draft-ietf-precis-framework-19.txt   draft-ietf-precis-framework-20.txt 
PRECIS P. Saint-Andre PRECIS P. Saint-Andre
Internet-Draft &yet Internet-Draft &yet
Obsoletes: 3454 (if approved) M. Blanchet Obsoletes: 3454 (if approved) M. Blanchet
Intended status: Standards Track Viagenie Intended status: Standards Track Viagenie
Expires: April 26, 2015 October 23, 2014 Expires: May 25, 2015 November 21, 2014
PRECIS Framework: Preparation, Enforcement, and Comparison of PRECIS Framework: Preparation, Enforcement, and Comparison of
Internationalized Strings in Application Protocols Internationalized Strings in Application Protocols
draft-ietf-precis-framework-19 draft-ietf-precis-framework-20
Abstract Abstract
Application protocols using Unicode characters in protocol strings Application protocols using Unicode characters in protocol strings
need to properly handle such strings in order to enforce need to properly handle such strings in order to enforce
internationalization rules for strings placed in various protocol internationalization rules for strings placed in various protocol
slots (such as addresses and identifiers) and to perform valid slots (such as addresses and identifiers) and 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, enforcements, and application protocols to perform the preparation, enforcement, and
comparison of internationalized strings ("PRECIS") in a way that comparison of internationalized strings ("PRECIS") in a way that
depends on the properties of Unicode characters and thus is agile depends on the properties of Unicode characters and thus is agile
with respect to versions of Unicode. As a result, this framework with respect to versions of Unicode. As a result, this framework
provides a more sustainable approach to the handling of provides a more sustainable approach to the handling of
internationalized strings than the previous framework, known as internationalized strings than the previous framework, known as
Stringprep (RFC 3454). This document obsoletes RFC 3454. Stringprep (RFC 3454). This document 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
skipping to change at page 1, line 44 skipping to change at page 1, line 44
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 April 26, 2015. This Internet-Draft will expire on May 25, 2015.
Copyright Notice Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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3. Preparation, Enforcement, and Comparison . . . . . . . . . . 6 3. Preparation, Enforcement, and Comparison . . . . . . . . . . 6
4. String Classes . . . . . . . . . . . . . . . . . . . . . . . 7 4. String Classes . . . . . . . . . . . . . . . . . . . . . . . 7
4.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 7 4.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 7
4.2. IdentifierClass . . . . . . . . . . . . . . . . . . . . . 8 4.2. IdentifierClass . . . . . . . . . . . . . . . . . . . . . 8
4.2.1. Valid . . . . . . . . . . . . . . . . . . . . . . . . 9 4.2.1. Valid . . . . . . . . . . . . . . . . . . . . . . . . 9
4.2.2. Contextual Rule Required . . . . . . . . . . . . . . 9 4.2.2. Contextual Rule Required . . . . . . . . . . . . . . 9
4.2.3. Disallowed . . . . . . . . . . . . . . . . . . . . . 9 4.2.3. Disallowed . . . . . . . . . . . . . . . . . . . . . 9
4.2.4. Unassigned . . . . . . . . . . . . . . . . . . . . . 10 4.2.4. Unassigned . . . . . . . . . . . . . . . . . . . . . 10
4.2.5. Examples . . . . . . . . . . . . . . . . . . . . . . 10 4.2.5. Examples . . . . . . . . . . . . . . . . . . . . . . 10
4.3. FreeformClass . . . . . . . . . . . . . . . . . . . . . . 10 4.3. FreeformClass . . . . . . . . . . . . . . . . . . . . . . 10
4.3.1. Valid . . . . . . . . . . . . . . . . . . . . . . . . 10 4.3.1. Valid . . . . . . . . . . . . . . . . . . . . . . . . 11
4.3.2. Contextual Rule Required . . . . . . . . . . . . . . 11 4.3.2. Contextual Rule Required . . . . . . . . . . . . . . 11
4.3.3. Disallowed . . . . . . . . . . . . . . . . . . . . . 11 4.3.3. Disallowed . . . . . . . . . . . . . . . . . . . . . 11
4.3.4. Unassigned . . . . . . . . . . . . . . . . . . . . . 11 4.3.4. Unassigned . . . . . . . . . . . . . . . . . . . . . 12
4.3.5. Examples . . . . . . . . . . . . . . . . . . . . . . 12 4.3.5. Examples . . . . . . . . . . . . . . . . . . . . . . 12
5. Profiles . . . . . . . . . . . . . . . . . . . . . . . . . . 12 5. Profiles . . . . . . . . . . . . . . . . . . . . . . . . . . 12
5.1. Profiles Must Not Be Multiplied Beyond Necessity . . . . 12 5.1. Profiles Must Not Be Multiplied Beyond Necessity . . . . 12
5.2. Rules . . . . . . . . . . . . . . . . . . . . . . . . . . 13 5.2. Rules . . . . . . . . . . . . . . . . . . . . . . . . . . 13
5.2.1. Width Mapping Rule . . . . . . . . . . . . . . . . . 13 5.2.1. Width Mapping Rule . . . . . . . . . . . . . . . . . 13
5.2.2. Additional Mapping Rule . . . . . . . . . . . . . . . 13 5.2.2. Additional Mapping Rule . . . . . . . . . . . . . . . 13
5.2.3. Case Mapping Rule . . . . . . . . . . . . . . . . . . 14 5.2.3. Case Mapping Rule . . . . . . . . . . . . . . . . . . 14
5.2.4. Normalization Rule . . . . . . . . . . . . . . . . . 14 5.2.4. Normalization Rule . . . . . . . . . . . . . . . . . 14
5.2.5. Exclusion Rule . . . . . . . . . . . . . . . . . . . 14 5.2.5. Directionality Rule . . . . . . . . . . . . . . . . . 14
5.2.6. Directionality Rule . . . . . . . . . . . . . . . . . 15 5.3. Further Excluded Characters . . . . . . . . . . . . . . . 15
5.3. Building Application-Layer Constructs . . . . . . . . . . 15 5.4. Building Application-Layer Constructs . . . . . . . . . . 15
5.4. A Note about Spaces . . . . . . . . . . . . . . . . . . . 16 5.5. A Note about Spaces . . . . . . . . . . . . . . . . . . . 16
6. Order of Operations . . . . . . . . . . . . . . . . . . . . . 17 6. Order of Operations . . . . . . . . . . . . . . . . . . . . . 17
7. Code Point Properties . . . . . . . . . . . . . . . . . . . . 17 7. Code Point Properties . . . . . . . . . . . . . . . . . . . . 17
8. Category Definitions Used to Calculate Derived Property . . . 20 8. Category Definitions Used to Calculate Derived Property . . . 20
8.1. LetterDigits (A) . . . . . . . . . . . . . . . . . . . . 20 8.1. LetterDigits (A) . . . . . . . . . . . . . . . . . . . . 20
8.2. Unstable (B) . . . . . . . . . . . . . . . . . . . . . . 21 8.2. Unstable (B) . . . . . . . . . . . . . . . . . . . . . . 20
8.3. IgnorableProperties (C) . . . . . . . . . . . . . . . . . 21 8.3. IgnorableProperties (C) . . . . . . . . . . . . . . . . . 21
8.4. IgnorableBlocks (D) . . . . . . . . . . . . . . . . . . . 21 8.4. IgnorableBlocks (D) . . . . . . . . . . . . . . . . . . . 21
8.5. LDH (E) . . . . . . . . . . . . . . . . . . . . . . . . . 21 8.5. LDH (E) . . . . . . . . . . . . . . . . . . . . . . . . . 21
8.6. Exceptions (F) . . . . . . . . . . . . . . . . . . . . . 21 8.6. Exceptions (F) . . . . . . . . . . . . . . . . . . . . . 21
8.7. BackwardCompatible (G) . . . . . . . . . . . . . . . . . 21 8.7. BackwardCompatible (G) . . . . . . . . . . . . . . . . . 21
8.8. JoinControl (H) . . . . . . . . . . . . . . . . . . . . . 22 8.8. JoinControl (H) . . . . . . . . . . . . . . . . . . . . . 21
8.9. OldHangulJamo (I) . . . . . . . . . . . . . . . . . . . . 22 8.9. OldHangulJamo (I) . . . . . . . . . . . . . . . . . . . . 22
8.10. Unassigned (J) . . . . . . . . . . . . . . . . . . . . . 22 8.10. Unassigned (J) . . . . . . . . . . . . . . . . . . . . . 22
8.11. ASCII7 (K) . . . . . . . . . . . . . . . . . . . . . . . 22 8.11. ASCII7 (K) . . . . . . . . . . . . . . . . . . . . . . . 22
8.12. Controls (L) . . . . . . . . . . . . . . . . . . . . . . 22 8.12. Controls (L) . . . . . . . . . . . . . . . . . . . . . . 22
