the steps involved are as follows:
1. The initiating entity opens a TCP connection and initiates the
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stream by sending the opening XML stream header to the receiving
entity, including the "version='1.0'" flag.
2. The receiving entity responds by opening a TCP connection and
sending an XML stream header to the initiating entity, including
the "version='1.0'" flag.
3. The receiving entity offers the STARTTLS extension to the
initiating entity by including it with the list of other
supported stream features (if TLS is required for interaction
with the receiving entity, it SHOULD signal that fact by
including a <required/> element as a child of the <starttls/>
element).
4. The initiating entity issues the STARTTLS command to instruct the
receiving entity that it wishes to begin a TLS negotiation to
secure the stream.
5. The receiving entity MUST reply with either a <proceed/> element
or a <failure/> element scoped by the
'urn:ietf:params:xml:ns:xmpp-tls' namespace. If the failure case
occurs, the receiving entity MUST terminate both the XML stream
and the underlying TCP connection. If the proceed case occurs,
the receiving entity MUST ignore any further XML data sent over
the XML stream but keep the underlying TCP connection open for
the purpose of completing the TLS negotiation.
6. The initiating entity and receiving entity attempt to complete a
TLS negotiation in accordance with RFC 2246 [13].
7. If the TLS negotiation is successful, the initiating entity
SHOULD initiate a new stream by sending an opening XML stream
header to the receiving entity. If the TLS negotiation is
unsuccessful, the receiving entity MUST terminate the TCP
connection.
8. Upon receiving the new stream header from the initiating entity,
the receiving entity SHOULD respond by sending a new XML stream
header to the initiating entity along with the remaining
available features (but NOT including the STARTTLS element).
5.3 Client-to-Server Example
The following example shows the data flow for a client securing a
stream using STARTTLS (the IANA registers port 5222 for
client-to-server communications using XMPP/Jabber, but another port
MAY be used).
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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'>
Step 2: Server responds by sending a stream tag to the client:
<stream:stream
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
id='12345678'
version='1.0'>
Step 3: Server sends the STARTTLS extension to the client along with
authentication mechanisms and any other stream features:
<stream:features>
<starttls xmlns='urn:ietf:params:xml:ns:xmpp-tls'>
<required/>
</starttls>
<mechanisms xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
<mechanism>DIGEST-MD5</mechanism>
<mechanism>PLAIN</mechanism>
</mechanisms>
</stream:features>
Step 4: Client sends the STARTTLS command to the server:
<starttls xmlns='urn:ietf:params:xml:ns:xmpp-tls'/>
Step 5: Server informs client to proceed:
<proceed xmlns='urn:ietf:params:xml:ns:xmpp-tls'/>
Step 5 (alt): Server informs client that TLS negotiation has failed
and closes both stream and TCP connection:
<failure xmlns='urn:ietf:params:xml:ns:xmpp-tls'/>
</stream:stream>
Step 6: Client and server attempt to complete TLS negotiation over
the existing TCP connection.
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Step 7: If TLS negotiation is successful, client initiates a new
stream to the server:
<stream:stream
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
to='capulet.com'
version='1.0'>
Step 7 (alt): If TLS negotiation is unsuccessful, server MUST close
TCP connection.
Step 8: Server responds by sending a stream header to the client
along with any remaining negotiable stream features:
<stream:stream
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
id='12345678'
version='1.0'>
<stream:features>
<mechanisms xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
<mechanism>DIGEST-MD5</mechanism>
<mechanism>PLAIN</mechanism>
<mechanism>EXTERNAL</mechanism>
</mechanisms>
</stream:features>
Step 9: Client SHOULD continue with stream authentication (Section
6).
5.4 Server-to-Server Example
The following example shows the data flow for two servers securing a
stream using STARTTLS (the IANA registers port 5269 for
server-to-server communications using XMPP/Jabber, but another port
MAY be used).
Step 1: Server1 initiates stream to Server2:
<stream:stream
xmlns='jabber:server'
xmlns:stream='http://etherx.jabber.org/streams'
version='1.0'>
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Step 2: Server2 responds by sending a stream tag to Server1:
<stream:stream
xmlns='jabber:server'
xmlns:stream='http://etherx.jabber.org/streams'
id='12345678'
version='1.0'>
Step 3: Server2 sends the STARTTLS extension to Server1 along with
authentication mechanisms and any other stream features:
<stream:features>
<starttls xmlns='urn:ietf:params:xml:ns:xmpp-tls'/>
<required/>
</starttls>
<mechanisms xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
<mechanism>DIGEST-MD5</mechanism>
<mechanism>KERBEROS_V4</mechanism>
</mechanisms>
</stream:features>
Step 4: Server1 sends the STARTTLS command to Server2:
<starttls xmlns='urn:ietf:params:xml:ns:xmpp-tls'/>
Step 5: Server2 informs Server1 to proceed:
<proceed xmlns='urn:ietf:params:xml:ns:xmpp-tls'/>
Step 5 (alt): Server2 informs Server1 that TLS negotiation has failed
and closes stream:
<failure xmlns='urn:ietf:params:xml:ns:xmpp-tls'/>
</stream:stream>
Step 6: Server1 and Server2 attempt to complete TLS negotiation via
TCP.
Step 7: If TLS negotiation is successful, Server1 initiates a new
stream to Server2:
<stream:stream
xmlns='jabber:server'
xmlns:stream='http://etherx.jabber.org/streams'
version='1.0'>
Step 7 (alt): If TLS negotiation is unsuccessful, server MUST close
TCP connection.
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Step 8: Server2 responds by sending a stream header to Server1 along
with any remaining negotiable stream features:
<stream:stream
xmlns='jabber:server'
xmlns:stream='http://etherx.jabber.org/streams'
id='12345678'
version='1.0'>
<stream:features>
<mechanisms xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
<mechanism>DIGEST-MD5</mechanism>
<mechanism>KERBEROS_V4</mechanism>
<mechanism>EXTERNAL</mechanism>
</mechanisms>
</stream:features>
Step 9: Server1 SHOULD continue with stream authentication (Section
6).
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6. Stream Authentication
XMPP includes two methods for enforcing authentication at the level
of XML streams. The secure and preferred method for authenticating
streams between two entities uses an XMPP adaptation of the Simple
Authentication and Security Layer (SASL) [15]. If SASL negotiation is
not possible, some level of trust MAY be established between servers
based on existing trust in DNS; the authentication method used in
this case is the server dialback protocol that is native to XMPP (no
such ad-hoc method is defined between a client and a server). If SASL
is used for server-to-server authentication, the servers MUST NOT use
dialback. For further information about the relative merits of these
two methods, consult Security Considerations (Section 11).
Stream authentication is REQUIRED for all direct communications
between two entities; if an entity sends a stanza to an
unauthenticated stream, the receiving entity SHOULD silently drop the
stanza, MUST NOT process it, and MAY terminate both the XML stream
and the underlying TCP connection.
6.1 SASL Authentication
6.1.1 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 [15] (the XMPP-specific namespace name is
'urn:ietf:params:xml:ns:xmpp-sasl'), which adheres to the format
defined in The IETF XML Registry [25].)
The following business rules apply:
1. If TLS is used for stream encryption, SASL SHOULD NOT be used for
anything except stream authentication (i.e., a security layer
SHOULD NOT be negotiated using SASL). Conversely, if a security
layer is to be negotiated via SASL, TLS SHOULD NOT be used.
2. If the initiating entity is capable of authenticating via SASL,
it MUST include the "version='1.0'" flag in the initiating stream
header.
3. If the receiving entity is capable of accepting authentications
via SASL, it MUST send one or more authentication mechanisms
within a <mechanisms/> element scoped by the
'urn:ietf:params:xml:ns:xmpp-sasl' namespace in response to the
opening stream tag received from the initiating entity.
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4. If the SASL negotiation involves negotiation of a security layer,
the receiving entity MUST discard any knowledge obtained from the
initiating entity which was not obtained from the SASL
negotiation itself.
5. If the SASL negotiation involves negotiation of a security layer,
the initiating entity MUST discard any knowledge obtained from
the receiving entity which was not obtained from the SASL
negotiation itself.
The following syntax rules apply:
1. The initial challenge MUST include a realm, nonce, qop, charset,
and algorithm.
2. The inital response for client-to-server negotiation MUST include
all and only a username, realm, nonce, cnonce, nc, qop,
digest-uri, response, charset, and authzid.
3. The inital response for server-to-server negotiation MUST include
all and only a realm, nonce, cnonce, nc, qop, digest-uri,
response, and charset.
4. The realm-value MUST be no more than 1023 bytes in length and
MUST conform to the nameprep [8] profile of stringprep [9].
5. The username-value MUST be no more than 1023 bytes in length and
MUST conform to the nodeprep [10] profile of stringprep [9].
6. The response-value MUST be computed in accordance with the
relevant SASL mechanism as defined by the appropriate RFC (e.g.,
RFC 2831 [16] for digest authentication).
7. The authzid-value MUST be a Jabber Identifier of the form
<user@domain/resource>, i.e., it MUST include a node identifier,
domain identifier, and resource identifier.
6.1.2 Narrative
When an initiating entity authenticates with a receiving entity, the
steps involved are as follows:
1. The initiating entity requests SASL authentication by including a
'version' attribute in the opening XML stream header sent to the
receiving entity, with the value set to "1.0".
