PRECIS P. Saint-Andre
Internet-Draft Cisco Systems, Inc.
Obsoletes: 3454 (if approved) M. Blanchet
Intended status: Standards Track Viagenie
Expires: June 8, 2014 December 5, 2013
PRECIS Framework: Preparation and Comparison of Internationalized
Strings in Application Protocols
draft-ietf-precis-framework-13
Abstract
Application protocols using Unicode characters in protocol strings
need to properly prepare such strings in order 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 and comparison of
internationalized strings ("PRECIS") in a way that depends on the
properties of Unicode characters and thus is 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 3454.
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 June 8, 2014.
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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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
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. String Classes . . . . . . . . . . . . . . . . . . . . . . . . 6
3.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.2. IdentifierClass . . . . . . . . . . . . . . . . . . . . . 7
3.3. FreeformClass . . . . . . . . . . . . . . . . . . . . . . 9
4. Profiles . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.1. Principles . . . . . . . . . . . . . . . . . . . . . . . . 10
4.2. Building Application-Layer Constructs . . . . . . . . . . 12
4.3. A Note about Spaces . . . . . . . . . . . . . . . . . . . 13
5. Order of Operations . . . . . . . . . . . . . . . . . . . . . 14
6. Code Point Properties . . . . . . . . . . . . . . . . . . . . 14
7. Category Definitions Used to Calculate Derived Property . . . 16
7.1. LetterDigits (A) . . . . . . . . . . . . . . . . . . . . . 16
7.2. Unstable (B) . . . . . . . . . . . . . . . . . . . . . . . 17
7.3. IgnorableProperties (C) . . . . . . . . . . . . . . . . . 17
7.4. IgnorableBlocks (D) . . . . . . . . . . . . . . . . . . . 17
7.5. LDH (E) . . . . . . . . . . . . . . . . . . . . . . . . . 17
7.6. Exceptions (F) . . . . . . . . . . . . . . . . . . . . . . 17
7.7. BackwardCompatible (G) . . . . . . . . . . . . . . . . . . 19
7.8. JoinControl (H) . . . . . . . . . . . . . . . . . . . . . 19
7.9. OldHangulJamo (I) . . . . . . . . . . . . . . . . . . . . 19
7.10. Unassigned (J) . . . . . . . . . . . . . . . . . . . . . . 20
7.11. ASCII7 (K) . . . . . . . . . . . . . . . . . . . . . . . . 20
7.12. Controls (L) . . . . . . . . . . . . . . . . . . . . . . . 20
7.13. PrecisIgnorableProperties (M) . . . . . . . . . . . . . . 20
7.14. Spaces (N) . . . . . . . . . . . . . . . . . . . . . . . . 21
7.15. Symbols (O) . . . . . . . . . . . . . . . . . . . . . . . 21
7.16. Punctuation (P) . . . . . . . . . . . . . . . . . . . . . 21
7.17. HasCompat (Q) . . . . . . . . . . . . . . . . . . . . . . 21
7.18. OtherLetterDigits (R) . . . . . . . . . . . . . . . . . . 21
8. Calculation of the Derived Property . . . . . . . . . . . . . 21
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23
9.1. PRECIS Derived Property Value Registry . . . . . . . . . . 23
9.2. PRECIS Base Classes Registry . . . . . . . . . . . . . . . 23
9.3. PRECIS Profiles Registry . . . . . . . . . . . . . . . . . 24
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10. Security Considerations . . . . . . . . . . . . . . . . . . . 25
10.1. General Issues . . . . . . . . . . . . . . . . . . . . . . 25
10.2. Use of the IdentifierClass . . . . . . . . . . . . . . . . 25
10.3. Use of the FreeformClass . . . . . . . . . . . . . . . . . 26
10.4. Local Character Set Issues . . . . . . . . . . . . . . . . 26
10.5. Visually Similar Characters . . . . . . . . . . . . . . . 26
10.6. Security of Passwords . . . . . . . . . . . . . . . . . . 28
11. Interoperability Considerations . . . . . . . . . . . . . . . 29
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 29
12.1. Normative References . . . . . . . . . . . . . . . . . . . 29
12.2. Informative References . . . . . . . . . . . . . . . . . . 30
Appendix A. Codepoint Table . . . . . . . . . . . . . . . . . . . 32
Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 63
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 63
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1. Introduction
As described in the problem statement for the preparation and
comparison of internationalized strings ("PRECIS") [RFC6885], many
IETF protocols have used the Stringprep framework [RFC3454] as the
basis for preparing and comparing protocol strings that contain
Unicode characters [UNICODE] outside the ASCII range [RFC20]. The
Stringprep framework was developed during work on the original
technology for internationalized domain names (IDNs), here called
"IDNA2003" [RFC3490], and Nameprep [RFC3491] was the Stringprep
profile for IDNs. At the time, Stringprep was designed as a general
framework so that other application protocols could define their own
Stringprep profiles for the preparation and comparison of strings and
identifiers. Indeed, a number of application protocols defined such
profiles.
After the publication of [RFC3454] in 2002, several significant
issues arose with the use of Stringprep in the IDN case, as
documented in the IAB's recommendations regarding IDNs [RFC4690]
(most significantly, Stringprep was tied to Unicode version 3.2).
Therefore, the newer IDNA specifications, here called "IDNA2008"
([RFC5890], [RFC5891], [RFC5892], [RFC5893], [RFC5894]), no longer
use Stringprep and Nameprep. This migration away from Stringprep for
IDNs has prompted other "customers" of Stringprep to consider new
approaches to the preparation and comparison of internationalized
strings, as described in [RFC6885].
This document defines a framework for a post-Stringprep approach to
the preparation and comparison of internationalized strings in
application protocols, based on several principles:
1. Define a small set of string classes that specify the Unicode
characters (i.e., specific "code points") appropriate for common
application protocol constructs.
2. Define each PRECIS string class in terms of Unicode code points
and their properties so that an algorithm can be used to
determine whether each code point or character category is (a)
valid, (b) allowed in certain contexts, (c) disallowed, or (d)
unassigned.
3. Use an "inclusion model" such that a string class consists only
of code points that are explicitly allowed, with the result that
any code point not explicitly allowed is forbidden.
4. Enable application protocols to define profiles of the PRECIS
string classes, addressing matters such as width mapping, case
folding and other forms of character mapping, Unicode
normalization, directionality, and further excluded code points
or character categories.
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Whereas the string classes define the "baseline" code points for a
range of applications, profiling enables application protocols to
further restrict the allowable code points beyond those specified for
the relevant string class (e.g., characters with special or reserved
meaning, such as "@" and "/" when used as separators within
identifiers) and to apply the string classes in ways that are
appropriate for constructs such as usernames and passwords
[I-D.ietf-precis-saslprepbis], nicknames [I-D.ietf-precis-nickname],
the localparts of instant messaging addresses
[I-D.ietf-xmpp-6122bis], and free-form strings
[I-D.ietf-xmpp-6122bis]. Profiles are responsible for defining the
handling of right-to-left characters as well as various mapping
operations of the kind also discussed for IDNs in [RFC5895], such as
case preservation or lowercasing, Unicode normalization, mapping of
certain characters to other characters or to nothing, and mapping of
full-width and half-width characters.
It is expected that this framework will yield the following benefits:
o Application protocols will be agile with regard to Unicode
versions.
o Implementers will be able to share code point tables and software
code across application protocols, most likely by means of
software libraries.
o End users will be able to acquire more accurate expectations about
the characters that are acceptable in various contexts. Given
this more uniform set of string classes, it is also expected that
copy/paste operations between software implementing different
application protocols will be more predictable and coherent.
Although this framework is similar to IDNA2008 and borrows some of
the character categories defined in [RFC5892], it defines additional
character categories to meet the needs of common application
protocols.
The character categories and calculation rules defined under
Section 7 and Section 8 are normative and apply to all Unicode code
points. The code point table provided under Appendix A is non-
normative and merely shows, for illustrative purposes, the
consequences of the character categories and calculation rules, as
well as the resulting property values.
2. Terminology
Many important terms used in this document are defined in [RFC5890],
[RFC6365], [RFC6885], and [UNICODE]. The terms "left-to-right" (LTR)
and "right-to-left" (RTL) are defined in Unicode Standard Annex #9
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[UAX9].
As of the date of writing, the version of Unicode published by the
Unicode Consortium is 6.3; however, PRECIS is not tied to a specific
version of Unicode.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
[RFC2119].
3. String Classes
3.1. Overview
IDNA2008 essentially defines a string class of internationalized
domain name (IDN), although it does not use the term "string class".
(This document does not define a string class for domain names, and
application protocols are strongly encouraged to use IDNA2008 as the
appropriate method to prepare domain names and hostnames.) Because
the IDN string class is designed to meet the particular requirements
of the Domain Name System (DNS), additional string classes are needed
for non-DNS applications.
Starting in 2010, various "customers" of Stringprep began to discuss
the need to define a post-Stringprep approach to the preparation and
comparison of internationalized strings other than IDNs. This
community analyzed the existing Stringprep profiles and also weighed
the costs and benefits of defining a relatively small set of Unicode
characters that would minimize the potential for user confusion
caused by visually similar characters (and thus be relatively "safe")
vs. defining a much larger set of Unicode characters that would
maximize the potential for user creativity (and thus be relatively
"expressive"). As a result, the community concluded that most
existing uses could be addressed by two string classes:
IdentifierClass: a sequence of letters, numbers, and some symbols
that is used to identify or address a network entity such as a
user account, a venue (e.g., a chatroom), an information source
(e.g., a data feed), or a collection of data (e.g., a file); the
intent is that this class will minimize user confusion in a wide
variety of application protocols, with the result that safety has
been prioritized over expressiveness for this class.
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FreeformClass: a sequence of letters, numbers, symbols, spaces, and
other characters that is used for free-form strings, including
passwords as well as display elements such as human-friendly
nicknames in chatrooms; the intent is that this class will allow
nearly any Unicode character, with the result that expressiveness
has been prioritized over safety for this class (e.g., protocol
designers, application developers, service providers, and end
users might not understand or be able to enter all of the
characters that can be included in the FreeformClass).
Future specifications might define additional PRECIS string classes,
such as a class that falls somewhere between the IdentifierClass and
the FreeformClass. At this time, it is not clear how useful such a
class would be. In any case, because application developers are able
to define profiles of PRECIS string classes, a protocol needing a
construct between the IdentiferClass and the FreeformClass could
define a restricted profile of the FreeformClass if needed.
The following subsections discuss the IdentifierClass and
FreeformClass in more detail, with reference to the dimensions
described in Section 3 of [RFC6885]. Each string class is defined by
the following behavioral rules:
Valid: Defines which code points and character categories are
treated as valid input to the string.
Contextual Rule Required: Defines which code points and character
categories are treated as allowed only if the requirements of a
contextual rule are met (i.e., either CONTEXTJ or CONTEXTO).
Disallowed: Defines which code points and character categories need
to be excluded from the string.
