draft-ietf-precis-7613bis-07.txt   draft-ietf-precis-7613bis-08.txt 
Network Working Group P. Saint-Andre Network Working Group P. Saint-Andre
Internet-Draft Filament Internet-Draft Filament
Obsoletes: 7613 (if approved) A. Melnikov Obsoletes: 7613 (if approved) A. Melnikov
Intended status: Standards Track Isode Ltd Intended status: Standards Track Isode Ltd
Expires: November 2, 2017 May 1, 2017 Expires: December 29, 2017 June 27, 2017
Preparation, Enforcement, and Comparison of Internationalized Strings Preparation, Enforcement, and Comparison of Internationalized Strings
Representing Usernames and Passwords Representing Usernames and Passwords
draft-ietf-precis-7613bis-07 draft-ietf-precis-7613bis-08
Abstract Abstract
This document describes updated methods for handling Unicode strings This document describes updated methods for handling Unicode strings
representing usernames and passwords. The previous approach was representing usernames and passwords. The previous approach was
known as SASLprep (RFC 4013) and was based on stringprep (RFC 3454). known as SASLprep (RFC 4013) and was based on stringprep (RFC 3454).
The methods specified in this document provide a more sustainable The methods specified in this document provide a more sustainable
approach to the handling of internationalized usernames and approach to the handling of internationalized usernames and
passwords. The preparation, enforcement, and comparison of passwords. This document obsoletes RFC 7613.
internationalized strings (PRECIS) framework, RFC 7564, obsoletes RFC
3454, and this document obsoletes RFC 7613.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on November 2, 2017. This Internet-Draft will expire on December 29, 2017.
Copyright Notice Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the Copyright (c) 2017 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
skipping to change at page 2, line 21 skipping to change at page 2, line 19
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Usernames . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Usernames . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Definition . . . . . . . . . . . . . . . . . . . . . . . 5 3.1. Definition . . . . . . . . . . . . . . . . . . . . . . . 5
3.2. Case Mapping vs. Case Preservation . . . . . . . . . . . 6 3.2. Case Mapping vs. Case Preservation . . . . . . . . . . . 6
3.3. UsernameCaseMapped Profile . . . . . . . . . . . . . . . 7 3.3. UsernameCaseMapped Profile . . . . . . . . . . . . . . . 7
3.3.1. Rules . . . . . . . . . . . . . . . . . . . . . . . . 7 3.3.1. Rules . . . . . . . . . . . . . . . . . . . . . . . . 7
3.3.2. Preparation . . . . . . . . . . . . . . . . . . . . . 8 3.3.2. Preparation . . . . . . . . . . . . . . . . . . . . . 8
3.3.3. Enforcement . . . . . . . . . . . . . . . . . . . . . 8 3.3.3. Enforcement . . . . . . . . . . . . . . . . . . . . . 8
3.3.4. Comparison . . . . . . . . . . . . . . . . . . . . . 8 3.3.4. Comparison . . . . . . . . . . . . . . . . . . . . . 9
3.4. UsernameCasePreserved Profile . . . . . . . . . . . . . . 9 3.4. UsernameCasePreserved Profile . . . . . . . . . . . . . . 9
3.4.1. Rules . . . . . . . . . . . . . . . . . . . . . . . . 9 3.4.1. Rules . . . . . . . . . . . . . . . . . . . . . . . . 9
3.4.2. Preparation . . . . . . . . . . . . . . . . . . . . . 9 3.4.2. Preparation . . . . . . . . . . . . . . . . . . . . . 9
3.4.3. Enforcement . . . . . . . . . . . . . . . . . . . . . 9 3.4.3. Enforcement . . . . . . . . . . . . . . . . . . . . . 10
3.4.4. Comparison . . . . . . . . . . . . . . . . . . . . . 10 3.4.4. Comparison . . . . . . . . . . . . . . . . . . . . . 10
3.5. Application-Layer Constructs . . . . . . . . . . . . . . 10 3.5. Application-Layer Constructs . . . . . . . . . . . . . . 10
3.6. Examples . . . . . . . . . . . . . . . . . . . . . . . . 10 3.6. Examples . . . . . . . . . . . . . . . . . . . . . . . . 10
4. Passwords . . . . . . . . . . . . . . . . . . . . . . . . . . 12 4. Passwords . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.1. Definition . . . . . . . . . . . . . . . . . . . . . . . 12 4.1. Definition . . . . . . . . . . . . . . . . . . . . . . . 12
4.2. OpaqueString Profile . . . . . . . . . . . . . . . . . . 13 4.2. OpaqueString Profile . . . . . . . . . . . . . . . . . . 13
4.2.1. Preparation . . . . . . . . . . . . . . . . . . . . . 13 4.2.1. Preparation . . . . . . . . . . . . . . . . . . . . . 13
4.2.2. Enforcement . . . . . . . . . . . . . . . . . . . . . 14 4.2.2. Enforcement . . . . . . . . . . . . . . . . . . . . . 14
4.2.3. Comparison . . . . . . . . . . . . . . . . . . . . . 14 4.2.3. Comparison . . . . . . . . . . . . . . . . . . . . . 14
4.3. Examples . . . . . . . . . . . . . . . . . . . . . . . . 15 4.3. Examples . . . . . . . . . . . . . . . . . . . . . . . . 15
5. Use in Application Protocols . . . . . . . . . . . . . . . . 16 5. Use in Application Protocols . . . . . . . . . . . . . . . . 16
6. Migration . . . . . . . . . . . . . . . . . . . . . . . . . . 16 6. Migration . . . . . . . . . . . . . . . . . . . . . . . . . . 16
6.1. Usernames . . . . . . . . . . . . . . . . . . . . . . . . 16 6.1. Usernames . . . . . . . . . . . . . . . . . . . . . . . . 17
6.2. Passwords . . . . . . . . . . . . . . . . . . . . . . . . 18 6.2. Passwords . . . . . . . . . . . . . . . . . . . . . . . . 18
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
7.1. UsernameCaseMapped Profile . . . . . . . . . . . . . . . 19 7.1. UsernameCaseMapped Profile . . . . . . . . . . . . . . . 19
7.2. UsernameCasePreserved Profile . . . . . . . . . . . . . . 19 7.2. UsernameCasePreserved Profile . . . . . . . . . . . . . . 20
7.3. OpaqueString Profile . . . . . . . . . . . . . . . . . . 20 7.3. OpaqueString Profile . . . . . . . . . . . . . . . . . . 20
7.4. Stringprep Profile . . . . . . . . . . . . . . . . . . . 21 7.4. Stringprep Profile . . . . . . . . . . . . . . . . . . . 21
