INTERNET-DRAFT                                   Kurt D. Zeilenga
Intended Category: Standards Track            OpenLDAP Foundation
Expires: January 2005                                18 July 2004

        SASLprep: Stringprep profile for user names and passwords

Status of Memo

  This document is intended to be, after appropriate review and
  revision, submitted to the RFC Editor as a Standards Track document.
  Distribution of this memo is unlimited.  Technical discussion of this
  document will take place on the IETF SASL mailing list
  <>.  Please send editorial comments directly to the
  document editor <>.

  By submitting this Internet-Draft, I accept the provisions of Section
  4 of RFC 3667.  By submitting this Internet-Draft, I certify that any
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  Copyright (C) The Internet Society (2004).  All Rights Reserved.

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  for more information.

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  This document describes how to prepare Unicode strings representing
  user names and passwords for comparison.  The document defines the
  "SASLprep" profile of the "stringprep" algorithm to be used for both
  user names and passwords.  This profile is intended to be used by
  Simple Authentication and Security Layer (SASL) mechanisms (such as
  PLAIN, CRAM-MD5, and DIGEST-MD5) as well as other protocols exchanging
  simple user names and/or passwords.

1. Introduction

  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 work in
  ways that make sense for typical users throughout the world, this
  document defines rules for preparing internationalized user names and
  passwords for comparison.  For simplicity and implementation ease, a
  single algorithm is defined for both user names and passwords.

  The algorithm assumes all strings are comprised of characters from the
  Unicode [Unicode] character set.

  This document defines the "SASLprep" profile of the "stringprep"
  algorithm [StringPrep].

  The profile is designed for use in Simple Authentication and Security
  Layer ([SASL]) mechanisms such as [PLAIN].  It may be applicable
  elsewhere simple user names and passwords are used.  This profile is
  not intended to be used to prepare identity strings which are not
  simple user names (e.g., email addresses, domain names, distinguished
  names), or where identity or password strings which are not character
  data, or require different handling (e.g., case folding).

  This document by itself does not alter the technical specification any
  existing protocols.  Any specification that wishes to use the
  algorithm described in this document needs to explicitly incorporate
  this document and provide precise details as to where and how this
  algorithm is used by implementations of that specification.

2. The SASLprep profile

  This section defines the "SASLprep" profile of the "stringprep"
  algorithm [StringPrep].  This profile is intended to be used to
  prepare strings representing simple user names and passwords.

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  This profile uses Unicode 3.2 [Unicode].

  Character names in this document use the notation for code points and
  names from the Unicode Standard [Unicode].  For example, the letter
  "a" may be represented as either <U+0061> or <LATIN SMALL LETTER A>.
  In the lists of mappings and the prohibited characters, the "U+" is
  left off to make the lists easier to read.  The comments for character
  ranges are shown in square brackets (such as "[CONTROL CHARACTERS]")
  and do not come from the standard.

  Note: a glossary of terms used in Unicode can be found in [Glossary].
  Information on the Unicode character encoding model can be found in

2.1. Mapping

  This profile specifies:
    - non-ASCII space characters [StringPrep, C.1.2] be mapped to SPACE
      (U+0020), and

    - the "commonly mapped to nothing" characters [StringPrep, B.1] be
      mapped to nothing.

2.2. Normalization

  This profile specifies using Unicode normalization form KC, as
  described in Section 4 of [StringPrep].

2.3. Prohibited Output

  This profile specifies the following characters:

    - Non-ASCII space characters [StringPrep, C.1.2],
    - ASCII control characters [StringPrep, C.2.1],
    - Non-ASCII control characters [StringPrep, C.2.2],
    - Private Use [StringPrep, C.3],
    - Non-character code points [StringPrep, C.4],
    - Surrogate code points [StringPrep, C.5],
    - Inappropriate for plain text [StringPrep, C.6],
    - Inappropriate for canonical representation [StringPrep, C.7],
    - Change display properties or are deprecated [StringPrep, C.8], and
    - Tagging characters [StringPrep, C.9].

  are prohibited output.

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2.4. Bidirectional characters

  This profile specifies checking bidirectional strings as described in
  [StringPrep, Section 6].

2.5. Unassigned Code Points

  This profile specifies [StringPrep, A.1] table as its list of
  unassigned code points.

