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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: February 5, 2014 August 4, 2013 8 Preparation and Comparison of Internationalized Strings Representing 9 Usernames and Passwords 10 draft-ietf-precis-saslprepbis-04 12 Abstract 14 This document describes how to handle Unicode strings representing 15 usernames and passwords. This profile is intended to be used by 16 protocols that exchange or otherwise make use of usernames and 17 passwords. This document obsoletes RFC 4013. 19 Status of this Memo 21 This Internet-Draft is submitted in full conformance with the 22 provisions of BCP 78 and BCP 79. 24 Internet-Drafts are working documents of the Internet Engineering 25 Task Force (IETF). Note that other groups may also distribute 26 working documents as Internet-Drafts. The list of current Internet- 27 Drafts is at http://datatracker.ietf.org/drafts/current/. 29 Internet-Drafts are draft documents valid for a maximum of six months 30 and may be updated, replaced, or obsoleted by other documents at any 31 time. It is inappropriate to use Internet-Drafts as reference 32 material or to cite them other than as "work in progress." 34 This Internet-Draft will expire on February 5, 2014. 36 Copyright Notice 38 Copyright (c) 2013 IETF Trust and the persons identified as the 39 document authors. All rights reserved. 41 This document is subject to BCP 78 and the IETF Trust's Legal 42 Provisions Relating to IETF Documents 43 (http://trustee.ietf.org/license-info) in effect on the date of 44 publication of this document. Please review these documents 45 carefully, as they describe your rights and restrictions with respect 46 to this document. Code Components extracted from this document must 47 include Simplified BSD License text as described in Section 4.e of 48 the Trust Legal Provisions and are provided without warranty as 49 described in the Simplified BSD License. 51 Table of Contents 53 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 54 2. What the Username and Password Profiles Provide . . . . . . . 3 55 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 56 4. Usernames . . . . . . . . . . . . . . . . . . . . . . . . . . 4 57 4.1. Definition . . . . . . . . . . . . . . . . . . . . . . . . 4 58 4.2. Preparation . . . . . . . . . . . . . . . . . . . . . . . 5 59 5. Passwords . . . . . . . . . . . . . . . . . . . . . . . . . . 6 60 5.1. Definition . . . . . . . . . . . . . . . . . . . . . . . . 7 61 5.2. Preparation . . . . . . . . . . . . . . . . . . . . . . . 7 62 6. Migration . . . . . . . . . . . . . . . . . . . . . . . . . . 8 63 6.1. Usernames . . . . . . . . . . . . . . . . . . . . . . . . 8 64 6.2. Passwords . . . . . . . . . . . . . . . . . . . . . . . . 9 65 7. Security Considerations . . . . . . . . . . . . . . . . . . . 10 66 7.1. Password/Passphrase Strength . . . . . . . . . . . . . . . 10 67 7.2. Identifier Comparison . . . . . . . . . . . . . . . . . . 10 68 7.3. Reuse of PRECIS . . . . . . . . . . . . . . . . . . . . . 10 69 7.4. Reuse of Unicode . . . . . . . . . . . . . . . . . . . . . 11 70 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 71 8.1. Use of IdentifierClass . . . . . . . . . . . . . . . . . . 11 72 8.2. Use of FreeformClass . . . . . . . . . . . . . . . . . . . 11 73 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12 74 9.1. Normative References . . . . . . . . . . . . . . . . . . . 12 75 9.2. Informative References . . . . . . . . . . . . . . . . . . 12 76 Appendix A. Differences from RFC 4013 . . . . . . . . . . . . . . 13 77 Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 14 78 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14 80 1. Introduction 82 Usernames and passwords are widely used for authentication and 83 authorization on the Internet, either directly when provided in 84 plaintext (as in the SASL PLAIN mechanism [RFC4616] or the HTTP Basic 85 scheme [RFC2617]) or indirectly when provided as the input to a 86 cryptographic algorithm such as a hash function (as in the SASL SCRAM 87 mechanism [RFC5802] or the HTTP Digest scheme [RFC2617]). To 88 increase the likelihood that the input and comparison of usernames 89 and passwords will work in ways that make sense for typical users 90 throughout the world, this document defines rules for preparing and 91 comparing internationalized strings that represent usernames and 92 passwords. 