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Network Working Group                                        K. ZeilengaRequest for Comments: 4013                           OpenLDAP FoundationCategory: Standards Track                                  February 2005SASLprep: Stringprep Profile for User Names and PasswordsStatus of This Memo   This document specifies an Internet standards track protocol for the   Internet community, and requests discussion and suggestions for   improvements.  Please refer to the current edition of the "Internet   Official Protocol Standards" (STD 1) for the standardization state   and status of this protocol.  Distribution of this memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (2005).Abstract   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], [CRAM-MD5], and   [DIGEST-MD5].  It may be applicable where simple user names andZeilenga                    Standards Track                     [Page 1]

RFC 4013                        SASLprep                   February 2005   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), or where   identity or password strings that are not character data, or require   different handling (e.g., case folding).   This document does not alter the technical specification of 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 for use in   preparing strings representing simple user names and passwords.   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   [CharModel].2.1.  Mapping   This profile specifies:      -  non-ASCII space characters [StringPrep, C.1.2] that can be         mapped to SPACE (U+0020), and      -  the "commonly mapped to nothing" characters [StringPrep, B.1]         that can be mapped to nothing.2.2.  Normalization   This profile specifies using Unicode normalization form KC, as   described in Section 4 of [StringPrep].Zeilenga                    Standards Track                     [Page 2]

RFC 4013                        SASLprep                   February 20052.3.  Prohibited Output   This profile specifies the following characters as prohibited input:      - 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 characters [StringPrep, C.3]      - Non-character code points [StringPrep, C.4]      - Surrogate code points [StringPrep, C.5]      - Inappropriate for plain text characters [StringPrep, C.6]      - Inappropriate for canonical representation characters        [StringPrep, C.7]      - Change display properties or deprecated characters        [StringPrep, C.8]      - Tagging characters [StringPrep, C.9]2.4.  Bidirectional Characters   This profile specifies checking bidirectional strings as described in   [StringPrep,Section 6].2.5.  Unassigned Code Points   This profile specifies the [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 the 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 check4.  Security Considerations   This profile is intended to prepare simple user name and password   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.Zeilenga                    Standards Track                     [Page 3]

RFC 4013                        SASLprep                   February 2005   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 for preparing identity strings that are not simple   user names (e.g., distinguished names, domain names), nor is the   profile intended for use of simple user names that require different   handling (such as case folding).  Protocols (or applications of those   protocols) that have application-specific 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 as if only ASCII was used.  Though SASLprep eliminates some   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 the [StringPrep]   protocol.  This profile has been registered in the stringprep profile   registry.      Name of this profile: SASLprep      RFC in which the profile is defined:RFC 4013      Indicator whether or not this is the newest version of the      profile: This is the first version of the SASPprep profile.6.  Acknowledgement   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   Blanchet.  This document is a product of the IETF SASL WG.Zeilenga                    Standards Track                     [Page 4]

RFC 4013                        SASLprep                   February 20057.  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" (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/).8.  Informative References   [Glossary]    The Unicode Consortium, "Unicode Glossary",                 <http://www.unicode.org/glossary/>.   [CharModel]   Whistler, K. and M. Davis, "Unicode Technical Report                 #17, Character Encoding Model", UTR17,                 <http://www.unicode.org/unicode/reports/tr17/>, August                 2000.   [SASL]        Melnikov, A., Ed., "Simple Authentication and Security                 Layer (SASL)", Work in Progress.   [CRAM-MD5]    Nerenberg, L.,"The CRAM-MD5 SASL Mechanism", Work in                 Progress.   [DIGEST-MD5]  Leach, P., Newman, C., and A. Melnikov, "Using Digest                 Authentication as a SASL Mechanism", Work in Progress.   [PLAIN]       Zeilenga, K., Ed.,"The Plain SASL Mechanism", Work in                 Progress.   [PR29]        "Public Review Issue #29: Normalization Issue",                 <http://www.unicode.org/review/pr-29.html>, February                 2004.Author's Address   Kurt D. Zeilenga   OpenLDAP Foundation   EMail: Kurt@OpenLDAP.orgZeilenga                    Standards Track                     [Page 5]

RFC 4013                        SASLprep                   February 2005Full Copyright Statement   Copyright (C) The Internet Society (2005).   This document is subject to the rights, licenses and restrictions   contained inBCP 78, and except as set forth therein, the authors   retain all their rights.   This document and the information contained herein are provided on an   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE   INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Intellectual Property   The IETF takes no position regarding the validity or scope of any   Intellectual Property Rights or other rights that might be claimed to   pertain to the implementation or use of the technology described in   this document or the extent to which any license under such rights   might or might not be available; nor does it represent that it has   made any independent effort to identify any such rights.  Information   on the IETF's procedures with respect to rights in IETF Documents can   be found inBCP 78 andBCP 79.   Copies of IPR disclosures made to the IETF Secretariat and any   assurances of licenses to be made available, or the result of an   attempt made to obtain a general license or permission for the use of   such proprietary rights by implementers or users of this   specification can be obtained from the IETF on-line IPR repository athttp://www.ietf.org/ipr.   The IETF invites any interested party to bring to its attention any   copyrights, patents or patent applications, or other proprietary   rights that may cover technology that may be required to implement   this standard.  Please address the information to the IETF at ietf-   ipr@ietf.org.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Zeilenga                    Standards Track                     [Page 6]