draft-ietf-precis-framework-07.txt   draft-ietf-precis-framework-08.txt 
PRECIS P. Saint-Andre PRECIS P. Saint-Andre
Internet-Draft Cisco Systems, Inc. Internet-Draft Cisco Systems, Inc.
Obsoletes: 3454 (if approved) M. Blanchet Obsoletes: 3454 (if approved) M. Blanchet
Intended status: Standards Track Viagenie Intended status: Standards Track Viagenie
Expires: September 27, 2013 March 26, 2013 Expires: October 27, 2013 April 25, 2013
PRECIS Framework: Preparation and Comparison of Internationalized PRECIS Framework: Preparation and Comparison of Internationalized
Strings in Application Protocols Strings in Application Protocols
draft-ietf-precis-framework-07 draft-ietf-precis-framework-08
Abstract Abstract
Application protocols using Unicode code points in protocol strings Application protocols using Unicode code points in protocol strings
need to properly prepare such strings in order to perform valid need to properly prepare such strings in order to perform valid
comparison operations (e.g., for purposes of authentication or comparison operations (e.g., for purposes of authentication or
authorization). This document defines a framework enabling authorization). This document defines a framework enabling
application protocols to perform the preparation and comparison of application protocols to perform the preparation and comparison of
internationalized strings (a.k.a. "PRECIS") in a way that depends on internationalized strings (a.k.a. "PRECIS") in a way that depends on
the properties of Unicode code points and thus is agile with respect the properties of Unicode code points and thus is agile with respect
skipping to change at page 1, line 35 skipping to change at page 1, line 35
specification that reuses this framework can either directly use the specification that reuses this framework can either directly use the
PRECIS string classes or subclass the PRECIS string classes as PRECIS string classes or subclass the PRECIS string classes as
needed. This framework takes an approach similar to the revised needed. This framework takes an approach similar to the revised
internationalized domain names (IDNs) in applications (IDNA) internationalized domain names (IDNs) in applications (IDNA)
technology (RFC 5890, RFC 5891, RFC 5892, RFC 5893, RFC 5894) and technology (RFC 5890, RFC 5891, RFC 5892, RFC 5893, RFC 5894) and
thus adheres to the high-level design goals described in the IAB's thus adheres to the high-level design goals described in the IAB's
recommendations regarding IDNs (RFC 4690), albeit for application recommendations regarding IDNs (RFC 4690), albeit for application
technologies other than the Domain Name System (DNS). This document technologies other than the Domain Name System (DNS). This document
obsoletes RFC 3454. obsoletes RFC 3454.
Status of This Memo Status of this Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 27, 2013. This Internet-Draft will expire on October 27, 2013.
Copyright Notice Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. String Classes . . . . . . . . . . . . . . . . . . . . . . . 5 3. String Classes . . . . . . . . . . . . . . . . . . . . . . . . 6
3.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 5 3.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.2. IdentifierClass . . . . . . . . . . . . . . . . . . . . . 7 3.2. Order of Operations . . . . . . . . . . . . . . . . . . . 8
3.3. FreeformClass . . . . . . . . . . . . . . . . . . . . . . 9 3.3. IdentifierClass . . . . . . . . . . . . . . . . . . . . . 8
4. Use of PRECIS String Classes . . . . . . . . . . . . . . . . 11 3.4. FreeformClass . . . . . . . . . . . . . . . . . . . . . . 10
4.1. Principles . . . . . . . . . . . . . . . . . . . . . . . 11 4. Use of PRECIS String Classes . . . . . . . . . . . . . . . . . 12
4.2. Subclassing . . . . . . . . . . . . . . . . . . . . . . . 11 4.1. Principles . . . . . . . . . . . . . . . . . . . . . . . . 12
4.3. Building Application-Layer Constructs . . . . . . . . . . 12 4.2. Subclassing . . . . . . . . . . . . . . . . . . . . . . . 13
4.4. A Note about Spaces . . . . . . . . . . . . . . . . . . . 13 4.3. Building Application-Layer Constructs . . . . . . . . . . 14
5. Code Point Properties . . . . . . . . . . . . . . . . . . . . 13 4.4. A Note about Spaces . . . . . . . . . . . . . . . . . . . 14
6. Category Definitions Used to Calculate Derived Property Value 15 5. Code Point Properties . . . . . . . . . . . . . . . . . . . . 15
6.1. LetterDigits (A) . . . . . . . . . . . . . . . . . . . . 16 6. Category Definitions Used to Calculate Derived Property
6.2. Unstable (B) . . . . . . . . . . . . . . . . . . . . . . 16 Value . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
6.3. IgnorableProperties (C) . . . . . . . . . . . . . . . . . 16 6.1. LetterDigits (A) . . . . . . . . . . . . . . . . . . . . . 17
6.4. IgnorableBlocks (D) . . . . . . . . . . . . . . . . . . . 17 6.2. Unstable (B) . . . . . . . . . . . . . . . . . . . . . . . 17
6.5. LDH (E) . . . . . . . . . . . . . . . . . . . . . . . . . 17 6.3. IgnorableProperties (C) . . . . . . . . . . . . . . . . . 17
6.6. Exceptions (F) . . . . . . . . . . . . . . . . . . . . . 17 6.4. IgnorableBlocks (D) . . . . . . . . . . . . . . . . . . . 18
6.7. BackwardCompatible (G) . . . . . . . . . . . . . . . . . 18 6.5. LDH (E) . . . . . . . . . . . . . . . . . . . . . . . . . 18
6.8. JoinControl (H) . . . . . . . . . . . . . . . . . . . . . 19 6.6. Exceptions (F) . . . . . . . . . . . . . . . . . . . . . . 18
6.9. OldHangulJamo (I) . . . . . . . . . . . . . . . . . . . . 19 6.7. BackwardCompatible (G) . . . . . . . . . . . . . . . . . . 19
6.10. Unassigned (J) . . . . . . . . . . . . . . . . . . . . . 19 6.8. JoinControl (H) . . . . . . . . . . . . . . . . . . . . . 20
6.11. ASCII7 (K) . . . . . . . . . . . . . . . . . . . . . . . 20 6.9. OldHangulJamo (I) . . . . . . . . . . . . . . . . . . . . 20
6.12. Controls (L) . . . . . . . . . . . . . . . . . . . . . . 20 6.10. Unassigned (J) . . . . . . . . . . . . . . . . . . . . . . 20
6.13. PrecisIgnorableProperties (M) . . . . . . . . . . . . . . 20 6.11. ASCII7 (K) . . . . . . . . . . . . . . . . . . . . . . . . 21
6.14. Spaces (N) . . . . . . . . . . . . . . . . . . . . . . . 20 6.12. Controls (L) . . . . . . . . . . . . . . . . . . . . . . . 21
6.15. Symbols (O) . . . . . . . . . . . . . . . . . . . . . . . 21 6.13. PrecisIgnorableProperties (M) . . . . . . . . . . . . . . 21
6.16. Punctuation (P) . . . . . . . . . . . . . . . . . . . . . 21 6.14. Spaces (N) . . . . . . . . . . . . . . . . . . . . . . . . 21
6.17. HasCompat (Q) . . . . . . . . . . . . . . . . . . . . . . 21 6.15. Symbols (O) . . . . . . . . . . . . . . . . . . . . . . . 21
6.18. OtherLetterDigits (R) . . . . . . . . . . . . . . . . . . 21 6.16. Punctuation (P) . . . . . . . . . . . . . . . . . . . . . 22
7. Calculation of the Derived Property . . . . . . . . . . . . . 21 6.17. HasCompat (Q) . . . . . . . . . . . . . . . . . . . . . . 22
8. Code Points . . . . . . . . . . . . . . . . . . . . . . . . . 23 6.18. OtherLetterDigits (R) . . . . . . . . . . . . . . . . . . 22
9. Security Considerations . . . . . . . . . . . . . . . . . . . 23 7. Calculation of the Derived Property . . . . . . . . . . . . . 22
9.1. General Issues . . . . . . . . . . . . . . . . . . . . . 23 8. Code Points . . . . . . . . . . . . . . . . . . . . . . . . . 23
9.2. Use of the IdentifierClass . . . . . . . . . . . . . . . 24 9. Security Considerations . . . . . . . . . . . . . . . . . . . 23
