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Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) -- Looks like a reference, but probably isn't: '0' on line 444 -- Duplicate reference: RFC5280, mentioned in 'RFC5280', was also mentioned in 'ID-lamps-rfc5280-i18n-update'. Summary: 0 errors (**), 0 flaws (~~), 2 warnings (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 LAMPS A. Melnikov, Ed. 3 Internet-Draft Isode Ltd 4 Intended status: Standards Track W. Chuang, Ed. 5 Expires: December 31, 2017 Google, Inc. 6 June 29, 2017 8 Internationalized Email Addresses in X.509 certificates 9 draft-ietf-lamps-eai-addresses-12 11 Abstract 13 This document defines a new name form for inclusion in the otherName 14 field of an X.509 Subject Alternative Name and Issuer Alternative 15 Name extension that allows a certificate subject to be associated 16 with an Internationalized Email Address. 18 Status of This Memo 20 This Internet-Draft is submitted in full conformance with the 21 provisions of BCP 78 and BCP 79. 23 Internet-Drafts are working documents of the Internet Engineering 24 Task Force (IETF). Note that other groups may also distribute 25 working documents as Internet-Drafts. The list of current Internet- 26 Drafts is at http://datatracker.ietf.org/drafts/current/. 28 Internet-Drafts are draft documents valid for a maximum of six months 29 and may be updated, replaced, or obsoleted by other documents at any 30 time. It is inappropriate to use Internet-Drafts as reference 31 material or to cite them other than as "work in progress." 33 This Internet-Draft will expire on December 31, 2017. 35 Copyright Notice 37 Copyright (c) 2017 IETF Trust and the persons identified as the 38 document authors. All rights reserved. 40 This document is subject to BCP 78 and the IETF Trust's Legal 41 Provisions Relating to IETF Documents 42 (http://trustee.ietf.org/license-info) in effect on the date of 43 publication of this document. Please review these documents 44 carefully, as they describe your rights and restrictions with respect 45 to this document. Code Components extracted from this document must 46 include Simplified BSD License text as described in Section 4.e of 47 the Trust Legal Provisions and are provided without warranty as 48 described in the Simplified BSD License. 50 Table of Contents 52 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 53 2. Conventions Used in This Document . . . . . . . . . . . . . . 2 54 3. Name Definitions . . . . . . . . . . . . . . . . . . . . . . 2 55 4. IDNA2008 . . . . . . . . . . . . . . . . . . . . . . . . . . 4 56 5. Matching of Internationalized Email Addresses in X.509 57 certificates . . . . . . . . . . . . . . . . . . . . . . . . 4 58 6. Name constraints in path validation . . . . . . . . . . . . . 5 59 7. Security Considerations . . . . . . . . . . . . . . . . . . . 7 60 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 61 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 62 9.1. Normative References . . . . . . . . . . . . . . . . . . 8 63 9.2. Informative References . . . . . . . . . . . . . . . . . 9 64 Appendix A. ASN.1 Module . . . . . . . . . . . . . . . . . . . . 9 65 Appendix B. Example of SmtpUTF8Name . . . . . . . . . . . . . . 10 66 Appendix C. Acknowledgements . . . . . . . . . . . . . . . . . . 11 67 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11 69 1. Introduction 71 [RFC5280] defines the rfc822Name subjectAltName name type for 72 representing [RFC5321] email addresses. The syntax of rfc822Name is 73 restricted to a subset of US-ASCII characters and thus can't be used 74 to represent Internationalized Email addresses [RFC6531]. This 75 document calls for a new otherName variant to represent 76 Internationalized Email addresses. In addition this document calls 77 for all email address domains in X.509 certificates to conform to 78 IDNA2008 [RFC5890]. 80 2. Conventions Used in This Document 82 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 83 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 84 document are to be interpreted as described in [RFC2119]. 86 The formal syntax use the Augmented Backus-Naur Form (ABNF) [RFC5234] 87 notation. 