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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(See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-10) exists of draft-ietf-precis-7564bis-08 -- Possible downref: Non-RFC (?) normative reference: ref. 'UAX11' -- Possible downref: Non-RFC (?) normative reference: ref. 'Unicode' -- Obsolete informational reference (is this intentional?): RFC 4013 (ref. 'Err1812') (Obsoleted by RFC 7613) -- Obsolete informational reference (is this intentional?): RFC 3454 (Obsoleted by RFC 7564) -- Obsolete informational reference (is this intentional?): RFC 3501 (Obsoleted by RFC 9051) -- Duplicate reference: RFC4013, mentioned in 'RFC4013', was also mentioned in 'Err1812'. -- Obsolete informational reference (is this intentional?): RFC 4013 (Obsoleted by RFC 7613) -- Obsolete informational reference (is this intentional?): RFC 7613 (Obsoleted by RFC 8265) Summary: 0 errors (**), 0 flaws (~~), 2 warnings (==), 9 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group P. Saint-Andre 3 Internet-Draft Filament 4 Obsoletes: 7613 (if approved) A. Melnikov 5 Intended status: Standards Track Isode Ltd 6 Expires: December 29, 2017 June 27, 2017 8 Preparation, Enforcement, and Comparison of Internationalized Strings 9 Representing Usernames and Passwords 10 draft-ietf-precis-7613bis-08 12 Abstract 14 This document describes updated methods for handling Unicode strings 15 representing usernames and passwords. The previous approach was 16 known as SASLprep (RFC 4013) and was based on stringprep (RFC 3454). 17 The methods specified in this document provide a more sustainable 18 approach to the handling of internationalized usernames and 19 passwords. This document obsoletes RFC 7613. 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 December 29, 2017. 38 Copyright Notice 40 Copyright (c) 2017 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 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 57 3. Usernames . . . . . . . . . . . . . . . . . . . . . . . . . . 5 58 3.1. Definition . . . . . . . . . . . . . . . . . . . . . . . 5 59 3.2. Case Mapping vs. Case Preservation . . . . . . . . . . . 6 60 3.3. UsernameCaseMapped Profile . . . . . . . . . . . . . . . 7 61 3.3.1. Rules . . . . . . . . . . . . . . . . . . . . . . . . 7 62 3.3.2. Preparation . . . . . . . . . . . . . . . . . . . . . 8 63 3.3.3. Enforcement . . . . . . . . . . . . . . . . . . . . . 8 64 3.3.4. Comparison . . . . . . . . . . . . . . . . . . . . . 9 65 3.4. UsernameCasePreserved Profile . . . . . . . . . . . . . . 9 66 3.4.1. Rules . . . . . . . . . . . . . . . . . . . . . . . . 9 67 3.4.2. Preparation . . . . . . . . . . . . . . . . . . . . . 9 68 3.4.3. Enforcement . . . . . . . . . . . . . . . . . . . . . 10 69 3.4.4. Comparison . . . . . . . . . . . . . . . . . . . . . 10 70 3.5. Application-Layer Constructs . . . . . . . . . . . . . . 10 71 3.6. Examples . . . . . . . . . . . . . . . . . . . . . . . . 10 72 4. Passwords . . . . . . . . . . . . . . . . . . . . . . . . . . 12 73 4.1. Definition . . . . . . . . . . . . . . . . . . . . . . . 12 74 4.2. OpaqueString Profile . . . . . . . . . . . . . . . . . . 13 75 4.2.1. Preparation . . . . . . . . . . . . . . . . . . . . . 13 76 4.2.2. Enforcement . . . . . . . . . . . . . . . . . . . . . 14 77 4.2.3. Comparison . . . . . . . . . . . . . . . . . . . . . 14 78 4.3. Examples . . . . . . . . . . . . . . . . . . . . . . . . 15 79 5. Use in Application Protocols . . . . . . . . . . . . . . . . 16 80 6. Migration . . . . . . . . . . . . . . . . . . . . . . . . . . 16 81 6.1. Usernames . . . . . . . . . . . . . . . . . . . . . . . . 17 82 6.2. Passwords . . . . . . . . . . . . . . . . . . . . . . . . 18 83 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 84 7.1. UsernameCaseMapped Profile . . . . . . . . . . . . . . . 19 85 7.2. UsernameCasePreserved Profile . . . . . . . . . . . . . . 20 86 7.3. OpaqueString Profile . . . . . . . . . . . . . . . . . . 20 87 7.4. Stringprep Profile . . . . . . . . . . . . . . . . . . . 21 88 8. Security Considerations . . . . . . . . . . . . . . . . . . . 21 89 8.1. Password/Passphrase Strength . . . . . . . . . . . . . . 21 90 8.2. Password/Passphrase Comparison . . . . . . . . . . . . . 21 91 8.3. Identifier Comparison . . . . . . . . . . . . . . . . . . 22 92 8.4. Reuse of PRECIS . . . . . . . . . . . . . . . . . . . . . 22 93 8.5. Reuse of Unicode . . . . . . . . . . . . . . . . . . . . 22 94 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 22 95 9.1. Normative References . . . . . . . . . . . . . . . . . . 22 96 9.2. Informative References . . . . . . . . . . . . . . . . . 23 98 Appendix A. Changes from RFC 7613 . . . . . . . . . . . . . . . 25 99 Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 25 100 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 25 102 1. Introduction 104 Usernames and passwords are widely used for authentication and 105 authorization on the Internet, either directly when provided in 106 plaintext (as in the PLAIN Simple Authentication and Security Layer 107 (SASL) mechanism [RFC4616] and the HTTP Basic scheme [RFC7617]) or 108 indirectly when provided as the input to a cryptographic algorithm 109 such as a hash function (as in the Salted Challenge Response 110 Authentication Mechanism (SCRAM) SASL mechanism [RFC5802] and the 111 HTTP Digest scheme [RFC7616]). 113 To increase the likelihood that the input and comparison of usernames 114 and passwords will work in ways that make sense for typical users 115 throughout the world, this document defines rules for preparing, 116 enforcing, and comparing internationalized strings that represent 117 usernames and passwords. Such strings consist of code points from 118 the Unicode coded character set [Unicode], with special attention to 119 code points outside the ASCII range [RFC20]. The rules for handling 120 such strings are specified through profiles of the string classes 121 defined in the preparation, enforcement, and comparison of 122 internationalized strings (PRECIS) framework specification 123 [I-D.ietf-precis-7564bis]. 