< draft-ietf-precis-saslprepbis-08.txt   draft-ietf-precis-saslprepbis-09.txt >
PRECIS P. Saint-Andre PRECIS P. Saint-Andre
Internet-Draft &yet Internet-Draft &yet
Obsoletes: 4013 (if approved) A. Melnikov Obsoletes: 4013 (if approved) A. Melnikov
Intended status: Standards Track Isode Ltd Intended status: Standards Track Isode Ltd
Expires: April 13, 2015 October 10, 2014 Expires: April 26, 2015 October 23, 2014
Preparation and Comparison of Internationalized Strings Representing Preparation, Enforcement, and Comparison of Internationalized Strings
Usernames and Passwords Representing Usernames and Passwords
draft-ietf-precis-saslprepbis-08 draft-ietf-precis-saslprepbis-09
Abstract Abstract
This document describes methods for handling Unicode strings This document describes methods for handling Unicode strings
representing usernames and passwords. This document obsoletes RFC representing usernames and passwords. This document obsoletes RFC
4013. 4013.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
skipping to change at page 1, line 34 skipping to change at page 1, line 34
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 13, 2015. This Internet-Draft will expire on April 26, 2015.
Copyright Notice Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Preparation, Comparison, and Enforcement . . . . . . . . . . 4 3. Usernames . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Usernames . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3.1. Definition . . . . . . . . . . . . . . . . . . . . . . . 4
4.1. Definition . . . . . . . . . . . . . . . . . . . . . . . 5 3.2. Preparation . . . . . . . . . . . . . . . . . . . . . . . 5
4.2. Preparation . . . . . . . . . . . . . . . . . . . . . . . 6 3.3. Enforcement . . . . . . . . . . . . . . . . . . . . . . . 5
4.3. Enforcement . . . . . . . . . . . . . . . . . . . . . . . 6 3.4. Comparison . . . . . . . . . . . . . . . . . . . . . . . 6
4.4. Comparison . . . . . . . . . . . . . . . . . . . . . . . 6 3.5. Case Mapping . . . . . . . . . . . . . . . . . . . . . . 6
4.5. Case Mapping . . . . . . . . . . . . . . . . . . . . . . 7 3.6. Application-Layer Constructs . . . . . . . . . . . . . . 7
4.6. Examples . . . . . . . . . . . . . . . . . . . . . . . . 8 3.7. Examples . . . . . . . . . . . . . . . . . . . . . . . . 7
5. Passwords . . . . . . . . . . . . . . . . . . . . . . . . . . 9 4. Passwords . . . . . . . . . . . . . . . . . . . . . . . . . . 9
5.1. Definition . . . . . . . . . . . . . . . . . . . . . . . 9 4.1. Definition . . . . . . . . . . . . . . . . . . . . . . . 9
5.2. Preparation . . . . . . . . . . . . . . . . . . . . . . . 10 4.2. Preparation . . . . . . . . . . . . . . . . . . . . . . . 10
5.3. Enforcement . . . . . . . . . . . . . . . . . . . . . . . 10 4.3. Enforcement . . . . . . . . . . . . . . . . . . . . . . . 10
5.4. Comparison . . . . . . . . . . . . . . . . . . . . . . . 11 4.4. Comparison . . . . . . . . . . . . . . . . . . . . . . . 11
5.5. Examples . . . . . . . . . . . . . . . . . . . . . . . . 11 4.5. Examples . . . . . . . . . . . . . . . . . . . . . . . . 11
6. Migration . . . . . . . . . . . . . . . . . . . . . . . . . . 12 5. Migration . . . . . . . . . . . . . . . . . . . . . . . . . . 12
6.1. Usernames . . . . . . . . . . . . . . . . . . . . . . . . 12 5.1. Usernames . . . . . . . . . . . . . . . . . . . . . . . . 12
6.2. Passwords . . . . . . . . . . . . . . . . . . . . . . . . 13 5.2. Passwords . . . . . . . . . . . . . . . . . . . . . . . . 13
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
7.1. UsernameIdentifierClass . . . . . . . . . . . . . . . . . 14 6.1. UsernameIdentifierClass . . . . . . . . . . . . . . . . . 14
7.2. PasswordFreeformClass . . . . . . . . . . . . . . . . . . 15 6.2. PasswordFreeformClass . . . . . . . . . . . . . . . . . . 15
8. Security Considerations . . . . . . . . . . . . . . . . . . . 16 7. Security Considerations . . . . . . . . . . . . . . . . . . . 15
8.1. Password/Passphrase Strength . . . . . . . . . . . . . . 16 7.1. Password/Passphrase Strength . . . . . . . . . . . . . . 15
8.2. Identifier Comparison . . . . . . . . . . . . . . . . . . 16 7.2. Identifier Comparison . . . . . . . . . . . . . . . . . . 15
8.3. Reuse of PRECIS . . . . . . . . . . . . . . . . . . . . . 16 7.3. Reuse of PRECIS . . . . . . . . . . . . . . . . . . . . . 16
8.4. Reuse of Unicode . . . . . . . . . . . . . . . . . . . . 16 7.4. Reuse of Unicode . . . . . . . . . . . . . . . . . . . . 16
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 16 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
9.1. Normative References . . . . . . . . . . . . . . . . . . 16 8.1. Normative References . . . . . . . . . . . . . . . . . . 16
9.2. Informative References . . . . . . . . . . . . . . . . . 17 8.2. Informative References . . . . . . . . . . . . . . . . . 16
Appendix A. Differences from RFC 4013 . . . . . . . . . . . . . 18 Appendix A. Differences from RFC 4013 . . . . . . . . . . . . . 18
Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 19 Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
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 SASL PLAIN mechanism [RFC4616] or the HTTP Basic plaintext (as in the SASL PLAIN mechanism [RFC4616] or the HTTP Basic
scheme [RFC2617]) or indirectly when provided as the input to a scheme [RFC2617]) or indirectly when provided as the input to a
cryptographic algorithm such as a hash function (as in the SASL SCRAM cryptographic algorithm such as a hash function (as in the SASL SCRAM
mechanism [RFC5802] or the HTTP Digest scheme [RFC2617]). mechanism [RFC5802] or the HTTP Digest scheme [RFC2617]).
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username in any particular SASL mechanism or application technology username in any particular SASL mechanism or application technology
is a matter for implementation and deployment, and that a username is a matter for implementation and deployment, and that a username
does not necessarily map to any particular application identifier does not necessarily map to any particular application identifier
(such as the localpart of an email address). (such as the localpart of an email address).
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in "OPTIONAL" in this document are to be interpreted as described in
[RFC2119]. [RFC2119].
3. Preparation, Comparison, and Enforcement 3. Usernames
This document distinguishes between three different actions that an
entity can take in handling a username or password:
o Enforcement entails applying all of the rules specified for a
particular profile (UsernameIdentifierClass or
PasswordFreeformClass) to an individual string.
o Comparison entails applying all of the rules specified for a
particular profile to two separate strings, for the purpose of
determining if the two strings are equivalent.
o Preparation entails only ensuring that the characters in an
individual string are allowed by the underlying PRECIS base class
(IdentifierClass or FreeformClass).
In most cases, "servers" are responsible for enforcement and
"clients" are responsible only for preparation. Although some
information regarding these responsibilities (e.g., the protocol
slots in which usernames or passwords can be placed) needs to be
provided in specifications that use the profiles defined in this
document, the general outlines of such responsibilities are explained
in the following sections.
4. Usernames Detailed rules for the preparation, enforcement, and comparision of
usernames are provided in the following sections (on the distinction
between these actions, refer to [I-D.ietf-precis-framework]).
4.1. 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], encoded using UTF-8 [RFC3629], and structured points [UNICODE], encoded using UTF-8 [RFC3629], and structured
either as an ordered sequence of "userparts" (where the complete either as an ordered sequence of "userparts" (where the complete
username can consist of a single userpart or a space-separated username can consist of a single userpart or a space-separated
sequence of userparts) or as a userpart@domainpart (where the sequence of userparts) or as a userpart@domainpart (where the
domainpart is an IP literal, an IPv4 address, or a fully-qualified domainpart is an IP literal, an IPv4 address, or a fully-qualified
domain name). domain name).
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*(1*SP userpart)] username = userpart [1*(1*SP userpart)]
/ userpart '@' domainpart userpart = 1*(idbyte)
userpart = 1*(idpoint)
;
; an "idpoint" is a UTF-8 encoded Unicode code point
; that conforms to the PRECIS "IdentifierClass"
;
domainpart = IP-literal / IPv4address / ifqdn
;
; the "IPv4address" and "IP-literal" rules are
; defined in RFC 3986, and the first-match-wins
; (a.k.a. "greedy") algorithm described in RFC 3986
; applies
;
; reuse of the IP-literal rule from RFC 3986 implies
; that IPv6 addresses are enclosed in square brackets
; (i.e., beginning with '[' and ending with ']')
;
ifqdn = 1*1023(domainpoint)
; ;
; a "domainpoint" is a UTF-8 encoded Unicode code ; an "idbyte" is a byte used to represent a
; point that conforms to RFC 5890 ; UTF-8 encoded Unicode code point that can be
; 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 characters, IdentifierClass are disallowed; this includes private use characters,
surrogate code points, and the other code points and blocks that were surrogate code points, and the other code points and blocks that were
defined as "Prohibited Output" in [RFC4013]. In addition, common defined as "Prohibited Output" in [RFC4013]. In addition, common
constructions such as "user@example.com" are allowed as usernames constructions such as "user@example.com" are allowed as usernames
under this specification, as they were under [RFC4013]. under this specification, as they were under [RFC4013].