Unassigned: Defines application behavior in the presence of code
points that are unknown (i.e., not yet designated) for the version
of Unicode used by the application.
This document defines the valid, contextual rule required,
disallowed, and unassigned rules for the IdentifierClass and
FreeformClass. As described under Section 4, profiles of these
string classes are responsible for defining the width mapping,
additional mapping, case mapping, normalization, directionality, and
exclusion rules.
3.2. IdentifierClass
Most application technologies need strings that can be used to refer
to, include, or communicate protocol strings like usernames, file
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names, data feed identifiers, and chatroom names. We group such
strings into a class called "IdentifierClass" having the following
features.
3.2.1. Valid
o Code points traditionally used as letters and numbers in writing
systems, i.e., the LetterDigits ("A") category first defined in
[RFC5892] and listed here under Section 7.1.
o Code points in the range U+0021 through U+007E, i.e., the
(printable) ASCII7 ("K") rule defined under Section 7.11. These
code points are "grandfathered" into PRECIS and thus are valid
even if they would otherwise be disallowed according to the
property-based rules specified in the next section.
Note: Although the PRECIS IdentifierClass re-uses the LetterDigits
category from IDNA2008, the range of characters allowed in the
IdentifierClass is wider than the range of characters allowed in
IDNA2008. The main reason is that IDNA2008 applies the Unstable
category before the LetterDigits category, thus disallowing uppercase
characters, whereas the IdentifierClass does not apply the Unstable
category.
3.2.2. Contextual Rule Required
o A number of characters from the Exceptions ("F") category defined
under Section 7.6 (see Section 7.6 for a full list).
o Joining characters, i.e., the JoinControl ("H") category defined
under Section 7.8.
3.2.3. Disallowed
o Old Hangul Jamo characters, i.e., the OldHangulJamo ("I") category
defined under Section 7.9.
o Control characters, i.e., the Controls ("L") category defined
under Section 7.12.
o Ignorable characters, i.e., the PrecisIgnorableProperties ("M")
category defined under Section 7.13.
o Space characters, i.e., the Spaces ("N") category defined under
Section 7.14.
o Symbol characters, i.e., the Symbols ("O") category defined under
Section 7.15.
o Punctuation characters, i.e., the Punctuation ("P") category
defined under Section 7.16.
o Any character that has a compatibility equivalent, i.e., the
HasCompat ("Q") category defined under Section 7.17. These code
points are disallowed even if they would otherwise be valid
according to the property-based rules specified in the previous
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section.
o Letters and digits other than the "traditional" letters and digits
allowed in IDNs, i.e., the OtherLetterDigits ("R") category
defined under Section 7.18.
3.2.4. Unassigned
Any code points that are not yet designated in the Unicode character
set SHALL be considered Unassigned for purposes of the
IdentifierClass, and a string containing such code points SHALL be
rejected.
3.3. FreeformClass
Some application technologies need strings that can be used in a
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-nickname]). We group such things into a class
called "FreeformClass" having the following features.
Note: Consult Section 10.6 for relevant security considerations when
strings conforming to the FreeformClass, or a profile thereof, are
used as passwords.
3.3.1. Valid
o Traditional letters and numbers, i.e., the LetterDigits ("A")
category first defined in [RFC5892] and listed here under
Section 7.1.
o Letters and digits other than the "traditional" letters and digits
allowed in IDNs, i.e., the OtherLetterDigits ("R") category
defined under Section 7.18.
o Code points in the range U+0021 through U+007E, i.e., the
(printable) ASCII7 ("K") rule defined under Section 7.11.
o Any character that has a compatibility equivalent, i.e., the
HasCompat ("Q") category defined under Section 7.17.
o Space characters, i.e., the Spaces ("N") category defined under
Section 7.14.
o Symbol characters, i.e., the Symbols ("O") category defined under
Section 7.15.
o Punctuation characters, i.e., the Punctuation ("P") category
defined under Section 7.16.
3.3.2. Contextual Rule Required
o A number of characters from the Exceptions ("F") category defined
under Section 7.6 (see Section 7.6 for a full list).
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o Joining characters, i.e., the JoinControl ("H") category defined
under Section 7.8.
3.3.3. Disallowed
o Old Hangul Jamo characters, i.e., the OldHangulJamo ("I") category
defined under Section 7.9.
o Control characters, i.e., the Controls ("L") category defined
under Section 7.12.
o Ignorable characters, i.e., the PrecisIgnorableProperties ("M")
category defined under Section 7.13.
3.3.4. Unassigned
Any code points that are not yet designated in the Unicode character
set SHALL be considered Unassigned for purposes of the FreeformClass,
and a string containing such code points SHALL be rejected.
4. Profiles
4.1. Principles
This framework document defines the valid, contextual-rule-required,
disallowed, and unassigned rules for the IdentifierClass and the
FreeformClass. A profile of a PRECIS string class MUST define the
width mapping, additional mapping (if any), case mapping,
normalization, directionality, and exclusion rules. A profile MAY
also restrict the allowable characters above and beyond the
definition of the relevant PRECIS string class (but MUST NOT add as
valid any code points or character categories that are disallowed by
the relevant PRECIS string class). These matters are discussed in
the following subsections.
Profiles of the PRECIS string classes MUST register with the IANA as
described under Section 9.3. It is RECOMMENDED for profile names to
be of the form "ProfilenameBaseClass", where the "Profilename" string
is a differentiator and "BaseClass" is the name of the PRECIS string
class being profiled; for example, the profile of the IdentifierClass
used for localparts of Jabber IDs in the Extensible Messaging and
Presence Protocol (XMPP) is named "JIDlocalIdentifierClass"
[I-D.ietf-xmpp-6122bis].
4.1.1. Width Mapping
The width mapping rule of a profile specifies whether width mapping
is performed on fullwidth and halfwidth characters, and how the
mapping is done. Typically such mapping consists of mapping
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fullwidth and halfwidth characters, i.e., code points with a
Decomposition Type of Wide or Narrow, to their decomposition
mappings; as an example, FULLWIDTH DIGIT ZERO (U+FF10) would be
mapped to DIGIT ZERO (U+0030).
The normalization form specified by a profile (see below) has an
impact on the need for width mapping. Because width mapping is
performed as a part of compatibility decomposition, a profile
employing either normalization form KD (NFKD) or normalization form
KC (NFKC) does not need to specify width mapping. However, if
Unicode normalization form C (NFC) is used then the profile 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 compatibility variants would
violate the principle of least user surprise. For more information
about the concept of width in East Asian scripts within Unicode, see
Unicode Standard Annex #11 [UAX11].
4.1.2. Additional Mappings
The additional mappings rule of a profile 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 locale or on locale and context (see
[I-D.ietf-precis-mappings]).
4.1.3. Case Mapping
The case mapping rule of a profile specifies whether 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).
If case preservation is not desired, it is RECOMMENDED to use Unicode
Default Case Folding as defined in Chapter 3 of the Unicode Standard
[UNICODE].
In order to maximize entropy and minimize the potential for false
positives, it is NOT RECOMMENDED for application protocols to map
uppercase and titlecase code points to their lowercase equivalents
when strings conforming to the FreeformClass, or a profile thereof,
are used in passwords; instead, it is RECOMMENDED to preserve the
case of all code points contained in such strings and then perform
case-sensitive comparison. See also the related discussion in
[I-D.ietf-precis-saslprepbis].
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4.1.4. Normalization
The normalization rule of a profile specifies which Unicode
normalization form (D, KD, C, or KC) is to be applied (see Unicode
Standard Annex #15 [UAX15] for background information).
In accordance with [RFC5198], normalization form C (NFC) is
RECOMMENDED.
4.1.5. Directionality
The directionality rule of a profile specifies which strings are to
be considered left-to-right (LTR) and right-to-left (RTL), and the
allowable sequences of characters in LTR and RTL strings (see Unicode
Standard Annex #9 [UAX9]); note that mixed-direction strings are not
supported, since there is currently no widely accepted and
implemented solution for the processing and display of mixed-
direction strings. Possible rules include, but are not limited to,
(a) considering any string that contains a right-to-left code point
to be a right-to-left string, or (b) applying the "Bidi Rule" from
[RFC5893].
4.1.6. Exclusions
The exclusions rule of a profile specifies whether the profile
excludes additional code points or character categories above and
beyond those excluded by the string class being profiled. That is, a
profile MAY do either of the following:
1. Exclude specific code points that are allowed by the relevant
string class.
2. Exclude characters matching certain Unicode properties (e.g.,
math symbols) that are included in the relevant PRECIS string
class.
As a result of such exclusions, code points that are defined as valid
for the PRECIS string class being profiled will be defined as
disallowed for the profile.
4.2. Building Application-Layer Constructs
Sometimes, an application-layer construct does not map in a
straightforward manner to one of the PRECIS string classes or a
profile thereof. Consider, for example, the "simple user name"
construct in the Simple Authentication and Security Layer (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 name
followed by a space and then the user's family name). Such a simple
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user name cannot be defined as an instance of the IdentifierClass or
a profile thereof, since space characters are not allowed in the
IdentifierClass; however, it could be defined using a space-separated
sequence of IdentifierClass instances, as in the following pseudo-
ABNF [RFC5234]:
fullname = namepart [1*(1*SP namepart)]
namepart = 1*(idpoint)
;
; an "idpoint" is a UTF-8 encoded Unicode code point
; that conforms to the PRECIS IdentifierClass
Similar techniques could be used to define many application-layer
constructs, say of the form "user@domain" or "/path/to/file".
4.3. A Note about Spaces
With regard to the IdentiferClass, the consensus of the PRECIS
Working Group was that spaces are problematic for many reasons,
including:
o Many Unicode characters are confusable with ASCII space.
o Even if non-ASCII space characters are mapped to ASCII space
(U+0020), space characters are often not rendered in user
interfaces, leading to the possibility that a human user might
consider a string containing spaces to be equivalent to the same
string without spaces.
o In some locales, some devices are known to generate a character
other than ASCII space (such as ZERO WIDTH JOINER, U+200D) when a
user performs an action like hit the space bar on a keyboard.
One consequence of disallowing space characters in the
IdentifierClass might be to effectively discourage the use of ASCII
space (or, even more problematically, non-ASCII space characters)
within identifiers created in newer application protocols; given the
challenges involved in properly handling space characters in
identifiers and other protocol strings, the Working Group considered
this to be a feature, not a bug.
However, the FreeformClass does allow spaces, which enables
application protocols to define profiles of the FreeformClass that
are more flexible than any profiles of the IdentifierClass. In
addition, as explained in the previous section, application protocols
can also define application-layer constructs containing spaces.
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5. Order of Operations
To ensure proper comparison, the following order of operations is
REQUIRED:
1. Width mapping
2. Optionally, additional mappings such as those 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. Behavioral rules for determining whether a code point is valid,
allowed under a contextual rule, disallowed, or unassigned
As already described, the width mapping, additional mapping, non-
local case mapping, and normalization operations are specified for
each profile, whereas the behavioral rules are specified for each
string class. Some of the logic behind this order is provided under
Section 4.1.1 and in [I-D.ietf-precis-mappings].
