💾 Archived View for gemini.bortzmeyer.org › rfc-mirror › rfc6122.txt captured on 2024-02-05 at 11:03:41.
⬅️ Previous capture (2021-11-30)
-=-=-=-=-=-=-
Internet Engineering Task Force (IETF) P. Saint-Andre
Request for Comments: 6122 Cisco
Updates: 3920 March 2011
Category: Standards Track
ISSN: 2070-1721
Extensible Messaging and Presence Protocol (XMPP): Address Format
Abstract
This document defines the format for addresses used in the Extensible
Messaging and Presence Protocol (XMPP), including support for
non-ASCII characters. This document updates RFC 3920.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6122.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Saint-Andre Standards Track [Page 1]
RFC 6122 XMPP Address Format March 2011
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. Addresses . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Fundamentals . . . . . . . . . . . . . . . . . . . . . . . 4
2.2. Domainpart . . . . . . . . . . . . . . . . . . . . . . . . 6
2.3. Localpart . . . . . . . . . . . . . . . . . . . . . . . . 7
2.4. Resourcepart . . . . . . . . . . . . . . . . . . . . . . . 8
3. Internationalization Considerations . . . . . . . . . . . . . 9
4. Security Considerations . . . . . . . . . . . . . . . . . . . 9
4.1. Reuse of Stringprep . . . . . . . . . . . . . . . . . . . 9
4.2. Reuse of Unicode . . . . . . . . . . . . . . . . . . . . . 9
4.3. Address Spoofing . . . . . . . . . . . . . . . . . . . . . 9
4.3.1. Address Forging . . . . . . . . . . . . . . . . . . . 10
4.3.2. Address Mimicking . . . . . . . . . . . . . . . . . . 10
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
5.1. Nodeprep Profile of Stringprep . . . . . . . . . . . . . . 13
5.2. Resourceprep Profile of Stringprep . . . . . . . . . . . . 14
6. Conformance Requirements . . . . . . . . . . . . . . . . . . . 14
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
7.1. Normative References . . . . . . . . . . . . . . . . . . . 16
7.2. Informative References . . . . . . . . . . . . . . . . . . 17
Appendix A. Nodeprep . . . . . . . . . . . . . . . . . . . . . . 19
A.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 19
A.2. Character Repertoire . . . . . . . . . . . . . . . . . . . 19
A.3. Mapping . . . . . . . . . . . . . . . . . . . . . . . . . 19
A.4. Normalization . . . . . . . . . . . . . . . . . . . . . . 19
A.5. Prohibited Output . . . . . . . . . . . . . . . . . . . . 20
A.6. Bidirectional Characters . . . . . . . . . . . . . . . . . 20
A.7. Notes . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Appendix B. Resourceprep . . . . . . . . . . . . . . . . . . . . 21
B.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 21
B.2. Character Repertoire . . . . . . . . . . . . . . . . . . . 22
B.3. Mapping . . . . . . . . . . . . . . . . . . . . . . . . . 22
B.4. Normalization . . . . . . . . . . . . . . . . . . . . . . 22
B.5. Prohibited Output . . . . . . . . . . . . . . . . . . . . 22
B.6. Bidirectional Characters . . . . . . . . . . . . . . . . . 22
Appendix C. Differences from RFC 3920 . . . . . . . . . . . . . . 22
Appendix D. Acknowledgements . . . . . . . . . . . . . . . . . . 23
Saint-Andre Standards Track [Page 2]
RFC 6122 XMPP Address Format March 2011
1. Introduction
1.1. Overview
The Extensible Messaging and Presence Protocol (XMPP) is an
application profile of the Extensible Markup Language [XML] for
streaming XML data in close to real time between any two or more
network-aware entities. The address format for XMPP entities was
originally developed in the Jabber open-source community in 1999,
first described by [XEP-0029] in 2002, and defined canonically by
[RFC3920] in 2004.
As specified in RFC 3920, the XMPP address format reuses the
"stringprep" technology for preparation of non-ASCII characters
[STRINGPREP], including the Nameprep profile for internationalized
domain names as specified in [NAMEPREP] and [IDNA2003] along with two
XMPP-specific profiles for the localpart and resourcepart.
Since the publication of RFC 3920, IDNA2003 has been superseded by
IDNA2008 (see [IDNA-PROTO] and related documents), which is not based
on stringprep. Following the lead of the IDNA community, other
technology communities that use stringprep have begun discussions
about migrating away from stringprep toward more "modern" approaches.
The XMPP community is participating in those discussions (mostly
within the PRECIS Working Group) in order to find a replacement for
the Nodeprep and Resourceprep profiles of stringprep defined in RFC
3920. Because all other aspects of revised documentation for XMPP
have been incorporated into [XMPP], the XMPP Working Group decided to
temporarily split the XMPP address format into a separate document so
as not to significantly delay publication of improved documentation
for XMPP. It is expected that this document will be obsoleted as
soon as work on a new approach to preparation and comparison of
internationalized addresses has been completed.
