idnits 2.17.1 draft-ietf-lamps-eai-addresses-07.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (March 8, 2017) is 2606 days in the past. 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 479 Summary: 0 errors (**), 0 flaws (~~), 1 warning (==), 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: September 9, 2017 Google, Inc. 6 March 8, 2017 8 Internationalized Email Addresses in X.509 certificates 9 draft-ietf-lamps-eai-addresses-07 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 Alternate Name 15 extension that allows a certificate subject to be associated with an 16 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 September 9, 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. Deployment Considerations . . . . . . . . . . . . . . . . . . 8 60 8. Security Considerations . . . . . . . . . . . . . . . . . . . 8 61 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 62 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 63 10.1. Normative References . . . . . . . . . . . . . . . . . . 9 64 10.2. Informative References . . . . . . . . . . . . . . . . . 10 65 Appendix A. ASN.1 Module . . . . . . . . . . . . . . . . . . . . 10 66 Appendix B. Example of SmtpUTF8Name . . . . . . . . . . . . . . 11 67 Appendix C. Acknowledgements . . . . . . . . . . . . . . . . . . 12 68 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12 70 1. Introduction 72 [RFC5280] defines rfc822Name subjectAltName choice for representing 73 [RFC5321] email addresses. This form is restricted to a subset of 74 US-ASCII characters and thus can't be used to represent 75 Internationalized Email addresses [RFC6531]. To facilitate use of 76 these Internationalized Email addresses with X.509 certificates, this 77 document specifies a new name form in otherName so that 78 subjectAltName and issuerAltName can carry them. In addition this 79 document calls for all email address domain in X.509 certificates to 80 conform to IDNA2008 [RFC5890]. 82 2. Conventions Used in This Document 84 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 85 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 86 document are to be interpreted as described in [RFC2119]. 88 The formal syntax use the Augmented Backus-Naur Form (ABNF) [RFC5234] 89 notation. 91 3. Name Definitions 93 The GeneralName structure is defined in [RFC5280], and supports many 94 different names forms including otherName for extensibility. This 95 section specifies the SmtpUTF8Name name form of otherName, so that 96 Internationalized Email addresses can appear in the subjectAltName of 97 a certificate, the issuerAltName of a certificate, or anywhere else 98 that GeneralName is used. 100 id-on-SmtpUTF8Name OBJECT IDENTIFIER ::= { id-on 9 } 102 SmtpUTF8Name ::= UTF8String (SIZE (1..MAX)) 104 When the subjectAltName (or issuerAltName) extension contains an 105 Internationalized Email address, the address MUST be stored in the 106 SmtpUTF8Name name form of otherName. The format of SmtpUTF8Name is 107 defined as the ABNF rule SmtpUTF8Mailbox. SmtpUTF8Mailbox is a 108 modified version of the Internationalized Mailbox which was defined 109 in Section 3.3 of [RFC6531] which was itself derived from SMTP 110 Mailbox from Section 4.1.2 of [RFC5321]. [RFC6531] defines the 111 following ABNF rules for Mailbox whose parts are modified for 112 internationalization: , , , 113 , , and . In particular, 114 was updated to also support UTF8-non-ascii. UTF8-non-ascii was 115 described by Section 3.1 of [RFC6532]. Also, sub-domain was extended 116 to support U-label, as defined in [RFC5890]. 118 This document further refines Internationalized [RFC6531] Mailbox 119 ABNF rules and calls this SmtpUTF8Mailbox. In SmtpUTF8Mailbox, sub- 120 domain that encode non-ASCII characters SHALL use U-label Unicode 121 native character labels and MUST NOT use A-label [RFC5890]. This 122 restriction prevents having to determine which label encoding A- or 123 U-label is present in the Domain. As per Section 2.3.2.1 of 124 [RFC5890], U-label use UTF-8 [RFC3629] with Normalization Form C and 125 other properties specified there. In SmtpUTF8Mailbox, sub-domain 126 that encode ASCII character labels SHALL use NR-LDH restrictions as 127 specified by section 2.3.1 of [RFC5890] and SHALL be restricted to 128 lower case letters. One suggested approach to apply these sub- 129 domains restriction is to restrict sub-domain so that labels not 130 start with two letters followed by two hyphen-minus characters. 