8. Security Considerations . . . . . . . . . . . . . . . . . . . 21 8. Security Considerations . . . . . . . . . . . . . . . . . . . 21
8.1. Password/Passphrase Strength . . . . . . . . . . . . . . 21 8.1. Password/Passphrase Strength . . . . . . . . . . . . . . 21
8.2. Identifier Comparison . . . . . . . . . . . . . . . . . . 21 8.2. Password/Passphrase Comparison . . . . . . . . . . . . . 21
8.3. Reuse of PRECIS . . . . . . . . . . . . . . . . . . . . . 21 8.3. Identifier Comparison . . . . . . . . . . . . . . . . . . 22
8.4. Reuse of Unicode . . . . . . . . . . . . . . . . . . . . 21 8.4. Reuse of PRECIS . . . . . . . . . . . . . . . . . . . . . 22
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 21 8.5. Reuse of Unicode . . . . . . . . . . . . . . . . . . . . 22
9.1. Normative References . . . . . . . . . . . . . . . . . . 21 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 22
9.2. Informative References . . . . . . . . . . . . . . . . . 22 9.1. Normative References . . . . . . . . . . . . . . . . . . 22
Appendix A. Changes from RFC 7613 . . . . . . . . . . . . . . . 24 9.2. Informative References . . . . . . . . . . . . . . . . . 23
Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 24
Appendix A. Changes from RFC 7613 . . . . . . . . . . . . . . . 25
Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 25 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 25
1. Introduction 1. Introduction
Usernames and passwords are widely used for authentication and Usernames and passwords are widely used for authentication and
authorization on the Internet, either directly when provided in authorization on the Internet, either directly when provided in
plaintext (as in the PLAIN Simple Authentication and Security Layer plaintext (as in the PLAIN Simple Authentication and Security Layer
(SASL) mechanism [RFC4616] and the HTTP Basic scheme [RFC7617]) or (SASL) mechanism [RFC4616] and the HTTP Basic scheme [RFC7617]) or
indirectly when provided as the input to a cryptographic algorithm indirectly when provided as the input to a cryptographic algorithm
such as a hash function (as in the Salted Challenge Response such as a hash function (as in the Salted Challenge Response
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To increase the likelihood that the input and comparison of usernames To increase the likelihood that the input and comparison of usernames
and passwords will work in ways that make sense for typical users and passwords will work in ways that make sense for typical users
throughout the world, this document defines rules for preparing, throughout the world, this document defines rules for preparing,
enforcing, and comparing internationalized strings that represent enforcing, and comparing internationalized strings that represent
usernames and passwords. Such strings consist of code points from usernames and passwords. Such strings consist of code points from
the Unicode coded character set [Unicode], with special attention to the Unicode coded character set [Unicode], with special attention to
code points outside the ASCII range [RFC20]. The rules for handling code points outside the ASCII range [RFC20]. The rules for handling
such strings are specified through profiles of the string classes such strings are specified through profiles of the string classes
defined in the preparation, enforcement, and comparison of defined in the preparation, enforcement, and comparison of
internationalized strings (PRECIS) framework specification [RFC7564]. internationalized strings (PRECIS) framework specification
[I-D.ietf-precis-7564bis].
Profiles of the PRECIS framework enable software to handle Unicode Profiles of the PRECIS framework enable software to handle Unicode
code points outside the ASCII range in an automated way, so that such code points outside the ASCII range in an automated way, so that such
code points are treated carefully and consistently in application code points are treated carefully and consistently in application
protocols. In large measure, these profiles are designed to protect protocols. In large measure, these profiles are designed to protect
application developers from the potentially negative consequences of application developers from the potentially negative consequences of
supporting the full range of Unicode code points. For instance, in supporting the full range of Unicode code points. For instance, in
almost all application protocols it would be dangerous to treat the almost all application protocols it would be dangerous to treat the
Unicode code point SUPERSCRIPT ONE (U+00B9) as equivalent to DIGIT Unicode code point SUPERSCRIPT ONE (U+00B9) as equivalent to DIGIT
ONE (U+0031), because that would result in false positives during ONE (U+0031), because that would result in false positives during
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desirable to support a wider range of characters so as to maximize desirable to support a wider range of characters so as to maximize
entropy for purposes of authentication.) entropy for purposes of authentication.)
The methods defined here might be applicable wherever usernames or The methods defined here might be applicable wherever usernames or
passwords are used. However, the methods are not intended for use in passwords are used. However, the methods are not intended for use in
preparing strings that are not usernames (e.g., Lightweight Directory preparing strings that are not usernames (e.g., Lightweight Directory
Access Protocol (LDAP) distinguished names), nor in cases where Access Protocol (LDAP) distinguished names), nor in cases where
identifiers or secrets are not strings (e.g., keys and certificates) identifiers or secrets are not strings (e.g., keys and certificates)
or require specialized handling. or require specialized handling.
