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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 467 Summary: 0 errors (**), 0 flaws (~~), 2 warnings (==), 2 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: March 16, 2018 Google, Inc. 6 September 12, 2017 8 Internationalized Email Addresses in X.509 certificates 9 draft-ietf-lamps-eai-addresses-15 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 https://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 March 16, 2018. 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 (https://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 . . . . . . . . . . . . . . . . . . . . . 8 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 SmtpUTF8Mailbox . . . . . . . . . . . . . 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 defines a new otherName variant to represent 76 Internationalized Email addresses. In addition this document 77 requires all email address domains in X.509 certificates to conform 78 to 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 uses the Augmented Backus-Naur Form (ABNF) 87 [RFC5234] 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 SmtpUTF8Mailbox 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-SmtpUTF8Mailbox OBJECT IDENTIFIER ::= { id-on 9 } 100 SmtpUTF8Mailbox ::= UTF8String (SIZE (1..MAX)) 101 -- SmtpUTF8Mailbox conforms to Mailbox as specified 102 -- in Section 3.3 of RFC 6531. 104 When the subjectAltName (or issuerAltName) extension contains an 105 Internationalized Email address with a non-ASCII local-part, the 106 address MUST be stored in the SmtpUTF8Mailbox name form of otherName. 107 The format of SmtpUTF8Mailbox is defined as the ABNF rule 108 SmtpUTF8Mailbox. SmtpUTF8Mailbox is a modified version of the 109 Internationalized Mailbox which was defined in Section 3.3 of 110 [RFC6531] which was itself derived from SMTP Mailbox from 111 Section 4.1.2 of [RFC5321]. [RFC6531] defines the following ABNF 112 rules for Mailbox whose parts are modified for internationalization: 113 , , , , 114 , and . In particular, was updated to 115 also support UTF8-non-ascii. UTF8-non-ascii was described by 116 Section 3.1 of [RFC6532]. Also, domain was extended to support 117 U-labels, as defined in [RFC5890]. 119 This document further refines Internationalized [RFC6531] Mailbox 120 ABNF rules and calls this SmtpUTF8Mailbox. In SmtpUTF8Mailbox, 121 labels that include non-ASCII characters MUST be stored in U-label 122 (rather than A-label) [RFC5890] form. This restriction removes the 123 need to determine which label encoding A- or U-label is present in 124 the Domain. As per Section 2.3.2.1 of [RFC5890], U-label are encoded 125 as UTF-8 [RFC3629] in Normalization Form C and other properties 126 specified there. In SmtpUTF8Mailbox, domain labels that solely use 127 ASCII characters (meaning not A- nor U-labels) SHALL use NR-LDH 128 restrictions as specified by Section 2.3.1 of [RFC5890] and SHALL be 129 restricted to lower case letters. NR-LDH stands for "Non-Reserved 130 Letters Digits Hyphen" and is the set of LDH labels that do not have 131 "--" characters in the third and forth character position, which 132 excludes "tagged domain names" such as A-labels. Consistent with the 133 treatment of rfc822Name in [RFC5280], SmtpUTF8Mailbox is an envelope 134 and has no phrase (such as a common name) before it, has no 135 comment (text surrounded in parentheses) after it, and is not 136 surrounded by "<" and ">". 138 Due to operational reasons to be described shortly and name 139 constraint compatibility reasons described in Section 6, 140 SmtpUTF8Mailbox subjectAltName MUST only be used when the local-part 141 of the email address contains non-ASCII characters. When the local- 142 part is ASCII, rfc822Name subjectAltName MUST be used instead of 143 SmtpUTF8Mailbox. This is compatible with legacy software that 144 supports only rfc822Name (and not SmtpUTF8Mailbox). The appropriate 145 usage of rfc822Name and SmtpUTF8Mailbox is summarized in Table 1 146 below. 