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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) ** Downref: Normative reference to an Informational RFC: RFC 5912 Summary: 2 errors (**), 0 flaws (~~), 1 warning (==), 1 comment (--). 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: May 4, 2017 Google, Inc. 6 October 31, 2016 8 Internationalized Email Addresses in X.509 certificates 9 draft-ietf-lamps-eai-addresses-02 11 Abstract 13 This document defines a new name form for inclusion in the otherName 14 field of an X.509 Subject Alternative Name extension that allows a 15 certificate subject to be associated with an Internationalized Email 16 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 May 4, 2017. 35 Copyright Notice 37 Copyright (c) 2016 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. Matching of Internationalized Email Addresses in X.509 56 certificates . . . . . . . . . . . . . . . . . . . . . . . . 3 57 5. Name constraints in path validation . . . . . . . . . . . . . 4 58 6. Resource Considerations . . . . . . . . . . . . . . . . . . . 6 59 7. Security Considerations . . . . . . . . . . . . . . . . . . . 6 60 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 61 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 62 9.1. Normative References . . . . . . . . . . . . . . . . . . 7 63 9.2. Informative References . . . . . . . . . . . . . . . . . 8 64 Appendix A. ASN.1 Module . . . . . . . . . . . . . . . . . . . . 8 65 Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 9 66 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 68 1. Introduction 70 [RFC5280] defines rfc822Name subjectAltName choice for representing 71 [RFC5322] email addresses. This form is restricted to a subset of 72 US-ASCII characters and thus can't be used to represent 73 Internationalized Email addresses [RFC6531]. To fascilitate use of 74 these Internationalized Email addresses with X.509 certificates, this 75 document specifies a new name form in otherName so that 76 subjectAltName and issuerAltName can carry them. 78 2. Conventions Used in This Document 80 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 81 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 82 document are to be interpreted as described in [RFC2119]. 84 The formal syntax use the Augmented Backus-Naur Form (ABNF) [RFC5234] 85 notation. 87 3. Name Definitions 89 The GeneralName structure is defined in [RFC5280], and supports many 90 different names forms including otherName for extensibility. This 91 section specifies the smtputf8Name name form of otherName, so that 92 Internationalized Email addresses can appear in the subjectAltName of 93 a certificate, the issuerAltName of a certificate, or anywhere else 94 that GeneralName is used. 96 id-on-smtputf8Name OBJECT IDENTIFIER ::= { id-on TBD } 97 Smtputf8Name ::= UTF8String (SIZE (1..MAX)) 99 When the subjectAltName (or issuerAltName) extension contains an 100 Internationalized Email address, the address MUST be stored in the 101 smtputf8Name name form of otherName. The format of smtputf8Name is 102 defined as the ABNF rule smtputf8Mailbox. smtputf8Mailbox is a 103 modified version of the Internationalized Mailbox which is defined in 104 Section 3.3 of [RFC6531] which is itself derived from SMTP Mailbox 105 from Section 4.1.2 of [RFC5321]. [RFC6531] defines the following 106 ABNF rules for Mailbox whose parts are modified for 107 internationalization: , , , 108 , , and . In particular was 109 updated to also support UTF8-non-ascii. UTF8-non-ascii is described 110 by Section 3.1 of [RFC6532]. Also sub-domain is extended to support 111 U-label, as defined in [RFC5890] 113 This document further refines Internationalized [RFC6531] Mailbox 114 ABNF rules and calls this smtputf8Mailbox. In smtputf8Mailbox, sub- 115 domain that encode non-ascii characters SHALL use U-label Unicode 116 native character labels and MUST NOT use A-label [RFC5890]. This 117 restriction prevents having to determine which label encoding A- or 118 U-label is present in the Domain. As per Section 2.3.2.1 of 119 [RFC5890], U-label use UTF-8 [RFC3629] with Normalization Form C and 120 other properties specified there. In smtputf8Mailbox, sub-domain 121 that encode solely ASCII character labels SHALL use NR-LDH 122 restrictions as specified by section 2.3.1 of [RFC5890]. Note that a 123 smtputf8Mailbox has no phrase (such as a common name) before it, has 124 no comment (text surrounded in parentheses) after it, and is not 125 surrounded by "<" and ">". 127 In the context of building name constraint as needed by [RFC5280], 128 the smtputf8Mailbox rules are modified to allow partial productions 129 to allow for additional forms required by Section 5. Name 130 constraints may specify a complete email address, host name, or 131 domain. This means that the local-part may be missing, and domain 132 partially specified. 134 smtputf8Name is encoded as UTF8String. The UTF8String encoding MUST 135 NOT contain a Byte-Order-Mark (BOM) [RFC3629] to aid consistency 136 across implementations particularly for comparison. 