125 Profiles of the PRECIS framework enable software to handle Unicode 126 code points outside the ASCII range in an automated way, so that such 127 code points are treated carefully and consistently in application 128 protocols. In large measure, these profiles are designed to protect 129 application developers from the potentially negative consequences of 130 supporting the full range of Unicode code points. For instance, in 131 almost all application protocols it would be dangerous to treat the 132 Unicode code point SUPERSCRIPT ONE (U+00B9) as equivalent to DIGIT 133 ONE (U+0031), because that would result in false positives during 134 comparison, authentication, and authorization (e.g., an attacker 135 could easy spoof an account "user1@example.com"). 137 Whereas a naive use of Unicode would make such attacks trivially 138 easy, the PRECIS profile defined here for usernames generally 139 protects applications from inadvertently causing such problems. 140 (Similar considerations apply to passwords, although here it is 141 desirable to support a wider range of characters so as to maximize 142 entropy for purposes of authentication.) 144 The methods defined here might be applicable wherever usernames or 145 passwords are used. However, the methods are not intended for use in 146 preparing strings that are not usernames (e.g., Lightweight Directory 147 Access Protocol (LDAP) distinguished names), nor in cases where 148 identifiers or secrets are not strings (e.g., keys and certificates) 149 or require specialized handling. 151 Although the historical predecessor of this document was the SASLprep 152 profile of stringprep [RFC3454]), the approach defined here can be 153 used by technologies other than SASL [RFC4422], such as HTTP 154 authentication as specified in [RFC7617] and [RFC7616]. 156 This document does not modify the handling of internationalized 157 strings in usernames and passwords as prescribed by existing 158 application protocols that use SASLprep. If the community that uses 159 such an application protocol wishes to modernize its handling of 160 internationalized strings to use PRECIS instead of stringprep, it 161 needs to explicitly update the existing application protocol 162 definition (one example is [RFC7622]. Non-coordinated updates to 163 protocol implementations are discouraged because they can have a 164 negative impact on interoperability and security. 166 2. Terminology 168 A "username" or "user identifier" is a string of characters 169 designating an account on a computing device or system, often but not 170 necessarily for use by a person. Although some devices and system 171 might allow a username to be part or all of a person's name, and a 172 person might want their account designator to be part or all of their 173 name, because of the complexities involved that outcome is not 174 guaranteed for all human names on all computing devices or systems 175 that follow the rules defined in this specification. Protocol 176 designers and application developers who wish to allow a wider range 177 of characters are encouraged to consider a separation between more 178 restrictive account identifiers and more expressive display names. 180 A "password" is a string of characters that allows access to a 181 computing device or system, often associated with a particular 182 username. A password is not literally limited to a word, because a 183 password could be a passphrase consisting of more than one word, 184 perhaps separated by spaces, punctuation, or other non-alphanumeric 185 characters. 187 Some SASL mechanisms (e.g., CRAM-MD5, DIGEST-MD5, and SCRAM) specify 188 that the authentication identity used in the context of such 189 mechanisms is a "simple user name" (see Section 2 of [RFC4422] as 190 well as [RFC4013]). Various application technologies also assume 191 that the identity of a user or account takes the form of a username 192 (e.g., authentication for the Hypertext Transfer Protocol as 193 specified in [RFC7617] and [RFC7616]), whether or not they use SASL. 195 Note well that the exact form of a username in any particular SASL 196 mechanism or application technology is a matter for implementation 197 and deployment, and that a username does not necessarily map to any 198 particular application identifier. 200 Many important terms used in this document are defined in [RFC5890], 201 [RFC6365], [I-D.ietf-precis-7564bis], and [Unicode]. The term "non- 202 ASCII space" refers to any Unicode code point having a Unicode 203 general category of "Zs", with the exception of U+0020 (here called 204 "ASCII space"). 206 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 207 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 208 "OPTIONAL" in this document are to be interpreted as described in 209 [RFC2119]. 211 3. Usernames 213 3.1. Definition 215 This document specifies that a username is a string of Unicode code 216 points [Unicode] that is structured as an ordered sequence of 217 "userparts" and expressed in a standard Unicode Encoding Form (such 218 as UTF-8 [RFC3629]). A userpart is allowed to contain only code 219 points that are allowed by the PRECIS IdentifierClass defined in 220 Section 4.2 of [I-D.ietf-precis-7564bis], and thus consists almost 221 exclusively of letters and digits. A username can consist of a 222 single userpart or a space-separated sequence of userparts. 224 The syntax for a username is defined as follows, using the Augmented 225 Backus-Naur Form (ABNF) [RFC5234]. 227 username = userpart *(1*SP userpart) 228 userpart = 1*(idpoint) 229 ; 230 ; an "idpoint" is a Unicode code point that 231 ; can be contained in a string conforming to 232 ; the PRECIS IdentifierClass 233 ; 235 All code points and blocks not explicitly allowed in the PRECIS 236 IdentifierClass are disallowed; this includes private use code 237 points, surrogate code points, and the other code points and blocks 238 that were defined as "Prohibited Output" in [RFC4013]. In addition, 239 common constructions such as "user@example.com" (e.g., the Network 240 Access Identifier from [RFC7542]) are allowed as usernames under this 241 specification, as they were under [RFC4013]. 243 Implementation Note: The username construct defined in this 244 document does not necessarily match what all deployed applications 245 might refer to as a "username" or "userid" but instead provides a 246 relatively safe subset of Unicode code points that can be used in 247 existing SASL mechanisms and in application protocols that use 248 SASL, and even in most application protocols that do not currently 249 use SASL. 251 A username MUST NOT be zero bytes in length. This rule is to be 252 enforced after any normalization and mapping of code points. 