This document obsoletes RFC 4013 (the SASLprep profile of stringprep Although the historical predecessor of this document was the SASLprep
[RFC3454]) but can be used by technologies other than SASL [RFC4422], profile of stringprep [RFC3454]), the approach defined here can be
such as HTTP authentication as specified in [RFC7617] and [RFC7616]. used by technologies other than SASL [RFC4422], such as HTTP
authentication as specified in [RFC7617] and [RFC7616].
This document does not modify the handling of internationalized This document does not modify the handling of internationalized
strings in usernames and passwords as prescribed by existing strings in usernames and passwords as prescribed by existing
application protocols that use SASLprep. If the community that uses application protocols that use SASLprep. If the community that uses
such an application protocol wishes to modernize its handling of such an application protocol wishes to modernize its handling of
internationalized strings to use PRECIS instead of stringprep, it internationalized strings to use PRECIS instead of stringprep, it
needs to explicitly update the existing application protocol needs to explicitly update the existing application protocol
definition (one example is [RFC7622]. Non-coordinated updates to definition (one example is [RFC7622]. Non-coordinated updates to
protocol implementations are discouraged because they can have a protocol implementations are discouraged because they can have a
negative impact on interoperability and security. negative impact on interoperability and security.
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perhaps separated by spaces, punctuation, or other non-alphanumeric perhaps separated by spaces, punctuation, or other non-alphanumeric
characters. characters.
Some SASL mechanisms (e.g., CRAM-MD5, DIGEST-MD5, and SCRAM) specify Some SASL mechanisms (e.g., CRAM-MD5, DIGEST-MD5, and SCRAM) specify
that the authentication identity used in the context of such that the authentication identity used in the context of such
mechanisms is a "simple user name" (see Section 2 of [RFC4422] as mechanisms is a "simple user name" (see Section 2 of [RFC4422] as
well as [RFC4013]). Various application technologies also assume well as [RFC4013]). Various application technologies also assume
that the identity of a user or account takes the form of a username that the identity of a user or account takes the form of a username
(e.g., authentication for the Hypertext Transfer Protocol as (e.g., authentication for the Hypertext Transfer Protocol as
specified in [RFC7617] and [RFC7616]), whether or not they use SASL. specified in [RFC7617] and [RFC7616]), whether or not they use SASL.
Note well that the exact form of a username in any particular SASL Note well that the exact form of a username in any particular SASL
mechanism or application technology is a matter for implementation mechanism or application technology is a matter for implementation
and deployment, and that a username does not necessarily map to any and deployment, and that a username does not necessarily map to any
particular application identifier. particular application identifier.
Many important terms used in this document are defined in [RFC5890], Many important terms used in this document are defined in [RFC5890],
[RFC6365], [RFC7564], and [Unicode]. The term "non-ASCII space" [RFC6365], [I-D.ietf-precis-7564bis], and [Unicode]. The term "non-
refers to any Unicode code point having a Unicode general category of ASCII space" refers to any Unicode code point having a Unicode
"Zs", with the exception of U+0020 (here called "ASCII space"). general category of "Zs", with the exception of U+0020 (here called
"ASCII space").
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. Usernames 3. Usernames
3.1. Definition 3.1. Definition
This document specifies that a username is a string of Unicode code This document specifies that a username is a string of Unicode code
points [Unicode] that is structured as an ordered sequence of points [Unicode] that is structured as an ordered sequence of
"userparts" and expressed in a standard Unicode Encoding Form (such "userparts" and expressed in a standard Unicode Encoding Form (such
as UTF-8 [RFC3629]). A userpart is allowed to contain only code as UTF-8 [RFC3629]). A userpart is allowed to contain only code
points that are allowed by the PRECIS IdentifierClass defined in points that are allowed by the PRECIS IdentifierClass defined in
Section 4.2 of [RFC7564], and thus consists almost exclusively of Section 4.2 of [I-D.ietf-precis-7564bis], and thus consists almost
letters and digits. A username can consist of a single userpart or a exclusively of letters and digits. A username can consist of a
space-separated sequence of userparts. single userpart or a space-separated sequence of userparts.
The syntax for a username is defined as follows, using the Augmented The syntax for a username is defined as follows, using the Augmented
Backus-Naur Form (ABNF) [RFC5234]. Backus-Naur Form (ABNF) [RFC5234].
username = userpart *(1*SP userpart) username = userpart *(1*SP userpart)
userpart = 1*(idpoint) userpart = 1*(idpoint)
; ;
; an "idpoint" is a Unicode code point that ; an "idpoint" is a Unicode code point that
; can be contained in a string conforming to ; can be contained in a string conforming to
; the PRECIS IdentifierClass ; the PRECIS IdentifierClass
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described in [RFC6943]) and can result in confusion among end users, described in [RFC6943]) and can result in confusion among end users,
given the prevalence of case mapping in many existing protocols and given the prevalence of case mapping in many existing protocols and
applications. However, there can be good reasons to apply the applications. However, there can be good reasons to apply the
UsernameCasePreserved profile and thus not perform case mapping, such UsernameCasePreserved profile and thus not perform case mapping, such
as backward compatibility with deployed infrastructure. as backward compatibility with deployed infrastructure.