3. Examples

  The following table provides examples of how various character data is
  transformed by SASLprep string preparation algorithm

  #  Input            Output     Comments
  -  -----            ------     --------
  1  I<U+00AD>X       IX         SOFT HYPHEN mapped to nothing
  2  user             user       no transformation
  3  USER             USER       case preserved, will not match #2
  4  <U+00AA>         a          output is NFKC, input in ISO 8859-1
  5  <U+2168>         IX         output is NFKC, will match #1
  6  <U+0007>                    Error - prohibited character
  7  <U+0627><U+0031>            Error - bidirectional check

4. Security Considerations

  This profile is intended to be used to prepare simple user names and
  passwords strings for comparison or use in cryptographic functions
  (e.g., message digests).  The preparation algorithm was specifically
  designed such that its output is canonical, and it is well-formed.
  However, due to an anomaly [PR29] in the specification of Unicode
  normalization, canonical equivalence is not guaranteed for a select
  few character sequences.  These sequences, however, do not appear in
  well-formed text.  This specification was published despite this known
  technical problem.  It is expected that this specification will be
  revised before further progression on the Standards Track (after
  [Unicode] and/or [StringPrep] specifications have been updated to
  address this problem).

  It is not intended to be used for to prepare identity strings which
  are not simple user names (e.g., distinguished names, domain names),
  nor is the profile intended to be used for simple user names which
  require different handling (such as case folding).  Protocols (or
  applications of those protocols) which have application-specific

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  identity forms and/or comparison algorithms should use mechanisms
  specifically designed for these forms and algorithms.

  Application of string preparation may have an impact upon the
  feasibility of brute force and dictionary attacks.  While the number
  of possible prepared strings is less than the number of possible
  Unicode strings, the number of usable names and passwords is greater
  than if only ASCII was used.  Though SASLprep eliminates some of
  Unicode code point sequences as possible prepared strings, that
  elimination generally makes the (canonical) output forms practicable
  and prohibits nonsensical inputs.

  User names and passwords should be protected from eavesdropping.

  General "stringprep" and Unicode security considerations apply.  Both
  are discussed in [StringPrep].

5. IANA Considerations

  This document details the "SASLprep" profile of [StringPrep] protocol.
  Upon Standards Action the profile should be registered in the
  stringprep profile registry.

      Name of this profile: SASLprep
      RFC in which the profile is defined: This RFC
      Indicator whether or not this is the newest version of the
      profile: This is the first version of the SASPprep profile.

6. Acknowledgment

  This document borrows text from "Preparation of Internationalized
  Strings ('stringprep')" and "Nameprep: A Stringprep Profile for
  Internationalized Domain Names", both by Paul Hoffman and Marc

  This document is a product of the IETF SASL WG.

7. Normative References

  [StringPrep]  Hoffman, P. and M. Blanchet, "Preparation of
                Internationalized Strings ('stringprep')", RFC 3454,
                December 2002.

  [Unicode]     The Unicode Consortium, "The Unicode Standard, Version
                3.2.0" is defined by "The Unicode Standard, Version 3.0"

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INTERNET-DRAFT       draft-ietf-sasl-saslprep-10.txt        18 July 2004

                (Reading, MA, Addison-Wesley, 2000. ISBN 0-201-61633-5),
                as amended by the "Unicode Standard Annex #27: Unicode
                3.1" ( and by the
                "Unicode Standard Annex #28: Unicode 3.2"

8. Informative References

  [Glossary]    The Unicode Consortium, "Unicode Glossary",

  [CharModel]   Whistler, K. and M. Davis, "Unicode Technical Report
                #17, Character Encoding Model", UTR17,
                <>, August

  [SASL]        Melnikov, A. (Editor), "Simple Authentication and
                Security Layer (SASL)",
                draft-ietf-sasl-rfc2222bis-xx.txt, a work in progress.

  [CRAM-MD5]    Nerenberg, L., "The CRAM-MD5 SASL Mechanism",
                draft-ietf-sasl-crammd5-xx.txt, a work in progress.

  [DIGEST-MD5]  Leach, P., C. Newman, and A. Melnikov, "Using Digest
                Authentication as a SASL Mechanism",
                draft-ietf-sasl-rfc2831bis-xx.txt, a work in progress.

  [PLAIN]       Zeilenga, K. (Editor), "The Plain SASL Mechanism",
                draft-ietf-sasl-plain-xx.txt, a work in progress.

  [PR29]        "Public Review Issue #29: Normalization Issue",
                <>, February

9. Author's Address

  Kurt D. Zeilenga
  OpenLDAP Foundation


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Full Copyright

  Copyright (C) The Internet Society (2004).  This document is subject
  to the rights, licenses and restrictions contained in BCP 78, and
  except as set forth therein, the authors retain all their rights.

  This document and the information contained herein are provided on an

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