2. After sending an XML stream header in response, the receiving
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entity sends a list of available SASL authentication mechanisms;
each of these is a <mechanism/> element included as a child
within a <mechanisms/> container element scoped by the
'urn:ietf:params:xml:ns:xmpp-sasl' namespace, which in turn is a
child of a <features/> element in the streams namespace. If
channel encryption must be established before a particular
authentication mechanism may be used, the receiving entity MUST
NOT provide that mechanism in the list of available SASL
authentication methods prior to channel encryption. If the
initiating entity presents a valid initiating entity certificate
during prior TLS negotiation, the receiving entity MAY offer the
SASL EXTERNAL mechanism to the initiating entity during stream
authentication (see RFC 2222 [15]).
3. The initiating entity selects a mechanism by sending an <auth/>
element scoped by the 'urn:ietf:params:xml:ns:xmpp-sasl'
namespace to the receiving entity and including the appropriate
value for the 'mechanism' attribute; this element MAY optionally
contain character data (in SASL terminology the "initial
response") if the mechanism supports or requires it. If the
initiating entity selects the EXTERNAL mechanism for
authentication, the authentication credentials shall be taken
from the certificate presented during prior TLS negotiation.
4. If necessary, the receiving entity challenges the initiating
entity by sending a <challenge/> element scoped by the
'urn:ietf:params:xml:ns:xmpp-sasl' namespace to the initiating
entity; this element MAY optionally contain character data (which
MUST be computed in accordance with the SASL mechanism chosen by
the initiating entity).
5. The initiating entity responds to the challenge by sending a
<response/> element scoped by the
'urn:ietf:params:xml:ns:xmpp-sasl' namespace to the receiving
entity; this element MAY optionally contain character data (which
MUST be computed in accordance with the SASL mechanism chosen by
the initiating entity).
6. If necessary, the receiving entity sends more challenges and the
initiating entity sends more responses.
This series of challenge/response pairs continues until one of three
things happens:
1. The initiating entity aborts the handshake by sending an <abort/>
element to the receiving entity.
2. The receiving entity reports failure of the handshake by sending
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a <failure/> element scoped by the
'urn:ietf:params:xml:ns:xmpp-sasl' namespace to the initiating
entity. The particular cause of failure SHOULD be communicated in
an appropriate child element of the <failure/> element. The
following conditions are defined:
* <authentication-mechanism-too-weak/>
* <invalid-realm/>
* <not-authorized/>
* <password-transition-required/>
* <temporary-authentication-failure/>
3. The receiving entity reports success of the handshake by sending
a <success/> element scoped by the
'urn:ietf:params:xml:ns:xmpp-sasl' namespace to the initiating
entity; this element MAY optionally contain character data (in
SASL terminology "additional data with success").
Any character data contained within these elements MUST be encoded
using base64.
6.1.3 SASL Definition
Section 4 of the SASL specification [15] requires that the following
information be supplied by a protocol definition:
service name: "xmpp"
initiation sequence: After the initiating entity provides an opening
XML stream header and the receiving entity replies in kind, the
receiving entity provides a list of acceptable authentication
methods. The initiating entity chooses one method from the list
and sends it to the receiving entity as the value of the
'mechanism' attribute possessed by an <auth/> element, optionally
including an initial response to avoid a round trip.
exchange sequence: Challenges and responses are carried through the
exchange of <challenge/> elements from receiving entity to
initiating entity and <response/> elements from initiating entity
to receiving entity. The receiving entity reports failure by
sending a <failure/> element and success by sending a <success/>
element; the initiating entity aborts the exchange by sending an
<abort/> element. (All of these elements are scoped by the
'urn:ietf:params:xml:ns:xmpp-sasl' namespace.)
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security layer negotiation: If a security layer is negotiated, both
sides consider the original stream closed and new <stream> headers
are sent by both entities. The security layer takes effect
immediately following the ">" character of the <response/> element
for the client and immediately following the closing ">" character
of the <succeed/> element for the server. (Both of these elements
are scoped by the 'urn:ietf:params:xml:ns:xmpp-sasl' namespace.)
use of the authorization identity: The authorization identity is used
by xmpp only in negotiation between a client and a server, and
denotes the "full JID" (user@domain/resource) requested by the
user or application associated with the client.
6.1.4 Client-to-Server Example
The following example shows the data flow for a client authenticating
with a server using SASL (the IANA registers port 5222 for
client-to-server communications using XMPP/Jabber, but another port
MAY be used).
Step 1: Client initiates stream to server:
<stream:stream
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
to='domain'
version='1.0'>
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'
from='domain'
version='1.0'>
Step 3: Server informs client of available authentication mechanisms:
<stream:features>
<mechanisms xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
<mechanism>DIGEST-MD5</mechanism>
<mechanism>PLAIN</mechanism>
</mechanisms>
</stream:features>
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Step 4: Client selects an authentication mechanism:
<auth
xmlns='urn:ietf:params:xml:ns:xmpp-sasl'
mechanism='DIGEST-MD5'/>
Step 5: Server sends a base64-encoded challenge to the client:
<challenge xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
cmVhbG09ImNhdGFjbHlzbS5jeCIsbm9uY2U9Ik9BNk1HOXRFUUdtMmhoIi
xxb3A9ImF1dGgiLGNoYXJzZXQ9dXRmLTgsYWxnb3JpdGhtPW1kNS1zZXNz
</challenge>
The decoded challenge is:
realm="cataclysm.cx",nonce="OA6MG9tEQGm2hh",\
qop="auth",charset=utf-8,algorithm=md5-sess
Step 6: Client responds to the challenge:
<response xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
dXNlcm5hbWU9InJvYiIscmVhbG09ImNhdGFjbHlzbS5jeCIsbm9uY2U9Ik
9BNk1HOXRFUUdtMmhoIixjbm9uY2U9Ik9BNk1IWGg2VnFUclJrIixuYz0w
MDAwMDAwMSxxb3A9YXV0aCxkaWdlc3QtdXJpPSJ4bXBwL2NhdGFjbHlzbS
5jeCIscmVzcG9uc2U9ZDM4OGRhZDkwZDRiYmQ3NjBhMTUyMzIxZjIxNDNh
ZjcsY2hhcnNldD11dGYtOCxhdXRoemlkPSJyb2JAY2F0YWNseXNtLmN4L2
15UmVzb3VyY2Ui
</response>
The decoded response is:
username="rob",realm="cataclysm.cx",\
nonce="OA6MG9tEQGm2hh",cnonce="OA6MHXh6VqTrRk",\
nc=00000001,qop=auth,digest-uri="xmpp/cataclysm.cx",\
response=d388dad90d4bbd760a152321f2143af7,charset=utf-8,\
authzid="rob@cataclysm.cx/myResource"
Step 7: Server sends another challenge to the client:
<challenge xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
cnNwYXV0aD1lYTQwZjYwMzM1YzQyN2I1NTI3Yjg0ZGJhYmNkZmZmZA==
</challenge>
The decoded challenge is:
rspauth=ea40f60335c427b5527b84dbabcdfffd
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Step 8: Client responds to the challenge:
<response xmlns='urn:ietf:params:xml:ns:xmpp-sasl'/>
Step 9: Server informs client of successful authentication:
<success xmlns='urn:ietf:params:xml:ns:xmpp-sasl'/>
Step 9 (alt): Server informs client of failed authentication:
<failure xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
<mechanism-too-weak/>
</failure>
Step 10: Client initiates a new stream to the server:
<stream:stream
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
to='domain'
version='1.0'>
Step 11: Server responds by sending a stream header to the client,
with the stream already authenticated (not followed by further stream
features):
<stream:stream
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
id='12345678'
from='domain'
version='1.0'>
6.1.5 Server-to-Server Example
The following example shows the data flow for a server authenticating
with another server using SASL (the IANA registers port 5269 for
server-to-server communications using XMPP/Jabber, but another port
MAY be used).
