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Zeilenga 3 Intended Category: Standard Track OpenLDAP Foundation 4 Expires in six months 9 February 2005 6 LDAP: Internationalized String Preparation 7 9 Status of this Memo 11 This document is intended to be published as a Standard Track RFC. 12 Distribution of this memo is unlimited. Technical discussion of this 13 document will take place on the IETF LDAP Revision Working Group 14 mailing list . Please send editorial 15 comments directly to the editor . 17 By submitting this Internet-Draft, I accept the provisions of Section 18 4 of RFC 3667. By submitting this Internet-Draft, I certify that any 19 applicable patent or other IPR claims of which I am aware have been 20 disclosed, or will be disclosed, and any of which I become aware will 21 be disclosed, in accordance with RFC 3668. 23 Internet-Drafts are working documents of the Internet Engineering Task 24 Force (IETF), its areas, and its working groups. Note that other 25 groups may also distribute working documents as Internet-Drafts. 27 Internet-Drafts are draft documents valid for a maximum of six months 28 and may be updated, replaced, or obsoleted by other documents at any 29 time. It is inappropriate to use Internet-Drafts as reference material 30 or to cite them other than as "work in progress." 32 The list of current Internet-Drafts can be accessed at 33 http://www.ietf.org/1id-abstracts.html 35 The list of Internet-Draft Shadow Directories can be accessed at 36 http://www.ietf.org/shadow.html 38 Copyright (C) The Internet Society (2005). All Rights Reserved. 40 Please see the Full Copyright section near the end of this document 41 for more information. 43 Abstract 45 The previous Lightweight Directory Access Protocol (LDAP) technical 46 specifications did not precisely define how character string matching 47 is to be performed. This led to a number of usability and 48 interoperability problems. This document defines string preparation 49 algorithms for character-based matching rules defined for use in LDAP. 51 Conventions and Terms 53 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 54 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 55 document are to be interpreted as described in BCP 14 [RFC2119]. 57 Character names in this document use the notation for code points and 58 names from the Unicode Standard [Unicode]. For example, the letter 59 "a" may be represented as either or . 60 In the lists of mappings and the prohibited characters, the "U+" is 61 left off to make the lists easier to read. The comments for character 62 ranges are shown in square brackets (such as "[CONTROL CHARACTERS]") 63 and do not come from the standard. 65 Note: a glossary of terms used in Unicode can be found in [Glossary]. 66 Information on the Unicode character encoding model can be found in 67 [CharModel]. 69 The term "combining mark", as used in this specification, refers to 70 any Unicode [Unicode] code point which has a mark property (Mn, Mc, 71 Me). Appendix A provides a complete list of combining marks. 73 1. Introduction 75 1.1. Background 77 A Lightweight Directory Access Protocol (LDAP) [Roadmap] matching rule 78 [Syntaxes] defines an algorithm for determining whether a presented 79 value matches an attribute value in accordance with the criteria 80 defined for the rule. The proposition may be evaluated to True, 81 False, or Undefined. 83 True - the attribute contains a matching value, 85 False - the attribute contains no matching value, 87 Undefined - it cannot be determined whether the attribute contains 88 a matching value or not. 90 For instance, the caseIgnoreMatch matching rule may be used to compare 91 whether the commonName attribute contains a particular value without 92 regard for case and insignificant spaces. 94 1.2. X.500 String Matching Rules 96 "X.520: Selected attribute types" [X.520] provides (amongst other 97 things) value syntaxes and matching rules for comparing values 98 commonly used in the Directory. These specifications are inadequate 99 for strings composed of Unicode [Unicode] characters. 