One document matched: draft-ietf-xmpp-6122bis-08.txt
Differences from draft-ietf-xmpp-6122bis-07.txt
XMPP P. Saint-Andre
Internet-Draft Cisco Systems, Inc.
Obsoletes: 6122 (if approved) October 18, 2013
Intended status: Standards Track
Expires: April 21, 2014
Extensible Messaging and Presence Protocol (XMPP): Address Format
draft-ietf-xmpp-6122bis-08
Abstract
This document defines the address format for the Extensible Messaging
and Presence Protocol (XMPP), including support for code points
outside the ASCII range. This document obsoletes RFC 6122.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 21, 2014.
Copyright Notice
Copyright (c) 2013 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.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Addresses . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Fundamentals . . . . . . . . . . . . . . . . . . . . . . . 3
3.2. Domainpart . . . . . . . . . . . . . . . . . . . . . . . . 5
3.3. Localpart . . . . . . . . . . . . . . . . . . . . . . . . 6
3.4. Resourcepart . . . . . . . . . . . . . . . . . . . . . . . 7
4. Enforcement in JIDs and JID Parts . . . . . . . . . . . . . . 9
5. Internationalization Considerations . . . . . . . . . . . . . 11
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
6.1. JIDlocalIdentifierClass . . . . . . . . . . . . . . . . . 11
6.2. JIDresourceFreeformClass . . . . . . . . . . . . . . . . . 12
7. Security Considerations . . . . . . . . . . . . . . . . . . . 12
7.1. Reuse of PRECIS . . . . . . . . . . . . . . . . . . . . . 12
7.2. Reuse of Unicode . . . . . . . . . . . . . . . . . . . . . 12
7.3. Address Spoofing . . . . . . . . . . . . . . . . . . . . . 12
7.3.1. Address Forging . . . . . . . . . . . . . . . . . . . 13
7.3.2. Address Mimicking . . . . . . . . . . . . . . . . . . 13
8. Conformance Requirements . . . . . . . . . . . . . . . . . . . 14
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
9.1. Normative References . . . . . . . . . . . . . . . . . . . 16
9.2. Informative References . . . . . . . . . . . . . . . . . . 17
Appendix A. Differences from RFC 6122 . . . . . . . . . . . . . . 20
Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 21
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 21
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1. Introduction
The Extensible Messaging and Presence Protocol (XMPP) [RFC6120] 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 then defined canonically
by [RFC3920] in 2004 and [RFC6122] in 2011.
As specified in RFC 3920 and RFC 6122, the XMPP address format used
the "stringprep" technology for preparation of non-ASCII characters
[RFC3454]. Following the migration of internationalized domain names
away from stringprep, this document defines the XMPP address format
in a way that no longer depends on stringprep (see [RFC6885]).
Instead, this document builds upon the internationalization framework
defined by the IETF's PRECIS Working Group
[I-D.ietf-precis-framework], while attempting to ensure that the
characters allowed in Jabber Identifers today under stringprep are
still allowed and handled in the same way under PRECIS.
This document obsoletes RFC 6122.
2. Terminology
Many important terms used in this document are defined in
[I-D.ietf-precis-framework], [RFC5890], [RFC6120], [RFC6365], and
[UNICODE].
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
[RFC2119].
3. Addresses
3.1. 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 ID ("JID"). A valid JID is a
string of Unicode code points [UNICODE], encoded using UTF-8
[RFC3629], 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).
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The syntax for a JID is defined as follows using the Augmented
Backus-Naur Form (ABNF) as specified in [RFC5234].
jid = [ localpart "@" ] domainpart [ "/" resourcepart ]
localpart = 1*1023(localpoint)
;
; a "localpoint" is a UTF-8 encoded
; Unicode code point that conforms to
; the "JIDlocalIdentifierClass" profile
; of the PRECIS IdentifierClass
;
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 ']')
;
ifqdn = 1*1023(domainpoint)
;
; a "domainpoint" is a UTF-8 encoded
; Unicode code point that conforms to
; RFC 5890
;
resourcepart = 1*1023(resourcepoint)
;
; a "resourcepoint" is a UTF-8 encoded
; Unicode code point that conforms to
; the "JIDresourceFreeformClass" profile
; of the PRECIS FreeformClass
;
All JIDs are based on the foregoing structure. However, note that
the foregoing structure does not capture all of the rules and
restrictions that apply to JIDs, which are described below.