94 The methods specified in this document define a PRECIS profile as 95 explained in the PRECIS framework specification 96 [I-D.ietf-precis-framework]. This document assumes that all strings 97 are comprised of characters from the Unicode character set [UNICODE], 98 with special attention to characters outside the ASCII range [RFC20]. 99 The methods defined here might be applicable wherever usernames or 100 passwords are used. However, the methods are not intended for use in 101 preparing strings that are not usernames (e.g., email addresses and 102 LDAP distinguished names), nor in cases where identifiers or secrets 103 are not strings (e.g., keys and certificates) or require specialized 104 handling. 106 This document obsoletes RFC 4013 (the "SASLprep" profile of 107 stringprep [RFC3454]) but can be used by technologies other than the 108 Simple Authentication and Security Layer (SASL) [RFC4422], such as 109 HTTP authentication [RFC2617]. 111 2. What the Username and Password Profiles Provide 113 Profiles of the PRECIS framework enable software to handle Unicode 114 characters outside the ASCII range in an automated way, so that such 115 characters are treated carefully and consistently in application 116 protocols. In large measure, these profiles are designed to protect 117 application developers from the potentially negative consequences of 118 supporting the full range of Unicode characters. For instance, in 119 almost all application protocols it would be dangerous to treat the 120 Unicode character SUPERSCRIPT ONE (U+0089) as equivalent to DIGIT ONE 121 (U+0031), since that would result in false positives during 122 comparison, authentication, and authorization (e.g., an attacker 123 could easy spoof an account "user1@example.com"). 125 Whereas a naive use of Unicode would make such attacks trivially 126 easy, the Username PRECIS profile defined in this document generally 127 protects applications from inadvertently causing such problems. 128 (Similar considerations apply to passwords, although here it is 129 desirable to support a wider range of characters so as to maximize 130 entropy during authentication.) 132 3. Terminology 134 Many important terms used in this document are defined in 135 [I-D.ietf-precis-framework], [RFC5890], [RFC6365], and [UNICODE]. 136 The term "non-ASCII space" refers to any Unicode code point having a 137 general category of "Zs", with the exception of U+0020 (here called 138 "ASCII space"). 140 As used here, the term "password" is not literally limited to a word; 141 i.e., a password could be a passphrase consisting of more than one 142 word, perhaps separated by spaces or other such characters. 144 Some SASL mechanisms (e.g., CRAM-MD5, DIGEST-MD5, and SCRAM) specify 145 that the authentication identity used in the context of such 146 mechanisms is a "simple user name" (see Section 2 of [RFC4422] as 147 well as [RFC4013]). Various application technologies also assume 148 that the identity of a user or account takes the form of a username 149 (e.g., authentication for the HyperText Transfer Protocol [RFC2617]), 150 whether or not they use SASL. Note well that the exact form of a 151 username in any particular SASL mechanism or application technology 152 is a matter for implementation and deployment, and that a username 153 does not necessarily map to any particular application identifier 154 (such as the localpart of an email address). 156 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 157 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 158 "OPTIONAL" in this document are to be interpreted as described in 159 [RFC2119]. 