Step 1: Server1 initiates stream to Server2:
<stream:stream
xmlns='jabber:server'
xmlns:stream='http://etherx.jabber.org/streams'
version='1.0'>
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Step 2: Server2 responds with a stream tag sent to Server1:
<stream:stream
xmlns='jabber:server'
xmlns:stream='http://etherx.jabber.org/streams'
id='12345678'
version='1.0'>
Step 3: Server2 informs Server1 of available authentication
mechanisms:
<stream:features>
<mechanisms xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
<mechanism>DIGEST-MD5</mechanism>
<mechanism>KERBEROS_V4</mechanism>
</mechanisms>
</stream:features>
Step 4: Server1 selects an authentication mechanism:
<auth
xmlns='urn:ietf:params:xml:ns:xmpp-sasl'
mechanism='DIGEST-MD5'/>
Step 5: Server2 sends a base64-encoded challenge to Server1:
<challenge xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
cmVhbG09ImNhdGFjbHlzbS5jeCIsbm9uY2U9Ik9BNk1HOXRFUUdtMmhoIi
xxb3A9ImF1dGgiLGNoYXJzZXQ9dXRmLTgsYWxnb3JpdGhtPW1kNS1zZXNz
</challenge>
The decoded challenge is:
realm="cataclysm.cx",nonce="OA6MG9tEQGm2hh",\
qop="auth",charset=utf-8,algorithm=md5-sess
Step 6: Server1 responds to the challenge:
<response xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
cmVhbG09ImNhdGFjbHlzbS5jeCIsbm9uY2U9Ik9BNk1HOXRFUUdtMmhoIi
xjbm9uY2U9Ik9BNk1IWGg2VnFUclJrIixuYz0wMDAwMDAwMSxxb3A9YXV0
aCxkaWdlc3QtdXJpPSJ4bXBwL2NhdGFjbHlzbS5jeCIscmVzcG9uc2U9ZD
M4OGRhZDkwZDRiYmQ3NjBhMTUyMzIxZjIxNDNhZjcsY2hhcnNldD11dGYt
OAo=
</response>
The decoded response is:
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realm="cataclysm.cx",nonce="OA6MG9tEQGm2hh",cnonce="OA6MHXh6VqTrRk",\
nc=00000001,qop=auth,digest-uri="xmpp/cataclysm.cx",\
response=d388dad90d4bbd760a152321f2143af7,charset=utf-8
Step 7: Server2 sends another challenge to Server1:
<challenge xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
cnNwYXV0aD1lYTQwZjYwMzM1YzQyN2I1NTI3Yjg0ZGJhYmNkZmZmZA==
</challenge>
The decoded challenge is:
rspauth=ea40f60335c427b5527b84dbabcdfffd
Step 8: Server1 responds to the challenge:
<response xmlns='urn:ietf:params:xml:ns:xmpp-sasl'/>
Step 9: Server2 informs Server1 of successful authentication:
<success xmlns='urn:ietf:params:xml:ns:xmpp-sasl'/>
Step 9 (alt): Server2 informs Server1 of failed authentication:
<failure xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
<temporary-auth-failure/>
</failure>
Step 10: Server1 initiates a new stream to Server2:
<stream:stream
xmlns='jabber:server'
xmlns:stream='http://etherx.jabber.org/streams'
version='1.0'>
Step 11: Server2 responds by sending a stream header to Server1, with
the stream already authenticated (not followed by further stream
features):
<stream:stream
xmlns='jabber:client'
xmlns:stream='http://etherx.jabber.org/streams'
id='12345678'
version='1.0'>
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6.2 Dialback Authentication
XMPP includes a protocol-level method for verifying that a connection
between two servers can be trusted as much as the DNS can 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 stanzas.
Dialback is decidedly not intended as a mechanism for securing or
encrypting the streams between servers as is done via SASL and TLS,
only for helping to prevent the spoofing of a server and the sending
of false data from it. In particular, dialback authentication is
susceptible to DNS poisoning attacks unless DNSSec [30] is used.
Furthermore, even if the DNS information is accurate, dialback
authentication cannot protect from attacks where the attacker is
capable of hijacking the IP address of the remote domain. Domains
requiring more robust security SHOULD use TLS and SASL as defined
above.
Server 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 hostname. All DNS hostname
resolutions MUST first resolve the hostname using an SRV [18] 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 [5].
The method for generating and verifying the keys used in the dialback
protocol MUST take into account the hostnames being used, the random
ID generated for the stream, and a secret known by the authoritative
server's network. Generating unique but verifiable keys is important
to prevent common man-in-the-middle attacks and server spoofing.
Any error that occurs during dialback negotiation MUST be considered
a stream error, resulting in termination of the stream and of the
underlying TCP connection. The possible error conditions are
specified in the protocol description below.
The following terminology applies:
o Originating Server -- the server that is attempting to establish a
connection between two domains.
o Receiving Server -- the server that is trying to authenticate that
Originating Server represents the domain which it claims to be.
o Authoritative Server -- the server that answers to the DNS
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hostname asserted by Originating Server; for basic environments
this will be Originating Server, but it could be a separate
machine in 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 informs Originating Server whether it is
authenticated or not.
We can represent this flow of events graphically as follows:
Originating Receiving
Server Server
----------- ---------
| |
| establish connection |
| ----------------------> |
| |
| send stream header |
| ----------------------> |
| |
| establish connection |
| <---------------------- |
| |
| send stream header |
| <---------------------- |
| | Authoritative
| send dialback key | Server
| ----------------------> | -------------
| | |
| establish connection |
| ----------------------> |
| |
| send stream header |
| ----------------------> |
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| |
| establish connection |
| <---------------------- |
| |
| send stream header |
| <---------------------- |
| |
| send dialback key |
| ----------------------> |
| |
| validate dialback key |
| <---------------------- |
|
| report dialback result |
| <---------------------- |
| |
6.2.1 Dialback Protocol
The interaction between the servers is as follows:
1. Originating Server establishes TCP connection to Receiving
Server.
2. Originating Server sends a stream header to Receiving Server:
<stream:stream
xmlns:stream='http://etherx.jabber.org/streams'
xmlns='jabber:server'
xmlns:db='jabber:server:dialback'>
Note: the 'to' and 'from' attributes are NOT REQUIRED on the
root stream element. The inclusion of the xmlns:db namespace
declaration with the name shown indicates to Receiving Server
that Originating Server supports dialback. If the namespace name
is incorrect, then Receiving Server MUST generate an
<invalid-namespace/> stream error condition and terminate both
the XML stream and the underlying TCP connection.
3. Receiving Server SHOULD send a stream header back to Originating
Server, including a unique ID for this interaction:
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<stream:stream
xmlns:stream='http://etherx.jabber.org/streams'
xmlns='jabber:server'
xmlns:db='jabber:server:dialback'
id='457F9224A0...'>
Note: The 'to' and 'from' attributes are NOT REQUIRED on the
root stream element. If the namespace name is incorrect, then
Originating Server MUST generate an <invalid-namespace/> stream
error condition and terminate both the XML stream and the
underlying TCP connection. Note well that Receiving Server is
NOT REQUIRED to reply and MAY silently terminate the XML stream
and underlying TCP connection depending on security policies in
place.
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
Receiving Server does not keep information about Originating
Server between sessions. The key generated by Originating Server
must be based in part on the value of the ID provided by
Receiving Server in the previous step, and in part on a secret
shared by Originating Server and Authoritative Server. If the
value of the 'to' address does not match a hostname recognized
by Receiving Server, then Receiving Server MUST generate a
<host-unknown/> stream error condition and terminate both the
XML stream and the underlying TCP connection. If the value of
the 'from' address matches a domain with which Receiving Server
already has an established connection, then Receiving Server
SHOULD generate a <not-authorized/> stream error condition and
terminate both the XML stream and the underlying TCP connection.
5. Receiving Server establishes a TCP connection back to the domain
name asserted by Originating Server, as a result of which it
connects to Authoritative Server. (Note: as an optimization, an
implementation MAY reuse an existing trusted connection here
rather than opening a new TCP connection.)
6. Receiving Server sends Authoritative 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'>
Note: the 'to' and 'from' attributes are NOT REQUIRED on the
root stream element. If the namespace name is incorrect, then
Authoritative Server MUST generate an <invalid-namespace/>
stream error condition and terminate both the XML stream and the
underlying TCP connection.
7. Authoritative Server sends Receiving Server a stream header:
<stream:stream
xmlns:stream='http://etherx.jabber.org/streams'
xmlns='jabber:server'
xmlns:db='jabber:server:dialback'
id='1251A342B...'>
Note: if the namespace name is incorrect, then Receiving Server
MUST generate an <invalid-namespace/> stream error condition and
terminate both the XML stream and the underlying TCP connection
between it and Authoritative Server. If the ID does not match
that provided by Receiving Server in Step 3, then Receiving
Server MUST generate an <invalid-id/> stream error condition and
terminate both the XML stream and the underlying TCP connection
between it and Authoritative Server. If either of the foregoing
stream errors occurs between Receiving Server and Authoritative
Server, then Receiving Server MUST generate a
<remote-connection-failed/> stream error condition and terminate
both the XML stream and the underlying TCP connection between it
and Originating Server.
8. Receiving Server sends Authoritative Server a stanza requesting
that Authoritative Server 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 3, and the key that Originating Server sent to Receiving
Server in Step 4. Based on this information as well as shared
secret information within the Authoritative Server's network,
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the key is verified. Any verifiable method MAY be used to
generate the key. If the value of the 'to' address does not
match a hostname recognized by Authoritative Server, then
Authoritative Server MUST generate a <host-unknown/> stream
error condition and terminate both the XML stream and the
underlying TCP connection. If the value of the 'from' address
does not match the hostname represented by Receiving Server when
opening the TCP connection (or any validated domain), then
Authoritative Server MUST generate a <nonmatching-hosts/> stream
error condition and terminate both the XML stream and the
underlying TCP connection.
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...'/>
Note: if the ID does not match that provided by Receiving Server
in Step 3, then Receiving Server MUST generate an <invalid-id/>
stream error condition and terminate both the XML stream and the
underlying TCP connection. If the value of the 'to' address does
not match a hostname recognized by Receiving Server, then
Receiving Server MUST generate a <host-unknown/> stream error
condition and terminate both the XML stream and the underlying
TCP connection. If the value of the 'from' address does not
match the hostname represented by Originating Server when
opening the TCP connection (or any validated domain), then
Receiving Server MUST generate a <nonmatching-hosts/> stream
error condition and terminate both the XML stream and the
underlying TCP connection.
