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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(See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: draft-ietf-precis-framework has been published as RFC 7564 -- Possible downref: Non-RFC (?)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 'UNICODE' == Outdated reference: draft-ietf-precis-mappings has been published as RFC 7790 -- Obsolete informational reference (is this intentional?): RFC 3454 (Obsoleted by RFC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: October 27, 2013 April 25, 2013 8 Preparation and Comparison of Internationalized Strings Representing 9 Simple User Names and Passwords 10 draft-ietf-precis-saslprepbis-02 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 October 27, 2013. 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 . . . . . . . . . . . . . . . . . . . . . . . 6 64 4. Migration . . . . . . . . . . . . . . . . . . . . . . . . . . 7 65 4.1. User Names . . . . . . . . . . . . . . . . . . . . . . . . 7 66 4.2. Passwords . . . . . . . . . . . . . . . . . . . . . . . . 8 67 5. Security Considerations . . . . . . . . . . . . . . . . . . . 9 68 5.1. Password/Passphrase Strength . . . . . . . . . . . . . . . 9 69 5.2. Reuse of PRECIS . . . . . . . . . . . . . . . . . . . . . 9 70 5.3. Reuse of Unicode . . . . . . . . . . . . . . . . . . . . . 9 71 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 72 6.1. Use of IdentifierClass . . . . . . . . . . . . . . . . . . 10 73 6.2. Use of FreeformClass . . . . . . . . . . . . . . . . . . . 10 74 7. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 10 75 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 76 8.1. Normative References . . . . . . . . . . . . . . . . . . . 11 77 8.2. Informative References . . . . . . . . . . . . . . . . . . 11 78 Appendix A. Differences from RFC 4013 . . . . . . . . . . . . . . 12 79 Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 12 80 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13 82 1. Introduction 84 1.1. Overview 86 User names and passwords are used pervasively in authentication and 87 authorization on the Internet. To increase the likelihood that the 88 input and comparison of user names and passwords will work in ways 89 that make sense for typical users throughout the world, this document 90 defines rules for preparing and comparing internationalized strings 91 that represent simple user names and passwords. (In many 92 authentication technologies passwords are not directly compared 93 because the actual password is used as input to an algorithm such as 94 a hash function; however, non-ASCII code points in the input string 95 still need to be handled correctly.) 97 The algorithms defined in this document assume that all strings are 98 comprised of characters from the Unicode character set [UNICODE]. 100 The algorithms are designed for use in Simple Authentication and 101 Security Layer (SASL) [RFC4422] mechanisms, such as PLAIN [RFC4616] 102 and SCRAM-SHA-1 [RFC5802]. However, they might be applicable 103 wherever simple user names or passwords are used. This profile is 104 not intended for use in preparing strings that are not simple user 105 names (e.g., email addresses, DNS domain names, LDAP distinguished 106 names), nor in cases where identifiers or secrets are not strings 107 (e.g., keys or certificates) or require different handling (e.g., 108 case folding). 110 This document builds upon the PRECIS framework defined in 111 [FRAMEWORK], which differs fundamentally from the stringprep 112 technology [RFC3454] used in SASLprep [RFC4013]. The primary 113 difference is that stringprep profiles allowed all characters except 114 those which were explicitly disallowed, whereas PRECIS profiles 115 disallow all characters except those which are explicitly allowed 116 (this "inclusion model" was originally used for internationalized 117 domain names in [RFC5891]; see [RFC5894] for further discussion). It 118 is important to keep this distinction in mind when comparing the 119 technology defined in this document to SASLprep [RFC4013]. 121 This document obsoletes RFC 4013. 123 1.2. Terminology 125 Many important terms used in this document are defined in 126 [FRAMEWORK], [RFC4422], [RFC5890], [RFC6365], and [UNICODE]. The 127 term "non-ASCII space" refers to any Unicode code point with a 128 general category of "Zs", with the exception of U+0020 (here called 129 "ASCII space"). 