89 3. Name Definitions 91 The GeneralName structure is defined in [RFC5280], and supports many 92 different name forms including otherName for extensibility. This 93 section specifies the SmtpUTF8Name name form of otherName, so that 94 Internationalized Email addresses can appear in the subjectAltName of 95 a certificate, the issuerAltName of a certificate, or anywhere else 96 that GeneralName is used. 98 id-on-SmtpUTF8Name OBJECT IDENTIFIER ::= { id-on 9 } 100 SmtpUTF8Name ::= UTF8String (SIZE (1..MAX)) 102 When the subjectAltName (or issuerAltName) extension contains an 103 Internationalized Email address with a non-ASCII local-part, the 104 address MUST be stored in the SmtpUTF8Name name form of otherName. 105 The format of SmtpUTF8Name is defined as the ABNF rule 106 SmtpUTF8Mailbox. SmtpUTF8Mailbox is a modified version of the 107 Internationalized Mailbox which was defined in Section 3.3 of 108 [RFC6531] which was itself derived from SMTP Mailbox from 109 Section 4.1.2 of [RFC5321]. [RFC6531] defines the following ABNF 110 rules for Mailbox whose parts are modified for internationalization: 111 , , , , 112 , and . In particular, was updated to 113 also support UTF8-non-ascii. UTF8-non-ascii was described by 114 Section 3.1 of [RFC6532]. Also, domain was extended to support 115 U-label, as defined in [RFC5890]. 117 This document further refines Internationalized [RFC6531] Mailbox 118 ABNF rules and calls this SmtpUTF8Mailbox. In SmtpUTF8Mailbox, 119 labels that include non-ASCII characters MUST be stored in U-label 120 (rather than A-label) [RFC5890] form. This restriction removes the 121 need to determine which label encoding A- or U-label is present in 122 the Domain. As per Section 2.3.2.1 of [RFC5890], U-label are encoded 123 as UTF-8 [RFC3629] in Normalization Form C and other properties 124 specified there. In SmtpUTF8Mailbox, domain labels that solely use 125 ASCII characters (meaning not A- nor U-labels) SHALL use NR-LDH 126 restrictions as specified by Section 2.3.1 of [RFC5890] and SHALL be 127 restricted to lower case letters. NR-LDH stands for "Non-Reserved 128 Letters Digits Hyphen" and is the set LDH labels that do not have 129 "--" characters in the third and forth character position, which 130 excludes "tagged domain names" such as A-labels. Consistent with the 131 treatment of rfc822Name in [RFC5280], SmtpUTF8Name is an envelope 132 and has no phrase (such as a common name) before it, has no 133 comment (text surrounded in parentheses) after it, and is not 134 surrounded by "<" and ">". 136 Due to operational reasons to be described shortly and name 137 constraint compatibility reasons described in Section 6, SmtpUTF8Name 138 subjectAltName MUST only be used when the local part of the email 139 address contains contains non-ASCII characters. When the local-part 140 is ASCII, rfc822Name subjectAltName MUST be used instead of 141 SmtpUTF8Name. This is compatible with legacy software that supports 142 only rfc822Name (and not SmtpUTF8Name). 144 SmtpUTF8Name is encoded as UTF8String. The UTF8String encoding MUST 145 NOT contain a Byte-Order- Mark (BOM) [RFC3629] to aid consistency 146 across implementations particularly for comparison. 148 4. IDNA2008 150 To facilitate comparison between email addresses, all email address 151 domains in X.509 certificates MUST conform to IDNA2008 [RFC5890] (and 152 avoids any "mappings" mentioned in that document). Use of non- 153 conforming email address domains introduces the possibility of 154 conversion errors between alternate forms. This applies to 155 SmtpUTF8Name and rfc822Name in subjectAltName, issuerAltName and 156 anywhere else that these are used. 158 5. Matching of Internationalized Email Addresses in X.509 certificates 160 In equivalence comparison with SmtpUTF8Name, there may be some setup 161 work on one or both inputs depending of whether the input is already 162 in comparison form. Comparing SmtpUTF8Names consists of a domain 163 part step and a local-part step. The comparison form for local-parts 164 always is UTF-8. The comparison form for domain parts depends on 165 context. While some contexts such as certificate path validation in 166 [RFC5280] specify transforming domain to A-label (Section 7.5 and 7.2 167 in [RFC5280] as updated by [ID-lamps-rfc5280-i18n-update]), this 168 document RECOMMENDS transforming to UTF-8 U-label instead. This 169 reduces the likelihood of errors by reducing conversions as more 170 implementations natively support U- label domains. 