8.13. PrecisIgnorableProperties (M) . . . . . . . . . . . . . . 22 8.13. PrecisIgnorableProperties (M) . . . . . . . . . . . . . . 22
8.14. Spaces (N) . . . . . . . . . . . . . . . . . . . . . . . 23 8.14. Spaces (N) . . . . . . . . . . . . . . . . . . . . . . . 23
8.15. Symbols (O) . . . . . . . . . . . . . . . . . . . . . . . 23 8.15. Symbols (O) . . . . . . . . . . . . . . . . . . . . . . . 23
8.16. Punctuation (P) . . . . . . . . . . . . . . . . . . . . . 23 8.16. Punctuation (P) . . . . . . . . . . . . . . . . . . . . . 23
8.17. HasCompat (Q) . . . . . . . . . . . . . . . . . . . . . . 23 8.17. HasCompat (Q) . . . . . . . . . . . . . . . . . . . . . . 23
8.18. OtherLetterDigits (R) . . . . . . . . . . . . . . . . . . 23 8.18. OtherLetterDigits (R) . . . . . . . . . . . . . . . . . . 23
9. Guidelines for Designated Experts . . . . . . . . . . . . . . 24 9. Guidelines for Designated Experts . . . . . . . . . . . . . . 23
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24
10.1. PRECIS Derived Property Value Registry . . . . . . . . . 24 10.1. PRECIS Derived Property Value Registry . . . . . . . . . 24
10.2. PRECIS Base Classes Registry . . . . . . . . . . . . . . 24 10.2. PRECIS Base Classes Registry . . . . . . . . . . . . . . 24
10.3. PRECIS Profiles Registry . . . . . . . . . . . . . . . . 25 10.3. PRECIS Profiles Registry . . . . . . . . . . . . . . . . 25
11. Security Considerations . . . . . . . . . . . . . . . . . . . 27 11. Security Considerations . . . . . . . . . . . . . . . . . . . 27
11.1. General Issues . . . . . . . . . . . . . . . . . . . . . 27 11.1. General Issues . . . . . . . . . . . . . . . . . . . . . 27
11.2. Use of the IdentifierClass . . . . . . . . . . . . . . . 28 11.2. Use of the IdentifierClass . . . . . . . . . . . . . . . 27
11.3. Use of the FreeformClass . . . . . . . . . . . . . . . . 28 11.3. Use of the FreeformClass . . . . . . . . . . . . . . . . 28
11.4. Local Character Set Issues . . . . . . . . . . . . . . . 28 11.4. Local Character Set Issues . . . . . . . . . . . . . . . 28
11.5. Visually Similar Characters . . . . . . . . . . . . . . 28 11.5. Visually Similar Characters . . . . . . . . . . . . . . 28
11.6. Security of Passwords . . . . . . . . . . . . . . . . . 30 11.6. Security of Passwords . . . . . . . . . . . . . . . . . 30
12. Interoperability Considerations . . . . . . . . . . . . . . . 31 12. Interoperability Considerations . . . . . . . . . . . . . . . 31
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 32 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 32
13.1. Normative References . . . . . . . . . . . . . . . . . . 32 13.1. Normative References . . . . . . . . . . . . . . . . . . 32
13.2. Informative References . . . . . . . . . . . . . . . . . 32 13.2. Informative References . . . . . . . . . . . . . . . . . 32
13.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 35 13.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 35 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 35
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 36 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 35
1. Introduction 1. Introduction
Application protocols using Unicode characters [Unicode7.0] in Application protocols using Unicode characters [Unicode7.0] in
protocol strings need to properly handle such strings in order to protocol strings need to properly handle such strings in order to
enforce internationalization rules for strings placed in various enforce internationalization rules for strings placed in various
protocol slots (such as addresses and identifiers) and to perform protocol slots (such as addresses and identifiers) and to perform
valid comparison operations (e.g., for purposes of authentication or valid 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, enforcement, and application protocols to perform the preparation, enforcement, and
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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 (a) determine whether each code point or character category is (a)
valid, (b) allowed in certain contexts, (c) disallowed, or (d) valid, (b) allowed in certain contexts, (c) disallowed, or (d)
unassigned. unassigned.
3. Use an "inclusion model" such that a string class consists only 3. Use an "inclusion model" such that a string class consists only
of code points that are explicitly allowed, with the result that of code points that are explicitly allowed, with the result that
any code point not explicitly allowed is forbidden. any code point not explicitly allowed is forbidden.
4. Enable application protocols to define profiles of the PRECIS 4. Enable application protocols to define profiles of the PRECIS
string classes if necessary, addressing matters such as width string classes if necessary (addressing matters such as width
mapping, case mapping, Unicode normalization, directionality, and mapping, case mapping, Unicode normalization, and directionality)
further excluded code points or character categories. but strongly discourage the multiplication of profiles beyond
necessity in order to avoid violations of the Principle of Least
User Astonishment.
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 agile with regard to Unicode o Application protocols will be agile with regard to Unicode
versions. versions.
o Implementers will be able to share code point tables and software o Implementers will be able to share code point tables and software
code across application protocols, most likely by means of code across application protocols, most likely by means of
software libraries. software libraries.
o End users will be able to acquire more accurate expectations about o End users will be able to acquire more accurate expectations about
the characters that are acceptable in various contexts. Given the characters that are acceptable in various contexts. Given
this more uniform set of string classes, it is also expected that this more uniform set of string classes, it is also expected that
copy/paste operations between software implementing different copy/paste operations between software implementing different
application protocols will be more predictable and coherent. application protocols will be more predictable and coherent.
Whereas the string classes define the "baseline" code points for a Whereas the string classes define the "baseline" code points for a
range of applications, profiling enables application protocols to range of applications, profiling enables application protocols to
further restrict the allowable code points beyond those specified for apply the string classes in ways that are appropriate for common
the relevant string class (e.g., characters with special or reserved constructs such as usernames and passwords
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], [I-D.ietf-precis-saslprepbis], nicknames [I-D.ietf-precis-nickname],
the localparts of instant messaging addresses the localparts of account names [I-D.ietf-xmpp-6122bis], and free-
[I-D.ietf-xmpp-6122bis], and free-form strings form strings [I-D.ietf-xmpp-6122bis]. Profiles are responsible for
[I-D.ietf-xmpp-6122bis]. Profiles are responsible for defining the defining the handling of right-to-left characters as well as various
handling of right-to-left characters as well as various mapping mapping operations of the kind also discussed for IDNs in [RFC5895],
operations of the kind also discussed for IDNs in [RFC5895], such as such as case preservation or lowercasing, Unicode normalization,
case preservation or lowercasing, Unicode normalization, mapping of mapping of certain characters to other characters or to nothing, and
certain characters to other characters or to nothing, and mapping of mapping of full-width and half-width characters.
full-width and half-width characters.