Each allowable portion of a JID (localpart, domainpart, and
resourcepart) MUST NOT be zero octets in length and MUST NOT be more
than 1023 octets in length, resulting in a maximum total size
(including the '@' and '/' separators) of 3071 octets.
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Implementation Note: The length limits on JIDs and JID parts are
based on octets (bytes), not characters. UTF-8 encoding can
result in more than one octet per character.
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., under Unicode Normalization Form KC U+FE6B SMALL COMMERCIAL
AT decomposes to U+0040 COMMERCIAL AT, although this is not true
under Unicode Normalization C, which is used in this
specification).
This document defines the native format for JIDs; see [RFC5122] for
information about the representation of a JID as a Uniform Resource
Identifier (URI) [RFC3986] or Internationalized Resource Identifier
(IRI) [RFC3987] and the extraction of a JID from an XMPP URI or IRI.
3.2. 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 [XEP-0045], a publish-subscribe service
[XEP-0060], or a user directory).
The domainpart for every XMPP service MUST be a fully-qualified
domain name (FQDN), an IPv4 address, an IPv6 address, or an
unqualified hostname (i.e., a text label that is resolvable on a
local network).
Informational Note: The term "fully-qualified domain name" is not
well defined. In [RFC1034] it also called an absolute domain
name, and the two terms are associated in [RFC1535]. The earliest
use of the term can be found in [RFC1123]. References to those
older specifications ought not to be construed as limiting the
characters of a fully-qualified domain name to the ASCII range;
for example, [RFC5890] mentions that a fully-qualified domain name
can contain one or more U-labels.
Interoperability Note: Domainparts that are IP addresses might not
be accepted by other services for the purpose of server-to-server
communication, and domainparts that are unqualified hostnames
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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 [RFC1034], 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 or IRI [RFC5122]. In particular, the
character MUST be stripped before any other canonicalization steps
are taken.
In general, the content of a domainpart is an Internationalized
Domain Name ("IDN") as described in the specifications for
Internationalized Domain Names in Applications (commonly called
"IDNA2008") [RFC5890], and a domainpart is an "IDNA-aware domain name
slot". The following rules apply to a domainpart that consists of a
fully-qualified domain name:
o The domainpart MUST contain only NR-LDH labels and U-labels as
defined in [RFC5890] and MUST consist only of Unicode code points
that conform to the rules specified in [RFC5892].
o The domainpart MUST NOT include A-labels as defined in [RFC5890];
each A-label MUST be converted to a U-label during preparation of
a domainpart, and comparison MUST be performed using U-labels, not
A-labels.
o After conversion of A-labels to U-labels if necessary, all
uppercase and titlecase code points within the domainpart MUST be
mapped to their lowercase equivalents.
o After (and in addition to) case mapping and width mapping, other
mappings MAY be applied to the domainpart, such as those defined
in [I-D.ietf-precis-mappings] or [RFC5895].
After any and all normalization, conversion, and mapping of code
points, a domainpart MUST NOT be zero octets in length and MUST NOT
be more than 1023 octets in length. (Naturally, the length limits of
[RFC1034] apply, and nothing in this document is to be interpreted as
overriding those more fundamental limits.)
3.3. 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 [XEP-0045]). The
entity represented by an XMPP localpart is addressed within the
context of a specific domain (i.e., <localpart@domainpart>).
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A localpart MUST NOT be zero octets in length and MUST NOT be more
than 1023 octets in length. This rule is to be enforced after any
normalization and mapping of code points.
A localpart MUST consist only of Unicode code points that conform to
the "JIDlocalIdentifierClass" profile of the "IdentifierClass" base
string class defined in [I-D.ietf-precis-framework]. The
JIDlocalIdentifierClass profile includes all code points allowed by
the IdentifierClass base class, with the exception of the following
characters that are explicitly disallowed in XMPP localparts:
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., @
The normalization and mapping rules for the JIDlocalIdentifierClass
are as follows, where the operations specified MUST be completed in
the order shown:
1. Fullwidth and halfwidth characters MUST be mapped to their
decomposition equivalents.
2. Additional mappings MAY be applied, such as those defined in
[I-D.ietf-precis-mappings].
3. Uppercase and titlecase characters MUST be mapped to their
lowercase equivalents.