254 In protocols that provide usernames as input to a cryptographic 255 algorithm such as a hash function, the client will need to perform 256 enforcement of the rules for the UsernameCaseMapped or 257 UsernameCasePreserved profile before applying the algorithm. 259 This specification defines two profiles for usernames: one that 260 performs case mapping and one that performs case preservation (see 261 further discussion under Section 3.2). 263 3.2. Case Mapping vs. Case Preservation 265 In order to accommodate the widest range of username constructs in 266 applications, this document defines two username profiles: 267 UsernameCaseMapped and UsernameCasePreserved. These two profiles 268 differ only in the Case-Mapping Rule and are otherwise identical. 270 Case mapping is a matter for the application protocol, protocol 271 implementation, or end deployment. In general, this document 272 suggests that it is preferable to apply the UsernameCaseMapped 273 profile and therefore perform case mapping, because not doing so can 274 lead to false positives during authentication and authorization (as 275 described in [RFC6943]) and can result in confusion among end users, 276 given the prevalence of case mapping in many existing protocols and 277 applications. However, there can be good reasons to apply the 278 UsernameCasePreserved profile and thus not perform case mapping, such 279 as backward compatibility with deployed infrastructure. 281 In particular: 283 o SASL mechanisms that follow the recommendations in this document 284 MUST specify whether and when case mapping is to be applied to 285 authentication identifiers. Because case mapping results in 286 information loss, in order to retain that information for as long 287 as possible during processing, implementations SHOULD delay any 288 case mapping to the last possible moment, such as when doing a 289 lookup by username, performing username comparisons, or generating 290 a cryptographic salt from a username (if the last possible moment 291 happens on a server, then decisions about case mapping can be a 292 matter of deployment policy). In keeping with [RFC4422], SASL 293 mechanisms are not to apply this or any other profile to 294 authorization identifiers, only to authentication identifiers. 296 o Application protocols that use SASL (such as IMAP [RFC3501] and 297 the Extensible Messaging and Presence Protocol (XMPP) [RFC6120]) 298 and that directly reuse this profile MUST specify whether or not 299 case mapping is to be applied to authorization identifiers. Such 300 "SASL application protocols" SHOULD delay any case-mapping of 301 authorization identifiers to the last possible moment, which 302 happens to necessarily be on the server side (this enables 303 decisions about case mapping to be a matter of deployment policy). 304 In keeping with [RFC4422], SASL application protocols are not to 305 apply this or any other profile to authentication identifiers, 306 only to authorization identifiers. 308 o Application protocols that do not use SASL (such as HTTP 309 authentication with the HTTP Basic and Digest schemes as specified 310 in [RFC7617] and [RFC7616]) but that directly reuse this profile 311 MUST specify whether and when case mapping is to be applied to 312 authentication identifiers or authorization identifiers, or both. 313 Such "non-SASL application protocols" SHOULD delay any case 314 mapping to the last possible moment, such as when doing a lookup 315 by username, performing username comparisons, or generating a 316 cryptographic salt from a username (if the last possible moment 317 happens on the server, then decisions about case mapping can be a 318 matter of deployment policy). 320 If the specification for a SASL mechanism, SASL application protocol, 321 or non-SASL application protocol uses the UsernameCaseMapped profile, 322 it MUST clearly describe whether case mapping is to be applied at the 323 level of the protocol itself, implementations thereof, or service 324 deployments (each of these approaches can be legitimate, depending on 325 the application in question). 327 3.3. UsernameCaseMapped Profile 329 3.3.1. Rules 331 The following rules are defined for use within the UsernameCaseMapped 332 profile of the PRECIS IdentifierClass. 334 1. Width-Mapping Rule: Map fullwidth and halfwidth code points to 335 their decomposition mappings (see Unicode Standard Annex #11 336 [UAX11]). 338 2. Additional Mapping Rule: There is no additional mapping rule. 340 3. Case-Mapping Rule: Map uppercase and titlecase code points to 341 their lowercase equivalents, preferably using the Unicode 342 toLower() operation as defined in the Unicode Standard [Unicode]; 343 see further discussion in Section 3.2. 345 4. Normalization Rule: Apply Unicode Normalization Form C (NFC) to 346 all strings. 348 5. Directionality Rule: Apply the "Bidi Rule" defined in [RFC5893] 349 to strings that contain right-to-left code points (i.e., each of 350 the six conditions of the Bidi Rule must be satisfied); for 351 strings that do not contain right-to-left code points, there is 352 no special processing for directionality. 354 3.3.2. Preparation 356 An entity that prepares a string for subsequent enforcement according 357 to this profile MUST proceed as follows (applying the steps in the 358 order shown). 360 1. Apply the width-mapping rule specified in Section 3.3.1. It is 361 necessary to apply the rule at this point because otherwise the 362 PRECIS "HasCompat" category specified in Section 9.17 of 363 [I-D.ietf-precis-7564bis] would forbid fullwidth and halfwidth 364 code points. 366 2. Ensure that the string consists only of Unicode code points that 367 are explicitly allowed by the PRECIS IdentifierClass defined in 368 Section 4.2 of [I-D.ietf-precis-7564bis]. 370 3.3.3. Enforcement 372 An entity that performs enforcement according to this profile MUST 373 prepare a string as described in Section 3.3.2 and MUST also apply 374 the following rules specified in Section 3.3.1 in the order shown: 376 1. Case-Mapping Rule 378 2. Normalization Rule 380 3. Directionality Rule 382 After all of the foregoing rules have been enforced, the entity MUST 383 ensure that the username is not zero bytes in length (this is done 384 after enforcing the rules to prevent applications from mistakenly 385 omitting a username entirely, because when internationalized strings 386 are accepted, a non-empty sequence of characters can result in a 387 zero-length username after canonicalization). 