Therefore, this specification provides corrected documentation of the
XMPP address format using the internationalization technologies
available in 2004 (when RFC 3920 was published). Although this
document normatively references [IDNA2003] and [NAMEPREP], XMPP
software implementations are encouraged to begin migrating to
IDNA2008 (see [IDNA-PROTO] and related documents) because the
specification that obsoletes this one will use IDNA2008 rather than
IDNA2003.
This document updates RFC 3920.
Saint-Andre Standards Track [Page 3]
RFC 6122 XMPP Address Format March 2011
1.2. Terminology
Many important terms used in this document are defined in [IDNA2003],
[STRINGPREP], [UNICODE], and [XMPP].
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in RFC
2119 [KEYWORDS].
2. Addresses
2.1. Fundamentals
An XMPP entity is anything that is network-addressable and that can
communicate using XMPP. For historical reasons, the native address
of an XMPP entity is called a Jabber Identifier or JID. A valid JID
is a string of [UNICODE] code points, encoded using [UTF-8], and
structured as an ordered sequence of localpart, domainpart, and
resourcepart (where the first two parts are demarcated by the '@'
character used as a separator, and the last two parts are similarly
demarcated by the '/' character).
The syntax for a JID is defined as follows using the Augmented
Backus-Naur Form as specified in [ABNF].
Saint-Andre Standards Track [Page 4]
RFC 6122 XMPP Address Format March 2011
jid = [ localpart "@" ] domainpart [ "/" resourcepart ]
localpart = 1*(nodepoint)
;
; a "nodepoint" is a UTF-8 encoded Unicode code
; point that satisfies the Nodeprep profile of
; stringprep
;
domainpart = IP-literal / IPv4address / ifqdn
;
; the "IPv4address" and "IP-literal" rules are
; defined in RFC 3986, and the first-match-wins
; (a.k.a. "greedy") algorithm described in RFC
; 3986 applies to the matching process
;
; note well that reuse of the IP-literal rule
; from RFC 3986 implies that IPv6 addresses are
; enclosed in square brackets (i.e., beginning
; with '[' and ending with ']'), which was not
; the case in RFC 3920
;
ifqdn = 1*(namepoint)
;
; a "namepoint" is a UTF-8 encoded Unicode
; code point that satisfies the Nameprep
; profile of stringprep
;
resourcepart = 1*(resourcepoint)
;
; a "resourcepoint" is a UTF-8 encoded Unicode
; code point that satisfies the Resourceprep
; profile of stringprep
;
All JIDs are based on the foregoing structure.
Each allowable portion of a JID (localpart, domainpart, and
resourcepart) MUST NOT be zero bytes in length and MUST NOT be more
than 1023 bytes in length, resulting in a maximum total size
(including the '@' and '/' separators) of 3071 bytes.
For the purpose of communication over an XMPP network (e.g., in the
'to' or 'from' address of an XMPP stanza), an entity's address MUST
be represented as a JID, not as a Uniform Resource Identifier [URI]
or Internationalized Resource Identifier [IRI]. An XMPP IRI
[XMPP-URI] is in essence a JID prepended with 'xmpp:'; however, the
native addressing format used in XMPP is that of a mere JID without a
URI scheme. [XMPP-URI] is provided only for identification and
interaction outside the context of XMPP itself, for example when
Saint-Andre Standards Track [Page 5]
RFC 6122 XMPP Address Format March 2011
linking to a JID from a web page. See [XMPP-URI] for a description
of the process for securely extracting a JID from an XMPP URI or IRI.
Implementation Note: When dividing a JID into its component parts,
an implementation needs to match the separator characters '@' and
'/' before applying any transformation algorithms, which might
decompose certain Unicode code points to the separator characters
(e.g., U+FE6B SMALL COMMERCIAL AT might decompose into U+0040
COMMERCIAL AT).
2.2. Domainpart
The domainpart of a JID is that portion after the '@' character (if
any) and before the '/' character (if any); it is the primary
identifier and is the only REQUIRED element of a JID (a mere
domainpart is a valid JID). Typically a domainpart identifies the
"home" server to which clients connect for XML routing and data
management functionality. However, it is not necessary for an XMPP
domainpart to identify an entity that provides core XMPP server
functionality (e.g., a domainpart can identify an entity such as a
multi-user chat service, a publish-subscribe service, or a user
directory).
The domainpart for every XMPP service MUST be a fully qualified
domain name (FQDN; see [DNS]), IPv4 address, IPv6 address, or
unqualified hostname (i.e., a text label that is resolvable on a
local network).
Interoperability Note: Domainparts that are IP addresses might not
be accepted by other services for the sake of server-to-server
communication, and domainparts that are unqualified hostnames
cannot be used on public networks because they are resolvable only
on a local network.
If the domainpart includes a final character considered to be a label
separator (dot) by [IDNA2003] or [DNS], this character MUST be
stripped from the domainpart before the JID of which it is a part is
used for the purpose of routing an XML stanza, comparing against
another JID, or constructing an [XMPP-URI]. In particular, the
character MUST be stripped before any other canonicalization steps
are taken, such as application of the [NAMEPREP] profile of
[STRINGPREP] or completion of the ToASCII operation as described in
[IDNA2003].
