< draft-ietf-precis-7613bis-08.txt   rfc7613.txt 
Network Working Group P. Saint-Andre Internet Engineering Task Force (IETF) P. Saint-Andre
Internet-Draft Filament Request for Comments: 7613 &yet
Obsoletes: 7613 (if approved) A. Melnikov Obsoletes: 4013 A. Melnikov
Intended status: Standards Track Isode Ltd Category: Standards Track Isode Ltd
Expires: December 29, 2017 June 27, 2017 ISSN: 2070-1721 August 2015
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-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. This document obsoletes RFC 7613. passwords. The preparation, enforcement, and comparison of
internationalized strings (PRECIS) framework, RFC 7564, obsoletes RFC
3454, and this document obsoletes RFC 4013.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This is an Internet Standards Track document.
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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Internet-Drafts are draft documents valid for a maximum of six months This document is a product of the Internet Engineering Task Force
and may be updated, replaced, or obsoleted by other documents at any (IETF). It represents the consensus of the IETF community. It has
time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
material or to cite them other than as "work in progress." Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
This Internet-Draft will expire on December 29, 2017. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7613.
Copyright Notice Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction ....................................................4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology .....................................................5
3. Usernames . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Usernames .......................................................6
3.1. Definition . . . . . . . . . . . . . . . . . . . . . . . 5 3.1. Definition .................................................6
3.2. Case Mapping vs. Case Preservation . . . . . . . . . . . 6 3.2. UsernameCaseMapped Profile .................................7
3.3. UsernameCaseMapped Profile . . . . . . . . . . . . . . . 7 3.2.1. Preparation .........................................7
3.3.1. Rules . . . . . . . . . . . . . . . . . . . . . . . . 7 3.2.2. Enforcement .........................................7
3.3.2. Preparation . . . . . . . . . . . . . . . . . . . . . 8 3.2.3. Comparison ..........................................8
3.3.3. Enforcement . . . . . . . . . . . . . . . . . . . . . 8 3.3. UsernameCasePreserved Profile ..............................8
3.3.4. Comparison . . . . . . . . . . . . . . . . . . . . . 9 3.3.1. Preparation .........................................8
3.4. UsernameCasePreserved Profile . . . . . . . . . . . . . . 9 3.3.2. Enforcement .........................................8
3.4.1. Rules . . . . . . . . . . . . . . . . . . . . . . . . 9 3.3.3. Comparison ..........................................9
3.4.2. Preparation . . . . . . . . . . . . . . . . . . . . . 9 3.4. Case Mapping vs. Case Preservation .........................9
3.4.3. Enforcement . . . . . . . . . . . . . . . . . . . . . 10 3.5. Application-Layer Constructs ..............................10
3.4.4. Comparison . . . . . . . . . . . . . . . . . . . . . 10 3.6. Examples ..................................................11
3.5. Application-Layer Constructs . . . . . . . . . . . . . . 10 4. Passwords ......................................................13
3.6. Examples . . . . . . . . . . . . . . . . . . . . . . . . 10 4.1. Definition ................................................13
4. Passwords . . . . . . . . . . . . . . . . . . . . . . . . . . 12 4.2. OpaqueString Profile ......................................14
4.1. Definition . . . . . . . . . . . . . . . . . . . . . . . 12 4.2.1. Preparation ........................................14
4.2. OpaqueString Profile . . . . . . . . . . . . . . . . . . 13 4.2.2. Enforcement ........................................14
4.2.1. Preparation . . . . . . . . . . . . . . . . . . . . . 13 4.2.3. Comparison .........................................15
4.2.2. Enforcement . . . . . . . . . . . . . . . . . . . . . 14 4.3. Examples ..................................................15
4.2.3. Comparison . . . . . . . . . . . . . . . . . . . . . 14 5. Use in Application Protocols ...................................16
4.3. Examples . . . . . . . . . . . . . . . . . . . . . . . . 15 6. Migration ......................................................16
5. Use in Application Protocols . . . . . . . . . . . . . . . . 16 6.1. Usernames .................................................17
6. Migration . . . . . . . . . . . . . . . . . . . . . . . . . . 16 6.2. Passwords .................................................18
6.1. Usernames . . . . . . . . . . . . . . . . . . . . . . . . 17 7. IANA Considerations ............................................19
6.2. Passwords . . . . . . . . . . . . . . . . . . . . . . . . 18 7.1. UsernameCaseMapped Profile ................................19
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 7.2. UsernameCasePreserved Profile .............................20
7.1. UsernameCaseMapped Profile . . . . . . . . . . . . . . . 19 7.3. OpaqueString Profile ......................................20
7.2. UsernameCasePreserved Profile . . . . . . . . . . . . . . 20 7.4. Stringprep Profile ........................................21
7.3. OpaqueString Profile . . . . . . . . . . . . . . . . . . 20 8. Security Considerations ........................................21
7.4. Stringprep Profile . . . . . . . . . . . . . . . . . . . 21 8.1. Password/Passphrase Strength ..............................21
8. Security Considerations . . . . . . . . . . . . . . . . . . . 21 8.2. Identifier Comparison .....................................21
8.1. Password/Passphrase Strength . . . . . . . . . . . . . . 21 8.3. Reuse of PRECIS ...........................................21
8.2. Password/Passphrase Comparison . . . . . . . . . . . . . 21 8.4. Reuse of Unicode ..........................................22
8.3. Identifier Comparison . . . . . . . . . . . . . . . . . . 22 9. References .....................................................22
8.4. Reuse of PRECIS . . . . . . . . . . . . . . . . . . . . . 22 9.1. Normative References ......................................22
8.5. Reuse of Unicode . . . . . . . . . . . . . . . . . . . . 22 9.2. Informative References ....................................23
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 22 Appendix A. Differences from RFC 4013 .............................26
9.1. Normative References . . . . . . . . . . . . . . . . . . 22 Acknowledgements ..................................................27
9.2. Informative References . . . . . . . . . . . . . . . . . 23 Authors' Addresses ................................................27
Appendix A. Changes from RFC 7613 . . . . . . . . . . . . . . . 25
Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 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
indirectly when provided as the input to a cryptographic algorithm [HTTP-BASIC-AUTH]) or indirectly when provided as the input to a
such as a hash function (as in the Salted Challenge Response cryptographic algorithm such as a hash function (as in the Salted
Authentication Mechanism (SCRAM) SASL mechanism [RFC5802] and the Challenge Response Authentication Mechanism (SCRAM) SASL mechanism
HTTP Digest scheme [RFC7616]). [RFC5802] and the HTTP Digest scheme [HTTP-DIGEST-AUTH]).
