--- 1/draft-ietf-lamps-eai-addresses-08.txt 2017-04-15 16:13:18.992731198 -0700 +++ 2/draft-ietf-lamps-eai-addresses-09.txt 2017-04-15 16:13:19.020731863 -0700 @@ -1,19 +1,19 @@ LAMPS A. Melnikov, Ed. Internet-Draft Isode Ltd Intended status: Standards Track W. Chuang, Ed. -Expires: September 13, 2017 Google, Inc. - March 12, 2017 +Expires: October 17, 2017 Google, Inc. + April 15, 2017 Internationalized Email Addresses in X.509 certificates - draft-ietf-lamps-eai-addresses-08 + draft-ietf-lamps-eai-addresses-09 Abstract This document defines a new name form for inclusion in the otherName field of an X.509 Subject Alternative Name and Issuer Alternate Name extension that allows a certificate subject to be associated with an Internationalized Email Address. Status of This Memo @@ -23,21 +23,21 @@ Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." - This Internet-Draft will expire on September 13, 2017. + This Internet-Draft will expire on October 17, 2017. Copyright Notice Copyright (c) 2017 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents @@ -49,30 +49,29 @@ Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Conventions Used in This Document . . . . . . . . . . . . . . 2 3. Name Definitions . . . . . . . . . . . . . . . . . . . . . . 2 4. IDNA2008 . . . . . . . . . . . . . . . . . . . . . . . . . . 4 5. Matching of Internationalized Email Addresses in X.509 certificates . . . . . . . . . . . . . . . . . . . . . . . . 4 6. Name constraints in path validation . . . . . . . . . . . . . 5 - 7. Deployment Considerations . . . . . . . . . . . . . . . . . . 10 - 8. Security Considerations . . . . . . . . . . . . . . . . . . . 10 - 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 - 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 - 10.1. Normative References . . . . . . . . . . . . . . . . . . 10 - 10.2. Informative References . . . . . . . . . . . . . . . . . 11 - Appendix A. ASN.1 Module . . . . . . . . . . . . . . . . . . . . 12 - Appendix B. Example of SmtpUTF8Name . . . . . . . . . . . . . . 13 - Appendix C. Acknowledgements . . . . . . . . . . . . . . . . . . 13 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13 + 7. Security Considerations . . . . . . . . . . . . . . . . . . . 7 + 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 + 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 + 9.1. Normative References . . . . . . . . . . . . . . . . . . 8 + 9.2. Informative References . . . . . . . . . . . . . . . . . 9 + Appendix A. ASN.1 Module . . . . . . . . . . . . . . . . . . . . 9 + Appendix B. Example of SmtpUTF8Name . . . . . . . . . . . . . . 10 + Appendix C. Acknowledgements . . . . . . . . . . . . . . . . . . 11 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11 1. Introduction [RFC5280] defines rfc822Name subjectAltName choice for representing [RFC5321] email addresses. This form is restricted to a subset of US-ASCII characters and thus can't be used to represent Internationalized Email addresses [RFC6531]. To facilitate use of these Internationalized Email addresses with X.509 certificates, this document specifies a new name form in otherName so that subjectAltName and issuerAltName can carry them. In addition this @@ -126,26 +125,31 @@ that encode ASCII character labels SHALL use NR-LDH restrictions as specified by section 2.3.1 of [RFC5890] and SHALL be restricted to lower case letters. One suggested approach to apply these sub- domains restriction is to restrict sub-domain so that labels not start with two letters followed by two hyphen-minus characters. Consistent with the treatment of rfc822Name in [RFC5280], SmtpUTF8Name is an envelope and has no phrase (such as a common name) before it, has no comment (text surrounded in parentheses) after it, and is not surrounded by "<" and ">". - In the context of building name constraint as needed by [RFC5280], - the SmtpUTF8Mailbox rules are modified to allow partial productions - to allow for additional forms required by Section 6. Name - constraints may specify a complete email address, host name, or - domain. This means that the local-part may be missing, and domain - partially specified. + Due to operational reasons described shortly and name constraint + compatibility reasons described in its section, SmtpUTF8Name + subjectAltName MUST only be used when the local part of the email + address contains UTF-8. When the local-part is ASCII, rfc822Name + subjectAltName MUST be used instead of SmtpUTF8Name. The use of + rfc822Name rather than SmtpUTF8Name is currently more likely to be + supported. Also use of SmtpUTF8Name incurs higher byte + representation overhead due to encoding with otherName and the + additional OID needed. This may be offset if domain requires non- + ASCII characters as SmtpUTF8Name supports U-label whereas rfc822Name + supports A-label. SmtpUTF8Name is encoded as UTF8String. The UTF8String encoding MUST NOT contain a Byte-Order- Mark (BOM) [RFC3629] to aid consistency across implementations particularly for comparison. 