9.3. Use of the FreeformClass . . . . . . . . . . . . . . . . 24 9.1. General Issues . . . . . . . . . . . . . . . . . . . . . . 23
9.4. Local Character Set Issues . . . . . . . . . . . . . . . 24 9.2. Use of the IdentifierClass . . . . . . . . . . . . . . . . 24
9.5. Visually Similar Characters . . . . . . . . . . . . . . . 24 9.3. Use of the FreeformClass . . . . . . . . . . . . . . . . . 24
9.6. Security of Passwords . . . . . . . . . . . . . . . . . . 26 9.4. Local Character Set Issues . . . . . . . . . . . . . . . . 24
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27 9.5. Visually Similar Characters . . . . . . . . . . . . . . . 25
10.1. PRECIS Derived Property Value Registry . . . . . . . . . 27 9.6. Security of Passwords . . . . . . . . . . . . . . . . . . 26
10.2. PRECIS Base Classes Registry . . . . . . . . . . . . . . 27 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27
10.3. PRECIS Subclasses Registry . . . . . . . . . . . . . . . 28 10.1. PRECIS Derived Property Value Registry . . . . . . . . . . 27
10.4. PRECIS Usage Registry . . . . . . . . . . . . . . . . . 30 10.2. PRECIS Base Classes Registry . . . . . . . . . . . . . . . 28
11. Interoperability Considerations . . . . . . . . . . . . . . . 31 10.3. PRECIS Subclasses Registry . . . . . . . . . . . . . . . . 29
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 31 10.4. PRECIS Usage Registry . . . . . . . . . . . . . . . . . . 30
12.1. Normative References . . . . . . . . . . . . . . . . . . 32 11. Interoperability Considerations . . . . . . . . . . . . . . . 31
12.2. Informative References . . . . . . . . . . . . . . . . . 32 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Appendix A. Codepoint Table . . . . . . . . . . . . . . . . . . 34 12.1. Normative References . . . . . . . . . . . . . . . . . . . 32
Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 69 12.2. Informative References . . . . . . . . . . . . . . . . . . 32
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 70 Appendix A. Codepoint Table . . . . . . . . . . . . . . . . . . . 35
Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 70
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 70
1. Introduction 1. Introduction
As described in the PRECIS problem statement [RFC6885], many IETF As described in the problem statement for the preparation and
protocols have used the Stringprep framework [RFC3454] as the basis comparison of internationalized strings ("PRECIS") [RFC6885], many
for preparing and comparing protocol strings that contain Unicode IETF protocols have used the Stringprep framework [RFC3454] as the
code points [UNICODE] outside the ASCII range [RFC20]. The basis for preparing and comparing protocol strings that contain
Unicode code points [UNICODE] outside the ASCII range [RFC20]. The
Stringprep framework was developed during work on the original Stringprep framework was developed during work on the original
technology for internationalized domain names (IDNs), here called technology for internationalized domain names (IDNs), here called
"IDNA2003" [RFC3490], and Nameprep [RFC3491] was the Stringprep "IDNA2003" [RFC3490], and Nameprep [RFC3491] was the Stringprep
profile for IDNs. At the time, Stringprep was designed as a general profile for IDNs. At the time, Stringprep was designed as a general
framework so that other application protocols could define their own framework so that other application protocols could define their own
Stringprep profiles for the preparation and comparison of strings and Stringprep profiles for the preparation and comparison of strings and
identifiers. Indeed, a number of application protocols defined such identifiers. Indeed, a number of application protocols defined such
profiles. profiles.
After the publication of [RFC3454] in 2002, several significant After the publication of [RFC3454] in 2002, several significant
issues arose with the use of Stringprep in the IDN case, as issues arose with the use of Stringprep in the IDN case, as
documented in the IAB's recommendations regarding IDNs [RFC4690] documented in the IAB's recommendations regarding IDNs [RFC4690]
(most significantly, Stringprep was tied to Unicode version 3.2). (most significantly, Stringprep was tied to Unicode version 3.2).
Therefore, the new IDNA specifications, here called "IDNA2008" Therefore, the newer IDNA specifications, here called "IDNA2008"
([RFC5890], [RFC5891], [RFC5892], [RFC5893], [RFC5894]), no longer ([RFC5890], [RFC5891], [RFC5892], [RFC5893], [RFC5894]), no longer
use Stringprep and Nameprep. This migration away from Stringprep for use Stringprep and Nameprep. This migration away from Stringprep for
IDNs has prompted other "customers" of Stringprep to consider new IDNs has prompted other "customers" of Stringprep to consider new
approaches to the preparation and comparison of internationalized approaches to the preparation and comparison of internationalized
strings (a.k.a. "PRECIS"), as described in [RFC6885]. strings (a.k.a. "PRECIS"), as described in [RFC6885].
This document defines a framework for a post-Stringprep approach to This document defines a framework for a post-Stringprep approach to
the preparation and comparison of internationalized strings in the preparation and comparison of internationalized strings in
application protocols, based on several principles: application protocols, based on several principles:
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approaches to the preparation and comparison of internationalized approaches to the preparation and comparison of internationalized
strings (a.k.a. "PRECIS"), as described in [RFC6885]. strings (a.k.a. "PRECIS"), as described in [RFC6885].
This document defines a framework for a post-Stringprep approach to This document defines a framework for a post-Stringprep approach to
the preparation and comparison of internationalized strings in the preparation and comparison of internationalized strings in
application protocols, based on several principles: application protocols, based on several principles:
1. Define a small set of string classes appropriate for common 1. Define a small set of string classes appropriate for common
application protocol constructs such as usernames and free-form application protocol constructs such as usernames and free-form
strings. strings.
2. Define each PRECIS string class in terms of Unicode code points 2. Define each PRECIS string class in terms of Unicode code points
and their properties so that an algorithm can be used to and their properties so that an algorithm can be used to
determine whether each code point or character category is valid, determine whether each code point or character category is valid,
disallowed, or unassigned. disallowed, or unassigned.
3. Define string classes in terms of allowable code points, so that 3. Define string classes in terms of allowable code points, so that
any code points not explicitly allowed are forbidden. any code point not explicitly allowed is forbidden.
4. Enable application protocols to subclass the PRECIS string 4. Enable application protocols to subclass the PRECIS string
classes if needed, mainly to disallow particular code points that classes if needed, mainly to disallow particular code points that
are currently disallowed in the relevant application protocol are currently disallowed in the relevant application protocol
(e.g., characters with special or reserved meaning, such as "@" (e.g., characters with special or reserved meaning, such as "@"
and "/" when used as separators within identifiers). and "/" when used as separators within identifiers).