A domainpart consisting of a fully qualified domain name MUST be an
"internationalized domain name" as defined in [IDNA2003]; that is, it
MUST be "a domain name in which every label is an internationalized
label" and MUST follow the rules for construction of
Saint-Andre Standards Track [Page 6]
RFC 6122 XMPP Address Format March 2011
internationalized domain names specified in [IDNA2003]. When
preparing a text label (consisting of a sequence of UTF-8 encoded
Unicode code points) for representation as an internationalized label
in the process of constructing an XMPP domainpart or comparing two
XMPP domainparts, an application MUST ensure that for each text label
it is possible to apply without failing the ToASCII operation
specified in [IDNA2003] with the UseSTD3ASCIIRules flag set (thus
forbidding ASCII code points other than letters, digits, and
hyphens). If the ToASCII operation can be applied without failing,
then the label is an internationalized label. (Note: The ToASCII
operation includes application of the [NAMEPREP] profile of
[STRINGPREP] and encoding using the algorithm specified in
[PUNYCODE]; for details, see [IDNA2003].) Although XMPP applications
do not communicate the output of the ToASCII operation (called an
"ACE label") over the wire, it MUST be possible to apply that
operation without failing to each internationalized label. If an
XMPP application receives as input an ACE label, it SHOULD convert
that ACE label to an internationalized label using the ToUnicode
operation (see [IDNA2003]) before including the label in an XMPP
domainpart that will be communicated over the wire on an XMPP network
(however, instead of converting the label, there are legitimate
reasons why an application might instead refuse the input altogether
and return an error to the entity that provided the offending data).
A domainpart MUST NOT be zero bytes in length and MUST NOT be more
than 1023 bytes in length. This rule is to be enforced after any
mapping or normalization resulting from application of the Nameprep
profile of stringprep (e.g., in Nameprep some characters can be
mapped to nothing, which might result in a string of zero length).
Naturally, the length limits of [DNS] apply, and nothing in this
document is to be interpreted as overriding those more fundamental
limits.
In the terms of IDNA2008 [IDNA-DEFS], the domainpart of a JID is a
"domain name slot".
2.3. Localpart
The localpart of a JID is an optional identifier placed before the
domainpart and separated from the latter by the '@' character.
Typically a localpart uniquely identifies the entity requesting and
using network access provided by a server (i.e., a local account),
although it can also represent other kinds of entities (e.g., a chat
room associated with a multi-user chat service). The entity
represented by an XMPP localpart is addressed within the context of a
specific domain (i.e., <localpart@domainpart>).
Saint-Andre Standards Track [Page 7]
RFC 6122 XMPP Address Format March 2011
A localpart MUST be formatted such that the Nodeprep profile of
[STRINGPREP] can be applied without failing (see Appendix A). Before
comparing two localparts, an application MUST first ensure that the
Nodeprep profile has been applied to each identifier (the profile
need not be applied each time a comparison is made, as long as it has
been applied before comparison).
A localpart MUST NOT be zero bytes in length and MUST NOT be more
than 1023 bytes in length. This rule is to be enforced after any
mapping or normalization resulting from application of the Nodeprep
profile of stringprep (e.g., in Nodeprep some characters can be
mapped to nothing, which might result in a string of zero length).
2.4. Resourcepart
The resourcepart of a JID is an optional identifier placed after the
domainpart and separated from the latter by the '/' character. A
resourcepart can modify either a <localpart@domainpart> address or a
mere <domainpart> address. Typically a resourcepart uniquely
identifies a specific connection (e.g., a device or location) or
object (e.g., an occupant in a multi-user chat room) belonging to the
entity associated with an XMPP localpart at a domain (i.e.,
<localpart@domainpart/resourcepart>).
A resourcepart MUST be formatted such that the Resourceprep profile
of [STRINGPREP] can be applied without failing (see Appendix B).
Before comparing two resourceparts, an application MUST first ensure
that the Resourceprep profile has been applied to each identifier
(the profile need not be applied each time a comparison is made, as
long as it has been applied before comparison).
A resourcepart MUST NOT be zero bytes in length and MUST NOT be more
than 1023 bytes in length. This rule is to be enforced after any
mapping or normalization resulting from application of the
Resourceprep profile of stringprep (e.g., in Resourceprep some
characters can be mapped to nothing, which might result in a string
of zero length).
Informational Note: For historical reasons, the term "resource
identifier" is often used in XMPP to refer to the optional portion
of an XMPP address that follows the domainpart and the "/"
separator character; to help prevent confusion between an XMPP
"resource identifier" and the meanings of "resource" and
"identifier" provided in Section 1.1 of [URI], this specification
uses the term "resourcepart" instead of "resource identifier" (as
in RFC 3920).