4. IDNA2008 To facilitate comparison between email addresses, all email address domain in X.509 certificates MUST conform to IDNA2008 [RFC5890]. Otherwise non-conforming email address domains introduces the @@ -204,256 +208,133 @@ This specification expressly does not define any wildcards characters and SmtpUTF8Name comparison implementations MUST NOT interpret any character as wildcards. Instead, to specify multiple email addresses through SmtpUTF8Name, the certificate SHOULD use multiple subjectAltNames or issuerAltNames to explicitly carry those email addresses. 6. Name constraints in path validation - This section defines use of SmtpUTF8Name name for name constraints. - The format for SmtpUTF8Name in name constraints is identical to the - use in subjectAltName as specified in Section 3 with the extension as - noted there for partial productions. - - Constraint comparison on complete email address with SmtpUTF8Name - name uses the matching procedure defined by Section 5. As with - rfc822Name name constraints as specified in Section 4.2.1.10 of - [RFC5280], SmtpUTF8Name name can specify a particular mailbox, all - addresses at a host, or all mailboxes in a domain by specifying the - complete email address, a host name, or a domain. Name constraint - comparisons in the context of [RFC5280] that are specified with - SmtpUTF8Name name are only done on the subjectAltName SmtpUTF8Name - name and not on other forms. Similarly rfc822Name name constraints - do not apply to subjectAltName SmtpUTF8Name name. This imposes - requirements on the certificate issuer as described next. - - When name constraints are used with SmtpUTF8Name subject alternative - names, the constraints are specified by the following changes to the - path validator to prevent bypass of the name constraints. The email - address path validator in Section 6 of [RFC5280] is modified to - consider: - - 1. When neither rfc822Name nor SmtpUTF8Name name constraints are - present in any issuer CA certificate, then path validation does - not add restrictions on children certificates with rfc822Name or - SmtpUTF8Name subject alternative names. That is any combination - of rfc822Name or SmtpUTF8Name subject alternative names may be - present. - - 2. If issuer CA certificates contain only rfc822Name name - constraints, then those constraints apply to rfc822Name subject - alternative name in children certificates. SmtpUTF8Name subject - alternative name are prohibited in those same certificates, that - is those certificates MUST be rejected by the path verifier. + This section updates [RFC5280] name constraints to work with + SmtpUTF8Name subjectAltName. In the following, a CA or path verifier + implementation that follows this specification is called SmtpUTF8Name + aware. - 3. When both rfc822Name and SmtpUTF8Name name constraints are - present in all issuer CA certificates that have either form, then - the path verifier applies the constraint of the subject - alternative name form in children certificates. This allows any - combination of rfc822Name or SmtpUTF8Name subject alternative - names to be present and implies that the issuer has applied - appropriate name constraints. While commonly the alternative - forms will be equivalent, they need not be, as the forms can - represent features not present in its counterpart. One instance - of this is when the issuer wants to name constrain domain or - hostname using the rules of a particular form. + SmtpUTF8Name aware path validators MUST be able to apply name + constraint to the subject distinguished name and both forms of + subject alternative name. That is rfc822Name name constraint applies + to emailAddress subject distinguished name, and to SmtpUTF8Name and + rfc822Name subject alternative name, as mentioned in Section 4.2.1.10 + of [RFC5280]. Constraint comparison with SmtpUTF8Name subjectAltName + uses the matching procedure defined by Section 