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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: draft-ietf-precis-framework has been published as RFC 7564 -- Possible downref: Non-RFC (?) normative reference: ref. 'UNICODE' == Outdated reference: draft-ietf-precis-mappings has been published as RFC 7790 -- Obsolete informational reference (is this intentional?): RFC 3454 (Obsoleted by RFC 7564) -- Obsolete informational reference (is this intentional?): RFC 4013 (Obsoleted by RFC 7613) Summary: 0 errors (**), 0 flaws (~~), 3 warnings (==), 4 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 PRECIS P. Saint-Andre 3 Internet-Draft Cisco Systems, Inc. 4 Obsoletes: 4013 (if approved) A. Melnikov 5 Intended status: Standards Track Isode Ltd 6 Expires: January 13, 2014 July 12, 2013 8 Preparation and Comparison of Internationalized Strings Representing 9 Simple User Names and Passwords 10 draft-ietf-precis-saslprepbis-03 12 Abstract 14 This document describes how to handle Unicode strings representing 15 simple user names and passwords, primarily for purposes of 16 comparison. This profile is intended to be used by Simple 17 Authentication and Security Layer (SASL) mechanisms (such as PLAIN 18 and SCRAM-SHA-1), as well as other protocols that exchange simple 19 user names or passwords. This document obsoletes RFC 4013. 21 Status of this Memo 23 This Internet-Draft is submitted in full conformance with the 24 provisions of BCP 78 and BCP 79. 26 Internet-Drafts are working documents of the Internet Engineering 27 Task Force (IETF). Note that other groups may also distribute 28 working documents as Internet-Drafts. The list of current Internet- 29 Drafts is at http://datatracker.ietf.org/drafts/current/. 31 Internet-Drafts are draft documents valid for a maximum of six months 32 and may be updated, replaced, or obsoleted by other documents at any 33 time. It is inappropriate to use Internet-Drafts as reference 34 material or to cite them other than as "work in progress." 36 This Internet-Draft will expire on January 13, 2014. 38 Copyright Notice 40 Copyright (c) 2013 IETF Trust and the persons identified as the 41 document authors. All rights reserved. 43 This document is subject to BCP 78 and the IETF Trust's Legal 44 Provisions Relating to IETF Documents 45 (http://trustee.ietf.org/license-info) in effect on the date of 46 publication of this document. Please review these documents 47 carefully, as they describe your rights and restrictions with respect 48 to this document. Code Components extracted from this document must 49 include Simplified BSD License text as described in Section 4.e of 50 the Trust Legal Provisions and are provided without warranty as 51 described in the Simplified BSD License. 53 Table of Contents 55 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 56 1.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 3 57 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 58 2. Simple User Names . . . . . . . . . . . . . . . . . . . . . . 4 59 2.1. Definition . . . . . . . . . . . . . . . . . . . . . . . . 4 60 2.2. Preparation . . . . . . . . . . . . . . . . . . . . . . . 5 61 3. Passwords . . . . . . . . . . . . . . . . . . . . . . . . . . 6 62 3.1. Definition . . . . . . . . . . . . . . . . . . . . . . . . 6 63 3.2. Preparation . . . . . . . . . . . . . . . . . . . . . . . 7 64 4. Migration . . . . . . . . . . . . . . . . . . . . . . . . . . 7 65 4.1. User Names . . . . . . . . . . . . . . . . . . . . . . . . 7 66 4.2. Passwords . . . . . . . . . . . . . . . . . . . . . . . . 9 67 5. Security Considerations . . . . . . . . . . . . . . . . . . . 9 68 5.1. Password/Passphrase Strength . . . . . . . . . . . . . . . 10 69 5.2. Identifier Comparison . . . . . . . . . . . . . . . . . . 10 70 5.3. Reuse of PRECIS . . . . . . . . . . . . . . . . . . . . . 10 71 5.4. Reuse of Unicode . . . . . . . . . . . . . . . . . . . . . 10 72 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 73 6.1. Use of IdentifierClass . . . . . . . . . . . . . . . . . . 10 74 6.2. Use of FreeformClass . . . . . . . . . . . . . . . . . . . 11 75 7. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 11 76 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 77 8.1. Normative References . . . . . . . . . . . . . . . . . . . 11 78 8.2. Informative References . . . . . . . . . . . . . . . . . . 12 79 Appendix A. Differences from RFC 4013 . . . . . . . . . . . . . . 