4. All characters MUST be mapped using Unicode Normalization Form C
(NFC).
With regard to directionality, applications MUST apply the "Bidi
Rule" defined in [RFC5893] (i.e., each of the six conditions of the
Bidi Rule must be satisfied).
3.4. 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 [XEP-0045])
belonging to the entity associated with an XMPP localpart at a domain
(i.e., <localpart@domainpart/resourcepart>).
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A resourcepart MUST NOT be zero octets in length and MUST NOT be more
than 1023 octets in length. This rule is to be enforced after any
normalization and mapping of code points.
A resourcepart MUST consist only of Unicode code points that conform
to the "JIDresourceFreeformClass" profile of the "FreeformClass" base
string class defined in [I-D.ietf-precis-framework].
The normalization and mapping rules for the resourcepart of a JID are
as follows, where the operations specified MUST be completed in the
order shown:
1. Fullwidth and halfwidth characters MAY be mapped to their
decomposition equivalents.
2. Map any instances of non-ASCII space to ASCII space (U+0020).
3. Other additional mappings MAY be applied, such as those defined
in [I-D.ietf-precis-mappings].
4. Uppercase and titlecase characters MAY be mapped to their
lowercase equivalents.
5. All characters MUST be mapped using Unicode Normalization Form C
(NFC).
6. Leading and trailing whitespace (i.e., one or more instances of
the ASCII space character at the beginning or end of a
resourcepart) MUST be removed (e.g., "stpeter " is mapped to
"stpeter").
With regard to directionality, applications MUST apply the "Bidi
Rule" defined in [RFC5893] (i.e., each of the six conditions of the
Bidi Rule must be satisfied).
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@domainpart".
o The '@' character is allowed in the resourcepart and is often used
in the "handle" shown in XMPP chatrooms [XEP-0045]. 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) handle of <user@host>. However, chatroom services do
not necessarily check such an asserted handle against the
occupant's real JID.
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In some contexts, it might be appropriate to apply more restrictive
rules to the preparation and comparison of XMPP resourceparts. For
example, in the context of XMPP Multi-User Chat [XEP-0045], it might
be appropriate to apply the rules specified in
[I-D.ietf-precis-nickname]. However, the application of such more
restrictive rules is out of scope for resourceparts in general and is
properly defined in specifications for the relevant XMPP extensions.
4. Enforcement in JIDs and JID Parts
Enforcement of the XMPP address format rules is the responsibility of
XMPP servers. Although XMPP clients SHOULD prepare complete JIDs and
parts of JIDs in accordance with this document before including them
in protocol slots within XML streams (such that JIDs and parts of
JIDs are in conformance), XMPP servers MUST enforce the rules
wherever possible and reject stanzas and other XML elements that
violate the rules (for stanzas, by returning a <jid-malformed/> error
to the sender as described in Section 8.3.3.8 of [RFC6120]).
Enforcement applies to complete JIDs and to parts of JIDs. To
facilitate implementation, this document defines the concepts of "JID
slot", "localpart slot", and "resourcepart slot" (similar to the
concept of a "domain name slot" for IDNA2008 defined in Section
2.3.2.6 of [RFC5890]):
JID Slot: An XML element or attribute explicitly designated in XMPP
or in XMPP extensions for carrying a complete JID.
Localpart Slot: An XML element or attribute explicitly designated in
XMPP or in XMPP extensions for carrying the localpart of a JID.
Resourcepart Slot: An XML element or attribute explicitly designated
in XMPP or in XMPP extensions for carrying the resourcepart of a
JID.
A server is responsible for enforcing the address format rules when
receiving protocol elements from clients where the server is expected
to handle such elements directly or to use them for purposes of
routing a stanza to another domain or delivering a stanza to a local
entity; two examples from [RFC6120] are the 'to' attribute on XML
stanzas (which is a JID slot used by XMPP servers for routing of
outbound stanzas) and the <resource/> child of the <bind/> element
(which is a resourcepart slot used by XMPP servers for binding of a
resource to an account for routing of stanzas between the server and
a particular client).