131 Consistent with the treatment of rfc822Name in [RFC5280], 132 SmtpUTF8Name is an envelope and has no phrase (such as a 133 common name) before it, has no comment (text surrounded in 134 parentheses) after it, and is not surrounded by "<" and ">". 136 In the context of building name constraint as needed by [RFC5280], 137 the SmtpUTF8Mailbox rules are modified to allow partial productions 138 to allow for additional forms required by Section 6. Name 139 constraints may specify a complete email address, host name, or 140 domain. This means that the local-part may be missing, and domain 141 partially specified. 143 SmtpUTF8Name is encoded as UTF8String. The UTF8String encoding MUST 144 NOT contain a Byte-Order- Mark (BOM) [RFC3629] to aid consistency 145 across implementations particularly for comparison. 147 4. IDNA2008 149 To facilitate comparison between email addresses, all email address 150 domain in X.509 certificates MUST conform to IDNA2008 [RFC5890]. 151 Otherwise non-conforming email address domains introduces the 152 possibility of conversion errors between alternate forms. This 153 applies to SmtpUTF8Mailbox and rfc822Name in subjectAltName, 154 issuerAltName and anywhere else that GeneralName is used. 156 5. Matching of Internationalized Email Addresses in X.509 certificates 158 In equivalence comparison with SmtpUTF8Name, there may be some setup 159 work to enable the comparison i.e. processing of the SmtpUTF8Name 160 content or the email address that is being compared against. The 161 process for setup for comparing with SmtpUTF8Name is split into 162 domain steps and local- part steps. The comparison form for local- 163 part always is UTF-8. The comparison form for domain depends on 164 context. While some contexts such as certificate path validation in 165 [RFC5280] specify transforming domain to A-label, this document 166 RECOMMENDS transforming to UTF-8 U-label instead. This reduces the 167 likelihood of errors by reducing conversions as more implementations 168 natively support U-label domains. 170 Comparison of two SmtpUTF8Name is straightforward with no setup work 171 needed. They are considered equivalent if there is an exact octet- 172 for-octet match. Comparison with other email address forms such as 173 Internationalized email address or rfc822Name requires additional 174 setup steps. Domain setup is particularly important for forms that 175 may contain A- or U-label such as International email address, or 176 A-label only forms such as rfc822Name. This document specifies the 177 process to transform the domain to U-label. (To convert the domain 178 to A-label, follow the process specified in section 7.5 and 7.2 in 179 [RFC5280]) The first step is to detect A-label by using section 5.1 180 of [RFC5891]. Next if necessary, transform the A-label to U-label 181 Unicode as specified in section 5.2 of [RFC5891]. Finally if 182 necessary convert the Unicode to UTF-8 as specified in section 3 of 183 [RFC3629]. For ASCII NR-LDH labels, upper case letters are converted 184 to lower case letters. In setup for SmtpUTF8Mailbox, the email 185 address local-part MUST conform to the requirements of [RFC6530] and 186 [RFC6531], including being a string in UTF-8 form. In particular, 187 the local-part MUST NOT be transformed in any way, such as by doing 188 case folding or normalization of any kind. The part of 189 an Internationalized email address is already in UTF-8. For 190 rfc822Name the local-part, which is IA5String (ASCII), trivially maps 191 to UTF-8 without change. Once setup is complete, they are again 192 compared octet-for-octet. 