Precis P. Saint-Andre
Internet-Draft Cisco Systems, Inc.
Obsoletes: 4013 (if approved) A. Melnikov
Intended status: Standards Track Isode Ltd
Expires: September 6, 2012 March 5, 2012
Username and Password Preparation Algorithms
draft-melnikov-precis-saslprepbis-00
Abstract
This document describes how to prepare Unicode strings representing
user names and passwords, primarily for purposes of comparison. This
profile is intended to be used by Simple Authentication and Security
Layer (SASL) mechanisms (such as PLAIN and SCRAM-SHA-1), as well as
other protocols that exchange simple user names or passwords. This
document obsoletes RFC 4013.
Status of this Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on September 6, 2012.
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3
2. User Name Preparation . . . . . . . . . . . . . . . . . . . . . 4
3. Password Preparation . . . . . . . . . . . . . . . . . . . . . 5
4. ToDo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
5.1. Password Strength . . . . . . . . . . . . . . . . . . . . . 6
5.2. Reuse of PRECIS . . . . . . . . . . . . . . . . . . . . . . 6
5.3. Reuse of Unicode . . . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
6.1. Use of NameClass . . . . . . . . . . . . . . . . . . . . . 6
6.2. Use of FreeClass . . . . . . . . . . . . . . . . . . . . . 6
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
7.1. Normative References . . . . . . . . . . . . . . . . . . . 7
7.2. Informative References . . . . . . . . . . . . . . . . . . 7
Appendix A. Differences from RFC 4013 . . . . . . . . . . . . . . 8
Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
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1. Introduction
1.1. Overview
The use of simple user names and passwords in authentication and
authorization is pervasive on the Internet. To increase the
likelihood that user name and password input and comparison both work
in ways that make sense for typical users throughout the world, this
document defines rules for preparing internationalized user names and
passwords, primarily for purposes of comparison.
The algorithms defined in this document assume that all strings are
comprised of characters from the Unicode [UNICODE] character set.
The Unicode string preparation algorithms are designed for use in
Simple Authentication and Security Layer ([SASL]) mechanisms, such as
PLAIN [RFC4616] and SCRAM-SHA-1 [RFC5802]. They may be applicable
where simple user names and passwords are used. This profile is not
intended for use in preparing identity strings that are not simple
user names (e.g., email addresses, domain names, distinguished
names), nor in cases where identity or password strings are not
character data or require different handling (e.g., case folding).
The PRECIS approach differs fundamentally from the stringprep
approach taken in RFC 4013. The primary difference is that
stringprep profiles allow all characters except those which are
explicitly disallowed, whereas PRECIS profiles disallow all
characters except those which are explicitly allowed (this "inclusion
model" was originally used in [IDNA-PROTO], see [IDNA-RATIONALE] for
further discussion). One result is that rarely-used Unicode
characters or blocks (e.g., surrogate code points) do not need to be
listed individually, since they are disallowed by default. It is
important to keep this distinction in mind when comparing this
document to RFC 4013.
This document obsoletes RFC 4013.
1.2. Terminology
Many important terms used in this document are defined in
[FRAMEWORK], [I18N-TERMS], [IDNA-DEFS], and [UNICODE].
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in RFC
2119 [KEYWORDS].
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2. User Name Preparation
A user name MUST be processed as follows, where the operations
specified MUST be completed in the order shown (note that some steps
can be combined and performed at the same time):
1. (MAPPING 1) Non-ASCII space characters from the "N" category
defined under Section 6.14 of [FRAMEWORK] MUST be mapped to SPACE
(U+0020).
2. (MAPPING 2) Characters from the "M" category defined under
Section 6.13 MUST be mapped to nothing (this category includes
all of the "characters commonly mapped to nothing" from Appendix
B.1 of [STRINGPREP]), except U+1806 MONGOLIAN TODO SOFT HYPHEN).
3. (MAPPING 3) Uppercase and titlecase characters MUST be mapped to
their lowercase equivalents.