13 80 Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 13 81 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13 83 1. Introduction 85 1.1. Overview 87 User names and passwords are used pervasively in authentication and 88 authorization on the Internet. To increase the likelihood that the 89 input and comparison of user names and passwords will work in ways 90 that make sense for typical users throughout the world, this document 91 defines rules for preparing and comparing internationalized strings 92 that represent simple user names and passwords. (In many 93 authentication technologies passwords are not directly compared 94 because the actual password is used as input to an algorithm such as 95 a hash function; however, non-ASCII code points in the input string 96 still need to be handled correctly.) 98 The algorithms defined in this document assume that all strings are 99 comprised of characters from the Unicode character set [UNICODE]. 101 The algorithms are designed for use in Simple Authentication and 102 Security Layer (SASL) [RFC4422] mechanisms, such as PLAIN [RFC4616] 103 and SCRAM-SHA-1 [RFC5802]. However, they might be applicable 104 wherever simple user names or passwords are used. This profile is 105 not intended for use in preparing strings that are not simple user 106 names (e.g., email addresses, DNS domain names, LDAP distinguished 107 names), nor in cases where identifiers or secrets are not strings 108 (e.g., keys or certificates) or require specialized handling (e.g., 109 case folding). 111 This document builds upon the PRECIS framework defined in 112 [I-D.ietf-precis-framework], which differs fundamentally from the 113 stringprep technology [RFC3454] used in SASLprep [RFC4013]. The 114 primary difference is that stringprep profiles allowed all characters 115 except those which were explicitly disallowed, whereas PRECIS 116 profiles disallow all characters except those which are explicitly 117 allowed (this "inclusion model" was originally used for 118 internationalized domain names in [RFC5891]; see [RFC5894] for 119 further discussion). It is important to keep this distinction in 120 mind when comparing the technology defined in this document to 121 SASLprep [RFC4013]. 123 This document obsoletes RFC 4013. 125 1.2. Terminology 127 Many important terms used in this document are defined in 128 [I-D.ietf-precis-framework], [RFC4422], [RFC5890], [RFC6365], and 129 [UNICODE]. The term "non-ASCII space" refers to any Unicode code 130 point with a general category of "Zs", with the exception of U+0020 131 (here called "ASCII space"). 133 As used here, the term "password" is not literally limited to a word; 134 i.e., a password could be a passphrase consisting of more than one 135 word, perhaps separated by spaces or other such characters. 137 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 138 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 139 "OPTIONAL" in this document are to be interpreted as described in 140 [RFC2119]. 142 2. Simple User Names 144 2.1. Definition 146 Some SASL mechanisms (e.g., CRAM-MD5, DIGEST-MD5, and SCRAM) specify 147 that the authentication identity used in the context of such 148 mechanisms is a "simple user name" (see Section 2 of [RFC4422] as 149 well as [RFC4013]). However, the exact form of a simple user name in 150 any particular mechanism or deployment thereof is a local matter, and 151 a simple user name does not necessarily map to an application 152 identifier such as the localpart of an email address. 154 For purposes of preparation and comparison of authentication 155 identities, this document specifies that a simple user name is a 156 string of Unicode code points [UNICODE], encoded using UTF-8 157 [RFC3629], and structured either as an ordered sequence of 158 "simpleparts" (where the complete simple user name can consist of a 159 single simplepart or a space-separated sequence of simpleparts) or as 160 a simplepart@domainpart (where the domainpart is an IP literal, an 161 IPv4 address, or a fully-qualified domain name). 163 Therefore the syntax for a simple user name is defined as follows 164 using the Augmented Backus-Naur Form (ABNF) as specified in 165 [RFC5234]. 