6. Code Point Properties
In order to implement the string classes described above, this
document does the following:
1. Reviews and classifies the collections of code points in the
Unicode character set by examining various code point properties.
2. Defines an algorithm for determining a derived property value,
which can vary depending on the string class being used by the
relevant application protocol.
This document is not intended to specify precisely how derived
property values are to be applied in protocol strings. That
information is the responsibility of the protocol specification that
uses or profiles a PRECIS string class from this document.
The value of the property is to be interpreted as follows.
PROTOCOL VALID Those code points that are allowed to be used in any
PRECIS string class (currently, IdentifierClass and
FreeformClass). Code points with this property value are
permitted for general use in any string class. The abbreviated
term "PVALID" is used to refer to this value in the remainder of
this document.
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SPECIFIC CLASS PROTOCOL VALID Those code points that are allowed to
be used in specific string classes. Code points with this
property value are permitted for use in specific string classes.
In the remainder of this document, the abbreviated term *_PVAL is
used, where * = (ID | FREE), i.e., either "FREE_PVAL" or
"ID_PVAL".
CONTEXTUAL RULE REQUIRED Some characteristics of the character, such
as its being invisible in certain contexts or problematic in
others, require that it not be used in labels unless specific
other characters or properties are present. As in IDNA2008, there
are two subdivisions of CONTEXTUAL RULE REQUIRED, the first for
Join_controls (called "CONTEXTJ") and the second for other
characters (called "CONTEXTO"). A character with the derived
property value CONTEXTJ or CONTEXTO MUST NOT be used unless an
appropriate rule has been established and the context of the
character is consistent with that rule. The most notable of the
CONTEXTUAL RULE REQUIRED characters are the Join Control
characters U+200D ZERO WIDTH JOINER and U+200C ZERO WIDTH NON-
JOINER, which have a derived property value of CONTEXTJ. See
Appendix A of [RFC5892] for more information.
DISALLOWED Those code points that are not permitted in any PRECIS
string class.
SPECIFIC CLASS DISALLOWED Those code points that are not to be
included in a specific string class. Code points with this
property value are not permitted in one of the string classes but
might be permitted in others. In the remainder of this document,
the abbreviated term *_DIS is used, where * = (ID | FREE), i.e.,
either "FREE_DIS" or "ID_DIS".
UNASSIGNED Those code points that are not designated (i.e. are
unassigned) in the Unicode Standard.
The mechanisms described here allow determination of the value of the
property for future versions of Unicode (including characters added
after Unicode 5.2 or 6.3 depending on the category, since some
categories in this document are reused from IDNA2008 and therefore
were defined at the time of Unicode 5.2). Changes in Unicode
properties that do not affect the outcome of this process therefore
do not affect this framework. For example, a character can have its
Unicode General_Category value [UNICODE] change from So to Sm, or
from Lo to Ll, without affecting the algorithm results. Moreover,
even if such changes were to result, the BackwardCompatible list
(Section 7.7) can be adjusted to ensure the stability of the results.
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7. Category Definitions Used to Calculate Derived Property
The derived property obtains its value based on a two-step procedure:
1. Characters are placed in one or more character categories either
(1) based on core properties defined by the Unicode Standard or
(2) by treating the code point as an exception and addressing the
code point based on its code point value. These categories are
not mutually exclusive.
2. Set operations are used with these categories to determine the
values for a property specific to a given string class. These
operations are specified under Section 8.
(Note: Unicode property names and property value names might have
short abbreviations, such as "gc" for the General_Category property
and "Ll" for the Lowercase_Letter property value of the gc property.)
In the following specification of character categories, the operation
that returns the value of a particular Unicode character property for
a code point is designated by using the formal name of that property
(from the Unicode PropertyAliases.txt [1]) followed by '(cp)' for
"code point". For example, the value of the General_Category
property for a code point is indicated by General_Category(cp).
The first ten categories (A-J) shown below were previously defined
for IDNA2008 and are copied directly from [RFC5892]. Some of these
categories are reused in PRECIS and some of them are not; however,
the lettering of categories is retained to prevent overlap and to
ease implementation of both IDNA2008 and PRECIS in a single software
application. The next eight categories (K-R) are specific to PRECIS.
7.1. LetterDigits (A)
Note: This category is defined in [RFC5892] and copied here for use
in PRECIS.
A: General_Category(cp) is in {Ll, Lu, Lm, Lo, Mn, Mc, Nd}
These rules identify characters commonly used in mnemonics and often
informally described as "language characters".
For more information, see Chapter 4 of the Unicode Standard
[UNICODE].
The categories used in this rule are:
o Ll - Lowercase_Letter
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o Lu - Uppercase_Letter
o Lm - Modifier_Letter
o Lo - Other_Letter
o Mn - Nonspacing_Mark
o Mc - Spacing_Mark
o Nd - Decimal_Number
7.2. Unstable (B)
Note: This category is defined in [RFC5892] but not used in PRECIS.
7.3. IgnorableProperties (C)
Note: This category is defined in [RFC5892] but not used in PRECIS.
See the "PrecisIgnorableProperties (M)" category below for a more
inclusive category used in PRECIS identifiers.
7.4. IgnorableBlocks (D)
Note: This category is defined in [RFC5892] but not used in PRECIS.
7.5. LDH (E)
Note: This category is defined in [RFC5892] but not used in PRECIS.
See the "ASCII7 (K)" category below for a more inclusive category
used in PRECIS identifiers.
7.6. Exceptions (F)
Note: This category is defined in [RFC5892] and used in PRECIS to
ensure consistent treatment of the relevant code points.
F: cp is in {00B7, 00DF, 0375, 03C2, 05F3, 05F4, 0640, 0660,
0661, 0662, 0663, 0664, 0665, 0666, 0667, 0668,
0669, 06F0, 06F1, 06F2, 06F3, 06F4, 06F5, 06F6,
06F7, 06F8, 06F9, 06FD, 06FE, 07FA, 0F0B, 3007,
302E, 302F, 3031, 3032, 3033, 3034, 3035, 303B,
30FB}
This category explicitly lists code points for which the category
cannot be assigned using only the core property values that exist in
the Unicode Standard. The values are according to the table below:
PVALID -- Would otherwise have been DISALLOWED
00DF; PVALID # LATIN SMALL LETTER SHARP S
03C2; PVALID # GREEK SMALL LETTER FINAL SIGMA
06FD; PVALID # ARABIC SIGN SINDHI AMPERSAND
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06FE; PVALID # ARABIC SIGN SINDHI POSTPOSITION MEN
0F0B; PVALID # TIBETAN MARK INTERSYLLABIC TSHEG
3007; PVALID # IDEOGRAPHIC NUMBER ZERO
CONTEXTO -- Would otherwise have been DISALLOWED
00B7; CONTEXTO # MIDDLE DOT
0375; CONTEXTO # GREEK LOWER NUMERAL SIGN (KERAIA)
05F3; CONTEXTO # HEBREW PUNCTUATION GERESH
05F4; CONTEXTO # HEBREW PUNCTUATION GERSHAYIM
30FB; CONTEXTO # KATAKANA MIDDLE DOT
CONTEXTO -- Would otherwise have been PVALID
0660; CONTEXTO # ARABIC-INDIC DIGIT ZERO
0661; CONTEXTO # ARABIC-INDIC DIGIT ONE
0662; CONTEXTO # ARABIC-INDIC DIGIT TWO
0663; CONTEXTO # ARABIC-INDIC DIGIT THREE
0664; CONTEXTO # ARABIC-INDIC DIGIT FOUR
0665; CONTEXTO # ARABIC-INDIC DIGIT FIVE
0666; CONTEXTO # ARABIC-INDIC DIGIT SIX
0667; CONTEXTO # ARABIC-INDIC DIGIT SEVEN
0668; CONTEXTO # ARABIC-INDIC DIGIT EIGHT
0669; CONTEXTO # ARABIC-INDIC DIGIT NINE
06F0; CONTEXTO # EXTENDED ARABIC-INDIC DIGIT ZERO
06F1; CONTEXTO # EXTENDED ARABIC-INDIC DIGIT ONE
06F2; CONTEXTO # EXTENDED ARABIC-INDIC DIGIT TWO
06F3; CONTEXTO # EXTENDED ARABIC-INDIC DIGIT THREE
06F4; CONTEXTO # EXTENDED ARABIC-INDIC DIGIT FOUR
06F5; CONTEXTO # EXTENDED ARABIC-INDIC DIGIT FIVE
06F6; CONTEXTO # EXTENDED ARABIC-INDIC DIGIT SIX
06F7; CONTEXTO # EXTENDED ARABIC-INDIC DIGIT SEVEN
06F8; CONTEXTO # EXTENDED ARABIC-INDIC DIGIT EIGHT
06F9; CONTEXTO # EXTENDED ARABIC-INDIC DIGIT NINE
DISALLOWED -- Would otherwise have been PVALID
0640; DISALLOWED # ARABIC TATWEEL
07FA; DISALLOWED # NKO LAJANYALAN
302E; DISALLOWED # HANGUL SINGLE DOT TONE MARK
302F; DISALLOWED # HANGUL DOUBLE DOT TONE MARK
3031; DISALLOWED # VERTICAL KANA REPEAT MARK
3032; DISALLOWED # VERTICAL KANA REPEAT WITH VOICED SOUND MARK
3033; DISALLOWED # VERTICAL KANA REPEAT MARK UPPER HALF
3034; DISALLOWED # VERTICAL KANA REPEAT WITH VOICED SOUND MARK
UPPER HA
3035; DISALLOWED # VERTICAL KANA REPEAT MARK LOWER HALF
303B; DISALLOWED # VERTICAL IDEOGRAPHIC ITERATION MARK
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7.7. BackwardCompatible (G)
Note: This category is defined in [RFC5892] and copied here for use
in PRECIS. Because of how the PRECIS string classes are defined,
only changes that would result in code points being added to or
removed from the LetterDigits ("A") category would result in
backward-incompatible modifications to code point assignments.
Therefore, management of this category is handled via the processes
specified in [RFC5892].
G: cp is in {}
This category includes the code points for which property values in
versions of Unicode after 5.2 have changed in such a way that the
derived property value would no longer be PVALID or DISALLOWED. If
changes are made to future versions of Unicode so that code points
might change property value from PVALID or DISALLOWED, then this
table can be updated and keep special exception values so that the
property values for code points stay stable.
7.8. JoinControl (H)
Note: This category is defined in [RFC5892] and copied here for use
in PRECIS.
H: Join_Control(cp) = True
This category consists of Join Control characters (i.e., they are not
in LetterDigits (Section 7.1) but are still required in strings under
some circumstances).
7.9. OldHangulJamo (I)
Note: This category is defined in [RFC5892] and copied here for use
in PRECIS.