[[NOTE: This differs from SASLprep, which allowed uppercase and
titlecase characters.]]
4. (PRECIS) A user name MUST consist only of Unicode code points
that conform to the "NameClass" base string class defined in
[FRAMEWORK].
[[OPEN ISSUE: SASLprep allowed spaces in user names, should they
be allowed here?]]
5. All characters MUST be mapped using Unicode Normalization Form C
(NFC).
[[OPEN ISSUE: This differs from SASLprep, which used NFKC.]]
6. After performing all of the above steps a user name MUST NOT be
zero bytes in length.
With regard to directionality, the "Bidi Rule" provided in
[IDNA-BIDI] applies.
As noted in the Introduction, all code points and blocks not
explicitly allowed in the PRECIS NameClass are disallowed; this
includes private use characters, surrogate code points, and the other
code points and blocks defined as "Prohibited Output" in Section 2.3
of RFC 4013.
[[TODO: Double-check that all SASLprep prohibited output is indeed
disallowed by the PRECIS NameClass.]]
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3. Password Preparation
A password MUST be processed as follows, where the operations
specified MUST be completed in the order shown (note that some steps
can be combined and performed at the same time):
1. (MAPPING 1) non-ASCII space characters from the "N" category
defined under Section 6.14 of [FRAMEWORK] MUST be mapped to SPACE
(U+0020).
2. (MAPPING 2) Characters from the "M" category defined under
Section 6.13 MUST be mapped to nothing (this category includes
all of the "characters commonly mapped to nothing" from Appendix
B.1 of [STRINGPREP]), except U+1806 MONGOLIAN TODO SOFT HYPHEN).
3. [[OPEN ISSUE: Map HasCompat ("Q") category?]]
4. (PRECIS) A password MUST consist only of Unicode code points that
conform to the "FreeClass" base string class defined in
[FRAMEWORK].
5. All characters MUST be mapped using Unicode Normalization Form C
(NFC).
[[OPEN ISSUE: Use NFKC as in the original SASLprep?]]
6. After performing all of the above steps, a password MUST NOT be
zero bytes in length.
With regard to directionality, the "Bidi Rule" provided in
[IDNA-BIDI] applies.
As noted in the Introduction, all code points and blocks not
explicitly allowed in the PRECIS FreeClass are disallowed; this
includes private use characters, surrogate code points, and the other
code points and blocks defined as "Prohibited Output" in Section 2.3
of RFC 4013.
[[TODO: Double-check that all SASLprep prohibited output is indeed
disallowed by the PRECIS FreeClass.]]
4. ToDo
Compare output of the new algorithms on Unicode 3.2 data with
SASLprep and make sure that the PRECIS and KITTEN WGs are comfortable
with the changes in which Unicode characters are allowed/disallowed
(if any).
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5. Security Considerations
5.1. Password Strength
The ability to include a wide range of characters in passwords is
intended to increase the potential for creating a strong password
with high entropy. However, in practice, the ability to include such
characters needs to be weighed against the possible need to reproduce
those characters on a various devices using various input methods.
5.2. Reuse of PRECIS
The security considerations described in [FRAMEWORK] apply to the
"NameClass" and "FreeClass" base string classes used in this document
for user names and passwords, respectively.
5.3. Reuse of Unicode
The security considerations described in [UTR39] apply to the use of
Unicode characters in user names and passwords.
6. IANA Considerations
6.1. Use of NameClass
The IANA shall add an entry to the PRECIS Usage Registry for reuse of
the PRECIS NameClass in SASL, as follows:
Application Protocol: SASL/Kerberos.
Base Class: NameClass.
Subclassing: Yes. See Section 2 of RFC XXXX.
Directionality: The "Bidi Rule" defined in RFC 5893 applies.
Casemapping: Uppercase and titlecase code points are mapped to their
lowercase equivalents.
Normalization: NFC.
Specification: RFC XXXX.