Implementation Note: The username construct defined in this Implementation Note: The username construct defined in this
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existing SASL mechanisms and SASL-using application protocols, and existing SASL mechanisms and SASL-using application protocols, and
even in most application protocols that do not currently use SASL. even in most application protocols that do not currently 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
proper preparation of the username before applying the algorithm. proper preparation of the username before applying the algorithm.
4.2. Preparation 3.2. Preparation
An entity that prepares a string for inclusion in a username slot An entity that prepares a string for inclusion in a username slot
MUST ensure that the string consists only of Unicode code points that MUST ensure that the string consists only of Unicode code points that
conform to the "IdentifierClass" base string class defined in conform to the "IdentifierClass" base string class defined in
[I-D.ietf-precis-framework]. In addition, the string MUST be encoded [I-D.ietf-precis-framework]. In addition, the string MUST be encoded
as UTF-8 [RFC3629]. as UTF-8 [RFC3629].
4.3. Enforcement 3.3. Enforcement
An entity that performs enforcement in username slots MUST prepare a An entity that performs enforcement in username slots MUST prepare a
string as described in the previous section and MUST also apply the string as described in the previous section and MUST also apply the
rules specified below for the UsernameIdentifierClass profile (these rules specified below for the UsernameIdentifierClass profile (these
rules MUST be applied in the order shown). rules MUST be applied in the order shown).
1. Width Mapping Rule: Fullwidth and halfwidth characters MUST be 1. Width Mapping Rule: Fullwidth and halfwidth characters MUST be
mapped to their decomposition mappings. mapped to their decomposition mappings.
2. Additional Mapping Rule: There is no additional mapping rule. 2. Additional Mapping Rule: There is no additional mapping rule.
3. Case Mapping Rule: There is no case mapping rule (although see 3. Case Mapping Rule: There is no case mapping rule (although see
Section 4.5 below). Section 3.5 below).
4. Normalization Rule: Unicode Normalization Form C (NFC) MUST be 4. Normalization Rule: Unicode Normalization Form C (NFC) MUST be
applied to all characters. applied to all characters.
5. Exclusion Rule: There is no exclusion rule. 5. Exclusion Rule: There is no exclusion rule.
6. Directionality Rule: The "Bidi Rule" provided in [RFC5893] 6. Directionaity Rule: Applications MUST apply the "Bidi Rule"
applies. defined in [RFC5893] (i.e., each of the six conditions of the
Bidi Rule must be satisfied).
4.4. Comparison 3.4. Comparison
An entity that performs comparison of two strings before or after An entity that performs comparison of two strings before or after
their inclusion in username slots MUST prepare each string and their inclusion in username slots MUST prepare each string and
enforce the rules specified in the previous two sections. The two enforce the rules specified in the previous two sections. The two
strings are to be considered equivalent if they are an exact octet- strings are to be considered equivalent if they are an exact octet-
for-octet match (sometimes called "bit-string identity"). for-octet match (sometimes called "bit-string identity").
4.5. Case Mapping 3.5. Case Mapping
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 perform case mapping, since not suggests that it is preferable to perform case mapping, since not
doing so can lead to false positives during authentication and doing so can lead to false positives during authentication and
authorization (as described in [RFC6943]) and can result in confusion authorization (as described in [RFC6943]) and can result in confusion
among end users given the prevalence of case mapping in many existing among end users given the prevalence of case mapping in many existing
protocols and applications. However, there can be good reasons to protocols and applications. However, there can be good reasons to
not perform case mapping, such as backward compatibility with not perform case mapping, such as backward compatibility with
deployed infrastructure. deployed infrastructure.
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decisions about case mapping can be a matter of deployment decisions about case mapping can be a matter of deployment
policy). 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 specifies the handling of case or non-SASL application protocol specifies the handling of case
mapping for strings that conform to the UsernameIdentifierClass, it mapping for strings that conform to the UsernameIdentifierClass, it
MUST clearly describe whether case mapping is required, recommended, MUST clearly describe whether case mapping is required, recommended,
or optional at the level of the protocol itself, implementations or optional at the level of the protocol itself, implementations
thereof, or service deployments. thereof, or service deployments.
4.6. Examples 3.6. Application-Layer Constructs
The following examples illustrate a small number of usernames that The username rule allows an application protocol, implementation, or
are consistent with the format defined above (note that the deployment to create application-layer constructs such as
characters < and > are used here to delineate the actual usernames "user@domain" or "Firstname Middlename Lastname" (e.g., because the
and are not part of the username strings). PRECIS IdentifierClass allows any ASCII7 character, because spaces
can be used to separate userpart instances, and because domain names
as specified in [RFC5890] and [RFC5892] are a subset of the PRECIS
IdentifierClass).