Saint-Andre Standards Track [Page 8]
RFC 6122 XMPP Address Format March 2011
XMPP entities SHOULD consider resourceparts to be opaque strings and
SHOULD NOT impute meaning to any given resourcepart. In particular:
o Use of the '/' character as a separator between the domainpart and
the resourcepart does not imply that XMPP addresses are
hierarchical in the way that, say, HTTP addresses are
hierarchical; thus for example an XMPP address of the form
<localpart@domainpart/foo/bar> does not identify a resource "bar"
that exists below a resource "foo" in a hierarchy of resources
associated with the entity "localpart@domain".
o The '@' character is allowed in the resourcepart and is often used
in the "nick" shown in XMPP chatrooms. For example, the JID
<room@chat.example.com/user@host> describes an entity who is an
occupant of the room <room@chat.example.com> with an (asserted)
nick of <user@host>. However, chatroom services do not
necessarily check such an asserted nick against the occupant's
real JID.
3. Internationalization Considerations
XMPP servers MUST, and XMPP clients SHOULD, support [IDNA2003] for
domainparts (including the [NAMEPREP] profile of [STRINGPREP]), the
Nodeprep (Appendix A) profile of [STRINGPREP] for localparts, and the
Resourceprep (Appendix B) profile of [STRINGPREP] for resourceparts;
this enables XMPP addresses to include a wide variety of characters
outside the US-ASCII range. Rules for enforcement of the XMPP
address format are provided in [XMPP].
4. Security Considerations
4.1. Reuse of Stringprep
The security considerations described in [STRINGPREP] apply to the
Nodeprep (Appendix A) and Resourceprep (Appendix B) profiles defined
in this document for XMPP localparts and resourceparts. The security
considerations described in [STRINGPREP] and [NAMEPREP] apply to the
Nameprep profile that is reused here for XMPP domainparts.
4.2. Reuse of Unicode
The security considerations described in [UNICODE-SEC] apply to the
use of Unicode characters in XMPP addresses.
4.3. Address Spoofing
There are two forms of address spoofing: forging and mimicking.
Saint-Andre Standards Track [Page 9]
RFC 6122 XMPP Address Format March 2011
4.3.1. Address Forging
In the context of XMPP technologies, address forging occurs when an
entity is able to generate an XML stanza whose 'from' address does
not correspond to the account credentials with which the entity
authenticated onto the network (or an authorization identity provided
during negotiation of SASL authentication [SASL] as described in
[XMPP]). For example, address forging occurs if an entity that
authenticated as "juliet@im.example.com" is able to send XML stanzas
from "nurse@im.example.com" or "romeo@example.net".
Address forging is difficult in XMPP systems, given the requirement
for sending servers to stamp 'from' addresses and for receiving
servers to verify sending domains via server-to-server authentication
(see [XMPP]). However, address forging is possible if:
o A poorly implemented server ignores the requirement for stamping
the 'from' address. This would enable any entity that
authenticated with the server to send stanzas from any
localpart@domainpart as long as the domainpart matches the sending
domain of the server.
o An actively malicious server generates stanzas on behalf of any
registered account.
Therefore, an entity outside the security perimeter of a particular
server cannot reliably distinguish between JIDs of the form
<localpart@domainpart> at that server and thus can authenticate only
the domainpart of such JIDs with any level of assurance. This
specification does not define methods for discovering or
counteracting such poorly implemented or rogue servers. However, the
end-to-end authentication or signing of XMPP stanzas could help to
mitigate this risk, since it would require the rogue server to
generate false credentials in addition to modifying 'from' addresses.
Furthermore, it is possible for an attacker to forge JIDs at other
domains by means of a DNS poisoning attack if DNS security extensions
[DNSSEC] are not used.
4.3.2. Address Mimicking
Address mimicking occurs when an entity provides legitimate
authentication credentials for and sends XML stanzas from an account
whose JID appears to a human user to be the same as another JID. For
example, in some XMPP clients the address "ju1iet@example.org"
(spelled with the number one as the third character of the localpart)
might appear to be the same as "juliet@example.org (spelled with the
lower-case version of the letter "L"), especially on casual visual
Saint-Andre Standards Track [Page 10]
RFC 6122 XMPP Address Format March 2011
inspection; this phenomenon is sometimes called "typejacking". A
more sophisticated example of address mimicking might involve the use
of characters from outside the familiar Latin extended-A block of
Unicode code points, such as the characters U+13DA U+13A2 U+13B5
U+13AC U+13A2 U+13AC U+13D2 from the Cherokee block instead of the
similar-looking US-ASCII characters "STPETER".
In some examples of address mimicking, it is unlikely that the
average user could tell the difference between the real JID and the
fake JID. (Indeed, there is no programmatic way to distinguish with
full certainty which is the fake JID and which is the real JID; in
some communication contexts, the JID formed of Cherokee characters
might be the real JID and the JID formed of US-ASCII characters might
thus appear to be the fake JID.) Because JIDs can contain almost any
properly encoded Unicode code point, it can be relatively easy to
mimic some JIDs in XMPP systems. The possibility of address
mimicking introduces security vulnerabilities of the kind that have
also plagued the World Wide Web, specifically the phenomenon known as
phishing.
