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Versions: (draft-saintandre-xmpp-6122bis) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 RFC 7622

XMPP                                                      P. Saint-Andre
Internet-Draft                                                     Cisco
Obsoletes: 6122 (if approved)                          November 17, 2011
Intended status: Standards Track
Expires: May 20, 2012


   Extensible Messaging and Presence Protocol (XMPP): Address Format
                       draft-ietf-xmpp-6122bis-00

Abstract

   This document defines the address format for the Extensible Messaging
   and Presence Protocol (XMPP), including support for code points
   outside the US-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 May 20, 2012.

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.




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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Overview . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Addresses  . . . . . . . . . . . . . . . . . . . . . . . . . .  3
     2.1.  Fundamentals . . . . . . . . . . . . . . . . . . . . . . .  3
     2.2.  Domainpart . . . . . . . . . . . . . . . . . . . . . . . .  5
     2.3.  Localpart  . . . . . . . . . . . . . . . . . . . . . . . .  6
     2.4.  Resourcepart . . . . . . . . . . . . . . . . . . . . . . .  7
   3.  Internationalization Considerations  . . . . . . . . . . . . .  8
   4.  Security Considerations  . . . . . . . . . . . . . . . . . . .  8
     4.1.  Reuse of PRECIS  . . . . . . . . . . . . . . . . . . . . .  8
     4.2.  Reuse of Unicode . . . . . . . . . . . . . . . . . . . . .  9
     4.3.  Address Spoofing . . . . . . . . . . . . . . . . . . . . .  9
       4.3.1.  Address Forging  . . . . . . . . . . . . . . . . . . .  9
       4.3.2.  Address Mimicking  . . . . . . . . . . . . . . . . . . 10
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 11
     5.1.  Use of NameClass . . . . . . . . . . . . . . . . . . . . . 11
     5.2.  Use of FreeClass . . . . . . . . . . . . . . . . . . . . . 11
   6.  Conformance Requirements . . . . . . . . . . . . . . . . . . . 12
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
     7.1.  Normative References . . . . . . . . . . . . . . . . . . . 13
     7.2.  Informative References . . . . . . . . . . . . . . . . . . 14
   Appendix A.  Differences from RFC 6122 . . . . . . . . . . . . . . 16
   Appendix B.  Acknowledgements  . . . . . . . . . . . . . . . . . . 17
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 17
























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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 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
   [STRINGPREP].  This document defines the XMPP address format in a way
   that no longer depends on stringprep.  Instead, this document depends
   on the internationalization framework defined by the IETF's PRECIS
   Working Group [FRAMEWORK].

   This document obsoletes RFC 6122.

1.2.  Terminology

   Many important terms used in this document are defined in
   [FRAMEWORK], [I18N-TERMS], [IDNA-DEFS], [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 ("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].




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      jid           = [ localpart "@" ] domainpart [ "/" resourcepart ]
      localpart     = 1*(localpoint)
                      ;
                      ; a "localpoint" is a UTF-8 encoded Unicode
                      ; code point that conforms to the localpart
                      ; subclass of the "NameClass" string class
                      ; defined in draft-blanchet-precis-framework
                      ;
      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*(domainpoint)
                      ;
                      ; a "domainpoint" is a UTF-8 encoded Unicode
                      ; code point that conforms to the "domain name"
                      ; string class effectively defined in RFC 5890
                      ;
      resourcepart  = 1*(resourcepoint)
                      ;
                      ; a "resourcepoint" is a UTF-8 encoded Unicode
                      ; code point that conforms to the localpart
                      ; subclass of the "FreeClass" string class
                      ; defined in draft-blanchet-precis-framework
                      ;

   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 purposes 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 URI or 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



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   interaction outside the context of XMPP itself, for example when
   linking to a JID from a web page.  See [XMPP-URI] for information
   about 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 to 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 [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; 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 [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.

   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 of code points.  Naturally, the length
   limits of [DNS] apply, and nothing in this document is to be
   interpreted as overriding those more fundamental limits.




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   In the terms of IDNA2008 [IDNA-DEFS], the domainpart of a JID is a
   "domain name slot".

   A domainpart consisting of a fully qualified domain name MUST be an
   "internationalized domain name" as defined in [IDNA-DEFS] and MUST
   consist only of Unicode code points that conform to the rules
   specified in [IDNA-CODE].