101 The caseIgnoreMatch matching rule [X.520], for example, is simply 102 defined as being a case insensitive comparison where insignificant 103 spaces are ignored. For printableString, there is only one space 104 character and case mapping is bijective, hence this definition is 105 sufficient. However, for Unicode string types such as 106 universalString, this is not sufficient. For example, a case 107 insensitive matching implementation which folded lower case characters 108 to upper case would yield different different results than an 109 implementation which used upper case to lower case folding. Or one 110 implementation may view space as referring to only SPACE (U+0020), a 111 second implementation may view any character with the space separator 112 (Zs) property as a space, and another implementation may view any 113 character with the whitespace (WS) category as a space. 115 The lack of precise specification for character string matching has 116 led to significant interoperability problems. When used in 117 certificate chain validation, security vulnerabilities can arise. To 118 address these problems, this document defines precise algorithms for 119 preparing character strings for matching. 121 1.3. Relationship to "stringprep" 123 The character string preparation algorithms described in this document 124 are based upon the "stringprep" approach [StringPrep]. In 125 "stringprep", presented and stored values are first prepared for 126 comparison and so that a character-by-character comparison yields the 127 "correct" result. 129 The approach used here is a refinement of the "stringprep" 130 [StringPrep] approach. Each algorithm involves two additional 131 preparation steps. 133 a) prior to applying the Unicode string preparation steps outlined in 134 "stringprep", the string is transcoded to Unicode; 136 b) after applying the Unicode string preparation steps outlined in 137 "stringprep", the string is modified to appropriately handle 138 characters insignificant to the matching rule. 140 Hence, preparation of character strings for X.500 matching involves 141 the following steps: 143 1) Transcode 144 2) Map 145 3) Normalize 146 4) Prohibit 147 5) Check Bidi (Bidirectional) 148 6) Insignificant Character Handling 150 These steps are described in Section 2. 152 1.4. Relationship to the LDAP Technical Specification 154 This document is a integral part of the LDAP technical specification 155 [Roadmap] which obsoletes the previously defined LDAP technical 156 specification [RFC3377] in its entirety. 158 This document details new LDAP internationalized character string 159 preparation algorithms used by [Syntaxes] and possible other technical 160 specifications defining LDAP syntaxes and/or matching rules. 162 1.5. Relationship to X.500 164 LDAP is defined [Roadmap] in X.500 terms as an X.500 access mechanism. 165 As such, there is a strong desire for alignment between LDAP and X.500 166 syntax and semantics. The character string preparation algorithms 167 described in this document are based upon "Internationalized String 168 Matching Rules for X.500" [XMATCH] proposal to ITU/ISO Joint Study 169 Group 2. 171 2. String Preparation 173 The following six-step process SHALL be applied to each presented and 174 attribute value in preparation for character string matching rule 175 evaluation. 177 1) Transcode 178 2) Map 179 3) Normalize 180 4) Prohibit 181 5) Check bidi 182 6) Insignificant Character Handling 184 Failure in any step causes the assertion to evaluate to Undefined. 186 The character repertoire of this process is Unicode 3.2 [Unicode]. 188 2.1. Transcode 190 Each non-Unicode string value is transcoded to Unicode. 192 PrintableString [X.680] value are transcoded directly to Unicode. 194 UniversalString, UTF8String, and bmpString [X.680] values need not be 195 transcoded as they are Unicode-based strings (in the case of 196 bmpString, a subset of Unicode). 