I: Hangul_Syllable_Type(cp) is in {L, V, T}
This category consists of all conjoining Hangul Jamo (Leading Jamo,
Vowel Jamo, and Trailing Jamo).
Elimination of conjoining Hangul Jamos from the set of PVALID
characters results in restricting the set of Korean PVALID characters
just to preformed, modern Hangul syllable characters. Old Hangul
syllables, which are spelled with sequences of conjoining Hangul
Jamos, are not PVALID for string classes.
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7.10. Unassigned (J)
Note: This category is defined in [RFC5892] and copied here for use
in PRECIS.
J: General_Category(cp) is in {Cn} and
Noncharacter_Code_Point(cp) = False
This category consists of code points in the Unicode character set
that are not (yet) designated. Implementers might want to keep in
mind that the Unicode Standard distinguishes between 'unassigned code
points' and 'unassigned characters'. The unassigned code points are
all but (Cn - Noncharacters), whereas the unassigned characters are
all but (Cn + Cs).
7.11. ASCII7 (K)
This PRECIS-specific category consists of all printable, non-space
characters from the 7-bit ASCII range. By applying this category,
the algorithm specified under Section 8 exempts these characters from
other rules that might be applied during PRECIS processing, on the
assumption that these code points are in such wide use that
disallowing them would be counter-productive.
K: cp is in {0021..007E}
7.12. Controls (L)
L: Control(cp) = True
7.13. PrecisIgnorableProperties (M)
This PRECIS-specific category is used to group code points that are
discouraged from use in PRECIS string classes.
M: Default_Ignorable_Code_Point(cp) = True or
Noncharacter_Code_Point(cp) = True
The definition for Default_Ignorable_Code_Point can be found in the
DerivedCoreProperties.txt [2] file, and at the time of Unicode 6.3 is
as follows:
Other_Default_Ignorable_Code_Point
+ Cf (Format characters)
+ Variation_Selector
- White_Space
- FFF9..FFFB (Annotation Characters)
- 0600..0604, 06DD, 070F, 110BD (exceptional Cf characters
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that should be visible)
7.14. Spaces (N)
This PRECIS-specific category is used to group code points that are
space characters.
N: General_Category(cp) is in {Zs}
7.15. Symbols (O)
This PRECIS-specific category is used to group code points that are
symbols.
O: General_Category(cp) is in {Sm, Sc, Sk, So}
7.16. Punctuation (P)
This PRECIS-specific category is used to group code points that are
punctuation characters.
P: General_Category(cp) is in {Pc, Pd, Ps, Pe, Pi, Pf, Po}
7.17. HasCompat (Q)
This PRECIS-specific category is used to group code points that have
compatibility equivalents as explained in Chapter 2 and Chapter 3 of
the Unicode Standard [UNICODE].
Q: toNFKC(cp) != cp
The toNFKC() operation returns the code point in normalization form
KC. For more information, see Section 5 of Unicode Standard Annex
#15 [UAX15].
7.18. OtherLetterDigits (R)
This PRECIS-specific category is used to group code points that are
letters and digits other than the "traditional" letters and digits
grouped under the LetterDigits (A) class (see Section 7.1).
R: General_Category(cp) is in {Lt, Nl, No, Me}
8. Calculation of the Derived Property
Possible values of the derived property are:
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o PVALID
o ID_PVAL
o FREE_PVAL
o CONTEXTJ
o CONTEXTO
o DISALLOWED
o ID_DIS
o FREE_DIS
o UNASSIGNED
Note: The value of the derived property calculated can depend on the
string class; for example, if an identifier used in an application
protocol is defined as profiling the PRECIS IdentifierClass then a
space character such as U+0020 would be assigned to ID_DIS, whereas
if an identifier is defined as profiling the PRECIS FreeformClass
then the character would be assigned to FREE_PVAL. For the sake of
brevity, the designation "FREE_PVAL" is used in the code point
tables, instead of the longer designation "ID_DIS or FREE_PVAL". In
practice, the derived properties ID_PVAL and FREE_DIS are not used in
this specification, since every ID_PVAL code point is PVALID and
every FREE_DIS code point is DISALLOWED.
The algorithm to calculate the value of the derived property is as
follows:
If .cp. .in. Exceptions Then Exceptions(cp);
Else If .cp. .in. BackwardCompatible Then BackwardCompatible(cp);
Else If .cp. .in. Unassigned Then UNASSIGNED;
Else If .cp. .in. ASCII7 Then PVALID;
Else If .cp. .in. JoinControl Then CONTEXTJ;
Else If .cp. .in. OldHangulJamo Then DISALLOWED;
Else If .cp. .in. PrecisIgnorableProperties Then DISALLOWED;
Else If .cp. .in. Controls Then DISALLOWED;
Else If .cp. .in. HasCompat Then ID_DIS or FREE_PVAL;
Else If .cp. .in. LetterDigits Then PVALID;
Else If .cp. .in. OtherLetterDigits Then ID_DIS or FREE_PVAL;
Else If .cp. .in. Spaces Then ID_DIS or FREE_PVAL;
Else If .cp. .in. Symbols Then ID_DIS or FREE_PVAL;
Else If .cp. .in. Punctuation Then ID_DIS or FREE_PVAL;
Else DISALLOWED;
Note: Use of the name of a rule (such as "Exceptions") implies the
set of code points that the rule defines, whereas the same name as a
function call (such as "Exceptions(cp)") implies the value that the
code point has in the Exceptions table.
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9. IANA Considerations
9.1. PRECIS Derived Property Value Registry
IANA is requested to create a PRECIS-specific registry with the
Derived Properties for the versions of Unicode that are released
after (and including) version 6.3. The derived property value is to
be calculated in cooperation with a designated expert [RFC5226]
according to the rules specified under Section 7 and Section 8, not
by copying the non-normative table found under Appendix A.
The IESG is to be notified if backward-incompatible changes to the
table of derived properties are discovered or if other problems arise
during the process of creating the table of derived property values
or during expert review. Changes to the rules defined under
Section 7 and Section 8 require IETF Review.
9.2. PRECIS Base Classes Registry
IANA is requested to create a registry of PRECIS string classes. In
accordance with [RFC5226], the registration policy is "RFC Required".
The registration template is as follows:
Base Class: [the name of the PRECIS string class]
Description: [a brief description of the PRECIS string class and its
intended use, e.g., "A sequence of letters, numbers, and symbols
that is used to identify or address a network entity."]
Specification: [the RFC number]
The initial registrations are as follows:
Base Class: FreeformClass.
Description: A sequence of letters, numbers, symbols, spaces, and
other code points that is used for free-form strings.
Specification: RFC XXXX. [Note to RFC Editor: please change XXXX to
the number issued for this specification.]
Base Class: IdentifierClass.
Description: A sequence of letters, numbers, and symbols that is
used to identify or address a network entity.
Specification: RFC XXXX. [Note to RFC Editor: please change XXXX to
the number issued for this specification.]
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9.3. PRECIS Profiles Registry
IANA is requested to create a registry of profiles that use the
PRECIS string classes. In accordance with [RFC5226], the
registration policy is "Expert Review". This policy was chosen in
order to ease the burden of registration while ensuring that
"customers" of PRECIS receive appropriate guidance regarding the
sometimes complex and subtle internationalization issues related to
profiles of PRECIS string classes.
The registration template is as follows:
Name: [the name of the profile]
Applicability: [the specific protocol elements to which this profile
applies, e.g., "Localparts in XMPP addresses."]
Base Class: [which PRECIS string class is being profiled]
Replaces: [the Stringprep profile that this PRECIS profile replaces,
if any]
Width Mapping: [the behavioral rule for handling of width, e.g.,
"Map fullwidth and halfwidth characters to their compatibility
variants."]
Additional Mappings: [any additional mappings are required or
recommended, e.g., "Map non-ASCII space characters to ASCII
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
code points, e.g., "The 'Bidi Rule' defined in RFC 5893 applies."]
Exclusions: [a brief description of the specific code points or
characters categories are excluded, e.g., "Eight legacy characters
in the ASCII range" or "Any character that has a compatibility
equivalent, i.e., the HasCompat category"]
Enforcement: [which entities enforce the rules, and when that
enforcement occurs during protocol operations]
Specification: [a pointer to relevant documentation, such as an RFC
or Internet-Draft]
In order to request a review, the registrant shall send a completed
template to the precis@ietf.org list or its designated successor.
Factors to focus on while defining profiles and reviewing profile
registrations include the following:
o Is the problem being addressed by this profile well-defined?
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o Does the specification define what kinds of applications are
involved and the protocol elements to which this profile applies?
o Would an existing PRECIS string class or profile solve the
problem?
o Is the profile clearly defined?
o Does the profile reduce the degree to which human users could be
surprised by application behavior (the "principle of least user
surprise")?
o Is the profile based on an appropriate dividing line between user
interface (culture, context, intent, locale, device limitations,
etc.) and the use of conformant strings in protocol elements?
o Are the width mapping, case mapping, additional mapping,
normalization, exclusion, and directionality rules appropriate for
the intended use?
o Does the profile explain which entities enforce the rules, and
when such enforcement occurs during protocol operations?
o Does the profile reduce the degree to which human users could be
surprised or confused by application behavior (the "principle of
least user surprise")?
o Does the profile introduce any new security concerns such as those
described under Section 10 of this document (e.g., false positives
for authentication or authorization)?
10. Security Considerations
10.1. General Issues
The security of applications that use this framework can depend in
part on the proper preparation and comparison of internationalized
strings. For example, such strings can be used to make
authentication and authorization decisions, and the security of an
application could be compromised if an entity providing a given
string is connected to the wrong account or online resource based on
different interpretations of the string.
Specifications of application protocols that use this framework are
encouraged to describe how internationalized strings are used in the
protocol, including the security implications of any false positives
and false negatives that might result from various comparison
operations. For some helpful guidelines, refer to [RFC6943],
[RFC5890], [UTR36], and [UTS39].
10.2. Use of the IdentifierClass
Strings that conform to the IdentifierClass and any profile thereof
are intended to be relatively safe for use in a broad range of
applications, primarily because they include only letters, digits,
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and "grandfathered" non-space characters from the ASCII range; thus
they exclude spaces, characters with compatibility equivalents, and
almost all symbols and punctuation marks. However, because such
strings can still include so-called confusable characters (see
Section 10.5), protocol designers and implementers are encouraged to
pay close attention to the security considerations described
elsewhere in this document.
10.3. Use of the FreeformClass
Strings that conform to the FreeformClass and many profiles thereof
can include virtually any Unicode character. This makes the
FreeformClass quite expressive, but also problematic from the
perspective of possible user confusion. Protocol designers are
hereby warned that the FreeformClass contains codepoints they might
not understand, and are encouraged to profile the IdentifierClass
wherever feasible; however, if an application protocol requires more
code points than are allowed by the IdentifierClass, protocol
designers are encouraged to define a profile of the FreeformClass
that restricts the allowable code points as tightly as possible.
(The PRECIS Working Group considered the option of allowing
superclasses as well as profiles of PRECIS string classes, but
decided against allowing superclasses to reduce the likelihood of
security and interoperability problems.)