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 characters from the
the Unicode coded character set [Unicode], with special attention to Unicode character set [Unicode], with special attention to characters
code points outside the ASCII range [RFC20]. The rules for handling outside the ASCII range [RFC20]. The rules for handling such strings
such strings are specified through profiles of the string classes are specified through profiles of the string classes defined in the
defined in the preparation, enforcement, and comparison of preparation, enforcement, and comparison of internationalized strings
internationalized strings (PRECIS) framework specification (PRECIS) framework specification [RFC7564].
[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 characters outside the ASCII range in an automated way, so that such
code points are treated carefully and consistently in application characters 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 characters. 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 character SUPERSCRIPT ONE (U+00B9) as equivalent to DIGIT ONE
ONE (U+0031), because that would result in false positives during (U+0031), because that would result in false positives during
comparison, authentication, and authorization (e.g., an attacker comparison, authentication, and authorization (e.g., an attacker
could easy spoof an account "user1@example.com"). could easy spoof an account "user1@example.com").
Whereas a naive use of Unicode would make such attacks trivially Whereas a naive use of Unicode would make such attacks trivially
easy, the PRECIS profile defined here for usernames generally easy, the PRECIS profile defined here for usernames generally
protects applications from inadvertently causing such problems. protects applications from inadvertently causing such problems.
(Similar considerations apply to passwords, although here it is (Similar considerations apply to passwords, although here it is
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.
Although the historical predecessor of this document was the SASLprep This document obsoletes RFC 4013 (the SASLprep profile of stringprep
profile of stringprep [RFC3454]), the approach defined here can be [RFC3454]) but can be used by technologies other than SASL [RFC4422],
used by technologies other than SASL [RFC4422], such as HTTP such as HTTP authentication as specified in [HTTP-BASIC-AUTH] and
authentication as specified in [RFC7617] and [RFC7616]. [HTTP-DIGEST-AUTH].
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 [XMPP-ADDR], which is intended to obsolete
protocol implementations are discouraged because they can have a [RFC6122]). Non-coordinated updates to protocol implementations are
negative impact on interoperability and security. discouraged because they can have a negative impact on
interoperability and security.
2. Terminology 2. Terminology
A "username" or "user identifier" is a string of characters Many important terms used in this document are defined in [RFC5890],
designating an account on a computing device or system, often but not [RFC6365], [RFC7564], and [Unicode]. The term "non-ASCII space"
necessarily for use by a person. Although some devices and system refers to any Unicode code point having a Unicode general category of
might allow a username to be part or all of a person's name, and a "Zs", with the exception of U+0020 (here called "ASCII space").
person might want their account designator to be part or all of their
name, because of the complexities involved that outcome is not
guaranteed for all human names on all computing devices or systems
that follow the rules defined in this specification. Protocol
designers and application developers who wish to allow a wider range
of characters are encouraged to consider a separation between more
restrictive account identifiers and more expressive display names.
A "password" is a string of characters that allows access to a As used here, the term "password" is not literally limited to a word;
computing device or system, often associated with a particular i.e., a password could be a passphrase consisting of more than one
username. A password is not literally limited to a word, because a word, perhaps separated by spaces, punctuation, or other
password could be a passphrase consisting of more than one word, non-alphanumeric characters.
perhaps separated by spaces, punctuation, or other non-alphanumeric
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 [HTTP-BASIC-AUTH] and [HTTP-DIGEST-AUTH]), whether or
not they use SASL. Note well that the exact form of a username in
Note well that the exact form of a username in any particular SASL any particular SASL mechanism or application technology is a matter
mechanism or application technology is a matter for implementation for implementation and deployment, and that a username does not
and deployment, and that a username does not necessarily map to any necessarily map to any particular application identifier (such as the
particular application identifier. localpart of an email address).
Many important terms used in this document are defined in [RFC5890],
[RFC6365], [I-D.ietf-precis-7564bis], and [Unicode]. The term "non-
ASCII space" refers to any Unicode code point having a Unicode
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], encoded using UTF-8 [RFC3629], and structured as an
"userparts" and expressed in a standard Unicode Encoding Form (such ordered sequence of "userparts". A userpart is allowed to contain
as UTF-8 [RFC3629]). A userpart is allowed to contain only code only code points that are in turn allowed by the PRECIS
points that are allowed by the PRECIS IdentifierClass defined in IdentifierClass defined in Section 4.2 of [RFC7564], and thus
Section 4.2 of [I-D.ietf-precis-7564bis], and thus consists almost consists almost exclusively of letters and digits. A username can
exclusively of letters and digits. A username can consist of a consist of a single userpart or a space-separated sequence of
single userpart or a space-separated sequence of userparts. 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*(idbyte)
; ;
; an "idpoint" is a Unicode code point that ; an "idbyte" is a byte used to represent a
; can be contained in a string conforming to ; UTF-8 encoded Unicode code point that can be
; the PRECIS IdentifierClass ; contained in a string that conforms to the
; PRECIS IdentifierClass
; ;
All code points and blocks not explicitly allowed in the PRECIS All code points and blocks not explicitly allowed in the PRECIS
IdentifierClass are disallowed; this includes private use code IdentifierClass are disallowed; this includes private use characters,
points, surrogate code points, and the other code points and blocks surrogate code points, and the other code points and blocks that were
that were defined as "Prohibited Output" in [RFC4013]. In addition, defined as "Prohibited Output" in [RFC4013]. In addition, common
common constructions such as "user@example.com" (e.g., the Network constructions such as "user@example.com" (e.g., the Network Access
Access Identifier from [RFC7542]) are allowed as usernames under this Identifier from [RFC7542]) are allowed as usernames under this
specification, as they were under [RFC4013]. specification, as they were under [RFC4013].
Implementation Note: The username construct defined in this Implementation Note: The username construct defined in this
document does not necessarily match what all deployed applications document does not necessarily match what all deployed applications
might refer to as a "username" or "userid" but instead provides a might refer to as a "username" or "userid" but instead provides a
relatively safe subset of Unicode code points that can be used in relatively safe subset of Unicode characters that can be used in
existing SASL mechanisms and in application protocols that use existing SASL mechanisms and in application protocols that use
SASL, and even in most application protocols that do not currently SASL, and even in most application protocols that do not currently
use SASL. use SASL.
A username MUST NOT be zero bytes in length. This rule is to be A username MUST NOT be zero bytes in length. This rule is to be
enforced after any normalization and mapping of code points. enforced after any normalization and mapping of code points.
In protocols that provide usernames as input to a cryptographic In protocols that provide usernames as input to a cryptographic
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 UsernameCaseMapped or enforcement of the rules for the UsernameCaseMapped or
UsernameCasePreserved profile before applying the algorithm. UsernameCasePreserved profile before applying the algorithm.
