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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 446 -- 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: March 3, 2018 Google, Inc. 6 August 30, 2017 8 Internationalized Email Addresses in X.509 certificates 9 draft-ietf-lamps-eai-addresses-13 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 March 3, 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 (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 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 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)) 101 -- SmtpUTF8Name 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 SmtpUTF8Name name form of otherName. 107 The format of SmtpUTF8Name 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], SmtpUTF8Name 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, SmtpUTF8Name 140 subjectAltName MUST only be used when the local part of the email 141 address contains contains non-ASCII characters. When the local-part 142 is ASCII, rfc822Name subjectAltName MUST be used instead of 143 SmtpUTF8Name. This is compatible with legacy software that supports 144 only rfc822Name (and not SmtpUTF8Name). 146 SmtpUTF8Name is encoded as UTF8String. The UTF8String encoding MUST 147 NOT contain a Byte-Order- Mark (BOM) [RFC3629] to aid consistency 148 across implementations particularly for comparison. 150 4. IDNA2008 152 To facilitate comparison between email addresses, all email address 153 domains in X.509 certificates MUST conform to IDNA2008 [RFC5890] (and 154 avoids any "mappings" mentioned in that document). Use of non- 155 conforming email address domains introduces the possibility of 156 conversion errors between alternate forms. This applies to 157 SmtpUTF8Name and rfc822Name in subjectAltName, issuerAltName and 158 anywhere else that these are used. 160 5. Matching of Internationalized Email Addresses in X.509 certificates 162 In equivalence comparison with SmtpUTF8Name, there may be some setup 163 work on one or both inputs depending of whether the input is already 164 in comparison form. Comparing SmtpUTF8Names consists of a domain 165 part step and a local-part step. The comparison form for local-parts 166 is always UTF-8. The comparison form for domain parts depends on 167 context. While some contexts such as certificate path validation in 168 [RFC5280] specify transforming domain to A-label (Section 7.5 and 7.2 169 in [RFC5280] as updated by [ID-lamps-rfc5280-i18n-update]), this 170 document RECOMMENDS transforming to UTF-8 U-label instead. This 171 reduces the likelihood of errors by reducing conversions as more 172 implementations natively support U-label domains. 174 Comparison of two SmtpUTF8Name is straightforward with no setup work 175 needed. They are considered equivalent if there is an exact octet- 176 for-octet match. Comparison with email addresses such as 177 Internationalized email address or rfc822Name requires additional 178 setup steps for domain part and local-part. The initial preparation 179 for the email addresses is to remove any phrases or comments, as well 180 as "<" and ">" present. This document calls for comparison of domain 181 labels that include non-ASCII characters be transformed to U-label if 182 not already in that form. The first step is to detect use of the 183 A-label by using Section 5.1 of [RFC5891]. Next if necessary, 184 transform any A-labels to U-labels Unicode as specified in 185 Section 5.2 of [RFC5891]. Finally if necessary convert the Unicode 186 to UTF-8 as specified in Section 3 of [RFC3629]. For ASCII NR-LDH 187 labels, upper case letters are converted to lower case letters. In 188 setup for SmtpUTF8Mailbox, the email address local-part MUST conform 189 to the requirements of [RFC6530] and [RFC6531], including being a 190 string in UTF-8 form. In particular, the local-part MUST NOT be 191 transformed in any way, such as by doing case folding or 192 normalization of any kind. The part of an 193 Internationalized email address is already in UTF-8. For rfc822Name 194 the local-part, which is IA5String (ASCII), trivially maps to UTF-8 195 without change. Once setup is complete, they are again compared 196 octet-for-octet. 198 To summarize non-normatively, the comparison steps including setup 199 are: 201 1. If the domain contains A-labels, transform them to U-labels. 203 2. If the domain contains ASCII NR-LDH labels, lowercase them. 205 3. Compare strings octet-for-octet for equivalence. 207 This specification expressly does not define any wildcard characters 208 and SmtpUTF8Name comparison implementations MUST NOT interpret any 209 character as wildcards. Instead, to specify multiple email addresses 210 through SmtpUTF8Name, the certificate MUST use multiple 211 subjectAltNames or issuerAltNames to explicitly carry any additional 212 email addresses. 