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Versions: 00 01 02 03 04 draft-ietf-precis-saslprepbis

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

   This Internet-Draft is submitted in full conformance with the
   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
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on September 6, 2012.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of



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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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