10.4. Local Character Set Issues
When systems use local character sets other than ASCII and Unicode,
this specification leaves the problem of converting between the local
character set and Unicode up to the application or local system. If
different applications (or different versions of one application)
implement different rules for conversions among coded character sets,
they could interpret the same name differently and contact different
application servers or other network entities. This problem is not
solved by security protocols, such as Transport Layer Security (TLS)
[RFC5246] and the Simple Authentication and Security Layer (SASL)
[RFC4422], that do not take local character sets into account.
10.5. Visually Similar Characters
Some characters are visually similar and thus can cause confusion
among humans. Such characters are often called "confusable
characters" or "confusables".
The problem of confusable characters is not necessarily caused by the
use of Unicode code points outside the ASCII range. For example, in
some presentations and to some individuals the string "ju1iet"
(spelled with DIGIT ONE, U+0031, as the third character) might appear
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to be the same as "juliet" (spelled with LATIN SMALL LETTER L,
U+006C), especially on casual visual inspection. This phenomenon is
sometimes called "typejacking".
However, the problem is made more serious by introducing the full
range of Unicode code points into protocol strings. For example, the
characters U+13DA U+13A2 U+13B5 U+13AC U+13A2 U+13AC U+13D2 from the
Cherokee block look similar to the ASCII characters "STPETER" as they
might appear when presented using a "creative" font family.
In some examples of confusable characters, it is unlikely that the
average human could tell the difference between the real string and
the fake string. (Indeed, there is no programmatic way to
distinguish with full certainty which is the fake string and which is
the real string; in some contexts, the string formed of Cherokee
characters might be the real string and the string formed of ASCII
characters might be the fake string.) Because PRECIS-compliant
strings can contain almost any properly-encoded Unicode code point,
it can be relatively easy to fake or mimic some strings in systems
that use the PRECIS framework. The fact that some strings are easily
confused introduces security vulnerabilities of the kind that have
also plagued the World Wide Web, specifically the phenomenon known as
phishing.
Despite the fact that some specific suggestions about identification
and handling of confusable characters appear in the Unicode Security
Considerations [UTR36] and the Unicode Security Mechanisms [UTS39],
it is also true (as noted in [RFC5890]) that "there are no
comprehensive technical solutions to the problems of confusable
characters". Because it is impossible to map visually similar
characters without a great deal of context (such as knowing the font
families used), the PRECIS framework does nothing to map similar-
looking characters together, nor does it prohibit some characters
because they look like others.
Nevertheless, specifications for application protocols that use this
framework MUST describe how confusable characters can be abused to
compromise the security of systems that use the protocol in question,
along with any protocol-specific suggestions for overcoming those
threats. In particular, software implementations and service
deployments that use PRECIS-based technologies are strongly
encouraged to define and implement consistent policies regarding the
registration, storage, and presentation of visually similar
characters. The following recommendations are appropriate:
1. An application service SHOULD define a policy that specifies the
scripts or blocks of characters that the service will allow to be
registered (e.g., in an account name) or stored (e.g., in a file
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name). Such a policy SHOULD be informed by the languages and
scripts that are used to write registered account names; in
particular, to reduce confusion, the service SHOULD forbid
registration or storage of strings that contain characters from
more than one script and SHOULD restrict registrations to
characters drawn from a very small number of scripts (e.g.,
scripts that are well-understood by the administrators of the
service, to improve manageability).
2. User-oriented application software SHOULD define a policy that
specifies how internationalized strings will be presented to a
human user. Because every human user of such software has a
preferred language or a small set of preferred languages, the
software SHOULD gather that information either explicitly from
the user or implicitly via the operating system of the user's
device. Furthermore, because most languages are typically
represented by a single script or a small set of scripts, and
because most scripts are typically contained in one or more
blocks of characters, the software SHOULD warn the user when
presenting a string that mixes characters from more than one
script or block, or that uses characters outside the normal range
of the user's preferred language(s). (Such a recommendation is
not intended to discourage communication across different
communities of language users; instead, it recognizes the
existence of such communities and encourages due caution when
presenting unfamiliar scripts or characters to human users.)
The challenges inherent in supporting the full range of Unicode code
points have in the past led some to hope for a way to
programmatically negotiate more restrictive ranges based on locale,
script, or other relevant factors, to tag the locale associated with
a particular string, etc. As a general-purpose internationalization
technology, the PRECIS framework does not include such mechanisms.
10.6. Security of Passwords
Two goals of passwords are to maximize the amount of entropy and to
minimize the potential for false positives. These goals can be
achieved in part by allowing a wide range of code points and by
ensuring that passwords are handled in such a way that code points
are not compared aggressively. Therefore, it is NOT RECOMMENDED for
application protocols to profile the FreeformClass for use in
passwords in a way that removes entire categories (e.g., by
disallowing symbols or punctuation). Furthermore, it is NOT
RECOMMENDED for application protocols to map uppercase and titlecase
code points to their lowercase equivalents in such strings; instead,
it is RECOMMENDED to preserve the case of all code points contained
in such strings and to compare them in a case-sensitive manner.
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That said, software implementers need to be aware that there exist
tradeoffs between entropy and usability. For example, allowing a
user to establish a password containing "uncommon" code points might
make it difficult for the user to access a service when using an
unfamiliar or constrained input device.
Some application protocols use passwords directly, whereas others
reuse technologies that themselves process passwords (one example of
such a technology is the Simple Authentication and Security Layer
[RFC4422]). Moreover, passwords are often carried by a sequence of
protocols with backend authentication systems or data storage systems
such as RADIUS [RFC2865] and LDAP [RFC4510]. Developers of
application protocols are encouraged to look into reusing these
profiles instead of defining new ones, so that end-user expectations
about passwords are consistent no matter which application protocol
is used.
11. Interoperability Considerations
Although strings that are consumed in PRECIS-based application
protocols are often encoded using UTF-8 [RFC3629], the exact encoding
is a matter for the application protocol that uses PRECIS, not for
the PRECIS framework.
It is known that some existing systems are unable to support the full
Unicode character set, or even any characters outside the ASCII
range. If two (or more) applications need to interoperate when
exchanging data (e.g., for the purpose of authenticating a username
or password), they will naturally need to have in common at least one
coded character set (as defined by [RFC6365]). Establishing such a
baseline is a matter for the application protocol that uses PRECIS,
not for the PRECIS framework.
The PRECIS framework, which is defined in terms of the latest version
of Unicode as of the time of this writing (6.3), treats the character
U+19DA NEW TAI LUE THAM as DISALLOWED. Implementers need to be aware
that this treatment is different from IDNA2008 (originally defined in
terms of Unicode 5.2), which treats U+19DA as PVALID.
12. References
12.1. Normative References
[I-D.ietf-precis-mappings]
Yoneya, Y. and T. NEMOTO, "Mapping characters for PRECIS
classes", draft-ietf-precis-mappings-05 (work in
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progress), October 2013.
[RFC20] Cerf, V., "ASCII format for network interchange", RFC 20,
October 1969.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5198] Klensin, J. and M. Padlipsky, "Unicode Format for Network
Interchange", RFC 5198, March 2008.
[UNICODE] The Unicode Consortium, "The Unicode Standard", 2013,
.
12.2. Informative References
[I-D.ietf-precis-nickname]
Saint-Andre, P., "Preparation and Comparison of
Nicknames", draft-ietf-precis-nickname-08 (work in
progress), December 2013.
[I-D.ietf-precis-saslprepbis]
Saint-Andre, P. and A. Melnikov, "Username and Password
Preparation Algorithms", draft-ietf-precis-saslprepbis-06
(work in progress), December 2013.
[I-D.ietf-xmpp-6122bis]
Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Address Format",
draft-ietf-xmpp-6122bis-09 (work in progress),
November 2013.
[RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson,
"Remote Authentication Dial In User Service (RADIUS)",
RFC 2865, June 2000.
[RFC3454] Hoffman, P. and M. Blanchet, "Preparation of
Internationalized Strings ("stringprep")", RFC 3454,
December 2002.
[RFC3490] Faltstrom, P., Hoffman, P., and A. Costello,
"Internationalizing Domain Names in Applications (IDNA)",
RFC 3490, March 2003.
[RFC3491] Hoffman, P. and M. Blanchet, "Nameprep: A Stringprep
Profile for Internationalized Domain Names (IDN)",
RFC 3491, March 2003.
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[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.
[RFC4422] Melnikov, A. and K. Zeilenga, "Simple Authentication and
Security Layer (SASL)", RFC 4422, June 2006.
[RFC4510] Zeilenga, K., "Lightweight Directory Access Protocol
(LDAP): Technical Specification Road Map", RFC 4510,
June 2006.
[RFC4690] Klensin, J., Faltstrom, P., Karp, C., and IAB, "Review and
Recommendations for Internationalized Domain Names
(IDNs)", RFC 4690, September 2006.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[RFC5890] Klensin, J., "Internationalized Domain Names for
Applications (IDNA): Definitions and Document Framework",
RFC 5890, August 2010.
[RFC5891] Klensin, J., "Internationalized Domain Names in
Applications (IDNA): Protocol", RFC 5891, August 2010.
[RFC5892] Faltstrom, P., "The Unicode Code Points and
Internationalized Domain Names for Applications (IDNA)",
RFC 5892, August 2010.
[RFC5893] Alvestrand, H. and C. Karp, "Right-to-Left Scripts for
Internationalized Domain Names for Applications (IDNA)",
RFC 5893, August 2010.
[RFC5894] Klensin, J., "Internationalized Domain Names for
Applications (IDNA): Background, Explanation, and
Rationale", RFC 5894, August 2010.
[RFC5895] Resnick, P. and P. Hoffman, "Mapping Characters for
Internationalized Domain Names in Applications (IDNA)
2008", RFC 5895, September 2010.
[RFC6365] Hoffman, P. and J. Klensin, "Terminology Used in
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Internationalization in the IETF", BCP 166, RFC 6365,
September 2011.
[RFC6885] Blanchet, M. and A. Sullivan, "Stringprep Revision and
Problem Statement for the Preparation and Comparison of
Internationalized Strings (PRECIS)", RFC 6885, March 2013.
[RFC6943] Thaler, D., "Issues in Identifier Comparison for Security
Purposes", RFC 6943, May 2013.
[UAX9] The Unicode Consortium, "Unicode Standard Annex #9:
Unicode Bidirectional Algorithm", September 2012,
.
[UAX11] The Unicode Consortium, "Unicode Standard Annex #11: East
Asian Width", September 2012,
.
[UAX15] The Unicode Consortium, "Unicode Standard Annex #15:
Unicode Normalization Forms", August 2012,
.
[UTR36] The Unicode Consortium, "Unicode Technical Report #36:
Unicode Security Considerations", July 2012,
.
[UTS39] The Unicode Consortium, "Unicode Technical Standard #39:
Unicode Security Mechanisms", July 2012,
.