161 4. Usernames 163 4.1. Definition 165 This document specifies that a username is a string of Unicode code 166 points [UNICODE], encoded using UTF-8 [RFC3629], and structured 167 either as an ordered sequence of "userparts" (where the complete 168 username can consist of a single userpart or a space-separated 169 sequence of userparts) or as a userpart@domainpart (where the 170 domainpart is an IP literal, an IPv4 address, or a fully-qualified 171 domain name). 173 The syntax for a username is defined as follows using the Augmented 174 Backus-Naur Form (ABNF) [RFC5234]. 176 username = userpart [1*(1*SP userpart)] 177 / userpart '@' domainpart 178 userpart = 1*(idpoint) 179 ; 180 ; an "idpoint" is a UTF-8 encoded Unicode code point 181 ; that conforms to the PRECIS "IdentifierClass" 182 ; 183 domainpart = IP-literal / IPv4address / ifqdn 184 ; 185 ; the "IPv4address" and "IP-literal" rules are 186 ; defined in RFC 3986, and the first-match-wins 187 ; (a.k.a. "greedy") algorithm described in RFC 3986 188 ; applies 189 ; 190 ; reuse of the IP-literal rule from RFC 3986 implies 191 ; that IPv6 addresses are enclosed in square brackets 192 ; (i.e., beginning with '[' and ending with ']') 193 ; 194 ifqdn = 1*1023(domainpoint) 195 ; 196 ; a "domainpoint" is a UTF-8 encoded Unicode code 197 ; point that conforms to RFC 5890 198 ; 200 All code points and blocks not explicitly allowed in the PRECIS 201 IdentifierClass are disallowed; this includes private use characters, 202 surrogate code points, and the other code points and blocks that were 203 defined as "Prohibited Output" in [RFC4013]. In addition, common 204 constructions such as "user@example.com" are allowed as usernames 205 under this specification, as they were under [RFC4013]. 207 4.2. Preparation 209 A username MUST NOT be zero bytes in length. This rule is to be 210 enforced after any normalization and mapping of code points. 212 Each userpart of a username MUST conform to the definition of the 213 PRECIS IdentifierClass provided in [I-D.ietf-precis-framework], where 214 the width mapping, additional mapping, case mapping, normalization, 215 and directionality rules are as follows. 217 1. Fullwidth and halfwidth characters MUST be mapped to their 218 decomposition equivalents. 220 2. So-called additional mappings MAY be applied, such as those 221 defined in [I-D.ietf-precis-mappings]. 222 3. Uppercase and titlecase characters SHOULD be mapped to their 223 lowercase equivalents (not doing so can lead to false positives 224 during authentication and authorization, as described in 225 [RFC6943]). 226 4. Unicode Normalization Form C (NFC) MUST be applied to all 227 characters. 229 With regard to directionality, the "Bidi Rule" provided in [RFC5893] 230 applies. 232 SASL mechanisms that directly re-use this profile MUST specify 233 whether and when case mapping is to be applied to authentication 234 identifiers. SASL mechanisms SHOULD delay any case mapping to the 235 last possible moment, such as when doing a lookup by username, 236 username comparisons, or generating a cryptographic salt from a 237 username. In keeping with RFC4422, SASL mechanisms are not to apply 238 this or any other profile to authorization identifiers. 240 Application protocols that use SASL (such as IMAP [RFC4616] and XMPP 241 [RFC6120]) and that directly re-use this profile MUST specify whether 242 case mapping is to be applied to authorization identifiers. Such 243 "SASL application protocols" SHOULD delay any case mapping of 244 authorization identifiers to the last possible moment, which happens 245 to necessarily be on the server side. In keeping with RFC4422, SASL 246 application protocols are not to apply this or any other profile to 247 authentication identifiers. 249 Application protoocls that do not use SASL (such as HTTP 250 authentication with the Basic and Digest schemes [RFC2617]) MUST 251 specify whether and when case mapping is to be applied to 252 authentication identifiers and authorization identifiers. Such 253 application protocols SHOULD delay any case mapping to the last 254 possible moment, such as when doing a lookup by username, username 255 comparisons, or generating a cryptographic salt from a username. 