148 SmtpUTF8Mailbox is encoded as UTF8String. The UTF8String encoding 149 MUST NOT contain a Byte-Order- Mark (BOM) [RFC3629] to aid 150 consistency across implementations particularly for comparison. 152 +-----------------+-------------+--------------+-----------------+ 153 | local-part char | domain char | domain label | subjectAltName | 154 +-----------------+-------------+--------------+-----------------+ 155 | ASCII-only | ASCII-only | NR-LDH label | rfc822Name | 156 | non-ASCII | ASCII-only | NR-LDH label | SmtpUTF8Mailbox | 157 | ASCII-only | non-ASCII | A-label | rfc822Name | 158 | non-ASCII | non-ASCII | U-label | SmtpUTF8Mailbox | 159 +-----------------+-------------+--------------+-----------------+ 161 non-ASCII may additionally include ASCII characters. 163 Table 1: Email address formatting 165 4. IDNA2008 167 To facilitate comparison between email addresses, all email address 168 domains in X.509 certificates MUST conform to IDNA2008 [RFC5890] (and 169 avoids any "mappings" mentioned in that document). Use of non- 170 conforming email address domains introduces the possibility of 171 conversion errors between alternate forms. This applies to 172 SmtpUTF8Mailbox and rfc822Name in subjectAltName, issuerAltName and 173 anywhere else that these are used. 175 5. Matching of Internationalized Email Addresses in X.509 certificates 177 In equivalence comparison with SmtpUTF8Mailbox, there may be some 178 setup work on one or both inputs depending of whether the input is 179 already in comparison form. Comparing SmtpUTF8Mailboxs consists of a 180 domain part step and a local-part step. The comparison form for 181 local-parts is always UTF-8. The comparison form for domain parts 182 depends on context. While some contexts such as certificate path 183 validation in [RFC5280] specify transforming domain to A-label 184 (Section 7.5 and 7.2 in [RFC5280] as updated by 185 [ID-lamps-rfc5280-i18n-update]), this document recommends 186 transforming to UTF-8 U-label instead. This reduces the likelihood 187 of errors by reducing conversions as more implementations natively 188 support U-label domains. 190 Comparison of two SmtpUTF8Mailbox is straightforward with no setup 191 work needed. They are considered equivalent if there is an exact 192 octet-for-octet match. Comparison with email addresses such as 193 Internationalized email address or rfc822Name requires additional 194 setup steps for domain part and local-part. The initial preparation 195 for the email addresses is to remove any phrases or comments, as well 196 as "<" and ">" present. This document calls for comparison of domain 197 labels that include non-ASCII characters be transformed to U-label if 198 not already in that form. The first step is to detect use of the 199 A-label by using Section 5.1 of [RFC5891]. Next if necessary, 200 transform any A-labels to U-labels Unicode as specified in 201 Section 5.2 of [RFC5891]. Finally if necessary convert the Unicode 202 to UTF-8 as specified in Section 3 of [RFC3629]. For ASCII NR-LDH 203 labels, upper case letters are converted to lower case letters. In 204 setup for SmtpUTF8Mailbox, the email address local-part MUST conform 205 to the requirements of [RFC6530] and [RFC6531], including being a 206 string in UTF-8 form. In particular, the local-part MUST NOT be 207 transformed in any way, such as by doing case folding or 208 normalization of any kind. The part of an 209 Internationalized email address is already in UTF-8. For rfc822Name 210 the local-part, which is IA5String (ASCII), trivially maps to UTF-8 211 without change. Once setup is complete, they are again compared 212 octet-for-octet. 