   For the purposes of communication over XMPP, the domainpart of a JID
   MUST be treated as follows, where the operations specified MUST be
   completed in the order shown:

   1.  Uppercase and titlecase characters MUST be mapped to their
       lowercase equivalents.

   2.  All characters MUST be mapped using Unicode Normalization Form C
       (NFC).  [[OPEN ISSUE: Use NFD instead?]]

   3.  Each A-label SHOULD be converted to a U-label (however, if it is
       not converted then the application MUST apply the Punycode
       algorithm [PUNYCODE] to each A-label and prepend the ACE prefix
       ("xn--") to the resulting DNS domain name).

   With regard to directionality, the "Bidi Rule" provided in
   [IDNA-BIDI] applies.

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 [XEP-0045]).  The
   entity represented by an XMPP localpart is addressed within the
   context of a specific domain (i.e., <localpart@domainpart>).

   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 of code points.

   A localpart MUST consist only of Unicode code points that conform to
   the "NameClass" base string class defined in [FRAMEWORK], with the
   exception of the following characters that are explicitly disallowed
   in XMPP localparts:






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      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., @

   For the purposes of communication over XMPP, the localpart of a JID
   MUST be treated as follows, where the operations specified MUST be
   completed in the order shown:

   1.  Uppercase and titlecase characters MUST be mapped to their
       lowercase equivalents.

   2.  All characters MUST be mapped using Unicode Normalization Form C
       (NFC).  [[OPEN ISSUE: Use NFD instead?]]

   With regard to directionality, the "Bidi Rule" provided in
   [IDNA-BIDI] applies.

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 [XEP-0045])
   belonging to the entity associated with an XMPP localpart at a domain
   (i.e., <localpart@domainpart/resourcepart>).

   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 of code points.

   A resourcepart MUST consist only of Unicode code points that conform
   to the "FreeClass" base string class defined in [FRAMEWORK].

   For the purposes of communication over XMPP, the localpart of a JID
   MUST be treated as follows, where the operations specified MUST be
   completed in the order shown:

   1.  Uppercase and titlecase characters MAY be mapped to their
       lowercase equivalents.





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   2.  All characters MUST be mapped using Unicode Normalization Form C
       (NFC).  [[OPEN ISSUE: Use NFD instead?]]

   With regard to directionality, the "Bidi Rule" provided in
   [IDNA-BIDI] applies.

   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 "nick" 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) 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 applications MUST support IDNA2008 for domainparts, the
   "NameClass" string class from [FRAMEWORK] for localparts (with the
   exception of certain ASCII characters specified under Section 2.3),
   and the "FreeClass" string class from [FRAMEWORK] 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] and specifications for various
   XMPP extensions.

   For backward compatibility, many XMPP applications support [IDNA2003]
   for domainparts, and the [STRINGPREP] profiles Nodeprep and
   Resourceprep [RFC3920] for localparts and resourceparts.


4.  Security Considerations

4.1.  Reuse of PRECIS

   The security considerations described in [FRAMEWORK] apply to the
   "NameClass" and "FreeClass" base string classes used in this document



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   for XMPP localparts and resourceparts.  The security considerations
   described in [IDNA-DEFS] apply to internationalized domain names,
   which are used here for XMPP domainparts.

4.2.  Reuse of Unicode

   The security considerations described in [UTR39] apply to the use of
   Unicode characters in XMPP addresses.

4.3.  Address Spoofing

   There are two forms of address spoofing: forging and mimicking.

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 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.



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   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.
   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 [IDNA-DEFS], [FRAMEWORK], [UTR36], and [UTR39], there
   is no straightforward solution to the problem of 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



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      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.

   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 [FRAMEWORK].


5.  IANA Considerations

5.1.  Use of NameClass

   The IANA shall add an entry to the PRECIS Usage Registry for reuse of
   the PRECIS NameClass in XMPP, as follows:

   Application Protocol:  XMPP.
   Base Class:  NameClass.
   Subclassing:  Yes. See Section 2.3 of RFC XXXX.
   Directionality:  If the string contains at least one right-to-left
      code point, the entire string is considered to be right-to-left.
   Casemapping:  Uppercase and titlecase code points are mapped to their
      lowercase equivalents.
   Normalization:  NFC.
   Specification:  RFC XXXX.