This specification defines two profiles for usernames: one that This specification defines two profiles for usernames: one that
performs case mapping and one that performs case preservation (see performs case mapping and one that performs case preservation (see
further discussion under Section 3.2). further discussion under Section 3.4).
3.2. Case Mapping vs. Case Preservation 3.2. UsernameCaseMapped Profile
The definition of the UsernameCaseMapped profile of the
IdentifierClass is provided in the following sections, including
detailed information about preparation, enforcement, and comparison
(for details on the distinction between these actions, refer to
[RFC7564]).
3.2.1. Preparation
An entity that prepares a string according to this profile MUST first
map fullwidth and halfwidth characters to their decomposition
mappings (see Unicode Standard Annex #11 [UAX11]). This is necessary
because the PRECIS "HasCompat" category specified in Section 9.17 of
[RFC7564] would otherwise forbid fullwidth and halfwidth characters.
After applying this width-mapping rule, the entity then MUST ensure
that the string consists only of Unicode code points that conform to
the PRECIS IdentifierClass defined in Section 4.2 of [RFC7564]. In
addition, the entity then MUST encode the string as UTF-8 [RFC3629].
3.2.2. Enforcement
An entity that performs enforcement according to this profile MUST
prepare a string as described in Section 3.2.1 and MUST also apply
the rules specified below for the UsernameCaseMapped profile (these
rules MUST be applied in the order shown):
1. Width-Mapping Rule: Applied as part of preparation (see above).
2. Additional Mapping Rule: There is no additional mapping rule.
3. Case-Mapping Rule: Uppercase and titlecase characters MUST be
mapped to their lowercase equivalents, preferably using Unicode
Default Case Folding as defined in the Unicode Standard [Unicode]
(at the time of this writing, the algorithm is specified in
Chapter 3 of [Unicode7.0], but the chapter number might change in
a future version of the Unicode Standard); see further discussion
in Section 3.4.
4. Normalization Rule: Unicode Normalization Form C (NFC) MUST be
applied to all characters.
5. Directionality Rule: Applications MUST apply the "Bidi Rule"
defined in [RFC5893] to strings that contain right-to-left
characters (i.e., each of the six conditions of the Bidi Rule
must be satisfied).
3.2.3. Comparison
An entity that performs comparison of two strings according to this
profile MUST prepare each string as specified in Section 3.2.1 and
then enforce the rules specified in Section 3.2.2. The two strings
are to be considered equivalent if they are an exact octet-for-octet
match (sometimes called "bit-string identity").
3.3. UsernameCasePreserved Profile
The definition of the UsernameCasePreserved profile of the
IdentifierClass is provided in the following sections, including
detailed information about preparation, enforcement, and comparison
(for details on the distinction between these actions, refer to
[RFC7564]).
3.3.1. Preparation
An entity that prepares a string according to this profile MUST first
map fullwidth and halfwidth characters to their decomposition
mappings (see Unicode Standard Annex #11 [UAX11]). This is necessary
because the PRECIS "HasCompat" category specified in Section 9.17 of
[RFC7564] would otherwise forbid fullwidth and halfwidth characters.
After applying this width-mapping rule, the entity then MUST ensure
that the string consists only of Unicode code points that conform to
the PRECIS IdentifierClass defined in Section 4.2 of [RFC7564]. In
addition, the entity then MUST encode the string as UTF-8 [RFC3629].
3.3.2. Enforcement
An entity that performs enforcement according to this profile MUST
prepare a string as described in Section 3.3.1 and MUST also apply
the rules specified below for the UsernameCasePreserved profile
(these rules MUST be applied in the order shown):
1. Width-Mapping Rule: Applied as part of preparation (see above).
2. Additional Mapping Rule: There is no additional mapping rule.
3. Case-Mapping Rule: Uppercase and titlecase characters MUST NOT be
mapped to their lowercase equivalents; see further discussion in
Section 3.4.
4. Normalization Rule: Unicode Normalization Form C (NFC) MUST be
applied to all characters.
5. Directionality Rule: Applications MUST apply the "Bidi Rule"
defined in [RFC5893] to strings that contain right-to-left
characters (i.e., each of the six conditions of the Bidi Rule
must be satisfied).
3.3.3. Comparison
An entity that performs comparison of two strings according to this
profile MUST prepare each string as specified in Section 3.3.1 and
then enforce the rules specified in Section 3.3.2. The two strings
are to be considered equivalent if they are an exact octet-for-octet
match (sometimes called "bit-string identity").
3.4. Case Mapping vs. Case Preservation
In order to accommodate the widest range of username constructs in In order to accommodate the widest range of username constructs in
applications, this document defines two username profiles: applications, this document defines two username profiles:
UsernameCaseMapped and UsernameCasePreserved. These two profiles UsernameCaseMapped and UsernameCasePreserved. These two profiles
differ only in the Case-Mapping Rule and are otherwise identical. differ only in the Case-Mapping Rule and are otherwise identical.
Case mapping is a matter for the application protocol, protocol Case mapping is a matter for the application protocol, protocol
implementation, or end deployment. In general, this document implementation, or end deployment. In general, this document
suggests that it is preferable to apply the UsernameCaseMapped suggests that it is preferable to apply the UsernameCaseMapped
profile and therefore perform case mapping, because not doing so can profile and therefore perform case mapping, because not doing so can
skipping to change at page 6, line 47 skipping to change at page 9, line 43
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. Because case mapping results in authentication identifiers. SASL mechanisms SHOULD delay any case
information loss, in order to retain that information for as long mapping to the last possible moment, such as when doing a lookup
as possible during processing, implementations SHOULD delay any by username, performing username comparisons, or generating a
case mapping to the last possible moment, such as when doing a cryptographic salt from a username (if the last possible moment
lookup by username, performing username comparisons, or generating happens on the server, then decisions about case mapping can be a
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
happens to necessarily be on the server side (this enables happens to necessarily be on the server side (this enables
decisions about case mapping to be a matter of deployment policy). decisions about case mapping to be a matter of deployment policy).