Table 1: A sample of legal usernames 3.7. Examples
+---------------------------------+---------------------------------+ The following examples illustrate a small number of userparts (not
| # | Username | Notes | usernames) that are consistent with the format defined above (note
+---------------------------------+---------------------------------+ that the characters < and > are used here to delineate the actual
| 1 | <juliet> | A userpart only | userparts and are not part of the userpart strings).
+---------------------------------+---------------------------------+
| 2 | <fussball@example.com> | A userpart and domainpart | Table 1: A sample of legal userparts
+---------------------------------+---------------------------------+
| 3 | <fu&#xDF;ball@example.com> | The third character is LATIN | +--------------------------+---------------------------------+
| | | SMALL LETTER SHARP S (U+00DF) | | # | Userpart | Notes |
+---------------------------------+---------------------------------+ +--------------------------+---------------------------------+
| 4 | <&#x3C0;@example.com> | A userpart of GREEK SMALL | | 1 | <juliet@example.com> | The at-sign is allowed in the |
| | | LETTER PI (U+03C0) | | | | PRECIS IdentifierClass |
+---------------------------------+---------------------------------+ +--------------------------+---------------------------------+
| 5 | <&#x3A3;@example.com> | A userpart of GREEK CAPITAL | | 2 | <fussball> | |
| | | LETTER SIGMA (U+03A3) | +--------------------------+---------------------------------+
+---------------------------------+---------------------------------+ | 3 | <fu&#xDF;ball> | The third character is LATIN |
| 6 | <&#x3C3;@example.com> | A userpart of GREEK SMALL | | | | SMALL LETTER SHARP S (U+00DF) |
| | | LETTER SIGMA (U+03C3) | +--------------------------+---------------------------------+
+---------------------------------+---------------------------------+ | 4 | <&#x3C0;> | A userpart of GREEK SMALL |
| 7 | <&#x3C2;@example.com> | A userpart of GREEK SMALL | | | | LETTER PI (U+03C0) |
| | | LETTER FINAL SIGMA (U+03C2) | +--------------------------+---------------------------------+
+---------------------------------+---------------------------------+ | 5 | <&#x3A3;> | A userpart of GREEK CAPITAL |
| | | LETTER SIGMA (U+03A3) |
+--------------------------+---------------------------------+
| 6 | <&#x3C3;> | A userpart of GREEK SMALL |
| | | LETTER SIGMA (U+03C3) |
+--------------------------+---------------------------------+
| 7 | <&#x3C2;> | A userpart of GREEK SMALL |
| | | LETTER FINAL SIGMA (U+03C2) |
+--------------------------+---------------------------------+
Several points are worth noting. Regarding examples 2 and 3: Several points are worth noting. Regarding examples 2 and 3:
although in German the character esszett (LATIN SMALL LETTER SHARP S, although in German the character esszett (LATIN SMALL LETTER SHARP S,
U+00DF) can mostly be used interchangeably with the two characters U+00DF) can mostly be used interchangeably with the two characters
"ss", the userparts in these examples are different and (if desired) "ss", the userparts in these examples are different and (if desired)
a server would need to enforce a registration policy that disallows a server would need to enforce a registration policy that disallows
one of them if the other is registered. Regarding examples 5, 6, and one of them if the other is registered. Regarding examples 5, 6, and
7: optional case-mapping of GREEK CAPITAL LETTER SIGMA (U+03A3) to 7: optional case-mapping of GREEK CAPITAL LETTER SIGMA (U+03A3) to
lowercase (i.e., to GREEK SMALL LETTER SIGMA, U+03C3) during lowercase (i.e., to GREEK SMALL LETTER SIGMA, U+03C3) during
comparison would result in matching the usernames in examples 5 and comparison would result in matching the userparts in examples 5 and
6; however, because the PRECIS mapping rules do not account for the 6; however, because the PRECIS mapping rules do not account for the
special status of GREEK SMALL LETTER FINAL SIGMA (U+03C2), the special status of GREEK SMALL LETTER FINAL SIGMA (U+03C2), the
usernames in examples 5 and 7 or examples 6 and 7 would not be userparts in examples 5 and 7 or examples 6 and 7 would not be
matched. matched.
The following examples illustrate strings that are not valid The following examples illustrate strings that are not valid
usernames because they violate the format defined above. userparts (not usernames) because they violate the format defined
above.