257 In protocols that provide usernames as input to a cryptographic 258 algorithm such as a hash function, the client will need to perform 259 proper preparation of the username before applying the algorithm, 260 since the username is not available to the server in plaintext form. 262 5. Passwords 263 5.1. Definition 265 This document specifies that a password is a string of Unicode code 266 points [UNICODE], encoded using UTF-8 [RFC3629], and conformant to 267 the PRECIS FreeformClass. 269 The syntax for a password is defined as follows using the Augmented 270 Backus-Naur Form (ABNF) [RFC5234]. 272 password = 1*(freepoint) 273 ; 274 ; a "freepoint" is a UTF-8 encoded 275 ; Unicode code point that conforms to 276 ; the PRECIS "FreeformClass" 277 ; 279 All code points and blocks not explicitly allowed in the PRECIS 280 FreeformClass are disallowed; this includes private use characters, 281 surrogate code points, and the other code points and blocks defined 282 as "Prohibited Output" in Section 2.3 of RFC 4013. 284 5.2. Preparation 286 A password MUST NOT be zero bytes in length. This rule is to be 287 enforced after any normalization and mapping of code points. 289 A password MUST conform to the definition of the PRECIS FreeformClass 290 provided in [I-D.ietf-precis-framework], where the width mapping, 291 additional mapping, case mapping, normalization, and directionality 292 rules are as described below. 294 1. Fullwidth and halfwidth characters MUST NOT be mapped to their 295 decomposition equivalents. 296 2. Any instances of non-ASCII space MUST be mapped to ASCII space 297 (U+0020). 298 3. So-called additional mappings MAY be applied, such as those 299 defined in [I-D.ietf-precis-mappings]. 300 4. Uppercase and titlecase characters MUST NOT be mapped to their 301 lowercase equivalents. 302 5. Unicode Normalization Form C (NFC) MUST be applied to all 303 characters. 305 With regard to directionality, the "Bidi Rule" (defined in [RFC5893]) 306 and similar rules are unnecessary and inapplicable to passwords, 307 since they can reduce the range of characters that are allowed in a 308 string and therefore reduce the amount of entropy that is possible in 309 a password. Furthermore, such rules are intended to minimize the 310 possibility that the same string will be displayed differently on a 311 system set for right-to-left display and a system set for left-to- 312 right display; however, passwords are typically not displayed at all 313 and are rarely meant to be interoperable across different systems in 314 the way that non-secret strings like domain names and usernames are. 316 In protocols that provide passwords as input to a cryptographic 317 algorithm such as a hash function, the client will need to perform 318 proper preparation of the password before applying the algorithm, 319 since the password is not available to the server in plaintext form. 321 6. Migration 323 The rules defined in this specification differ slightly from those 324 defined by the SASLprep specification [RFC4013]. The following 325 sections describe these differences, along with their implications 326 for migration, in more detail. 328 6.1. Usernames 330 Deployments that currently use SASLprep for handling usernames might 331 need to scrub existing data when migrating to use of the rules 332 defined in this specification. In particular: 334 o SASLprep specified the use of Unicode Normalization Form KC 335 (NFKC), whereas this usage of the PRECIS IdentifierClass employs 336 Unicode Normalization Form C (NFC). In practice this change is 337 unlikely to cause significant problems, because NFKC provides 338 methods for mapping Unicode code points with compatibility 339 equivalents to those equivalents, whereas the PRECIS 340 IdentifierClass entirely disallows Unicode code points with 341 compatibility equivalents (i.e., during comparison NFKC is more 342 "aggressive" about finding matches than is NFC). A few examples 343 might suffice to indicate the nature of the problem: (1) U+017F 344 LATIN SMALL LETTER LONG S is compatibility equivalent to U+0073 345 LATIN SMALL LETTER S (2) U+2163 ROMAN NUMERAL FOUR is 346 compatibility equivalent to U+0049 LATIN CAPITAL LETTER I and 347 U+0056 LATIN CAPITAL LETTER V (3) U+FB01 LATIN SMALL LIGATURE FI 348 is compatibility equivalent to U+0066 LATIN SMALL LETTER F and 349 U+0069 LATIN SMALL LETTER I. Under SASLprep, the use of NFKC also 350 handled the mapping of fullwidth and halfwidth code points to 351 their decomposition equivalents (see [I-D.ietf-precis-mappings]). 