389 3.3.4. Comparison 391 An entity that performs comparison of two strings according to this 392 profile MUST prepare each string as specified in Section 3.3.2 and 393 then MUST enforce the rules specified in Section 3.3.3. The two 394 strings are to be considered equivalent if and only if they are an 395 exact octet-for-octet match (sometimes called "bit-string identity"). 397 3.4. UsernameCasePreserved Profile 399 3.4.1. Rules 401 The following rules are defined for use within the 402 UsernameCasePreserved profile of the PRECIS IdentifierClass. 404 1. Width-Mapping Rule: Map fullwidth and halfwidth code points to 405 their decomposition mappings (see Unicode Standard Annex #11 406 [UAX11]). 408 2. Additional Mapping Rule: There is no additional mapping rule. 410 3. Case-Mapping Rule: There is no case-mapping rule. 412 4. Normalization Rule: Apply Unicode Normalization Form C (NFC) to 413 all strings. 415 5. Directionality Rule: Apply the "Bidi Rule" defined in [RFC5893] 416 to strings that contain right-to-left code points (i.e., each of 417 the six conditions of the Bidi Rule must be satisfied); for 418 strings that do not contain right-to-left code points, there is 419 no special processing for directionality. 421 3.4.2. Preparation 423 An entity that prepares a string for subsequent enforcement according 424 to this profile MUST proceed as follows (applying the steps in the 425 order shown). 427 1. Apply the width-mapping rule specified in Section 3.3.1. It is 428 necessary to apply the rule at this point because otherwise the 429 PRECIS "HasCompat" category specified in Section 9.17 of 430 [I-D.ietf-precis-7564bis] would forbid fullwidth and halfwidth 431 code points. 433 2. Ensure that the string consists only of Unicode code points that 434 are explicitly allowed by the PRECIS IdentifierClass defined in 435 Section 4.2 of [I-D.ietf-precis-7564bis]. 437 3.4.3. Enforcement 439 An entity that performs enforcement according to this profile MUST 440 prepare a string as described in Section 3.4.2 and MUST also apply 441 the following rules specified in Section 3.4.1 in the order shown: 443 1. Normalization Rule 445 2. Directionality Rule 447 After all of the foregoing rules have been enforced, the entity MUST 448 ensure that the username is not zero bytes in length (this is done 449 after enforcing the rules to prevent applications from mistakenly 450 omitting a username entirely, because when internationalized strings 451 are accepted, a non-empty sequence of characters can result in a 452 zero-length username after canonicalization). 454 3.4.4. Comparison 456 An entity that performs comparison of two strings according to this 457 profile MUST prepare each string as specified in Section 3.4.2 and 458 then MUST enforce the rules specified in Section 3.4.3. The two 459 strings are to be considered equivalent if and only if they are an 460 exact octet-for-octet match (sometimes called "bit-string identity"). 462 3.5. Application-Layer Constructs 464 Both the UsernameCaseMapped and UsernameCasePreserved profiles enable 465 an application protocol, implementation, or deployment to create 466 application-layer constructs such as a username that is a space- 467 separated set of userparts like "Firstname Middlename Lastname". 468 Although such a construct is not a profile of the PRECIS 469 IdentifierClass (because U+0020 SPACE is not allowed in the 470 IdentifierClass), it can be created at the application layer because 471 U+0020 SPACE can be used as a separator between instances of the 472 PRECIS IdentifierClass (e.g., userparts as defined in this 473 specification). 475 3.6. Examples 477 The following examples illustrate a small number of userparts (not 478 usernames) that are consistent with the format defined above (note 479 that the characters "<" and ">" are used here to delineate the actual 480 userparts and are not part of the userpart strings). 482 +--------------------------+---------------------------------+ 483 | # | Userpart | Notes | 484 +--------------------------+---------------------------------+ 485 | 1 | | The at-sign is allowed in the | 486 | | | PRECIS IdentifierClass | 487 +--------------------------+---------------------------------+ 488 | 2 | | | 489 +--------------------------+---------------------------------+ 490 | 3 | | The third character is LATIN | 491 | | | SMALL LETTER SHARP S (U+00DF) | 492 +--------------------------+---------------------------------+ 493 | 4 | <π> | A userpart of GREEK SMALL | 494 | | | LETTER PI (U+03C0) | 495 +--------------------------+---------------------------------+ 496 | 5 | <Σ> | A userpart of GREEK CAPITAL | 497 | | | LETTER SIGMA (U+03A3) | 498 +--------------------------+---------------------------------+ 499 | 6 | <σ> | A userpart of GREEK SMALL | 500 | | | LETTER SIGMA (U+03C3) | 501 +--------------------------+---------------------------------+ 502 | 7 | <ς> | A userpart of GREEK SMALL | 503 | | | LETTER FINAL SIGMA (U+03C2) | 504 +--------------------------+---------------------------------+ 506 Table 1: A Sample of Legal Userparts 508 Several points are worth noting. Regarding examples 2 and 3: 509 although in German the character eszett (LATIN SMALL LETTER SHARP S 510 (U+00DF)) can mostly be used interchangeably with the two characters 511 "ss", the userparts in these examples are different and (if desired) 512 a server would need to enforce a registration policy that disallows 513 one of them if the other is registered. Regarding examples 5, 6, and 514 7: optional case-mapping of GREEK CAPITAL LETTER SIGMA (U+03A3) to 515 lowercase (i.e., to GREEK SMALL LETTER SIGMA (U+03C3)) during 516 comparison would result in matching the userparts in examples 5 and 517 6; however, because the PRECIS mapping rules do not account for the 518 special status of GREEK SMALL LETTER FINAL SIGMA (U+03C2), the 519 userparts in examples 5 and 7 or examples 6 and 7 would not be 520 matched during comparison. 522 The following examples illustrate strings that are not valid 523 userparts (not usernames) because they violate the format defined 524 above. 