Table 2: A sample of strings that violate the username rules Table 2: A sample of strings that violate the userpart rule
+---------------------------------+---------------------------------+ +--------------------------+---------------------------------+
| # | Non-Username string | Notes | | # | Non-Userpart string | Notes |
+---------------------------------+---------------------------------+ +--------------------------+---------------------------------+
| 8 | <"juliet"@example.com> | Quotation marks (U+0022) in | | 8 | <foo bar> | Space (U+0020) is disallowed in |
| | | userpart | | | | the userpart |
+---------------------------------+---------------------------------+ +--------------------------+---------------------------------+
| 9 | <foo bar@example.com> | Space (U+0020) in userpart | | 9 | <> | Zero-length userpart |
+---------------------------------+---------------------------------+ +--------------------------+---------------------------------+
| 10| <@example.com> | Zero-length userpart | | 10| <henry&#x2163;> | The sixth character is ROMAN |
+---------------------------------+---------------------------------+ | | | NUMERAL FOUR (U+2163) |
| 11| <henry&#x2163;@example.com> | The sixth character is ROMAN | +--------------------------+---------------------------------+
| | | NUMERAL FOUR (U+2163) | | 11| <&#x265A;> | A localpart of BLACK CHESS KING |
+---------------------------------+---------------------------------+ | | | (U+265A) |
| 12| <&#x265A;@example.com> | A localpart of BLACK CHESS KING | +--------------------------+---------------------------------+
| | | (U+265A) |
+---------------------------------+---------------------------------+
Here again, several points are worth noting. Regarding example 11, Here again, several points are worth noting. Regarding example 10,
the Unicode character ROMAN NUMERAL FOUR (U+2163) has a compatibility the Unicode character ROMAN NUMERAL FOUR (U+2163) has a compatibility
equivalent of the string formed of LATIN CAPITAL LETTER I (U+0049) equivalent of the string formed of LATIN CAPITAL LETTER I (U+0049)
and LATIN CAPITAL LETTER V (U+0056), but characters 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
IdentiferClass. Regarding example 12: symbol characters such as IdentiferClass. 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.
5. Passwords 4. Passwords
5.1. Definition Detailed rules for the preparation, enforcement, and comparision of
passwords are provided in the following sections (on the distinction
between these actions, refer to [I-D.ietf-precis-framework]).
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], encoded using UTF-8 [RFC3629], and conformant to points [UNICODE], encoded using UTF-8 [RFC3629], and conformant to
the PRECIS FreeformClass. the PRECIS FreeformClass.
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)
; ;
skipping to change at page 10, line 25 skipping to change at page 10, line 18
as "Prohibited Output" in Section 2.3 of RFC 4013. as "Prohibited Output" in Section 2.3 of RFC 4013.
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.
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
proper preparation of the password before applying the algorithm, proper preparation of the password before applying the algorithm,
since the password is not available to the server in plaintext form. since the password is not available to the server in plaintext form.
5.2. Preparation 4.2. Preparation
An entity that prepares a string for inclusion in a password slot An entity that prepares a string for inclusion in a password slot
MUST ensure that the string consists only of Unicode code points that MUST ensure that the string consists only of Unicode code points that
conform to the "FreeformClass" base string class defined in conform to the "FreeformClass" base string class defined in
[I-D.ietf-precis-framework]. In addition, the string MUST be encoded [I-D.ietf-precis-framework]. In addition, the string MUST be encoded
as UTF-8 [RFC3629]. as UTF-8 [RFC3629].
5.3. Enforcement 4.3. Enforcement
An entity that performs enforcement in password slots MUST prepare a An entity that performs enforcement in password slots MUST prepare a
string as described in the previous section and MUST also apply the string as described in the previous section and MUST also apply the
rules specified below for the PasswordFreeformClass (these rules MUST rules specified below for the PasswordFreeformClass (these rules MUST
be applied in the order shown). be applied in the order shown).
1. Width Mapping Rule: Fullwidth and halfwidth characters MUST NOT 1. Width Mapping Rule: Fullwidth and halfwidth characters MUST NOT
be mapped to their decomposition mappings. be mapped to their decomposition mappings.
2. Additional Mapping Rule: Any instances of non-ASCII space MUST be 2. Additional Mapping Rule: Any instances of non-ASCII space MUST be
skipping to change at page 11, line 10 skipping to change at page 10, line 51
U+3000 IDEOGRAPHIC SPACE). U+3000 IDEOGRAPHIC SPACE).
3. Case Mapping Rule: Uppercase and titlecase characters MUST NOT be 3. Case Mapping Rule: Uppercase and titlecase characters MUST NOT be
mapped to their lowercase equivalents. mapped to their lowercase equivalents.
4. Normalization Rule: Unicode Normalization Form C (NFC) MUST be 4. Normalization Rule: Unicode Normalization Form C (NFC) MUST be
applied to all characters. applied to all characters.
