1 2 3 4 5 6 7Network Working Group K. Zeilenga 8Request for Comments: 4013 OpenLDAP Foundation 9Category: Standards Track February 2005 10 11 12 SASLprep: Stringprep Profile for User Names and Passwords 13 14Status of This Memo 15 16 This document specifies an Internet standards track protocol for the 17 Internet community, and requests discussion and suggestions for 18 improvements. Please refer to the current edition of the "Internet 19 Official Protocol Standards" (STD 1) for the standardization state 20 and status of this protocol. Distribution of this memo is unlimited. 21 22Copyright Notice 23 24 Copyright (C) The Internet Society (2005). 25 26Abstract 27 28 This document describes how to prepare Unicode strings representing 29 user names and passwords for comparison. The document defines the 30 "SASLprep" profile of the "stringprep" algorithm to be used for both 31 user names and passwords. This profile is intended to be used by 32 Simple Authentication and Security Layer (SASL) mechanisms (such as 33 PLAIN, CRAM-MD5, and DIGEST-MD5), as well as other protocols 34 exchanging simple user names and/or passwords. 35 361. Introduction 37 38 The use of simple user names and passwords in authentication and 39 authorization is pervasive on the Internet. To increase the 40 likelihood that user name and password input and comparison work in 41 ways that make sense for typical users throughout the world, this 42 document defines rules for preparing internationalized user names and 43 passwords for comparison. For simplicity and implementation ease, a 44 single algorithm is defined for both user names and passwords. 45 46 The algorithm assumes all strings are comprised of characters from 47 the Unicode [Unicode] character set. 48 49 This document defines the "SASLprep" profile of the "stringprep" 50 algorithm [StringPrep]. 51 52 The profile is designed for use in Simple Authentication and Security 53 Layer ([SASL]) mechanisms, such as [PLAIN], [CRAM-MD5], and 54 [DIGEST-MD5]. It may be applicable where simple user names and 55 56 57 58Zeilenga Standards Track [Page 1] 59 60RFC 4013 SASLprep February 2005 61 62 63 passwords are used. This profile is not intended for use in 64 preparing identity strings that are not simple user names (e.g., 65 email addresses, domain names, distinguished names), or where 66 identity or password strings that are not character data, or require 67 different handling (e.g., case folding). 68 69 This document does not alter the technical specification of any 70 existing protocols. Any specification that wishes to use the 71 algorithm described in this document needs to explicitly incorporate 72 this document and provide precise details as to where and how this 73 algorithm is used by implementations of that specification. 74 752. The SASLprep Profile 76 77 This section defines the "SASLprep" profile of the "stringprep" 78 algorithm [StringPrep]. This profile is intended for use in 79 preparing strings representing simple user names and passwords. 80 81 This profile uses Unicode 3.2 [Unicode]. 82 83 Character names in this document use the notation for code points and 84 names from the Unicode Standard [Unicode]. For example, the letter 85 "a" may be represented as either <U+0061> or <LATIN SMALL LETTER A>. 86 In the lists of mappings and the prohibited characters, the "U+" is 87 left off to make the lists easier to read. The comments for 88 character ranges are shown in square brackets (such as "[CONTROL 89 CHARACTERS]") and do not come from the standard. 90 91 Note: A glossary of terms used in Unicode can be found in [Glossary]. 92 Information on the Unicode character encoding model can be found in 93 [CharModel]. 94 952.1. Mapping 96 97 This profile specifies: 98 99 - non-ASCII space characters [StringPrep, C.1.2] that can be 100 mapped to SPACE (U+0020), and 101 102 - the "commonly mapped to nothing" characters [StringPrep, B.1] 103 that can be mapped to nothing. 104 1052.2. Normalization 106 107 This profile specifies using Unicode normalization form KC, as 108 described in Section 4 of [StringPrep]. 109 110 111 112 113 114Zeilenga Standards Track [Page 2] 115 116RFC 4013 SASLprep February 2005 117 118 1192.3. Prohibited Output 120 121 This profile specifies the following characters as prohibited input: 122 123 - Non-ASCII space characters [StringPrep, C.1.2] 124 - ASCII control characters [StringPrep, C.2.1] 125 - Non-ASCII control characters [StringPrep, C.2.2] 126 - Private Use characters [StringPrep, C.3] 127 - Non-character code points [StringPrep, C.4] 128 - Surrogate code points [StringPrep, C.5] 129 - Inappropriate for plain text characters [StringPrep, C.6] 130 - Inappropriate for canonical representation characters 131 [StringPrep, C.7] 132 - Change display properties or deprecated characters 133 [StringPrep, C.8] 134 - Tagging characters [StringPrep, C.9] 135 1362.4. Bidirectional Characters 137 138 This profile specifies checking bidirectional strings as described in 139 [StringPrep, Section 6]. 140 1412.5. Unassigned Code Points 142 143 This profile specifies the [StringPrep, A.1] table as its list of 144 unassigned code points. 145 1463. Examples 147 148 The following table provides examples of how various character data 149 is transformed by the SASLprep string preparation algorithm 150 151 # Input Output Comments 152 - ----- ------ -------- 153 1 I<U+00AD>X IX SOFT HYPHEN mapped to nothing 154 2 user user no transformation 155 3 USER USER case preserved, will not match #2 156 4 <U+00AA> a output is NFKC, input in ISO 8859-1 157 5 <U+2168> IX output is NFKC, will match #1 158 6 <U+0007> Error - prohibited character 159 7 <U+0627><U+0031> Error - bidirectional check 160 1614. Security Considerations 162 163 This profile is intended to prepare simple user name and password 164 strings for comparison or use in cryptographic functions (e.g., 165 message digests). The preparation algorithm was specifically 166 designed such that its output is canonical, and it is well-formed. 