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. If the connection is
invalid, then Receiving Server MUST terminate both the XML
stream and the underlying TCP connection. If the connection is
validated, data can be sent by Originating Server and read by
Receiving Server; before that, all data stanzas sent to
Receiving Server SHOULD be silently dropped.
Even if dialback negotiation is successful, a server MUST verify that
all XML stanzas received from the other server include a 'from'
attribute and a 'to' attribute; if a stanza does not meet this
restriction, the server that receives the stanza MUST generate an
<invalid-xml/> stream error condition and terminate both the XML
stream and the underlying TCP connection. Furthermore, a server MUST
verify that the 'from' attribute of stanzas received from the other
server includes a validated domain for the stream; if a stanza does
not meet this restriction, the server that receives the stanza MUST
generate a <nonmatching-hosts/> stream error condition and terminate
both the XML stream and the underlying TCP connection. Both of these
checks help to prevent spoofing related to particular stanzas.
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7. XML Stanzas
7.1 Overview
Once the XML streams in each direction have been authenticated and
(if desired) encrypted, XML stanzas can be sent over the streams.
Three XML stanza types are defined for the 'jabber:client' and
'jabber:server' namespaces: <message/>, <presence/>, and <iq/>.
In essence, the <message/> stanza type can be seen as a "push"
mechanism whereby one entity pushes information to another entity,
similar to the communications that occur in a system such as email.
The <presence/> element can be seen as a basic broadcast or
"publish-subscribe" mechanism, whereby multiple entities receive
information (in this case, presence information) about an entity to
which they have subscribed. The <iq/> element can be seen as a
"request-response" mechanism similar to HTTP, whereby two entities
can engage in a structured conversation using 'get' or 'set' requests
and 'result' or 'error' responses.
7.2 Common Attributes
The following five attributes are common to message, presence, and IQ
stanzas:
7.2.1 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; if a server receives a stanza that does not meet this
restriction, it MUST generate an <invalid-xml/> stream error
condition and terminate both the XML stream and the underlying TCP
connection.
If the value of the 'to' attribute is invalid or cannot be contacted,
the entity discovering that fact (usually the sender's or recipient's
server) MUST return an appropriate error to the sender.
7.2.2 from
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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 and MAY return an error
to the sender. 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 as defined by the authzid provided
in the SASL negotiation.
In the 'jabber:server' namespace, a stanza MUST possess a 'from'
attribute; if a server receives a stanza that does not meet this
restriction, it MUST generate an <invalid-xml/> stream error
condition. Furthermore, the domain identifier portion of the JID
contained in the 'from' attribute MUST match the hostname of the
sending server (or any validated domain) as communicated in the SASL
negotiation or dialback negotiation; if a server receives a stanza
that does not meet this restriction, it MUST generate a
<nonmatching-hosts/> stream error condition. Both of these conditions
MUST result in closing of the stream and termination of the
underlying TCP connection.
7.2.3 id
The optional 'id' attribute MAY be used by a sending entity for
internal tracking of stanzas that it sends and receives (especially
for tracking the request-response interaction inherent in the use of
IQ stanzas). If the stanza sent by the sending entity is an IQ stanza
of type "get" or "set", the receiving entity MUST include an 'id'
attribute with the same value in any replies of type "result" or
"error". The value of the 'id' attribute is NOT REQUIRED to be unique
either globally, within a domain, or within a stream.
7.2.4 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 defined in the
following sections.
7.2.5 xml:lang
A stanza SHOULD possess an 'xml:lang' attribute (as defined in
Section 2.12 of the XML specification [1]) specifying the default
language of any XML character data contained in the stanza or its
child elements. The value of the 'xml:lang' attribute MUST be an
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NMTOKEN and MUST conform to the format defined in RFC 3066 [17].
7.3 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.
7.3.1 Types of Message
The 'type' attribute of a message stanza is OPTIONAL; if included, it
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 the following values:
o chat
o error
o groupchat
o headline
For information about the meaning of these message types, refer to
XMPP IM [23].
7.3.2 Children
As described under extended namespaces (Section 7.6), a message
stanza MAY contain any properly-namespaced child element.
In accordance with the default namespace declaration, by default a
message stanza is in the 'jabber:client' or 'jabber:server'
namespace, which defines certain allowable children of message
stanzas. If the message stanza is of type "error", it MUST include an
<error/> child; for details, see Section 7.7. If the message stanza
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 without an explicit namespace declaration:
7.3.2.1 Subject
The <subject/> element specifies the topic of the message. The
<subject/> element SHOULD NOT possess any attributes, with the
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exception of the 'xml:lang' attribute. Multiple instances of the
<subject/> element MAY be included for the purpose of providing
alternate versions of the same subject, but only if each instance
possesses an 'xml:lang' attribute with a distinct language value. The
<subject> element MUST NOT contain mixed content.
7.3.2.2 Body
The <body/> element contains the textual contents of the message;
this child element is normally included but NOT REQUIRED. The <body/>
element SHOULD 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. The <body> element MUST NOT
contain mixed content.
7.3.2.3 Thread
The <thread/> element contains a random string that is generated by
the sender and that SHOULD be copied back in replies; it is used for
tracking a conversation thread (sometimes referred to as an "IM
session") between two entities. If used, it MUST be unique to that
conversation thread within the stream and MUST be consistent
throughout that conversation. The use of the <thread/> element is
optional and is not used to identify individual messages, only
conversations. Only one <thread/> element MAY be included in a
message stanza, and it MUST NOT possess any attributes. The <thread/>
element MUST be treated as an opaque string by entities; no semantic
meaning may be derived from it, and only exact, case-insensitve
comparisons may be made against it. The <thread> element MUST NOT
contain mixed content.
The method for generating thread IDs SHOULD be as follows:
1. concatenate the sender's full JID (user@domain/resource) with the
recipient's full JID
2. concatenate these JID strings with a full ISO-8601 timestamp
including year, month, day, hours, minutes, seconds, and UTC
offset in the following format: YYYY-MM-DD-Thh:mm:ssTZD (where
TZD is either "Z" for UTC or "[+|-]hh:mm" for an offset from UTC)
3. hash the resulting string according to the SHA1 algorithm
4. convert the hexidecimal SHA1 output to all lowercase
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7.4 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 optional
user-defined descriptive text) and to communicate that status to
other entities. Presence stanzas are also used to negotiate and
manage subscriptions to the presence of other entities.
7.4.1 Types of Presence
The 'type' attribute of a presence stanza is optional. A presence
stanza that does not possess a 'type' attribute is used to signal to
the server that the sender is online and available for communication.
If included, the 'type' attribute specifies a lack of availability, 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. In general
SHOULD NOT be sent by a client.
o error -- An error has occurred regarding processing or delivery of
a previously-sent presence stanza.
Detailed information about presence semantics and about the
subscription model used within XMPP can be found in XMPP IM [23].
7.4.2 Children
As described under extended namespaces (Section 7.6), a presence
stanza MAY contain any properly-namespaced child element.
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In accordance with the default namespace declaration, by default a
presence stanza is in the 'jabber:client' or 'jabber:server'
namespace, which defines certain allowable children of presence
stanzas. If the presence stanza is of type "error", it MUST include
an <error/> child; for details, see Section 7.7. If the 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"):
7.4.2.1 Show
The optional <show/> element specifies a particular availability
status of an entity or specific resource (if a <show/> element is not
provided, default availability is assumed). Only one <show/> element
MAY be included in a presence stanza, and it SHOULD NOT possess any
attributes. The CDATA value SHOULD be one of the following (values
other than these four SHOULD be ignored; additional availability
types could be defined through a properly-namespaced child element of
the presence stanza):
o away
o chat
o xa
o dnd
For information about the meaning of these values, refer to XMPP IM
[23].
7.4.2.2 Status
The optional <status/> element contains a natural-language
description of availability status. It is 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 SHOULD 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.
7.4.2.3 Priority
The optional <priority/> element specifies the priority level of the
connected resource. The value may be any integer between -128 and
127. Only one <priority/> element MAY be included in a presence
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stanza, and it MUST NOT possess any attributes. For information
regarding the semantics of priority values in stanza routing within
IM applications, see XMPP IM [23].
7.5 IQ Stanzas
7.5.1 Overview
Info/Query, or IQ, is a request-response mechanism, similar in some
ways to HTTP [31]. 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, and the interaction is
tracked by the requesting entity through use of the 'id' attribute.
Most IQ interactions follow a common pattern of structured data
exchange such as get/result or set/result (although an error may be
returned in response to a request if appropriate):
Requesting Responding
Entity Entity
---------- ----------
| |
| <iq type='get' id='1'> |
| ------------------------> |
| |
| <iq type='result' id='1'> |
| <------------------------ |
| |
| <iq type='set' id='2'> |
| ------------------------> |
| |
| <iq type='error' id='2'> |
| <------------------------ |
| |
An entity that receives an IQ request of type "get" or "set" MUST
reply with an IQ response of type "result" or "error" (which response
MUST preserve the 'id' attribute of the request). An entity that
receives a stanza of type "result" or "error" MUST NOT respond to the
stanza by sending a further IQ response of type "result" or "error";
however, as shown above, the requesting entity MAY send another
request (e.g., an IQ of type "set" in order to provide required
information discovered through a get/result pair).
7.5.2 Types of IQ
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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 SHOULD be ignored):
o get -- The stanza is a request for information or requirements.