352 Although it is expected that code points with compatibility 353 equivalents are rare in existing usernames, for migration purposes 354 deployments might want to search their database of usernames for 355 Unicode code points with compatibility equivalents and map those 356 code points to their compatibility equivalents. 358 o SASLprep mapped non-ASCII spaces to ASCII space (U+0020), whereas 359 the PRECIS IdentifierClass entirely disallows non-ASCII spaces. 360 The non-ASCII space characters are U+00A0 NO-BREAK SPACE, U+1680 361 OGHAM SPACE MARK, U+180E MONGOLIAN VOWEL SEPARATOR, U+2000 EN QUAD 362 through U+200A HAIR SPACE, U+202F NARROW NO-BREAK SPACE, U+205F 363 MEDIUM MATHEMATICAL SPACE, and U+3000 IDEOGRAPHIC SPACE. For 364 migration purposes, deployments might want to convert non-ASCII 365 space characters to ASCII space in usernames. 367 o SASLprep mapped the "characters commonly mapped to nothing" from 368 Appendix B.1 of [RFC3454]) to nothing, whereas the PRECIS 369 IdentifierClass entirely disallows most of these characters, which 370 correspond to the code points from the "M" category defined under 371 Section 6.13 of [I-D.ietf-precis-framework] (with the exception of 372 U+1806 MONGOLIAN TODO SOFT HYPHEN, which was "commonly mapped to 373 nothing" in Unicode 3.2 but at the time of this writing does not 374 have a derived property of Default_Ignorable_Code_Point in Unicode 375 6.2). For migration purposes, deployments might want to remove 376 code points contained in the PRECIS "M" category from usernames. 378 o SASLprep allowed uppercase and titlecase characters, whereas this 379 usage of the PRECIS IdentifierClass maps uppercase and titlecase 380 characters to their lowercase equivalents. For migration 381 purposes, deployments can either convert uppercase and titlecase 382 characters to their lowercase equivalents in usernames (thus 383 losing the case information) or preserve uppercase and titlecase 384 characters and ignore the case difference when comparing 385 usernames. 387 6.2. Passwords 389 Depending on local service policy, migration from RFC 4013 to this 390 specification might not involve any scrubbing of data (since 391 passwords might not be stored in the clear anyway); however, service 392 providers need to be aware of possible issues that might arise during 393 migration. In particular: 395 o SASLprep specified the use of Unicode Normalization Form KC 396 (NFKC), whereas this usage of the PRECIS FreeformClass employs 397 Unicode Normalization Form C (NFC). Because NFKC is more 398 aggressive about finding matches than NFC, in practice this change 399 is unlikely to cause significant problems and indeed has the 400 security benefit of probably resulting in fewer false positives 401 when comparing passwords. A few examples might suffice to 402 indicate the nature of the problem: (1) U+017F LATIN SMALL LETTER 403 LONG S is compatibility equivalent to U+0073 LATIN SMALL LETTER S 404 (2) U+2163 ROMAN NUMERAL FOUR is compatibility equivalent to 405 U+0049 LATIN CAPITAL LETTER I and U+0056 LATIN CAPITAL LETTER V 406 (3) U+FB01 LATIN SMALL LIGATURE FI is compatibility equivalent to 407 U+0066 LATIN SMALL LETTER F and U+0069 LATIN SMALL LETTER I. Under 408 SASLprep, the use of NFKC also handled the mapping of fullwidth 409 and halfwidth code points to their decomposition equivalents (see 410 [I-D.ietf-precis-mappings]). Although it is expected that code 411 points with compatibility equivalents are rare in existing 412 passwords, some passwords that matched when SASLprep was used 413 might no longer work when the rules in this specification are 414 applied. 