138 4. Matching of Internationalized Email Addresses in X.509 certificates 140 In equivalence comparison with smtputf8Name, there may be some setup 141 work to enable the comparison i.e. processing of the smtputf8Name 142 content or the email address that is being compared against. The 143 process for setup for comparing with smtputf8Name is split into 144 domain steps and local-part steps. The comparison form for local- 145 part always is UTF-8. The comparison form for domain depends on 146 context. While some contexts such as certificate path validation in 147 [RFC5280] specify transforming to A-label, this document RECOMMENDS 148 transforming to UTF-8 U-label even in place of those other 149 specifications. As more implementations natively support U-label 150 domain, requiring U-label reduces conversions required, which then 151 reduces likelihood of errors caused by bugs in implementation. 153 Comparison of two smtputf8Name can be straightforward. No setup work 154 is needed and it can be an octet for octet comparison. For other 155 email address forms such as Internationalized email address or 156 rfc822Name, the comparison requires additional setup to convert the 157 format for comparison. Domain setup is particularly important for 158 forms that may contain A- or U-label such as International email 159 address, or A-label only forms such as rfc822Name. This document 160 specifies the process to transform the domain to U-label. (To 161 convert the domain to A-label, follow the process process specified 162 in section 7.5 and 7.2 in [RFC5280]) The first step is to detect 163 A-label by using section 5.1 of [RFC5891]. Next if necessary, 164 transform the A-label to U-label Unicode as specified in section 5.2 165 of [RFC5891]. Finally if necessary convert the Unicode to UTF-8 as 166 specified in section 3 of [RFC3629]. In setup for smtputf8Mailbox, 167 the email address local-part MUST be converted to UTF-8 if it is not 168 already. The part of an Internationalized email address 169 is already in UTF-8. For the rfc822Name local-part is IA5String 170 (ASCII), and conversion to UTF-8 is trivial since ASCII octets maps 171 to UTF-8 without change. Once the setup is completed, comparison is 172 an octet for octet comparison. 174 This specification expressly does not define any wildcards characters 175 and smtputf8Name comparison implementations MUST NOT interpret any 176 character as wildcards. Instead, to specify multiple specifying 177 multiple email addresses through smtputf8Name, the certificate should 178 use multiple subjectAltNames or issuerAltNames to explicitly carry 179 those email addresses. 181 5. Name constraints in path validation 183 This section defines use of smtputf8Name name for name constraints. 184 The format for smtputf8Name in name constraints is identical to the 185 use in subjectAltName as specified in Section 3 with the extension as 186 noted there for partial productions. 188 Constraint comparison on complete email address with smtputf8Name 189 name uses the matching procedure defined by Section 4. As with 190 rfc822Name name constraints as specified in Section 4.2.1.10 of 191 [RFC5280], smtputf8Name name can specify a particular mailbox, all 192 addresses at a host, or all mailboxes in a domain by specifying the 193 complete email address, a host name, or a domain. 195 Name constraint comparisons in the context [RFC5280] is specified 196 with smtputf8Name name are only done on the subjectAltName (and 197 issuerAltName) smtputf8Name name, and says nothing more about 198 constaints on other email address forms such as rfc822Name. 199 Consequently it may be necessary to include other name constraints 200 such as rfc822Name in addition to smtputf8Name to constrain all 201 potential email addresses. For example a domain with both ascii and 202 non-ascii local-part email addresses may require both rfc822Name and 203 smtputf8Name name constraints. This can be illustrated in the 204 following non-normative diagram Figure 1 which shows a name 205 constraint set in the intermediate CA certificate, which then applies 206 to the children entity certificates. Note that a constraint on 207 rfc822Name does not apply to smtputf8Name and vice versa. 209 +------------------------------------------------------+ 210 | Root CA Cert | 211 +------------------------------------------------------+ 212 | 213 v 214 +------------------------------------------------------+ 215 | Intermediate CA Cert | 216 | Name Constraint Extension | 217 | Permitted | 218 | rfc822Name: allowed.example.com | 219 | smtputf8Name: allowed.example.com | 220 | Excluded | 221 | rfc822Name: ignored.example.com | 222 +------------------------------------------------------+ 223 | | 224 v | 225 +------------------------------------------------------+ 226 | Entity Cert (w/explicitly permitted subjects) | 227 | SubjectAltName Extension | 228 | rfc822Name: student@allowed.example.com | 229 | smtputf8Name: \u8001\u5E2B@allowed.example.com | 230 +------------------------------------------------------+ 231 | 232 v 233 +------------------------------------------------------+ 234 | Entity Cert (w/permitted subject- excluded | 235 | rfc822Name