526 +--------------------------+---------------------------------+ 527 | # | Non-Userpart String | Notes | 528 +--------------------------+---------------------------------+ 529 | 8 | | Space (U+0020) is disallowed in | 530 | | | the userpart | 531 +--------------------------+---------------------------------+ 532 | 9 | <> | Zero-length userpart | 533 +--------------------------+---------------------------------+ 534 | 10| | The sixth character is ROMAN | 535 | | | NUMERAL FOUR (U+2163) | 536 +--------------------------+---------------------------------+ 537 | 11| <♚> | A user part of BLACK CHESS KING | 538 | | | (U+265A) | 539 +--------------------------+---------------------------------+ 541 Table 2: A Sample of Strings That Violate the Userpart Rule 543 Here again, several points are worth noting. Regarding example 8: 544 although this is not a valid userpart, it is a valid username because 545 it is a space-separated sequence of userparts. Regarding example 10: 546 the Unicode code point ROMAN NUMERAL FOUR (U+2163) has a 547 compatibility equivalent of the string formed of LATIN CAPITAL LETTER 548 I (U+0049) and LATIN CAPITAL LETTER V (U+0056), but code points with 549 compatibility equivalents are not allowed in the PRECIS 550 IdentifierClass. Regarding example 11: symbol characters such as 551 BLACK CHESS KING (U+265A) are not allowed in the PRECIS 552 IdentifierClass. 554 4. Passwords 556 4.1. Definition 558 This document specifies that a password is a string of Unicode code 559 points [Unicode] that is conformant to the OpaqueString profile 560 (specified below) of the PRECIS FreeformClass defined in Section 4.3 561 of [I-D.ietf-precis-7564bis], and that is expressed in a standard 562 Unicode Encoding Form (such as UTF-8 [RFC3629]). 564 The syntax for a password is defined as follows, using the Augmented 565 Backus-Naur Form (ABNF) [RFC5234]. 567 password = 1*(freepoint) 568 ; 569 ; a "freepoint" is a Unicode code point that 570 ; can be contained in a string conforming to 571 ; the PRECIS FreeformClass 572 ; 574 All code points and blocks not explicitly allowed in the PRECIS 575 FreeformClass are disallowed; this includes private use code points, 576 surrogate code points, and the other code points and blocks defined 577 as "Prohibited Output" in Section 2.3 of RFC 4013 (when corrected per 578 [Err1812]). 580 A password MUST NOT be zero bytes in length. This rule is to be 581 enforced after any normalization and mapping of code points. 583 Note: Some existing systems allow an empty string in places where 584 a password would be expected (e.g., command-line tools that might 585 be called from an automated script, or servers that might need to 586 be restarted without human intervention). From the perspective of 587 this document (and RFC 4013 before it), these empty strings are 588 not passwords but are workarounds for the practical difficulty of 589 using passwords in certain scenarios. The prohibition of zero- 590 length passwords is not a recommendation regarding password 591 strength (because a password of only one byte is highly insecure) 592 but is meant to prevent applications from mistakenly omitting a 593 password entirely; such an outcome is possible when 594 internationalized strings are accepted, because a non-empty 595 sequence of characters can result in a zero-length password after 596 canonicalization. 598 In protocols that provide passwords as input to a cryptographic 599 algorithm such as a hash function, the client will need to perform 600 enforcement of the rules for the OpaqueString profile before applying 601 the algorithm, because the password is not available to the server in 602 plaintext form. 604 4.2. OpaqueString Profile 606 The definition of the OpaqueString profile is provided in the 607 following sections, including detailed information about preparation, 608 enforcement, and comparison (for details on the distinction between 609 these actions, refer to [I-D.ietf-precis-7564bis]). 611 4.2.1. Preparation 613 An entity that prepares a string according to this profile MUST 614 ensure that the string consists only of Unicode code points that are 615 explicitly allowed by the FreeformClass base string class defined in 616 [I-D.ietf-precis-7564bis]. 618 4.2.2. Enforcement 620 An entity that performs enforcement according to this profile MUST 621 prepare a string as described in Section 4.2.1 and MUST also apply 622 the rules specified below for the OpaqueString profile (these rules 623 MUST be applied in the order shown): 625 1. Width-Mapping Rule: Fullwidth and halfwidth code points MUST NOT 626 be mapped to their decomposition mappings (see Unicode Standard 627 Annex #11 [UAX11]). 629 2. Additional Mapping Rule: Any instances of non-ASCII space MUST be 630 mapped to ASCII space (U+0020); a non-ASCII space is any Unicode 631 code point having a Unicode general category of "Zs" (with the 632 exception of U+0020). As was the case in RFC 4013, the inclusion 633 of only ASCII space prevents confusion with various non-ASCII 634 space code points, many of which are difficult to reproduce 635 across different input methods. 637 3. Case-Mapping Rule: There is no case mapping rule (because mapping 638 uppercase and titlecase code points to their lowercase 639 equivalents would lead to false positives and thus to reduced 640 security). 642 4. Normalization Rule: Unicode Normalization Form C (NFC) MUST be 643 applied to all strings. 645 5. Directionality Rule: There is no directionality rule. The "Bidi 646 Rule" (defined in [RFC5893]) and similar rules are unnecessary 647 and inapplicable to passwords, because they can reduce the 648 repertoire of characters that are allowed in a string and 649 therefore reduce the amount of entropy that is possible in a 650 password. Such rules are intended to minimize the possibility 651 that the same string will be displayed differently on a layout 652 system set for right-to-left display and a layout system set for 653 left-to-right display; however, passwords are typically not 654 displayed at all and are rarely meant to be interoperable across 655 different layout systems in the way that non-secret strings like 656 domain names and usernames are. Furthermore, it is perfectly 657 acceptable for opaque strings other than passwords to be 658 presented differently in different layout systems, as long as the 659 presentation is consistent in any given layout system. 661 4.2.3. Comparison 663 An entity that performs comparison of two strings according to this 664 profile MUST prepare each string as specified in Section 4.2.1 and 665 then MUST enforce the rules specified in Section 4.2.2. The two 666 strings are to be considered equivalent if and only if they are an 667 exact octet-for-octet match (sometimes called "bit-string identity"). 