167 168 169 170Zeilenga Standards Track [Page 3] 171 172RFC 4013 SASLprep February 2005 173 174 175 However, due to an anomaly [PR29] in the specification of Unicode 176 normalization, canonical equivalence is not guaranteed for a select 177 few character sequences. These sequences, however, do not appear in 178 well-formed text. This specification was published despite this 179 known technical problem. It is expected that this specification will 180 be revised before further progression on the Standards Track (after 181 [Unicode] and/or [StringPrep] specifications have been updated to 182 address this problem). 183 184 It is not intended for preparing identity strings that are not simple 185 user names (e.g., distinguished names, domain names), nor is the 186 profile intended for use of simple user names that require different 187 handling (such as case folding). Protocols (or applications of those 188 protocols) that have application-specific identity forms and/or 189 comparison algorithms should use mechanisms specifically designed for 190 these forms and algorithms. 191 192 Application of string preparation may have an impact upon the 193 feasibility of brute force and dictionary attacks. While the number 194 of possible prepared strings is less than the number of possible 195 Unicode strings, the number of usable names and passwords is greater 196 than as if only ASCII was used. Though SASLprep eliminates some 197 Unicode code point sequences as possible prepared strings, that 198 elimination generally makes the (canonical) output forms practicable 199 and prohibits nonsensical inputs. 200 201 User names and passwords should be protected from eavesdropping. 202 203 General "stringprep" and Unicode security considerations apply. Both 204 are discussed in [StringPrep]. 205 2065. IANA Considerations 207 208 This document details the "SASLprep" profile of the [StringPrep] 209 protocol. This profile has been registered in the stringprep profile 210 registry. 211 212 Name of this profile: SASLprep 213 RFC in which the profile is defined: RFC 4013 214 Indicator whether or not this is the newest version of the 215 profile: This is the first version of the SASPprep profile. 216 2176. Acknowledgement 218 219 This document borrows text from "Preparation of Internationalized 220 Strings ('stringprep')" and "Nameprep: A Stringprep Profile for 221 Internationalized Domain Names", both by Paul Hoffman and Marc 222 Blanchet. This document is a product of the IETF SASL WG. 223 224 225 226Zeilenga Standards Track [Page 4] 227 228RFC 4013 SASLprep February 2005 229 230 2317. Normative References 232 233 [StringPrep] Hoffman, P. and M. Blanchet, "Preparation of 234 Internationalized Strings ("stringprep")", RFC 3454, 235 December 2002. 236 237 [Unicode] The Unicode Consortium, "The Unicode Standard, Version 238 3.2.0" is defined by "The Unicode Standard, Version 239 3.0" (Reading, MA, Addison-Wesley, 2000. ISBN 0-201- 240 61633-5), as amended by the "Unicode Standard Annex 241 #27: Unicode 3.1" 242 (http://www.unicode.org/reports/tr27/) and by the 243 "Unicode Standard Annex #28: Unicode 3.2" 244 (http://www.unicode.org/reports/tr28/). 245 2468. Informative References 247 248 [Glossary] The Unicode Consortium, "Unicode Glossary", 249 <http://www.unicode.org/glossary/>. 250 251 [CharModel] Whistler, K. and M. Davis, "Unicode Technical Report 252 #17, Character Encoding Model", UTR17, 253 <http://www.unicode.org/unicode/reports/tr17/>, August 254 2000. 255 256 [SASL] Melnikov, A., Ed., "Simple Authentication and Security 257 Layer (SASL)", Work in Progress. 258 259 [CRAM-MD5] Nerenberg, L., "The CRAM-MD5 SASL Mechanism", Work in 260 Progress. 261 262 [DIGEST-MD5] Leach, P., Newman, C., and A. Melnikov, "Using Digest 263 Authentication as a SASL Mechanism", Work in Progress. 264 265 [PLAIN] Zeilenga, K., Ed., "The Plain SASL Mechanism", Work in 266 Progress. 267 268 [PR29] "Public Review Issue #29: Normalization Issue", 269 <http://www.unicode.org/review/pr-29.html>, February 270 2004. 271 272Author's Address 273 274 Kurt D. Zeilenga 275 OpenLDAP Foundation 276 277 EMail: Kurt@OpenLDAP.org 278 279 280 281 282Zeilenga Standards Track [Page 5] 283 284RFC 4013 SASLprep February 2005 285 286 287Full Copyright Statement 288 289 Copyright (C) The Internet Society (2005). 290 291 This document is subject to the rights, licenses and restrictions 292 contained in BCP 78, and except as set forth therein, the authors 293 retain all their rights. 294 295 This document and the information contained herein are provided on an 296 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 297 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET 298 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, 299 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE 300 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 301 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 302 303Intellectual Property 304 305 The IETF takes no position regarding the validity or scope of any 306 Intellectual Property Rights or other rights that might be claimed to 307 pertain to the implementation or use of the technology described in 308 this document or the extent to which any license under such rights 309 might or might not be available; nor does it represent that it has 310 made any independent effort to identify any such rights. 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