131 As used here, the term "password" is not literally limited to a word; 132 i.e., a password could be a passphrase consisting of more than one 133 word, perhaps separated by spaces or other such characters. 135 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 136 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 137 "OPTIONAL" in this document are to be interpreted as described in 138 [RFC2119]. 140 2. Simple User Names 142 2.1. Definition 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]). However, the exact form of a simple user name in 148 any particular mechanism or deployment thereof is a local matter, and 149 a simple user name does not necessarily map to an application 150 identifier such as the localpart of an email address. 152 For purposes of preparation and comparison of authentication 153 identities, this document specifies that a simple user name is a 154 string of Unicode code points [UNICODE], encoded using UTF-8 155 [RFC3629], and structured either as an ordered sequence of 156 "simpleparts" (where the complete simple user name can consist of a 157 single simplepart or a space-separated sequence of simpleparts) or as 158 a simplepart@domainpart (where the domainpart is an IP literal, an 159 IPv4 address, or a fully-qualified domain name). 161 Therefore the syntax for a simple user name is defined as follows 162 using the Augmented Backus-Naur Form (ABNF) as specified in 163 [RFC5234]. 165 simpleusername = simplepart [1*(1*SP simplepart)] 166 / simplepart '@' domainpart 167 simplepart = 1*(idpoint) 168 ; 169 ; an "idpoint" is a UTF-8 encoded 170 ; Unicode code point that conforms to 171 ; the PRECIS "IdentifierClass" 172 ; 173 domainpart = IP-literal / IPv4address / ifqdn 174 ; 175 ; the "IPv4address" and "IP-literal" 176 ; rules are defined in RFC 3986, and 177 ; the first-match-wins (a.k.a. "greedy") 178 ; algorithm described in RFC 3986 179 ; applies to the matching process 180 ; 181 ; note well that reuse of the IP-literal 182 ; rule from RFC 3986 implies that IPv6 183 ; addresses are enclosed in square 184 ; brackets (i.e., beginning with '[' 185 ; and ending with ']') 186 ; 187 ifqdn = 1*1023(domainpoint) 188 ; 189 ; a "domainpoint" is a UTF-8 encoded 190 ; Unicode code point that conforms to 191 ; RFC 5890 192 ; 194 Note well that all code points and blocks not explicitly allowed in 195 the PRECIS IdentifierClass are disallowed; this includes private use 196 characters, surrogate code points, and the other code points and 197 blocks defined as "Prohibited Output" in Section 2.3 of RFC 4013. 199 Note also that common constructions such as "user@example.com" are 200 allowed as simple user names when using software that conforms to 201 this specification, as they were under [RFC4013]. 203 2.2. Preparation 205 A simple user name MUST NOT be zero bytes in length. This rule is to 206 be enforced after any normalization and mapping of code points. 208 Each simplepart of a simple user name MUST conform to the definition 209 of the PRECIS IdentifierClass provided in [FRAMEWORK], where the 210 width mapping, additional mapping, case mapping, normalization, and 211 directionality rules are as described below. 213 1. Fullwidth and halfwidth characters MUST be mapped to their 214 decomposition equivalents. 215 2. Additional mappings MAY be applied, such as those defined in 216 [I-D.ietf-precis-mappings]. 217 3. Uppercase and titlecase characters MUST be mapped to their 218 lowercase equivalents. 219 4. Unicode Normalization Form C (NFC) MUST be applied to all 220 characters. 222 With regard to directionality, the "Bidi Rule" provided in [RFC5893] 223 applies. 225 3. Passwords 227 3.1. Definition 229 For purposes of preparation and comparison of passwords, this 230 document specifies that a password is a string of Unicode code points 231 [UNICODE], encoded using UTF-8 [RFC3629], and conformant to the 232 PRECIS FreeformClass. 234 Therefore the syntax for a password is defined as follows using the 235 Augmented Backus-Naur Form (ABNF) as specified in [RFC5234]. 237 password = 1*(freepoint) 238 ; 239 ; a "freepoint" is a UTF-8 encoded 240 ; Unicode code point that conforms to 241 ; the PRECIS "FreeformClass" 242 ; 244 Note well that all code points and blocks not explicitly allowed in 245 the PRECIS FreeformClass are disallowed; this includes private use 246 characters, surrogate code points, and the other code points and 247 blocks defined as "Prohibited Output" in Section 2.3 of RFC 4013. 249 3.2. Preparation 251 A password MUST NOT be zero bytes in length. This rule is to be 252 enforced after any normalization and mapping of code points. 