198 TeletexString [X.680] values are transcoded to Unicode. As there is 199 no standard for mapping TelexString values to Unicode, the mapping is 200 left a local matter. 202 For these and other reasons, use of TeletexString is NOT RECOMMENDED. 204 The output is the transcoded string. 206 2.2. Map 208 SOFT HYPHEN (U+00AD) and MONGOLIAN TODO SOFT HYPHEN (U+1806) code 209 points are mapped to nothing. COMBINING GRAPHEME JOINER (U+034F) and 210 VARIATION SELECTORs (U+180B-180D, FF00-FE0F) code points are also 211 mapped to nothing. The OBJECT REPLACEMENT CHARACTER (U+FFFC) is 212 mapped to nothing. 214 CHARACTER TABULATION (U+0009), LINE FEED (LF) (U+000A), LINE 215 TABULATION (U+000B), FORM FEED (FF) (U+000C), CARRIAGE RETURN (CR) 216 (U+000D), and NEXT LINE (NEL) (U+0085) are mapped to SPACE (U+0020). 218 All other control code (e.g., Cc) points or code points with a control 219 function (e.g., Cf) are mapped to nothing. The following is a 220 complete list of these code points: U+0000-0008, 000E-001F, 007F-0084, 221 0086-009F, 06DD, 070F, 180E, 200C-200F, 202A-202E, 2060-2063, 222 206A-206F, FEFF, FFF9-FFFB, 1D173-1D17A, E0001, E0020-E007F. 224 ZERO WIDTH SPACE (U+200B) is mapped to nothing. All other code points 225 with Separator (space, line, or paragraph) property (e.g, Zs, Zl, or 226 Zp) are mapped to SPACE (U+0020). The following is a complete list of 227 these code points: U+0020, 00A0, 1680, 2000-200A, 2028-2029, 202F, 228 205F, 3000. 230 For case ignore, numeric, and stored prefix string matching rules, 231 characters are case folded per B.2 of [StringPrep]. 233 The output is the mapped string. 235 2.3. Normalize 237 The input string is be normalized to Unicode Form KC (compatibility 238 composed) as described in [UAX15]. The output is the normalized 239 string. 241 2.4. Prohibit 243 All Unassigned code points are prohibited. Unassigned code points are 244 listed in Table A.1 of [StringPrep]. 246 Characters which, per Section 5.8 of [Stringprep], change display 247 properties or are deprecated are prohibited. These characters are are 248 listed in Table C.8 of [StringPrep]. 250 Private Use code points are prohibited. These characters are listed 251 in Table C.3 of [StringPrep]. 253 All non-character code points are prohibited. These code points are 254 listed in Table C.4 of [StringPrep]. 256 Surrogate codes are prohibited. These characters are listed in Table 257 C.5 of [StringPrep]. 259 The REPLACEMENT CHARACTER (U+FFFD) code point is prohibited. 261 The step fails if the input string contains any prohibited code point. 262 Otherwise, the output is the input string. 264 2.5. Check bidi 266 Bidirectional characters are ignored. 268 2.6. Insignificant Character Handling 270 In this step, the string is modified to ensure proper handling of 271 characters insignificant to the matching rule. This modification 272 differs from matching rule to matching rule. 274 Section 2.6.1 applies to case ignore and exact string matching. 275 Section 2.6.2 applies to numericString matching. 276 Section 2.6.3 applies to telephoneNumber matching. 278 2.6.1. Insignificant Space Handling 280 For the purposes of this section, a space is defined to be the SPACE 281 (U+0020) code point followed by no combining marks. 283 NOTE - The previous steps ensure that the string cannot contain any 284 code points in the separator class, other than SPACE (U+0020). 286 If the input string contains at least one non-space character, then 287 the string is modified such that the string starts with exactly one 288 space character, ends with exactly one SPACE character, and that any 289 inner (non-empty) sequence of space characters is replaced with 290 exactly two SPACE characters. For instance, the input strings 291 "foobar", results in the output 292 "foobar". 294 Otherwise, if the string being prepared is an initial, any, or final 295 substring, then the output string is exactly one SPACE character, else 296 the output string is exactly two SPACEs. 