When an application applies a profile of a PRECIS string class, it When an application applies a profile of a PRECIS string class, it
can achieve the following objectives: can achieve the following objectives:
a. Determine if a given string conforms to the profile, thus a. Determine if a given string conforms to the profile, thus
enabling enforcement of the rules (e.g., to determine if a string enabling enforcement of the rules (e.g., to determine if a string
is allowed for use in the relevant "slot" specified by an is allowed for use in the relevant protocol slot specified by an
application protocol). application protocol).
b. Determine if any two given strings are equivalent, thus enabling b. Determine if any two given strings are equivalent, thus enabling
comparision (e.g., to make an access decision for purposes of comparision (e.g., to make an access decision for purposes of
authentication or authorization as further described in authentication or authorization as further described in
[RFC6943]). [RFC6943]).
The opportunity to define profiles naturally introduces the The opportunity to define profiles naturally introduces the
possibility of a proliferation of profiles, thus potentially possibility of a proliferation of profiles, thus potentially
mitigating the benefits of common code and violating user mitigating the benefits of common code and violating user
expectations. See Section 5 for a discussion of this important expectations. See Section 5 for a discussion of this important
topic. topic.
Although this framework is similar to IDNA2008 and borrows some of Although this framework is similar to IDNA2008 and includes by
the character categories defined in [RFC5892], it defines additional reference some of the character categories defined in [RFC5892], it
character categories to meet the needs of common application defines additional character categories to meet the needs of common
protocols. application protocols.
The character categories and calculation rules defined under The character categories and calculation rules defined under
Section 7 and Section 8 are normative and apply to all Unicode code Section 7 and Section 8 are normative and apply to all Unicode code
points. The code point table that results from applying the points. The code point table that results from applying the
character categories and calculation rules to the latest version of character categories and calculation rules to the latest version of
Unicode are provided in an IANA registry. Unicode can be found in an IANA registry.
2. Terminology 2. Terminology
Many important terms used in this document are defined in [RFC5890], Many important terms used in this document are defined in [RFC5890],
[RFC6365], [RFC6885], and [Unicode7.0]. The terms "left-to-right" [RFC6365], [RFC6885], and [Unicode7.0]. The terms "left-to-right"
(LTR) and "right-to-left" (RTL) are defined in Unicode Standard Annex (LTR) and "right-to-left" (RTL) are defined in Unicode Standard Annex
#9 [UAX9]. #9 [UAX9].
As of the date of writing, the version of Unicode published by the As of the date of writing, the version of Unicode published by the
Unicode Consortium is 6.3 [Unicode7.0]; however, PRECIS is not tied Unicode Consortium is 7.0 [Unicode7.0]; however, PRECIS is not tied
to a specific version of Unicode. The latest version of Unicode is to a specific version of Unicode. The latest version of Unicode is
always available [UnicodeCurrent]. always available [UnicodeCurrent].
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in "OPTIONAL" in this document are to be interpreted as described in
[RFC2119]. [RFC2119].
3. Preparation, Enforcement, and Comparison 3. Preparation, Enforcement, and Comparison
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o Comparison entails applying all of the rules specified for a o Comparison entails applying all of the rules specified for a
particular string class or profile thereof to two separate particular string class or profile thereof to two separate
strings, for the purpose of determining if the two strings are strings, for the purpose of determining if the two strings are
equivalent. equivalent.
o Preparation entails only ensuring that the characters in an o Preparation entails only ensuring that the characters in an
individual string are allowed by the underlying PRECIS string individual string are allowed by the underlying PRECIS string
class. class.
In most cases, authoritative entities such as servers are responsible In most cases, authoritative entities such as servers are responsible
for enforcement and subsidiary entities such as clients are for enforcement, whereas subsidiary entities such as clients are
responsible only for preparation. The rationale for this distinction responsible only for preparation. The rationale for this distinction
is that clients might not have the facilities (in terms of device is that clients might not have the facilities (in terms of device
memory and processing power) to enforce all the rules regarding memory and processing power) to enforce all the rules regarding
internationalized strings (such as width mapping and Unicode internationalized strings (such as width mapping and Unicode
normalization), although often they can limit the repertoire of normalization), although they can more easily limit the repertoire of
characters they offer to an end user. By contrast, it is assumed characters they offer to an end user. By contrast, it is assumed
that a server would have more capacity to enforce the rules, and in that a server would have more capacity to enforce the rules, and in
any case acts as an authority regarding allowable strings in protocol any case acts as an authority regarding allowable strings in protocol
slots such as addresses and endpoint identifiers (since a client slots such as addresses and endpoint identifiers. In addition, a
cannot necessarily be trusted to properly generate such strings, client cannot necessarily be trusted to properly generate such
especially for security-sensitive contexts such as authentication and strings, especially for security-sensitive contexts such as
authorization). authentication and authorization.
4. String Classes 4. String Classes
4.1. Overview 4.1. Overview
Starting in 2010, various "customers" of Stringprep began to discuss Starting in 2010, various "customers" of Stringprep began to discuss
the need to define a post-Stringprep approach to the preparation and the need to define a post-Stringprep approach to the preparation and
comparison of internationalized strings other than IDNs. This comparison of internationalized strings other than IDNs. This
community analyzed the existing Stringprep profiles and also weighed community analyzed the existing Stringprep profiles and also weighed
the costs and benefits of defining a relatively small set of Unicode the costs and benefits of defining a relatively small set of Unicode
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that is used to identify or address a network entity such as a that is used to identify or address a network entity such as a
user account, a venue (e.g., a chatroom), an information source 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 (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 intent is that this class will minimize user confusion in a wide
variety of application protocols, with the result that safety has variety of application protocols, with the result that safety has
been prioritized over expressiveness for this class. been prioritized over expressiveness for this class.
FreeformClass: a sequence of letters, numbers, symbols, spaces, and FreeformClass: a sequence of letters, numbers, symbols, spaces, and
other characters that is used for free-form strings, including other characters that is used for free-form strings, including
passwords as well as display elements such as human-friendly passwords as well as display elements such as human-friendly
nicknames in chatrooms; the intent is that this class will allow nicknames for devices or for participants in a chatroom; the
nearly any Unicode character, with the result that expressiveness intent is that this class will allow nearly any Unicode character,
has been prioritized over safety for this class (e.g., protocol with the result that expressiveness has been prioritized over
designers, application developers, service providers, and end safety for this class. Note well that protocol designers,
users might not understand or be able to enter all of the application developers, service providers, and end users might not
characters that can be included in the FreeformClass - see understand or be able to enter all of the characters that can be
Section 11.3 for details). included in the FreeformClass - see Section 11.3 for details.
Future specifications might define additional PRECIS string classes, Future specifications might define additional PRECIS string classes,
such as a class that falls somewhere between the IdentifierClass and such as a class that falls somewhere between the IdentifierClass and
the FreeformClass. At this time, it is not clear how useful such a the FreeformClass. At this time, it is not clear how useful such a
class would be. In any case, because application developers are able class would be. In any case, because application developers are able
to define profiles of PRECIS string classes, a protocol needing a to define profiles of PRECIS string classes, a protocol needing a
construct between the IdentiferClass and the FreeformClass could construct between the IdentiferClass and the FreeformClass could
define a restricted profile of the FreeformClass if needed. define a restricted profile of the FreeformClass if needed.
The following subsections discuss the IdentifierClass and The following subsections discuss the IdentifierClass and
skipping to change at page 8, line 41 skipping to change at page 8, line 41
to be excluded from the string. to be excluded from the string.