5. Exclusion Rule: There is no exclusion rule. 5. Exclusion Rule: There is no exclusion rule.
6. Directionality Rule: There is no directionality rule. 6. Directionality Rule: There is no directionality rule. The "Bidi
Rule" (defined in [RFC5893]) and similar rules are unnecessary
With regard to directionality, the "Bidi Rule" (defined in [RFC5893]) and inapplicable to passwords, since they can reduce the range of
and similar rules are unnecessary and inapplicable to passwords, characters that are allowed in a string and therefore reduce the
since they can reduce the range of characters that are allowed in a amount of entropy that is possible in a password. Furthermore,
string and therefore reduce the amount of entropy that is possible in such rules are intended to minimize the possibility that the same
a password. Furthermore, such rules are intended to minimize the string will be displayed differently on a system set for right-
possibility that the same string will be displayed differently on a to-left display and a system set for left-to-right display;
system set for right-to-left display and a system set for left-to- however, passwords are typically not displayed at all and are
right display; however, passwords are typically not displayed at all rarely meant to be interoperable across different systems in the
and are rarely meant to be interoperable across different systems in way that non-secret strings like domain names and usernames are.
the way that non-secret strings like domain names and usernames are.
5.4. Comparison 4.4. Comparison
An entity that performs comparison of two strings before or after An entity that performs comparison of two strings before or after
their inclusion in password slots MUST prepare each string and their inclusion in password slots MUST prepare each string and
enforce the rules specified in the previous two sections. The two enforce the rules specified in the previous two sections. The two
strings are to be considered equivalent if they are an exact octet- strings are to be considered equivalent if they are an exact octet-
for-octet match (sometimes called "bit-string identity"). for-octet match (sometimes called "bit-string identity").
5.5. Examples 4.5. 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 passwords characters < and > are used here to delineate the actual passwords
and are not part of the username strings). and are not part of the username strings).
Table 3: A sample of legal passwords Table 3: A sample of legal passwords
+------------------------------------+------------------------------+ +------------------------------------+------------------------------+
| # | Password | Notes | | # | Password | Notes |
skipping to change at page 12, line 37 skipping to change at page 12, line 17
+------------------------------------+------------------------------+ +------------------------------------+------------------------------+
| # | Password | Notes | | # | Password | Notes |
+------------------------------------+------------------------------+ +------------------------------------+------------------------------+
| 17| <foo&#x1680;bar> | Non-ASCII space (here, OGHAM | | 17| <foo&#x1680;bar> | Non-ASCII space (here, OGHAM |
| | | SPACE MARK, U+1680) is not | | | | SPACE MARK, U+1680) is not |
| | | allowed | | | | allowed |
+------------------------------------+------------------------------+ +------------------------------------+------------------------------+
| 18| <my cat is a &#x9;by> | Controls are disallowed | | 18| <my cat is a &#x9;by> | Controls are disallowed |
+------------------------------------+------------------------------+ +------------------------------------+------------------------------+
6. Migration 5. 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]. The following
sections describe these differences, along with their implications sections describe these differences, along with their implications
for migration, in more detail. for migration, in more detail.
6.1. Usernames 5.1. 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 migrating to use of the rules need to scrub existing data when migrating to use of the rules
defined in this specification. In particular: defined in 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 this usage of the PRECIS IdentifierClass employs (NFKC), whereas this usage of the PRECIS IdentifierClass employs
Unicode Normalization Form C (NFC). In practice this change is Unicode Normalization Form C (NFC). In practice this change is
unlikely to cause significant problems, because NFKC provides unlikely to cause significant problems, because NFKC provides
methods for mapping Unicode code points with compatibility methods for mapping Unicode code points with compatibility
skipping to change at page 13, line 45 skipping to change at page 13, line 25
o SASLprep allowed uppercase and titlecase characters, whereas this o SASLprep allowed uppercase and titlecase characters, whereas this
usage of the PRECIS IdentifierClass maps uppercase and titlecase usage of the PRECIS IdentifierClass maps uppercase and titlecase
characters to their lowercase equivalents. For migration characters to their lowercase equivalents. For migration
purposes, deployments can either convert uppercase and titlecase purposes, deployments can either convert uppercase and titlecase
characters to their lowercase equivalents in usernames (thus characters to their lowercase equivalents in usernames (thus
losing the case information) or preserve uppercase and titlecase losing the case information) or preserve uppercase and titlecase
characters and ignore the case difference when comparing characters and ignore the case difference when comparing
usernames. usernames.