298 Appendix B discusses the rationale for the behavior. 300 2.6.2. numericString Insignificant Character Handling 302 For the purposes of this section, a space is defined to be the SPACE 303 (U+0020) code point followed by no combining marks. 305 All spaces are regarded as insignificant and are to be removed. 307 For example, removal of spaces from the Form KC string: 308 "123456" 309 would result in the output string: 310 "123456" 311 and the Form KC string: 312 "" 313 would result in the output string: 314 "" (an empty string). 316 2.6.3. telephoneNumber Insignificant Character Handling 318 For the purposes of this section, a hyphen is defined to be 319 HYPHEN-MINUS (U+002D), ARMENIAN HYPHEN (U+058A), HYPHEN (U+2010), 320 NON-BREAKING HYPHEN (U+2011), MINUS SIGN (U+2212), SMALL HYPHEN-MINUS 321 (U+FE63), or FULLWIDTH HYPHEN-MINUS (U+FF0D) code point followed by no 322 combining marks and a space is defined to be the SPACE (U+0020) code 323 point followed by no combining marks. 325 All hyphens and spaces are considered insignificant and are to be 326 removed. 328 For example, removal of hyphens and spaces from the Form KC string: 329 "123456" 330 would result in the output string: 331 "123456" 332 and the Form KC string: 333 "" 334 would result in the (empty) output string: 335 "". 337 3. Security Considerations 339 "Preparation for International Strings ('stringprep')" [StringPrep] 340 security considerations generally apply to the algorithms described 341 here. 343 4. Acknowledgments 345 The approach used in this document is based upon design principles and 346 algorithms described in "Preparation of Internationalized Strings 347 ('stringprep')" [StringPrep] by Paul Hoffman and Marc Blanchet. Some 348 additional guidance was drawn from Unicode Technical Standards, 349 Technical Reports, and Notes. 351 This document is a product of the IETF LDAP Revision (LDAPBIS) Working 352 Group. 354 5. Author's Address 356 Kurt D. Zeilenga 357 OpenLDAP Foundation 359 Email: Kurt@OpenLDAP.org 361 6. References 363 [[Note to the RFC Editor: please replace the citation tags used in 364 referencing Internet-Drafts with tags of the form RFCnnnn where 365 possible.]] 367 6.1. Normative References 369 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 370 Requirement Levels", BCP 14 (also RFC 2119), March 1997. 372 [Roadmap] Zeilenga, K. (editor), "LDAP: Technical Specification 373 Road Map", draft-ietf-ldapbis-roadmap-xx.txt, a work in 374 progress. 376 [StringPrep] Hoffman P. and M. Blanchet, "Preparation of 377 Internationalized Strings ('stringprep')", 378 draft-hoffman-rfc3454bis-xx.txt, a work in progress. 380 [Syntaxes] Legg, S. (editor), "LDAP: Syntaxes and Matching Rules", 381 draft-ietf-ldapbis-syntaxes-xx.txt, a work in progress. 383 [Unicode] The Unicode Consortium, "The Unicode Standard, Version 384 3.2.0" is defined by "The Unicode Standard, Version 3.0" 385 (Reading, MA, Addison-Wesley, 2000. ISBN 0-201-61633-5), 386 as amended by the "Unicode Standard Annex #27: Unicode 387 3.1" (http://www.unicode.org/reports/tr27/) and by the 388 "Unicode Standard Annex #28: Unicode 3.2" 389 (http://www.unicode.org/reports/tr28/). 391 [UAX15] Davis, M. and M. Duerst, "Unicode Standard Annex #15: 392 Unicode Normalization Forms, Version 3.2.0". 393 , 394 March 2002. 396 [X.680] International Telecommunication Union - 397 Telecommunication Standardization Sector, "Abstract 398 Syntax Notation One (ASN.1) - Specification of Basic 399 Notation", X.680(1997) (also ISO/IEC 8824-1:1998). 401 6.2. Informative References 403 [X.500] International Telecommunication Union - 404 Telecommunication Standardization Sector, "The Directory 405 -- Overview of concepts, models and services," 406 X.500(1993) (also ISO/IEC 9594-1:1994). 408 [X.501] International Telecommunication Union - 409 Telecommunication Standardization Sector, "The Directory 410 -- Models," X.501(1993) (also ISO/IEC 9594-2:1994). 