In keeping with [RFC4422], SASL application protocols are not to In keeping with [RFC4422], SASL application protocols are not to
apply this or any other profile to authentication identifiers, apply this or any other profile to authentication identifiers,
only to authorization identifiers. only to authorization identifiers.
o Application protocols that do not use SASL (such as HTTP o Application protocols that do not use SASL (such as HTTP
authentication with the HTTP Basic and Digest schemes as specified authentication with the HTTP Basic and Digest schemes as specified
in [RFC7617] and [RFC7616]) but that directly reuse this profile in [HTTP-BASIC-AUTH] and [HTTP-DIGEST-AUTH]) but that directly
MUST specify whether and when case mapping is to be applied to reuse this profile MUST specify whether and when case mapping is
authentication identifiers or authorization identifiers, or both. to be applied to authentication identifiers or authorization
Such "non-SASL application protocols" SHOULD delay any case identifiers, or both. Such "non-SASL application protocols"
mapping to the last possible moment, such as when doing a lookup SHOULD delay any case mapping to the last possible moment, such as
by username, performing username comparisons, or generating a when doing a lookup by username, performing username comparisons,
cryptographic salt from a username (if the last possible moment or generating a cryptographic salt from a username (if the last
happens on the server, then decisions about case mapping can be a possible moment happens on the server, then decisions about case
matter of deployment policy). mapping can be a matter of deployment policy).
If the specification for a SASL mechanism, SASL application protocol, If the specification for a SASL mechanism, SASL application protocol,
or non-SASL application protocol uses the UsernameCaseMapped profile, or non-SASL application protocol uses the UsernameCaseMapped profile,
it MUST clearly describe whether case mapping is to be applied at the it MUST clearly describe whether case mapping is to be applied at the
level of the protocol itself, implementations thereof, or service level of the protocol itself, implementations thereof, or service
deployments (each of these approaches can be legitimate, depending on deployments (each of these approaches can be legitimate, depending on
the application in question). the application in question).
3.3. UsernameCaseMapped Profile
3.3.1. Rules
The following rules are defined for use within the UsernameCaseMapped
profile of the PRECIS IdentifierClass.
1. Width-Mapping Rule: Map fullwidth and halfwidth code points to
their decomposition mappings (see Unicode Standard Annex #11
[UAX11]).
2. Additional Mapping Rule: There is no additional mapping rule.
3. Case-Mapping Rule: Map uppercase and titlecase code points to
their lowercase equivalents, preferably using the Unicode
toLower() operation as defined in the Unicode Standard [Unicode];
see further discussion in Section 3.2.
4. Normalization Rule: Apply Unicode Normalization Form C (NFC) to
all strings.
5. Directionality Rule: Apply the "Bidi Rule" defined in [RFC5893]
to strings that contain right-to-left code points (i.e., each of
the six conditions of the Bidi Rule must be satisfied); for
strings that do not contain right-to-left code points, there is
no special processing for directionality.
3.3.2. Preparation
An entity that prepares a string for subsequent enforcement according
to this profile MUST proceed as follows (applying the steps in the
order shown).
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
PRECIS "HasCompat" category specified in Section 9.17 of
[I-D.ietf-precis-7564bis] would forbid fullwidth and halfwidth
code points.
2. Ensure that the string consists only of Unicode code points that
are explicitly allowed by the PRECIS IdentifierClass defined in
Section 4.2 of [I-D.ietf-precis-7564bis].
3.3.3. Enforcement
An entity that performs enforcement according to this profile MUST
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:
1. Case-Mapping Rule
2. Normalization Rule
3. Directionality Rule
After all of the foregoing rules have been enforced, the entity MUST
ensure that the username is not zero bytes in length (this is done
after enforcing the rules to prevent applications from mistakenly
omitting a username entirely, because when internationalized strings
are accepted, a non-empty sequence of characters can result in a
zero-length username after canonicalization).
3.3.4. Comparison
An entity that performs comparison of two strings according to this
profile MUST prepare each string as specified in Section 3.3.2 and
then MUST enforce the rules specified in Section 3.3.3. The two
strings are to be considered equivalent if and only if they are an
exact octet-for-octet match (sometimes called "bit-string identity").
3.4. UsernameCasePreserved Profile
3.4.1. Rules
The following rules are defined for use within the
UsernameCasePreserved profile of the PRECIS IdentifierClass.
1. Width-Mapping Rule: Map fullwidth and halfwidth code points to
their decomposition mappings (see Unicode Standard Annex #11
[UAX11]).
2. Additional Mapping Rule: There is no additional mapping rule.
3. Case-Mapping Rule: There is no case-mapping rule.
4. Normalization Rule: Apply Unicode Normalization Form C (NFC) to
all strings.
5. Directionality Rule: Apply the "Bidi Rule" defined in [RFC5893]
to strings that contain right-to-left code points (i.e., each of
the six conditions of the Bidi Rule must be satisfied); for
strings that do not contain right-to-left code points, there is
no special processing for directionality.
3.4.2. Preparation
An entity that prepares a string for subsequent enforcement according
to this profile MUST proceed as follows (applying the steps in the
order shown).
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
PRECIS "HasCompat" category specified in Section 9.17 of
[I-D.ietf-precis-7564bis] would forbid fullwidth and halfwidth
code points.
2. Ensure that the string consists only of Unicode code points that
are explicitly allowed by the PRECIS IdentifierClass defined in
Section 4.2 of [I-D.ietf-precis-7564bis].
3.4.3. Enforcement
An entity that performs enforcement according to this profile MUST
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:
1. Normalization Rule
2. Directionality Rule
After all of the foregoing rules have been enforced, the entity MUST
ensure that the username is not zero bytes in length (this is done
after enforcing the rules to prevent applications from mistakenly
omitting a username entirely, because when internationalized strings
are accepted, a non-empty sequence of characters can result in a
zero-length username after canonicalization).
3.4.4. Comparison
An entity that performs comparison of two strings according to this
profile MUST prepare each string as specified in Section 3.4.2 and
then MUST enforce the rules specified in Section 3.4.3. The two
strings are to be considered equivalent if and only if they are an
exact octet-for-octet match (sometimes called "bit-string identity").
3.5. Application-Layer Constructs 3.5. Application-Layer Constructs
Both the UsernameCaseMapped and UsernameCasePreserved profiles enable Both the UsernameCaseMapped and UsernameCasePreserved profiles enable
an application protocol, implementation, or deployment to create an application protocol, implementation, or deployment to create
application-layer constructs such as a username that is a space- application-layer constructs such as a username that is a space-
separated set of userparts like "Firstname Middlename Lastname". separated set of userparts like "Firstname Middlename Lastname".