URIs
[1]
[2]
Appendix A. Codepoint Table
If one applies the property calculation rules from Section 8 to the
code points 0x0000 to 0x10FFFF in Unicode 6.3, the result is as shown
in the following table, in Unicode Character Database (UCD) format.
The columns of the table are as follows:
1. The code point or codepoint range.
2. The assignment for the code point or range, where the value is
one of PVALID, DISALLOWED, UNASSIGNED, CONTEXTO, CONTEXTJ, or
FREE_PVAL (where the latter includes ID_DIS).
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3. The name or names for the code point or range.
This table is non-normative, is included only for illustrative
purposes, and applies only to Unicode 6.3, not to past or future
versions of Unicode. Please note that the strings displayed in the
third column are not necessarily the formal name of the code point
(as defined in [UNICODE]) because the fixed width of the RFC format
necessitated truncation of many names.
0000..001F ; DISALLOWED #
0020 ; FREE_PVAL # SPACE
0021..007E ; PVALID # EXCLAM MARK..TILDE
007F..009F ; DISALLOWED #
00A0..00AC ; FREE_PVAL # NO-BREAK SPACE..NOT SIGN
00AD ; DISALLOWED # SOFT HYPH
00AE..00B6 ; FREE_PVAL # REGISTERED SIGN..PILCROW SIGN
00B7 ; CONTEXTO # MIDDLE DOT
00B8..00BF ; FREE_PVAL # CEDILLA..INV QUEST IND
00C0..00D6 ; PVALID # LAT CAP LET A W GRAV..LAT CAP O
00D7 ; FREE_PVAL # MULTIPLICATION SIGN
00D8..00F6 ; PVALID # LAT CAP LET O W STROKE..LAT SM
00F7 ; FREE_PVAL # DIVISION SIGN
00F8..0131 ; PVALID # LAT SM LET O W STROKE..LAT SM LET
0132..0133 ; FREE_PVAL # LAT CAP LIG IJ..LAT SM LIB IJ
0134..013E ; PVALID # LAT CAP LET J W CIRCUM..LAT SM LET
013F..0140 ; FREE_PVAL # LAT CAP LET L W MID DOT..LAT SM LET
0141..0148 ; PVALID # LAT CAP LET L W STROKE..LAT SM LET
0149 ; FREE_PVAL # LAT SM LET N PRECEDED BY APOS
014A..017E ; PVALID # LAT CAP LET ENG..LAT SM LET Z W CA
017F ; FREE_PVAL # LAT SM LET LONG S
0180..01C3 ; PVALID # LAT SM LET B W STROKE..LAT LET RETR
01C4..01CC ; FREE_PVAL # LAT CAP LET DZ W CARON..LAT SM
01CD..01F0 ; PVALID # LAT CAP LET A W CARON..LAT SM LET J
01F1..01F3 ; FREE_PVAL # LAT CAP LET DZ..LAT SM LET DZ
01F4..02AF ; PVALID # LAT CAP LET G W ACUTE..LAT SM
02B0..02B8 ; FREE_PVAL # MOD LET SM H..MOD LET SM Y
02B9..02C1 ; PVALID # MOD LET PRIME..MOD LET REV GLOT ST
02C2..02C5 ; FREE_PVAL # MOD LET L ARROW..MOD LET D ARROW
02C6..02D1 ; PVALID # MOD LET CIRCUM ACC..MOD LET HALF TR
02D2..02EB ; FREE_PVAL # MOD LET CENT R HALF RING..MOD LET Y
02EC ; PVALID # MOD LET VOICING
02ED ; FREE_PVAL # MOD LET UNASPIRATED
02EE ; PVALID # MOD LET DOUBLE APOS
02EF..02FF ; FREE_PVAL # MOD LET LOW D ARR..MOD LET LOW L AR
0300..034E ; PVALID # COMB GRAVE ACCENT..COMB UP ARROW BE
034F ; DISALLOWED # COMB GRAPHEME JOINER
0350..0374 ; PVALID # COMB RIGHT ARROWHEAD..GREEK NUM SIG
0375 ; CONTEXTO # GREEK LOW NUM SIGN
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0376..0377 ; PVALID # GR CAP LET PAMPHYLIAN DIGAMMA..GR S
0378..0379 ; UNASSIGNED # ..
037A ; FREE_PVAL # GR YPOGEGRAMMENI..GR SM REV DOT LUN
037B..037D ; PVALID # GR SM REV LUN SIG..GR SM REV DOT LU
037E ; FREE_PVAL # GREEK QUEST MARK
037F..0383 ; UNASSIGNED # ..
0384..0385 ; FREE_PVAL # GREEK TONOS..GREEK DIALYTIKA TONOS
0386 ; PVALID # GR CAP LET ALPHA W TONOS
0387 ; FREE_PVAL # GREEK ANO TELEIA
0388..038A ; PVALID # GR CAP LET EPSILON W TONOS..GR CAP
038B ; UNASSIGNED #
038C ; PVALID # GREEK CAP LET OMICRON W TONOS
038D ; UNASSIGNED #
038E..03A1 ; PVALID # GR CAP LET EPSILON W TONOS..GR CAP
03A2 ; UNASSIGNED #
03A3..03CF ; PVALID # GREEK CAP LET SIGMA..GR CAP
03D0..03D2 ; FREE_PVAL # GR BETA SYM..GR UPSILON W HOOK
03D3..03D4 ; FREE_PVAL # GR UPSILON W ACUTE AND HOOK..GR UP
03D5..03D6 ; FREE_PVAL # GR PHI SYM..GR PI SYM
03D7..03EF ; PVALID # GR KAI SYM..COPT SM LET DEI
03F0..03F2 ; FREE_PVAL # GR KAPPA SYM..GR LUNATE SIGMA
03F3 ; PVALID # GREEK LET YOT
03F4..03F6 ; FREE_PVAL # GR CAP THETA..GR REV LUNATE EPSILON
03F7..03F8 ; PVALID # GR CAP LET SHO..GR SM LET SHO
03F9 ; FREE_PVAL # GREEK CAP LUNATE SIGMA SYM
03FA..0481 ; PVALID # GR CAP LET SAN..CYR SML LET KOPPA
0482 ; FREE_PVAL # CYR THOUSANDS SIGN
0483..0487 ; PVALID # COMB CYR TITLO..COMB CYR POK
0488..0489 ; FREE_PVAL # COMB CYR HUNDRED THOUSANDS SIGN..C
048A..0527 ; PVALID # CYR CAP LET SH I W TAIL..CYR S
0528..0530 ; UNASSIGNED # ..
0531..0556 ; PVALID # ARM CAP LET AYB..ARM CAP LET FEH
0557..0558 ; UNASSIGNED # ..
0559 ; PVALID # ARM MOD LET LEFT HALF RING
055A..055F ; FREE_PVAL # ARM APOS..ARM ABBREV
0560 ; UNASSIGNED #
0561..0586 ; PVALID # ARM SM LET AYB..ARMENIAN SM LE
0587 ; FREE_PVAL # ARM SM LIG ECH YIWN
0588 ; UNASSIGNED #
0589..058A ; FREE_PVAL # ARMENIAN FULL STOP..ARMENIAN HYPH
058B..058E ; UNASSIGNED # ..
058F ; FREE_PVAL # ARMENIAN DRAM SIGN
0590 ; UNASSIGNED #
0591..05BD ; PVALID # HEBR ACC ETNAHTA..HEBR PNT ME
05BE ; FREE_PVAL # HEBR PUNCT MAQAF
05BF ; PVALID # HEBR PNT RAFE
05C0 ; FREE_PVAL # HEBR PUNCT PASEQ
05C1..05C2 ; PVALID # HEBR PNT SHIN DOT..HEBR PNT SIN DOT
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05C3 ; FREE_PVAL # HEBR PUNCT SOF PASUQ
05C4..05C5 ; PVALID # HEBR MARK UP DOT..HEBR MARK LOW DOT
05C6 ; FREE_PVAL # HEBR PUNCT NUN HAFUKHA
05C7 ; PVALID # HEBR PNT QAMATS QATAN
05C8..05CF ; UNASSIGNED # ..
05D0..05EA ; PVALID # HEBR LET ALEF..HEBR LET TAV
05EB..05EF ; UNASSIGNED # ..
05F0..05F2 ; PVALID # HEBR LIG YIDDISH DOUBLE VAV..HEBR L
05F3..05F4 ; CONTEXTO # HEBR PUNCT GERESH..HEBR PUNCTUATIO
05F5..05FF ; UNASSIGNED # ..
0600..0604 ; DISALLOWED # ARAB NUM SIGN..ARAB SIGN SAM
0605 ; UNASSIGNED # ..
0606..060F ; FREE_PVAL # AR-IND CUBE ROOT..ARAB SIGN MISRA
0610..061A ; PVALID # ARAB SIGN SALLALLAHOU ALAYHE ..AR
061B ; FREE_PVAL # ARAB SEMICOLON
061C ; DISALLOWED # ARAB LET MARK
061D..061D ; UNASSIGNED # ..
061E..061F ; FREE_PVAL # ARAB TRIPLE DOT PUNCT MARK..ARAB Q
0620..063F ; PVALID # ARAB LET KASH..ARAB LET FARSI YEH
0640 ; DISALLOWED # ARAB TATWEEL
0641..065F ; PVALID # ARAB LET FEH..ARAB WAVY HAMZA BEL
0660..0669 ; CONTEXTO # AR-IND DIG ZERO..AR-IND DIG
066A..066D ; FREE_PVAL # ARAB PCT SIGN..ARAB FIVE PNTED STA
066E..0674 ; PVALID # ARAB LET DOTLESS BEH..ARAB LET HIG
0675..0678 ; FREE_PVAL # ARAB LET HIGH HAMZA ALEF..ARAB LET
0679..06D3 ; PVALID # ARAB LET TTEH..ARAB LET YEH BARREE
06D4 ; FREE_PVAL # ARAB FULL STOP
06D5..06DC ; PVALID # ARAB LET AE..ARAB SM HIGH SEEN
06DD ; DISALLOWED # ARAB END OF AYAH
06DE ; FREE_PVAL # ARAB START OF RUB EL HIZB
06DF..06E8 ; PVALID # ARAB SM HIGH ROUNDED ZERO..ARAB SM
06E9 ; FREE_PVAL # ARAB PLACE OF SAJDAH
06EA..06EF ; PVALID # ARAB EMPTY CENTRE LOW STOP..ARAB LET
06F0..06F9 ; CONTEXTO # EXT AR-IND DIG ZERO..EXT A
06FA..06FF ; PVALID # ARAB LET SHEEN W DOT BEL..ARAB
0700..070D ; FREE_PVAL # SYR END OF PARA..SYR HARKLEAN AST
070E ; UNASSIGNED #
070F ; DISALLOWED # SYR ABBR MARK
0710..074A ; PVALID # SYR LET ALAPH..SYR BARREKH
074B..074C ; UNASSIGNED # ..