194 To summarize non-normatively, the comparison steps including setup 195 are: 197 1. If the domain contains A-labels, transform them to U-label. 199 2. If the domain contains ASCII NR-LDH labels, lowercase them. 201 3. Ensure local-part is UTF-8. 203 4. Compare strings octet-for-octet for equivalence. 205 This specification expressly does not define any wildcards 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 SHOULD use multiple 209 subjectAltNames or issuerAltNames to explicitly carry those email 210 addresses. 212 6. Name constraints in path validation 214 This section defines use of SmtpUTF8Name name for name constraints. 215 The format for SmtpUTF8Name in name constraints is identical to the 216 use in subjectAltName as specified in Section 3 with the extension as 217 noted there for partial productions. 219 Constraint comparison on complete email address with SmtpUTF8Name 220 name uses the matching procedure defined by Section 5. As with 221 rfc822Name name constraints as specified in Section 4.2.1.10 of 222 [RFC5280], SmtpUTF8Name name can specify a particular mailbox, all 223 addresses at a host, or all mailboxes in a domain by specifying the 224 complete email address, a host name, or a domain. Name constraint 225 comparisons in the context of [RFC5280] that are specified with 226 SmtpUTF8Name name are only done on the subjectAltName SmtpUTF8Name 227 name and not on other forms. Similarly rfc822Name name constraints 228 do not apply to subjectAltName SmtpUTF8Name name. This imposes 229 requirements on the certificate issuer as described next. 231 When name constraints are used with SmtpUTF8Name subjectAltName 232 names, they are specified in the following profile to prevent 233 bypassing of name constraints. Host name and domain constraints MUST 234 use both rfc822Name and SmtpUTF8Name forms in the issuing certificate 235 with the constraint. Complete email address constraint with UTF-8 236 local-part MUST only use SmtpUTF8Name form. Complete email address 237 constraint with ASCII local-part MUST use both rfc822Name and 238 SmtpUTF8Name forms. When both rfc822Name and SmtpUTF8Name name 239 constraints forms are present, they MUST carry the equivalent 240 constraints as defined by Section 5 and MUST be found in the same 241 node and in the same permittedSubtrees or excludedSubtrees. This 242 specification intentionally leaves unchanged rfc822Name name 243 constraint processing as described in Section 4.2.1.10 of [RFC5280]. 245 This document specifies that SmtpUTF8Name aware path validators check 246 for SmtpUTF8Name name constraint profiles as an additional path 247 validation step in Section 6 of [RFC5280]. SmtpUTF8Name aware 248 validators MUST NOT accept any certificate whose path contains an 249 issuing certificate whose rfc822Name or SmtpUTF8Name name constraints 250 do not match the above profile. That is the path validator verifies 251 that a rfc822Name name constraint has a corresponding SmtpUTF8Name 252 constraint and that a SmtpUTF8Name name constraint has a 253 corresponding rfc822Name constraint when the constraint contains host 254 name, domain or email address with an ASCII local-part. This 255 correspondence is required to be in the same issuing certificate node 256 and in the same nameConstraint permittedSubtrees or excludedSubtrees. 258 The name constraint requirement with SmtpUTF8Name subjectAltName is 259 illustrated in the following non-normative diagram Figure 1. This 260 show a SmtpUTF8Name aware issuer that constrained the intermediate CA 261 with host name and email address name constraints. In particular the 262 email address constraint with UTF8 local-part only used a single 263 SmtpUTF8Name name constraint, while the email address constraint with 264 ASCII local-part used both rfc822Name and SmtpUTF8Name name 265 constraints. The next non-normative diagram Figure 2 illustrates 266 legacy name constraints to contrasts the changes this document 267 specifies. The legacy approach has only a single rfc822Name name 268 email address name constraint. 