Although such a construct is not a profile of the PRECIS Although such a construct is not a profile of the PRECIS
IdentifierClass (because U+0020 SPACE is not allowed in the IdentifierClass (because U+0020 SPACE is not allowed in the
IdentifierClass), it can be created at the application layer because IdentifierClass), it can be created at the application layer because
U+0020 SPACE can be used as a separator between instances of the U+0020 SPACE can be used as a separator between instances of the
skipping to change at page 12, line 16 skipping to change at page 12, line 20
| # | Non-Userpart String | Notes | | # | Non-Userpart String | Notes |
+--------------------------+---------------------------------+ +--------------------------+---------------------------------+
| 8 | <foo bar> | Space (U+0020) is disallowed in | | 8 | <foo bar> | Space (U+0020) is disallowed in |
| | | the userpart | | | | the userpart |
+--------------------------+---------------------------------+ +--------------------------+---------------------------------+
| 9 | <> | Zero-length userpart | | 9 | <> | Zero-length userpart |
+--------------------------+---------------------------------+ +--------------------------+---------------------------------+
| 10| <henry&#x2163;> | The sixth character is ROMAN | | 10| <henry&#x2163;> | The sixth character is ROMAN |
| | | NUMERAL FOUR (U+2163) | | | | NUMERAL FOUR (U+2163) |
+--------------------------+---------------------------------+ +--------------------------+---------------------------------+
| 11| <&#x265A;> | A user part of BLACK CHESS KING | | 11| <&#x265A;> | A localpart of BLACK CHESS KING |
| | | (U+265A) | | | | (U+265A) |
+--------------------------+---------------------------------+ +--------------------------+---------------------------------+
Table 2: A Sample of Strings That Violate the Userpart Rule Table 2: A Sample of Strings That Violate the Userpart Rule
Here again, several points are worth noting. Regarding example 8: Here again, several points are worth noting. Regarding example 8:
although this is not a valid userpart, it is a valid username because although this is not a valid userpart, it is a valid username because
it is a space-separated sequence of userparts. Regarding example 10: it is a space-separated sequence of userparts. Regarding example 10:
the Unicode code point ROMAN NUMERAL FOUR (U+2163) has a the Unicode character ROMAN NUMERAL FOUR (U+2163) has a compatibility
compatibility equivalent of the string formed of LATIN CAPITAL LETTER equivalent of the string formed of LATIN CAPITAL LETTER I (U+0049)
I (U+0049) and LATIN CAPITAL LETTER V (U+0056), but code points with and LATIN CAPITAL LETTER V (U+0056), but characters with
compatibility equivalents are not allowed in the PRECIS compatibility equivalents are not allowed in the PRECIS
IdentifierClass. Regarding example 11: symbol characters such as IdentifierClass. Regarding example 11: symbol characters such as
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], encoded using UTF-8 [RFC3629], and conformant to
(specified below) of the PRECIS FreeformClass defined in Section 4.3 the OpaqueString profile (specified below) of the PRECIS
of [I-D.ietf-precis-7564bis], and that is expressed in a standard FreeformClass defined in Section 4.3 of [RFC7564].
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*(freebyte)
; ;
; a "freepoint" is a Unicode code point that ; a "freebyte" is a byte used to represent a
; can be contained in a string conforming to ; UTF-8 encoded Unicode code point that can be
; the PRECIS FreeformClass ; contained in a string that conforms to the
; PRECIS FreeformClass
; ;
All code points and blocks not explicitly allowed in the PRECIS All code points and blocks not explicitly allowed in the PRECIS
FreeformClass are disallowed; this includes private use code points, FreeformClass are disallowed; this includes private use characters,
surrogate code points, and the other code points and blocks defined surrogate code points, and the other code points and blocks defined
as "Prohibited Output" in Section 2.3 of RFC 4013 (when corrected per as "Prohibited Output" in Section 2.3 of RFC 4013 (when corrected per
[Err1812]). [Err1812]).
A password MUST NOT be zero bytes in length. This rule is to be A password MUST NOT be zero bytes in length. This rule is to be
enforced after any normalization and mapping of code points. enforced after any normalization and mapping of code points.
Note: Some existing systems allow an empty string in places where Note: Some existing systems allow an empty string in places where
a password would be expected (e.g., command-line tools that might a password would be expected (e.g., command-line tools that might
be called from an automated script, or servers that might need to be called from an automated script, or servers that might need to
be restarted without human intervention). From the perspective of be restarted without human intervention). From the perspective of
this document (and RFC 4013 before it), these empty strings are this document (and RFC 4013 before it), these empty strings are
not passwords but are workarounds for the practical difficulty of not passwords but are workarounds for the practical difficulty of
using passwords in certain scenarios. The prohibition of zero- using passwords in certain scenarios. The prohibition of
length passwords is not a recommendation regarding password zero-length passwords is not a recommendation regarding password
strength (because a password of only one byte is highly insecure) strength (because a password of only one byte is highly insecure)
but is meant to prevent applications from mistakenly omitting a but is meant to prevent applications from mistakenly omitting a
password entirely; such an outcome is possible when password entirely; such an outcome is possible when
internationalized strings are accepted, because a non-empty internationalized characters are accepted, because a non-empty
sequence of characters can result in a zero-length password after sequence of characters can result in a zero-length password after
canonicalization. canonicalization.
In protocols that provide passwords as input to a cryptographic In protocols that provide passwords as input to a cryptographic
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 [I-D.ietf-precis-7564bis]). these actions, refer to [RFC7564]).
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
explicitly allowed by the FreeformClass base string class defined in conform to the FreeformClass base string class defined in [RFC7564].
[I-D.ietf-precis-7564bis]. In addition, the entity MUST encode the string as UTF-8 [RFC3629].
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 characters MUST NOT
be mapped to their decomposition mappings (see Unicode Standard be mapped to their decomposition mappings (see Unicode Standard
Annex #11 [UAX11]). Annex #11 [UAX11]).
2. Additional Mapping Rule: Any instances of non-ASCII space MUST be 2. Additional Mapping Rule: Any instances of non-ASCII space MUST be
mapped to ASCII space (U+0020); a non-ASCII space is any Unicode mapped to ASCII space (U+0020); a non-ASCII space is any Unicode
code point having a Unicode general category of "Zs" (with the code point having a Unicode general category of "Zs" (with the
exception of U+0020). As was the case in RFC 4013, the inclusion exception of U+0020).
of only ASCII space prevents confusion with various non-ASCII
space code points, many of which are difficult to reproduce
across different input methods.
3. Case-Mapping Rule: There is no case mapping rule (because mapping 3. Case-Mapping Rule: Uppercase and titlecase characters MUST NOT be
uppercase and titlecase code points to their lowercase mapped to their lowercase equivalents.
equivalents would lead to false positives and thus to reduced
security).
4. Normalization Rule: Unicode Normalization Form C (NFC) MUST be 4. Normalization Rule: Unicode Normalization Form C (NFC) MUST be
applied to all strings. applied to all characters.