416 o SASLprep mapped the "characters commonly mapped to nothing" from 417 Appendix B.1 of [RFC3454]) to nothing, whereas the PRECIS 418 FreeformClass entirely disallows such characters, which correspond 419 to the code points from the "M" category defined under Section 420 6.13 of [I-D.ietf-precis-framework] (with the exception of U+1806 421 MONGOLIAN TODO SOFT HYPHEN, which was commonly mapped to nothing 422 in Unicode 3.2 but at the time of this writing is allowed by 423 Unicode 6.2). In practice, this change will probably have no 424 effect on comparison, but user-oriented software might reject such 425 code points instead of ignoring them during password preparation. 427 7. Security Considerations 429 7.1. Password/Passphrase Strength 431 The ability to include a wide range of characters in passwords and 432 passphrases can increase the potential for creating a strong password 433 with high entropy. However, in practice, the ability to include such 434 characters ought to be weighed against the possible need to reproduce 435 them on various devices using various input methods. 437 7.2. Identifier Comparison 439 The process of comparing identifiers (such as SASL simple user names, 440 authentication identifiers, and authorization identifiers) can lead 441 to either false negatives or false positives, both of which have 442 security implications. A more detailed discussion can be found in 443 [RFC6943]. 445 7.3. Reuse of PRECIS 447 The security considerations described in [I-D.ietf-precis-framework] 448 apply to the "IdentifierClass" and "FreeformClass" base string 449 classes used in this document for usernames and passwords, 450 respectively. 452 7.4. Reuse of Unicode 454 The security considerations described in [UTR39] apply to the use of 455 Unicode characters in usernames and passwords. 457 8. IANA Considerations 459 [Note to RFC Editor: please change XXXX to the number issued for this 460 specification.] 462 8.1. Use of IdentifierClass 464 The IANA shall add an entry to the PRECIS Usage Registry for reuse of 465 the PRECIS IdentifierClass, as follows: 467 Applicability: Usernames in security and application protocols. 468 Base Class: IdentifierClass. 469 Subclass: No. 470 Replaces: The SASLprep profile of Stringprep. 471 Width Mapping: Map fullwidth and halfwidth characters to their 472 decomposition equivalents. 473 Additional Mappings: None. 474 Case Mapping: Not recommended, but to be defined by application 475 protocols that use this profile. 476 Normalization: NFC. 477 Directionality: The "Bidi Rule" defined in RFC 5893 applies. 478 Specification: RFC XXXX. 480 8.2. Use of FreeformClass 482 The IANA shall add an entry to the PRECIS Usage Registry for reuse of 483 the PRECIS FreeformClass, as follows: 485 Applicability: Passwords in security and application protocols. 486 Base Class: FreeformClass 487 Subclass: No. 488 Replaces: The SASLprep profile of Stringprep. 489 Width Mapping: None. 490 Additional Mappings: Map non-ASCII space characters to ASCII space. 491 Case Mapping: None. 492 Normalization: NFC. 493 Directionality: None. 494 Specification: RFC XXXX. 496 9. References 497 9.1. Normative References 499 [I-D.ietf-precis-framework] 500 Saint-Andre, P. and M. Blanchet, "Precis Framework: 501 Handling Internationalized Strings in Protocols", 502 draft-ietf-precis-framework-09 (work in progress), 503 July 2013. 505 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 506 Requirement Levels", BCP 14, RFC 2119, March 1997. 508 [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 509 10646", STD 63, RFC 3629, November 2003. 511 [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax 512 Specifications: ABNF", STD 68, RFC 5234, January 2008. 514 [UNICODE] The Unicode Consortium, "The Unicode Standard, Version 515 6.1", 2012, 516 . 518 9.2. Informative References 520 [I-D.ietf-precis-mappings] 521 YONEYA, Y. and T. NEMOTO, "Mapping characters for PRECIS 522 classes", draft-ietf-precis-mappings-02 (work in 523 progress), May 2013. 525 [RFC20] Cerf, V., "ASCII format for network interchange", RFC 20, 526 October 1969. 