These problems arise because Unicode and ISO/IEC 10646 repertoires
have many characters that look similar (so-called "confusable
characters" or "confusables"). In many cases, XMPP users might
perform visual matching, such as when comparing the JIDs of
communication partners. Because it is impossible to map similar-
looking characters without a great deal of context (such as knowing
the fonts used), stringprep and stringprep-based technologies such as
Nameprep, Nodeprep, and Resourceprep do nothing to map similar-
looking characters together, nor do they prohibit some characters
because they look like others. As a result, XMPP localparts and
resourceparts could contain confusable characters, producing JIDs
that appear to mimic other JIDs and thus leading to security
vulnerabilities such as the following:
o A localpart can be employed as one part of an entity's address in
XMPP. One common usage is as the username of an instant messaging
user; another is as the name of a multi-user chat room; and many
other kinds of entities could use localparts as part of their
addresses. The security of such services could be compromised
based on different interpretations of the internationalized
localpart; for example, a user entering a single internationalized
localpart could access another user's account information, or a
user could gain access to a hidden or otherwise restricted chat
room or service.
o A resourcepart can be employed as one part of an entity's address
in XMPP. One common usage is as the name for an instant messaging
user's connected resource; another is as the nickname of a user in
Saint-Andre Standards Track [Page 11]
RFC 6122 XMPP Address Format March 2011
a multi-user chat room; and many other kinds of entities could use
resourceparts as part of their addresses. The security of such
services could be compromised based on different interpretations
of the internationalized resourcepart; for example, two or more
confusable resources could be bound at the same time to the same
account (resulting in inconsistent authorization decisions in an
XMPP application that uses full JIDs), or a user could send a
message to someone other than the intended recipient in a multi-
user chat room.
Despite the fact that some specific suggestions about identification
and handling of confusable characters appear in the Unicode Security
Considerations [UNICODE-SEC], it is also true (as noted in
[IDNA-DEFS]) that "there are no comprehensive technical solutions to
the problems of confusable characters". Mimicked JIDs that involve
characters from only one script, or from the script typically
employed by a particular user or community of language users, are not
easy to combat (e.g., the simple typejacking attack previously
described, which relies on a surface similarity between the
characters "1" and "l" in some presentations). However, mimicked
addresses that involve characters from more than one script, or from
a script not typically employed by a particular user or community of
language users, can be mitigated somewhat through the application of
appropriate registration policies at XMPP services and presentation
policies in XMPP client software. Therefore, the following policies
are encouraged:
1. Because an XMPP service that allows registration of XMPP user
accounts (localparts) plays a role similar to that of a registry
for DNS domain names, such a service SHOULD establish a policy
about the scripts or blocks of characters it will allow in
localparts at the service. Such a policy is likely to be
informed by the languages and scripts that are used to write
registered account names; in particular, to reduce confusion, the
service MAY forbid registration of XMPP localparts that contain
characters from more than one script and to restrict
registrations to characters drawn from a very small number of
scripts (e.g., scripts that are well-understood by the
administrators of the service). Such policies are also
appropriate for XMPP services that allow temporary or permanent
registration of XMPP resourceparts, e.g., during resource binding
[XMPP] or upon joining an XMPP-based chat room [XEP-0045]. For
related considerations in the context of domain name
registration, refer to Section 4.3 of [IDNA-PROTO] and Section
3.2 of [IDNA-RATIONALE]. Note well that methods for enforcing
such restrictions are out of scope for this document.
Saint-Andre Standards Track [Page 12]
RFC 6122 XMPP Address Format March 2011
2. Because every human user of an XMPP client presumably has a
preferred language (or, in some cases, a small set of preferred
languages), an XMPP client SHOULD gather that information either
explicitly from the user or implicitly via the operating system
of the user's device. Furthermore, because most languages are
typically represented by a single script (or a small set of
scripts) and most scripts are typically contained in one or more
blocks of characters, an XMPP client SHOULD warn the user when
presenting a JID that mixes characters from more than one script
or block, or that uses characters outside the normal range of the
user's preferred language(s). This recommendation is not
intended to discourage communication across different communities
of language users; instead, it recognizes the existence of such
communities and encourages due caution when presenting unfamiliar
scripts or characters to human users.
5. IANA Considerations
The following sections update the registrations provided in
[RFC3920].
5.1. Nodeprep Profile of Stringprep
The Nodeprep profile of stringprep is defined under Nodeprep
(Appendix A). The IANA has registered Nodeprep in the "Stringprep
Profiles" registry.
Name of this profile:
Nodeprep
RFC in which the profile is defined:
RFC 6122
Indicator whether or not this is the newest version of the profile:
This is the first version of Nodeprep
Saint-Andre Standards Track [Page 13]
RFC 6122 XMPP Address Format March 2011
5.2. Resourceprep Profile of Stringprep
The Resourceprep profile of stringprep is defined under Resourceprep
(Appendix B). The IANA has registered Resourceprep in the
"Stringprep Profiles" registry.