5. Directionality Rule: There is no directionality rule. The "Bidi 5. Directionality Rule: There is no directionality rule. The "Bidi
Rule" (defined in [RFC5893]) and similar rules are unnecessary Rule" (defined in [RFC5893]) and similar rules are unnecessary
and inapplicable to passwords, because they can reduce the and inapplicable to passwords, because they can reduce the range
repertoire of characters that are allowed in a string and of characters that are allowed in a string and therefore reduce
therefore reduce the amount of entropy that is possible in a the amount of entropy that is possible in a password. Such rules
password. Such rules are intended to minimize the possibility are intended to minimize the possibility that the same string
that the same string will be displayed differently on a layout will be displayed differently on a layout system set for
system set for right-to-left display and a layout system set for right-to-left display and a layout system set for left-to-right
left-to-right display; however, passwords are typically not display; however, passwords are typically not displayed at all
displayed at all and are rarely meant to be interoperable across and are rarely meant to be interoperable across different layout
different layout systems in the way that non-secret strings like systems in the way that non-secret strings like domain names and
domain names and usernames are. Furthermore, it is perfectly usernames are. Furthermore, it is perfectly acceptable for
acceptable for opaque strings other than passwords to be opaque strings other than passwords to be presented differently
presented differently in different layout systems, as long as the in different layout systems, as long as the presentation is
presentation is consistent in any given layout system. 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 enforce the rules specified in Section 4.2.2. The two strings
strings are to be considered equivalent if and only if they are an are to be considered equivalent if they are an exact octet-for-octet
exact octet-for-octet match (sometimes called "bit-string identity"). 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 16, line 8 skipping to change at page 16, line 11
+------------------------------------+------------------------------+ +------------------------------------+------------------------------+
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| <> | Zero-length passwords are | | 17| <my cat is a &#x9;by> | Controls are disallowed |
| | | disallowed |
+------------------------------------+------------------------------+
| 18| <my cat is a &#x9;by> | Control characters like TAB |
| | | are disallowed |
+------------------------------------+------------------------------+ +------------------------------------+------------------------------+
Table 4: A Sample of Strings That Violate the Password Rules Table 4: A String That Violates 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 handling the rules need to be enforced. See Section 6 of [RFC7564]
[I-D.ietf-precis-7564bis] for guidelines on using PRECIS profiles in for guidelines on using PRECIS profiles in applications.
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 characters 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
passwords such a policy can be problematic, because it can lead to passwords such a policy can be problematic, because it can lead to
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
idempotent procedure for all code points. Therefore, implementations
might need to apply the rules more than once to an internationalized
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] (but not from defined by the SASLprep specification [RFC4013]. The following
[RFC7613]). In order to smooth the process of migrating from sections describe these differences, along with their implications
SASLprep to the approach defined herein, the following sections for migration, in more detail.
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 45 skipping to change at page 17, line 42
Under SASLprep, the use of NFKC also handled the mapping of Under SASLprep, the use of NFKC also handled the mapping of
fullwidth and halfwidth code points to their decomposition fullwidth and halfwidth code points to their decomposition
mappings. mappings.
For migration purposes, operators might want to search their For migration purposes, operators might want to search their
database of usernames for names containing Unicode code points database of usernames for names containing Unicode code points
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 characters
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 characters, which
which correspond to the code points from the PRECIS "M" category correspond to the code points from the PRECIS "M" category defined
defined under Section 9.13 of [I-D.ietf-precis-7564bis]. For under Section 9.13 of [RFC7564] (with the exception of MONGOLIAN
migration purposes, the operator might want to remove from TODO SOFT HYPHEN (U+1806), which was "commonly mapped to nothing"
in Unicode 3.2 but at the time of this writing does not have a
derived property of Default_Ignorable_Code_Point in Unicode 7.0).
For migration purposes, the operator might want to remove from
usernames any code points contained in the PRECIS "M" category usernames any code points contained in the PRECIS "M" category
(e.g., SOFT HYPHEN (U+00AD)). Because these code points would (e.g., SOFT HYPHEN (U+00AD)). Because these code points would
have been "mapped to nothing" in stringprep, in practice a user have been "mapped to nothing" in stringprep, in practice a user
would not notice the difference if, upon migration to PRECIS, the would not notice the difference if, upon migration to PRECIS, the
code points are removed. code points are removed.
o SASLprep allowed uppercase and titlecase code points, whereas the o SASLprep allowed uppercase and titlecase characters, whereas the
UsernameCaseMapped profile maps uppercase and titlecase code UsernameCaseMapped profile maps uppercase and titlecase characters
points to their lowercase equivalents (by contrast, the 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 SASLprep to this Depending on local service policy, migration from RFC 4013 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 18 skipping to change at page 19, line 18
Under SASLprep, the use of NFKC also handled the mapping of Under SASLprep, the use of NFKC also handled the mapping of
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 characters, which correspond
correspond to the code points from the PRECIS "M" category defined to the code points from the PRECIS "M" category defined under
under Section 9.13 of [I-D.ietf-precis-7564bis]. In practice, Section 9.13 of [RFC7564] (with the exception of MONGOLIAN TODO
this change will probably have no effect on comparison, but user- SOFT HYPHEN (U+1806), which was commonly mapped to nothing in
oriented software might reject such code points instead of Unicode 3.2 but at the time of this writing is allowed by
ignoring them during password preparation. Unicode 7.0). In practice, this change will probably have no
effect on comparison, but user-oriented software might reject such
code points instead of 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.
Base Class: IdentifierClass. Base Class: IdentifierClass.
Applicability: Usernames in security and application protocols. Applicability: Usernames in security and application protocols.
Replaces: The SASLprep profile of stringprep. Replaces: The SASLprep profile of stringprep.
Width-Mapping Rule: Map fullwidth and halfwidth code points to their Width-Mapping Rule: Map fullwidth and halfwidth characters to their
decomposition mappings. decomposition mappings.
Additional Mapping Rule: None. Additional Mapping Rule: None.
Case-Mapping Rule: Map uppercase and titlecase code points to Case-Mapping Rule: Map uppercase and titlecase characters 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: [[this document]], Section 3.2. Specification: RFC 7613 (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.
Replaces: The SASLprep profile of stringprep. Replaces: The SASLprep profile of stringprep.
Width-Mapping Rule: Map fullwidth and halfwidth code points to their Width-Mapping Rule: Map fullwidth and halfwidth characters to their
decomposition mappings. decomposition mappings.
Additional Mapping Rule: None. Additional Mapping Rule: None.
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: [[this document]], Section 3.3. Specification: RFC 7613 (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
application protocols. application protocols.
Replaces: The SASLprep profile of stringprep. Replaces: The SASLprep profile of stringprep.