5. Leave various mapping operations (e.g., case preservation or 5. Leave various mapping operations (e.g., case preservation or
lowercasing, Unicode normalization, mapping of certain characters lowercasing, Unicode normalization, mapping of certain characters
to other characters or to nothing, handling of full-width and to other characters or to nothing, handling of full-width and
half-width characters, handling of right-to-left characters) as half-width characters, handling of right-to-left characters) as
the responsibility of application protocols, as was done for the responsibility of application protocols, as was done for
IDNA2008 through an IDNA-specific mapping document [RFC5895]. IDNA2008 through an IDNA-specific mapping document [RFC5895].
It is expected that this framework will yield the following benefits: It is expected that this framework will yield the following benefits:
o Application protocols will be more version-agile with regard to o Application protocols will be more version-agile with regard to
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The following subsections discuss the IdentifierClass and The following subsections discuss the IdentifierClass and
FreeformClass in more detail, with reference to the dimensions FreeformClass in more detail, with reference to the dimensions
described in Section 3 of [RFC6885]. (Naturally, future documents described in Section 3 of [RFC6885]. (Naturally, future documents
can define PRECIS string classes beyond the IdentifierClass and can define PRECIS string classes beyond the IdentifierClass and
FreeformClass; see Section 10.2.) Each string class (or a particular FreeformClass; see Section 10.2.) Each string class (or a particular
usage thereof) is defined by the following behavioral rules: usage thereof) is defined by the following behavioral rules:
Valid: defines which code points and character categories are Valid: defines which code points and character categories are
treated as valid input to the string. treated as valid input to the string.
Disallowed: defines which code points and character categories are Disallowed: defines which code points and character categories are
treated as disallowed for the string. treated as disallowed for the string.
Unassigned: defines application behavior in the presence of code Unassigned: defines application behavior in the presence of code
points that are unassigned, i.e. unknown for the version of points that are unassigned, i.e. unknown for the version of
Unicode the application is built upon. Unicode the application is built upon.
Normalization: defines which Unicode normalization form (D, KD, C,
or KC) is to be applied (see [UAX15]).
Case Mapping: specifies if case mapping is performed (instead of
case preservation) on uppercase and titlecase characters, and how
the mapping is done (e.g., mapping uppercase and titlecase
characters to their lowercase equivalents).
Width Mapping: specifies if width mapping is performed on fullwidth Width Mapping: specifies if width mapping is performed on fullwidth
and halfwidth characters, and how the mapping is done (e.g., and halfwidth characters, and how the mapping is done (e.g.,
mapping fullwidth and halfwidth characters to their decomposition mapping fullwidth and halfwidth characters to their decomposition
equivalents). equivalents).
Additional Mappings: specifies whether additional mappings are to be
applied, such as mapping of delimiter characters, mapping of
special characters (e.g., non-ASCII space characters to ASCII
space or certain characters to nothing), and case mapping based on
language and local context (see [I-D.ietf-precis-mappings]).
Case Mapping: specifies if case mapping is performed (instead of
case preservation) on uppercase and titlecase characters, and how
the mapping is done (e.g., mapping uppercase and titlecase
characters to their lowercase equivalents).
Normalization: defines which Unicode normalization form (D, KD, C,
or KC) is to be applied (see [UAX15]).
Directionality: defines application behavior in the presence of code Directionality: defines application behavior in the presence of code
points that have directionality, in particular right-to-left code points that have directionality, in particular right-to-left code
points as defined in the Unicode database (see [UAX9]). points as defined in the Unicode database (see [UAX9]).
This document defines the valid, disallowed, and unassigned rules for This document defines the valid, disallowed, and unassigned rules for
the IdentifierClass and FreeformClass. Application protocols that the IdentifierClass and FreeformClass. Application protocols that
use these string classes are responsible for defining the use these string classes are responsible for defining the
normalization, case mapping, width mapping, and directionality rules, normalization, case mapping, width mapping, and directionality rules,
as well as any additional mappings to be applied as well as any additional mappings to be applied
Note: In order to ensure proper comparison, any normalization MUST be 3.2. Order of Operations
completed before the application of additional mappings or the
process of checking whether a code point is valid, disallowed, or
unassigned.
3.2. IdentifierClass To ensure proper comparison, the following order of operations is
REQUIRED:
1. Width mapping
2. Additional mappings as specified in [I-D.ietf-precis-mappings]:
1. Delimiter mapping
2. Special mapping
3. Local case mapping
3. Non-local case mapping
4. Normalization
5. PRECIS protocol
3.3. IdentifierClass
Most application technologies need strings that can be used to refer Most application technologies need strings that can be used to refer
to, include, or communicate protocol strings like usernames, file to, include, or communicate protocol strings like usernames, file
names, data feed identifiers, and chatroom names. We group such names, data feed identifiers, and chatroom names. We group such
strings into a class called "IdentifierClass" having the following strings into a class called "IdentifierClass" having the following
features. features.
3.2.1. Valid 3.3.1. Valid
o Code points traditionally used as letters and numbers in writing o Code points traditionally used as letters and numbers in writing
systems, i.e., the LetterDigits ("A") category first defined in systems, i.e., the LetterDigits ("A") category first defined in
[RFC5892] and listed here under Section 6.1. [RFC5892] and listed here under Section 6.1.
o Code points in the range U+0021 through U+007E, i.e., the ASCII7 o Code points in the range U+0021 through U+007E, i.e., the ASCII7
("K") rule defined under Section 6.11. These code points are ("K") rule defined under Section 6.11. These code points are
"grandfathered" into PRECIS and thus are valid even if they would "grandfathered" into PRECIS and thus are valid even if they would
otherwise be disallowed according to the property-based rules otherwise be disallowed according to the property-based rules
specified in the next section. specified in the next section.
Although the PRECIS IdentifierClass re-uses the LetterDigits category Although the PRECIS IdentifierClass re-uses the LetterDigits category
from IDNA2008, the range of characters allowed in the IdentifierClass from IDNA2008, the range of characters allowed in the IdentifierClass
is wider than the range of characters allowed in IDNA2008. The main is wider than the range of characters allowed in IDNA2008. The main
reason is that IDNA2008 applies the Unstable category before the reason is that IDNA2008 applies the Unstable category before the
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otherwise be disallowed according to the property-based rules otherwise be disallowed according to the property-based rules
specified in the next section. specified in the next section.
Although the PRECIS IdentifierClass re-uses the LetterDigits category Although the PRECIS IdentifierClass re-uses the LetterDigits category
from IDNA2008, the range of characters allowed in the IdentifierClass from IDNA2008, the range of characters allowed in the IdentifierClass
is wider than the range of characters allowed in IDNA2008. The main is wider than the range of characters allowed in IDNA2008. The main
reason is that IDNA2008 applies the Unstable category before the reason is that IDNA2008 applies the Unstable category before the
LetterDigits category, thus disallowing uppercase characters, whereas LetterDigits category, thus disallowing uppercase characters, whereas
the IdentifierClass does not apply the Unstable category. the IdentifierClass does not apply the Unstable category.