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.
7.5.3 Children
As described under extended namespaces (Section 7.6), an IQ stanza
MAY contain any properly-namespaced child element. Note that an IQ
stanza contains no children in the 'jabber:client' or 'jabber:server'
namespace since it is a vessel for XML in another namespace.
An IQ stanza of type "get" or "set" MUST include one and only one
child element. An IQ stanza of type "error" SHOULD include the child
element contained in the associated "set" or "get" and MUST include
an <error/> child; for details, see Section 7.7.
7.6 Extended Namespaces
While the core data elements in the "jabber:client" or
"jabber:server" namespace (along with their attributes and child
elements) 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
have any name and MUST possess an 'xmlns' namespace declaration
(other than "jabber:client", "jabber:server", or "http://
etherx.jabber.org/streams") 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, the entity's expected behavior depends on whether the
entity is (1) the recipient or (2) an entity that is routing the
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stanza to the recipient. In particular:
Recipient: If a recipient receives a stanza that contains a child
element it does not understand, it SHOULD ignore that specific XML
data, i.e., it SHOULD not process it or present it to a user or
associated application (if any). In particular:
* If an entity receives a message or presence stanza that
contains XML data in an extended namespace it 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 the entire
stanza.
* 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 condition of <feature-not-implemented/>.
Router: If a routing entity (usually a server) handles a stanza that
contains a child element it does not understand, it SHOULD ignore
the associated XML data by passing it on untouched to the
recipient.
7.7 Stanza Errors
As defined herein, stanza-related errors are handled in a manner
similar to stream errors (Section 4.5).
7.7.1 Rules
The following rules apply to stanza-related errors:
o A stanza whose 'type' attribute has a value of "error" MUST
contain an <error/> child element.
o The receiving or processing entity that returns an error to the
sending entity SHOULD include the original XML sent along with the
<error/> element and its children so that the sender can inspect
and if necessary correct the XML before re-sending.
o An entity that receives a stanza whose 'type' attribute has a
value of "error" MUST NOT respond to the stanza with a further
stanza of type "error"; this helps to prevent looping.
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o An <error/> child MUST NOT be included if the 'type' attribute has
a value other than "error".
7.7.2 Syntax
The syntax for stanza-related errors is as follows:
<stanza-name to='sender' type='error'>
[include sender XML here]
<error class='error-class'>
<condition xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'>
<descriptive-element-name/>
</condition>
</error>
</stanza-name>
The stanza-name is one of message, presence, or iq.
The value of the 'class' attribute MUST be one of the following:
o access -- the condition relates to access rights, permissions, or
authorization
o address -- the condition relates to the JID or domain to which the
stanza was addressed
o format -- the condition relates to XML format or structure
o recipient -- the condition relates to the state or capabilities of
the recipient (which may be the server)
o server -- the condition relates to the internal state of the
server
The <condition/> element MUST contain a child element that specifies
a particular stanza-related error condition, and its namespace name
MUST be 'urn:ietf:params:xml:ns:xmpp-stanzas', which adheres to the
format defined in The IETF XML Registry [25].
7.7.3 Conditions
The following stanza-related error conditions are defined:
o <bad-request/> -- the sender has sent XML that is malformed or
cannot be processed (e.g., a client-generated stanza includes a
'from' address, or an IQ stanza includes an unrecognized value of
the 'type' attribute); the associated class is "format".
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o <conflict/> -- access cannot be granted because an existing
resource or session exists with the same name or address; the
associated class is "access".
o <feature-not-implemented/> -- the feature requested is not
implemented by the recipient or server and therefore cannot be
processed; the associated class is "recipient".
o <forbidden/> -- the stanza is understood but the action is
forbidden; the associated class is "access".
o <internal-server-error/> -- the server could not process the
stanza because of a misconfiguration or an otherwise-undefined
internal server error; the associated class is "server".
o <item-not-found/> -- the addressed JID or item requested cannot be
found; the associated class is "address".
o <jid-malformed/> -- the value of the 'to' attribute in the
sender's stanza does not adhere to the syntax defined in
Addressing (Section 3); the associated class is "address".
o <not-allowed/> -- the action is not permitted when attempted by
the sender; the associated class is "access".
o <recipient-unavailable/> -- the specific recipient requested is
currently unavailable; the associated class is "recipient".
o <registration-required/> -- the user is not authorized to access
the requested service because registration is required; the
associated class is "access".
o <remote-server-not-found/> -- a remote server or service specified
as part or all of the JID of the intended recipient does not
exist; the associated class is "address".
o <remote-server-timeout/> -- a remote server or service specified
as part or all of the JID of the intended recipient could not be
contacted within a reasonable amount of time; the associated class
is "server".
o <service-unavailable/> -- the service requested is currently
unavailable on the server; the associated class is "server".
7.7.4 Extensibility
If desired, an XMPP application MAY provide custom error information
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by including a properly-namespaced child of the appropriate
descriptive element name, for example:
<iq type='error' id='some-id'>
<error class='format'>
<condition xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'>
<bad-request>
<too-many-parameters xmlns='some-ns'/>
</bad-request>
</condition>
</error>
</iq>
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8. XML Usage within XMPP
8.1 Restrictions
XMPP is a simplified and specialized protocol for streaming XML
elements in order to exchange messages and presence information in
close to real time. Because XMPP does not require the parsing of
arbitrary and complete XML documents, there is no requirement that
XMPP must support the full XML specification [1]. In particular, the
following restrictions apply:
With regard to XML generation, an XMPP implementation MUST NOT inject
into an XML stream any of the following:
o comments (as defined in Section 2.5 of the XML specification [1])
o processing instructions (Section 2.6)
o internal or external DTD subsets (Section 2.8)
o internal or external entity references (Section 4.2) with the
exception of predefined entities (Section 4.6)
With regard to XML processing, if an XMPP implementation receives
such restricted XML data, it MUST ignore the data.
8.2 Namespaces
XML Namespaces [12] 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.
Additionally, an XMPP implementation MAY be more strict about
namespace prefixes than the XML namespace specification requires.
8.3 Validation
Except as noted with regard to 'to' and 'from' addresses for stanzas
within the 'jabber:server' namespace, a server is not responsible for
validating the XML elements forwarded to a client or another server;
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,
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and schemas are included herein for descriptive purposes only.
8.4 Character Encodings
Software implementing XML streams MUST support the UTF-8 (RFC 2279
[19]) and UTF-16 (RFC 2781 [20]) transformations of Universal
Character Set (ISO/IEC 10646-1 [21]) characters. Software MUST NOT
attempt to use any other encoding for transmitted data. The encodings
of the transmitted and received 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]. For historical reasons, existing implementations
MAY support UTF-8 only.
8.5 Inclusion of Text Declaration
An application MAY send a text declaration. Applications MUST follow
the rules in the XML specification [1] regarding the circumstances
under which a text declaration is included.
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9. IANA Considerations
9.1 XML Namespace Name for TLS Data
A URN sub-namespace for TLS-related data in the Extensible Messaging
and Presence Protocol (XMPP) is defined as follows.
URI: urn:ietf:params:xml:ns:xmpp-tls
Specification: [RFCXXXX]
Description: This is the XML namespace name for TLS-related data in
the Extensible Messaging and Presence Protocol (XMPP) as defined
by [RFCXXXX].
Registrant Contact: IETF, XMPP Working Group, <xmppwg@jabber.org>
9.2 XML Namespace Name for SASL Data
A URN sub-namespace for SASL-related data in the Extensible Messaging
and Presence Protocol (XMPP) is defined as follows.
URI: urn:ietf:params:xml:ns:xmpp-sasl
Specification: [RFCXXXX]
Description: This is the XML namespace name for SASL-related data in
the Extensible Messaging and Presence Protocol (XMPP) as defined
by [RFCXXXX].
Registrant Contact: IETF, XMPP Working Group, <xmppwg@jabber.org>
9.3 XML Namespace Name for Stream Errors
A URN sub-namespace for stream-related error data in the Extensible
Messaging and Presence Protocol (XMPP) is defined as follows.
URI: urn:ietf:params:xml:ns:xmpp-streams
Specification: [RFCXXXX]
Description: This is the XML namespace name for stream-related error
data in the Extensible Messaging and Presence Protocol (XMPP) as
defined by [RFCXXXX].
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Registrant Contact: IETF, XMPP Working Group, <xmppwg@jabber.org>
9.4 XML Namespace Name for Stanza Errors
A URN sub-namespace for stanza-related error data in the Extensible
Messaging and Presence Protocol (XMPP) is defined as follows.
URI: urn:ietf:params:xml:ns:xmpp-stanzas
Specification: [RFCXXXX]
Description: This is the XML namespace name for stanza-related error
data in the Extensible Messaging and Presence Protocol (XMPP) as
defined by [RFCXXXX].
Registrant Contact: IETF, XMPP Working Group, <xmppwg@jabber.org>
9.5 Existing Registrations
The IANA registers "xmpp" as a GSSAPI [22] service name, as specified
in Section 6.1.3.
Additionally, the IANA registers "jabber-client" and "jabber-server"
as keywords for TCP ports 5222 and 5269 respectively.
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10. Internationalization Considerations
Each XML stanza SHOULD include the 'xml:lang' attribute as described
above. Servers MUST NOT modify or delete 'xml:lang' attributes from
stanzas they receive from other entities.