Width-Mapping Rule: None. Width-Mapping Rule: None.
Additional Mapping Rule: Map non-ASCII space code points to ASCII Additional Mapping Rule: Map non-ASCII space characters to ASCII
space. space.
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: [[this document]], Section 4.2. Specification: RFC 7613 (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 RFC 7613 obsoleted RFC 4013, which or "Not Current". Because this document obsoletes RFC 4013, which
registered the SASLprep profile of stringprep, IANA previously marked registered the SASLprep profile of stringprep, IANA has marked that
that profile as "Not Current" and cited RFC 7613 as an additional profile as "Not Current" and cited this document as an additional
reference. IANA is requested to modify the profile so that this reference.
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. Password/Passphrase Comparison 8.2. Identifier 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].
8.4. Reuse of PRECIS 8.3. Reuse of PRECIS
The security considerations described in [I-D.ietf-precis-7564bis] The security considerations described in [RFC7564] apply to the
apply to the IdentifierClass and FreeformClass base string classes IdentifierClass and FreeformClass base string classes used in this
used in this document for usernames and passwords, respectively. document for usernames and passwords, respectively.
8.5. Reuse of Unicode 8.4. 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 characters 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
10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November ISO 10646", STD 63, RFC 3629, DOI 10.17487/RFC3629,
2003, <http://www.rfc-editor.org/info/rfc3629>. November 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
Specifications: ABNF", STD 68, RFC 5234, Syntax Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008, DOI 10.17487/RFC5234, January 2008,
<http://www.rfc-editor.org/info/rfc5234>. <http://www.rfc-editor.org/info/rfc5234>.
[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/>.
[Unicode7.0]
The Unicode Consortium, "The Unicode Standard,
Version 7.0.0", (Mountain View, CA: The Unicode
Consortium, 2014 ISBN 978-1-936213-09-2),
<http://www.unicode.org/versions/Unicode7.0.0/>.
9.2. Informative References 9.2. Informative References
[Err1812] RFC Errata, "Erratum ID 1812", RFC 4013, [Err1812] RFC Errata, Erratum ID 1812, RFC 4013,
<http://www.rfc-editor.org>. <http://www.rfc-editor.org>.
[HTTP-BASIC-AUTH]
Reschke, J., "The 'Basic' HTTP Authentication Scheme",
Work in Progress, draft-ietf-httpauth-basicauth-update-07,
February 2015.
[HTTP-DIGEST-AUTH]
Shekh-Yusef, R., Ed., Ahrens, D., and S. Bremer, "HTTP
Digest Access Authentication", Work in Progress,
draft-ietf-httpauth-digest-19, April 2015.
[RFC20] Cerf, V., "ASCII format for network interchange", STD 80, [RFC20] Cerf, V., "ASCII format for network interchange", STD 80,
RFC 20, DOI 10.17487/RFC0020, October 1969, RFC 20, DOI 10.17487/RFC0020, October 1969,
<http://www.rfc-editor.org/info/rfc20>. <http://www.rfc-editor.org/info/rfc20>.
[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,
DOI 10.17487/RFC3454, December 2002, DOI 10.17487/RFC3454, December 2002,
<http://www.rfc-editor.org/info/rfc3454>. <http://www.rfc-editor.org/info/rfc3454>.
[RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION [RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL -
4rev1", RFC 3501, DOI 10.17487/RFC3501, March 2003, VERSION 4rev1", RFC 3501, DOI 10.17487/RFC3501,
<http://www.rfc-editor.org/info/rfc3501>. March 2003, <http://www.rfc-editor.org/info/rfc3501>.
[RFC4013] Zeilenga, K., "SASLprep: Stringprep Profile for User Names [RFC4013] Zeilenga, K., "SASLprep: Stringprep Profile for User Names
and Passwords", RFC 4013, DOI 10.17487/RFC4013, February and Passwords", RFC 4013, DOI 10.17487/RFC4013,
2005, <http://www.rfc-editor.org/info/rfc4013>. February 2005, <http://www.rfc-editor.org/info/rfc4013>.
[RFC4422] Melnikov, A., Ed. and K. Zeilenga, Ed., "Simple [RFC4422] Melnikov, A., Ed., and K. Zeilenga, Ed., "Simple
Authentication and Security Layer (SASL)", RFC 4422, Authentication and Security Layer (SASL)", RFC 4422,
DOI 10.17487/RFC4422, June 2006, DOI 10.17487/RFC4422, June 2006,
<http://www.rfc-editor.org/info/rfc4422>. <http://www.rfc-editor.org/info/rfc4422>.
[RFC4616] Zeilenga, K., Ed., "The PLAIN Simple Authentication and [RFC4616] Zeilenga, K., Ed., "The PLAIN Simple Authentication and
Security Layer (SASL) Mechanism", RFC 4616, Security Layer (SASL) Mechanism", RFC 4616,
DOI 10.17487/RFC4616, August 2006, DOI 10.17487/RFC4616, August 2006,
<http://www.rfc-editor.org/info/rfc4616>. <http://www.rfc-editor.org/info/rfc4616>.
[RFC5802] Newman, C., Menon-Sen, A., Melnikov, A., and N. Williams, [RFC5802] Newman, C., Menon-Sen, A., Melnikov, A., and N. Williams,
"Salted Challenge Response Authentication Mechanism "Salted Challenge Response Authentication Mechanism
(SCRAM) SASL and GSS-API Mechanisms", RFC 5802, (SCRAM) SASL and GSS-API Mechanisms", RFC 5802,
DOI 10.17487/RFC5802, July 2010, DOI 10.17487/RFC5802, July 2010,
<http://www.rfc-editor.org/info/rfc5802>. <http://www.rfc-editor.org/info/rfc5802>.
[RFC5893] Alvestrand, H., Ed. and C. Karp, "Right-to-Left Scripts [RFC5891] Klensin, J., "Internationalized Domain Names in
Applications (IDNA): Protocol", RFC 5891,
DOI 10.17487/RFC5891, August 2010,
<http://www.rfc-editor.org/info/rfc5891>.
[RFC5893] Alvestrand, H., Ed., and C. Karp, "Right-to-Left Scripts
for Internationalized Domain Names for Applications for Internationalized Domain Names for Applications
(IDNA)", RFC 5893, DOI 10.17487/RFC5893, August 2010, (IDNA)", RFC 5893, DOI 10.17487/RFC5893, August 2010,
<http://www.rfc-editor.org/info/rfc5893>. <http://www.rfc-editor.org/info/rfc5893>.
[RFC5894] Klensin, J., "Internationalized Domain Names for
Applications (IDNA): Background, Explanation, and
Rationale", RFC 5894, DOI 10.17487/RFC5894, August 2010,
<http://www.rfc-editor.org/info/rfc5894>.