3.2.2. Disallowed 3.3.2. Disallowed
o Control characters, i.e., the Controls ("L") category defined o Control characters, i.e., the Controls ("L") category defined
under Section 6.12. under Section 6.12.
o Ignorable characters, i.e., the PrecisIgnorableProperties ("M") o Ignorable characters, i.e., the PrecisIgnorableProperties ("M")
category defined under Section 6.13. category defined under Section 6.13.
o Space characters, i.e., the Spaces ("N") category defined under o Space characters, i.e., the Spaces ("N") category defined under
Section 6.14. Section 6.14.
o Symbol characters, i.e., the Symbols ("O") category defined under o Symbol characters, i.e., the Symbols ("O") category defined under
Section 6.15. Section 6.15.
o Punctuation characters, i.e., the Punctuation ("P") category o Punctuation characters, i.e., the Punctuation ("P") category
defined under Section 6.16. defined under Section 6.16.
o Any character that has a compatibility equivalent, i.e., the o Any character that has a compatibility equivalent, i.e., the
HasCompat ("Q") category defined under Section 6.17. These code HasCompat ("Q") category defined under Section 6.17. These code
points are disallowed even if they would otherwise be valid points are disallowed even if they would otherwise be valid
according to the property-based rules specified in the previous according to the property-based rules specified in the previous
section. section.
o Letters and digits other than the "traditional" letters and digits o Letters and digits other than the "traditional" letters and digits
allowed in IDNs, i.e., the OtherLetterDigits ("R") category allowed in IDNs, i.e., the OtherLetterDigits ("R") category
defined under Section 6.18. defined under Section 6.18.
3.2.3. Unassigned 3.3.3. Unassigned
Any code points that are not yet assigned in the Unicode character Any code points that are not yet assigned in the Unicode character
set SHALL be considered Unassigned for purposes of the set SHALL be considered Unassigned for purposes of the
IdentifierClass. IdentifierClass.
3.2.4. Normalization 3.3.4. Width Mapping
The Unicode normalization form MUST be specified by each application The width mapping rule MUST be specified by each application protocol
protocol that uses or subclasses the IdentifierClass. that uses or subclasses the IdentifierClass.
However, in accordance with [RFC5198], normalization form C (NFC) is 3.3.5. Additional Mappings
RECOMMENDED.
3.2.5. Case Mapping Additional mapping rules (if any) MUST be specified by each
application protocol that uses or subclasses the IdentifierClass (see
[I-D.ietf-precis-mappings]).
3.3.6. Case Mapping
The case mapping rule MUST be specified by each application protocol The case mapping rule MUST be specified by each application protocol
that uses or subclasses the IdentifierClass. that uses or subclasses the IdentifierClass.
3.2.6. Width Mapping 3.3.7. Normalization
The width mapping rule MUST be specified by each application protocol The Unicode normalization form MUST be specified by each application
that uses or subclasses the IdentifierClass. protocol that uses or subclasses the IdentifierClass.
3.2.7. Additional Mappings However, in accordance with [RFC5198], normalization form C (NFC) is
Additional mapping rules (if any) MUST be specified by each RECOMMENDED.
application protocol that uses or subclasses the IdentifierClass.
3.2.8. Directionality 3.3.8. Directionality
The directionality rule MUST be specified by each application The directionality rule MUST be specified by each application
protocol that uses or subclasses the IdentifierClass. protocol that uses or subclasses the IdentifierClass.
3.3. FreeformClass 3.4. FreeformClass
Some application technologies need strings that can be used in a Some application technologies need strings that can be used in a
free-form way, e.g., as a password in an authentication exchange (see free-form way, e.g., as a password in an authentication exchange (see
[I-D.ietf-precis-saslprepbis] or a nickname in a chatroom (see [I-D.ietf-precis-saslprepbis] or a nickname in a chatroom (see
[I-D.ietf-precis-nickname]). We group such things into a class [I-D.ietf-precis-nickname]). We group such things into a class
called "FreeformClass" having the following features. called "FreeformClass" having the following features.
Note: Consult Section 9.6 for relevant security considerations when Note: Consult Section 9.6 for relevant security considerations when
strings conforming to the FreeformClass, or a subclass thereof, are strings conforming to the FreeformClass, or a subclass thereof, are
used as passwords. used as passwords.
3.3.1. Valid 3.4.1. Valid
o Traditional letters and numbers, i.e., the LetterDigits ("A") o Traditional letters and numbers, i.e., the LetterDigits ("A")
category first defined in [RFC5892] and listed here under category first defined in [RFC5892] and listed here under
Section 6.1. Section 6.1.
o Letters and digits other than the "traditional" letters and digits o Letters and digits other than the "traditional" letters and digits
allowed in IDNs, i.e., the OtherLetterDigits ("R") category allowed in IDNs, i.e., the OtherLetterDigits ("R") category
defined under Section 6.18. defined under Section 6.18.
o Code points in the range U+0021 through U+007E, i.e., the ASCII7 o Code points in the range U+0021 through U+007E, i.e., the ASCII7
("K") rule defined under Section 6.11. ("K") rule defined under Section 6.11.
o Any character that has a compatibility equivalent, i.e., the o Any character that has a compatibility equivalent, i.e., the
HasCompat ("Q") category defined under Section 6.17. HasCompat ("Q") category defined under Section 6.17.
o Space characters, i.e., the Spaces ("N") category defined under o Space characters, i.e., the Spaces ("N") category defined under
Section 6.14. Section 6.14.
o Symbol characters, i.e., the Symbols ("O") category defined under o Symbol characters, i.e., the Symbols ("O") category defined under
Section 6.15. Section 6.15.
o Punctuation characters, i.e., the Punctuation ("P") category o Punctuation characters, i.e., the Punctuation ("P") category
defined under Section 6.16. defined under Section 6.16.
3.3.2. Disallowed 3.4.2. Disallowed
o Control characters, i.e., the Controls ("L") category defined o Control characters, i.e., the Controls ("L") category defined
under Section 6.12. under Section 6.12.
o Ignorable characters, i.e., the PrecisIgnorableProperties ("M") o Ignorable characters, i.e., the PrecisIgnorableProperties ("M")
category defined under Section 6.13. category defined under Section 6.13.
3.3.3. Unassigned 3.4.3. Unassigned
Any code points that are not yet assigned in the Unicode character Any code points that are not yet assigned in the Unicode character
set SHALL be considered Unassigned for purposes of the FreeformClass. set SHALL be considered Unassigned for purposes of the FreeformClass.
3.3.4. Normalization 3.4.4. Width Mapping
The Unicode normalization form MUST be specified by each application The width mapping rule MUST be specified by each application protocol
protocol that uses or subclasses the FreeformClass. that uses or subclasses the FreeformClass.
However, in accordance with [RFC5198], normalization form C (NFC) is Because one aspect of Unicode normalization form KC is width mapping,
RECOMMENDED. a PRECIS usage or subclass that uses NFKC does not need to specify
width mapping. However, if NFC is used then the usage or subclass
needs to specify whether to apply width mapping; in this case, width
mapping is in general RECOMMENDED because allowing fullwidth and
halfwidth characters to remain unmapped to their decomposition
equivalents would violate the principle of least user surprise. For
more information about the concept of width in East Asian scripts
within Unicode, see for instance [UAX11].
3.3.5. Case Mapping 3.4.5. Additional Mappings
Additional mapping rules (if any) MUST be specified by each
application protocol that uses or subclasses the FreeformClass (see
[I-D.ietf-precis-mappings]).
3.4.6. Case Mapping
The case mapping rule MUST be specified by each application protocol The case mapping rule MUST be specified by each application protocol
that uses or subclasses the FreeformClass. that uses or subclasses the FreeformClass.
In general, the combination of case preservation and case-insensitive In general, the combination of case preservation and case-insensitive
comparison of internationalized strings is NOT RECOMMENDED; instead, comparison of internationalized strings is NOT RECOMMENDED; instead,
application protocols SHOULD either (a) not preserve case but perform application protocols SHOULD either (a) not preserve case but perform
case-insensitive comparison or (b) preserve case but perform case- case-insensitive comparison or (b) preserve case but perform case-
sensitive comparison. sensitive comparison.