254 A password MUST be treated as follows, where the operations specified 255 MUST be completed in the order shown: 257 1. Width mapping is not applied. 259 2. Map any instances of non-ASCII space to ASCII space (U+0020). 260 3. Case mapping is not applied. 261 4. Apply Unicode Normalization Form C (NFC) to all characters. 262 5. Ensure that the resulting string conforms to the definition of 263 the PRECIS FreeformClass. 265 With regard to directionality, the "Bidi Rule" (defined in [RFC5893]) 266 and similar rules are unnecessary and inapplicable to passwords, 267 since they can reduce the range of characters that are allowed in a 268 string and therefore reduce the amount of entropy that is possible in 269 a password. Furthermore, such rules are intended to minimize the 270 possibility that the same string will be displayed differently on a 271 system set for right-to-left display and a system set for left-to- 272 right display; however, passwords are typically not displayed at all 273 and are rarely meant to be interoperable across different systems in 274 the way that non-secret strings like domain names and user names are. 276 4. Migration 278 The rules defined in this specification differ slightly from those 279 defined by the SASLprep specification [RFC4013]. The following 280 sections describe these differences, along with their implications 281 for migration, in more detail. 283 4.1. User Names 285 Deployments that currently use SASLprep for handling user names might 286 need to scrub existing data when migrating to use of the rules 287 defined in this specification. In particular: 289 o SASLprep specified the use of Unicode Normalization Form KC 290 (NFKC), whereas this usage of the PRECIS IdentifierClass employs 291 Unicode Normalization Form C (NFC). In practice this change is 292 unlikely to cause significant problems, because NFKC provides 293 methods for mapping Unicode code points with compatibility 294 equivalents to those equivalents, whereas the PRECIS 295 IdentifierClass entirely disallows Unicode code points with 296 compatibility equivalents (i.e., during comparison NFKC is more 297 "aggressive" about finding matches than is NFC). A few examples 298 might suffice to indicate the nature of the problem: (1) U+017F 299 LATIN SMALL LETTER LONG S is compatibility equivalent to U+0073 300 LATIN SMALL LETTER S (2) U+2163 ROMAN NUMERAL FOUR is 301 compatibility equivalent to U+0049 LATIN CAPITAL LETTER I and 302 U+0056 LATIN CAPITAL LETTER V (3) U+FB01 LATIN SMALL LIGATURE FI 303 is compatibility equivalent to U+0066 LATIN SMALL LETTER F and 304 U+0069 LATIN SMALL LETTER I. Under SASLprep, the use of NFKC also 305 handled the mapping of fullwidth and halfwidth code points to 306 their decomposition equivalents (see [I-D.ietf-precis-mappings]). 307 Although it is expected that code points with compatibility 308 equivalents are rare in existing user names, for migration 309 purposes deployments might want to search their database of user 310 names for Unicode code points with compatibility equivalents and 311 map those code points to their compatibility equivalents. 312 o SASLprep mapped non-ASCII spaces to ASCII space (U+0020), whereas 313 the PRECIS IdentifierClass entirely disallows non-ASCII spaces. 314 The non-ASCII space characters are U+00A0 NO-BREAK SPACE, U+1680 315 OGHAM SPACE MARK, U+180E MONGOLIAN VOWEL SEPARATOR, U+2000 EN QUAD 316 through U+200A HAIR SPACE, U+202F NARROW NO-BREAK SPACE, U+205F 317 MEDIUM MATHEMATICAL SPACE, and U+3000 IDEOGRAPHIC SPACE. For 318 migration purposes, deployments might want to convert non-ASCII 319 space characters to ASCII space in simple user names. 320 o SASLprep mapped the "characters commonly mapped to nothing" from 321 Appendix B.1 of [RFC3454]) to nothing, whereas the PRECIS 322 IdentifierClass entirely disallows most of these characters, which 323 correspond to the code points from the "M" category defined under 324 Section 6.13 of [FRAMEWORK] (with the exception of U+1806 325 MONGOLIAN TODO SOFT HYPHEN, which was "commonly mapped to nothing" 326 in Unicode 3.2 but at the time of this writing does not have a 327 derived property of Default_Ignorable_Code_Point in Unicode 6.1). 328 For migration purposes, deployments might want to remove code 329 points contained in the PRECIS "M" category from simple user 330 names. 