669 See Section 8.2 regarding comparison of passwords and passphrases. 671 4.3. Examples 673 The following examples illustrate a small number of passwords that 674 are consistent with the format defined above (note that the 675 characters "<" and ">" are used here to delineate the actual 676 passwords and are not part of the password strings). 678 +------------------------------------+------------------------------+ 679 | # | Password | Notes | 680 +------------------------------------+------------------------------+ 681 | 12| | ASCII space is allowed | 682 +------------------------------------+------------------------------+ 683 | 13| | Differs by case from | 684 | | | example 12 | 685 +------------------------------------+------------------------------+ 686 | 14| <πßå> | Non-ASCII letters are OK | 687 | | | (e.g., GREEK SMALL LETTER | 688 | | | PI (U+03C0)) | 689 +------------------------------------+------------------------------+ 690 | 15| | Symbols are OK (e.g., BLACK | 691 | | | DIAMOND SUIT (U+2666)) | 692 +------------------------------------+------------------------------+ 693 | 16| | OGHAM SPACE MARK (U+1680) is | 694 | | | mapped to U+0020, and thus | 695 | | | the full string is mapped to | 696 | | | | 697 +------------------------------------+------------------------------+ 699 Table 3: A Sample of Legal Passwords 701 The following example illustrates a string that is not a valid 702 password because it violates the format defined above. 704 +------------------------------------+------------------------------+ 705 | # | Password | Notes | 706 +------------------------------------+------------------------------+ 707 | 17| <> | Zero-length passwords are | 708 | | | disallowed | 709 +------------------------------------+------------------------------+ 710 | 18| | Control characters like TAB | 711 | | | are disallowed | 712 +------------------------------------+------------------------------+ 714 Table 4: A Sample of Strings That Violate the Password Rules 716 5. Use in Application Protocols 718 This specification defines only the PRECIS-based rules for the 719 handling of strings conforming to the UsernameCaseMapped and 720 UsernameCasePreserved profiles of the PRECIS IdentifierClass, and 721 strings conforming to the OpaqueString profile of the PRECIS 722 FreeformClass. It is the responsibility of an application protocol 723 to specify the protocol slots in which such strings can appear, the 724 entities that are expected to enforce the rules governing such 725 strings, and at what points during protocol processing or interface 726 handling the rules need to be enforced. See Section 6 of 727 [I-D.ietf-precis-7564bis] for guidelines on using PRECIS profiles in 728 applications. 730 Above and beyond the PRECIS-based rules specified here, application 731 protocols can also define application-specific rules governing such 732 strings (rules regarding minimum or maximum length, further 733 restrictions on allowable code points or character ranges, safeguards 734 to mitigate the effects of visually similar characters, etc.), 735 application-layer constructs (see Section 3.5), and related matters. 737 Some PRECIS profile definitions encourage entities that enforce the 738 rules to be liberal in what they accept. However, for usernames and 739 passwords such a policy can be problematic, because it can lead to 740 false positives. An in-depth discussion can be found in [RFC6943]. 742 Applying the rules for any given PRECIS profile is not necessarily an 743 idempotent procedure for all code points. Therefore, implementations 744 might need to apply the rules more than once to an internationalized 745 string. 747 6. Migration 749 The rules defined in this specification differ slightly from those 750 defined by the SASLprep specification [RFC4013] (but not from 751 [RFC7613]). In order to smooth the process of migrating from 752 SASLprep to the approach defined herein, the following sections 753 describe these differences, along with their implications for 754 migration, in more detail. 756 6.1. Usernames 758 Deployments that currently use SASLprep for handling usernames might 759 need to scrub existing data when they migrate to the rules defined in 760 this specification. In particular: 762 o SASLprep specified the use of Unicode Normalization Form KC 763 (NFKC), whereas the UsernameCaseMapped and UsernameCasePreserved 764 profiles employ Unicode Normalization Form C (NFC). In practice, 765 this change is unlikely to cause significant problems, because 766 NFKC provides methods for mapping Unicode code points with 767 compatibility equivalents to those equivalents, whereas the PRECIS 768 IdentifierClass entirely disallows Unicode code points with 769 compatibility equivalents (i.e., during comparison, NFKC is more 770 "aggressive" about finding matches than NFC). A few examples 771 might suffice to indicate the nature of the problem: 773 1. LATIN SMALL LETTER LONG S (U+017F) is compatibility equivalent 774 to LATIN SMALL LETTER S (U+0073). 776 2. ROMAN NUMERAL FOUR (U+2163) is compatibility equivalent to 777 LATIN CAPITAL LETTER I (U+0049) and LATIN CAPITAL LETTER V 778 (U+0056). 780 3. LATIN SMALL LIGATURE FI (U+FB01) is compatibility equivalent 781 to LATIN SMALL LETTER F (U+0066) and LATIN SMALL LETTER I 782 (U+0069). 784 Under SASLprep, the use of NFKC also handled the mapping of 785 fullwidth and halfwidth code points to their decomposition 786 mappings. 788 For migration purposes, operators might want to search their 789 database of usernames for names containing Unicode code points 790 with compatibility equivalents and, where there is no conflict, 791 map those code points to their equivalents. Naturally, it is 792 possible that during this process the operator will discover 793 conflicting usernames (e.g., HENRYIV with the last two code points 794 being LATIN CAPITAL LETTER I (U+0049) and LATIN CAPITAL LETTER V 795 (U+0056) vs. "HENRYIV" with the last character being ROMAN NUMERAL 796 FOUR (U+2163), which is compatibility equivalent to U+0049 and 797 U+0056); in these cases, the operator will need to determine how 798 to proceed -- for instance, by disabling the account whose name 799 contains a Unicode code point with a compatibility equivalent. 