A server is not responsible for enforcing the rules when the protocol
elements are intended for communication among other entities,
typically within the payload of a stanza that the server is merely
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routing to another domain or delivering to a local entity, such as a
connected client or an add-on service. Two examples are the
'initiator' attribute in the Jingle extension [XEP-0166] (which is a
JID slot used for client-to-client coordination of multimedia
sessions) and the 'nick' attribute in the Multi-User Chat extension
[XEP-0045] (which is a resourcepart slot used for administrative
purposes in the context of XMPP chatrooms). In such cases, clients
SHOULD enforce the rules themselves and not depend on the server to
do so, and client implementers need to understand that not enforcing
the rules can lead to a degraded user experience or to security
vulnerabilities. However, when an add-on service (e.g., a multi-user
chat service) handles a stanza directly, it ought to enforce the
rules as well, as defined by the relevant specification for that type
of service.
This document does not provide an exhaustive list of JID slots,
localpart slots, or resourcepart slots. However, implementers of
core XMPP servers are advised to consider as JID slots at least the
following elements and attributes when they are handled directly or
used for purposes of routing to another domain or delivering to a
local entity:
o The 'from' and 'to' stream attributes and the 'from' and 'to'
stanza attributes [RFC6120].
o The 'jid' attribute of the roster <item/> element for contact list
management [RFC6121].
o The 'value' attribute of the <item/> element for Privacy Lists
[RFC3921] [XEP-0016] when the value of the 'type' attribute is
"jid".
o The 'jid' attribute of the <item/> element for Service Discovery
defined in [XEP-0030].
o The <value/> element for Data Forms [XEP-0004], when the 'type'
attribute is "jid-single" or "jid-multi".
o The 'jid' attribute of the <conference/> element for Bookmark
Storage [XEP-0048].
o The <JABBERID/> of the <vCard/> element for vCard 3.0 [XEP-0054]
and the <uri/> child of the <impp/> element for vCard 4.0
[XEP-0292] when the XML character data identifies an XMPP URI
[RFC5122].
o The 'from' attribute of the <delay/> element for Delayed Delivery
[XEP-0203].
o The 'jid' attribute of the <item/> element for the Blocking
Command [XEP-0191].
o The 'from' and 'to' attributes of the <result/> and <verify/>
elements for Server Dialback [RFC3921], [XEP-0220].
o The 'from' and 'to' attributes of the <iq/>, <message/>, and
<presence/> elements for the Jabber Component Protocol [XEP-0114].
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Developers of XMPP clients and specialized XMPP add-on services are
advised to check the appropriate specifications for JID slots,
localpart slots, and resourcepart slots in XMPP protocol extensions
such as Service Discovery [XEP-0030], Multi-User Chat [XEP-0045],
Publish-Subscribe [XEP-0060], SOCKS5 Bytestreams [XEP-0065], In-Band
Registration [XEP-0077], Roster Item Exchange [XEP-0144], and Jingle
[XEP-0166].
5. Internationalization Considerations
XMPP applications MUST support IDNA2008 for domainparts as described
under Section 3.2, the "JIDlocalIdentifierClass" profile for
localparts as described under Section 3.3, and the
"JIDresourceFreeformClass" profile for resourceparts as described
under Section 3.4. This enables XMPP addresses to include a wide
variety of characters outside the ASCII range. Rules for enforcement
of the XMPP address format are provided in [RFC6120] and
specifications for various XMPP extensions.
Interoperability Note: For backward compatibility, many existing
XMPP implementations and deployments support IDNA2003 [RFC3490]
for domainparts, and the stringprep [RFC3454] profiles Nodeprep
and Resourceprep [RFC3920] for localparts and resourceparts.
6. IANA Considerations
The IANA shall add the following entries to the PRECIS Profiles
Registry.
6.1. JIDlocalIdentifierClass
Name: JIDlocalIdentifierClass.
Applicability: Localparts of XMPP addresses.
Base Class: IdentifierClass.
Replaces: Nodeprep.
Width Mapping: Map fullwidth and halfwidth characters to their
decomposition equivalents.
Additional Mappings: None required or recommended.
Case Mapping: Map uppercase and titlecase characters to lowercase.
Normalization: NFC.
Directionality: The "Bidi Rule" defined in RFC 5893 applies.
Exclusions: Eight legacy characters in the ASCII range.
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Enforcement: In general, XMPP servers are responsible for enforcing
the rules (although XMPP clients and components can also be
responsible for doing so, depending on the JID slots, localpart
slots, and resourcepart slots where JIDs or JID parts are used).