Name of this profile:
Resourceprep
RFC in which the profile is defined:
RFC 6122
Indicator whether or not this is the newest version of the profile:
This is the first version of Resourceprep
6. Conformance Requirements
This section describes a protocol feature set that summarizes the
conformance requirements of this specification. This feature set is
appropriate for use in software certification, interoperability
testing, and implementation reports. For each feature, this section
provides the following information:
o A human-readable name
o An informational description
o A reference to the particular section of this document that
normatively defines the feature
o Whether the feature applies to the Client role, the Server role,
or both (where "N/A" signifies that the feature is not applicable
to the specified role)
o Whether the feature MUST or SHOULD be implemented, where the
capitalized terms are to be understood as described in [KEYWORDS]
The feature set specified here attempts to adhere to the concepts and
formats proposed by Larry Masinter within the IETF's NEWTRK Working
Group in 2005, as captured in [INTEROP]. Although this feature set
is more detailed than called for by [REPORTS], it provides a suitable
basis for the generation of implementation reports to be submitted in
support of advancing this specification from Proposed Standard to
Draft Standard in accordance with [PROCESS].
Saint-Andre Standards Track [Page 14]
RFC 6122 XMPP Address Format March 2011
Feature: address-domain-length
Description: Ensure that the domainpart of an XMPP address is at
least one byte in length and at most 1023 bytes in length, and
conforms to the underlying length limits of the DNS.
Section: Section 2.2
Roles: Both MUST.
Feature: address-domain-prep
Description: Ensure that the domainpart of an XMPP address conforms
to the Nameprep profile of stringprep.
Section: Section 2.2
Roles: Client SHOULD, Server MUST.
Feature: address-localpart-length
Description: Ensure that the localpart of an XMPP address is at
least one byte in length and at most 1023 bytes in length.
Section: Section 2.3
Roles: Both MUST.
Feature: address-localpart-prep
Description: Ensure that the localpart of an XMPP address conforms
to the Nodeprep profile of stringprep.
Section: Section 2.3
Roles: Client SHOULD, Server MUST.
Feature: address-resource-length
Description: Ensure that the resourcepart of an XMPP address is at
least one byte in length and at most 1023 bytes in length.
Section: Section 2.4
Roles: Both MUST.
Feature: address-resource-prep
Description: Ensure that the resourcepart of an XMPP address
conforms to the Resourceprep profile of stringprep.
Section: Section 2.4
Roles: Client SHOULD, Server MUST.
Saint-Andre Standards Track [Page 15]
RFC 6122 XMPP Address Format March 2011
7. References
7.1. Normative References
[ABNF] Crocker, D., Ed. and P. Overell, "Augmented BNF for
Syntax Specifications: ABNF", STD 68, RFC 5234,
January 2008.
[DNS] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[IDNA2003] Faltstrom, P., Hoffman, P., and A. Costello,
"Internationalizing Domain Names in Applications
(IDNA)", RFC 3490, March 2003.
See Section 1 for an explanation of why the
normative reference to an obsoleted specification
is needed.
[KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[NAMEPREP] Hoffman, P. and M. Blanchet, "Nameprep: A
Stringprep Profile for Internationalized Domain
Names (IDN)", RFC 3491, March 2003.
See Section 1 for an explanation of why the
normative reference to an obsoleted specification
is needed.
[STRINGPREP] Hoffman, P. and M. Blanchet, "Preparation of
Internationalized Strings ("stringprep")",
RFC 3454, December 2002.
[UNICODE] The Unicode Consortium, "The Unicode Standard,
Version 3.2.0", 2000. The Unicode Standard,
Version 3.2.0 is defined by The Unicode Standard,
Version 3.0 (Reading, MA, Addison-Wesley, 2000.
ISBN 0-201-61633-5), as amended by the Unicode
Standard Annex #27: Unicode 3.1
(http://www.unicode.org/reports/tr27/) and by the
Unicode Standard Annex #28: Unicode 3.2
(http://www.unicode.org/reports/tr28/).
[UNICODE-SEC] The Unicode Consortium, "Unicode Technical Report
#36: Unicode Security Considerations", 2008,
<http://www.unicode.org/reports/tr36/>.
Saint-Andre Standards Track [Page 16]
RFC 6122 XMPP Address Format March 2011
[UTF-8] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.
[XMPP] Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Core", RFC 6120, March 2011.
7.2. Informative References
[DNSSEC] Arends, R., Austein, R., Larson, M., Massey, D.,
and S. Rose, "DNS Security Introduction and
Requirements", RFC 4033, March 2005.
[IDNA-DEFS] Klensin, J., "Internationalized Domain Names for
Applications (IDNA): Definitions and Document
Framework", RFC 5890, August 2010.
[IDNA-PROTO] Klensin, J., "Internationalized Domain Names in
Applications (IDNA): Protocol", RFC 5891,
August 2010.
[IDNA-RATIONALE] Klensin, J., "Internationalized Domain Names for
Applications (IDNA): Background, Explanation, and
Rationale", RFC 5894, August 2010.
[INTEROP] Masinter, L., "Formalizing IETF Interoperability
Reporting", Work in Progress, October 2005.
[IRI] Duerst, M. and M. Suignard, "Internationalized
Resource Identifiers (IRIs)", RFC 3987,
January 2005.
[PROCESS] Bradner, S., "The Internet Standards Process --
Revision 3", BCP 9, RFC 2026, October 1996.