214 6. Name constraints in path validation 216 This section updates Section 4.2.1.10 of [RFC5280] to extend 217 rfc822Name name constraints to SmtpUTF8Name subjectAltNames. A 218 SmtpUTF8Name aware path validators will apply name constraint 219 comparison to the subject distinguished name and both forms of 220 subject alternative name rfc822Name and SmtpUTF8Name. 222 Both rfc822Name and SmtpUTF8Name subject alternative names represent 223 the same underlying email address namespace. Since legacy CAs 224 constrained to issue certificates for a specific set of domains would 225 lack corresponding UTF-8 constraints, [ID-lamps-rfc5280-i18n-update] 226 updates modifies and extends rfc822Name name constraints defined in 227 [RFC5280] to cover SmtpUTF8Name subject alternative names. This 228 ensures that the introduction of SmtpUTF8Name does not violate 229 existing name constraints. Since it is not valid to include non- 230 ASCII UTF-8 characters in the local-part of rfc822Name name 231 constraints, and since name constraints that include a local-part are 232 rarely, if at all, used in practice, name constraints updated in 233 [ID-lamps-rfc5280-i18n-update] admit the forms that represent all 234 addresses at a host or all mailboxes in a domain, and deprecates 235 rfc822Name name constraints that represent a particular mailbox. 236 That is, rfc822Name constraints with a local-part SHOULD NOT be used. 238 Constraint comparison with SmtpUTF8Name subjectAltName starts with 239 the setup steps defined by Section 5. Setup converts the inputs of 240 the comparison which is one of a subject distinguished name or a 241 rfc822Name or SmtpUTF8Name subjectAltName, and one of a rfc822Name 242 name constraint, to constraint comparison form. For rfc822Name name 243 constraint, this will convert any domain A-labels to U-labels. For 244 both the name constraint and the subject, this will lower case any 245 domain NR-LDH labels. Strip the local-part and "@" separator from 246 each rfc822Name and SmtpUTF8Name, leaving just the domain-part. 247 After setup, this follows the comparison steps defined in 4.2.1.10 of 248 [RFC5280] as follows. If the resulting name constraint domain starts 249 with a "." character, then for the name constraint to match, a suffix 250 of the resulting subject alternative name domain MUST match the name 251 constraint (including the leading ".") octet for octet. If the 252 resulting name constraint domain does not start with a "." character, 253 then for the name constraint to match, the entire resulting subject 254 alternative name domain MUST match the name constraint octet for 255 octet. 257 Certificate Authorities that wish to issue CA certificates with email 258 address name constraint MUST use rfc822Name subject alternative names 259 only. These MUST be IDNA2008 conformant names with no mappings, and 260 with non-ASCII domains encoded in A-labels only. 262 The name constraint requirement with SmtpUTF8Name subject alternative 263 name is illustrated in the non-normative diagram Figure 1. The first 264 example (1) illustrates a permitted rfc822Name ASCII only hostname 265 name constraint, and the corresponding valid rfc822Name 266 subjectAltName and SmtpUTF8Name subjectAltName email addresses. The 267 second example (2) illustrates a permitted rfc822Name hostname name 268 constraint with A-label, and the corresponding valid rfc822Name 269 subjectAltName and SmtpUTF8Name subjectAltName email addresses. Note 270 that an email address with ASCII only local-part is encoded as 271 rfc822Name despite also having unicode present in the domain. 273 +-------------------------------------------------------------------+ 274 | Root CA Cert | 275 +-------------------------------------------------------------------+ 276 | 277 v 278 +-------------------------------------------------------------------+ 279 | Intermediate CA Cert | 280 | Permitted | 281 | rfc822Name: elementary.school.example.com (1) | 282 | | 283 | rfc822Name: xn--pss25c.example.com (2) | 284 | | 285 +-------------------------------------------------------------------+ 286 | 287 v 288 +-------------------------------------------------------------------+ 289 | Entity Cert (w/explicitly permitted subjects) | 290 | SubjectAltName Extension | 291 | rfc822Name: student@elemenary.school.example.com (1) | 292 | SmtpUTF8Name: u+5B66u+751F@elementary.school.example.com (1) | 293 | | 294 | rfc822Name: student@xn--pss25c.example.com (2) | 295 | SmtpUTF8Name: u+533Bu+751F@u+5927u+5B66.example.com (2) | 296 | | 297 +-------------------------------------------------------------------+ 299 Name constraints with SmtpUTF8Name and rfc822Name 301 Figure 1 303 7. Security Considerations 305 Use of SmtpUTF8Name for certificate subjectAltName (and 306 issuerAltName) will incur many of the same security considerations as 307 in Section 8 in [RFC5280], but introduces a new issue by permitting 308 non-ASCII characters in the email address local-part. This issue, as 309 mentioned in Section 4.4 of [RFC5890] and in Section 4 of [RFC6532], 310 is that use of Unicode introduces the risk of visually similar and 311 identical characters which can be exploited to deceive the recipient. 312 The former document references some means to mitigate against these 313 attacks. 