528 [RFC2617] Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S., 529 Leach, P., Luotonen, A., and L. Stewart, "HTTP 530 Authentication: Basic and Digest Access Authentication", 531 RFC 2617, June 1999. 533 [RFC3454] Hoffman, P. and M. Blanchet, "Preparation of 534 Internationalized Strings ("stringprep")", RFC 3454, 535 December 2002. 537 [RFC4013] Zeilenga, K., "SASLprep: Stringprep Profile for User Names 538 and Passwords", RFC 4013, February 2005. 540 [RFC4422] Melnikov, A., Ed. and K. Zeilenga, Ed., "Simple 541 Authentication and Security Layer (SASL)", RFC 4422, 542 June 2006. 544 [RFC4616] Zeilenga, K., "The PLAIN Simple Authentication and 545 Security Layer (SASL) Mechanism", RFC 4616, August 2006. 547 [RFC5802] Newman, C., Menon-Sen, A., Melnikov, A., and N. Williams, 548 "Salted Challenge Response Authentication Mechanism 549 (SCRAM) SASL and GSS-API Mechanisms", RFC 5802, July 2010. 551 [RFC5890] Klensin, J., "Internationalized Domain Names for 552 Applications (IDNA): Definitions and Document Framework", 553 RFC 5890, August 2010. 555 [RFC5891] Klensin, J., "Internationalized Domain Names in 556 Applications (IDNA): Protocol", RFC 5891, August 2010. 558 [RFC5893] Alvestrand, H. and C. Karp, "Right-to-Left Scripts for 559 Internationalized Domain Names for Applications (IDNA)", 560 RFC 5893, August 2010. 562 [RFC5894] Klensin, J., "Internationalized Domain Names for 563 Applications (IDNA): Background, Explanation, and 564 Rationale", RFC 5894, August 2010. 566 [RFC6120] Saint-Andre, P., "Extensible Messaging and Presence 567 Protocol (XMPP): Core", RFC 6120, March 2011. 569 [RFC6365] Hoffman, P. and J. Klensin, "Terminology Used in 570 Internationalization in the IETF", BCP 166, RFC 6365, 571 September 2011. 573 [RFC6943] Thaler, D., "Issues in Identifier Comparison for Security 574 Purposes", RFC 6943, May 2013. 576 [UTR39] The Unicode Consortium, "Unicode Technical Report #39: 577 Unicode Security Mechanisms", August 2010, 578 . 580 Appendix A. Differences from RFC 4013 582 This document builds upon the PRECIS framework defined in 583 [I-D.ietf-precis-framework], which differs fundamentally from the 584 stringprep technology [RFC3454] used in SASLprep [RFC4013]. The 585 primary difference is that stringprep profiles allowed all characters 586 except those which were explicitly disallowed, whereas PRECIS 587 profiles disallow all characters except those which are explicitly 588 allowed (this "inclusion model" was originally used for 589 internationalized domain names in [RFC5891]; see [RFC5894] for 590 further discussion). It is important to keep this distinction in 591 mind when comparing the technology defined in this document to 592 SASLprep [RFC4013]. 594 The following substantive modifications were made from RFC 4013. 596 o A single SASLprep algorithm was replaced by two separate 597 algorithms: one for usernames and another for passwords. 598 o The new preparation algorithms use PRECIS instead of a stringprep 599 profile. The new algorithms work independenctly of Unicode 600 versions. 601 o As recommended in the PRECIS framwork, changed the Unicode 602 normalization form to NFC (from NFKC). 603 o Some Unicode code points that were mapped to nothing in RFC 4013 604 are simply disallowed by PRECIS. 606 Appendix B. Acknowledgements 608 The following individuals provided helpful feedback on this document: 609 Marc Blanchet, Alan DeKok, Joe Hildebrand, Jeffrey Hutzelman, Simon 610 Josefsson, Jonathan Lennox, Matt Miller, Chris Newman, Yutaka OIWA, 611 Pete Resnick, Andrew Sullivan, and Nico Williams (Nico in particular 612 provided text that was used in Section 2.2). Thanks also to Yoshiro 613 YONEYA and Takahiro NEMOTO for implementation feedback. 615 This document borrows some text from [RFC4013] and [RFC6120]. 617 Authors' Addresses 619 Peter Saint-Andre 620 Cisco Systems, Inc. 621 1899 Wynkoop Street, Suite 600 622 Denver, CO 80202 623 USA 625 Phone: +1-303-308-3282 626 Email: psaintan@cisco.com 628 Alexey Melnikov 629 Isode Ltd 630 5 Castle Business Village 631 36 Station Road 632 Hampton, Middlesex TW12 2BX 633 UK 635 Email: Alexey.Melnikov@isode.com