167 simpleusername = simplepart [1*(1*SP simplepart)] 168 / simplepart '@' domainpart 169 simplepart = 1*(idpoint) 170 ; 171 ; an "idpoint" is a UTF-8 encoded 172 ; Unicode code point that conforms to 173 ; the PRECIS "IdentifierClass" 174 ; 175 domainpart = IP-literal / IPv4address / ifqdn 176 ; 177 ; the "IPv4address" and "IP-literal" 178 ; rules are defined in RFC 3986, and 179 ; the first-match-wins (a.k.a. "greedy") 180 ; algorithm described in RFC 3986 181 ; applies to the matching process 182 ; 183 ; note well that reuse of the IP-literal 184 ; rule from RFC 3986 implies that IPv6 185 ; addresses are enclosed in square 186 ; brackets (i.e., beginning with '[' 187 ; and ending with ']') 188 ; 189 ifqdn = 1*1023(domainpoint) 190 ; 191 ; a "domainpoint" is a UTF-8 encoded 192 ; Unicode code point that conforms to 193 ; RFC 5890 194 ; 196 Note well that all code points and blocks not explicitly allowed in 197 the PRECIS IdentifierClass are disallowed; this includes private use 198 characters, surrogate code points, and the other code points and 199 blocks defined as "Prohibited Output" in Section 2.3 of RFC 4013. 201 Note also that common constructions such as "user@example.com" are 202 allowed as simple user names when using software that conforms to 203 this specification, as they were under [RFC4013]. 205 2.2. Preparation 207 A simple user name MUST NOT be zero bytes in length. This rule is to 208 be enforced after any normalization and mapping of code points. 210 Each simplepart of a simple user name MUST conform to the definition 211 of the PRECIS IdentifierClass provided in 212 [I-D.ietf-precis-framework], where the width mapping, additional 213 mapping, case mapping, normalization, and directionality rules are as 214 described below. 216 1. Fullwidth and halfwidth characters MUST be mapped to their 217 decomposition equivalents. 218 2. So-called additional mappings MAY be applied, such as those 219 defined in [I-D.ietf-precis-mappings]. 220 3. Uppercase and titlecase characters MAY be mapped to their 221 lowercase equivalents. 222 4. Unicode Normalization Form C (NFC) MUST be applied to all 223 characters. 225 With regard to directionality, the "Bidi Rule" provided in [RFC5893] 226 applies. 228 SASL mechanisms that directly re-use this profile MUST specify 229 whether case mapping is to be applied to authentication IDs, and 230 when. SASL mechanisms SHOULD delay any case mapping to the last 231 possible moment, such as when doing a lookup by username, username 232 comparisons, or generating a cryptographic salt from a username. 234 Application protocols that use SASL (such as IMAP [RFC4616] and XMPP 235 [RFC6120]) and that directly re-use this profile MUST specify whether 236 case mapping is to be applied to authorization IDs. Such "SASL 237 application protocols" SHOULD delay any case mapping of authorization 238 IDs to the last possible moment, which happens to necessarily be on 239 the server side. 241 In keeping with RFC4422, SASL application protocols are not to apply 242 this or any other profile to authentication IDs, and SASL mechanisms 243 are not to apply this or any other profile to authorization IDs. 245 3. Passwords 247 3.1. Definition 249 For purposes of preparation and comparison of passwords, this 250 document specifies that a password is a string of Unicode code points 251 [UNICODE], encoded using UTF-8 [RFC3629], and conformant to the 252 PRECIS FreeformClass. 254 Therefore the syntax for a password is defined as follows using the 255 Augmented Backus-Naur Form (ABNF) as specified in [RFC5234]. 257 password = 1*(freepoint) 258 ; 259 ; a "freepoint" is a UTF-8 encoded 260 ; Unicode code point that conforms to 261 ; the PRECIS "FreeformClass" 262 ; 264 Note well that all code points and blocks not explicitly allowed in 265 the PRECIS FreeformClass are disallowed; this includes private use 266 characters, surrogate code points, and the other code points and 267 blocks defined as "Prohibited Output" in Section 2.3 of RFC 4013. 269 3.2. Preparation 271 A password MUST NOT be zero bytes in length. This rule is to be 272 enforced after any normalization and mapping of code points. 274 A password MUST be treated as follows, where the operations specified 275 MUST be completed in the order shown: 277 1. Width mapping is not applied. 278 2. Map any instances of non-ASCII space to ASCII space (U+0020). 279 3. Case mapping is not applied. 280 4. Apply Unicode Normalization Form C (NFC) to all characters. 281 5. Ensure that the resulting string conforms to the definition of 282 the PRECIS FreeformClass. 