Unassigned: Defines application behavior in the presence of code Unassigned: Defines application behavior in the presence of code
points that are unknown (i.e., not yet designated) for the version points that are unknown (i.e., not yet designated) for the version
of Unicode used by the application. of Unicode used by the application.
This document defines the valid, contextual rule required, This document defines the valid, contextual rule required,
disallowed, and unassigned rules for the IdentifierClass and disallowed, and unassigned rules for the IdentifierClass and
FreeformClass. As described under Section 5, profiles of these FreeformClass. As described under Section 5, profiles of these
string classes are responsible for defining the width mapping, string classes are responsible for defining the width mapping,
additional mappings, case mapping, normalization, directionality, and additional mappings, case mapping, normalization, and directionality
exclusion rules. rules.
4.2. IdentifierClass 4.2. 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.
4.2.1. Valid 4.2.1. Valid
skipping to change at page 10, line 19 skipping to change at page 10, line 19
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 8.18. defined under Section 8.18.
4.2.4. Unassigned 4.2.4. Unassigned
Any code points that are not yet designated in the Unicode character Any code points that are not yet designated in the Unicode character
set are considered Unassigned for purposes of the IdentifierClass, set are considered Unassigned for purposes of the IdentifierClass,
and such code points are to be treated as Disallowed. and such code points are to be treated as Disallowed. See
Section 8.10.
4.2.5. Examples 4.2.5. Examples
As described in the Introduction to this document, the string classes As described in the Introduction to this document, the string classes
do not handle all issues related to string preparation and comparison do not handle all issues related to string preparation and comparison
(such as case mapping); instead, such issues are handled at the level (such as case mapping); instead, such issues are handled at the level
of profiles. Examples for two profiles of the IdentifierClass can be of profiles. Examples for two profiles of the IdentifierClass can be
found in [I-D.ietf-precis-saslprepbis] (the UsernameIdentifierClass found in [I-D.ietf-precis-saslprepbis] (the UsernameIdentifierClass
profile) and in [I-D.ietf-xmpp-6122bis] (the JIDlocalIdentifierClass profile) and in [I-D.ietf-xmpp-6122bis] (the LocalpartIdentifierClass
profile). profile).
4.3. FreeformClass 4.3. 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.
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such code points are to be treated as Disallowed. such code points are to be treated as Disallowed.
4.3.5. Examples 4.3.5. Examples
As described in the Introduction to this document, the string classes As described in the Introduction to this document, the string classes
do not handle all issues related to string preparation and comparison do not handle all issues related to string preparation and comparison
(such as case mapping); instead, such issues are handled at the level (such as case mapping); instead, such issues are handled at the level
of profiles. Examples for two profiles of the FreeformClass can be of profiles. Examples for two profiles of the FreeformClass can be
found in [I-D.ietf-precis-nickname] (the NicknameFreeformClass found in [I-D.ietf-precis-nickname] (the NicknameFreeformClass
profile) and in [I-D.ietf-xmpp-6122bis] (the profile) and in [I-D.ietf-xmpp-6122bis] (the
JIDresourceIdentifierClass profile). ResourcepartIdentifierClass profile).
5. Profiles 5. Profiles
This framework document defines the valid, contextual-rule-required, This framework document defines the valid, contextual-rule-required,
disallowed, and unassigned rules for the IdentifierClass and the disallowed, and unassigned rules for the IdentifierClass and the
FreeformClass. A profile of a PRECIS string class MUST define the FreeformClass. A profile of a PRECIS string class MUST define the
width mapping, additional mappings (if any), case mapping, width mapping, additional mappings (if any), case mapping,
normalization, directionality, and exclusion rules. A profile MAY normalization, and directionality rules. A profile MAY also restrict
also restrict the allowable characters above and beyond the the allowable characters above and beyond the definition of the
definition of the relevant PRECIS string class (but MUST NOT add as relevant PRECIS string class (but MUST NOT add as valid any code
valid any code points or character categories that are disallowed by points or character categories that are disallowed by the relevant
the relevant PRECIS string class). These matters are discussed in PRECIS string class). These matters are discussed in the following
the following subsections. subsections.
Profiles of the PRECIS string classes are registered with the IANA as Profiles of the PRECIS string classes are registered with the IANA as
described under Section 10.3. Profile names use the following described under Section 10.3. Profile names use the following
convention: they are of the form "ProfilenameBaseClass", where the convention: they are of the form "ProfilenameBaseClass", where the
"Profilename" string is a differentiator and "BaseClass" is the name "Profilename" string is a differentiator and "BaseClass" is the name
of the PRECIS string class being profiled; for example, the profile of the PRECIS string class being profiled; for example, the profile
of the IdentifierClass used for localparts of Jabber Identifiers of the IdentifierClass used for localparts of Jabber Identifiers
(JIDs) in the Extensible Messaging and Presence Protocol (XMPP) is (JIDs) in the Extensible Messaging and Presence Protocol (XMPP) is
named "JIDlocalIdentifierClass" [I-D.ietf-xmpp-6122bis]. named "LocalpartIdentifierClass" [I-D.ietf-xmpp-6122bis].
5.1. Profiles Must Not Be Multiplied Beyond Necessity 5.1. Profiles Must Not Be Multiplied Beyond Necessity
The risk of profile proliferation is significant because having too The risk of profile proliferation is significant because having too
many profiles will result in different behavior across various many profiles will result in different behavior across various
applications, thus violating what is known in user interface design applications, thus violating what is known in user interface design
as the Principle of Least Astonishment. as the Principle of Least Astonishment.
Indeed, we already have too many profiles. Ideally we would have at Indeed, we already have too many profiles. Ideally we would have at
most two or three profiles. Unfortunately, numerous application most two or three profiles. Unfortunately, numerous application
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5.2.4. Normalization Rule 5.2.4. Normalization Rule
The normalization rule of a profile specifies which Unicode The normalization rule of a profile specifies which Unicode
normalization form (D, KD, C, or KC) is to be applied (see Unicode normalization form (D, KD, C, or KC) is to be applied (see Unicode
Standard Annex #15 [UAX15] for background information). Standard Annex #15 [UAX15] for background information).
In accordance with [RFC5198], normalization form C (NFC) is In accordance with [RFC5198], normalization form C (NFC) is
RECOMMENDED. RECOMMENDED.
5.2.5. Exclusion Rule 5.2.5. Directionality Rule
The exclusion rule of a profile specifies any particular characters
or character categories that are not allowed in strings conforming to
the profile, 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.
Typically, an exclusion rule is defined for the purpose of backward-
compatibility with legacy formats. Profiles for newly-defined string
types SHOULD NOT have an exclusion rule.
5.2.6. Directionality Rule
The directionality rule of a profile specifies how to treat strings The directionality rule of a profile specifies how to treat strings
containing left-to-right (LTR) and right-to-left (RTL) characters containing left-to-right (LTR) and right-to-left (RTL) characters
(see Unicode Standard Annex #9 [UAX9]). A profile usually specifies (see Unicode Standard Annex #9 [UAX9]). A profile usually specifies
a directionality rule that restricts strings to be entirely LTR a directionality rule that restricts strings to be entirely LTR
strings or entirely RTL strings and defines the allowable sequences strings or entirely RTL strings and defines the allowable sequences
of characters in LTR and RTL strings. Possible rules include, but of characters in LTR and RTL strings. Possible rules include, but
are not limited to, (a) considering any string that contains a right- 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 to-left code point to be a right-to-left string, or (b) applying the
"Bidi Rule" from [RFC5893]. "Bidi Rule" from [RFC5893].
Mixed-direction strings are not directly supported by the PRECIS Mixed-direction strings are not directly supported by the PRECIS
framework itself, since there is currently no widely accepted and framework itself, since there is currently no widely accepted and
implemented solution for the safe display of mixed-direction strings. implemented solution for the safe display of mixed-direction strings.