801 Such cases are probably rare, but it is important for operators to 802 be aware of them. 804 o SASLprep mapped the "characters commonly mapped to nothing" from 805 Appendix B.1 of [RFC3454]) to nothing, whereas the PRECIS 806 IdentifierClass entirely disallows most of these code points, 807 which correspond to the code points from the PRECIS "M" category 808 defined under Section 9.13 of [I-D.ietf-precis-7564bis]. For 809 migration purposes, the operator might want to remove from 810 usernames any code points contained in the PRECIS "M" category 811 (e.g., SOFT HYPHEN (U+00AD)). Because these code points would 812 have been "mapped to nothing" in stringprep, in practice a user 813 would not notice the difference if, upon migration to PRECIS, the 814 code points are removed. 816 o SASLprep allowed uppercase and titlecase code points, whereas the 817 UsernameCaseMapped profile maps uppercase and titlecase code 818 points to their lowercase equivalents (by contrast, the 819 UsernameCasePreserved profile matches SASLprep in this regard). 820 For migration purposes, the operator can use either the 821 UsernameCaseMapped profile (thus losing the case information) or 822 the UsernameCasePreserved profile (thus ignoring case difference 823 when comparing usernames). 825 6.2. Passwords 827 Depending on local service policy, migration from SASLprep to this 828 specification might not involve any scrubbing of data (because 829 passwords might not be stored in the clear anyway); however, service 830 providers need to be aware of possible issues that might arise during 831 migration. In particular: 833 o SASLprep specified the use of Unicode Normalization Form KC 834 (NFKC), whereas the OpaqueString profile employs Unicode 835 Normalization Form C (NFC). Because NFKC is more aggressive about 836 finding matches than NFC, in practice this change is unlikely to 837 cause significant problems and indeed has the security benefit of 838 probably resulting in fewer false positives when comparing 839 passwords. A few examples might suffice to indicate the nature of 840 the problem: 842 1. LATIN SMALL LETTER LONG S (U+017F) is compatibility equivalent 843 to LATIN SMALL LETTER S (U+0073). 845 2. ROMAN NUMERAL FOUR (U+2163) is compatibility equivalent to 846 LATIN CAPITAL LETTER I (U+0049) and LATIN CAPITAL LETTER V 847 (U+0056). 849 3. LATIN SMALL LIGATURE FI (U+FB01) is compatibility equivalent 850 to LATIN SMALL LETTER F (U+0066) and LATIN SMALL LETTER I 851 (U+0069). 853 Under SASLprep, the use of NFKC also handled the mapping of 854 fullwidth and halfwidth code points to their decomposition 855 mappings. Although it is expected that code points with 856 compatibility equivalents are rare in existing passwords, some 857 passwords that matched when SASLprep was used might no longer work 858 when the rules in this specification are applied. 860 o SASLprep mapped the "characters commonly mapped to nothing" from 861 Appendix B.1 of [RFC3454]) to nothing, whereas the PRECIS 862 FreeformClass entirely disallows such code points, which 863 correspond to the code points from the PRECIS "M" category defined 864 under Section 9.13 of [I-D.ietf-precis-7564bis]. In practice, 865 this change will probably have no effect on comparison, but user- 866 oriented software might reject such code points instead of 867 ignoring them during password preparation. 869 7. IANA Considerations 871 IANA has made the updates described below. 873 7.1. UsernameCaseMapped Profile 875 IANA has added the following entry to the "PRECIS Profiles" registry. 877 Name: UsernameCaseMapped. 879 Base Class: IdentifierClass. 881 Applicability: Usernames in security and application protocols. 883 Replaces: The SASLprep profile of stringprep. 885 Width-Mapping Rule: Map fullwidth and halfwidth code points to their 886 decomposition mappings. 888 Additional Mapping Rule: None. 890 Case-Mapping Rule: Map uppercase and titlecase code points to 891 lowercase. 893 Normalization Rule: NFC. 895 Directionality Rule: The "Bidi Rule" defined in RFC 5893 applies. 897 Enforcement: To be defined by security or application protocols that 898 use this profile. 900 Specification: [[this document]], Section 3.2. 902 7.2. UsernameCasePreserved Profile 904 IANA has added the following entry to the "PRECIS Profiles" registry. 906 Name: UsernameCasePreserved. 908 Base Class: IdentifierClass. 910 Applicability: Usernames in security and application protocols. 912 Replaces: The SASLprep profile of stringprep. 914 Width-Mapping Rule: Map fullwidth and halfwidth code points to their 915 decomposition mappings. 917 Additional Mapping Rule: None. 919 Case-Mapping Rule: None. 921 Normalization Rule: NFC. 923 Directionality Rule: The "Bidi Rule" defined in RFC 5893 applies. 925 Enforcement: To be defined by security or application protocols that 926 use this profile. 928 Specification: [[this document]], Section 3.3. 930 7.3. OpaqueString Profile 932 IANA has added the following entry to the "PRECIS Profiles" registry. 934 Name: OpaqueString. 936 Base Class: FreeformClass. 938 Applicability: Passwords and other opaque strings in security and 939 application protocols. 941 Replaces: The SASLprep profile of stringprep. 943 Width-Mapping Rule: None. 945 Additional Mapping Rule: Map non-ASCII space code points to ASCII 946 space. 948 Case-Mapping Rule: None. 950 Normalization Rule: NFC. 952 Directionality Rule: None. 954 Enforcement: To be defined by security or application protocols that 955 use this profile. 957 Specification: [[this document]], Section 4.2. 959 7.4. Stringprep Profile 961 The stringprep specification [RFC3454] did not provide for entries in 962 the "Stringprep Profiles" registry to have any state except "Current" 963 or "Not Current". Because RFC 7613 obsoleted RFC 4013, which 964 registered the SASLprep profile of stringprep, IANA previously marked 965 that profile as "Not Current" and cited RFC 7613 as an additional 966 reference. IANA is requested to modify the profile so that this 967 document is cited at the additional reference. 969 8. Security Considerations 971 8.1. Password/Passphrase Strength 973 The ability to include a wide range of characters in passwords and 974 passphrases can increase the potential for creating a strong password 975 with high entropy. However, in practice, the ability to include such 976 characters ought to be weighed against the possible need to reproduce 977 them on various devices using various input methods. 