315 8. IANA Considerations 317 In Section 3 and the ASN.1 module identifier defined in Appendix A. 318 IANA is kindly requested to make the following assignments for: 320 The LAMPS-EaiAddresses-2016 ASN.1 module in the "SMI Security for 321 PKIX Module Identifier" registry (1.3.6.1.5.5.7.0). 323 The SmtpUTF8Name otherName in the "PKIX Other Name Forms" registry 324 (1.3.6.1.5.5.7.8). 326 9. References 328 9.1. Normative References 330 [ID-lamps-rfc5280-i18n-update] 331 Housley, R., "Internationalization Updates to RFC 5280", 332 June 2017, . 335 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 336 Requirement Levels", BCP 14, RFC 2119, 337 DOI 10.17487/RFC2119, March 1997, . 340 [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 341 10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November 342 2003, . 344 [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax 345 Specifications: ABNF", STD 68, RFC 5234, 346 DOI 10.17487/RFC5234, January 2008, . 349 [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., 350 Housley, R., and W. Polk, "Internet X.509 Public Key 351 Infrastructure Certificate and Certificate Revocation List 352 (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008, 353 . 355 [RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321, 356 DOI 10.17487/RFC5321, October 2008, . 359 [RFC5890] Klensin, J., "Internationalized Domain Names for 360 Applications (IDNA): Definitions and Document Framework", 361 RFC 5890, DOI 10.17487/RFC5890, August 2010, 362 . 364 [RFC5891] Klensin, J., "Internationalized Domain Names in 365 Applications (IDNA): Protocol", RFC 5891, 366 DOI 10.17487/RFC5891, August 2010, . 369 [RFC6530] Klensin, J. and Y. Ko, "Overview and Framework for 370 Internationalized Email", RFC 6530, DOI 10.17487/RFC6530, 371 February 2012, . 373 [RFC6531] Yao, J. and W. Mao, "SMTP Extension for Internationalized 374 Email", RFC 6531, DOI 10.17487/RFC6531, February 2012, 375 . 377 [RFC6532] Yang, A., Steele, S., and N. Freed, "Internationalized 378 Email Headers", RFC 6532, DOI 10.17487/RFC6532, February 379 2012, . 381 9.2. Informative References 383 [RFC5912] Hoffman, P. and J. Schaad, "New ASN.1 Modules for the 384 Public Key Infrastructure Using X.509 (PKIX)", RFC 5912, 385 DOI 10.17487/RFC5912, June 2010, . 388 Appendix A. ASN.1 Module 390 The following ASN.1 module normatively specifies the SmtpUTF8Name 391 structure. This specification uses the ASN.1 definitions from 392 [RFC5912] with the 2002 ASN.1 notation used in that document. 393 [RFC5912] updates normative documents using older ASN.1 notation. 395 LAMPS-EaiAddresses-2016 396 { iso(1) identified-organization(3) dod(6) 397 internet(1) security(5) mechanisms(5) pkix(7) id-mod(0) 398 id-mod-lamps-eai-addresses-2016(TBD) } 400 DEFINITIONS IMPLICIT TAGS ::= 401 BEGIN 403 IMPORTS 404 OTHER-NAME 405 FROM PKIX1Implicit-2009 406 { iso(1) identified-organization(3) dod(6) internet(1) security(5) 407 mechanisms(5) pkix(7) id-mod(0) id-mod-pkix1-implicit-02(59) } 409 id-pkix 410 FROM PKIX1Explicit-2009 411 { iso(1) identified-organization(3) dod(6) internet(1) security(5) 412 mechanisms(5) pkix(7) id-mod(0) id-mod-pkix1-explicit-02(51) } ; 414 -- 415 -- otherName carries additional name types for subjectAltName, 416 -- issuerAltName, and other uses of GeneralNames. 417 -- 419 id-on OBJECT IDENTIFIER ::= { id-pkix 8 } 421 SmtpUtf8OtherNames OTHER-NAME ::= { on-SmtpUTF8Name, ... } 423 on-SmtpUTF8Name OTHER-NAME ::= { 424 SmtpUTF8Name IDENTIFIED BY id-on-SmtpUTF8Name 425 } 427 id-on-SmtpUTF8Name OBJECT IDENTIFIER ::= { id-on 9 } 429 SmtpUTF8Name ::= UTF8String (SIZE (1..MAX)) 431 END 433 Appendix B. Example of SmtpUTF8Name 435 This non-normative example demonstrates using SmtpUTF8Name as an 436 otherName in GeneralName to encode the email address 437 "u+8001u+5E2B@example.com". 439 The hexadecimal DER encoding of the email address is: 440 A022060A 2B060105 05070012 0809A014 0C12E880 81E5B8AB 40657861 441 6D706C65 2E636F6D 443 The text decoding is: 444 0 34: [0] { 445 2 10: OBJECT IDENTIFIER '1 3 6 1 5 5 7 0 18 8 9' 446 14 20: [0] { 447 16 18: UTF8String '..@example.com' 448 : } 449 : } 451 Figure 2 453 The example was encoded on the OSS Nokalva ASN.1 Playground and the 454 above text decoding is an output of Peter Gutmann's "dumpasn1" 455 program. 457 Appendix C. Acknowledgements 459 Thank you to Magnus Nystrom for motivating this document. Thanks to 460 Russ Housley, Nicolas Lidzborski, Laetitia Baudoin, Ryan Sleevi, Sean 461 Leonard, Sean Turner, John Levine, and Patrik Falstrom for their 462 feedback. Also special thanks to John Klensin for his valuable input 463 on internationalization, Unicode and ABNF formatting, to Jim Schaad 464 for his help with the ASN.1 example and his helpful feedback, and to 465 Viktor Dukhovni for his help with name constraints. 467 Authors' Addresses 469 Alexey Melnikov (editor) 470 Isode Ltd 471 14 Castle Mews 472 Hampton, Middlesex TW12 2NP 473 UK 475 Email: Alexey.Melnikov@isode.com 477 Weihaw Chuang (editor) 478 Google, Inc. 479 1600 Amphitheater Parkway 480 Mountain View, CA 94043 481 US 483 Email: weihaw@google.com