In particular: In particular:
o SASL mechanisms that follow the recommendations in this document o SASL mechanisms that follow the recommendations in this document
MUST specify whether and when case mapping is to be applied to MUST specify whether and when case mapping is to be applied to
authentication identifiers. SASL mechanisms SHOULD delay any case authentication identifiers. Because case mapping results in
mapping to the last possible moment, such as when doing a lookup information loss, in order to retain that information for as long
by username, performing username comparisons, or generating a as possible during processing, implementations SHOULD delay any
cryptographic salt from a username (if the last possible moment case mapping to the last possible moment, such as when doing a
happens on the server, then decisions about case mapping can be a lookup by username, performing username comparisons, or generating
a cryptographic salt from a username (if the last possible moment
happens on a server, then decisions about case mapping can be a
matter of deployment policy). In keeping with [RFC4422], SASL matter of deployment policy). In keeping with [RFC4422], SASL
mechanisms are not to apply this or any other profile to mechanisms are not to apply this or any other profile to
authorization identifiers, only to authentication identifiers. authorization identifiers, only to authentication identifiers.
o Application protocols that use SASL (such as IMAP [RFC3501] and o Application protocols that use SASL (such as IMAP [RFC3501] and
the Extensible Messaging and Presence Protocol (XMPP) [RFC6120]) the Extensible Messaging and Presence Protocol (XMPP) [RFC6120])
and that directly reuse this profile MUST specify whether or not and that directly reuse this profile MUST specify whether or not
case mapping is to be applied to authorization identifiers. Such case mapping is to be applied to authorization identifiers. Such
"SASL application protocols" SHOULD delay any case-mapping of "SASL application protocols" SHOULD delay any case-mapping of
authorization identifiers to the last possible moment, which authorization identifiers to the last possible moment, which
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3.3.2. Preparation 3.3.2. Preparation
An entity that prepares a string for subsequent enforcement according An entity that prepares a string for subsequent enforcement according
to this profile MUST proceed as follows (applying the steps in the to this profile MUST proceed as follows (applying the steps in the
order shown). order shown).
1. Apply the width-mapping rule specified in Section 3.3.1. It is 1. Apply the width-mapping rule specified in Section 3.3.1. It is
necessary to apply the rule at this point because otherwise the necessary to apply the rule at this point because otherwise the
PRECIS "HasCompat" category specified in Section 9.17 of PRECIS "HasCompat" category specified in Section 9.17 of
[RFC7564] would forbid fullwidth and halfwidth code points. [I-D.ietf-precis-7564bis] would forbid fullwidth and halfwidth
code points.
2. Ensure that the string consists only of Unicode code points that 2. Ensure that the string consists only of Unicode code points that
are explicitly allowed by the PRECIS IdentifierClass defined in are explicitly allowed by the PRECIS IdentifierClass defined in
Section 4.2 of [RFC7564]. Section 4.2 of [I-D.ietf-precis-7564bis].
3.3.3. Enforcement 3.3.3. Enforcement
An entity that performs enforcement according to this profile MUST An entity that performs enforcement according to this profile MUST
prepare a string as described in Section 3.3.2 and MUST also apply prepare a string as described in Section 3.3.2 and MUST also apply
the following rules specified in Section 3.3.1 in the order shown: the following rules specified in Section 3.3.1 in the order shown:
1. Case-Mapping Rule 1. Case-Mapping Rule
2. Normalization Rule 2. Normalization Rule
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3.4.2. Preparation 3.4.2. Preparation
An entity that prepares a string for subsequent enforcement according An entity that prepares a string for subsequent enforcement according
to this profile MUST proceed as follows (applying the steps in the to this profile MUST proceed as follows (applying the steps in the
order shown). order shown).
1. Apply the width-mapping rule specified in Section 3.3.1. It is 1. Apply the width-mapping rule specified in Section 3.3.1. It is
necessary to apply the rule at this point because otherwise the necessary to apply the rule at this point because otherwise the
PRECIS "HasCompat" category specified in Section 9.17 of PRECIS "HasCompat" category specified in Section 9.17 of
[RFC7564] would forbid fullwidth and halfwidth code points. [I-D.ietf-precis-7564bis] would forbid fullwidth and halfwidth
code points.
2. Ensure that the string consists only of Unicode code points that 2. Ensure that the string consists only of Unicode code points that
are explicitly allowed by the PRECIS IdentifierClass defined in are explicitly allowed by the PRECIS IdentifierClass defined in
Section 4.2 of [RFC7564]. Section 4.2 of [I-D.ietf-precis-7564bis].
3.4.3. Enforcement 3.4.3. Enforcement
An entity that performs enforcement according to this profile MUST An entity that performs enforcement according to this profile MUST
prepare a string as described in Section 3.4.2 and MUST also apply prepare a string as described in Section 3.4.2 and MUST also apply
the following rules specified in Section 3.4.1 in the order shown: the following rules specified in Section 3.4.1 in the order shown:
1. Normalization Rule 1. Normalization Rule
2. Directionality Rule 2. Directionality Rule
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BLACK CHESS KING (U+265A) are not allowed in the PRECIS BLACK CHESS KING (U+265A) are not allowed in the PRECIS
IdentifierClass. IdentifierClass.
4. Passwords 4. Passwords
4.1. Definition 4.1. Definition
This document specifies that a password is a string of Unicode code This document specifies that a password is a string of Unicode code
points [Unicode] that is conformant to the OpaqueString profile points [Unicode] that is conformant to the OpaqueString profile
(specified below) of the PRECIS FreeformClass defined in Section 4.3 (specified below) of the PRECIS FreeformClass defined in Section 4.3
of [RFC7564], and that is expressed in a standard Unicode Encoding of [I-D.ietf-precis-7564bis], and that is expressed in a standard
Form (such as UTF-8 [RFC3629]). Unicode Encoding Form (such as UTF-8 [RFC3629]).
The syntax for a password is defined as follows, using the Augmented The syntax for a password is defined as follows, using the Augmented
Backus-Naur Form (ABNF) [RFC5234]. Backus-Naur Form (ABNF) [RFC5234].
password = 1*(freepoint) password = 1*(freepoint)
; ;
; a "freepoint" is a Unicode code point that ; a "freepoint" is a Unicode code point that
; can be contained in a string conforming to ; can be contained in a string conforming to
; the PRECIS FreeformClass ; the PRECIS FreeformClass
; ;
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algorithm such as a hash function, the client will need to perform algorithm such as a hash function, the client will need to perform
enforcement of the rules for the OpaqueString profile before applying enforcement of the rules for the OpaqueString profile before applying
the algorithm, because the password is not available to the server in the algorithm, because the password is not available to the server in
plaintext form. plaintext form.
