PRECIS Framework: Preparation, Enforcement, and Comparison of Internationalized Strings in Application Protocols
RFC 8264

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Internet Engineering Task Force (IETF)                    P. Saint-Andre
Request for Comments: 8264                                    Jabber.org
Obsoletes: 7564                                              M. Blanchet
Category: Standards Track                                       Viagenie
ISSN: 2070-1721                                             October 2017

     PRECIS Framework: Preparation, Enforcement, and Comparison of
           Internationalized Strings in Application Protocols

Abstract

   Application protocols using Unicode code points in protocol strings
   need to properly handle such strings in order to enforce
   internationalization rules for strings placed in various protocol
   slots (such as addresses and identifiers) and to perform valid
   comparison operations (e.g., for purposes of authentication or
   authorization).  This document defines a framework enabling
   application protocols to perform the preparation, enforcement, and
   comparison of internationalized strings ("PRECIS") in a way that
   depends on the properties of Unicode code points and thus is more
   agile with respect to versions of Unicode.  As a result, this
   framework provides a more sustainable approach to the handling of
   internationalized strings than the previous framework, known as
   Stringprep (RFC 3454).  This document obsoletes RFC 7564.

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 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8264.

Copyright Notice

   Copyright (c) 2017 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
   (https://trustee.ietf.org/license-info) in effect on the date of

Saint-Andre & Blanchet       Standards Track                    [Page 1]
RFC 8264                    PRECIS Framework                October 2017

   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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   6
   3.  Preparation, Enforcement, and Comparison  . . . . . . . . . .   6
   4.  String Classes  . . . . . . . . . . . . . . . . . . . . . . .   8
     4.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .   8
     4.2.  IdentifierClass . . . . . . . . . . . . . . . . . . . . .   9
       4.2.1.  Valid . . . . . . . . . . . . . . . . . . . . . . . .   9
       4.2.2.  Contextual Rule Required  . . . . . . . . . . . . . .  10
       4.2.3.  Disallowed  . . . . . . . . . . . . . . . . . . . . .  10
       4.2.4.  Unassigned  . . . . . . . . . . . . . . . . . . . . .  10
       4.2.5.  Examples  . . . . . . . . . . . . . . . . . . . . . .  11
     4.3.  FreeformClass . . . . . . . . . . . . . . . . . . . . . .  11
       4.3.1.  Valid . . . . . . . . . . . . . . . . . . . . . . . .  11
       4.3.2.  Contextual Rule Required  . . . . . . . . . . . . . .  12
       4.3.3.  Disallowed  . . . . . . . . . . . . . . . . . . . . .  12
       4.3.4.  Unassigned  . . . . . . . . . . . . . . . . . . . . .  12
       4.3.5.  Examples  . . . . . . . . . . . . . . . . . . . . . .  12
     4.4.  Summary . . . . . . . . . . . . . . . . . . . . . . . . .  12
   5.  Profiles  . . . . . . . . . . . . . . . . . . . . . . . . . .  14
     5.1.  Profiles Must Not Be Multiplied beyond Necessity  . . . .  14
     5.2.  Rules . . . . . . . . . . . . . . . . . . . . . . . . . .  15
       5.2.1.  Width Mapping Rule  . . . . . . . . . . . . . . . . .  15
       5.2.2.  Additional Mapping Rule . . . . . . . . . . . . . . .  15
       5.2.3.  Case Mapping Rule . . . . . . . . . . . . . . . . . .  16
       5.2.4.  Normalization Rule  . . . . . . . . . . . . . . . . .  16
       5.2.5.  Directionality Rule . . . . . . . . . . . . . . . . .  17
     5.3.  A Note about Spaces . . . . . . . . . . . . . . . . . . .  18
   6.  Applications  . . . . . . . . . . . . . . . . . . . . . . . .  18
     6.1.  How to Use PRECIS in Applications . . . . . . . . . . . .  18
     6.2.  Further Excluded Characters . . . . . . . . . . . . . . .  20