Specification: RFC XXXX. [Note to RFC Editor: please change XXXX to
the number issued for this specification.]
6.2. JIDresourceFreeformClass
Profile: JIDresourceFreeformClass.
Applicability: Resourceparts of XMPP addresses.
Base Class: FreeformClass
Replaces: The Resourceprep profile of Stringprep.
Width Mapping: Optional.
Additional Mappings: Map non-ASCII space to ASCII space.
Case Mapping: Optional.
Normalization: NFC.
Directionality: The "Bidi Rule" defined in RFC 5893 applies.
Exclusions: None.
Enforcement: In general, XMPP servers are responsible for enforcing
the rules (although XMPP clients and components can also be
resonsible for doing so, depending on the JID slots, localpart
slots, and resourcepart slots where JIDs or JID parts are used).
Specification: RFC XXXX. [Note to RFC Editor: please change XXXX to
the number issued for this specification.]
7. Security Considerations
7.1. Reuse of PRECIS
The security considerations described in [I-D.ietf-precis-framework]
apply to the "IdentifierClass" and "FreeformClass" base string
classes used in this document for XMPP localparts and resourceparts.
The security considerations described in [RFC5890] apply to
internationalized domain names, which are used here for XMPP
domainparts.
7.2. Reuse of Unicode
The security considerations described in [UTS39] apply to the use of
Unicode characters in XMPP addresses.
7.3. Address Spoofing
There are two forms of address spoofing: forging and mimicking.
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7.3.1. 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 [RFC4422] as described in
[RFC6120]). 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 [RFC6120]). 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 at the domain or domains hosted at that server.
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 the kind of poorly implemented or rogue servers just
described. 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 for signing or encryption
of each stanza, in addition to modifying 'from' addresses.
7.3.2. 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.
Because many characters are visually similar, it is relatively easy
to mimic JIDs in XMPP systems. As one simple example, the localpart
"ju1iet" (using the Arabic numeral one as the third character) might
appear the same as the localpart "juliet" (using lowercase "L" as the
third character).
As explained in [RFC5890], [I-D.ietf-precis-framework], [UTR36], and
[UTS39], there is no straightforward solution to the problem of
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visually similar characters. Furthermore, IDNA and PRECIS
technologies do not attempt to define such a solution. As a result,
XMPP domainparts, localparts, and resourceparts could contain such
characters, leading to security vulnerabilities such as the
following:
o A domainpart is always employed as one part of an entity's address
in XMPP. One common usage is as the address of a server or
server-side service, such as a multi-user chat service [XEP-0045].
The security of such services could be compromised based on
different interpretations of the internationalized domainpart; for
example, a user might authorize a malicious entity at a fake
server to view the user's presence information, or a user could
join chatrooms at a fake multi-user chat service.
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
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
private message to someone other than the intended recipient in a
multi-user chat room.
XMPP services and clients are strongly encouraged to define and
implement consistent policies regarding the registration, storage,
and presentation of visually similar characters in XMPP systems. In
particular, service providers and software implementers are strongly
encouraged to use the policies recommended in
[I-D.ietf-precis-framework].
8. Conformance Requirements
This section describes a protocol feature set that summarizes the
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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 [RFC2119]
The feature set specified here provides a basis for interoperability
testing and follows the spirit of a proposal made by Larry Masinter
within the IETF's NEWTRK Working Group in 2005 [INTEROP].
Feature: address-domain-length
Description: Ensure that the domainpart of an XMPP address is at
least one octet in length and at most 1023 octets in length, and
that it conforms to the underlying length limits of the DNS.
Section: Section 3.2
Roles: Server MUST, client SHOULD.
Feature: address-domain-prep
Description: Ensure that the domainpart of an XMPP address conforms
to IDNA2008, that it contains only NR-LDH labels and U-labels (not
A-labels), and that all uppercase and titlecase code points are
mapped to their lowercase equivalents.
Section: Section 3.2
Roles: Server MUST, client SHOULD.
Feature: address-localpart-length
Description: Ensure that the localpart of an XMPP address is at
least one octet in length and at most 1023 octets in length.
Section: Section 3.3
Roles: Server MUST, client SHOULD.
Feature: address-localpart-prep
Description: Ensure that the localpart of an XMPP address conforms
to the "JIDlocalIdentifierClass" profile.
Section: Section 3.3
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Roles: Server MUST, client SHOULD.