An application protocol that uses the PRECIS framework (or an An application protocol that uses the PRECIS framework (or an
extension to the framework) could define better ways to present extension to the framework) could define better ways to present
mixed-direction strings; however, that work is outside the scope of mixed-direction strings; however, that work is outside the scope of
this framework and would likely require a great deal of careful this framework and would likely require a great deal of careful
research into the problems of displaying bidirectional text. research into the problems of displaying bidirectional text.
5.3. Building Application-Layer Constructs 5.3. Further Excluded Characters
An application protocol that uses a profile MAY specify particular
characters or character categories that are not allowed in relevant
slots within that application protocol, above and beyond those
excluded by the string class or profile.
That is, an application protocol 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 or profile will be defined as disallowed
for the relevant protocol slot.
Typically, such exclusions are defined for the purpose of backward-
compatibility with legacy formats within an application protocol.
These are defined for application protocols, not profiles, in order
to prevent multiplication of profiles beyond necessity (see
Section 5.1).
5.4. Building Application-Layer Constructs
Sometimes, an application-layer construct does not map in a Sometimes, an application-layer construct does not map in a
straightforward manner to one of the base string classes or a profile straightforward manner to one of the base string classes or a profile
thereof. Consider, for example, the "simple user name" construct in thereof. Consider, for example, the "simple user name" construct in
the Simple Authentication and Security Layer (SASL) [RFC4422]. the Simple Authentication and Security Layer (SASL) [RFC4422].
Depending on the deployment, a simple user name might take the form 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 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 user name space and then the user's family name). Such a simple user name
cannot be defined as an instance of the IdentifierClass or a profile cannot be defined as an instance of the IdentifierClass or a profile
thereof, since space characters are not allowed in the thereof, 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 ABNF sequence of IdentifierClass instances, as in the following ABNF
[RFC5234] from [I-D.ietf-precis-saslprepbis]: [RFC5234] from [I-D.ietf-precis-saslprepbis]:
username = userpart [1*(1*SP userpart)] username = userpart *(1*SP userpart)
userpart = 1*(idbyte) userpart = 1*(idbyte)
; ;
; an "idbyte" is a byte used to represent a ; an "idbyte" is a byte used to represent a
; UTF-8 encoded Unicode code point that can be ; UTF-8 encoded Unicode code point that can be
; contained in a string that conforms to the ; contained in a string that conforms to the
; PRECIS "IdentifierClass" ; 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".
5.4. A Note about Spaces 5.5. 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:
o Many Unicode characters are confusable with ASCII space. o Many Unicode characters are confusable with ASCII space.
o Even if non-ASCII space characters are mapped to ASCII space o Even if non-ASCII space characters are mapped to ASCII space
(U+0020), space characters are often not rendered in user (U+0020), space characters are often not rendered in user
interfaces, leading to the possibility that a human user might interfaces, leading to the possibility that a human user might
consider a string containing spaces to be equivalent to the same consider a string containing spaces to be equivalent to the same
string without spaces. string without spaces.
o In some locales, some devices are known to generate a character 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 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. user performs an action like hitting the space bar on a keyboard.
One consequence of disallowing space characters in the One consequence of disallowing space characters in the
IdentifierClass might be to effectively discourage their use within IdentifierClass might be to effectively discourage their use within
identifiers created in newer application protocols; given the identifiers created in newer application protocols; given the
challenges involved in properly handling space characters (especially challenges involved with properly handling space characters
non-ASCII space characters) in identifiers and other protocol (especially non-ASCII space characters) in identifiers and other
strings, the Working Group considered this to be a feature, not a protocol strings, the PRECIS Working Group considered this to be a
bug. feature, not a bug.
However, the FreeformClass does allow spaces, which enables However, the FreeformClass does allow spaces, which enables
application protocols to define profiles of the FreeformClass that application protocols to define profiles of the FreeformClass that
are more flexible than any profiles of the IdentifierClass. In are more flexible than any profiles of the IdentifierClass. In
addition, as explained in the previous section, application protocols addition, as explained in the previous section, application protocols
can also define application-layer constructs containing spaces. can also define application-layer constructs containing spaces.
6. Order of Operations 6. Order of Operations
To ensure proper comparison, the rules specified for a particular To ensure proper comparison, the rules specified for a particular
string class or profile MUST be applied in the following order: string class or profile MUST be applied in the following order:
1. Width Mapping Rule 1. Width Mapping Rule
2. Additional Mapping Rule 2. Additional Mapping Rule
3. Case Mapping Rule 3. Case Mapping Rule
4. Normalization Rule 4. Normalization Rule
5. Exclusion Rule 5. Directionality Rule
6. Behavioral rules for determining whether a code point is valid, 6. Behavioral rules for determining whether a code point is valid,
allowed under a contextual rule, disallowed, or unassigned allowed under a contextual rule, disallowed, or unassigned
As already described, the width mapping, additional mapping, case As already described, the width mapping, additional mapping, case
mapping, normalization, and exclusion rules are specified for each mapping, normalization, and directionality rules are specified for
profile, whereas the behavioral rules are specified for each string each profile, whereas the behavioral rules are specified for each
class. Some of the logic behind this order is provided under string class. Some of the logic behind this order is provided under
Section 5.2.1 (see also the PRECIS mappings document Section 5.2.1 (see also the PRECIS mappings document
[I-D.ietf-precis-mappings]). [I-D.ietf-precis-mappings]).
7. Code Point Properties 7. Code Point Properties
In order to implement the string classes described above, this In order to implement the string classes described above, this
document does the following: document does the following:
1. Reviews and classifies the collections of code points in the 1. Reviews and classifies the collections of code points in the
Unicode character set by examining various code point properties. Unicode character set by examining various code point properties.
skipping to change at page 17, line 50 skipping to change at page 18, line 7
relevant application protocol. relevant application protocol.
This document is not intended to specify precisely how derived This document is not intended to specify precisely how derived
property values are to be applied in protocol strings. That property values are to be applied in protocol strings. That
information is the responsibility of the protocol specification that information is the responsibility of the protocol specification that
uses or profiles a PRECIS string class from this document. The value uses or profiles a PRECIS string class from this document. The value
of the property is to be interpreted as follows. 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 (currently, IdentifierClass and PRECIS string class (currently, IdentifierClass and
FreeformClass). Code points with this property value are FreeformClass). The abbreviated term "PVALID" is used to refer to
permitted for general use in any string class. The abbreviated this value in the remainder of this document.
term "PVALID" is used to refer to 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. In the remainder of this
property value are permitted for use in specific string classes. document, the abbreviated term *_PVAL is used, where * = (ID |
In the remainder of this document, the abbreviated term *_PVAL is FREE), i.e., either "FREE_PVAL" or "ID_PVAL". In practice, the
used, where * = (ID | FREE), i.e., either "FREE_PVAL" or derived property ID_PVAL is not used in this specification, since
"ID_PVAL". In practice, the derived property ID_PVAL is not used every ID_PVAL code point is PVALID.
in this specification, since every ID_PVAL code point is PVALID.
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. As in IDNA2008, there other characters or properties are present. As in IDNA2008, there
are two subdivisions of CONTEXTUAL RULE REQUIRED, the first for are two subdivisions of CONTEXTUAL RULE REQUIRED, the first for
Join_controls (called "CONTEXTJ") and the second for other Join_controls (called "CONTEXTJ") and the second for other
characters (called "CONTEXTO"). A character with the derived characters (called "CONTEXTO"). A character with the derived
property value CONTEXTJ or CONTEXTO MUST NOT be used unless an property value CONTEXTJ or CONTEXTO MUST NOT be used unless an
appropriate rule has been established and the context of the appropriate rule has been established and the context of the
character is consistent with that rule. The most notable of the character is consistent with that rule. The most notable of the
CONTEXTUAL RULE REQUIRED characters are the Join Control CONTEXTUAL RULE REQUIRED characters are the Join Control
characters U+200D ZERO WIDTH JOINER and U+200C ZERO WIDTH NON- characters U+200D ZERO WIDTH JOINER and U+200C ZERO WIDTH NON-
JOINER, which have a derived property value of CONTEXTJ. See JOINER, which have a derived property value of CONTEXTJ. See
Appendix A of [RFC5892] for more information. Appendix A of [RFC5892] for more information.