412 [X.520] International Telecommunication Union - 413 Telecommunication Standardization Sector, "The 414 Directory: Selected Attribute Types", X.520(1993) (also 415 ISO/IEC 9594-6:1994). 417 [Glossary] The Unicode Consortium, "Unicode Glossary", 418 . 420 [CharModel] Whistler, K. and M. Davis, "Unicode Technical Report 421 #17, Character Encoding Model", UTR17, 422 , August 423 2000. 425 [XMATCH] Zeilenga, K., "Internationalized String Matching Rules 426 for X.500", draft-zeilenga-ldapbis-strmatch-xx.txt, a 427 work in progress. 429 [RFC1345] Simonsen, K., "Character Mnemonics & Character Sets", 430 RFC 1345, June 1992. 432 Appendix A. Combining Marks 434 This appendix is normative. 436 0300-034F 0360-036F 0483-0486 0488-0489 0591-05A1 05A3-05B9 05BB-05BC 437 05BF 05C1-05C2 05C4 064B-0655 0670 06D6-06DC 06DE-06E4 06E7-06E8 438 06EA-06ED 0711 0730-074A 07A6-07B0 0901-0903 093C 093E-094F 0951-0954 439 0962-0963 0981-0983 09BC 09BE-09C4 09C7-09C8 09CB-09CD 09D7 09E2-09E3 440 0A02 0A3C 0A3E-0A42 0A47-0A48 0A4B-0A4D 0A70-0A71 0A81-0A83 0ABC 441 0ABE-0AC5 0AC7-0AC9 0ACB-0ACD 0B01-0B03 0B3C 0B3E-0B43 0B47-0B48 442 0B4B-0B4D 0B56-0B57 0B82 0BBE-0BC2 0BC6-0BC8 0BCA-0BCD 0BD7 0C01-0C03 443 0C3E-0C44 0C46-0C48 0C4A-0C4D 0C55-0C56 0C82-0C83 0CBE-0CC4 0CC6-0CC8 444 0CCA-0CCD 0CD5-0CD6 0D02-0D03 0D3E-0D43 0D46-0D48 0D4A-0D4D 0D57 445 0D82-0D83 0DCA 0DCF-0DD4 0DD6 0DD8-0DDF 0DF2-0DF3 0E31 0E34-0E3A 446 0E47-0E4E 0EB1 0EB4-0EB9 0EBB-0EBC 0EC8-0ECD 0F18-0F19 0F35 0F37 0F39 447 0F3E-0F3F 0F71-0F84 0F86-0F87 0F90-0F97 0F99-0FBC 0FC6 102C-1032 448 1036-1039 1056-1059 1712-1714 1732-1734 1752-1753 1772-1773 17B4-17D3 449 180B-180D 18A9 20D0-20EA 302A-302F 3099-309A FB1E FE00-FE0F FE20-FE23 450 1D165-1D169 1D16D-1D172 1D17B-1D182 1D185-1D18B 1D1AA-1D1AD 452 Appendix B. Substrings Matching 453 In absence of substrings matching, the insignificant space handling 454 for case ignore/exact matching could be simplified. Specifically, 455 the handling could be as require all sequences of one or more spaces 456 be replaced with one space and, if string contains non-space 457 characters, removal of all all leading spaces and trailing spaces. 459 In the presence of substrings matching, this simplified space handling 460 this simplified space handling would lead to unexpected and 461 undesirable matching behavior. For instance: 462 1) (CN=foo\20*\20bar) would match the CN value "foobar" but not 463 "foobar" nor "foobar"; 464 2) (CN=*\20foobar\20*) would match "foobar", but (CN=*\20*foobar*\20*) 465 would not; 466 3) (CN=foo\20*\20bar) would match "fooXbar" but not 467 "foobar". 469 The first case illustrates that this simplified space handling would 470 cause leading and trailing spaces in substrings of the string to be 471 regarded as insignificant. However, only leading and trailing (as 472 well as multiple consecutive spaces) of the string (as a whole) are 473 insignificant. 475 The second case illustrates that this simplified space handling would 476 cause sub-partitioning failures. That is, if a prepared any substring 477 matches a partition of the attribute value, then an assertion 478 constructed by subdividing that substring into multiple substrings 479 should also match. 481 The third case illustrates that this simplified space handling causes 482 another partitioning failure. Though both the initial or final 483 strings match different portions of "fooXbar" with 484 neither matching the X portion, they don't match a string consisting 485 of the two matched portions less the unmatched X portion. 487 In designing an appropriate approach for space handling for substrings 488 matching, one must study key aspects of X.500 case exact/ignore 489 matching. X.520 [X.520] says: 490 The [substrings] rule returns TRUE if there is a partitioning of 491 the attribute value (into portions) such that: 492 - the specified substrings (initial, any, final) match different 493 portions of the value in the order of the strings sequence; 494 - initial, if present, matches the first portion of the value; 495 - final, if present, matches the last portion of the value; 496 - any, if present, matches some arbitrary portion of the value. 