5 including any setup + steps. The lack of a SmtpUTF8Name name constraint form is + intentional and motivated as described next. - 4. If some issuer CA certificates contain only SmtpUTF8Name name - constraints, then those are at risk of bypass with rfc822Name - subject alternative names when processed by legacy verifiers. To - prevent this, issuers MUST also publish rfc822Name name - constraint that prevent those bypasses. This occurs when both - rfc822Name and SmtpUTF8Name constraint forms can represents the - same host, domain or email address, and both are needed. Even - when the constraints are asymmetric such as when the issuer - wishes to constrain an email address with an UTF-8 local part, a - non empty rfc822Name name constraint may be needed if there isn't - one already so that the path verifier initializes correctly. + This specification requires that SmtpUTF8Name aware CAs continue to + issue certificates with rfc822Name name constraints form due to + compatibility concerns with legacy systems. Using rfc822Name name + constraints allows backwards compatibility with legacy path verifiers + that only understand rfc822Name form, yet is forward compatible by + being able to describe the intent of the CA to constrain both + rfc822Name and SmtpUTF8Name subjectAltName to SmtpUTF8Name aware path + verifiers. Oblivious legacy path verifier will not see the + SmtpUTF8Name subjectAltName (nor the unknown otherNames), and thereby + prevent the use of an unconstrained SmtpUTF8Name subjectAltName. - When both name constraints are present, the contents depends on the - usage. If the issuer desires to represent the same NR-LDH host or - domain, then it is the same string in both rfc822Name and - SmtpUTF8Name. If the host or domain labels contain UTF-8, then the - labels may be used directly in SmtpUTF8Name noting the restriction in - Section 5 and transformed to A-label for rfc822Name using the process - described in [RFC5280]. Email addresses that use ASCII local-part - use the same processing procedures for host or domain. + Other implementations may detect an unknown otherNames, along with + the critical bit set on the name constraints extension and then fail + path verification. This too prevents use of an unconstrained + SmtpUTF8Name subjectAltName. A legacy CA will use rfc822Name name + constraints. As the CA's intent is to constrain all email addresses + matching the constraint, this will be forward compatible with a + SmtpUTF8Name aware path verifiers that applies the name constraint to + either forms rfc822Name and SmtpUTF8Name subjectAltName. - If the issuer wishes to represent the name constraint asymmetrically, - with either rfc822Name or SmtpUTF8Name to respectively represent some - A-label or U-label in the domain or host, the alternate name - constraint form must still be present. If nothing needs be - represented by the alternate form, then empty name constraint can - described by the "invalid" TLD that helps initialize the name - constraint path validation set. Or alternatively it may be omitted - if some other name constraint pair, provides a name constraint of - that form. In particular this initialization may be needed when - SmtpUTF8Name is used to represent an email address name constraint - with an UTF-8 local-part and rfc822Name cannot represent such a email - address constraint. + The representation of name constraints are specified in + Section 4.2.1.10 of [RFC5280] and there MAY represent a particular + mailbox, all addresses at a host, or all mailboxes in a domain by + specifying the complete email address, a host name, or a domain. + This specification modifies [RFC5280] name constraint to only require + with a MAY that it represents all addresses at a host or all + mailboxes in a domain, and require with a MAY NOT that it represent a + particular mailbox. This is motivated by rfc822Name name constraints + inability to represent a specific mailbox with a UTF-8 email local + part email address. Certificate issuers should be aware of this + lessened support. The name constraint requirement with SmtpUTF8Name subject alternative - name is illustrated in the non-normative diagram Figure 1 with - several examples. (3a) shows an issuer constraining a NR-LDH - hostname with rfc822Name and SmtpUTF8Name so that they can issue - ASCII and UTF-8 local-name email addresses certificates. (3b) shows - an issuer constraining a hostname containing a non-ASCII label for - u+5C0Fu+5B66 (elementary school). (3c) demonstrates that a hostname - constraint with an rfc822Name is distinguishable from its - SmtpUTF8Name constraint, and that only the rfc822Name form is - permitted. No 'invalid' SmtpUTF8Name constraint is needed since - other SmtpUTF8Name constraints are present. (3d) similarly - demonstrates this capability to restrict a name constraint to - SmtpUTF8Name only. (3e) shows that a non-ASCII local- part email - address can also be constrained to be permitted using SmtpUTF8Name. - It too does not need an 'invalid' rfc822Name as other rfc822Name - constrains are present. Diagram Figure 2 illustrates (non- - normatively) a different certificate chain that does need the - 'invalid' name constraint. (3f) constrains a non-ASCII local-part - email address using a SmtpUTF8Name name constraint but requires a - rfc822Name 'invalid' constraint because it lacks any other rfc822Name - constraints needed to initialize the name constraint path - verification. The next non-normative diagram Figure 3 illustrates - legacy name constraints that contrasts the changes this document - specifies. The legacy approach (2) has only a single rfc822Name name - email address name constraint. + name is illustrated in the non-normative diagram Figure 1. The first + example (1) illustrates a permitted rfc822Name ASCII only hostname + name constraint, and the corresponding valid rfc822Name + subjectAltName and SmtpUTF8Name subjectAltName email addresses. The + second example (2) illustrates a permitted rfc822Name hostname name + constraint with A-label, and the corresponding valid rfc822Name + subjectAltName and SmtpUTF8Name subjectAltName email addresses. +-------------------------------------------------------------------+ | Root CA Cert | +-------------------------------------------------------------------+ | v +-------------------------------------------------------------------+ | Intermediate CA Cert | | Permitted | - | rfc822Name: nr.ldh.host.example.com (3a) | - | SmtpUTF8Name: nr.ldh.host.example.com (3a) | - | | - | rfc822Name: u+5C0Fu+5B66.host.example.com (3b) | - | SmtpUTF8Name: xn--48s3o.host.example.com (3b) | - | | - | rfc822Name: xn--pss25c.a.label.example.com (3c) | + | rfc822Name: elementary.school.example.com (1) | | | - | SmtpUTF8Name: u+4E2Du+5B66.u.label.example.com (3d) | + | rfc822Name: xn--pss25c.example.com (2) | | | - | SmtpUTF8Name: u+8001u+5E2B@i18n.email.example.com (3e) | +-------------------------------------------------------------------+ | v +-------------------------------------------------------------------+ | Entity Cert (w/explicitly permitted subjects) | | SubjectAltName Extension | - | rfc822Name: student@nr.ldh.host.example.com (3a) | - | SmtpUTF8Name: u+5B66u+751F@nr.ldh.host.example.com (3a) | - | | - | rfc822Name: student@u+5C0Fu+5B66.host.example.com (3b) | - | SmtpUTF8Name: u+5B66u+751F@xn--48s3o.host.example.com (3b) | - | | - | rfc822Name: student@xn--pss25c.a.label.example.com (3c) | + | rfc822Name: student@elemenary.school.example.com (1) | + | SmtpUTF8Name: u+5B66u+751F@elementary.school.example.com (1) | | | - | SmtpUTF8Name: student@u+4E2Du+5B66.u.label.example.com (3d) | + | rfc822Name: student@xn--pss25c.example.com (2) | + | SmtpUTF8Name: u+533Bu+751F@xn--pss25c.example.com (2) | | | - | SmtpUTF8Name: u+8001u+5E2B@i18n.email.example.com (3e) | +-------------------------------------------------------------------+ Name constraints with SmtpUTF8Name and rfc822Name Figure 1 - +-------------------------------------------------------------------+ - | Root CA Cert | - +-------------------------------------------------------------------+ - | - v - +-------------------------------------------------------------------+ - | Intermediate CA Cert | - | Name Constraint Extension | - | Permitted | - | rfc822Name: invalid (3f) | - | SmtpUTF8Name: u+8001u+5E2B@i18n.email.example.com (3f) | - +-------------------------------------------------------------------+ - | - v - +-------------------------------------------------------------------+ - | Entity Cert (w/explicitly permitted subjects) | - | SubjectAltName Extension | - | SmtpUTF8Name: u+8001u+5E2B@i18n.email.example.com (3f) | - +-------------------------------------------------------------------+ - - Name constraints with SmtpUTF8Name email address and empty rfc822Name - - Figure 2 - - +-------------------------------------------------------------------+ - | Root CA Cert | - +-------------------------------------------------------------------+ - | - v - +-------------------------------------------------------------------+ - | Intermediate CA Cert | - | Name Constraint Extension | - | Permitted | - | rfc822Name: student@email.example.com (2) | - +-------------------------------------------------------------------+ - | - v - +-------------------------------------------------------------------+ - | Entity Cert (w/explicitly permitted subjects) | - | SubjectAltName Extension | - | rfc822Name: student@email.example.com (2) | - +-------------------------------------------------------------------+ - - Legacy name constraints with rfc822Name - - Figure 3 - -7. Deployment Considerations - - For email addresses whose local-part is ASCII it may be more - reasonable to continue using rfc822Name instead of SmtpUTF8Name. The - use of rfc822Name rather than SmtpUTF8Name is currently more likely - to be supported. Also use of SmtpUTF8Name incurs higher byte - representation overhead due to encoding with otherName and the - additional OID needed. This may be offset if domain requires non- - ASCII characters as SmtpUTF8Name supports U-label whereas rfc822Name - supports A-label. This document RECOMMENDS using SmtpUTF8Name when - local-part contains non-ASCII characters, and otherwise rfc822Name. - -8. Security Considerations +7. Security Considerations Use for SmtpUTF8Name for certificate subjectAltName (and issuerAltName) will incur many of the same security considerations of Section 8 in [RFC5280] but is further complicated by permitting non- ASCII characters in the email address local-part. This complication, as mentioned in Section 4.4 of [RFC5890] and in Section 4 of [RFC6532], is that use of Unicode introduces the risk of visually similar and identical characters which can be exploited to deceive the recipient. The former document references some means to mitigate against these attacks. -9. IANA Considerations +8. IANA Considerations in Section Section 3 and the ASN.1 module identifier defined in Section Appendix A. IANA is kindly requested to make the following assignments for: The LAMPS-EaiAddresses-2016 ASN.1 module in the "SMI Security for PKIX Module Identifier" registry (1.3.6.1.5.5.7.0). The SmtpUTF8Name otherName in the "PKIX Other Name Forms" registry (1.3.6.1.5.5.7.8). -10. References +9. References -10.1. Normative References +9.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November 2003, . @@ -487,21 +368,21 @@ February 2012, . [RFC6531] Yao, J. and W. Mao, "SMTP Extension for Internationalized Email", RFC 6531, DOI 10.17487/RFC6531, February 2012, . [RFC6532] Yang, A., Steele, S., and N. Freed, "Internationalized Email Headers", RFC 6532, DOI 10.17487/RFC6532, February 2012, . -10.2. Informative References +9.2. Informative References [RFC5912] Hoffman, P. and J. Schaad, "New ASN.1 Modules for the Public Key Infrastructure Using X.509 (PKIX)", RFC 5912, DOI 10.17487/RFC5912, June 2010, . Appendix A. ASN.1 Module The following ASN.1 module normatively specifies the SmtpUTF8Name structure. This specification uses the ASN.1 definitions from @@ -539,41 +420,41 @@ on-SmtpUTF8Name OTHER-NAME ::= { SmtpUTF8Name IDENTIFIED BY id-on-SmtpUTF8Name } id-on-SmtpUTF8Name OBJECT IDENTIFIER ::= { id-on 9 } SmtpUTF8Name ::= UTF8String (SIZE (1..MAX)) END - Figure 4 + Figure 2 Appendix B. Example of SmtpUTF8Name This non-normative example demonstrates using SmtpUTF8Name as an otherName in GeneralName to encode the email address "u+8001u+5E2B@example.com". The hexadecimal DER encoding of the email address is: A022060A 2B060105 05070012 0809A014 0C12E880 81E5B8AB 40657861 6D706C65 2E636F6D The text decoding is: 0 34: [0] { 2 10: OBJECT IDENTIFIER '1 3 6 1 5 5 7 0 18 8 9' 14 20: [0] { 16 18: UTF8String '..@example.com' : } : } - Figure 5 + Figure 3 The example was encoded on the OSS Nokalva ASN.1 Playground and the above text decoding is an output of Peter Gutmann's "dumpasn1" program. Appendix C. Acknowledgements Thank you to Magnus Nystrom for motivating this document. Thanks to Russ Housley, Nicolas Lidzborski, Laetitia Baudoin, Ryan Sleevi, Sean Leonard, Sean Turner, John Levine, and Patrik Falstrom for their @@ -584,17 +465,18 @@ Authors' Addresses Alexey Melnikov (editor) Isode Ltd 14 Castle Mews Hampton, Middlesex TW12 2NP UK Email: Alexey.Melnikov@isode.com + Weihaw Chuang (editor) Google, Inc. - 1600 Amphitheatre Parkway + 1600 Amphitheater Parkway Mountain View, CA 94043 US Email: weihaw@google.com