INTERNET-DRAFT Kurt D. Zeilenga Intended Category: Standards Track OpenLDAP Foundation Expires:
SeptemberOctober 2004 1228 April 2004 SASLprep: Stringprep profile for user names and passwords <draft-ietf-sasl-saslprep-08.txt><draft-ietf-sasl-saslprep-09.txt> Status of Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC 2026. 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 <firstname.lastname@example.org>. Please send editorial comments directly to the document editor <Kurt@OpenLDAP.org>. By submitting this Internet-Draft, I certify that any applicable patent or other IPR claims of which I am aware have been disclosed, and any of which I become aware will be disclosed, in accordance with RFC 3668. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as ``work"work in progress.''progress." The list of current Internet-Drafts can be accessed at <http://www.ietf.org/ietf/1id-abstracts.txt>.http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-DraftInternet- Draft Shadow Directories can be accessed at <http://www.ietf.org/shadow.html>.http://www.ietf.org/shadow.html. Copyright (C) The Internet Society (2004). All Rights Reserved. Please see the Full Copyright section near the end of this document for more information. 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 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., e-mail addresses, domain names, distinguished names), or where identity or password strings which are not character data.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. 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] 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. 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 #3 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 used to prepare simple user names and passwords strings for comparison or use in cryptographic functions (e.g., message digests). The preparation algorithm is specifically designed such that its output is canonical. It is not intended to be used for to prepare identity strings which are not simple user names (e.g., distinguished names and domain names). Nor is the profile intended to be used for simple user names which require different handling.handling (such as case folding). Protocols (or applications of those protocols) which 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 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]. 4.5. 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. 5.6. 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 Blanchet. This document is a product of the IETF SASL WG. 6.7. 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" (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/). 7.8. 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. (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. 8. Editor's9. Author's Address Kurt D. Zeilenga OpenLDAP Foundation Email: Kurt@OpenLDAP.org Intellectual Property Rights 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 procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. 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