does not exclude smtputf8Name) | 236 | SubjectAltName Extension | 237 | smtputf8Name: \u4E0D\u5C0D@ignored.example.com | 238 +------------------------------------------------------+ 240 Figure 1 242 6. Resource Considerations 244 For email addresses whose local-part is ASCII it may be more 245 reasonable to continue using rfc822Name instead of smtputf8Name. Use 246 of smtputf8Name incurs higher byte representation overhead due to 247 encoding with otherName and the additional OID needed. This document 248 RECOMMENDS using smtputf8Name when local-part contains non-ASCII 249 characters, and otherwise rfc822Name. 251 7. Security Considerations 253 Use for smtputf8Name for certificate subjectAltName (and 254 issuerAltName) will incur many of the same security considerations of 255 Section 8 in [RFC5280] but further complicated by permitting non- 256 ASCII characters in the email address local-part. As mentioned in 257 Section 4.4 of [RFC5890] and in Section 4 of [RFC6532] Unicode 258 introduces the risk for visually similar characters which can be 259 exploited to deceive the recipient. The former document references 260 some means to mitigate against these attacks. 262 8. IANA Considerations 264 This document makes use of object identifiers for the smtputf8Name 265 defined in Section Section 3 and the ASN.1 module identifier defined 266 in Section Appendix A. IANA is kindly requested to make the 267 following assignments for: 269 The LAMPS-EaiAddresses-2016 ASN.1 module in the "SMI Security for 270 PKIX Module Identifier" registry (1.3.6.1.5.5.7.0). 272 The smtputf8Name otherName in the "PKIX Other Name Forms" registry 273 (1.3.6.1.5.5.7.8). 275 9. References 277 9.1. Normative References 279 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 280 Requirement Levels", BCP 14, RFC 2119, 281 DOI 10.17487/RFC2119, March 1997, 282 . 284 [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 285 10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November 286 2003, . 288 [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax 289 Specifications: ABNF", STD 68, RFC 5234, 290 DOI 10.17487/RFC5234, January 2008, 291 . 293 [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., 294 Housley, R., and W. Polk, "Internet X.509 Public Key 295 Infrastructure Certificate and Certificate Revocation List 296 (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008, 297 . 299 [RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321, 300 DOI 10.17487/RFC5321, October 2008, 301 . 303 [RFC5890] Klensin, J., "Internationalized Domain Names for 304 Applications (IDNA): Definitions and Document Framework", 305 RFC 5890, DOI 10.17487/RFC5890, August 2010, 306 . 308 [RFC5891] Klensin, J., "Internationalized Domain Names in 309 Applications (IDNA): Protocol", RFC 5891, 310 DOI 10.17487/RFC5891, August 2010, 311 . 313 [RFC5912] Hoffman, P. and J. Schaad, "New ASN.1 Modules for the 314 Public Key Infrastructure Using X.509 (PKIX)", RFC 5912, 315 DOI 10.17487/RFC5912, June 2010, 316 . 318 [RFC6531] Yao, J. and W. Mao, "SMTP Extension for Internationalized 319 Email", RFC 6531, DOI 10.17487/RFC6531, February 2012, 320 . 322 [RFC6532] Yang, A., Steele, S., and N. Freed, "Internationalized 323 Email Headers", RFC 6532, DOI 10.17487/RFC6532, February 324 2012, . 326 9.2. Informative References 328 [RFC5322] Resnick, P., Ed., "Internet Message Format", RFC 5322, 329 DOI 10.17487/RFC5322, October 2008, 330 . 332 Appendix A. ASN.1 Module 334 The following ASN.1 module normatively specifies the Smtputf8Name 335 structure. This specification uses the ASN.1 definitions from 336 [RFC5912] with the 2002 ASN.1 notation used in that document. 338 LAMPS-EaiAddresses-2016 339 { iso(1) identified-organization(3) dod(6) 340 internet(1) security(5) mechanisms(5) pkix(7) id-mod(0) 341 id-mod-lamps-eai-addresses-2016(TBD) } 343 DEFINITIONS IMPLICIT TAGS ::= 344 BEGIN 346 IMPORTS 348 id-pkix OBJECT IDENTIFIER ::= 349 {iso(1) identified-organization(3) dod(6) internet(1) security(5) 350 mechanisms(5) pkix(7)} 352 -- 353 -- otherName carries additional name types for subjectAltName, issuerAltName, 354 -- and other uses of GeneralNames. 355 -- 357 id-on OBJECT IDENTIFIER ::= { id-pkix 8 } 359 SmtpUtf8OtherNames OTHER-NAME ::= { on-smtputf8Name, ... } 361 on-smtputf8Name OTHER-NAME ::= { 362 SmtpUtf8Name IDENTIFIED BY id-on-smtputf8Name 363 } 365 id-on-smtputf8Name OBJECT IDENTIFIER ::= { id-on TBD } 367 SmtpUtf8Name ::= UTF8String (SIZE (1..MAX)) 369 END 371 Figure 2 373 Appendix B. Acknowledgements 375 Thank you to Magnus Nystrom for motivating this document. Thanks to 376 Russ Housley, Nicolas Lidzborski, Laetitia Baudoin, Ryan Sleevi, Sean 377 Leonard, Sean Turner, and Jim Schaad for their feedback. Also thanks 378 to John Klensin for his valuable input on internationalization, 379 Unicode and ABNF formatting. 381 Authors' Addresses 382 Alexey Melnikov (editor) 383 Isode Ltd 384 14 Castle Mews 385 Hampton, Middlesex TW12 2NP 386 UK 388 Email: Alexey.Melnikov@isode.com 390 Weihaw Chuang (editor) 391 Google, Inc. 392 1600 Amphitheatre Parkway 393 Mountain View, CA 94043 394 US 396 Email: weihaw@google.com