[RFC6120] Saint-Andre, P., "Extensible Messaging and Presence [RFC6120] Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Core", RFC 6120, DOI 10.17487/RFC6120, Protocol (XMPP): Core", RFC 6120, DOI 10.17487/RFC6120,
March 2011, <http://www.rfc-editor.org/info/rfc6120>. March 2011, <http://www.rfc-editor.org/info/rfc6120>.
[RFC6122] Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Address Format", RFC 6122,
DOI 10.17487/RFC6122, March 2011,
<http://www.rfc-editor.org/info/rfc6122>.
[RFC6943] Thaler, D., Ed., "Issues in Identifier Comparison for [RFC6943] Thaler, D., Ed., "Issues in Identifier Comparison for
Security Purposes", RFC 6943, DOI 10.17487/RFC6943, May Security Purposes", RFC 6943, DOI 10.17487/RFC6943,
2013, <http://www.rfc-editor.org/info/rfc6943>. May 2013, <http://www.rfc-editor.org/info/rfc6943>.
[RFC7542] DeKok, A., "The Network Access Identifier", RFC 7542, [RFC7542] DeKok, A., "The Network Access Identifier", RFC 7542,
DOI 10.17487/RFC7542, May 2015, DOI 10.17487/RFC7542, May 2015,
<http://www.rfc-editor.org/info/rfc7542>. <http://www.rfc-editor.org/info/rfc7542>.
[RFC7613] Saint-Andre, P. and A. Melnikov, "Preparation,
Enforcement, and Comparison of Internationalized Strings
Representing Usernames and Passwords", RFC 7613,
DOI 10.17487/RFC7613, August 2015,
<http://www.rfc-editor.org/info/rfc7613>.
[RFC7616] Shekh-Yusef, R., Ed., Ahrens, D., and S. Bremer, "HTTP
Digest Access Authentication", RFC 7616,
DOI 10.17487/RFC7616, September 2015,
<http://www.rfc-editor.org/info/rfc7616>.
[RFC7617] Reschke, J., "The 'Basic' HTTP Authentication Scheme",
RFC 7617, DOI 10.17487/RFC7617, September 2015,
<http://www.rfc-editor.org/info/rfc7617>.
[RFC7622] Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Address Format", RFC 7622,
DOI 10.17487/RFC7622, September 2015,
<http://www.rfc-editor.org/info/rfc7622>.
[UTS39] Unicode Technical Standard #39, "Unicode Security [UTS39] Unicode Technical Standard #39, "Unicode Security
Mechanisms", edited by Mark Davis and Michel Suignard, Mechanisms", edited by Mark Davis and Michel Suignard,
<http://unicode.org/reports/tr39/>. <http://unicode.org/reports/tr39/>.
Appendix A. Changes from RFC 7613 [XMPP-ADDR]
Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Address Format", Work in Progress,
draft-ietf-xmpp-6122bis-24, June 2015.
The following changes were made from [RFC7613]. Appendix A. Differences from RFC 4013
o Corrected the order of operations for the UsernameCaseMapped This document builds upon the PRECIS framework defined in [RFC7564],
profile to ensure consistency with RFC 7564. which differs fundamentally from the stringprep technology [RFC3454]
used in SASLprep [RFC4013]. The primary difference is that
stringprep profiles allowed all characters except those characters
that were explicitly disallowed, whereas PRECIS profiles disallow all
characters except those characters that are explicitly allowed (this
"inclusion model" was originally used for internationalized domain
names in [RFC5891]; see [RFC5894] for further discussion). It is
important to keep this distinction in mind when comparing the
technology defined in this document to SASLprep [RFC4013].
o In accordance with working group discussions and updates to The following substantive modifications were made from RFC 4013.
[I-D.ietf-precis-7564bis], removed the use of the Unicode
CaseFold() operation in favor of the Unicode toLower() operation.
o Modified the presentation (but not the content) of the rules. o A single SASLprep algorithm was replaced by three separate
algorithms: one for usernames with case mapping, one for usernames
with case preservation, and one for passwords.
o Removed UTF-8 as a mandatory encoding, because that is a matter o The new preparation algorithms use PRECIS instead of a stringprep
for the application. profile. The new algorithms work independently of Unicode
versions.
o Clarified several editorial matters. o As recommended in the PRECIS framework, changed the Unicode
normalization form from NFKC to NFC.
o Updated references. o Some Unicode code points that were mapped to nothing in RFC 4013
are simply disallowed by PRECIS.
See [RFC7613] for a description of the differences from [RFC4013]. Acknowledgements
Appendix B. Acknowledgements This document borrows some text from [RFC4013] and [RFC6120].
Thanks to Christian Schudt and Sam Whited for their bug reports and The following individuals provided helpful feedback on this document:
feedback. Marc Blanchet, Ben Campbell, Alan DeKok, Joe Hildebrand, Jeffrey
Hutzelman, Simon Josefsson, Jonathan Lennox, James Manger, Matt
Miller, Chris Newman, Yutaka OIWA, Pete Resnick, Andrew Sullivan,
Nico Williams, and Yoshiro YONEYA. Nico Williams in particular
deserves special recognition for providing text that was used in
Section 3.4. Thanks also to Takahiro NEMOTO and Yoshiro YONEYA for
implementation feedback.
See [RFC7613] for acknowledgements related to the specification that Robert Sparks and Derek Atkins reviewed the document on behalf of the
this document supersedes. General Area Review Team and the Security Directorate, respectively.
Benoit Claise and Stephen Farrell provided helpful input during IESG
review.
Thanks to Matt Miller as document shepherd, Marc Blanchet and Yoshiro
YONEYA as working group chairs, and Pete Resnick and Barry Leiba as
area directors.
Peter Saint-Andre wishes to acknowledge Cisco Systems, Inc., for
employing him during his work on earlier draft versions of this
document.
Authors' Addresses Authors' Addresses
Peter Saint-Andre Peter Saint-Andre
Filament &yet
P.O. Box 787
Parker, CO 80134 Email: peter@andyet.com
USA URI: https://andyet.com/
Phone: +1 720 256 6756
Email: peter@filament.com
URI: https://filament.com/
Alexey Melnikov Alexey Melnikov
Isode Ltd Isode Ltd
5 Castle Business Village 5 Castle Business Village
36 Station Road 36 Station Road
Hampton, Middlesex TW12 2BX Hampton, Middlesex TW12 2BX
United Kingdom United Kingdom
Email: Alexey.Melnikov@isode.com Email: Alexey.Melnikov@isode.com
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