DISALLOWED Those code points that are not permitted in any PRECIS DISALLOWED Those code points that are 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 one of the string classes but that might be permitted
property value are not permitted in one of the string classes but in others. In the remainder of this document, the abbreviated
might be permitted in others. In the remainder of this document, term *_DIS is used, where * = (ID | FREE), i.e., either "FREE_DIS"
the abbreviated term *_DIS is used, where * = (ID | FREE), i.e., or "ID_DIS". In practice, the derived property FREE_DIS is not
either "FREE_DIS" or "ID_DIS". In practice, the derived property used in this specification, since every FREE_DIS code point is
FREE_DIS is not used in this specification, since every FREE_DIS DISALLOWED.
code point is DISALLOWED.
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.
To summarize, the assigned values of the derived property are:
o PVALID
o FREE_PVAL
o CONTEXTJ
o CONTEXTO
o DISALLOWED
o UNASSIGNED
The algorithm to calculate the value of the derived property is as The algorithm to calculate the value of the derived property is as
follows: follows:
If .cp. .in. Exceptions Then Exceptions(cp); If .cp. .in. Exceptions Then Exceptions(cp);
Else If .cp. .in. BackwardCompatible Then BackwardCompatible(cp); Else If .cp. .in. BackwardCompatible Then BackwardCompatible(cp);
Else If .cp. .in. Unassigned Then UNASSIGNED; Else If .cp. .in. Unassigned Then UNASSIGNED;
Else If .cp. .in. ASCII7 Then PVALID; Else If .cp. .in. ASCII7 Then PVALID;
Else If .cp. .in. JoinControl Then CONTEXTJ; Else If .cp. .in. JoinControl Then CONTEXTJ;
Else If .cp. .in. OldHangulJamo Then DISALLOWED; Else If .cp. .in. OldHangulJamo Then DISALLOWED;
Else If .cp. .in. PrecisIgnorableProperties Then DISALLOWED; Else If .cp. .in. PrecisIgnorableProperties Then DISALLOWED;
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Else If .cp. .in. Symbols 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 If .cp. .in. Punctuation Then ID_DIS or FREE_PVAL;
Else DISALLOWED; Else DISALLOWED;
The value of the derived property calculated can depend on the string The value of the derived property calculated can depend on the string
class; for example, if an identifier used in an application protocol class; for example, if an identifier used in an application protocol
is defined as profiling the PRECIS IdentifierClass then a space is defined as profiling the PRECIS IdentifierClass then a space
character such as U+0020 would be assigned to ID_DIS, whereas if an character such as U+0020 would be assigned to ID_DIS, whereas if an
identifier is defined as profiling the PRECIS FreeformClass then the identifier is defined as profiling the PRECIS FreeformClass then the
character would be assigned to FREE_PVAL. For the sake of brevity, character would be assigned to FREE_PVAL. For the sake of brevity,
the designation "FREE_PVAL" is used in the code point tables, instead the designation "FREE_PVAL" is used herein, instead of the longer
of the longer designation "ID_DIS or FREE_PVAL". In practice, the designation "ID_DIS or FREE_PVAL". In practice, the derived
derived properties ID_PVAL and FREE_DIS are not used in this properties ID_PVAL and FREE_DIS are not used in this specification,
specification, since every ID_PVAL code point is PVALID and every since every ID_PVAL code point is PVALID and every FREE_DIS code
FREE_DIS code point is DISALLOWED. point is DISALLOWED.
Use of the name of a rule (such as "Exceptions") implies the set of 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 code points that the rule defines, whereas the same name as a
function call (such as "Exceptions(cp)") implies the value that the function call (such as "Exceptions(cp)") implies the value that the
code point has in the Exceptions table. code point has in the Exceptions table.
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 7.0 depending on the category, since some after Unicode 5.2 or 7.0 depending on the category, since some
categories in this document are reused from IDNA2008 and therefore categories mentioned in this document are simply pointers to IDNA2008
were defined at the time of Unicode 5.2). Changes in Unicode and therefore were defined at the time of Unicode 5.2). Changes in
properties that do not affect the outcome of this process therefore Unicode properties that do not affect the outcome of this process
do not affect this framework. For example, a character can have its therefore do not affect this framework. For example, a character can
Unicode General_Category value (see Chapter 4 of the Unicode Standard have its Unicode General_Category value (see Chapter 4 of the Unicode
[Unicode7.0]) change from So to Sm, or from Lo to Ll, without Standard [Unicode7.0]) change from So to Sm, or from Lo to Ll,
affecting the algorithm results. Moreover, even if such changes were without affecting the algorithm results. Moreover, even if such
to result, the BackwardCompatible list (Section 8.7) can be adjusted changes were to result, the BackwardCompatible list (Section 8.7) can
to ensure the stability of the results. be adjusted to ensure the stability of the results.
8. Category Definitions Used to Calculate Derived Property 8. Category Definitions Used to Calculate Derived Property
The derived property obtains its value based on a two-step procedure: The derived property obtains its value based on a two-step procedure:
1. Characters are placed in one or more character categories either 1. Characters are placed in one or more character categories either
(1) based on core properties defined by the Unicode Standard or (1) based on core properties defined by the Unicode Standard or
(2) by treating the code point as an exception and addressing the (2) by treating the code point as an exception and addressing the
code point based on its code point value. These categories are code point based on its code point value. These categories are
not mutually exclusive. not mutually exclusive.
skipping to change at page 20, line 38 skipping to change at page 20, line 32
gc property. gc property.
In the following specification of character categories, the operation In the following specification of character categories, the operation
that returns the value of a particular Unicode character property for that returns the value of a particular Unicode character property for
a code point is designated by using the formal name of that property a code point is designated by using the formal name of that property
(from the Unicode PropertyAliases.txt [1]) followed by '(cp)' for (from the Unicode PropertyAliases.txt [1]) followed by '(cp)' for
"code point". For example, the value of the General_Category "code point". For example, the value of the General_Category
property for a code point is indicated by General_Category(cp). property for a code point is indicated by General_Category(cp).
The first ten categories (A-J) shown below were previously defined The first ten categories (A-J) shown below were previously defined
for IDNA2008 and are copied directly from [RFC5892] to ease the for IDNA2008 and are referenced from [RFC5892] to ease the
understanding of how PRECIS handles various characters. Some of understanding of how PRECIS handles various characters. Some of
these categories are reused in PRECIS and some of them are not; these categories are reused in PRECIS and some of them are not;
however, the lettering of categories is retained to prevent overlap however, the lettering of categories is retained to prevent overlap
and to ease implementation of both IDNA2008 and PRECIS in a single and to ease implementation of both IDNA2008 and PRECIS in a single
software application. The next eight categories (K-R) are specific software application. The next eight categories (K-R) are specific
to PRECIS. to PRECIS.
8.1. LetterDigits (A) 8.1. LetterDigits (A)
This category is defined in Secton 2.1 of [RFC5892] and is included This category is defined in Secton 2.1 of [RFC5892] and is included
by reference for use in PRECIS. by reference for use in PRECIS.
8.2. Unstable (B) 8.2. Unstable (B)
This category is defined in Secton 2.2 of [RFC5892] but not used in This category is defined in Secton 2.2 of [RFC5892] but is not used
PRECIS. in PRECIS.