284 With regard to directionality, the "Bidi Rule" (defined in [RFC5893]) 285 and similar rules are unnecessary and inapplicable to passwords, 286 since they can reduce the range of characters that are allowed in a 287 string and therefore reduce the amount of entropy that is possible in 288 a password. Furthermore, such rules are intended to minimize the 289 possibility that the same string will be displayed differently on a 290 system set for right-to-left display and a system set for left-to- 291 right display; however, passwords are typically not displayed at all 292 and are rarely meant to be interoperable across different systems in 293 the way that non-secret strings like domain names and user names are. 295 4. Migration 297 The rules defined in this specification differ slightly from those 298 defined by the SASLprep specification [RFC4013]. The following 299 sections describe these differences, along with their implications 300 for migration, in more detail. 302 4.1. User Names 304 Deployments that currently use SASLprep for handling user names might 305 need to scrub existing data when migrating to use of the rules 306 defined in this specification. In particular: 308 o SASLprep specified the use of Unicode Normalization Form KC 309 (NFKC), whereas this usage of the PRECIS IdentifierClass employs 310 Unicode Normalization Form C (NFC). In practice this change is 311 unlikely to cause significant problems, because NFKC provides 312 methods for mapping Unicode code points with compatibility 313 equivalents to those equivalents, whereas the PRECIS 314 IdentifierClass entirely disallows Unicode code points with 315 compatibility equivalents (i.e., during comparison NFKC is more 316 "aggressive" about finding matches than is NFC). A few examples 317 might suffice to indicate the nature of the problem: (1) U+017F 318 LATIN SMALL LETTER LONG S is compatibility equivalent to U+0073 319 LATIN SMALL LETTER S (2) U+2163 ROMAN NUMERAL FOUR is 320 compatibility equivalent to U+0049 LATIN CAPITAL LETTER I and 321 U+0056 LATIN CAPITAL LETTER V (3) U+FB01 LATIN SMALL LIGATURE FI 322 is compatibility equivalent to U+0066 LATIN SMALL LETTER F and 323 U+0069 LATIN SMALL LETTER I. Under SASLprep, the use of NFKC also 324 handled the mapping of fullwidth and halfwidth code points to 325 their decomposition equivalents (see [I-D.ietf-precis-mappings]). 326 Although it is expected that code points with compatibility 327 equivalents are rare in existing user names, for migration 328 purposes deployments might want to search their database of user 329 names for Unicode code points with compatibility equivalents and 330 map those code points to their compatibility equivalents. 332 o SASLprep mapped non-ASCII spaces to ASCII space (U+0020), whereas 333 the PRECIS IdentifierClass entirely disallows non-ASCII spaces. 334 The non-ASCII space characters are U+00A0 NO-BREAK SPACE, U+1680 335 OGHAM SPACE MARK, U+180E MONGOLIAN VOWEL SEPARATOR, U+2000 EN QUAD 336 through U+200A HAIR SPACE, U+202F NARROW NO-BREAK SPACE, U+205F 337 MEDIUM MATHEMATICAL SPACE, and U+3000 IDEOGRAPHIC SPACE. For 338 migration purposes, deployments might want to convert non-ASCII 339 space characters to ASCII space in simple user names. 341 o SASLprep mapped the "characters commonly mapped to nothing" from 342 Appendix B.1 of [RFC3454]) to nothing, whereas the PRECIS 343 IdentifierClass entirely disallows most of these characters, which 344 correspond to the code points from the "M" category defined under 345 Section 6.13 of [I-D.ietf-precis-framework] (with the exception of 346 U+1806 MONGOLIAN TODO SOFT HYPHEN, which was "commonly mapped to 347 nothing" in Unicode 3.2 but at the time of this writing does not 348 have a derived property of Default_Ignorable_Code_Point in Unicode 349 6.1). For migration purposes, deployments might want to remove 350 code points contained in the PRECIS "M" category from simple user 351 names. 353 o SASLprep allowed uppercase and titlecase characters, whereas this 354 usage of the PRECIS IdentifierClass maps uppercase and titlecase 355 characters to their lowercase equivalents. For migration 356 purposes, deployments can either convert uppercase and titlecase 357 characters to their lowercase equivalents in simple user names 358 (thus losing the case information) or preserve uppercase and 359 titlecase characters and ignore the case difference when comparing 360 simple user names. 