In order to maximize entropy and minimize the potential for false In order to maximize entropy and minimize the potential for false
positives, it is NOT RECOMMENDED for application protocols to map positives, it is NOT RECOMMENDED for application protocols to map
uppercase and titlecase code points to their lowercase equivalents uppercase and titlecase code points to their lowercase equivalents
when strings conforming to the FreeformClass, or a subclass thereof, when strings conforming to the FreeformClass, or a subclass thereof,
are used in passwords; instead, it is RECOMMENDED to preserve the are used in passwords; instead, it is RECOMMENDED to preserve the
case of all code points contained in such strings and then perform case of all code points contained in such strings and then perform
case-sensitive comparison. See also the related discussion in case-sensitive comparison. See also the related discussion in
[I-D.ietf-precis-saslprepbis]. [I-D.ietf-precis-saslprepbis].
3.3.6. Width Mapping 3.4.7. Normalization
The width mapping rule MUST be specified by each application protocol
that uses or subclasses the FreeformClass.
Because one aspect of Unicode normalization form KC is width mapping,
a PRECIS usage or subclass that uses NFKC does not need to specify
width mapping. However, if NFC is used then the usage or subclass
needs to specify whether to apply width mapping; in this case, width
mapping is in general RECOMMENDED because allowing fullwidth and
halfwidth characters to remain unmapped to their decomposition
equivalents would violate the principle of least user surprise. For
more information about the concept of width in East Asian scripts
within Unicode, see for instance [UAX11].
3.3.7. Additional Mappings The Unicode normalization form MUST be specified by each application
protocol that uses or subclasses the FreeformClass.
Additional mapping rules (if any) MUST be specified by each However, in accordance with [RFC5198], normalization form C (NFC) is
application protocol that uses or subclasses the FreeformClass. RECOMMENDED.
3.3.8. Directionality 3.4.8. Directionality
The directionality rule MUST be specified by each application The directionality rule MUST be specified by each application
protocol that uses or subclasses the FreeformClass. protocol that uses or subclasses the FreeformClass.
4. Use of PRECIS String Classes 4. Use of PRECIS String Classes
4.1. Principles 4.1. Principles
This document defines the valid, disallowed, and unassigned rules. This document defines the valid, disallowed, and unassigned rules.
Application protocols that use the PRECIS string classes MUST define Application protocols that use the PRECIS string classes MUST define
the normalization, case mapping, width mapping, and directionality the width mapping, additional mapping (if any), case mapping,
rules. Such definitions MUST at a minimum specify the following: normalization, and directionality rules. That is, such definitions
MUST at a minimum specify the following:
Width Mapping: Whether fullwidth and halfwidth code points are to be
mapped to their decomposition equivalents.
Additional Mappings: Whether additional mappings are to be applied,
such as mapping of delimiter characters, mapping of special
characters (e.g., non-ASCII space characters to ASCII space or
certain characters to nothing), and case mapping based on language
and local context (see [I-D.ietf-precis-mappings]).
Case Mapping: Whether uppercase and titlecase code points are to be
(a) preserved or (b) mapped to lowercase.
Normalization: Which Unicode normalization form (D, KD, C, or KC) is Normalization: Which Unicode normalization form (D, KD, C, or KC) is
to be applied (see [UAX15] for background information); in to be applied (see [UAX15] for background information); in
accordance with [RFC5198], NFC is RECOMMENDED. accordance with [RFC5198], NFC is RECOMMENDED.
Case Mapping: Whether uppercase and titlecase code points are to be
(a) preserved or (b) mapped to lowercase.
Additional Mappings: Whether additional mappings are to be applied,
such as mapping fullwidth and halfwidth characters to their
decomposition equivalents, mapping non-ASCII space characters to
ASCII space, or mapping certain characters to nothing.
Directionality: Whether any instance of the class that contains a Directionality: Whether any instance of the class that contains a
right-to-left code point is to be considered a right-to-left right-to-left code point is to be considered a right-to-left
string, or whether some other rule is to be applied (e.g., the string, or whether some other rule is to be applied (e.g., the
"Bidi Rule" from [RFC5893]). "Bidi Rule" from [RFC5893]).
4.2. Subclassing 4.2. Subclassing
Application protocols are allowed to subclass the PRECIS string Application protocols are allowed to subclass the PRECIS string
classes specified in this document. As the word "subclass" implies, classes specified in this document. As the word "subclass" implies,
a subclass MUST NOT add as valid any code points or character a subclass MUST NOT add as valid any code points or character
categories that are disallowed by the relevant PRECIS string class. categories that are disallowed by the relevant PRECIS string class.
However, a subclass MAY do either of the following: However, a subclass MAY do either of the following:
1. Exclude specific code points that are included in the relevant 1. Exclude specific code points that are included in the relevant
PRECIS string class. PRECIS string class.
2. Exclude characters matching certain Unicode properties (e.g., 2. Exclude characters matching certain Unicode properties (e.g.,
math symbols) that are included in the relevant PRECIS string math symbols) that are included in the relevant PRECIS string
class. class.
As a result, code points that are defined as valid for the PRECIS As a result, code points that are defined as valid for the PRECIS
string class being subclassed will be defined as disallowed for the string class being subclassed will be defined as disallowed for the
subclass. subclass.
Application protocols that subclass the PRECIS string classes MUST Application protocols that subclass the PRECIS string classes MUST
register with the IANA as described under Section 10.3. register with the IANA as described under Section 10.3.
skipping to change at page 12, line 45 skipping to change at page 14, line 19
user name" construct in the Simple Authentication and Security Layer user name" construct in the Simple Authentication and Security Layer
(SASL) [RFC4422]. Depending on the deployment, a simple user name (SASL) [RFC4422]. Depending on the deployment, a simple user name
might take the form of a user's full name (e.g., the user's personal might take the form of a user's full name (e.g., the user's personal
name followed by a space and then the user's family name). Such a name followed by a space and then the user's family name). Such a
simple user name cannot be defined as an instance of the simple user name cannot be defined as an instance of the
IdentifierClass, since space characters are not allowed in the IdentifierClass, since space characters are not allowed in the
IdentifierClass; however, it could be defined using a space-separated IdentifierClass; however, it could be defined using a space-separated
sequence of IdentifierClass instances, as in the following pseudo- sequence of IdentifierClass instances, as in the following pseudo-
ABNF [RFC5234]: ABNF [RFC5234]:
fullname = namepart [1*(1*SP namepart)] fullname = namepart [1*(1*SP namepart)]
namepart = 1*(idpoint) namepart = 1*(idpoint)
; ;
; an "idpoint" is a UTF-8 encoded Unicode code point ; an "idpoint" is a UTF-8 encoded Unicode code point
; that conforms to the PRECIS IdentifierClass ; that conforms to the PRECIS IdentifierClass
Similar techniques could be used to define many application-layer Similar techniques could be used to define many application-layer
constructs, say of the form "user@domain" or "/path/to/file". constructs, say of the form "user@domain" or "/path/to/file".
4.4. A Note about Spaces 4.4. A Note about Spaces
With regard to the IdentiferClass, the consensus of the PRECIS With regard to the IdentiferClass, the consensus of the PRECIS
Working Group was that spaces are problematic for many reasons, Working Group was that spaces are problematic for many reasons,
including: including:
skipping to change at page 14, line 17 skipping to change at page 15, line 30
information is the responsibility of the protocol specification that information is the responsibility of the protocol specification that
uses or subclasses a PRECIS string class from this document. uses or subclasses a PRECIS string class from this document.
The value of the property is to be interpreted as follows. The value of the property is to be interpreted as follows.