214 To summarize non-normatively, the comparison steps including setup 215 are: 217 1. If the domain contains A-labels, transform them to U-labels. 219 2. If the domain contains ASCII NR-LDH labels, lowercase them. 221 3. Compare strings octet-for-octet for equivalence. 223 This specification expressly does not define any wildcard characters 224 and SmtpUTF8Mailbox comparison implementations MUST NOT interpret any 225 character as wildcards. Instead, to specify multiple email addresses 226 through SmtpUTF8Mailbox, the certificate MUST use multiple 227 subjectAltNames or issuerAltNames to explicitly carry any additional 228 email addresses. 230 6. Name constraints in path validation 232 This section updates Section 4.2.1.10 of [RFC5280] to extend 233 rfc822Name name constraints to SmtpUTF8Mailbox subjectAltNames. A 234 SmtpUTF8Mailbox aware path validators will apply name constraint 235 comparison to the subject distinguished name and both forms of 236 subject alternative name rfc822Name and SmtpUTF8Mailbox. 238 Both rfc822Name and SmtpUTF8Mailbox subject alternative names 239 represent the same underlying email address namespace. Since legacy 240 CAs constrained to issue certificates for a specific set of domains 241 would lack corresponding UTF-8 constraints, 242 [ID-lamps-rfc5280-i18n-update] updates modifies and extends 243 rfc822Name name constraints defined in [RFC5280] to cover 244 SmtpUTF8Mailbox subject alternative names. This ensures that the 245 introduction of SmtpUTF8Mailbox does not violate existing name 246 constraints. Since it is not valid to include non-ASCII UTF-8 247 characters in the local-part of rfc822Name name constraints, and 248 since name constraints that include a local-part are rarely, if at 249 all, used in practice, name constraints updated in 250 [ID-lamps-rfc5280-i18n-update] admit the forms that represent all 251 addresses at a host or all mailboxes in a domain, and deprecates 252 rfc822Name name constraints that represent a particular mailbox. 253 That is, rfc822Name constraints with a local-part SHOULD NOT be used. 255 Constraint comparison with SmtpUTF8Mailbox subjectAltName starts with 256 the setup steps defined by Section 5. Setup converts the inputs of 257 the comparison which is one of a subject distinguished name or a 258 rfc822Name or SmtpUTF8Mailbox subjectAltName, and one of a rfc822Name 259 name constraint, to constraint comparison form. For rfc822Name name 260 constraint, this will convert any domain A-labels to U-labels. For 261 both the name constraint and the subject, this will lower case any 262 domain NR-LDH labels. Strip the local-part and "@" separator from 263 each rfc822Name and SmtpUTF8Mailbox, leaving just the domain-part. 264 After setup, this follows the comparison steps defined in 4.2.1.10 of 265 [RFC5280] as follows. If the resulting name constraint domain starts 266 with a "." character, then for the name constraint to match, a suffix 267 of the resulting subject alternative name domain MUST match the name 268 constraint (including the leading ".") octet for octet. If the 269 resulting name constraint domain does not start with a "." character, 270 then for the name constraint to match, the entire resulting subject 271 alternative name domain MUST match the name constraint octet for 272 octet. 