362 4.2. Passwords 364 Depending on local service policy, migration from RFC 4013 to this 365 specification might not involve any scrubbing of data (since 366 passwords might not be stored in the clear anyway); however, service 367 providers need to be aware of possible issues that might arise during 368 migration. In particular: 370 o SASLprep specified the use of Unicode Normalization Form KC 371 (NFKC), whereas this usage of the PRECIS FreeformClass employs 372 Unicode Normalization Form C (NFC). Because NFKC is more 373 aggressive about finding matches than NFC, in practice this change 374 is unlikely to cause significant problems and indeed has the 375 security benefit of probably resulting in fewer false positives 376 when comparing passwords. A few examples might suffice to 377 indicate the nature of the problem: (1) U+017F LATIN SMALL LETTER 378 LONG S is compatibility equivalent to U+0073 LATIN SMALL LETTER S 379 (2) U+2163 ROMAN NUMERAL FOUR is compatibility equivalent to 380 U+0049 LATIN CAPITAL LETTER I and U+0056 LATIN CAPITAL LETTER V 381 (3) U+FB01 LATIN SMALL LIGATURE FI is compatibility equivalent to 382 U+0066 LATIN SMALL LETTER F and U+0069 LATIN SMALL LETTER I. Under 383 SASLprep, the use of NFKC also handled the mapping of fullwidth 384 and halfwidth code points to their decomposition equivalents (see 385 [I-D.ietf-precis-mappings]). Although it is expected that code 386 points with compatibility equivalents are rare in existing 387 passwords, some passwords that matched when SASLprep was used 388 might no longer work when the rules in this specification are 389 applied. 391 o SASLprep mapped the "characters commonly mapped to nothing" from 392 Appendix B.1 of [RFC3454]) to nothing, whereas the PRECIS 393 FreeformClass entirely disallows such characters, which correspond 394 to the code points from the "M" category defined under Section 395 6.13 of [I-D.ietf-precis-framework] (with the exception of U+1806 396 MONGOLIAN TODO SOFT HYPHEN, which was commonly mapped to nothing 397 in Unicode 3.2 but at the time of this writing is allowed by 398 Unicode 6.1). In practice, this change will probably have no 399 effect on comparison, but user-oriented software might reject such 400 code points instead of ignoring them during password preparation. 402 5. Security Considerations 403 5.1. Password/Passphrase Strength 405 The ability to include a wide range of characters in passwords and 406 passphrases can increase the potential for creating a strong password 407 with high entropy. However, in practice, the ability to include such 408 characters ought to be weighed against the possible need to reproduce 409 them on various devices using various input methods. 411 5.2. Identifier Comparison 413 The process of comparing identifiers (such as SASL simple user names, 414 authentication identifiers, and authorization identifiers) can lead 415 to either false negatives or false positives, both of which have 416 security implications. A more detailed discussion can be found in 417 [RFC6943]. 419 5.3. Reuse of PRECIS 421 The security considerations described in [I-D.ietf-precis-framework] 422 apply to the "IdentifierClass" and "FreeformClass" base string 423 classes used in this document for simple user names and passwords, 424 respectively. 426 5.4. Reuse of Unicode 428 The security considerations described in [UTR39] apply to the use of 429 Unicode characters in user names and passwords. 431 6. IANA Considerations 433 6.1. Use of IdentifierClass 435 The IANA shall add an entry to the PRECIS Usage Registry for reuse of 436 the PRECIS IdentifierClass in SASL, as follows: 438 Applicability: Usernames in SASL and Kerberos. 439 Base Class: IdentifierClass. 440 Subclass: No. 441 Replaces: The SASLprep profile of Stringprep. 442 Width Mapping: Map fullwidth and halfwidth characters to their 443 decomposition equivalents. 444 Additional Mappings: None. 445 Case Mapping: To be defined by application protocols that use this 446 profile. 448 Normalization: NFC. 449 Directionality: The "Bidi Rule" defined in RFC 5893 applies. 450 Specification: RFC XXXX. [Note to RFC Editor: please change XXXX to 451 the number issued for this specification.] 453 6.2. Use of FreeformClass 455 The IANA shall add an entry to the PRECIS Usage Registry for reuse of 456 the PRECIS FreeformClass in SASL, as follows: 458 Applicability: Passwords in SASL and Kerberos. 459 Base Class: FreeformClass 460 Subclass: No. 461 Replaces: The SASLprep profile of Stringprep. 462 Width Mapping: None. 463 Additional Mappings: Map non-ASCII space characters to ASCII space. 464 Case Mapping: None. 465 Normalization: NFC. 466 Directionality: None. 467 Specification: RFC XXXX. [Note to RFC Editor: please change XXXX to 468 the number issued for this specification.] 