PROTOCOL VALID Those code points that are allowed to be used in any PROTOCOL VALID Those code points that are allowed to be used in any
PRECIS string class (IdentifierClass and FreeformClass). Code PRECIS string class (IdentifierClass and FreeformClass). Code
points with this property value are permitted for general use in points with this property value are permitted for general use in
any string class. The abbreviated term PVALID is used to refer to any string class. The abbreviated term PVALID is used to refer to
this value in the remainder of this document. this value in the remainder of this document.
SPECIFIC CLASS PROTOCOL VALID Those code points that are allowed to SPECIFIC CLASS PROTOCOL VALID Those code points that are allowed to
be used in specific string classes. Code points with this be used in specific string classes. Code points with this
property value are permitted for use in specific string classes. property value are permitted for use in specific string classes.
In the remainder of this document, the abbreviated term *_PVAL is In the remainder of this document, the abbreviated term *_PVAL is
used, where * = (NAME | FREE), i.e., either FREE_PVAL or used, where * = (NAME | FREE), i.e., either FREE_PVAL or
SAFE_PVAL. SAFE_PVAL.
CONTEXTUAL RULE REQUIRED Some characteristics of the character, such CONTEXTUAL RULE REQUIRED Some characteristics of the character, such
as its being invisible in certain contexts or problematic in as its being invisible in certain contexts or problematic in
others, require that it not be used in labels unless specific others, require that it not be used in labels unless specific
other characters or properties are present. The abbreviated term other characters or properties are present. The abbreviated term
CONTEXT is used to refer to this value in the remainder of this CONTEXT is used to refer to this value in the remainder of this
document. As in IDNA2008, there are two subdivisions of document. As in IDNA2008, there are two subdivisions of
CONTEXTUAL RULE REQUIRED, the first for Join_controls (called CONTEXTUAL RULE REQUIRED, the first for Join_controls (called
CONTEXTJ) and the second for other characters (called CONTEXTO). CONTEXTJ) and the second for other characters (called CONTEXTO).
DISALLOWED Those code points that must not permitted in any PRECIS DISALLOWED Those code points that must not permitted in any PRECIS
string class. string class.
SPECIFIC CLASS DISALLOWED Those code points that are not to be SPECIFIC CLASS DISALLOWED Those code points that are not to be
included in a specific string class. Code points with this included in a specific string class. Code points with this
property value are not permitted in one of the string classes but property value are not permitted in one of the string classes but
might be permitted in others. In the remainder of this document, might be permitted in others. In the remainder of this document,
the abbreviated term *_DIS is used, where * = (NAME | FREE), i.e., the abbreviated term *_DIS is used, where * = (NAME | FREE), i.e.,
either FREE_DIS or SAFE_DIS. either FREE_DIS or SAFE_DIS.
UNASSIGNED Those code points that are not designated (i.e. are
UNASSIGNED Those code points that are not designated (i.e. are
unassigned) in the Unicode Standard. unassigned) in the Unicode Standard.
The mechanisms described here allow determination of the value of the The mechanisms described here allow determination of the value of the
property for future versions of Unicode (including characters added property for future versions of Unicode (including characters added
after Unicode 5.2 or 6.1 depending on the category, since some after Unicode 5.2 or 6.1 depending on the category, since some
categories in this document are reused from IDNA2008 and therefore categories in this document are reused from IDNA2008 and therefore
were defined at the time of Unicode 5.2). Changes in Unicode were defined at the time of Unicode 5.2). Changes in Unicode
properties that do not affect the outcome of this process do not properties that do not affect the outcome of this process do not
affect this framework. For example, a character can have its Unicode affect this framework. For example, a character can have its Unicode
General_Category value [UNICODE] change from So to Sm, or from Lo to General_Category value [UNICODE] change from So to Sm, or from Lo to
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[RFC5226]. [RFC5226].
10.2. PRECIS Base Classes Registry 10.2. PRECIS Base Classes Registry
IANA is requested to create a registry of PRECIS string classes. In IANA is requested to create a registry of PRECIS string classes. In
accordance with [RFC5226], the registration policy is "RFC Required". accordance with [RFC5226], the registration policy is "RFC Required".
The registration template is as follows: The registration template is as follows:
Base Class: [the name of the PRECIS string class] Base Class: [the name of the PRECIS string class]
Description: [a brief description of the PRECIS string class and its Description: [a brief description of the PRECIS string class and its
intended use, e.g., "A sequence of letters, numbers, and symbols intended use, e.g., "A sequence of letters, numbers, and symbols
that is used to identify or address a network entity."] that is used to identify or address a network entity."]
Width Mapping: [the behavioral rule for handling of width, e.g.,
Normalization: [which Unicode normalization form is applied, e.g., "Map fullwidth and halfwidth characters to their decomposition
"NFC"; or "Application Specific" if to be defined by protocols equivalents."]
Additional Mappings: [any additional mappings are required or
recommended, e.g., "Map non-ASCII space characters to ASCII
space."; or "Application Specific" if to be defined by protocols
that use the PRECIS string class] that use the PRECIS string class]
Case Mapping: [the behavioral rule for handling of case, e.g., "Map Case Mapping: [the behavioral rule for handling of case, e.g., "Map
uppercase and titlecase characters to lowercase."; or "Application uppercase and titlecase characters to lowercase."; or "Application
Specific" if to be defined by protocols that use the PRECIS string Specific" if to be defined by protocols that use the PRECIS string
class] class]
Normalization: [which Unicode normalization form is applied, e.g.,
Additional Mappings: [any additional mappings are required or "NFC"; or "Application Specific" if to be defined by protocols
recommended, e.g., "Map non-ASCII space characters to ASCII
space."; or "Application Specific" if to be defined by protocols
that use the PRECIS string class] that use the PRECIS string class]
Directionality: [the behavioral rule for handling of right-to-left Directionality: [the behavioral rule for handling of right-to-left
code points, e.g., "The 'Bidi Rule' defined in RFC 5893 applies."; code points, e.g., "The 'Bidi Rule' defined in RFC 5893 applies.";
or "Application Specific" if to be defined by protocols that use or "Application Specific" if to be defined by protocols that use
the PRECIS string class] the PRECIS string class]
Specification: [the RFC number] Specification: [the RFC number]
The initial registrations are as follows: The initial registrations are as follows:
Base Class: FreeformClass. Base Class: FreeformClass.
Description: A sequence of letters, numbers, symbols, spaces, and Description: A sequence of letters, numbers, symbols, spaces, and
other code points that is used for free-form strings. other code points that is used for free-form strings.
Normalization: Application Specific. Width Mapping: Application Specific.
Case Mapping: Application Specific.
Additional Mappings: Application Specific. Additional Mappings: Application Specific.
Case Mapping: Application Specific.
Normalization: Application Specific.
Directionality: Application Specific. Directionality: Application Specific.
Specification: RFC XXXX. [Note to RFC Editor: please change XXXX to Specification: RFC XXXX. [Note to RFC Editor: please change XXXX to
the number issued for this specification.] the number issued for this specification.]
Base Class: IdentifierClass. Base Class: IdentifierClass.
Description: A sequence of letters, numbers, and symbols that is Description: A sequence of letters, numbers, and symbols that is
used to identify or address a network entity. used to identify or address a network entity.
Normalization: Application Specific. Width Mapping: Application Specific.
Case Mapping: Application Specific.
Additional Mappings: Application Specific. Additional Mappings: Application Specific.
Case Mapping: Application Specific.
Normalization: Application Specific.
Directionality: Application Specific. Directionality: Application Specific.