331 o SASLprep allowed uppercase and titlecase characters, whereas this 332 usage of the PRECIS IdentifierClass maps uppercase and titlecase 333 characters to their lowercase equivalents. For migration 334 purposes, deployments can either convert uppercase and titlecase 335 characters to their lowercase equivalents in simple user names 336 (thus losing the case information) or preserve uppercase and 337 titlecase characters and ignore the case difference when comparing 338 simple user names. 340 4.2. Passwords 342 Depending on local service policy, migration from RFC 4013 to this 343 specification might not involve any scrubbing of data (since 344 passwords might not be stored in the clear anyway); however, service 345 providers need to be aware of possible issues that might arise during 346 migration. In particular: 348 o SASLprep specified the use of Unicode Normalization Form KC 349 (NFKC), whereas this usage of the PRECIS FreeformClass employs 350 Unicode Normalization Form C (NFC). Because NFKC is more 351 aggressive about finding matches than NFC, in practice this change 352 is unlikely to cause significant problems and indeed has the 353 security benefit of probably resulting in fewer false positives 354 when comparing passwords. A few examples might suffice to 355 indicate the nature of the problem: (1) U+017F LATIN SMALL LETTER 356 LONG S is compatibility equivalent to U+0073 LATIN SMALL LETTER S 357 (2) U+2163 ROMAN NUMERAL FOUR is compatibility equivalent to 358 U+0049 LATIN CAPITAL LETTER I and U+0056 LATIN CAPITAL LETTER V 359 (3) U+FB01 LATIN SMALL LIGATURE FI is compatibility equivalent to 360 U+0066 LATIN SMALL LETTER F and U+0069 LATIN SMALL LETTER I. Under 361 SASLprep, the use of NFKC also handled the mapping of fullwidth 362 and halfwidth code points to their decomposition equivalents (see 363 [I-D.ietf-precis-mappings]). Although it is expected that code 364 points with compatibility equivalents are rare in existing 365 passwords, some passwords that matched when SASLprep was used 366 might no longer work when the rules in this specification are 367 applied. 368 o SASLprep mapped the "characters commonly mapped to nothing" from 369 Appendix B.1 of [RFC3454]) to nothing, whereas the PRECIS 370 FreeformClass entirely disallows such characters, which correspond 371 to the code points from the "M" category defined under Section 372 6.13 of [FRAMEWORK] (with the exception of U+1806 MONGOLIAN TODO 373 SOFT HYPHEN, which was commonly mapped to nothing in Unicode 3.2 374 but at the time of this writing is allowed by Unicode 6.1). In 375 practice, this change will probably have no effect on comparison, 376 but user-oriented software might reject such code points instead 377 of ignoring them during password preparation. 379 5. Security Considerations 381 5.1. Password/Passphrase Strength 383 The ability to include a wide range of characters in passwords and 384 passphrases can increase the potential for creating a strong password 385 with high entropy. However, in practice, the ability to include such 386 characters ought to be weighed against the possible need to reproduce 387 them on various devices using various input methods. 389 5.2. Reuse of PRECIS 391 The security considerations described in [FRAMEWORK] apply to the 392 "IdentifierClass" and "FreeformClass" base string classes used in 393 this document for simple user names and passwords, respectively. 395 5.3. Reuse of Unicode 397 The security considerations described in [UTR39] apply to the use of 398 Unicode characters in user names and passwords. 400 6. IANA Considerations 402 6.1. Use of IdentifierClass 404 The IANA shall add an entry to the PRECIS Usage Registry for reuse of 405 the PRECIS IdentifierClass in SASL, as follows: 407 Applicability: Usernames in SASL and Kerberos. 408 Base Class: IdentifierClass. 409 Subclass: No. 410 Replaces: The SASLprep profile of Stringprep. 411 Width Mapping: Map fullwidth and halfwidth characters to their 412 decomposition equivalents. 413 Additional Mappings: None. 414 Case Mapping: Map uppercase and titlecase characters to lowercase. 415 Normalization: NFC. 416 Directionality: The "Bidi Rule" defined in RFC 5893 applies. 417 Specification: RFC XXXX. [Note to RFC Editor: please change XXXX to 418 the number issued for this specification.] 420 6.2. Use of FreeformClass 422 The IANA shall add an entry to the PRECIS Usage Registry for reuse of 423 the PRECIS FreeformClass in SASL, as follows: 425 Applicability: Passwords in SASL and Kerberos. 426 Base Class: FreeformClass 427 Subclass: No. 428 Replaces: The SASLprep profile of Stringprep. 