470 7. Open Issues 472 We need to compare the output obtained when applying the new rules 473 with Unicode 3.2 and Unicode 6.1 data to the output obtained when 474 applying the SASLprep rules with Unicode 3.2 data, then make sure 475 that the PRECIS Working Group and KITTEN Working Group are 476 comfortable with any changes to the Unicode characters that are 477 allowed and disallowed. (See also the migration issues described 478 under Section 4.) 480 8. References 482 8.1. Normative References 484 [I-D.ietf-precis-framework] 485 Saint-Andre, P. and M. Blanchet, "Precis Framework: 486 Handling Internationalized Strings in Protocols", 487 draft-ietf-precis-framework-09 (work in progress), 488 July 2013. 490 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 491 Requirement Levels", BCP 14, RFC 2119, March 1997. 493 [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 494 10646", STD 63, RFC 3629, November 2003. 496 [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax 497 Specifications: ABNF", STD 68, RFC 5234, January 2008. 499 [UNICODE] The Unicode Consortium, "The Unicode Standard, Version 500 6.1", 2012, 501 . 503 8.2. Informative References 505 [I-D.ietf-precis-mappings] 506 YONEYA, Y. and T. NEMOTO, "Mapping characters for PRECIS 507 classes", draft-ietf-precis-mappings-02 (work in 508 progress), May 2013. 510 [RFC3454] Hoffman, P. and M. Blanchet, "Preparation of 511 Internationalized Strings ("stringprep")", RFC 3454, 512 December 2002. 514 [RFC4013] Zeilenga, K., "SASLprep: Stringprep Profile for User Names 515 and Passwords", RFC 4013, February 2005. 517 [RFC4422] Melnikov, A., Ed. and K. Zeilenga, Ed., "Simple 518 Authentication and Security Layer (SASL)", RFC 4422, 519 June 2006. 521 [RFC4616] Zeilenga, K., "The PLAIN Simple Authentication and 522 Security Layer (SASL) Mechanism", RFC 4616, August 2006. 524 [RFC5802] Newman, C., Menon-Sen, A., Melnikov, A., and N. Williams, 525 "Salted Challenge Response Authentication Mechanism 526 (SCRAM) SASL and GSS-API Mechanisms", RFC 5802, July 2010. 528 [RFC5890] Klensin, J., "Internationalized Domain Names for 529 Applications (IDNA): Definitions and Document Framework", 530 RFC 5890, August 2010. 532 [RFC5891] Klensin, J., "Internationalized Domain Names in 533 Applications (IDNA): Protocol", RFC 5891, August 2010. 535 [RFC5893] Alvestrand, H. and C. Karp, "Right-to-Left Scripts for 536 Internationalized Domain Names for Applications (IDNA)", 537 RFC 5893, August 2010. 539 [RFC5894] Klensin, J., "Internationalized Domain Names for 540 Applications (IDNA): Background, Explanation, and 541 Rationale", RFC 5894, August 2010. 543 [RFC6120] Saint-Andre, P., "Extensible Messaging and Presence 544 Protocol (XMPP): Core", RFC 6120, March 2011. 546 [RFC6365] Hoffman, P. and J. Klensin, "Terminology Used in 547 Internationalization in the IETF", BCP 166, RFC 6365, 548 September 2011. 550 [RFC6943] Thaler, D., "Issues in Identifier Comparison for Security 551 Purposes", RFC 6943, May 2013. 553 [UTR39] The Unicode Consortium, "Unicode Technical Report #39: 554 Unicode Security Mechanisms", August 2010, 555 . 557 Appendix A. Differences from RFC 4013 559 The following substantive modifications were made from RFC 4013. 561 o A single SASLprep algorithm was replaced by two separate 562 algorithms: one for simple user names and another for passwords. 563 o The new preparation algorithms use PRECIS instead of a stringprep 564 profile. The new algorithms work independenctly of Unicode 565 versions. 566 o As recommended in the PRECIS framwork, changed the Unicode 567 normalization form to NFC (from NFKC). 568 o Some Unicode code points that were mapped to nothing in RFC 4013 569 are simply disallowed by PRECIS. 571 Appendix B. Acknowledgements 573 The following individuals provided helpful feedback on this document: 574 Marc Blanchet, Alan DeKok, Joe Hildebrand, Jeffrey Hutzelman, Simon 575 Josefsson, Jonathan Lennox, Matt Miller, Chris Newman, Pete Resnick, 576 Andrew Sullivan, and Nico Williams (Nico in particular provided text 577 that was used in Section 2.2). Thanks also to Yoshiro YONEYA and 578 Takahiro NEMOTO for implementation feedback. 580 This document borrows some text from [RFC4013] and [RFC6120]. 582 Authors' Addresses 584 Peter Saint-Andre 585 Cisco Systems, Inc. 586 1899 Wynkoop Street, Suite 600 587 Denver, CO 80202 588 USA 590 Phone: +1-303-308-3282 591 Email: psaintan@cisco.com 593 Alexey Melnikov 594 Isode Ltd 595 5 Castle Business Village 596 36 Station Road 597 Hampton, Middlesex TW12 2BX 598 UK 600 Email: Alexey.Melnikov@isode.com