6.2. Passwords 5.2. Passwords
Depending on local service policy, migration from RFC 4013 to this Depending on local service policy, migration from RFC 4013 to this
specification might not involve any scrubbing of data (since specification might not involve any scrubbing of data (since
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 this usage of the PRECIS FreeformClass employs (NFKC), whereas this usage of the PRECIS FreeformClass employs
Unicode Normalization Form C (NFC). Because NFKC is more Unicode Normalization Form C (NFC). Because NFKC is more
skipping to change at page 14, line 36 skipping to change at page 14, line 16
Appendix B.1 of [RFC3454]) to nothing, whereas the PRECIS Appendix B.1 of [RFC3454]) to nothing, whereas the PRECIS
FreeformClass entirely disallows such characters, which correspond FreeformClass entirely disallows such characters, which correspond
to the code points from the "M" category defined under to the code points from the "M" category defined under
Section 6.13 of [I-D.ietf-precis-framework] (with the exception of Section 6.13 of [I-D.ietf-precis-framework] (with the exception of
U+1806 MONGOLIAN TODO SOFT HYPHEN, which was commonly mapped to U+1806 MONGOLIAN TODO SOFT HYPHEN, which was commonly mapped to
nothing in Unicode 3.2 but at the time of this writing is allowed nothing in Unicode 3.2 but at the time of this writing is allowed
by Unicode 6.2). In practice, this change will probably have no by Unicode 6.2). In practice, this change will probably have no
effect on comparison, but user-oriented software might reject such effect on comparison, but user-oriented software might reject such
code points instead of ignoring them during password preparation. code points instead of ignoring them during password preparation.
7. IANA Considerations 6. IANA Considerations
The IANA shall add the following entries to the PRECIS Profiles The IANA shall add the following entries to the PRECIS Profiles
Registry. Registry.
7.1. UsernameIdentifierClass 6.1. UsernameIdentifierClass
Name: UsernameIdentifierClass. Name: UsernameIdentifierClass.
Applicability: Usernames in security and application protocols. Applicability: Usernames in security and application protocols.
Base Class: IdentifierClass. Base Class: IdentifierClass.
Replaces: The SASLprep profile of Stringprep. Replaces: The SASLprep profile of Stringprep.
Width Mapping Rule: Map fullwidth and halfwidth characters to their Width Mapping Rule: Map fullwidth and halfwidth characters to their
skipping to change at page 15, line 22 skipping to change at page 15, line 5
Exclusion Rule: None. Exclusion Rule: None.
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 XXXX. [Note to RFC Editor: please change XXXX to Specification: RFC XXXX. [Note to RFC Editor: please change XXXX to
the number issued for this specification.] the number issued for this specification.]
7.2. PasswordFreeformClass 6.2. PasswordFreeformClass
Name: PasswordFreeformClass. Name: PasswordFreeformClass.
Applicability: Passwords in security and application protocols. Applicability: Passwords in security and application protocols.
Base Class: FreeformClass Base Class: FreeformClass
Replaces: The SASLprep profile of Stringprep. Replaces: The SASLprep profile of Stringprep.
Width Mapping Rule: None. Width Mapping Rule: None.
skipping to change at page 16, line 5 skipping to change at page 15, line 34
Exclusion Rule: None. Exclusion Rule: None.
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 XXXX. [Note to RFC Editor: please change XXXX to Specification: RFC XXXX. [Note to RFC Editor: please change XXXX to
the number issued for this specification.] the number issued for this specification.]
8. Security Considerations 7. Security Considerations
8.1. Password/Passphrase Strength 7.1. 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 7.2. 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 7.3. Reuse of PRECIS
The security considerations described in [I-D.ietf-precis-framework] The security considerations described in [I-D.ietf-precis-framework]
apply to the "IdentifierClass" and "FreeformClass" base string apply to the "IdentifierClass" and "FreeformClass" base string
classes used in this document for usernames and passwords, classes used in this document for usernames and passwords,
respectively. respectively.
8.4. Reuse of Unicode 7.4. 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 characters in usernames and passwords. Unicode characters in usernames and passwords.
9. References 8. References
9.1. Normative References 8.1. Normative References
[I-D.ietf-precis-framework] [I-D.ietf-precis-framework]
Saint-Andre, P. and M. Blanchet, "Precis Framework: Saint-Andre, P. and M. Blanchet, "Precis Framework:
Handling Internationalized Strings in Protocols", draft- Handling Internationalized Strings in Protocols", draft-
ietf-precis-framework-18 (work in progress), September ietf-precis-framework-19 (work in progress), October 2014.
2014.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003. 10646", STD 63, RFC 3629, November 2003.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008. Specifications: ABNF", STD 68, RFC 5234, January 2008.
[UNICODE] The Unicode Consortium, "The Unicode Standard, Version [UNICODE] The Unicode Consortium, "The Unicode Standard, Version
6.3", 2013, 6.3", 2013,
<http://www.unicode.org/versions/Unicode6.3.0/>. <http://www.unicode.org/versions/Unicode6.3.0/>.