4.2. OpaqueString Profile 4.2. OpaqueString Profile
The definition of the OpaqueString profile is provided in the The definition of the OpaqueString profile is provided in the
following sections, including detailed information about preparation, following sections, including detailed information about preparation,
enforcement, and comparison (for details on the distinction between enforcement, and comparison (for details on the distinction between
these actions, refer to [RFC7564]). these actions, refer to [I-D.ietf-precis-7564bis]).
4.2.1. Preparation 4.2.1. Preparation
An entity that prepares a string according to this profile MUST An entity that prepares a string according to this profile MUST
ensure that the string consists only of Unicode code points that are ensure that the string consists only of Unicode code points that are
explicitly allowed by the FreeformClass base string class defined in explicitly allowed by the FreeformClass base string class defined in
[RFC7564]. [I-D.ietf-precis-7564bis].
4.2.2. Enforcement 4.2.2. Enforcement
An entity that performs enforcement according to this profile MUST An entity that performs enforcement according to this profile MUST
prepare a string as described in Section 4.2.1 and MUST also apply prepare a string as described in Section 4.2.1 and MUST also apply
the rules specified below for the OpaqueString profile (these rules the rules specified below for the OpaqueString profile (these rules
MUST be applied in the order shown): MUST be applied in the order shown):
1. Width-Mapping Rule: Fullwidth and halfwidth code points MUST NOT 1. Width-Mapping Rule: Fullwidth and halfwidth code points MUST NOT
be mapped to their decomposition mappings (see Unicode Standard be mapped to their decomposition mappings (see Unicode Standard
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presentation is consistent in any given layout system. presentation is consistent in any given layout system.
4.2.3. Comparison 4.2.3. Comparison
An entity that performs comparison of two strings according to this An entity that performs comparison of two strings according to this
profile MUST prepare each string as specified in Section 4.2.1 and profile MUST prepare each string as specified in Section 4.2.1 and
then MUST enforce the rules specified in Section 4.2.2. The two then MUST enforce the rules specified in Section 4.2.2. The two
strings are to be considered equivalent if and only if they are an strings are to be considered equivalent if and only if they are an
exact octet-for-octet match (sometimes called "bit-string identity"). exact octet-for-octet match (sometimes called "bit-string identity").
See Section 8.2 regarding comparison of passwords and passphrases.
4.3. Examples 4.3. Examples
The following examples illustrate a small number of passwords that The following examples illustrate a small number of passwords that
are consistent with the format defined above (note that the are consistent with the format defined above (note that the
characters "<" and ">" are used here to delineate the actual characters "<" and ">" are used here to delineate the actual
passwords and are not part of the password strings). passwords and are not part of the password strings).
+------------------------------------+------------------------------+ +------------------------------------+------------------------------+
| # | Password | Notes | | # | Password | Notes |
+------------------------------------+------------------------------+ +------------------------------------+------------------------------+
skipping to change at page 15, line 43 skipping to change at page 16, line 8
+------------------------------------+------------------------------+ +------------------------------------+------------------------------+
Table 3: A Sample of Legal Passwords Table 3: A Sample of Legal Passwords
The following example illustrates a string that is not a valid The following example illustrates a string that is not a valid
password because it violates the format defined above. password because it violates the format defined above.
+------------------------------------+------------------------------+ +------------------------------------+------------------------------+
| # | Password | Notes | | # | Password | Notes |
+------------------------------------+------------------------------+ +------------------------------------+------------------------------+
| 17| <my cat is a &#x9;by> | Controls are disallowed | | 17| <> | Zero-length passwords are |
| | | disallowed |
+------------------------------------+------------------------------+
| 18| <my cat is a &#x9;by> | Control characters like TAB |
| | | are disallowed |
+------------------------------------+------------------------------+ +------------------------------------+------------------------------+
Table 4: A String That Violates the Password Rules Table 4: A Sample of Strings That Violate the Password Rules
5. Use in Application Protocols 5. Use in Application Protocols
This specification defines only the PRECIS-based rules for the This specification defines only the PRECIS-based rules for the
handling of strings conforming to the UsernameCaseMapped and handling of strings conforming to the UsernameCaseMapped and
UsernameCasePreserved profiles of the PRECIS IdentifierClass, and UsernameCasePreserved profiles of the PRECIS IdentifierClass, and
strings conforming to the OpaqueString profile of the PRECIS strings conforming to the OpaqueString profile of the PRECIS
FreeformClass. It is the responsibility of an application protocol FreeformClass. It is the responsibility of an application protocol
to specify the protocol slots in which such strings can appear, the to specify the protocol slots in which such strings can appear, the
entities that are expected to enforce the rules governing such entities that are expected to enforce the rules governing such
strings, and at what points during protocol processing or interface strings, and at what points during protocol processing or interface
handling the rules need to be enforced. See Section 6 of [RFC7564] handling the rules need to be enforced. See Section 6 of
for guidelines on using PRECIS profiles in applications. [I-D.ietf-precis-7564bis] for guidelines on using PRECIS profiles in
applications.
Above and beyond the PRECIS-based rules specified here, application Above and beyond the PRECIS-based rules specified here, application
protocols can also define application-specific rules governing such protocols can also define application-specific rules governing such
strings (rules regarding minimum or maximum length, further strings (rules regarding minimum or maximum length, further
restrictions on allowable code points or character ranges, safeguards restrictions on allowable code points or character ranges, safeguards
to mitigate the effects of visually similar characters, etc.), to mitigate the effects of visually similar characters, etc.),
application-layer constructs (see Section 3.5), and related matters. application-layer constructs (see Section 3.5), and related matters.