172 Comparison of two SmtpUTF8Name is straightforward with no setup work 173 needed. They are considered equivalent if there is an exact octet- 174 for-octet match. Comparison with email addresses such as 175 Internationalized email address or rfc822Name requires additional 176 setup steps for domain part and local-part. The initial preparation 177 for the email addresses is to remove any phrases or comments, as well 178 as "<" and ">" present. This document calls for comparison of domain 179 labels that include non-ASCII characters be tranformed to U-label if 180 not already in that form. The first step is to detect use of the 181 A-label by using Section 5.1 of [RFC5891]. Next if necessary, 182 transform any A-labels to U-labels Unicode as specified in 183 Section 5.2 of [RFC5891]. Finally if necessary convert the Unicode 184 to UTF-8 as specified in Section 3 of [RFC3629]. For ASCII NR-LDH 185 labels, upper case letters are converted to lower case letters. In 186 setup for SmtpUTF8Mailbox, the email address local-part MUST conform 187 to the requirements of [RFC6530] and [RFC6531], including being a 188 string in UTF-8 form. In particular, the local-part MUST NOT be 189 transformed in any way, such as by doing case folding or 190 normalization of any kind. The part of an 191 Internationalized email address is already in UTF-8. For rfc822Name 192 the local-part, which is IA5String (ASCII), trivially maps to UTF-8 193 without change. Once setup is complete, they are again compared 194 octet-for-octet. 196 To summarize non-normatively, the comparison steps including setup 197 are: 199 1. If the domain contains A-labels, transform them to U-labels. 201 2. If the domain contains ASCII NR-LDH labels, lowercase them. 203 3. Compare strings octet-for-octet for equivalence. 205 This specification expressly does not define any wildcard characters 206 and SmtpUTF8Name comparison implementations MUST NOT interpret any 207 character as wildcards. Instead, to specify multiple email addresses 208 through SmtpUTF8Name, the certificate MUST use multiple 209 subjectAltNames or issuerAltNames to explicitly carry any additional 210 email addresses. 212 6. Name constraints in path validation 214 This section updates Section 4.2.1.10 of [RFC5280] to extend 215 rfc822Name name constraints to SmtpUTF8Name subjectAltNames. A 216 SmtpUTF8Name aware path validators will apply name constraint 217 comparison to the subject distinguished name and both forms of 218 subject alternative name rfc822Name and SmtpUTF8Name. 220 Both rfc822Name and SmtpUTF8Name subject alternative names represent 221 the same underlying email address namespace. Since legacy CAs 222 constrained to issue certificates for a specific set of domains would 223 lack corresponding UTF-8 constraints, [ID-lamps-rfc5280-i18n-update] 224 updates modifies and extends rfc822Name name constraints defined in 225 [RFC5280] to cover SmtpUTF8Name subject alternative names. This 226 ensures that the introduction of SmtpUTF8Name does not violate 227 existing name constraints. Since it is not valid to include non- 228 ASCII UTF-8 characters in the local-part of rfc822Name name 229 constraints, and since name constraints that include a local-part are 230 rarely, if at all, used in practice, name constraints updated in 231 [ID-lamps-rfc5280-i18n-update] admit the forms that represent all 232 addresses at a host or all mailboxes in a domain, and deprecates 233 rfc822Name name constraints that represent a particular mailbox. 