429 Width Mapping: None. 430 Additional Mappings: Map non-ASCII space characters to ASCII space. 431 Case Mapping: None. 432 Normalization: NFC. 433 Directionality: None. 434 Specification: RFC XXXX. [Note to RFC Editor: please change XXXX to 435 the number issued for this specification.] 437 7. Open Issues 439 We need to compare the output obtained when applying the new rules 440 with Unicode 3.2 and Unicode 6.1 data to the output obtained when 441 applying the SASLprep rules with Unicode 3.2 data, then make sure 442 that the PRECIS Working Group and KITTEN Working Group are 443 comfortable with any changes to the Unicode characters that are 444 allowed and disallowed. (See also the migration issues described 445 under Section 4.) 447 8. References 449 8.1. Normative References 451 [FRAMEWORK] 452 Saint-Andre, P. and M. Blanchet, "Precis Framework: 453 Handling Internationalized Strings in Protocols", 454 draft-ietf-precis-framework-07 (work in progress), 455 March 2013. 457 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 458 Requirement Levels", BCP 14, RFC 2119, March 1997. 460 [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 461 10646", STD 63, RFC 3629, November 2003. 463 [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax 464 Specifications: ABNF", STD 68, RFC 5234, January 2008. 466 [UNICODE] The Unicode Consortium, "The Unicode Standard, Version 467 6.1", 2012, 468 . 470 8.2. Informative References 472 [I-D.ietf-precis-mappings] 473 YONEYA, Y. and T. NEMOTO, "Mapping characters for PRECIS 474 classes", draft-ietf-precis-mappings-01 (work in 475 progress), December 2012. 477 [RFC3454] Hoffman, P. and M. Blanchet, "Preparation of 478 Internationalized Strings ("stringprep")", RFC 3454, 479 December 2002. 481 [RFC4013] Zeilenga, K., "SASLprep: Stringprep Profile for User Names 482 and Passwords", RFC 4013, February 2005. 484 [RFC4422] Melnikov, A., Ed. and K. Zeilenga, Ed., "Simple 485 Authentication and Security Layer (SASL)", RFC 4422, 486 June 2006. 488 [RFC4616] Zeilenga, K., "The PLAIN Simple Authentication and 489 Security Layer (SASL) Mechanism", RFC 4616, August 2006. 491 [RFC5802] Newman, C., Menon-Sen, A., Melnikov, A., and N. Williams, 492 "Salted Challenge Response Authentication Mechanism 493 (SCRAM) SASL and GSS-API Mechanisms", RFC 5802, July 2010. 495 [RFC5890] Klensin, J., "Internationalized Domain Names for 496 Applications (IDNA): Definitions and Document Framework", 497 RFC 5890, August 2010. 499 [RFC5891] Klensin, J., "Internationalized Domain Names in 500 Applications (IDNA): Protocol", RFC 5891, August 2010. 502 [RFC5893] Alvestrand, H. and C. Karp, "Right-to-Left Scripts for 503 Internationalized Domain Names for Applications (IDNA)", 504 RFC 5893, August 2010. 506 [RFC5894] Klensin, J., "Internationalized Domain Names for 507 Applications (IDNA): Background, Explanation, and 508 Rationale", RFC 5894, August 2010. 510 [RFC6365] Hoffman, P. and J. Klensin, "Terminology Used in 511 Internationalization in the IETF", BCP 166, RFC 6365, 512 September 2011. 514 [UTR39] The Unicode Consortium, "Unicode Technical Report #39: 515 Unicode Security Mechanisms", August 2010, 516 . 518 Appendix A. Differences from RFC 4013 520 The following substantive modifications were made from RFC 4013. 522 o A single SASLprep algorithm was replaced by two separate 523 algorithms: one for simple user names and another for passwords. 524 o The new preparation algorithms use PRECIS instead of a stringprep 525 profile. The new algorithms work independenctly of Unicode 526 versions. 527 o As recommended in the PRECIS framwork, changed the Unicode 528 normalization form from NFKC to NFC. 529 o Some Unicode code points that were mapped to nothing in RFC 4013 530 are simply disallowed by PRECIS. 532 Appendix B. Acknowledgements 534 Thanks to Yoshiro YONEYA and Takahiro NEMOTO for implementation 535 feedback. Thanks also to Marc Blanchet, Joe Hildebrand, Alan DeKok, 536 Simon Josefsson, Jonathan Lennox, Matt Miller, Chris Newman, Pete 537 Resnick, Andrew Sullivan, and Nico Williams for their input. 539 This document borrows some text from RFC 4013 and RFC 6120. 541 Authors' Addresses 543 Peter Saint-Andre 544 Cisco Systems, Inc. 545 1899 Wynkoop Street, Suite 600 546 Denver, CO 80202 547 USA 549 Phone: +1-303-308-3282 550 Email: psaintan@cisco.com 552 Alexey Melnikov 553 Isode Ltd 554 5 Castle Business Village 555 36 Station Road 556 Hampton, Middlesex TW12 2BX 557 UK 559 Email: Alexey.Melnikov@isode.com