Some PRECIS profile definitions encourage entities that enforce the Some PRECIS profile definitions encourage entities that enforce the
rules to be liberal in what they accept. However, for usernames and rules to be liberal in what they accept. However, for usernames and
skipping to change at page 16, line 38 skipping to change at page 16, line 51
false positives. An in-depth discussion can be found in [RFC6943]. false positives. An in-depth discussion can be found in [RFC6943].
Applying the rules for any given PRECIS profile is not necessarily an Applying the rules for any given PRECIS profile is not necessarily an
idempotent procedure for all code points. Therefore, implementations idempotent procedure for all code points. Therefore, implementations
might need to apply the rules more than once to an internationalized might need to apply the rules more than once to an internationalized
string. string.
6. Migration 6. Migration
The rules defined in this specification differ slightly from those The rules defined in this specification differ slightly from those
defined by the SASLprep specification [RFC4013]. The following defined by the SASLprep specification [RFC4013] (but not from
sections describe these differences, along with their implications [RFC7613]). In order to smooth the process of migrating from
for migration, in more detail. SASLprep to the approach defined herein, the following sections
describe these differences, along with their implications for
migration, in more detail.
6.1. Usernames 6.1. Usernames
Deployments that currently use SASLprep for handling usernames might Deployments that currently use SASLprep for handling usernames might
need to scrub existing data when they migrate to the rules defined in need to scrub existing data when they migrate to the rules defined in
this specification. In particular: this specification. In particular:
o SASLprep specified the use of Unicode Normalization Form KC o SASLprep specified the use of Unicode Normalization Form KC
(NFKC), whereas the UsernameCaseMapped and UsernameCasePreserved (NFKC), whereas the UsernameCaseMapped and UsernameCasePreserved
profiles employ Unicode Normalization Form C (NFC). In practice, profiles employ Unicode Normalization Form C (NFC). In practice,
skipping to change at page 17, line 37 skipping to change at page 18, line 4
with compatibility equivalents and, where there is no conflict, with compatibility equivalents and, where there is no conflict,
map those code points to their equivalents. Naturally, it is map those code points to their equivalents. Naturally, it is
possible that during this process the operator will discover possible that during this process the operator will discover
conflicting usernames (e.g., HENRYIV with the last two code points conflicting usernames (e.g., HENRYIV with the last two code points
being LATIN CAPITAL LETTER I (U+0049) and LATIN CAPITAL LETTER V being LATIN CAPITAL LETTER I (U+0049) and LATIN CAPITAL LETTER V
(U+0056) vs. "HENRYIV" with the last character being ROMAN NUMERAL (U+0056) vs. "HENRYIV" with the last character being ROMAN NUMERAL
FOUR (U+2163), which is compatibility equivalent to U+0049 and FOUR (U+2163), which is compatibility equivalent to U+0049 and
U+0056); in these cases, the operator will need to determine how U+0056); in these cases, the operator will need to determine how
to proceed -- for instance, by disabling the account whose name to proceed -- for instance, by disabling the account whose name
contains a Unicode code point with a compatibility equivalent. contains a Unicode code point with a compatibility equivalent.
Such cases are probably rare, but it is important for operators to Such cases are probably rare, but it is important for operators to
be aware of them. be aware of them.
o SASLprep mapped the "characters commonly mapped to nothing" from o SASLprep mapped the "characters commonly mapped to nothing" from
Appendix B.1 of [RFC3454]) to nothing, whereas the PRECIS Appendix B.1 of [RFC3454]) to nothing, whereas the PRECIS
IdentifierClass entirely disallows most of these code points, IdentifierClass entirely disallows most of these code points,
which correspond to the code points from the PRECIS "M" category which correspond to the code points from the PRECIS "M" category
defined under Section 9.13 of [RFC7564]. For migration purposes, defined under Section 9.13 of [I-D.ietf-precis-7564bis]. For
the operator might want to remove from usernames any code points migration purposes, the operator might want to remove from
contained in the PRECIS "M" category (e.g., SOFT HYPHEN (U+00AD)). usernames any code points contained in the PRECIS "M" category
Because these code points would have been "mapped to nothing" in (e.g., SOFT HYPHEN (U+00AD)). Because these code points would
stringprep, in practice a user would not notice the difference if, have been "mapped to nothing" in stringprep, in practice a user
upon migration to PRECIS, the code points are removed. would not notice the difference if, upon migration to PRECIS, the
code points are removed.
o SASLprep allowed uppercase and titlecase code points, whereas the o SASLprep allowed uppercase and titlecase code points, whereas the
UsernameCaseMapped profile maps uppercase and titlecase code UsernameCaseMapped profile maps uppercase and titlecase code
points to their lowercase equivalents (by contrast, the points to their lowercase equivalents (by contrast, the
UsernameCasePreserved profile matches SASLprep in this regard). UsernameCasePreserved profile matches SASLprep in this regard).
For migration purposes, the operator can use either the For migration purposes, the operator can use either the
UsernameCaseMapped profile (thus losing the case information) or UsernameCaseMapped profile (thus losing the case information) or
the UsernameCasePreserved profile (thus ignoring case difference the UsernameCasePreserved profile (thus ignoring case difference
when comparing usernames). when comparing usernames).