074D..07B1 ; PVALID # SYR LET SOGDIAN ZHAIN..THAANA LET N
07B2..07BF ; UNASSIGNED # ..
07C0..07F5 ; PVALID # NKO DIG ZERO..NKO LOW TONE APOS
07F6..07F9 ; FREE_PVAL # NKO SYM OO DENNEN..NKO EXCLAMATI
07FA ; DISALLOWED # NKO LAJANYALAN
07FB..07FF ; UNASSIGNED # ..
0800..082D ; PVALID # SAMAR LET ALAF..SAMAR MARK NEQUDA
082E..082F ; UNASSIGNED # ..
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0830..083E ; FREE_PVAL # SAMAR PUNCT NEQUDAA..SAMAR PUN
083F ; UNASSIGNED #
0840..085B ; PVALID # MANDAIC LET HALQA..MANDAIC GEM
085C..085D ; UNASSIGNED # ..
085E ; FREE_PVAL # MANDAIC PUNCTUATION
085F..089F ; UNASSIGNED # ..
08A0 ; PVALID # ARAB LET BEH W SM V BEL
08A1 ; UNASSIGNED #
08A2..08AC ; PVALID # ARAB LET JEEM W 2 DOTS AB..ARAB
08AD..08E3 ; UNASSIGNED # ..
08E4..08FE ; PVALID # ARAB CURLY FATHA..ARAB DAMMA W
08FF ; UNASSIGNED #
0900..0963 ; PVALID # DEVAN SIGN INV CANDRABINDU..DEVAN V
0964..0965 ; FREE_PVAL # DEVAN DANDA..DEVAN DOUBLE DANDA
0966..096F ; PVALID # DEVAN DIG ZERO..DEVAN DIG NINE
0970 ; FREE_PVAL # DEVAN ABBR SIGN
0971..0977 ; PVALID # DEVAN SIGN HIGH SPACING DOT..DEVAN
0978 ; UNASSIGNED #
0979..097F ; PVALID # DEVAN SIGN HIGH SPACING DOT..DEVAN
0980 ; UNASSIGNED #
0981..0983 ; PVALID # BENG SIGN CANDRABINDU..BENG SIGN VIS
0984 ; UNASSIGNED #
0985..098C ; PVALID # BENG LET A..BENG LET VOC L
098D..098E ; UNASSIGNED # ..
098F..0990 ; PVALID # BENG LET E..BENG LET AI
0991..0992 ; UNASSIGNED # ..
0993..09A8 ; PVALID # BENG LET O..BENG LET NA
09A9 ; UNASSIGNED #
09AA..09B0 ; PVALID # BENG LET PA..BENG LET RA
09B1 ; UNASSIGNED #
09B2 ; PVALID # BENG LET LA
09B3..09B5 ; UNASSIGNED # ..
09B6..09B9 ; PVALID # BENG LET SHA..BENG LET HA
09BA..09BB ; UNASSIGNED # ..
09BC..09C4 ; PVALID # BENG SIGN NUKTA..BENG VOW SIGN VOCAL
09C5..09C6 ; UNASSIGNED # ..
09C7..09C8 ; PVALID # BENG VOW SIGN E..BENG VOW SIGN AI
09C9..09CA ; UNASSIGNED # ..
09CB..09CE ; PVALID # BENG VOW SIGN O..BENG LET KHANDA
09CF..09D6 ; UNASSIGNED # ..
09D7 ; PVALID # BENG AU LEN MARK
09D8..09DB ; UNASSIGNED # ..
09DC..09DD ; PVALID # BENG LET RRA..BENG LET RHA
09DE ; UNASSIGNED #
09DF..09E3 ; PVALID # BENG LET YYA..BENG VOW SIG
09E4..09E5 ; UNASSIGNED # ..
09E6..09F1 ; PVALID # BENG DIG ZERO..BENG LET RA W L
09F2..09FB ; FREE_PVAL # BENG RUPEE MARK..BENG GANDA MARK
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09FC..0A00 ; UNASSIGNED # ..
0A01..0A03 ; PVALID # GURMUKHI SIGN ADAK BINDI..GURMUKHI
0A04 ; UNASSIGNED #
0A05..0A0A ; PVALID # GURMUKHI LET A..GURMUKHI LET UU
0A0B..0A0E ; UNASSIGNED # ..
0A0F..0A10 ; PVALID # GURMUKHI LET EE..GURMUKHI LET AI
0A11..0A12 ; UNASSIGNED # ..
0A13..0A28 ; PVALID # GURMUKHI LET OO..GURMUKHI LET NA
0A29 ; UNASSIGNED #
0A2A..0A30 ; PVALID # GURMUKHI LET PA..GURMUKHI LET RA
0A31 ; UNASSIGNED #
0A32..0A33 ; PVALID # GURMUKHI LET LA..GURMUKHI LET LLA
0A34 ; UNASSIGNED #
0A35.OA36 ; PVALID # GURMUKHI LET VA..GURMUKHI LET SHA
0A37 ; UNASSIGNED #
0A38..0A39 ; PVALID # GURMUKHI LET SA..GURMUKHI LET HA
0A3A..0A3B ; UNASSIGNED # ..
0A3C ; PVALID # GURMUKHI SIGN NUKTA
0A3D ; UNASSIGNED #
0A3E..0A42 ; PVALID # GURMUKHI VOW SIGN AA..GURMUKHI V
0A43..0A46 ; UNASSIGNED # ..
0A47..0A48 ; PVALID # GURMUKHI VOW SIGN EE..GURMUKHI V
0A49..0A4A ; UNASSIGNED # ..
0A4B..0A4D ; PVALID # GURMUKHI VOW SIGN OO..GURMUKHI S
0A4E..0A50 ; UNASSIGNED # ..
0A51 ; PVALID # GURMUKHI SIGN UDAAT
0A52..0A58 ; UNASSIGNED # ..
0A59..0A5C ; PVALID # GURMUKHI LET KHHA..GURMUKHI LET RRA
0A5D ; UNASSIGNED #
0A5E ; PVALID # GURMUKHI LET FA
0A5F..0A65 ; UNASSIGNED # ..
0A66..0A75 ; PVALID # GURMUKHI DIG ZERO..GURMUKHI SIGN YA
0A76..0A80 ; UNASSIGNED # ..
0A81..0A83 ; PVALID # GUJARATI SIGN CANDRABINDU..GUJARATI
0A84 ; UNASSIGNED #
0A85..0A8D ; PVALID # GUJARATI LET A..GUJARATI VOW CAND
0A8E ; UNASSIGNED #
0A8F..0A91 ; PVALID # GUJARATI LET E..GUJARATI VOW CAND
0A92 ; UNASSIGNED #
0A93..0AA8 ; PVALID # GUJARATI LET O..GUJARATI LET NA
0AA9 ; UNASSIGNED #
0AAA..0AB0 ; PVALID # GUJARATI LET PA..GUJARATI LET RA
0AB1 ; UNASSIGNED #
0AB2..0AB3 ; PVALID # GUJARATI LET LA..GUJARATI LET LLA
0AB4 ; UNASSIGNED #
0AB5..0AB9 ; PVALID # GUJARATI LET VA..GUJARATI LET HA
0ABA..0ABB ; UNASSIGNED # ..
0ABC..0AC5 ; PVALID # GUJARATI SIGN NUKTA..GUJARATI VOW
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0AC6 ; UNASSIGNED #
0AC7..0AC9 ; PVALID # GUJARATI VOW SIGN E..GUJARATI VOW
0ACA ; UNASSIGNED #
0ACB..0ACD ; PVALID # GUJARATI VOW SIGN O..GUJARATI SIG
0ACE..0ACF ; UNASSIGNED # ..
0AD0 ; PVALID # GUJARATI OM
0AD1..0ADF ; UNASSIGNED # ..
0AE0..0AE3 ; PVALID # GUJARATI LET VOC RR..GUJARATI V
0AE4..0AE5 ; UNASSIGNED # ..
0AE6..0AEF ; PVALID # GUJARATI DIG ZERO..GUJARATI DIG NINE
0AF0..0AF1 ; FREE_PVAL # GUJARATI ABBR SIGN..GUJARATI RUPEE S
0AF2..0B00 ; UNASSIGNED # ..
0B01..0B03 ; PVALID # ORIYA SIGN CANDRABINDU..ORIYA SIGN V
0B04 ; UNASSIGNED #
0B05..0B0C ; PVALID # ORIYA LET A..ORIYA LET VOC L
0B0D..0B0E ; UNASSIGNED # ..
0B0F..0B10 ; PVALID # ORIYA LET E..ORIYA LET AI
0B11..0B12 ; UNASSIGNED # ..
0B13..0B28 ; PVALID # ORIYA LET O..ORIYA LET NA
0B29 ; UNASSIGNED #
0B2A..0B30 ; PVALID # ORIYA LET PA..ORIYA LET RA
0B31 ; UNASSIGNED #
0B32..0B33 ; PVALID # ORIYA LET LA..ORIYA LET LLA
0B34 ; UNASSIGNED #
0B35..0B39 ; PVALID # ORIYA LET VA..ORIYA LET HA
0B3A..0B3B ; UNASSIGNED # ..
0B3C..0B44 ; PVALID # ORIYA SIGN NUKTA..ORIYA VOW SIGN
0B45..0B46 ; UNASSIGNED # ..
0B47..0B48 ; PVALID # ORIYA VOW SIGN E..ORIYA VOW SIG
0B49..0B4A ; UNASSIGNED # ..
0B4B..0B4D ; PVALID # ORIYA VOW SIGN O..ORIYA SIGN VIRA
0B4E..0B55 ; UNASSIGNED # ..
0B56..0B57 ; PVALID # ORIYA AI LEN MARK..ORIYA AU LENG
0B58..0B5B ; UNASSIGNED # ..
0B5C..0B5D ; PVALID # ORIYA LET RRA..ORIYA LET RHA
0B5E ; UNASSIGNED #
0B5F..0B63 ; PVALID # ORIYA LET YYA..ORIYA VOW SIGN VOCA
0B64..0B65 ; UNASSIGNED # ..
0B66..0B6F ; PVALID # ORIYA DIG ZERO..ORIYA DIG NINE
0B70 ; FREE_PVAL # ORIYA ISSHAR
0B71 ; PVALID # ORIYA LET WA
0B72..0B77 ; FREE_PVAL # ORIYA FRACT ONE QUART..ORIYA FRACT
0B78..0B81 ; UNASSIGNED # ..
0B82..0B83 ; PVALID # TAMIL SIGN ANUSVARA..TAMIL SIGN VIS
0B84 ; UNASSIGNED #
0B85..0B8A ; PVALID # TAMIL LET A..TAMIL LET UU
0B8B..0B8D ; UNASSIGNED # ..
0B8E..0B90 ; PVALID # TAMIL LET E..TAMIL LET AI
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0B91 ; UNASSIGNED #
0B92..0B95 ; PVALID # TAMIL LET O..TAMIL LET KA
0B96..0B98 ; UNASSIGNED # ..