8.3. IgnorableProperties (C) 8.3. IgnorableProperties (C)
This category is defined in Secton 2.3 of [RFC5892] but not used in This category is defined in Secton 2.3 of [RFC5892] but is not used
PRECIS. in PRECIS.
Note: See the "PrecisIgnorableProperties (M)" category below for a Note: See the "PrecisIgnorableProperties (M)" category below for a
more inclusive category used in PRECIS identifiers. more inclusive category used in PRECIS identifiers.
8.4. IgnorableBlocks (D) 8.4. IgnorableBlocks (D)
This category is defined in Secton 2.4 of [RFC5892] but not used in This category is defined in Secton 2.4 of [RFC5892] but is not used
PRECIS. in PRECIS.
8.5. LDH (E) 8.5. LDH (E)
This category is defined in Secton 2.5 of [RFC5892] but not used in This category is defined in Secton 2.5 of [RFC5892] but is not used
PRECIS. in PRECIS.
Note: See the "ASCII7 (K)" category below for a more inclusive Note: See the "ASCII7 (K)" category below for a more inclusive
category used in PRECIS identifiers. category used in PRECIS identifiers.
8.6. Exceptions (F) 8.6. Exceptions (F)
This category is defined in Secton 2.6 of [RFC5892] and is included This category is defined in Secton 2.6 of [RFC5892] and is included
by reference for use in PRECIS. by reference for use in PRECIS.
8.7. BackwardCompatible (G) 8.7. BackwardCompatible (G)
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characters from the 7-bit ASCII range. By applying this category, characters from the 7-bit ASCII range. By applying this category,
the algorithm specified under Section 7 exempts these characters from the algorithm specified under Section 7 exempts these characters from
other rules that might be applied during PRECIS processing, on the other rules that might be applied during PRECIS processing, on the
assumption that these code points are in such wide use that assumption that these code points are in such wide use that
disallowing them would be counter-productive. disallowing them would be counter-productive.
K: cp is in {0021..007E} K: cp is in {0021..007E}
8.12. Controls (L) 8.12. Controls (L)
This PRECIS-specific category consists of all control characters.
L: Control(cp) = True L: Control(cp) = True
8.13. PrecisIgnorableProperties (M) 8.13. PrecisIgnorableProperties (M)
This PRECIS-specific category is used to group code points that are This PRECIS-specific category is used to group code points that are
discouraged from use in PRECIS string classes. discouraged from use in PRECIS string classes.
M: Default_Ignorable_Code_Point(cp) = True or M: Default_Ignorable_Code_Point(cp) = True or
Noncharacter_Code_Point(cp) = True Noncharacter_Code_Point(cp) = True
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provide a stable specification documenting the profile. provide a stable specification documenting the profile.
Internationalization can be difficult and contentious; the designated Internationalization can be difficult and contentious; the designated
experts and applicants are strongly encouraged to work together in a experts and applicants are strongly encouraged to work together in a
spirit of good faith and mutual understanding to achieve rough spirit of good faith and mutual understanding to achieve rough
consensus on progressing registrations through the process. They are consensus on progressing registrations through the process. They are
also encouraged to bring additional expertise into the discussion if also encouraged to bring additional expertise into the discussion if
that would be helpful in adding perspective or otherwise resolving that would be helpful in adding perspective or otherwise resolving
issues. issues.
Registrants and designated experts alike are strongly encouraged to
help prevent the multiplication of profiles beyond necessity, as
described under Section 5.1.
Further considerations for profile registrants and designated experts Further considerations for profile registrants and designated experts
can be found under Section 10.3. can be found under Section 10.3.
10. IANA Considerations 10. IANA Considerations
10.1. PRECIS Derived Property Value Registry 10.1. PRECIS Derived Property Value Registry
IANA is requested to create a PRECIS-specific registry with the IANA is requested to create a PRECIS-specific registry with the
Derived Properties for the versions of Unicode that are released Derived Properties for the versions of Unicode that are released
after (and including) version 7.0. The derived property value is to after (and including) version 7.0. The derived property value is to
be calculated in cooperation with a designated expert [RFC5226] be calculated in cooperation with a designated expert [RFC5226]
according to the rules specified under Section 8 and Section 7. according to the rules specified under Section 7 and Section 8.
The IESG is to be notified if backward-incompatible changes to the The IESG is to be notified if backward-incompatible changes to the
table of derived properties are discovered or if other problems arise table of derived properties are discovered or if other problems arise
during the process of creating the table of derived property values during the process of creating the table of derived property values
or during expert review. Changes to the rules defined under or during expert review. Changes to the rules defined under
Section 8 and Section 7 require IETF Review. Section 7 and Section 8 require IETF Review.
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."]
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
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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."]
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.
Specification: Section 3.3 of this document. Specification: Section 4.3 of this document.
[Note to RFC Editor: please change "this document" [Note to RFC Editor: please change "this document"
to the RFC number issued for this specification.] to the RFC 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.
Specification: Section 3.2 of this document. Specification: Section 4.2 of this document.
[Note to RFC Editor: please change "this document" [Note to RFC Editor: please change "this document"
to the RFC number issued for this specification.] to the RFC number issued for this specification.]
10.3. PRECIS Profiles Registry 10.3. PRECIS Profiles Registry
IANA is requested to create a registry of profiles that use the IANA is requested to create a registry of profiles 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 ease the burden of registration while ensuring that order to ease the burden of registration while ensuring that
"customers" of PRECIS receive appropriate guidance regarding the "customers" of PRECIS receive appropriate guidance regarding the
skipping to change at page 26, line 15 skipping to change at page 26, line 11
Additional Mapping Rule: [any additional mappings are required or Additional Mapping Rule: [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 Rule: [the behavioral rule for handling of case, e.g., Case Mapping Rule: [the behavioral rule for handling of case, e.g.,
"Unicode Default Case Folding"] "Unicode Default Case Folding"]
Normalization Rule: [which Unicode normalization form is applied, Normalization Rule: [which Unicode normalization form is applied,
e.g., "NFC"] e.g., "NFC"]
Exclusion Rule: [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"]
Directionality Rule: [the behavioral rule for handling of right-to- Directionality Rule: [the behavioral rule for handling of right-to-
left code points, e.g., "The 'Bidi Rule' defined in RFC 5893 left code points, e.g., "The 'Bidi Rule' defined in RFC 5893
applies."] applies."]
Enforcement: [which entities enforce the rules, and when that Enforcement: [which entities enforce the rules, and when that
enforcement occurs during protocol operations] enforcement occurs during protocol operations]
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 defining profiles and reviewing profile Factors to focus on while defining profiles and reviewing profile
registrations include the following: registrations include the following:
o Would an existing PRECIS string class or profile solve the
problem? If not, why not? (See Section 5.1 for related
considerations.)
o Is the problem being addressed by this profile well-defined? o Is the problem being addressed by this profile well-defined?