274 Certificate Authorities that wish to issue CA certificates with email 275 address name constraint MUST use rfc822Name subject alternative names 276 only. These MUST be IDNA2008 conformant names with no mappings, and 277 with non-ASCII domains encoded in A-labels only. 279 The name constraint requirement with SmtpUTF8Mailbox subject 280 alternative name is illustrated in the non-normative diagram 281 Figure 1. The first example (1) illustrates a permitted rfc822Name 282 ASCII only hostname name constraint, and the corresponding valid 283 rfc822Name subjectAltName and SmtpUTF8Mailbox subjectAltName email 284 addresses. The second example (2) illustrates a permitted rfc822Name 285 hostname name constraint with A-label, and the corresponding valid 286 rfc822Name subjectAltName and SmtpUTF8Mailbox subjectAltName email 287 addresses. Note that an email address with ASCII only local-part is 288 encoded as rfc822Name despite also having unicode present in the 289 domain. 291 +-------------------------------------------------------------------+ 292 | Root CA Cert | 293 +-------------------------------------------------------------------+ 294 | 295 v 296 +-------------------------------------------------------------------+ 297 | Intermediate CA Cert | 298 | Permitted | 299 | rfc822Name: elementary.school.example.com (1) | 300 | | 301 | rfc822Name: xn--pss25c.example.com (2) | 302 | | 303 +-------------------------------------------------------------------+ 304 | 305 v 306 +-------------------------------------------------------------------+ 307 | Entity Cert (w/explicitly permitted subjects) | 308 | SubjectAltName Extension | 309 | rfc822Name: student@elemenary.school.example.com (1) | 310 | SmtpUTF8Mailbox: u+5B66u+751F@elementary.school.example.com | 311 | (1) | 312 | | 313 | rfc822Name: student@xn--pss25c.example.com (2) | 314 | SmtpUTF8Mailbox: u+533Bu+751F@u+5927u+5B66.example.com (2) | 315 | | 316 +-------------------------------------------------------------------+ 318 Name constraints with SmtpUTF8Name and rfc822Name 320 Figure 1 322 7. Security Considerations 324 Use of SmtpUTF8Mailbox for certificate subjectAltName (and 325 issuerAltName) will incur many of the same security considerations as 326 in Section 8 in [RFC5280], but introduces a new issue by permitting 327 non-ASCII characters in the email address local-part. This issue, as 328 mentioned in Section 4.4 of [RFC5890] and in Section 4 of [RFC6532], 329 is that use of Unicode introduces the risk of visually similar and 330 identical characters which can be exploited to deceive the recipient. 331 The former document references some means to mitigate against these 332 attacks. 334 8. IANA Considerations 336 In Section 3 and the ASN.1 module identifier defined in Appendix A. 337 IANA is kindly requested to make the following assignments for: 339 The LAMPS-EaiAddresses-2016 ASN.1 module in the "SMI Security for 340 PKIX Module Identifier" registry (1.3.6.1.5.5.7.0). 342 The SmtpUTF8Mailbox otherName in the "PKIX Other Name Forms" 343 registry (1.3.6.1.5.5.7.8). 345 9. References 347 9.1. Normative References 349 [ID-lamps-rfc5280-i18n-update] 350 Housley, R., "Internationalization Updates to RFC 5280", 351 June 2017, . 354 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 355 Requirement Levels", BCP 14, RFC 2119, 356 DOI 10.17487/RFC2119, March 1997, 357 . 359 [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 360 10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November 361 2003, . 363 [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax 364 Specifications: ABNF", STD 68, RFC 5234, 365 DOI 10.17487/RFC5234, January 2008, 366 . 368 [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., 369 Housley, R., and W. Polk, "Internet X.509 Public Key 370 Infrastructure Certificate and Certificate Revocation List 371 (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008, 372 . 374 [RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321, 375 DOI 10.17487/RFC5321, October 2008, 376 . 378 [RFC5890] Klensin, J., "Internationalized Domain Names for 379 Applications (IDNA): Definitions and Document Framework", 380 RFC 5890, DOI 10.17487/RFC5890, August 2010, 381 . 