Specification: RFC XXXX. [Note to RFC Editor: please change XXXX to Specification: RFC XXXX. [Note to RFC Editor: please change XXXX to
the number issued for this specification.] the number issued for this specification.]
10.3. PRECIS Subclasses Registry 10.3. PRECIS Subclasses Registry
IANA is requested to create a registry of subclasses that use the IANA is requested to create a registry of subclasses that use the
PRECIS string classes. In accordance with [RFC5226], the PRECIS string classes. In accordance with [RFC5226], the
registration policy is "Expert Review". This policy was chosen in registration policy is "Expert Review". This policy was chosen in
order to ensure that "customers" of PRECIS receive appropriate order to ensure that "customers" of PRECIS receive appropriate
skipping to change at page 29, line 32 skipping to change at page 30, line 7
Specification: [a pointer to relevant documentation, such as an RFC Specification: [a pointer to relevant documentation, such as an RFC
or Internet-Draft] or Internet-Draft]
In order to request a review, the registrant shall send a completed In order to request a review, the registrant shall send a completed
template to the precis@ietf.org list or its designated successor. template to the precis@ietf.org list or its designated successor.
Factors to focus on while reviewing subclass registrations include Factors to focus on while reviewing subclass registrations include
the following: the following:
o Is the problem well-defined? o Is the problem well-defined?
o Is it clear what applications will use this subclass? o Is it clear what applications will use this subclass?
o Would an existing PRECIS string class or subclass solve the o Would an existing PRECIS string class or subclass solve the
problem? problem?
o Are the defined exclusions a reasonable solution to the problem o Are the defined exclusions a reasonable solution to the problem
for the relevant applications? for the relevant applications?
o Is the subclass clearly defined? o Is the subclass clearly defined?
o Does the subclass reduce the degree to which human users could be o Does the subclass reduce the degree to which human users could be
surprised by application behavior (the "principle of least user surprised by application behavior (the "principle of least user
surprise")? surprise")?
o Is the subclass based on an appropriate dividing line between user o Is the subclass based on an appropriate dividing line between user
interface (culture, context, intent, locale, device limitations, interface (culture, context, intent, locale, device limitations,
etc.) and the use of conformant strings in protocol elements? etc.) and the use of conformant strings in protocol elements?
o Does the subclass introduce any new security concerns (e.g., false o Does the subclass introduce any new security concerns (e.g., false
positives for authentication or authorization)? positives for authentication or authorization)?
10.4. PRECIS Usage Registry 10.4. PRECIS Usage Registry
IANA is requested to create a registry of application protocols that IANA is requested to create a registry of application protocols that
use the PRECIS string classes. The registry will include one entry use the PRECIS string classes. The registry will include one entry
for each use (e.g., if a protocol uses both the IdentifierClass and for each use (e.g., if a protocol uses both the IdentifierClass and
the FreeformClass then the specification for that protocol would the FreeformClass then the specification for that protocol would
submit two registrations). In accordance with [RFC5226], the submit two registrations). In accordance with [RFC5226], the
skipping to change at page 30, line 24 skipping to change at page 30, line 38
submit two registrations). In accordance with [RFC5226], the submit two registrations). In accordance with [RFC5226], the
registration policy is "Expert Review". This policy was chosen in registration policy is "Expert Review". This policy was chosen in
order to ensure that "customers" of PRECIS receive appropriate order to ensure that "customers" of PRECIS receive appropriate
guidance regarding the sometimes complex and subtle guidance regarding the sometimes complex and subtle
internationalization issues related to use of PRECIS string classes. internationalization issues related to use of PRECIS string classes.
The registration template is as follows: The registration template is as follows:
Applicability: [the specific protocol elements to which this usage Applicability: [the specific protocol elements to which this usage
applies, e.g., "Localparts in XMPP addresses."] applies, e.g., "Localparts in XMPP addresses."]
Base Class: [the PRECIS string class that is being used or Base Class: [the PRECIS string class that is being used or
subclassed] subclassed]
Subclass: [whether the protocol has defined a subclass of the PRECIS Subclass: [whether the protocol has defined a subclass of the PRECIS
string class and, if so, the name of the subclass, e.g., "Yes, string class and, if so, the name of the subclass, e.g., "Yes,
LocalpartIdentifierClass."] LocalpartIdentifierClass."]
Replaces: [the Stringprep profile that this PRECIS usage replaces, Replaces: [the Stringprep profile that this PRECIS usage replaces,
if any] if any]
Normalization: [which Unicode normalization form is applied, e.g.,
"NFC"]
Case Mapping: [the behavioral rule for handling of case, e.g., "Map
uppercase and titlecase characters to lowercase."]
Width Mapping: [the behavioral rule for handling of width, e.g., Width Mapping: [the behavioral rule for handling of width, e.g.,
"Map fullwidth and halfwidth characters to their decomposition "Map fullwidth and halfwidth characters to their decomposition
equivalents."] equivalents."]
Additional Mappings: [any additional mappings are required or Additional Mappings: [any additional mappings are required or
recommended, e.g., "Map non-ASCII space characters to ASCII recommended, e.g., "Map non-ASCII space characters to ASCII
space."] space."]
Case Mapping: [the behavioral rule for handling of case, e.g., "Map
uppercase and titlecase characters to lowercase."]
Normalization: [which Unicode normalization form is applied, e.g.,
"NFC"]
Directionality: [the behavioral rule for handling of right-to-left Directionality: [the behavioral rule for handling of right-to-left
code points, e.g., "The 'Bidi Rule' defined in RFC 5893 applies."] code points, e.g., "The 'Bidi Rule' defined in RFC 5893 applies."]
Specification: [a pointer to relevant documentation, such as an RFC Specification: [a pointer to relevant documentation, such as an RFC
or Internet-Draft] or Internet-Draft]
In order to request a review, the registrant shall send a completed In order to request a review, the registrant shall send a completed
template to the precis@ietf.org list or its designated successor. template to the precis@ietf.org list or its designated successor.
Factors to focus on while reviewing usage registrations include the Factors to focus on while reviewing usage registrations include the
following: following:
o Does the specification define what kinds of applications are o Does the specification define what kinds of applications are
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or Internet-Draft] or Internet-Draft]
In order to request a review, the registrant shall send a completed In order to request a review, the registrant shall send a completed
template to the precis@ietf.org list or its designated successor. template to the precis@ietf.org list or its designated successor.
Factors to focus on while reviewing usage registrations include the Factors to focus on while reviewing usage registrations include the
following: following:
o Does the specification define what kinds of applications are o Does the specification define what kinds of applications are
involved and the protocol elements to which this usage applies? involved and the protocol elements to which this usage applies?
o Is there a PRECIS string class or subclass that would be more o Is there a PRECIS string class or subclass that would be more
appropriate to use? appropriate to use?
o Are the normalization, case mapping, width mapping, additional o Are the normalization, case mapping, width mapping, additional
mapping, and directionality rules appropriate for the intended mapping, and directionality rules appropriate for the intended
use? use?
o Does the usage reduce the degree to which human users could be o Does the usage reduce the degree to which human users could be
surprised by application behavior (the "principle of least user surprised by application behavior (the "principle of least user
surprise")? surprise")?
o Is the usage based on an appropriate dividing line between user o Is the usage based on an appropriate dividing line between user
interface (culture, context, intent, locale, device limitations, interface (culture, context, intent, locale, device limitations,
etc.) and the use of conformant strings in protocol elements? etc.) and the use of conformant strings in protocol elements?
o Does the usage introduce any new security concerns (e.g., false o Does the usage introduce any new security concerns (e.g., false
positives for authentication or authorization)? positives for authentication or authorization)?