Feature: address-resource-length
Description: Ensure that the resourcepart of an XMPP address is at
least one octet in length and at most 1023 octets in length.
Section: Section 3.4
Roles: Server MUST, client SHOULD.
Feature: address-resource-prep
Description: Ensure that the resourcepart of an XMPP address
conforms to the "JIDresourceFreeformClass" profile.
Section: Section 3.4
Roles: Server MUST, client SHOULD.
9. References
9.1. Normative References
[I-D.ietf-precis-framework]
Saint-Andre, P. and M. Blanchet, "Precis Framework:
Handling Internationalized Strings in Protocols",
draft-ietf-precis-framework-10 (work in progress),
October 2013.
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, November 1987.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
[RFC5890] Klensin, J., "Internationalized Domain Names for
Applications (IDNA): Definitions and Document Framework",
RFC 5890, August 2010.
[RFC5891] Klensin, J., "Internationalized Domain Names in
Applications (IDNA): Protocol", RFC 5891, August 2010.
[RFC5892] Faltstrom, P., "The Unicode Code Points and
Internationalized Domain Names for Applications (IDNA)",
RFC 5892, August 2010.
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[RFC5893] Alvestrand, H. and C. Karp, "Right-to-Left Scripts for
Internationalized Domain Names for Applications (IDNA)",
RFC 5893, August 2010.
[RFC6120] Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Core", RFC 6120, March 2011.
[UNICODE] The Unicode Consortium, "The Unicode Standard, Version
6.2", 2012,
<http://www.unicode.org/versions/Unicode6.2.0/>.
[UTR36] The Unicode Consortium, "Unicode Technical Report #36:
Unicode Security Considerations", July 2012,
<http://www.unicode.org/reports/tr36/>.
9.2. Informative References
[I-D.ietf-precis-mappings]
Yoneya, Y. and T. NEMOTO, "Mapping characters for PRECIS
classes", draft-ietf-precis-mappings-04 (work in
progress), October 2013.
[I-D.ietf-precis-nickname]
Saint-Andre, P., "Preparation and Comparison of
Nicknames", draft-ietf-precis-nickname-06 (work in
progress), July 2013.
[INTEROP] Masinter, L., "Formalizing IETF Interoperability
Reporting", Work in Progress, October 2005.
[RFC1123] Braden, R., "Requirements for Internet Hosts - Application
and Support", STD 3, RFC 1123, October 1989.
[RFC1535] Gavron, E., "A Security Problem and Proposed Correction
With Widely Deployed DNS Software", RFC 1535,
October 1993.
[RFC3454] Hoffman, P. and M. Blanchet, "Preparation of
Internationalized Strings ("stringprep")", RFC 3454,
December 2002.
[RFC3490] 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.
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[RFC3920] Saint-Andre, P., Ed., "Extensible Messaging and Presence
Protocol (XMPP): Core", RFC 3920, October 2004.
[RFC3921] Saint-Andre, P., Ed., "Extensible Messaging and Presence
Protocol (XMPP): Instant Messaging and Presence",
RFC 3921, October 2004.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, January 2005.
[RFC3987] Duerst, M. and M. Suignard, "Internationalized Resource
Identifiers (IRIs)", RFC 3987, January 2005.
[RFC4422] Melnikov, A. and K. Zeilenga, "Simple Authentication and
Security Layer (SASL)", RFC 4422, June 2006.
[RFC5122] Saint-Andre, P., "Internationalized Resource Identifiers
(IRIs) and Uniform Resource Identifiers (URIs) for the
Extensible Messaging and Presence Protocol (XMPP)",
RFC 5122, February 2008.
[RFC5894] Klensin, J., "Internationalized Domain Names for
Applications (IDNA): Background, Explanation, and
Rationale", RFC 5894, August 2010.
[RFC5895] Resnick, P. and P. Hoffman, "Mapping Characters for
Internationalized Domain Names in Applications (IDNA)
2008", RFC 5895, September 2010.
[RFC6121] Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Instant Messaging and Presence",
RFC 6121, March 2011.
[RFC6122] Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Address Format", RFC 6122, March 2011.
[RFC6365] Hoffman, P. and J. Klensin, "Terminology Used in
Internationalization in the IETF", BCP 166, RFC 6365,
September 2011.