[PUNYCODE] Costello, A., "Punycode: A Bootstring encoding of
Unicode for Internationalized Domain Names in
Applications (IDNA)", RFC 3492, March 2003.
[REPORTS] Dusseault, L. and R. Sparks, "Guidance on
Interoperation and Implementation Reports for
Advancement to Draft Standard", BCP 9, RFC 5657,
September 2009.
[RFC3920] Saint-Andre, P., Ed., "Extensible Messaging and
Presence Protocol (XMPP): Core", RFC 3920,
October 2004.
Saint-Andre Standards Track [Page 17]
RFC 6122 XMPP Address Format March 2011
[RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation
for IPv6 Address Text Representation", RFC 5952,
August 2010.
[SASL] Melnikov, A., Ed. and K. Zeilenga, Ed., "Simple
Authentication and Security Layer (SASL)",
RFC 4422, June 2006.
[URI] Berners-Lee, T., Fielding, R., and L. Masinter,
"Uniform Resource Identifier (URI): Generic
Syntax", STD 66, RFC 3986, January 2005.
[XEP-0029] Kaes, C., "Definition of Jabber Identifiers
(JIDs)", XSF XEP 0029, October 2003.
[XEP-0030] Hildebrand, J., Millard, P., Eatmon, R., and P.
Saint-Andre, "Service Discovery", XSF XEP 0030,
June 2008.
[XEP-0045] Saint-Andre, P., "Multi-User Chat", XSF XEP 0045,
July 2008.
[XEP-0060] Millard, P., Saint-Andre, P., and R. Meijer,
"Publish-Subscribe", XSF XEP 0060, July 2010.
[XEP-0165] Saint-Andre, P., "Best Practices to Discourage JID
Mimicking", XSF XEP 0045, December 2007.
[XML] Paoli, J., Maler, E., Sperberg-McQueen, C.,
Yergeau, F., and T. Bray, "Extensible Markup
Language (XML) 1.0 (Fourth Edition)", World Wide
Web Consortium Recommendation REC-xml-20060816,
August 2006,
<http://www.w3.org/TR/2006/REC-xml-20060816>.
[XMPP-URI] Saint-Andre, P., "Internationalized Resource
Identifiers (IRIs) and Uniform Resource Identifiers
(URIs) for the Extensible Messaging and Presence
Protocol (XMPP)", RFC 5122, February 2008.
Saint-Andre Standards Track [Page 18]
RFC 6122 XMPP Address Format March 2011
Appendix A. Nodeprep
A.1. Introduction
This appendix defines the "Nodeprep" profile of stringprep. As such,
it specifies processing rules that will enable users to enter
internationalized localparts in the Extensible Messaging and Presence
Protocol (XMPP) and have the highest chance of getting the content of
the strings correct. (An XMPP localpart is the optional portion of
an XMPP address that precedes an XMPP domainpart and the '@'
separator; it is often but not exclusively associated with an instant
messaging username.) These processing rules are intended only for
XMPP localparts and are not intended for arbitrary text or any other
aspect of an XMPP address.
This profile defines the following, as required by [STRINGPREP]:
o The intended applicability of the profile: internationalized
localparts within XMPP
o The character repertoire that is the input and output to
stringprep: Unicode 3.2, specified in A.2
o The mappings used: specified in A.3
o The Unicode normalization used: specified in A.4
o The characters that are prohibited as output: specified in A.5
o Bidirectional character handling: specified in A.6
A.2. Character Repertoire
This profile uses Unicode 3.2 with the list of unassigned code points
in Table A.1, both as defined in Appendix A of [STRINGPREP].
A.3. Mapping
This profile specifies mapping using the following tables from
[STRINGPREP]:
Table B.1
Table B.2
A.4. Normalization
This profile specifies the use of Unicode Normalization Form KC, as
described in [STRINGPREP].
Saint-Andre Standards Track [Page 19]
RFC 6122 XMPP Address Format March 2011
A.5. Prohibited Output
This profile specifies the prohibition of using the following tables
from [STRINGPREP].
Table C.1.1
Table C.1.2
Table C.2.1
Table C.2.2
Table C.3
Table C.4
Table C.5
Table C.6
Table C.7
Table C.8
Table C.9
In addition, the following additional Unicode characters are also
prohibited:
U+0022 (QUOTATION MARK), i.e., "
U+0026 (AMPERSAND), i.e., &
U+0027 (APOSTROPHE), i.e., '
U+002F (SOLIDUS), i.e., /
U+003A (COLON), i.e., :
U+003C (LESS-THAN SIGN), i.e., <
U+003E (GREATER-THAN SIGN), i.e., >
U+0040 (COMMERCIAL AT), i.e., @
A.6. Bidirectional Characters
This profile specifies checking bidirectional strings, as described
in Section 6 of [STRINGPREP].