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11. Security Considerations
11.1 High Security
For the purposes of XMPP communications (client-to-server and
server-to-server), the term "high security" refers to the use of
security technologies that provide both mutual authentication and
integrity-checking; in particular, when using certificate-based
authentication to provide high security, a chain-of-trust SHOULD be
established out-of-band, although a shared certificate authority
signing certificates could allow a previously unknown certificate to
establish trust in-band.
Standalone, self-signed service certificates SHOULD NOT be used;
rather, an entity that wishes to generate a self-signed service
certificate SHOULD first generate a self-signed Root CA certificate
and then generate a signed service certificate. Entities that
communicate with the service SHOULD be configured with the Root CA
certificate rather than the service certificate; this avoids problems
associated with simple comparison of service certificates. If a
self-signed service certificate is used, an entity SHOULD NOT trust
it if it is changed to another self-signed certificate or a
certificate signed by an unrecognized authority.
Implementations MUST support high security. Service provisioning
SHOULD use high security, subject to local security policies.
11.2 Client-to-Server Communications
The TLS protocol for encrypting XML streams (defined under Section 5)
provides a reliable mechanism for helping to ensure the
confidentiality and data integrity of data exchanged between two
entities.
The SASL protocol for authenticating XML streams (defined under
Section 6.1) 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 to 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 the methods defined in
End-to-End Object Encryption in XMPP [32].
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11.3 Server-to-Server Communications
A compliant implementation MUST support both TLS and SASL for
inter-domain communications. For historical reasons, a compliant
implementation SHOULD also support the lower-security Dialback
Protocol (Section 6.2) as a fallback mechanism that helps to prevent
the spoofing of domains.
Because service provisioning is a matter of policy, it is OPTIONAL
for any given domain to communicate with other domains, and
server-to-server communications MAY be disabled by the administrator
of any given deployment. If a particular domain enables inter-domain
communications, it SHOULD enable high security. In the absence of
high security, a domain MAY use server dialback for inter-domain
communications.
Administrators may want to require use of SASL for server-to-server
communications in order to ensure authentication and confidentiality
(e.g., on an organization's private network). Compliant
implementations SHOULD support SASL for this purpose.
11.4 Firewalls
Communications using XMPP normally occur over TCP sockets on port
5222 (client-to-server) or port 5269 (server-to-server), as
registered with the IANA [5]. Use of these well-known ports allows
administrators to easily enable or disable XMPP activity through
existing and commonly-deployed firewalls.
11.5 Mandatory to Implement Technologies
At a minimum, all implementations MUST support the following
mechanisms:
for authentication: the SASL DIGEST-MD5 mechanism
for confidentiality: TLS (using the TLS_RSA_WITH_3DES_EDE_CBC_SHA
cipher)
for both: TLS (using the TLS_RSA_WITH_3DES_EDE_CBC_SHA cipher
supporting client-side certificates)
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Normative 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] 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>.
[3] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[4] University of Southern California, "Transmission Control
Protocol", RFC 793, September 1981, <http://www.ietf.org/rfc/
rfc0793.txt>.
[5] Internet Assigned Numbers Authority, "Internet Assigned Numbers
Authority", January 1998, <http://www.iana.org/>.
[6] Harrenstien, K., Stahl, M. and E. Feinler, "DoD Internet host
table specification", RFC 952, October 1985.
[7] Braden, R., "Requirements for Internet Hosts - Application and
Support", STD 3, RFC 1123, October 1989.
[8] Hoffman, P. and M. Blanchet, "Nameprep: A Stringprep Profile
for Internationalized Domain Names (draft-ietf-idn-nameprep-11,
work in progress)", June 2002.
[9] Hoffman, P. and M. Blanchet, "Preparation of Internationalized
Strings ("stringprep")", RFC 3454, December 2002.
[10] Saint-Andre, P. and J. Hildebrand, "Nodeprep: A Stringprep
Profile for Node Identifiers in XMPP
(draft-ietf-xmpp-nodeprep-02, work in progress)", April 2003.
[11] Saint-Andre, P. and J. Hildebrand, "Resourceprep: A Stringprep
Profile for Resource Identifiers in XMPP
(draft-ietf-xmpp-resourceprep-02, work in progress)", April
2003.
[12] World Wide Web Consortium, "Namespaces in XML", W3C xml-names,
January 1999, <http://www.w3.org/TR/1999/
REC-xml-names-19990114/>.
[13] Dierks, T., Allen, C., Treese, W., Karlton, P., Freier, A. and
P. Kocher, "The TLS Protocol Version 1.0", RFC 2246, January
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1999.
[14] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[15] Myers, J., "Simple Authentication and Security Layer (SASL)",
RFC 2222, October 1997.
[16] Leach, P. and C. Newman, "Using Digest Authentication as a SASL
Mechanism", RFC 2831, May 2000.
[17] Alvestrand, H., "Tags for the Identification of Languages", BCP
47, RFC 3066, January 2001.
[18] Gulbrandsen, A. and P. Vixie, "A DNS RR for specifying the
location of services (DNS SRV)", RFC 2052, October 1996.
[19] Yergeau, F., "UTF-8, a transformation format of ISO 10646", RFC
2279, January 1998.
[20] Hoffman, P. and F. Yergeau, "UTF-16, an encoding of ISO 10646",
RFC 2781, February 2000.
[21] International Organization for Standardization, "Information
Technology - Universal Multiple-octet coded Character Set (UCS)
- Amendment 2: UCS Transformation Format 8 (UTF-8)", ISO
Standard 10646-1 Addendum 2, October 1996.
[22] Linn, J., "Generic Security Service Application Program
Interface, Version 2", RFC 2078, January 1997.
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Informative References
[23] Saint-Andre, P. and J. Miller, "XMPP Instant Messaging
(draft-ietf-xmpp-im-11, work in progress)", May 2003.
[24] 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>.
[25] Mealling, M., "The IANA XML Registry",
draft-mealling-iana-xmlns-registry-04 (work in progress), June
2002.
[26] Crispin, M., "Internet Message Access Protocol - Version
4rev1", RFC 2060, December 1996.
[27] Myers, J. and M. Rose, "Post Office Protocol - Version 3", STD
53, RFC 1939, May 1996.
[28] Newman, C. and J. Myers, "ACAP -- Application Configuration
Access Protocol", RFC 2244, November 1997.
[29] Newman, C., "Using TLS with IMAP, POP3 and ACAP", RFC 2595,
June 1999.
[30] Eastlake, D., "Domain Name System Security Extensions", RFC
2535, March 1999.
[31] Fielding, R., Gettys, J., Mogul, J., Nielsen, H., Masinter, L.,
Leach, P. and T. Berners-Lee, "Hypertext Transfer Protocol --
HTTP/1.1", RFC 2616, June 1999.
[32] Saint-Andre, P. and J. Hildebrand, "End-to-End Object
Encryption in XMPP (draft-ietf-xmpp-e2e-02, work in progress)",
April 2003.
Authors' Addresses
Peter Saint-Andre
Jabber Software Foundation
EMail: stpeter@jabber.org
URI: http://www.jabber.org/people/stpeter.php
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Jeremie Miller
Jabber Software Foundation
EMail: jeremie@jabber.org
URI: http://www.jabber.org/people/jer.php
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Appendix A. XML Schemas
The following XML schemas are descriptive, not normative.