[RFC6885] Blanchet, M. and A. Sullivan, "Stringprep Revision and
Problem Statement for the Preparation and Comparison of
Internationalized Strings (PRECIS)", RFC 6885, March 2013.
[UTS39] The Unicode Consortium, "Unicode Technical Standard #39:
Unicode Security Mechanisms", July 2012,
<http://unicode.org/reports/tr39/>.
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[XEP-0004]
Eatmon, R., Hildebrand, J., Miller, J., Muldowney, T., and
P. Saint-Andre, "Data Forms", XSF XEP 0004, August 2007.
[XEP-0016]
Millard, P. and P. Saint-Andre, "Privacy Lists", XSF
XEP 0016, February 2007.
[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,
February 2012.
[XEP-0048]
Blackman, R., Millard, P., and P. Saint-Andre,
"Bookmarks", XSF XEP 0048, November 2007.
[XEP-0054]
Saint-Andre, P., "vcard-temp", XSF XEP 0054, July 2008.
[XEP-0060]
Millard, P., Saint-Andre, P., and R. Meijer, "Publish-
Subscribe", XSF XEP 0060, July 2010.
[XEP-0065]
Smith, D., Miller, M., Saint-Andre, P., and J. Karneges,
"SOCKS5 Bytestreams", XSF XEP 0065, April 2011.
[XEP-0077]
Saint-Andre, P., "In-Band Registration", XSF XEP 0077,
January 2012.
[XEP-0114]
Saint-Andre, P., "Jabber Component Protocol", XSF
XEP 0114, March 2005.
[XEP-0144]
Saint-Andre, P., "Roster Item Exchange", XSF XEP 0144,
August 2005.
[XEP-0165]
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Saint-Andre, P., "Best Practices to Discourage JID
Mimicking", XSF XEP 0165, December 2007.
[XEP-0166]
Ludwig, S., Beda, J., Saint-Andre, P., McQueen, R., Egan,
S., and J. Hildebrand, "Jingle", XSF XEP 0166,
December 2009.
[XEP-0191]
Saint-Andre, P., "Blocking Command", XSF XEP 0191,
July 2012.
[XEP-0203]
Saint-Andre, P., "Delayed Delivery", XSF XEP 0203,
September 2009.
[XEP-0220]
Miller, J., Saint-Andre, P., and P. Hancke, "Server
Dialback", XSF XEP 0220, August 2012.
[XEP-0292]
Saint-Andre, P. and S. Mizzi, "vCard4 Over XMPP", XSF
XEP 0292, October 2011.
[XML] Maler, E., Yergeau, F., Sperberg-McQueen, C., Paoli, J.,
and T. Bray, "Extensible Markup Language (XML) 1.0 (Fifth
Edition)", World Wide Web Consortium Recommendation REC-
xml-20081126, November 2008,
<http://www.w3.org/TR/2008/REC-xml-20081126>.
Appendix A. Differences from RFC 6122
Based on consensus derived from working group discussion,
implementation and deployment experience, and formal interoperability
testing, the following substantive modifications were made from RFC
6122.
o Changed domainpart preparation to use IDNA2008 (instead of
IDNA2003).
o Changed localpart preparation to use the JIDlocalIdentifierClass
profile of the PRECIS IdentifierClass (instead of the Nodeprep
profile of Stringprep).
o Changed resourcepart preparation to use the
JIDresourceFreeformClass profile of the PRECIS FreeformClass
(instead of the Resourceprep profile of Stringprep).
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o Specified that internationalized labels within domainparts must be
U-labels (instead of should be U-labels).
o Specified that fullwidth and halfwidth must be mapped to their
decomposition equivalents (previously handled through the use of
NFKC).
o Specified the use of Unicode normalization form C (instead of KC
as specified in the Nodeprep and Resourceprep profiles of
Stringprep).
o Specified that servers must enforce the address formatting rules.
Appendix B. Acknowledgements
Thanks to Miguel Garcia, Joe Hildebrand, and Florian Zeitz for their
feedback.
Some text in this document was borrowed or adapted from [RFC5890],
[RFC5891], [RFC5894], and [XEP-0165].
Author's Address
Peter Saint-Andre
Cisco Systems, Inc.
1899 Wynkoop Street, Suite 600
Denver, CO 80202
USA
Phone: +1-303-308-3282
Email: psaintan@cisco.com
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