979 8.2. Password/Passphrase Comparison 981 In systems that conform to modern best practices for security, 982 verification of passwords during authentication will not use the 983 comparison defined in Section 4.2.3. Instead, because the system 984 performs cryptographic calculations to verify the password, it will 985 prepare the password as defined in Section 4.2.1 and enforce the 986 rules as defined in Section 4.2.2 before performing the relevant 987 calculations. 989 8.3. Identifier Comparison 991 The process of comparing identifiers (such as SASL simple user names, 992 authentication identifiers, and authorization identifiers) can lead 993 to either false negatives or false positives, both of which have 994 security implications. A more detailed discussion can be found in 995 [RFC6943]. 997 8.4. Reuse of PRECIS 999 The security considerations described in [I-D.ietf-precis-7564bis] 1000 apply to the IdentifierClass and FreeformClass base string classes 1001 used in this document for usernames and passwords, respectively. 1003 8.5. Reuse of Unicode 1005 The security considerations described in [UTS39] apply to the use of 1006 Unicode code points in usernames and passwords. 1008 9. References 1010 9.1. Normative References 1012 [I-D.ietf-precis-7564bis] 1013 Saint-Andre, P. and M. Blanchet, "PRECIS Framework: 1014 Preparation, Enforcement, and Comparison of 1015 Internationalized Strings in Application Protocols", 1016 draft-ietf-precis-7564bis-08 (work in progress), June 1017 2017. 1019 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1020 Requirement Levels", BCP 14, RFC 2119, 1021 DOI 10.17487/RFC2119, March 1997, 1022 . 1024 [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 1025 10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November 1026 2003, . 1028 [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax 1029 Specifications: ABNF", STD 68, RFC 5234, 1030 DOI 10.17487/RFC5234, January 2008, 1031 . 1033 [RFC5890] Klensin, J., "Internationalized Domain Names for 1034 Applications (IDNA): Definitions and Document Framework", 1035 RFC 5890, DOI 10.17487/RFC5890, August 2010, 1036 . 1038 [RFC6365] Hoffman, P. and J. Klensin, "Terminology Used in 1039 Internationalization in the IETF", BCP 166, RFC 6365, 1040 DOI 10.17487/RFC6365, September 2011, 1041 . 1043 [UAX11] Unicode Standard Annex #11, "East Asian Width", edited by 1044 Ken Lunde. An integral part of The Unicode Standard, 1045 . 1047 [Unicode] The Unicode Consortium, "The Unicode Standard", 1048 . 1050 9.2. Informative References 1052 [Err1812] RFC Errata, "Erratum ID 1812", RFC 4013, 1053 . 1055 [RFC20] Cerf, V., "ASCII format for network interchange", STD 80, 1056 RFC 20, DOI 10.17487/RFC0020, October 1969, 1057 . 1059 [RFC3454] Hoffman, P. and M. Blanchet, "Preparation of 1060 Internationalized Strings ("stringprep")", RFC 3454, 1061 DOI 10.17487/RFC3454, December 2002, 1062 . 1064 [RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION 1065 4rev1", RFC 3501, DOI 10.17487/RFC3501, March 2003, 1066 . 1068 [RFC4013] Zeilenga, K., "SASLprep: Stringprep Profile for User Names 1069 and Passwords", RFC 4013, DOI 10.17487/RFC4013, February 1070 2005, . 1072 [RFC4422] Melnikov, A., Ed. and K. Zeilenga, Ed., "Simple 1073 Authentication and Security Layer (SASL)", RFC 4422, 1074 DOI 10.17487/RFC4422, June 2006, 1075 . 1077 [RFC4616] Zeilenga, K., Ed., "The PLAIN Simple Authentication and 1078 Security Layer (SASL) Mechanism", RFC 4616, 1079 DOI 10.17487/RFC4616, August 2006, 1080 . 1082 [RFC5802] Newman, C., Menon-Sen, A., Melnikov, A., and N. Williams, 1083 "Salted Challenge Response Authentication Mechanism 1084 (SCRAM) SASL and GSS-API Mechanisms", RFC 5802, 1085 DOI 10.17487/RFC5802, July 2010, 1086 . 1088 [RFC5893] Alvestrand, H., Ed. and C. Karp, "Right-to-Left Scripts 1089 for Internationalized Domain Names for Applications 1090 (IDNA)", RFC 5893, DOI 10.17487/RFC5893, August 2010, 1091 . 1093 [RFC6120] Saint-Andre, P., "Extensible Messaging and Presence 1094 Protocol (XMPP): Core", RFC 6120, DOI 10.17487/RFC6120, 1095 March 2011, . 1097 [RFC6943] Thaler, D., Ed., "Issues in Identifier Comparison for 1098 Security Purposes", RFC 6943, DOI 10.17487/RFC6943, May 1099 2013, . 1101 [RFC7542] DeKok, A., "The Network Access Identifier", RFC 7542, 1102 DOI 10.17487/RFC7542, May 2015, 1103 . 1105 [RFC7613] Saint-Andre, P. and A. Melnikov, "Preparation, 1106 Enforcement, and Comparison of Internationalized Strings 1107 Representing Usernames and Passwords", RFC 7613, 1108 DOI 10.17487/RFC7613, August 2015, 1109 . 1111 [RFC7616] Shekh-Yusef, R., Ed., Ahrens, D., and S. Bremer, "HTTP 1112 Digest Access Authentication", RFC 7616, 1113 DOI 10.17487/RFC7616, September 2015, 1114 . 1116 [RFC7617] Reschke, J., "The 'Basic' HTTP Authentication Scheme", 1117 RFC 7617, DOI 10.17487/RFC7617, September 2015, 1118 . 1120 [RFC7622] Saint-Andre, P., "Extensible Messaging and Presence 1121 Protocol (XMPP): Address Format", RFC 7622, 1122 DOI 10.17487/RFC7622, September 2015, 1123 . 1125 [UTS39] Unicode Technical Standard #39, "Unicode Security 1126 Mechanisms", edited by Mark Davis and Michel Suignard, 1127 . 1129 Appendix A. Changes from RFC 7613 1131 The following changes were made from [RFC7613]. 1133 o Corrected the order of operations for the UsernameCaseMapped 1134 profile to ensure consistency with RFC 7564. 1136 o In accordance with working group discussions and updates to 1137 [I-D.ietf-precis-7564bis], removed the use of the Unicode 1138 CaseFold() operation in favor of the Unicode toLower() operation. 1140 o Modified the presentation (but not the content) of the rules. 1142 o Removed UTF-8 as a mandatory encoding, because that is a matter 1143 for the application. 1145 o Clarified several editorial matters. 1147 o Updated references. 1149 See [RFC7613] for a description of the differences from [RFC4013]. 1151 Appendix B. Acknowledgements 1153 Thanks to Christian Schudt and Sam Whited for their bug reports and 1154 feedback. 1156 See [RFC7613] for acknowledgements related to the specification that 1157 this document supersedes. 1159 Authors' Addresses 1161 Peter Saint-Andre 1162 Filament 1163 P.O. Box 787 1164 Parker, CO 80134 1165 USA 1167 Phone: +1 720 256 6756 1168 Email: peter@filament.com 1169 URI: https://filament.com/ 1170 Alexey Melnikov 1171 Isode Ltd 1172 5 Castle Business Village 1173 36 Station Road 1174 Hampton, Middlesex TW12 2BX 1175 United Kingdom 1177 Email: Alexey.Melnikov@isode.com