9.2. Informative References 8.2. Informative References
[RFC20] Cerf, V., "ASCII format for network interchange", RFC 20, [RFC20] Cerf, V., "ASCII format for network interchange", RFC 20,
October 1969. October 1969.
[RFC2617] Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S., [RFC2617] Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
Leach, P., Luotonen, A., and L. Stewart, "HTTP Leach, P., Luotonen, A., and L. Stewart, "HTTP
Authentication: Basic and Digest Access Authentication", Authentication: Basic and Digest Access Authentication",
RFC 2617, June 1999. RFC 2617, June 1999.
[RFC3454] Hoffman, P. and M. Blanchet, "Preparation of [RFC3454] Hoffman, P. and M. Blanchet, "Preparation of
skipping to change at page 17, line 47 skipping to change at page 17, line 29
"Salted Challenge Response Authentication Mechanism "Salted Challenge Response Authentication Mechanism
(SCRAM) SASL and GSS-API Mechanisms", RFC 5802, July 2010. (SCRAM) SASL and GSS-API Mechanisms", RFC 5802, July 2010.
[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, August 2010. RFC 5890, August 2010.
[RFC5891] Klensin, J., "Internationalized Domain Names in [RFC5891] Klensin, J., "Internationalized Domain Names in
Applications (IDNA): Protocol", RFC 5891, August 2010. Applications (IDNA): Protocol", RFC 5891, August 2010.
[RFC5892] Faltstrom, P., "The Unicode Code Points and
Internationalized Domain Names for Applications (IDNA)",
RFC 5892, August 2010.
[RFC5893] Alvestrand, H. and C. Karp, "Right-to-Left Scripts for [RFC5893] Alvestrand, H. and C. Karp, "Right-to-Left Scripts for
Internationalized Domain Names for Applications (IDNA)", Internationalized Domain Names for Applications (IDNA)",
RFC 5893, August 2010. RFC 5893, August 2010.
[RFC5894] Klensin, J., "Internationalized Domain Names for [RFC5894] Klensin, J., "Internationalized Domain Names for
Applications (IDNA): Background, Explanation, and Applications (IDNA): Background, Explanation, and
Rationale", RFC 5894, August 2010. Rationale", RFC 5894, August 2010.
[RFC6120] Saint-Andre, P., "Extensible Messaging and Presence [RFC6120] Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Core", RFC 6120, March 2011. Protocol (XMPP): Core", RFC 6120, March 2011.
skipping to change at page 18, line 46 skipping to change at page 18, line 32
The following substantive modifications were made from RFC 4013. The following substantive modifications were made from RFC 4013.
o A single SASLprep algorithm was replaced by two separate o A single SASLprep algorithm was replaced by two separate
algorithms: one for usernames and another for passwords. algorithms: one for usernames and another for passwords.
o The new preparation algorithms use PRECIS instead of a stringprep o The new preparation algorithms use PRECIS instead of a stringprep
profile. The new algorithms work independenctly of Unicode profile. The new algorithms work independenctly of Unicode
versions. versions.
o As recommended in the PRECIS framwork, changed the Unicode o As recommended in the PRECIS framework, changed the Unicode
normalization form from NFKC to NFC. normalization form from NFKC to NFC.
o Some Unicode code points that were mapped to nothing in RFC 4013 o Some Unicode code points that were mapped to nothing in RFC 4013
are simply disallowed by PRECIS. are simply disallowed by PRECIS.
Appendix B. Acknowledgements Appendix B. Acknowledgements
The following individuals provided helpful feedback on this document: The following individuals provided helpful feedback on this document:
Marc Blanchet, Alan DeKok, Joe Hildebrand, Jeffrey Hutzelman, Simon Marc Blanchet, Alan DeKok, Joe Hildebrand, Jeffrey Hutzelman, Simon
Josefsson, Jonathan Lennox, Matt Miller, Chris Newman, Yutaka OIWA, Josefsson, Jonathan Lennox, Matt Miller, Chris Newman, Yutaka OIWA,
Pete Resnick, Andrew Sullivan, and Nico Williams. Nico in particular Pete Resnick, Andrew Sullivan, and Nico Williams. Nico in particular
deserves special recognition for providing text that was used in deserves special recognition for providing text that was used in
Section 4.5. Thanks also to Yoshiro YONEYA and Takahiro NEMOTO for Section 3.5. Thanks also to Yoshiro YONEYA and Takahiro NEMOTO for
implementation feedback. implementation feedback.
This document borrows some text from [RFC4013] and [RFC6120]. This document borrows some text from [RFC4013] and [RFC6120].
Authors' Addresses Authors' Addresses
Peter Saint-Andre Peter Saint-Andre
&yet &yet
Email: peter@andyet.com Email: peter@andyet.com
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