A.1 Streams namespace
<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
xmlns:xs='http://www.w3.org/2001/XMLSchema'
targetNamespace='http://etherx.jabber.org/streams'
xmlns='http://etherx.jabber.org/streams'
elementFormDefault='qualified'>
<xs:element name='stream'>
<xs:complexType>
<xs:element ref='features' minOccurs='0' maxOccurs='1'/>
<xs:element ref='error' minOccurs='0' maxOccurs='1'/>
<xs:choice maxOccurs='1'>
<xs:any namespace='jabber:client'/>
<xs:any namespace='jabber:server'/>
</xs:choice>
<xs:attribute name='to' type='xs:string' use='optional'/>
<xs:attribute name='from' type='xs:string' use='optional'/>
<xs:attribute name='id' type='xs:ID' use='optional'/>
<xs:attribute name='version' type='xs:decimal' use='optional'/>
</xs:complexType>
</xs:element>
<xs:element name='features'>
<xs:complexType>
<xs:any
namespace='##other'
minOccurs='0'
maxOccurs='unbounded'/>
</xs:complexType>
</xs:element>
<xs:element name='error'>
<xs:complexType>
<xs:any maxOccurs='1'
namespace='urn:ietf:params:xml:ns:xmpp-streams'/>
<xs:attribute name='class' use='required'/>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='address'/>
<xs:enumeration value='format'/>
<xs:enumeration value='redirect'/>
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<xs:enumeration value='server'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:complexType>
</xs:element>
</xs:schema>
A.2 TLS namespace
<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
xmlns:xs='http://www.w3.org/2001/XMLSchema'
targetNamespace='urn:ietf:params:xml:ns:xmpp-tls'
xmlns='urn:ietf:params:xml:ns:xmpp-tls'
elementFormDefault='qualified'>
<xs:element name='starttls'>
<xs:complexType>
<xs:element
ref='required'
minOccurs='0'
maxOccurs='1'>
</xs:complexType>
</xs:element>
<xs:element name='proceed'/>
<xs:element name='failure'/>
<xs:element name='required'/>
</xs:schema>
A.3 SASL namespace
<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
xmlns:xs='http://www.w3.org/2001/XMLSchema'
targetNamespace='urn:ietf:params:xml:ns:xmpp-sasl'
xmlns='urn:ietf:params:xml:ns:xmpp-sasl'
elementFormDefault='qualified'>
<xs:element name='mechanisms'>
<xs:complexType>
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<xs:element ref='mechanism' maxOccurs='unbounded'>
</xs:complexType>
</xs:element>
<xs:element name='mechanism' type='xs:string'/>
<xs:element name='auth'>
<xs:complexType>
<xs:attribute name='mechanism'
type='xs:string' use='optional'/>
</xs:complexType>
</xs:element>
<xs:element name='challenge' type='xs:string'/>
<xs:element name='response' type='xs:string'/>
<xs:element name='abort'/>
<xs:element name='success'/>
<xs:element name='failure'>
<xs:complexType>
<xs:choice maxOccurs='1'>
<xs:element ref='invalid-realm'/>
<xs:element ref='mechanism-too-weak'/>
<xs:element ref='not-authorized'/>
<xs:element ref='password-transition-required'/>
<xs:element ref='temporary-auth-failure'/>
</xs:choice>
</xs:complexType>
</xs:element>
<xs:element name='invalid-realm'/>
<xs:element name='mechanism-too-weak'/>
<xs:element name='not-authorized'/>
<xs:element name='password-transition-required'/>
<xs:element name='temporary-auth-failure'/>
</xs:schema>
A.4 Dialback namespace
<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
xmlns:xs='http://www.w3.org/2001/XMLSchema'
targetNamespace='jabber:server:dialback'
xmlns='jabber:server:dialback'
elementFormDefault='qualified'>
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<xs:element name='result'>
<xs:complexType>
<xs:simpleContent>
<xs:extension base='xs:string'>
<xs:attribute name='from' type='xs:string' use='required'/>
<xs:attribute name='to' type='xs:string' use='required'/>
<xs:attribute name='type' use='optional'>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='invalid'/>
<xs:enumeration value='valid'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
<xs:element name='verify'>
<xs:complexType>
<xs:simpleContent>
<xs:extension base='xs:string'>
<xs:attribute name='from' type='xs:string' use='required'/>
<xs:attribute name='to' type='xs:string' use='required'/>
<xs:attribute name='id' type='xs:string' use='required'/>
<xs:attribute name='type' use='optional'>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='invalid'/>
<xs:enumeration value='valid'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
</xs:schema>
A.5 Client namespace
<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
xmlns:xs='http://www.w3.org/2001/XMLSchema'
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targetNamespace='jabber:client'
xmlns='jabber:client'
elementFormDefault='qualified'>
<xs:element name='message'>
<xs:complexType>
<xs:sequence>
<xs:element ref='subject'
minOccurs='0' maxOccurs='unbounded'/>
<xs:element ref='body'
minOccurs='0' maxOccurs='unbounded'/>
<xs:element ref='thread' minOccurs='0' maxOccurs='1'/>
<xs:any
namespace='##other'
minOccurs='0'
maxOccurs='unbounded'/>
<xs:element ref='error' minOccurs='0' maxOccurs='1'/>
</xs:sequence>
<xs:attribute name='to' type='xs:string' use='optional'/>
<xs:attribute name='from' type='xs:string' use='optional'/>
<xs:attribute name='id' type='xs:ID' use='optional'/>
<xs:attribute name='xml:lang'
type='xs:NMTOKEN'
use='optional'/>
<xs:attribute name='type' use='optional'>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='chat'/>
<xs:enumeration value='groupchat'/>
<xs:enumeration value='headline'/>
<xs:enumeration value='error'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:complexType>
</xs:element>
<xs:element name='body' type='xs:string'>
<xs:complexType>
<xs:simpleContent>
<xs:extension base='xs:NMTOKEN'>
<xs:attribute name='xml:lang' use='optional'/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
<xs:element name='subject' type='xs:string'>
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<xs:complexType>
<xs:simpleContent>
<xs:extension base='xs:NMTOKEN'>
<xs:attribute name='xml:lang' use='optional'/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
<xs:element name='thread' type='xs:string'/>
<xs:element name='presence'>
<xs:complexType>
<xs:sequence>
<xs:element ref='show' minOccurs='0' maxOccurs='1'/>
<xs:element ref='status'
minOccurs='0' maxOccurs='unbounded'/>
<xs:element ref='priority' minOccurs='0' maxOccurs='1'/>
<xs:any
namespace='##other'
minOccurs='0'
maxOccurs='unbounded'/>
<xs:element ref='error' minOccurs='0' maxOccurs='1'/>
</xs:sequence>
<xs:attribute name='to' type='xs:string' use='optional'/>
<xs:attribute name='from' type='xs:string' use='optional'/>
<xs:attribute name='id' type='xs:ID' use='optional'/>
<xs:attribute name='xml:lang'
type='xs:NMTOKEN'
use='optional'/>
<xs:attribute name='type' use='optional'>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='subscribe'/>
<xs:enumeration value='subscribed'/>
<xs:enumeration value='unsubscribe'/>
<xs:enumeration value='unsubscribed'/>
<xs:enumeration value='unavailable'/>
<xs:enumeration value='error'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:complexType>
</xs:element>
<xs:element name='show'>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
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<xs:enumeration value='away'/>
<xs:enumeration value='chat'/>
<xs:enumeration value='xa'/>
<xs:enumeration value='dnd'/>
</xs:restriction>
</xs:simpleType>
</xs:element>
<xs:element name='status' type='xs:string'>
<xs:complexType>
<xs:simpleContent>
<xs:extension base='xs:NMTOKEN'>
<xs:attribute name='xml:lang' use='optional'/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
<xs:element name='priority' type='xs:byte'/>
<xs:element name='iq'>
<xs:complexType>
<xs:sequence>
<xs:any
namespace='##other'
minOccurs='0'
maxOccurs='1'/>
<xs:element ref='error' minOccurs='0' maxOccurs='1'/>
</xs:sequence>
<xs:attribute name='to' type='xs:string' use='optional'/>
<xs:attribute name='from' type='xs:string' use='optional'/>
<xs:attribute name='id' type='xs:ID' use='optional'/>
<xs:attribute name='type' use='required'>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='get'/>
<xs:enumeration value='set'/>
<xs:enumeration value='result'/>
<xs:enumeration value='error'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute name='xml:lang'
type='xs:NMTOKEN'
use='optional'/>
</xs:complexType>
</xs:element>
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<xs:element name='error'>
<xs:complexType>
<xs:any maxOccurs='1'
namespace='urn:ietf:params:xml:ns:xmpp-stanzas'/>
<xs:attribute name='class' use='required'/>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='access'/>
<xs:enumeration value='address'/>
<xs:enumeration value='format'/>
<xs:enumeration value='recipient'/>
<xs:enumeration value='server'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:complexType>
</xs:element>
</xs:schema>
A.6 Server namespace
<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
xmlns:xs='http://www.w3.org/2001/XMLSchema'
targetNamespace='jabber:server'
xmlns='jabber:server'
elementFormDefault='qualified'>
<xs:element name='message'>
<xs:complexType>
<xs:sequence>
<xs:element ref='subject'
minOccurs='0' maxOccurs='unbounded'/>
<xs:element ref='body'
minOccurs='0' maxOccurs='unbounded'/>
<xs:element ref='thread' minOccurs='0' maxOccurs='1'/>
<xs:any
namespace='##other'
minOccurs='0'
maxOccurs='unbounded'/>
<xs:element ref='error' minOccurs='0' maxOccurs='1'/>
</xs:sequence>
<xs:attribute name='to' type='xs:string' use='required'/>
<xs:attribute name='from' type='xs:string' use='required'/>
<xs:attribute name='id' type='xs:ID' use='optional'/>
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<xs:attribute name='xml:lang'
type='xs:NMTOKEN'
use='optional'/>
<xs:attribute name='type' use='optional'>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='chat'/>
<xs:enumeration value='groupchat'/>
<xs:enumeration value='headline'/>
<xs:enumeration value='error'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:complexType>
</xs:element>
<xs:element name='body' type='xs:string'>
<xs:complexType>
<xs:simpleContent>
<xs:extension base='xs:NMTOKEN'>
<xs:attribute name='xml:lang' use='optional'/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
<xs:element name='subject' type='xs:string'>
<xs:complexType>
<xs:simpleContent>
<xs:extension base='xs:NMTOKEN'>