5.2.  Use of FreeClass

   The IANA shall add an entry to the PRECIS Usage Registry for reuse of
   the PRECIS FreeClass in XMPP, as follows:

   Application Protocol:  XMPP.
   Base Class:  FreeClass
   Subclassing:  No.
   Directionality:  If the string contains at least one right-to-left
      code point, the entire string is considered to be right-to-left.
   Casemapping:  None.
   Normalization:  NFC.
   Specification:  RFC XXXX.







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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].

   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 IDNA2008, mapped to lowercase and normalized using NFC.
   Section:  Section 2.2
   Roles:  Both 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.







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   Feature:  address-localpart-prep
   Description:  Ensure that the localpart of an XMPP address conforms
      to the "NameClass" base string class from the PRECIS framework,
      excluding the eight XMPP prohibited code points (U+0022, U+0026,
      U+0027, U+002F, U+003A, U+003C, U+003E, and U+0040), with all code
      points mapped to lowercase and normalized using NFC.
   Section:  Section 2.3
   Roles:  Both 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 "FreeClass" base string class from the PRECIS
      framework, with all code points normalized using NFC.
   Section:  Section 2.4
   Roles:  Both MUST.


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.

   [FRAMEWORK]
              Blanchet, M. and P. Saint-Andre, "Precis Framework:
              Handling Internationalized Strings in Protocols",
              draft-blanchet-precis-framework-03 (work in progress),
              August 2011.

   [IDNA-BIDI]
              Alvestrand, H. and C. Karp, "Right-to-Left Scripts for
              Internationalized Domain Names for Applications (IDNA)",
              RFC 5893, August 2010.

   [IDNA-CODE]
              Faltstrom, P., "The Unicode Code Points and
              Internationalized Domain Names for Applications (IDNA)",
              RFC 5892, August 2010.



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   [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.

   [KEYWORDS]
              Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [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/).

   [UTF-8]    Yergeau, F., "UTF-8, a transformation format of ISO
              10646", STD 63, RFC 3629, November 2003.

   [UTR36]    The Unicode Consortium, "Unicode Technical Report #36:
              Unicode Security Considerations", 2008,
              <http://www.unicode.org/reports/tr36/>.

   [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.

   [I18N-TERMS]
              Hoffman, P. and J. Klensin, "Terminology Used in
              Internationalization in the IETF",
              draft-hoffman-rfc3536bis-02 (work in progress),
              April 2011.

   [IDNA2003]
              Faltstrom, P., Hoffman, P., and A. Costello,



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              "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.

   [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.

   [RFC6122]  Saint-Andre, P., "Extensible Messaging and Presence
              Protocol (XMPP): Address Format", RFC 6122, March 2011.

   [SASL]     Melnikov, A., Ed. and K. Zeilenga, Ed., "Simple
              Authentication and Security Layer (SASL)", RFC 4422,
              June 2006.

   [STRINGPREP]
              Hoffman, P. and M. Blanchet, "Preparation of
              Internationalized Strings ("stringprep")", RFC 3454,
              December 2002.

   [URI]      Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, January 2005.




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   [UTR39]    The Unicode Consortium, "Unicode Technical Report #39:
              Unicode Security Mechanisms", August 2010,
              <http://unicode.org/reports/tr39/>.

   [XEP-0029]
              Kaes, C., "Definition of Jabber Identifiers (JIDs)", XSF
              XEP 0029, October 2003.

   [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 0165, 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.


Appendix A.  Differences from RFC 6122

   Based on consensus derived from implementation and deployment
   experience as well as formal interoperability testing, the following
   substantive modifications were made from RFC 3920.

   o  Changed domainpart preparation to use IDNA2008 instead of
      IDNA2003.
   o  Changed localpart preparation to use PRECIS instead of the
      Nodeprep profile of Stringprep.
   o  Changed resourcepart preparation to use PRECIS instead of the
      Resourceprep profile of Stringprep.






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Appendix B.  Acknowledgements

   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 Wynkoop Street, Suite 600
   Denver, CO  80202
   USA

   Phone: +1-303-308-3282
   Email: psaintan@cisco.com



































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