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. Information
311 on the IETF's procedures with respect to rights in IETF Documents can
312 be found in BCP 78 and BCP 79.
313
314 Copies of IPR disclosures made to the IETF Secretariat and any
315 assurances of licenses to be made available, or the result of an
316 attempt made to obtain a general license or permission for the use of
317 such proprietary rights by implementers or users of this
318 specification can be obtained from the IETF on-line IPR repository at
319 http://www.ietf.org/ipr.
320
321 The IETF invites any interested party to bring to its attention any
322 copyrights, patents or patent applications, or other proprietary
323 rights that may cover technology that may be required to implement
324 this standard. Please address the information to the IETF at ietf-
325 ipr@ietf.org.
326
327
328Acknowledgement
329
330 Funding for the RFC Editor function is currently provided by the
331 Internet Society.
332
333
334
335
336
337
338Zeilenga Standards Track [Page 6]
339
340