6.2. Passwords 6.2. Passwords
Depending on local service policy, migration from RFC 4013 to this Depending on local service policy, migration from SASLprep to this
specification might not involve any scrubbing of data (because specification might not involve any scrubbing of data (because
passwords might not be stored in the clear anyway); however, service passwords might not be stored in the clear anyway); however, service
providers need to be aware of possible issues that might arise during providers need to be aware of possible issues that might arise during
migration. In particular: migration. In particular:
o SASLprep specified the use of Unicode Normalization Form KC o SASLprep specified the use of Unicode Normalization Form KC
(NFKC), whereas the OpaqueString profile employs Unicode (NFKC), whereas the OpaqueString profile employs Unicode
Normalization Form C (NFC). Because NFKC is more aggressive about Normalization Form C (NFC). Because NFKC is more aggressive about
finding matches than NFC, in practice this change is unlikely to finding matches than NFC, in practice this change is unlikely to
cause significant problems and indeed has the security benefit of cause significant problems and indeed has the security benefit of
skipping to change at page 19, line 4 skipping to change at page 19, line 20
fullwidth and halfwidth code points to their decomposition fullwidth and halfwidth code points to their decomposition
mappings. Although it is expected that code points with mappings. Although it is expected that code points with
compatibility equivalents are rare in existing passwords, some compatibility equivalents are rare in existing passwords, some
passwords that matched when SASLprep was used might no longer work passwords that matched when SASLprep was used might no longer work
when the rules in this specification are applied. when the rules in this specification are applied.
o SASLprep mapped the "characters commonly mapped to nothing" from o SASLprep mapped the "characters commonly mapped to nothing" from
Appendix B.1 of [RFC3454]) to nothing, whereas the PRECIS Appendix B.1 of [RFC3454]) to nothing, whereas the PRECIS
FreeformClass entirely disallows such code points, which FreeformClass entirely disallows such code points, which
correspond to the code points from the PRECIS "M" category defined correspond to the code points from the PRECIS "M" category defined
under Section 9.13 of [RFC7564]. In practice, this change will under Section 9.13 of [I-D.ietf-precis-7564bis]. In practice,
probably have no effect on comparison, but user-oriented software this change will probably have no effect on comparison, but user-
might reject such code points instead of ignoring them during oriented software might reject such code points instead of
password preparation. ignoring them during password preparation.
7. IANA Considerations 7. IANA Considerations
IANA has made the updates described below. IANA has made the updates described below.
7.1. UsernameCaseMapped Profile 7.1. UsernameCaseMapped Profile
IANA has added the following entry to the "PRECIS Profiles" registry. IANA has added the following entry to the "PRECIS Profiles" registry.
Name: UsernameCaseMapped. Name: UsernameCaseMapped.
skipping to change at page 19, line 40 skipping to change at page 20, line 8
Case-Mapping Rule: Map uppercase and titlecase code points to Case-Mapping Rule: Map uppercase and titlecase code points to
lowercase. lowercase.
Normalization Rule: NFC. Normalization Rule: NFC.
Directionality Rule: The "Bidi Rule" defined in RFC 5893 applies. Directionality Rule: The "Bidi Rule" defined in RFC 5893 applies.
Enforcement: To be defined by security or application protocols that Enforcement: To be defined by security or application protocols that
use this profile. use this profile.
Specification: RFC 7613 (this document), Section 3.2. Specification: [[this document]], Section 3.2.
7.2. UsernameCasePreserved Profile 7.2. UsernameCasePreserved Profile
IANA has added the following entry to the "PRECIS Profiles" registry. IANA has added the following entry to the "PRECIS Profiles" registry.
Name: UsernameCasePreserved. Name: UsernameCasePreserved.
Base Class: IdentifierClass. Base Class: IdentifierClass.
Applicability: Usernames in security and application protocols. Applicability: Usernames in security and application protocols.
skipping to change at page 20, line 21 skipping to change at page 20, line 36
Case-Mapping Rule: None. Case-Mapping Rule: None.
Normalization Rule: NFC. Normalization Rule: NFC.
Directionality Rule: The "Bidi Rule" defined in RFC 5893 applies. Directionality Rule: The "Bidi Rule" defined in RFC 5893 applies.
Enforcement: To be defined by security or application protocols that Enforcement: To be defined by security or application protocols that
use this profile. use this profile.
Specification: RFC 7613 (this document), Section 3.3. Specification: [[this document]], Section 3.3.
7.3. OpaqueString Profile 7.3. OpaqueString Profile
IANA has added the following entry to the "PRECIS Profiles" registry. IANA has added the following entry to the "PRECIS Profiles" registry.
Name: OpaqueString. Name: OpaqueString.
Base Class: FreeformClass. Base Class: FreeformClass.
Applicability: Passwords and other opaque strings in security and Applicability: Passwords and other opaque strings in security and
skipping to change at page 20, line 50 skipping to change at page 21, line 17
Case-Mapping Rule: None. Case-Mapping Rule: None.
Normalization Rule: NFC. Normalization Rule: NFC.
Directionality Rule: None. Directionality Rule: None.
Enforcement: To be defined by security or application protocols that Enforcement: To be defined by security or application protocols that
use this profile. use this profile.
Specification: RFC 7613 (this document), Section 4.2. Specification: [[this document]], Section 4.2.
7.4. Stringprep Profile 7.4. Stringprep Profile
The stringprep specification [RFC3454] did not provide for entries in The stringprep specification [RFC3454] did not provide for entries in
the "Stringprep Profiles" registry to have any state except "Current" the "Stringprep Profiles" registry to have any state except "Current"
or "Not Current". Because this document obsoletes RFC 4013, which or "Not Current". Because RFC 7613 obsoleted RFC 4013, which
registered the SASLprep profile of stringprep, IANA has marked that registered the SASLprep profile of stringprep, IANA previously marked
profile as "Not Current" and cited this document as an additional that profile as "Not Current" and cited RFC 7613 as an additional
reference. reference. IANA is requested to modify the profile so that this
document is cited at the additional reference.