A.7. Notes
Because the additional characters prohibited by Nodeprep are
prohibited after normalization, an implementation MUST NOT enable a
human user to input any Unicode code point whose decomposition
includes those characters; such code points include but are not
necessarily limited to the following (refer to [UNICODE] for complete
information):
Saint-Andre Standards Track [Page 20]
RFC 6122 XMPP Address Format March 2011
o U+2100 (ACCOUNT OF)
o U+2101 (ADDRESSED TO THE SUBJECT)
o U+2105 (CARE OF)
o U+2106 (CADA UNA)
o U+226E (NOT LESS-THAN)
o U+226F (NOT GREATER-THAN)
o U+2A74 (DOUBLE COLON EQUAL)
o U+FE13 (PRESENTATION FORM FOR VERTICAL COLON)
o U+FE60 (SMALL AMPERSAND)
o U+FE64 (SMALL LESS-THAN SIGN)
o U+FE65 (SMALL GREATER-THAN SIGN)
o U+FE6B (SMALL COMMERCIAL AT)
o U+FF02 (FULLWIDTH QUOTATION MARK)
o U+FF06 (FULLWIDTH AMPERSAND)
o U+FF07 (FULLWIDTH APOSTROPHE)
o U+FF0F (FULLWIDTH SOLIDUS)
o U+FF1A (FULLWIDTH COLON)
o U+FF1C (FULLWIDTH LESS-THAN SIGN)
o U+FF1E (FULLWIDTH GREATER-THAN SIGN)
o U+FF20 (FULLWIDTH COMMERCIAL AT)
Appendix B. Resourceprep
B.1. Introduction
This appendix defines the "Resourceprep" profile of stringprep. As
such, it specifies processing rules that will enable users to enter
internationalized resourceparts in the Extensible Messaging and
Presence Protocol (XMPP) and have the highest chance of getting the
content of the strings correct. (An XMPP resourcepart is the
optional portion of an XMPP address that follows an XMPP domainpart
and the '/' separator.) These processing rules are intended only for
XMPP resourceparts and are not intended for arbitrary text or any
other aspect of an XMPP address.
This profile defines the following, as required by [STRINGPREP]:
o The intended applicability of the profile: internationalized
resourceparts within XMPP
o The character repertoire that is the input and output to
stringprep: Unicode 3.2, specified in B.2
o The mappings used: specified in B.3
o The Unicode normalization used: specified in B.4
o The characters that are prohibited as output: specified in B.5
Saint-Andre Standards Track [Page 21]
RFC 6122 XMPP Address Format March 2011
o Bidirectional character handling: specified in B.6
B.2. Character Repertoire
This profile uses Unicode 3.2 with the list of unassigned code points
in Table A.1, both as defined in Appendix A of [STRINGPREP].
B.3. Mapping
This profile specifies mapping using the following tables from
[STRINGPREP]:
Table B.1
B.4. Normalization
This profile specifies the use of Unicode Normalization Form KC, as
described in [STRINGPREP].
B.5. Prohibited Output
This profile specifies the prohibition of using the following tables
from [STRINGPREP].
Table C.1.2
Table C.2.1
Table C.2.2
Table C.3
Table C.4
Table C.5
Table C.6
Table C.7
Table C.8
Table C.9
B.6. Bidirectional Characters
This profile specifies checking bidirectional strings, as described
in Section 6 of [STRINGPREP].
Appendix C. Differences from RFC 3920
Based on consensus derived from implementation and deployment
experience as well as formal interoperability testing, the following
substantive modifications were made from RFC 3920.
Saint-Andre Standards Track [Page 22]
RFC 6122 XMPP Address Format March 2011
o Corrected the ABNF syntax to ensure consistency with [URI] and
[IRI], including consistency with RFC 3986 and [RFC5952] with
regard to IPv6 addresses (e.g., enclosing the IPv6 address in
square brackets '[' and ']' -- see also Section 4.9.3.19 of
[XMPP]).
o Corrected the ABNF syntax to prevent zero-length localparts,
domainparts, and resourceparts (and also noted that the underlying
length limits from the DNS apply to domainparts).
o To avoid confusion with the term "node" as used in [XEP-0030] and
[XEP-0060], changed the term "node identifier" to "localpart" (but
retained the name "Nodeprep" for backward compatibility).
o To avoid confusion with the terms "resource" and "identifier" as
used in [URI], changed the term "resource identifier" to
"resourcepart".
o Corrected the Nameprep processing rules to require use of the
UseSTD3ASCIIRules flag.
Appendix D. Acknowledgements
Thanks to Ben Campbell, Waqas Hussain, Jehan Pages, and Florian Zeitz
for their feedback. Thanks also to Richard Barnes and Elwyn Davies
for their reviews on behalf of the Security Directorate and the
General Area Review Team, respectively.
The Working Group chairs were Ben Campbell and Joe Hildebrand. The
responsible Area Director was Gonzalo Camarillo.
Some text in this document was borrowed or adapted from [IDNA-DEFS],
[IDNA-PROTO], [IDNA-RATIONALE], and [XEP-0165].
Author's Address
Peter Saint-Andre
Cisco
1899 Wyknoop Street, Suite 600
Denver, CO 80202
USA
Phone: +1-303-308-3282
EMail: psaintan@cisco.com
Saint-Andre Standards Track [Page 23]