270 +--------------------------------------------------------------+ 271 | Root CA Cert | 272 +--------------------------------------------------------------+ 273 | 274 v 275 +--------------------------------------------------------------+ 276 | Intermediate CA Cert | 277 | Name Constraint Extension | 278 | Permitted | 279 | rfc822Name: allowed_host.example.com | 280 | SmtpUTF8Name: allowed_host.example.com | 281 | | 282 | SmtpUTF8Name: u+8001u+5E2B@allowed_email.example.com | 283 | | 284 | rfc822Name: student@allowed_email.example.com | 285 | SmtpUTF8Name: student@allowed_email.example.com | 286 +--------------------------------------------------------------+ 287 | 288 v 289 +--------------------------------------------------------------+ 290 | Entity Cert (w/explicitly permitted subjects) | 291 | SubjectAltName Extension | 292 | SmtpUTF8Name: u+533Bu+751F@allowed_host.example.com | 293 | | 294 | SmtpUTF8Name: u+8001u+5E2B@allowed_email.example.com | 295 | | 296 | rfc822Name: student@allowed_email.example.com | 297 +--------------------------------------------------------------+ 299 Name constraints with SmtpUTF8Name 301 Figure 1 303 +--------------------------------------------------------------+ 304 | Root CA Cert | 305 +--------------------------------------------------------------+ 306 | 307 v 308 +--------------------------------------------------------------+ 309 | Intermediate CA Cert | 310 | Name Constraint Extension | 311 | Permitted | 312 | rfc822Name: allowed_host.example.com | 313 +--------------------------------------------------------------+ 314 | 315 v 316 +--------------------------------------------------------------+ 317 | Entity Cert (w/explicitly permitted subjects) | 318 | SubjectAltName Extension | 319 | rfc822Name: student@allowed_host.example.com | 320 +--------------------------------------------------------------+ 322 Legacy name constraints with rfc822Name 324 Figure 2 326 7. Deployment Considerations 328 For email addresses whose local-part is ASCII it may be more 329 reasonable to continue using rfc822Name instead of SmtpUTF8Name. The 330 use of rfc822Name rather than SmtpUTF8Name is currently more likely 331 to be supported. Also use of SmtpUTF8Name incurs higher byte 332 representation overhead due to encoding with otherName and the 333 additional OID needed. This may be offset if domain requires non- 334 ASCII characters as smptUtf8Name supports U-label whereas rfc822Name 335 supports A-label. This document RECOMMENDS using SmtpUTF8Name when 336 local-part contains non-ASCII characters, and otherwise rfc822Name. 338 8. Security Considerations 340 Use for SmtpUTF8Name for certificate subjectAltName (and 341 issuerAltName) will incur many of the same security considerations of 342 Section 8 in [RFC5280] but is further complicated by permitting non- 343 ASCII characters in the email address local-part. This complication, 344 as mentioned in Section 4.4 of [RFC5890] and in Section 4 of 345 [RFC6532], is that use of Unicode introduces the risk of visually 346 similar and identical characters which can be exploited to deceive 347 the recipient. The former document references some means to mitigate 348 against these attacks. 350 9. IANA Considerations 352 in Section Section 3 and the ASN.1 module identifier defined in 353 Section Appendix A. IANA is kindly requested to make the following 354 assignments for: 356 The LAMPS-EaiAddresses-2016 ASN.1 module in the "SMI Security for 357 PKIX Module Identifier" registry (1.3.6.1.5.5.7.0). 359 The SmtpUTF8Name otherName in the "PKIX Other Name Forms" registry 360 (1.3.6.1.5.5.7.8). 362 10. References 364 10.1. Normative References 366 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 367 Requirement Levels", BCP 14, RFC 2119, 368 DOI 10.17487/RFC2119, March 1997, 369 . 371 [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 372 10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November 373 2003, . 375 [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax 376 Specifications: ABNF", STD 68, RFC 5234, 377 DOI 10.17487/RFC5234, January 2008, 378 . 