8. Security Considerations 8. Security Considerations
8.1. Password/Passphrase Strength 8.1. Password/Passphrase Strength
The ability to include a wide range of characters in passwords and The ability to include a wide range of characters in passwords and
passphrases can increase the potential for creating a strong password passphrases can increase the potential for creating a strong password
with high entropy. However, in practice, the ability to include such with high entropy. However, in practice, the ability to include such
characters ought to be weighed against the possible need to reproduce characters ought to be weighed against the possible need to reproduce
them on various devices using various input methods. them on various devices using various input methods.
8.2. Identifier Comparison 8.2. Password/Passphrase Comparison
In systems that conform to modern best practices for security,
verification of passwords during authentication will not use the
comparison defined in Section 4.2.3. Instead, because the system
performs cryptographic calculations to verify the password, it will
prepare the password as defined in Section 4.2.1 and enforce the
rules as defined in Section 4.2.2 before performing the relevant
calculations.
8.3. Identifier Comparison
The process of comparing identifiers (such as SASL simple user names, The process of comparing identifiers (such as SASL simple user names,
authentication identifiers, and authorization identifiers) can lead authentication identifiers, and authorization identifiers) can lead
to either false negatives or false positives, both of which have to either false negatives or false positives, both of which have
security implications. A more detailed discussion can be found in security implications. A more detailed discussion can be found in
[RFC6943]. [RFC6943].
8.3. Reuse of PRECIS 8.4. Reuse of PRECIS
The security considerations described in [RFC7564] apply to the The security considerations described in [I-D.ietf-precis-7564bis]
IdentifierClass and FreeformClass base string classes used in this apply to the IdentifierClass and FreeformClass base string classes
document for usernames and passwords, respectively. used in this document for usernames and passwords, respectively.
8.4. Reuse of Unicode 8.5. Reuse of Unicode
The security considerations described in [UTS39] apply to the use of The security considerations described in [UTS39] apply to the use of
Unicode code points in usernames and passwords. Unicode code points in usernames and passwords.
9. References 9. References
9.1. Normative References 9.1. Normative References
[I-D.ietf-precis-7564bis]
Saint-Andre, P. and M. Blanchet, "PRECIS Framework:
Preparation, Enforcement, and Comparison of
Internationalized Strings in Application Protocols",
draft-ietf-precis-7564bis-08 (work in progress), June
2017.
[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, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>. <http://www.rfc-editor.org/info/rfc2119>.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November 10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
2003, <http://www.rfc-editor.org/info/rfc3629>. 2003, <http://www.rfc-editor.org/info/rfc3629>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
skipping to change at page 22, line 24 skipping to change at page 23, line 10
[RFC5890] Klensin, J., "Internationalized Domain Names for [RFC5890] Klensin, J., "Internationalized Domain Names for
Applications (IDNA): Definitions and Document Framework", Applications (IDNA): Definitions and Document Framework",
RFC 5890, DOI 10.17487/RFC5890, August 2010, RFC 5890, DOI 10.17487/RFC5890, August 2010,
<http://www.rfc-editor.org/info/rfc5890>. <http://www.rfc-editor.org/info/rfc5890>.
[RFC6365] Hoffman, P. and J. Klensin, "Terminology Used in [RFC6365] Hoffman, P. and J. Klensin, "Terminology Used in
Internationalization in the IETF", BCP 166, RFC 6365, Internationalization in the IETF", BCP 166, RFC 6365,
DOI 10.17487/RFC6365, September 2011, DOI 10.17487/RFC6365, September 2011,
<http://www.rfc-editor.org/info/rfc6365>. <http://www.rfc-editor.org/info/rfc6365>.
[RFC7564] Saint-Andre, P. and M. Blanchet, "PRECIS Framework:
Preparation, Enforcement, and Comparison of
Internationalized Strings in Application Protocols",
RFC 7564, DOI 10.17487/RFC7564, May 2015,
<http://www.rfc-editor.org/info/rfc7564>.
[UAX11] Unicode Standard Annex #11, "East Asian Width", edited by [UAX11] Unicode Standard Annex #11, "East Asian Width", edited by
Ken Lunde. An integral part of The Unicode Standard, Ken Lunde. An integral part of The Unicode Standard,
<http://unicode.org/reports/tr11/>. <http://unicode.org/reports/tr11/>.
[Unicode] The Unicode Consortium, "The Unicode Standard", [Unicode] The Unicode Consortium, "The Unicode Standard",
<http://www.unicode.org/versions/latest/>. <http://www.unicode.org/versions/latest/>.
9.2. Informative References 9.2. Informative References
[Err1812] RFC Errata, "Erratum ID 1812", RFC 4013, [Err1812] RFC Errata, "Erratum ID 1812", RFC 4013,
skipping to change at page 24, line 31 skipping to change at page 25, line 13
<http://unicode.org/reports/tr39/>. <http://unicode.org/reports/tr39/>.
Appendix A. Changes from RFC 7613 Appendix A. Changes from RFC 7613
The following changes were made from [RFC7613]. The following changes were made from [RFC7613].
o Corrected the order of operations for the UsernameCaseMapped o Corrected the order of operations for the UsernameCaseMapped
profile to ensure consistency with RFC 7564. profile to ensure consistency with RFC 7564.
o In accordance with working group discussions and updates to o In accordance with working group discussions and updates to
[RFC7564], removed the use of the Unicode CaseFold() operation in [I-D.ietf-precis-7564bis], removed the use of the Unicode
favor of the Unicode toLower() operation. CaseFold() operation in favor of the Unicode toLower() operation.
o Modified the presentation (but not the content) of the rules. o Modified the presentation (but not the content) of the rules.
o Removed UTF-8 as a mandatory encoding, because that is a matter o Removed UTF-8 as a mandatory encoding, because that is a matter
for the application. for the application.
o Clarified several editorial matters. o Clarified several editorial matters.
o Updated references. o Updated references.
 End of changes. 42 change blocks. 
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