6.2. Use of FreeClass
The IANA shall add an entry to the PRECIS Usage Registry for reuse of
the PRECIS FreeClass in SASL, as follows:
Application Protocol: SASL/Kerberos.
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Base Class: FreeClass
Subclassing: No.
Directionality: The "Bidi Rule" defined in RFC 5893 applies.
Casemapping: None.
Normalization: NFC.
Specification: RFC XXXX.
7. References
7.1. Normative References
[FRAMEWORK]
Blanchet, M. and P. Saint-Andre, "Precis Framework:
Handling Internationalized Strings in Protocols",
draft-ietf-precis-framework-01 (work in progress),
October 2011.
[KEYWORDS]
Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[UNICODE] The Unicode Consortium, "The Unicode Standard, Version
3.2.0", 2000.
The Unicode Standard, Version 3.2.0 is defined by The
Unicode Standard, Version 3.0 (Reading, MA, Addison-
Wesley, 2000. ISBN 0-201-61633-5), as amended by the
Unicode Standard Annex #27: Unicode 3.1
(http://www.unicode.org/reports/tr27/) and by the Unicode
Standard Annex #28: Unicode 3.2
(http://www.unicode.org/reports/tr28/).
7.2. Informative References
[RFC4616] Zeilenga, K., "The PLAIN Simple Authentication and
Security Layer (SASL) Mechanism", RFC 4616, August 2006.
[RFC5802] Newman, C., Menon-Sen, A., Melnikov, A., and N. Williams,
"Salted Challenge Response Authentication Mechanism
(SCRAM) SASL and GSS-API Mechanisms", RFC 5802, July 2010.
[IDNA-BIDI]
Alvestrand, H. and C. Karp, "Right-to-Left Scripts for
Internationalized Domain Names for Applications (IDNA)",
RFC 5893, August 2010.
[IDNA-DEFS]
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Klensin, J., "Internationalized Domain Names for
Applications (IDNA): Definitions and Document Framework",
RFC 5890, August 2010.
[IDNA-PROTO]
Klensin, J., "Internationalized Domain Names in
Applications (IDNA): Protocol", RFC 5891, August 2010.
[I18N-TERMS]
Hoffman, P. and J. Klensin, "Terminology Used in
Internationalization in the IETF",
draft-hoffman-rfc3536bis-02 (work in progress),
April 2011.
[IDNA-RATIONALE]
Klensin, J., "Internationalized Domain Names for
Applications (IDNA): Background, Explanation, and
Rationale", RFC 5894, August 2010.
[SASL] Melnikov, A., Ed. and K. Zeilenga, Ed., "Simple
Authentication and Security Layer (SASL)", RFC 4422,
June 2006.
[STRINGPREP]
Hoffman, P. and M. Blanchet, "Preparation of
Internationalized Strings ("stringprep")", RFC 3454,
December 2002.
[UTR39] The Unicode Consortium, "Unicode Technical Report #39:
Unicode Security Mechanisms", August 2010,
<http://unicode.org/reports/tr39/>.
Appendix A. Differences from RFC 4013
Based on consensus derived from implementation and deployment
experience as well as formal interoperability testing, the following
substantive modifications were made from RFC 4013.
o A single SASLprep algorithm was replaced by two separate
algorithms: one for user names and another for passwords.
o The new preparation algorithms use PRECIS instead of a Stringprep
profile. The algorithms are now Unicode version independent.
Appendix B. Acknowledgements
This document is partially based on text from RFC 4013.
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Authors' Addresses
Peter Saint-Andre
Cisco Systems, Inc.
1899 Wynkoop Street, Suite 600
Denver, CO 80202
USA
Phone: +1-303-308-3282
Email: psaintan@cisco.com
Alexey Melnikov
Isode Ltd
5 Castle Business Village
36 Station Road
Hampton, Middlesex TW12 2BX
UK
Email: Alexey.Melnikov@isode.com
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