383 [RFC5891] Klensin, J., "Internationalized Domain Names in 384 Applications (IDNA): Protocol", RFC 5891, 385 DOI 10.17487/RFC5891, August 2010, 386 . 388 [RFC6530] Klensin, J. and Y. Ko, "Overview and Framework for 389 Internationalized Email", RFC 6530, DOI 10.17487/RFC6530, 390 February 2012, . 392 [RFC6531] Yao, J. and W. Mao, "SMTP Extension for Internationalized 393 Email", RFC 6531, DOI 10.17487/RFC6531, February 2012, 394 . 396 [RFC6532] Yang, A., Steele, S., and N. Freed, "Internationalized 397 Email Headers", RFC 6532, DOI 10.17487/RFC6532, February 398 2012, . 400 9.2. Informative References 402 [RFC5912] Hoffman, P. and J. Schaad, "New ASN.1 Modules for the 403 Public Key Infrastructure Using X.509 (PKIX)", RFC 5912, 404 DOI 10.17487/RFC5912, June 2010, 405 . 407 Appendix A. ASN.1 Module 409 The following ASN.1 module normatively specifies the SmtpUTF8Mailbox 410 structure. This specification uses the ASN.1 definitions from 411 [RFC5912] with the 2002 ASN.1 notation used in that document. 412 [RFC5912] updates normative documents using older ASN.1 notation. 414 LAMPS-EaiAddresses-2016 415 { iso(1) identified-organization(3) dod(6) 416 internet(1) security(5) mechanisms(5) pkix(7) id-mod(0) 417 id-mod-lamps-eai-addresses-2016(TBD) } 419 DEFINITIONS IMPLICIT TAGS ::= 420 BEGIN 422 IMPORTS 423 OTHER-NAME 424 FROM PKIX1Implicit-2009 425 { iso(1) identified-organization(3) dod(6) internet(1) security(5) 426 mechanisms(5) pkix(7) id-mod(0) id-mod-pkix1-implicit-02(59) } 428 id-pkix 429 FROM PKIX1Explicit-2009 430 { iso(1) identified-organization(3) dod(6) internet(1) security(5) 431 mechanisms(5) pkix(7) id-mod(0) id-mod-pkix1-explicit-02(51) } ; 433 -- 434 -- otherName carries additional name types for subjectAltName, 435 -- issuerAltName, and other uses of GeneralNames. 436 -- 438 id-on OBJECT IDENTIFIER ::= { id-pkix 8 } 440 SmtpUtf8OtherNames OTHER-NAME ::= { on-SmtpUTF8Mailbox, ... } 442 on-SmtpUTF8Mailbox OTHER-NAME ::= { 443 SmtpUTF8Mailbox IDENTIFIED BY id-on-SmtpUTF8Mailbox 444 } 446 id-on-SmtpUTF8Mailbox OBJECT IDENTIFIER ::= { id-on 9 } 448 SmtpUTF8Mailbox ::= UTF8String (SIZE (1..MAX)) 449 -- SmtpUTF8Mailbox conforms to Mailbox as specified 450 -- in Section 3.3 of RFC 6531. 452 END 454 Appendix B. Example of SmtpUTF8Mailbox 456 This non-normative example demonstrates using SmtpUTF8Mailbox as an 457 otherName in GeneralName to encode the email address 458 "u+8001u+5E2B@example.com". 460 The hexadecimal DER encoding of the email address is: 461 A022060A 2B060105 05070012 0809A014 0C12E880 81E5B8AB 40657861 462 6D706C65 2E636F6D 464 The text decoding is: 465 0 34: [0] { 466 2 10: OBJECT IDENTIFIER '1 3 6 1 5 5 7 0 18 8 9' 467 14 20: [0] { 468 16 18: UTF8String '..@example.com' 469 : } 470 : } 472 Figure 2 474 The example was encoded on the OSS Nokalva ASN.1 Playground and the 475 above text decoding is an output of Peter Gutmann's "dumpasn1" 476 program. 478 Appendix C. Acknowledgements 480 Thank you to Magnus Nystrom for motivating this document. Thanks to 481 Russ Housley, Nicolas Lidzborski, Laetitia Baudoin, Ryan Sleevi, Sean 482 Leonard, Sean Turner, John Levine, and Patrik Falstrom for their 483 feedback. Also special thanks to John Klensin for his valuable input 484 on internationalization, Unicode and ABNF formatting, to Jim Schaad 485 for his help with the ASN.1 example and his helpful feedback, and 486 especially to Viktor Dukhovni for helping us with name constraints 487 and his many detailed document reviews. 489 Authors' Addresses 491 Alexey Melnikov (editor) 492 Isode Ltd 493 14 Castle Mews 494 Hampton, Middlesex TW12 2NP 495 UK 497 Email: Alexey.Melnikov@isode.com 499 Weihaw Chuang (editor) 500 Google, Inc. 501 1600 Amphitheater Parkway 502 Mountain View, CA 94043 503 US 505 Email: weihaw@google.com