<xs:attribute name='xml:lang' use='optional'/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
<xs:element name='thread' type='xs:string'/>
<xs:element name='presence'>
<xs:complexType>
<xs:sequence>
<xs:element ref='show' minOccurs='0' maxOccurs='1'/>
<xs:element ref='status'
minOccurs='0' maxOccurs='unbounded'/>
<xs:element ref='priority' minOccurs='0' maxOccurs='1'/>
<xs:any
namespace='##other'
minOccurs='0'
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maxOccurs='unbounded'/>
<xs:element ref='error' minOccurs='0' maxOccurs='1'/>
</xs:sequence>
<xs:attribute name='to' type='xs:string' use='required'/>
<xs:attribute name='from' type='xs:string' use='required'/>
<xs:attribute name='id' type='xs:ID' use='optional'/>
<xs:attribute name='xml:lang'
type='xs:NMTOKEN'
use='optional'/>
<xs:attribute name='type' use='optional'>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='subscribe'/>
<xs:enumeration value='subscribed'/>
<xs:enumeration value='unsubscribe'/>
<xs:enumeration value='unsubscribed'/>
<xs:enumeration value='unavailable'/>
<xs:enumeration value='error'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:complexType>
</xs:element>
<xs:element name='show'>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='away'/>
<xs:enumeration value='chat'/>
<xs:enumeration value='xa'/>
<xs:enumeration value='dnd'/>
</xs:restriction>
</xs:simpleType>
</xs:element>
<xs:element name='status' type='xs:string'>
<xs:complexType>
<xs:simpleContent>
<xs:extension base='xs:NMTOKEN'>
<xs:attribute name='xml:lang' use='optional'/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
<xs:element name='priority' type='xs:byte'/>
<xs:element name='iq'>
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<xs:complexType>
<xs:sequence>
<xs:any
namespace='##other'
minOccurs='0'
maxOccurs='1'/>
<xs:element ref='error' minOccurs='0' maxOccurs='1'/>
</xs:sequence>
<xs:attribute name='to' type='xs:string' use='required'/>
<xs:attribute name='from' type='xs:string' use='required'/>
<xs:attribute name='id' type='xs:ID' use='optional'/>
<xs:attribute name='type' use='required'>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='get'/>
<xs:enumeration value='set'/>
<xs:enumeration value='result'/>
<xs:enumeration value='error'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute name='xml:lang'
type='xs:NMTOKEN'
use='optional'/>
</xs:complexType>
</xs:element>
<xs:element name='error'>
<xs:complexType>
<xs:any maxOccurs='1'
namespace='urn:ietf:params:xml:ns:xmpp-stanzas'/>
<xs:attribute name='class' use='required'/>
<xs:simpleType>
<xs:restriction base='xs:NCName'>
<xs:enumeration value='access'/>
<xs:enumeration value='address'/>
<xs:enumeration value='format'/>
<xs:enumeration value='recipient'/>
<xs:enumeration value='server'/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:complexType>
</xs:element>
</xs:schema>
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A.7 Stream error namespace
<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
xmlns:xs='http://www.w3.org/2001/XMLSchema'
targetNamespace='urn:ietf:params:xml:ns:xmpp-streams'
xmlns='urn:ietf:params:xml:ns:xmpp-streams'
elementFormDefault='qualified'>
<xs:element name='condition'>
<xs:complexType>
<xs:any
namespace='##other'
minOccurs='0'
maxOccurs='1'/>
<xs:choice maxOccurs='1'>
<xs:element ref='host-gone'/>
<xs:element ref='host-unknown'/>
<xs:element ref='internal-server-error'/>
<xs:element ref='invalid-id'/>
<xs:element ref='invalid-namespace'/>
<xs:element ref='nonmatching-hosts'/>
<xs:element ref='not-authorized'/>
<xs:element ref='remote-connection-failed'/>
<xs:element ref='resource-constraint'/>
<xs:element ref='see-other-host'/>
<xs:element ref='system-shutdown'/>
<xs:element ref='unsupported-stanza-type'/>
<xs:element ref='unsupported-version'/>
<xs:element ref='xml-not-well-formed'/>
</xs:choice>
</xs:complexType>
<xs:element name='host-gone'/>
<xs:element name='host-unknown'/>
<xs:element name='internal-server-error'/>
<xs:element name='invalid-id'/>
<xs:element name='invalid-namespace'/>
<xs:element name='nonmatching-hosts'/>
<xs:element name='not-authorized'/>
<xs:element name='remote-connection-failed'/>
<xs:element name='resource-constraint'/>
<xs:element name='see-other-host' type='xs:string'/>
<xs:element name='system-shutdown'/>
<xs:element name='unsupported-stanza-type'/>
<xs:element name='unsupported-version' type='xs:string'/>
<xs:element name='xml-not-well-formed'/>
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</xs:schema>
A.8 Stanza error namespace
<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
xmlns:xs='http://www.w3.org/2001/XMLSchema'
targetNamespace='urn:ietf:params:xml:ns:xmpp-stanzas'
xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'
elementFormDefault='qualified'>
<xs:element name='condition'>
<xs:complexType>
<xs:choice>
<xs:element ref='bad-request'/>
<xs:element ref='feature-not-implemented'/>
<xs:element ref='forbidden'/>
<xs:element ref='internal-server-error'/>
<xs:element ref='item-not-found'/>
<xs:element ref='jid-malformed'/>
<xs:element ref='not-allowed'/>
<xs:element ref='recipient-unavailable'/>
<xs:element ref='registration-required'/>
<xs:element ref='remote-server-not-found'/>
<xs:element ref='remove-server-timeout'/>
<xs:element ref='service-unavailable'/>
</xs:choice>
</xs:complexType>
<xs:element name='bad-request' type='conditionType'/>
<xs:element name='feature-not-implemented' type='conditionType'/>
<xs:element name='forbidden' type='conditionType'/>
<xs:element name='internal-server-error' type='conditionType'/>
<xs:element name='item-not-found' type='conditionType'/>
<xs:element name='jid-malformed' type='conditionType'/>
<xs:element name='not-allowed' type='conditionType'/>
<xs:element name='recipient-unavailable' type='conditionType'/>
<xs:element name='registration-required' type='conditionType'/>
<xs:element name='remote-server-not-found' type='conditionType'/>
<xs:element name='remote-server-timeout' type='conditionType'/>
<xs:element name='service-unavailable' type='conditionType'/>
<xs:complexType name='conditionType'>
<xs:any namespace='##other' minOccurs='0' maxOccurs='1'/>
</xs:complexType>
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</xs:schema>
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Appendix B. Revision History
Note to RFC Editor: please remove this entire appendix, and the
corresponding entries in the table of contents, prior to publication.
B.1 Changes from draft-ietf-xmpp-core-09
o Adjusted TLS content regarding certificate validation process.
o Specified that stanza error extensions for specific applications
are to be properly namespaced children of the relevant descriptive
element.
o Clarified rules for inclusion of the 'id' attribute.
o Specified that the 'xml:lang' attribute SHOULD be included (per
list discussion).
o Made small editorial changes and fixed several schema errors.
B.2 Changes from draft-ietf-xmpp-core-09
o Fixed several dialback error conditions.
o Cleaned up business rules regarding TLS and certificate processing
based on off-list feedback.
o Changed <stream-condition/> and <stanza-condition/> elements to
<condition/>.
o Added or modified several stream and stanza error conditions.
o Specified only one child allowed for IQ, or two if type="error".
o Fixed several errors in the schemas.
B.3 Changes from draft-ietf-xmpp-core-08
o Incorporated list discussion regarding addressing, SASL, TLS, TCP,
dialback, namespaces, extensibility, and the meaning of 'ignore'
for routers and recipients.
o Specified dialback error conditions.
o Made small editorial changes to address RFC Editor requirements.
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B.4 Changes from draft-ietf-xmpp-core-07
o Made several small editorial changes.
B.5 Changes from draft-ietf-xmpp-core-06
o Added text regarding certificate validation in TLS negotiation per
list discussion.
o Clarified nature of XML restrictions per discussion with W3C, and
moved XML Restrictions subsection under "XML Usage within XMPP".
o Further clarified that XML streams are unidirectional.
o Changed stream error and stanza error namespace names to conform
to the format defined in The IETF XML Registry [25].
o Removed note to RFC Editor regarding provisional namespace names.
B.6 Changes from draft-ietf-xmpp-core-05
o Added <invalid-namespace/> as a stream error condition.
o Adjusted security considerations per discussion at IETF 56 and on
list.
B.7 Changes from draft-ietf-xmpp-core-04
o Added server-to-server examples for TLS and SASL.
o Changed error syntax, rules, and examples based on list
discussion.
o Added schemas for the TLS, stream error, and stanza error
namespaces.
o Added note to RFC Editor regarding provisional namespace names.
o Made numerous small editorial changes and clarified text
throughout.
B.8 Changes from draft-ietf-xmpp-core-03
o Clarified rules and procedures for TLS and SASL.
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o Amplified stream error code syntax per list discussion.
o Made numerous small editorial changes.
B.9 Changes from draft-ietf-xmpp-core-02
o Added dialback schema.
o Removed all DTDs since schemas provide more complete definitions.
o Added stream error codes.
o Clarified error code "philosophy".
B.10 Changes from draft-ietf-xmpp-core-01
o Updated the addressing restrictions per list discussion and added
references to the new nodeprep and resourceprep profiles.
o Corrected error in Stream Authentication regarding "version='1.0'"
flag.
o Made numerous small editorial changes.
B.11 Changes from draft-ietf-xmpp-core-00
o Added information about TLS from list discussion.
o Clarified meaning of "ignore" based on list discussion.
o Clarified information about Universal Character Set data and
character encodings.
o Provided base64-decoded information for examples.
o Fixed several errors in the schemas.
o Made numerous small editorial fixes.
B.12 Changes from draft-miller-xmpp-core-02
o Brought Streams Authentication section into line with discussion
on list and at IETF 55 meeting.
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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
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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