380 [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., 381 Housley, R., and W. Polk, "Internet X.509 Public Key 382 Infrastructure Certificate and Certificate Revocation List 383 (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008, 384 . 386 [RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321, 387 DOI 10.17487/RFC5321, October 2008, 388 . 390 [RFC5890] Klensin, J., "Internationalized Domain Names for 391 Applications (IDNA): Definitions and Document Framework", 392 RFC 5890, DOI 10.17487/RFC5890, August 2010, 393 . 395 [RFC5891] Klensin, J., "Internationalized Domain Names in 396 Applications (IDNA): Protocol", RFC 5891, 397 DOI 10.17487/RFC5891, August 2010, 398 . 400 [RFC6530] Klensin, J. and Y. Ko, "Overview and Framework for 401 Internationalized Email", RFC 6530, DOI 10.17487/RFC6530, 402 February 2012, . 404 [RFC6531] Yao, J. and W. Mao, "SMTP Extension for Internationalized 405 Email", RFC 6531, DOI 10.17487/RFC6531, February 2012, 406 . 408 [RFC6532] Yang, A., Steele, S., and N. Freed, "Internationalized 409 Email Headers", RFC 6532, DOI 10.17487/RFC6532, February 410 2012, . 412 10.2. Informative References 414 [RFC5912] Hoffman, P. and J. Schaad, "New ASN.1 Modules for the 415 Public Key Infrastructure Using X.509 (PKIX)", RFC 5912, 416 DOI 10.17487/RFC5912, June 2010, 417 . 419 Appendix A. ASN.1 Module 421 The following ASN.1 module normatively specifies the SmtpUTF8Name 422 structure. This specification uses the ASN.1 definitions from 423 [RFC5912] with the 2002 ASN.1 notation used in that document. 424 [RFC5912] updates normative documents using older ASN.1 notation. 426 LAMPS-EaiAddresses-2016 427 { iso(1) identified-organization(3) dod(6) 428 internet(1) security(5) mechanisms(5) pkix(7) id-mod(0) 429 id-mod-lamps-eai-addresses-2016(TBD) } 431 DEFINITIONS IMPLICIT TAGS ::= 432 BEGIN 434 IMPORTS 435 OTHER-NAME 436 FROM PKIX1Implicit-2009 437 { iso(1) identified-organization(3) dod(6) internet(1) security(5) 438 mechanisms(5) pkix(7) id-mod(0) id-mod-pkix1-implicit-02(59) } 440 id-pkix 441 FROM PKIX1Explicit-2009 442 { iso(1) identified-organization(3) dod(6) internet(1) security(5) 443 mechanisms(5) pkix(7) id-mod(0) id-mod-pkix1-explicit-02(51) } ; 445 -- 446 -- otherName carries additional name types for subjectAltName, 447 -- issuerAltName, and other uses of GeneralNames. 448 -- 450 id-on OBJECT IDENTIFIER ::= { id-pkix 8 } 452 SmtpUtf8OtherNames OTHER-NAME ::= { on-SmtpUTF8Name, ... } 454 on-SmtpUTF8Name OTHER-NAME ::= { 455 SmtpUTF8Name IDENTIFIED BY id-on-SmtpUTF8Name 456 } 458 id-on-SmtpUTF8Name OBJECT IDENTIFIER ::= { id-on 9 } 460 SmtpUTF8Name ::= UTF8String (SIZE (1..MAX)) 462 END 464 Figure 3 466 Appendix B. Example of SmtpUTF8Name 468 This non-normative example demonstrates using SmtpUTF8Name as an 469 otherName in GeneralName to encode the email address 470 "u+8001u+5E2B@example.com". 472 The hexadecimal DER encoding of the email address is: 473 A022060A 2B060105 05070012 0809A014 0C12E880 81E5B8AB 40657861 474 6D706C65 2E636F6D 476 The text decoding is: 477 0 34: [0] { 478 2 10: OBJECT IDENTIFIER '1 3 6 1 5 5 7 0 18 8 9' 479 14 20: [0] { 480 16 18: UTF8String '..@example.com' 481 : } 482 : } 484 Figure 4 486 The example was encoded on the OSS Nokalva ASN.1 Playground and the 487 above text decoding is an output of Peter Gutmann's "dumpasn1" 488 program. 490 Appendix C. Acknowledgements 492 Thank you to Magnus Nystrom for motivating this document. Thanks to 493 Russ Housley, Nicolas Lidzborski, Laetitia Baudoin, Ryan Sleevi, Sean 494 Leonard, Sean Turner, John Levine, Viktor Dukhovni and Patrik 495 Falstrom for their feedback. Also special thanks to John Klensin for 496 his valuable input on internationalization, Unicode and ABNF 497 formatting, and to Jim Schaad for his help with the ASN.1 example and 498 his helpful feedback. 500 Authors' Addresses 502 Alexey Melnikov (editor) 503 Isode Ltd 504 14 Castle Mews 505 Hampton, Middlesex TW12 2NP 506 UK 508 Email: Alexey.Melnikov@isode.com 510 Weihaw Chuang (editor) 511 Google, Inc. 512 1600 Amphitheatre Parkway 513 Mountain View, CA 94043 514 US 516 Email: weihaw@google.com