0B99..0B9A ; PVALID # TAMIL LET NGA..TAMIL LET CA
0B9B ; UNASSIGNED #
0B9C ; PVALID # TAMIL LET JA
0B9D ; UNASSIGNED #
0B9E..0B9F ; PVALID # TAMIL LET NYA..TAMIL LET TTA
0BA0..0BA2 ; UNASSIGNED # ..
0BA3..0BA4 ; PVALID # TAMIL LET NNA..TAMIL LET TA
0BA5..0BA7 ; UNASSIGNED # ..
0BA8..0BAA ; PVALID # TAMIL LET NA..TAMIL LET PA
0BAB..0BAD ; UNASSIGNED # ..
0BAE..0BB9 ; PVALID # TAMIL LET MA..TAMIL LET HA
0BBA..0BBD ; UNASSIGNED # ..
0BBE..0BC2 ; PVALID # TAMIL VOW SIGN AA..TAMIL VOW SI
0BC3..0BC5 ; UNASSIGNED # ..
0BC6..0BC8 ; PVALID # TAMIL VOW SIGN E..TAMIL VOW SIG
0BC9 ; UNASSIGNED #
0BCA..0BCD ; PVALID # TAMIL VOW SIGN O..TAMIL SIGN VIRA
0BCE..0BCF ; UNASSIGNED # ..
0BD0 ; PVALID # TAMIL OM
0BD1..0BD6 ; UNASSIGNED # ..
0BD7 ; PVALID # TAMIL AU LEN MARK
0BD8..0BE5 ; UNASSIGNED # ..
0BE6..0BEF ; PVALID # TAMIL DIG ZERO..TAMIL DIG NINE
0BF0..0BFA ; FREE_PVAL # TAMIL NUM TEN..TAMIL NUM SIGN
0BFB..0C00 ; UNASSIGNED # ..
0C01..0C03 ; PVALID # TELUGU SIGN CANDRABINDU..TELUGU SIG
0C04 ; UNASSIGNED #
0C05..0C0C ; PVALID # TELUGU LET A..TELUGU LET VOC L
0C0D ; UNASSIGNED #
0C0E..0C10 ; PVALID # TELUGU LET E..TELUGU LET AI
0C11 ; UNASSIGNED #
0C12..0C28 ; PVALID # TELUGU LET O..TELUGU LET NA
0C29 ; UNASSIGNED #
0C2A..0C33 ; PVALID # TELUGU LET PA..TELUGU LET LLA
0C34 ; UNASSIGNED #
0C35..0C39 ; PVALID # TELUGU LET VA..TELUGU LET HA
0C3A..0C3C ; UNASSIGNED # ..
0C3D..0C44 ; PVALID # TELUGU SIGN AVAGRAHA..TELUGU VOW SI
0C45 ; UNASSIGNED #
0C46..0C48 ; PVALID # TELUGU VOW SIGN E..TELUGU VOW SIGN
0C49 ; UNASSIGNED #
0C4A..0C4D ; PVALID # TELUGU VOW SIGN O..TELUGU SIGN VIRA
0C4E..0C54 ; UNASSIGNED # ..
0C55..0C56 ; PVALID # TELUGU LEN MARK..TELUGU AI LEN MARK
0C57 ; UNASSIGNED #
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0C58..0C59 ; PVALID # TELUGU LET TSA..TELUGU LET DZA
0C5A..0C5F ; UNASSIGNED # ..
0C60..0C63 ; PVALID # TELUGU LET VOC RR..TELUGU VOW S
0C64..0C65 ; UNASSIGNED # ..
0C66..0C6F ; PVALID # TELUGU DIG ZERO..TELUGU DIG NINE
0C70..0C77 ; UNASSIGNED # ..
0C78..0C7F ; FREE_PVAL # TELUGU FRACTION DIG ZERO..TELUGU S
0C80..0C81 ; UNASSIGNED # ..
0C82..0C83 ; PVALID # KANNADA SIGN ANUSVARA..KANNADA SIGN
0C84 ; UNASSIGNED #
0C85..0C8C ; PVALID # KANNADA LET A..KANNADA LET VOC L
0C8D ; UNASSIGNED #
0C8E..0C90 ; PVALID # KANNADA LET E..KANNADA LET AI
0C91 ; UNASSIGNED #
0C92..0CA8 ; PVALID # KANNADA LET O..KANNADA LET NA
0CA9 ; UNASSIGNED #
0CAA..0CB3 ; PVALID # KANNADA LET PA..KANNADA LET LLA
0CB4 ; UNASSIGNED #
0CB5..0CB9 ; PVALID # KANNADA LET VA..KANNADA LET HA
0CBA..0CBB ; UNASSIGNED # ..
0CBC..0CC4 ; PVALID # KANNADA SIGN NUKTA..KANNADA VOW SIG
0CC5 ; UNASSIGNED #
0CC6..0CC8 ; PVALID # KANNADA VOW SIGN E..KANNADA VOW SIG
0CC9 ; UNASSIGNED #
0CCA..0CCD ; PVALID # KANNADA VOW SIGN O..KANNADA SIGN VI
0CCE..0CD4 ; UNASSIGNED # ..
0CD5..0CD6 ; PVALID # KANNADA LEN MARK..KANNADA AI LEN MA
0CD7..0CDD ; UNASSIGNED # ..
0CDE ; PVALID # KANNADA LET FA
0CDF ; UNASSIGNED #
0CE0..0CE3 ; PVALID # KANNADA LET VOC RR..KANNADA VOW SIG
0CE4..0CE5 ; UNASSIGNED # ..
0CE6..0CEF ; PVALID # KANNADA DIG ZERO..KANNADA DIG NINE
0CF0 ; UNASSIGNED #
0CF1..0CF2 ; PVALID # KANNADA SIGN JIHVAMULIYA..KANNADA S
0CF3..0D01 ; UNASSIGNED # ..
0D02..0D03 ; PVALID # MALAY SIGN ANUSVARA..MALAY SIGN VIS
0D04 ; UNASSIGNED #
0D05..0D0C ; PVALID # MALAY LET A..MALAY LET VOC
0D0D ; UNASSIGNED #
0D0E..0D10 ; PVALID # MALAY LET E..MALAY LET AI
0D11 ; UNASSIGNED #
0D12..0D3A ; PVALID # MALAY LET O..MALAY LET TTTA
0D3B..0D3C ; UNASSIGNED # ..
0D3D..0D44 ; PVALID # MALAY SIGN AVAGRAHA..MALAY VOW SIG
0D45 ; UNASSIGNED #
0D46..0D48 ; PVALID # MALAY VOW SIGN E..MALAY VOW SIGN
0D49 ; UNASSIGNED #
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0D4A..0D4E ; PVALID # MALAY VOW SIGN O..MALAY LET DOT REP
0D4F..0D56 ; UNASSIGNED # ..
0D57 ; PVALID # MALAY AU LEN MARK
0D58..0D5F ; UNASSIGNED # ..
0D60..0D63 ; PVALID # MALAY LET VOC RR..MALAY VOW
0D64..0D65 ; UNASSIGNED # ..
0D66..0D6F ; PVALID # MALAY DIG ZERO..MALAY DIG NINE
0D70..0D75 ; FREE_PVAL # MALAY NUM TEN..MALAY FRACTION THR
0D76..0D78 ; UNASSIGNED # ..
0D79 ; FREE_PVAL # MALAY DATE MARK
0D7A..0D7F ; PVALID # MALAY LET CHILLU NN..MALAY LET
0D80..0D81 ; UNASSIGNED # ..
0D82..0D83 ; PVALID # SINH SIGN ANUSVARAYA..SINH SIGN VIS
0D84 ; UNASSIGNED #
0D85..0D96 ; PVALID # SINH LET AYANNA..SINH LET AUYANN
0D97..0D99 ; UNASSIGNED # ..
0D9A..0DB1 ; PVALID # SINH LET ALPAPRAANA KAYANNA..SINH L
0DB2 ; UNASSIGNED #
0DB3..0DBB ; PVALID # SINH LET SANYAKA DAYANNA..SINH LETT
0DBC ; UNASSIGNED #
0DBD ; PVALID # SINH LET DANTAJA LAYANNA
0DBE..0DBF ; UNASSIGNED # ..
0DC0..0DC6 ; PVALID # SINH LET VAYANNA..SINH LET FAYAN
0DC7..0DC9 ; UNASSIGNED # ..
0DCA ; PVALID # SINH SIGN AL-LAKUNA
0DCB..0DCE ; UNASSIGNED # ..
0DCF..0DD4 ; PVALID # SINH VOW SIGN AELA-PILLA..SINH VOW
0DD5 ; UNASSIGNED #
0DD6 ; PVALID # SINH VOW SIGN DIGA PAA-PILLA
0DD7 ; UNASSIGNED #
0DD8..0DDF ; PVALID # SINH VOW SIGN GAETTA-PILLA..SINH VO
0DE0..0DF1 ; UNASSIGNED # ..
0DF2..0DF3 ; PVALID # SINH VOW SIGN DIGA GAETTA-PILLA..SI
0DF4 ; FREE_PVAL # SINH PUNCT KUNDDALIYA
0DF5..0E00 ; UNASSIGNED # ..
0E01..0E32 ; PVALID # THAI CHAR KO KAI..THAI CHAR SARA A
0E33 ; FREE_PVAL # THAI CHAR SARA AM
0E34..0E3A ; PVALID # THAI CHAR SARA I..THAI CHAR PHINTH
0E3B..0E3E ; UNASSIGNED # ..
0E3F ; FREE_PVAL # THAI CURRENCY SYM BAHT
0E40..0E4E ; PVALID # THAI CHAR SARA E..THAI CHAR YAMAKK
0E4F ; FREE_PVAL # THAI CHAR FONGMAN
0E50..0E59 ; PVALID # THAI DIG ZERO..THAI DIG NINE
0E5A..0E5B ; FREE_PVAL # THAI CHAR ANGKHANKHU..THAI CHAR KH
0E5C..0E80 ; UNASSIGNED # ..
0E81..0E82 ; PVALID # LAO LET KO..LAO LET KHO SUNG
0E83 ; UNASSIGNED #
0E84 ; PVALID # LAO LET KHO TAM
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0E85..0E86 ; UNASSIGNED # ..
0E87..0E88 ; PVALID # LAO LET NGO..LAO LET CO
0E89 ; UNASSIGNED #
0E8A ; PVALID # LAO LET SO TAM
0E8B..0E8C ; UNASSIGNED # ..
0E8D ; PVALID # LAO LET NYO
0E8E..0E93 ; UNASSIGNED # ..
0E94..0E97 ; PVALID # LAO LET DO..LAO LET THO TAM
0E98 ; UNASSIGNED #
0E99..0E9F ; PVALID # LAO LET NO..LAO LET FO SUNG
0EA0 ; UNASSIGNED #
0EA1..0EA3 ; PVALID # LAO LET MO..LAO LET LO LING
0EA4 ; UNASSIGNED #