234 That is, rfc822Name constraints with a local-part SHOULD NOT be used. 236 Constraint comparison with SmtpUTF8Name subjectAltName starts with 237 the setup steps defined by Section 5. Setup converts the inputs of 238 the comparison which is one of a subject distinguished name or a 239 rfc822Name or SmtpUTF8Name subjectAltName, and one of a rfc822Name 240 name constraint, to constraint comparison form. For rfc822Name name 241 constraint, this will convert any domain A-labels to U-labels. For 242 both the name constraint and the subject, this will lower case any 243 domain NR-LDH labels. Strip the local-part and "@" separator from 244 each rfc822Name and SmtpUTF8Name, leaving just the domain-part. 245 After setup, this follows the comparison steps defined in 4.2.1.10 of 246 [RFC5280] as follows. If the resulting name constraint domain starts 247 with a "." character, then for the name constraint to match, a suffix 248 of the resulting subject alternative name domain MUST match the name 249 constraint (including the leading ".") octet for octet. If the 250 resulting name constraint domain does not start with a "." character, 251 then for the name constraint to match, the entire resulting subject 252 alternative name domain MUST match the name constraint octet for 253 octet. 255 Certificate Authorities that wish to issue CA certificates with email 256 address name constraint MUST use rfc822Name subject alternative names 257 only. These MUST be IDNA2008 conformant names with no mappings, and 258 with non-ASCII domains encoded in A-labels only. 260 The name constraint requirement with SmtpUTF8Name subject alternative 261 name is illustrated in the non-normative diagram Figure 1. The first 262 example (1) illustrates a permitted rfc822Name ASCII only hostname 263 name constraint, and the corresponding valid rfc822Name 264 subjectAltName and SmtpUTF8Name subjectAltName email addresses. The 265 second example (2) illustrates a permitted rfc822Name hostname name 266 constraint with A-label, and the corresponding valid rfc822Name 267 subjectAltName and SmtpUTF8Name subjectAltName email addresses. Note 268 that an email address with ASCII only local-part is encoded as 269 rfc822Name despite also having unicode present in the domain. 271 +-------------------------------------------------------------------+ 272 | Root CA Cert | 273 +-------------------------------------------------------------------+ 274 | 275 v 276 +-------------------------------------------------------------------+ 277 | Intermediate CA Cert | 278 | Permitted | 279 | rfc822Name: elementary.school.example.com (1) | 280 | | 281 | rfc822Name: xn--pss25c.example.com (2) | 282 | | 283 +-------------------------------------------------------------------+ 284 | 285 v 286 +-------------------------------------------------------------------+ 287 | Entity Cert (w/explicitly permitted subjects) | 288 | SubjectAltName Extension | 289 | rfc822Name: student@elemenary.school.example.com (1) | 290 | SmtpUTF8Name: u+5B66u+751F@elementary.school.example.com (1) | 291 | | 292 | rfc822Name: student@xn--pss25c.example.com (2) | 293 | SmtpUTF8Name: u+533Bu+751F@u+5927u+5B66.example.com (2) | 294 | | 295 +-------------------------------------------------------------------+ 297 Name constraints with SmtpUTF8Name and rfc822Name 299 Figure 1 301 7. Security Considerations 303 Use of SmtpUTF8Name for certificate subjectAltName (and 304 issuerAltName) will incur many of the same security considerations as 305 in Section 8 in [RFC5280] , but introduces a new issue by permitting 306 non-ASCII characters in the email address local-part. This issue, as 307 mentioned in Section 4.4 of [RFC5890] and in Section 4 of [RFC6532], 308 is that use of Unicode introduces the risk of visually similar and 309 identical characters which can be exploited to deceive the recipient. 310 The former document references some means to mitigate against these 311 attacks. 313 8. IANA Considerations 315 In Section 3 and the ASN.1 module identifier defined in Appendix A. 316 IANA is kindly requested to make the following assignments for: 318 The LAMPS-EaiAddresses-2016 ASN.1 module in the "SMI Security for 319 PKIX Module Identifier" registry (1.3.6.1.5.5.7.0). 321 The SmtpUTF8Name otherName in the "PKIX Other Name Forms" registry 322 (1.3.6.1.5.5.7.8). 324 9. References 326 9.1. Normative References 328 [ID-lamps-rfc5280-i18n-update] 329 Housley, R., "Internationalization Updates to RFC 5280", 330 June 2017, . 333 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 334 Requirement Levels", BCP 14, RFC 2119, 335 DOI 10.17487/RFC2119, March 1997, 336 . 338 [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 339 10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November 340 2003, . 