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 profile applies? 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 Is the profile clearly defined?
o Is the profile based on an appropriate dividing line between user o Is the profile 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 Are the width mapping, case mapping, additional mappings, o Are the width mapping, case mapping, additional mappings,
normalization, exclusion, and directionality rules appropriate for normalization, and directionality rules appropriate for the
the intended use? intended use?
o Does the profile explain which entities enforce the rules, and o Does the profile explain which entities enforce the rules, and
when such enforcement occurs during protocol operations? when such enforcement occurs during protocol operations?
o Does the profile reduce the degree to which human users could be o Does the profile reduce the degree to which human users could be
surprised or confused by application behavior (the "Principle of surprised or confused by application behavior (the "Principle of
Least Astonishment")? Least Astonishment")?
o Does the profile introduce any new security concerns such as those o Does the profile introduce any new security concerns such as those
described under Section 11 of this document (e.g., false positives described under Section 11 of this document (e.g., false positives
skipping to change at page 27, line 30 skipping to change at page 27, line 23
If input strings that appear "the same" to users are programmatically If input strings that appear "the same" to users are programmatically
considered to be distinct in different systems, or if input strings considered to be distinct in different systems, or if input strings
that appear distinct to users are programmatically considered to be that appear distinct to users are programmatically considered to be
"the same" in different systems, then users can be confused. Such "the same" in different systems, then users can be confused. Such
confusion can have security implications, such as the false positives confusion can have security implications, such as the false positives
and false negatieves discussed in [RFC6943]. One starting goal of and false negatieves discussed in [RFC6943]. One starting goal of
work on the PRECIS framework was to limit the number of times that work on the PRECIS framework was to limit the number of times that
users are confused (consistent with the "Principle of Least users are confused (consistent with the "Principle of Least
Astonishment"). Unfortunately, this goal has been difficult to Astonishment"). Unfortunately, this goal has been difficult to
achieve given the large number of application protocols already in achieve given the large number of application protocols already in
existence, each with its own conventions regarding allowable existence. Despite these difficulties, profiles should not be
characters (see for example [I-D.saintandre-username-interop] with multiplied beyond necessity (see Section 5.1. In particular,
regard to various username constructs). Despite these difficulties,
profiles should not be multiplied beyond necessity. In particular,
application protocol designers should think long and hard before application protocol designers should think long and hard before
defining a new profile instead of using one that has already been defining a new profile instead of using one that has already been
defined, and if they decide to define a new profile then they should defined, and if they decide to define a new profile then they should
clearly explain their reasons for doing so. clearly explain their reasons for doing so.
The security of applications that use this framework can depend in The security of applications that use this framework can depend in
part on the proper preparation and comparison of internationalized part on the proper preparation, enforcement, and comparison of
strings. For example, such strings can be used to make internationalized strings. For example, such strings can be used to
authentication and authorization decisions, and the security of an make authentication and authorization decisions, and the security of
application could be compromised if an entity providing a given an application could be compromised if an entity providing a given
string is connected to the wrong account or online resource based on string is connected to the wrong account or online resource based on
different interpretations of the string. different interpretations of the string (again, see [RFC6943]).
Specifications of application protocols that use this framework are Specifications of application protocols that use this framework are
strongly encouraged to describe how internationalized strings are strongly encouraged to describe how internationalized strings are
used in the protocol, including the security implications of any used in the protocol, including the security implications of any
false positives and false negatives that might result from various false positives and false negatives that might result from various
comparison operations. For some helpful guidelines, refer to enforcement and comparison operations. For some helpful guidelines,
[RFC6943], [RFC5890], [UTR36], and [UTS39]. refer to [RFC6943], [RFC5890], [UTR36], and [UTS39].
11.2. Use of the IdentifierClass 11.2. Use of the IdentifierClass
Strings that conform to the IdentifierClass and any profile thereof Strings that conform to the IdentifierClass and any profile thereof
are intended to be relatively safe for use in a broad range of are intended to be relatively safe for use in a broad range of
applications, primarily because they include only letters, digits, applications, primarily because they include only letters, digits,
and "grandfathered" non-space characters from the ASCII range; thus and "grandfathered" non-space characters from the ASCII range; thus
they exclude spaces, characters with compatibility equivalents, and they exclude spaces, characters with compatibility equivalents, and
almost all symbols and punctuation marks. However, because such almost all symbols and punctuation marks. However, because such
strings can still include so-called confusable characters (see strings can still include so-called confusable characters (see
skipping to change at page 28, line 31 skipping to change at page 28, line 22
can include virtually any Unicode character. This makes the can include virtually any Unicode character. This makes the
FreeformClass quite expressive, but also problematic from the FreeformClass quite expressive, but also problematic from the
perspective of possible user confusion. Protocol designers are perspective of possible user confusion. Protocol designers are
hereby warned that the FreeformClass contains codepoints they might hereby warned that the FreeformClass contains codepoints they might
not understand, and are encouraged to profile the IdentifierClass not understand, and are encouraged to profile the IdentifierClass
wherever feasible; however, if an application protocol requires more wherever feasible; however, if an application protocol requires more
code points than are allowed by the IdentifierClass, protocol code points than are allowed by the IdentifierClass, protocol
designers are encouraged to define a profile of the FreeformClass designers are encouraged to define a profile of the FreeformClass
that restricts the allowable code points as tightly as possible. that restricts the allowable code points as tightly as possible.
(The PRECIS Working Group considered the option of allowing (The PRECIS Working Group considered the option of allowing
superclasses as well as profiles of PRECIS string classes, but "superclasses" as well as profiles of PRECIS string classes, but
decided against allowing superclasses to reduce the likelihood of decided against allowing superclasses to reduce the likelihood of
security and interoperability problems.) security and interoperability problems.)
11.4. Local Character Set Issues 11.4. Local Character Set Issues
When systems use local character sets other than ASCII and Unicode, When systems use local character sets other than ASCII and Unicode,
this specification leaves the problem of converting between the local this specification leaves the problem of converting between the local
character set and Unicode up to the application or local system. If character set and Unicode up to the application or local system. If
different applications (or different versions of one application) different applications (or different versions of one application)
implement different rules for conversions among coded character sets, implement different rules for conversions among coded character sets,
skipping to change at page 32, line 5 skipping to change at page 31, line 43
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 to have in common at least one or password), they will naturally need to 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 uses PRECIS, baseline is a matter for the application protocol that uses PRECIS,
not for the PRECIS framework. not for the PRECIS framework.
Three Unicode code points underwent changes in their GeneralCategory Changes to the properties of Unicode code points can occur as the
between Unicode 5.2 (current at the time IDNA2008 was originally Unicode Standard is modified from time to time. For example, three
published) and Unicode 6.0, as described in [RFC6452]. Implementers code points underwent changes in their GeneralCategory between
might need to be aware that the treatment of these characters differs Unicode 5.2 (current at the time IDNA2008 was originally published)
depending on which version of Unicode is available on the system that and Unicode 6.0, as described in [RFC6452]. Implementers might need
is using IDNA2008 or PRECIS, and that other such differences are to be aware that the treatment of these characters differs depending
possible between the version of Unicode current at the time of this on which version of Unicode is available on the system that is using
writing (7.0) and future versions. IDNA2008 or PRECIS. Other such differences might arise between the
version of Unicode current at the time of this writing (7.0) and
future versions.
13. References 13. References
13.1. Normative References 13.1. Normative References
[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.
skipping to change at page 32, line 41 skipping to change at page 32, line 34
13.2. Informative References 13.2. Informative References
[I-D.ietf-precis-mappings] [I-D.ietf-precis-mappings]
Yoneya, Y. and T. NEMOTO, "Mapping characters for PRECIS Yoneya, Y. and T. NEMOTO, "Mapping characters for PRECIS
classes", draft-ietf-precis-mappings-08 (work in classes", draft-ietf-precis-mappings-08 (work in
progress), June 2014. progress), June 2014.
[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-11 (work in Nicknames", draft-ietf-precis-nickname-12 (work in
progress), October 2014. progress), November 2014.
[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-09 Preparation Algorithms", draft-ietf-precis-saslprepbis-10
(work in progress), October 2014. (work in progress), November 2014.
[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", draft-ietf-xmpp-
6122bis-15 (work in progress), October 2014. 6122bis-16 (work in progress), November 2014.
[I-D.saintandre-username-interop]
Saint-Andre, P., "An Interoperable Subset of Characters
for Internationalized Usernames", draft-saintandre-
username-interop-03 (work in progress), March 2014.
[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)", RFC
2865, June 2000. 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,
 End of changes. 68 change blocks. 
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