11. Interoperability Considerations 11. Interoperability Considerations
Although strings that are consumed in PRECIS-based application Although strings that are consumed in PRECIS-based application
protocols are often encoded using UTF-8 [RFC3629], the exact encoding protocols are often encoded using UTF-8 [RFC3629], the exact encoding
is a matter for the application protocol that reuses PRECIS, not for is a matter for the application protocol that reuses PRECIS, not for
the PRECIS framework. the PRECIS framework.
skipping to change at page 32, line 4 skipping to change at page 32, line 8
It is known that some existing systems are unable to support the full It is known that some existing systems are unable to support the full
Unicode character set, or even any characters outside the ASCII Unicode character set, or even any characters outside the ASCII
range. If two (or more) applications need to interoperate when range. If two (or more) applications need to interoperate when
exchanging data (e.g., for the purpose of authenticating a username exchanging data (e.g., for the purpose of authenticating a username
or password), they will naturally need have in common at least one or password), they will naturally need have in common at least one
coded character set (as defined by [RFC6365]). Establishing such a coded character set (as defined by [RFC6365]). Establishing such a
baseline is a matter for the application protocol that reuses PRECIS, baseline is a matter for the application protocol that reuses PRECIS,
not for the PRECIS framework. not for the PRECIS framework.
12. References 12. References
12.1. Normative References 12.1. Normative References
[I-D.ietf-precis-mappings]
Yoneya, Y. and T. NEMOTO, "Mapping characters for precis
classes", draft-ietf-precis-mappings-01 (work in
progress), December 2012.
[RFC20] Cerf, V., "ASCII format for network interchange", RFC 20, [RFC20] Cerf, V., "ASCII format for network interchange", RFC 20,
October 1969. October 1969.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5198] Klensin, J. and M. Padlipsky, "Unicode Format for Network [RFC5198] Klensin, J. and M. Padlipsky, "Unicode Format for Network
Interchange", RFC 5198, March 2008. Interchange", RFC 5198, March 2008.
[UNICODE] The Unicode Consortium, "The Unicode Standard, Version [UNICODE] The Unicode Consortium, "The Unicode Standard, Version
skipping to change at page 32, line 33 skipping to change at page 32, line 43
Purposes", draft-iab-identifier-comparison-09 (work in Purposes", draft-iab-identifier-comparison-09 (work in
progress), March 2013. progress), March 2013.
[I-D.ietf-precis-nickname] [I-D.ietf-precis-nickname]
Saint-Andre, P., "Preparation and Comparison of Saint-Andre, P., "Preparation and Comparison of
Nicknames", draft-ietf-precis-nickname-05 (work in Nicknames", draft-ietf-precis-nickname-05 (work in
progress), November 2012. progress), November 2012.
[I-D.ietf-precis-saslprepbis] [I-D.ietf-precis-saslprepbis]
Saint-Andre, P. and A. Melnikov, "Username and Password Saint-Andre, P. and A. Melnikov, "Username and Password
Preparation Algorithms", draft-ietf-precis-saslprepbis-00 Preparation Algorithms", draft-ietf-precis-saslprepbis-01
(work in progress), February 2012. (work in progress), March 2013.
[I-D.ietf-xmpp-6122bis] [I-D.ietf-xmpp-6122bis]
Saint-Andre, P., "Extensible Messaging and Presence Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Address Format", draft-ietf-xmpp- Protocol (XMPP): Address Format",
6122bis-05 (work in progress), November 2013. draft-ietf-xmpp-6122bis-06 (work in progress), March 2013.
[RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson, [RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson,
"Remote Authentication Dial In User Service (RADIUS)", RFC "Remote Authentication Dial In User Service (RADIUS)",
2865, June 2000. RFC 2865, June 2000.
[RFC3454] Hoffman, P. and M. Blanchet, "Preparation of [RFC3454] Hoffman, P. and M. Blanchet, "Preparation of
Internationalized Strings ("stringprep")", RFC 3454, Internationalized Strings ("stringprep")", RFC 3454,
December 2002. December 2002.
[RFC3490] Faltstrom, P., Hoffman, P., and A. Costello, [RFC3490] Faltstrom, P., Hoffman, P., and A. Costello,
"Internationalizing Domain Names in Applications (IDNA)", "Internationalizing Domain Names in Applications (IDNA)",
RFC 3490, March 2003. RFC 3490, March 2003.
[RFC3491] Hoffman, P. and M. Blanchet, "Nameprep: A Stringprep [RFC3491] Hoffman, P. and M. Blanchet, "Nameprep: A Stringprep
Profile for Internationalized Domain Names (IDN)", RFC Profile for Internationalized Domain Names (IDN)",
3491, March 2003. RFC 3491, March 2003.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003. 10646", STD 63, RFC 3629, November 2003.
[RFC4422] Melnikov, A. and K. Zeilenga, "Simple Authentication and [RFC4422] Melnikov, A. and K. Zeilenga, "Simple Authentication and
Security Layer (SASL)", RFC 4422, June 2006. Security Layer (SASL)", RFC 4422, June 2006.
[RFC4510] Zeilenga, K., "Lightweight Directory Access Protocol [RFC4510] Zeilenga, K., "Lightweight Directory Access Protocol
(LDAP): Technical Specification Road Map", RFC 4510, June (LDAP): Technical Specification Road Map", RFC 4510,
2006. June 2006.
[RFC4690] Klensin, J., Faltstrom, P., Karp, C., IAB, "Review and [RFC4690] Klensin, J., Faltstrom, P., Karp, C., and IAB, "Review and
Recommendations for Internationalized Domain Names Recommendations for Internationalized Domain Names
(IDNs)", RFC 4690, September 2006. (IDNs)", RFC 4690, September 2006.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226, IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008. May 2008.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008. Specifications: ABNF", STD 68, RFC 5234, January 2008.
skipping to change at page 34, line 37 skipping to change at page 34, line 47
<http://unicode.org/reports/tr9/>. <http://unicode.org/reports/tr9/>.
[UTR36] The Unicode Consortium, "Unicode Technical Report #36: [UTR36] The Unicode Consortium, "Unicode Technical Report #36:
Unicode Security Considerations", July 2012, Unicode Security Considerations", July 2012,
<http://unicode.org/reports/tr36/>. <http://unicode.org/reports/tr36/>.
[UTR39] The Unicode Consortium, "Unicode Technical Report #39: [UTR39] The Unicode Consortium, "Unicode Technical Report #39:
Unicode Security Mechanisms", July 2012, Unicode Security Mechanisms", July 2012,
<http://unicode.org/reports/tr39/>. <http://unicode.org/reports/tr39/>.
URIs
[1] <http://unicode.org/Public/UNIDATA/PropertyAliases.txt>
[2] <http://unicode.org/Public/UNIDATA/DerivedCoreProperties.txt>
Appendix A. Codepoint Table Appendix A. Codepoint Table
WARNING: The following table is incomplete and very likely contains WARNING: The following table is incomplete and very likely contains
errors! errors!
If one applies the property calculation rules from Section 7 to the If one applies the property calculation rules from Section 7 to the
code points 0x0000 to 0x10FFFF in Unicode 6.1, the result is as shown code points 0x0000 to 0x10FFFF in Unicode 6.1, the result is as shown
in the following table, in Unicode Character Database (UCD) format. in the following table, in Unicode Character Database (UCD) format.
The columns of the table are as follows: The columns of the table are as follows:
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