342 [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax 343 Specifications: ABNF", STD 68, RFC 5234, 344 DOI 10.17487/RFC5234, January 2008, 345 . 347 [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., 348 Housley, R., and W. Polk, "Internet X.509 Public Key 349 Infrastructure Certificate and Certificate Revocation List 350 (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008, 351 . 353 [RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321, 354 DOI 10.17487/RFC5321, October 2008, 355 . 357 [RFC5890] Klensin, J., "Internationalized Domain Names for 358 Applications (IDNA): Definitions and Document Framework", 359 RFC 5890, DOI 10.17487/RFC5890, August 2010, 360 . 362 [RFC5891] Klensin, J., "Internationalized Domain Names in 363 Applications (IDNA): Protocol", RFC 5891, 364 DOI 10.17487/RFC5891, August 2010, 365 . 367 [RFC6530] Klensin, J. and Y. Ko, "Overview and Framework for 368 Internationalized Email", RFC 6530, DOI 10.17487/RFC6530, 369 February 2012, . 371 [RFC6531] Yao, J. and W. Mao, "SMTP Extension for Internationalized 372 Email", RFC 6531, DOI 10.17487/RFC6531, February 2012, 373 . 375 [RFC6532] Yang, A., Steele, S., and N. Freed, "Internationalized 376 Email Headers", RFC 6532, DOI 10.17487/RFC6532, February 377 2012, . 379 9.2. Informative References 381 [RFC5912] Hoffman, P. and J. Schaad, "New ASN.1 Modules for the 382 Public Key Infrastructure Using X.509 (PKIX)", RFC 5912, 383 DOI 10.17487/RFC5912, June 2010, 384 . 386 Appendix A. ASN.1 Module 388 The following ASN.1 module normatively specifies the SmtpUTF8Name 389 structure. This specification uses the ASN.1 definitions from 390 [RFC5912] with the 2002 ASN.1 notation used in that document. 391 [RFC5912] updates normative documents using older ASN.1 notation. 393 LAMPS-EaiAddresses-2016 394 { iso(1) identified-organization(3) dod(6) 395 internet(1) security(5) mechanisms(5) pkix(7) id-mod(0) 396 id-mod-lamps-eai-addresses-2016(TBD) } 398 DEFINITIONS IMPLICIT TAGS ::= 399 BEGIN 401 IMPORTS 402 OTHER-NAME 403 FROM PKIX1Implicit-2009 404 { iso(1) identified-organization(3) dod(6) internet(1) security(5) 405 mechanisms(5) pkix(7) id-mod(0) id-mod-pkix1-implicit-02(59) } 407 id-pkix 408 FROM PKIX1Explicit-2009 409 { iso(1) identified-organization(3) dod(6) internet(1) security(5) 410 mechanisms(5) pkix(7) id-mod(0) id-mod-pkix1-explicit-02(51) } ; 412 -- 413 -- otherName carries additional name types for subjectAltName, 414 -- issuerAltName, and other uses of GeneralNames. 415 -- 417 id-on OBJECT IDENTIFIER ::= { id-pkix 8 } 419 SmtpUtf8OtherNames OTHER-NAME ::= { on-SmtpUTF8Name, ... } 421 on-SmtpUTF8Name OTHER-NAME ::= { 422 SmtpUTF8Name IDENTIFIED BY id-on-SmtpUTF8Name 423 } 425 id-on-SmtpUTF8Name OBJECT IDENTIFIER ::= { id-on 9 } 427 SmtpUTF8Name ::= UTF8String (SIZE (1..MAX)) 429 END 431 Appendix B. Example of SmtpUTF8Name 433 This non-normative example demonstrates using SmtpUTF8Name as an 434 otherName in GeneralName to encode the email address 435 "u+8001u+5E2B@example.com". 437 The hexadecimal DER encoding of the email address is: 438 A022060A 2B060105 05070012 0809A014 0C12E880 81E5B8AB 40657861 439 6D706C65 2E636F6D 441 The text decoding is: 442 0 34: [0] { 443 2 10: OBJECT IDENTIFIER '1 3 6 1 5 5 7 0 18 8 9' 444 14 20: [0] { 445 16 18: UTF8String '..@example.com' 446 : } 447 : } 449 Figure 2 451 The example was encoded on the OSS Nokalva ASN.1 Playground and the 452 above text decoding is an output of Peter Gutmann's "dumpasn1" 453 program. 455 Appendix C. Acknowledgements 457 Thank you to Magnus Nystrom for motivating this document. Thanks to 458 Russ Housley, Nicolas Lidzborski, Laetitia Baudoin, Ryan Sleevi, Sean 459 Leonard, Sean Turner, John Levine, and Patrik Falstrom for their 460 feedback. Also special thanks to John Klensin for his valuable input 461 on internationalization, Unicode and ABNF formatting, to Jim Schaad 462 for his help with the ASN.1 example and his helpful feedback, and to 463 Viktor Dukhovni for his help with name constraints. 465 Authors' Addresses 467 Alexey Melnikov (editor) 468 Isode Ltd 469 14 Castle Mews 470 Hampton, Middlesex TW12 2NP 471 UK 473 Email: Alexey.Melnikov@isode.com 475 Weihaw Chuang (editor) 476 Google, Inc. 477 1600 Amphitheater Parkway 478 Mountain View, CA 94043 479 US 481 Email: weihaw@google.com