498 That is, the substrings assertion (CN=foo\20*\20bar) matches the 499 attribute value "foobar" as the value can be partitioned 500 into the portions "foo" and "bar" meeting the above 501 requirements. 503 X.520 also says: 504 [T]he following spaces are regarded as not significant: 505 - leading spaces (i.e. those preceding the first character that is 506 not a space); 507 - trailing spaces (i.e. those following the last character that is 508 not a space); 509 - multiple consecutive spaces (these are taken as equivalent to a 510 single space character). 512 This statement applies to the assertion values and attribute values 513 as whole strings, and not individually to substrings of an assertion 514 value. In particular, the statements should be taken to mean that 515 if an assertion value and attribute value match without any 516 consideration to insignificant characters, then that assertion value 517 should also match any attribute value which differs only by inclusion 518 or removal of insignificant characters. 520 Hence, the assertion (CN=foo\20*\20bar) matches 521 "foobar" and "foobar" as these values 522 only differ from "foobar" by the inclusion or removal 523 of insignificant spaces. 525 Astute readers of this text will also note that there are special 526 cases where the specified space handling does not ignore spaces 527 which could be considered insignificant. For instance, the assertion 528 (CN=\20*\20*\20) does not match "" 529 (insignificant spaces present in value) nor " " (insignificant 530 spaces not present in value). However, as these cases have no 531 practical application that cannot be met by simple assertions, e.g. 532 (cn=\20), and this minor anomaly can only be fully addressed by a 533 preparation algorithm to be used in conjunction with 534 character-by-character partitioning and matching, the anomaly is 535 considered acceptable. 537 Intellectual Property Rights 539 The IETF takes no position regarding the validity or scope of any 540 Intellectual Property Rights or other rights that might be claimed 541 to pertain to the implementation or use of the technology described 542 in this document or the extent to which any license under such 543 rights might or might not be available; nor does it represent that 544 it has made any independent effort to identify any such rights. 545 Information on the procedures with respect to rights in RFC documents 546 can be found in BCP 78 and BCP 79. 548 Copies of IPR disclosures made to the IETF Secretariat and any 549 assurances of licenses to be made available, or the result of an 550 attempt made to obtain a general license or permission for the use 551 of such proprietary rights by implementers or users of this 552 specification can be obtained from the IETF on-line IPR repository 553 at http://www.ietf.org/ipr. 555 The IETF invites any interested party to bring to its attention any 556 copyrights, patents or patent applications, or other proprietary 557 rights that may cover technology that may be required to implement 558 this standard. Please address the information to the IETF at 559 ietf-ipr@ietf.org. 561 Full Copyright 563 Copyright (C) The Internet Society (2005). This document is subject 564 to the rights, licenses and restrictions contained in BCP 78, and 565 except as set forth therein, the authors retain all their rights. 567 This document and the information contained herein are provided on an 568 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE 569 REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE 570 INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR 571 IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 572 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 573 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.