Network Working Group A. Melnikov, Ed.
Internet-Draft Isode Ltd
Intended status: Standards Track W. Chuang, Ed.
Expires: November 28, 2016 Google, Inc.
May 27, 2016

Internationalized Email Addresses in X.509 certificates


This document defines a new name form for inclusion in the otherName field of an X.509 Subject Alternative Name extension that allows a certificate subject to be associated with an Internationalized Email Address.

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Table of Contents

1. Introduction

[RFC5280] defines rfc822Name subjectAltName choice for representing [RFC5322] 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].

2. Conventions Used in This Document

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].

The formal syntax use the Augmented Backus-Naur Form (ABNF) [RFC5234] notation.

3. Name Definitions

This section defines the eaiName name as a form of otherName from the GeneralName structure in SubjectAltName defined in [RFC5280].

id-on-eaiAddr OBJECT IDENTIFIER ::= { id-on XXX }

eaiName ::= UTF8String (SIZE (1..MAX))

When the subjectAltName extension contains an Internationalized Email address, the address MUST be stored in the eaiName name form of otherName. The format of eaiName is a eaiMailbox, and this is a modified version of the internationalized Mailbox which is defined in Section 3.3 of [RFC6531] which is itself derived from SMTP Mailbox from Section 4.1.2 of [RFC5321]. [RFC6531] defines the following ABNF rules for Mailbox whose parts are modified for internationalization: <Local-part>, <Dot-string>, <Quoted-string>, <QcontentSMTP>, <Domain>, and <Atom>. In particular <Local-part> is updated to also support UTF8-non-ascii. UTF8-non-ascii is described by Section 3.1 of [RFC6532].

This document refines [RFC6531] Mailbox ABNF rules for eaiMailbox. In eaiMailbox, Domain is restricted to a single format, the ASCII Compatible Encoding (ACE) format (as defined in [RFC5280]), which makes comparison simpler. With eaiMailbox comparison there is no need to check for an alternate IDNA Domain form, nor convert from IDNA to ACE format. Note that a eaiMailbox 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 ">".

4. Matching of Internationalized Email Addresses in X.509 certificates

Comparison of two eaiName is straightforward. No setup work is needed and it can be an octet for octet comparison. Comparison of other email address forms such as Internationalized email address or rfc822Name may require additional setup to normalize the format for comparison. The <Local-part> part of an Internationalized email address is in UTF-8, and the rfc822Name local-part MUST be converted to UTF-8. The <Domain> for either International email address or rfc822Name can contain either IDNA domain or an ASCII Compatible Encoding (ACE) format. When comparing against eaiName, the <Domain>s MUST be converted to the ACE form as described in section 7.2 of [RFC5280] in UTF-8.

5. Name constraints in path validation

This section defines use of eaiName name for name constraints. The format for eaiName in name constraints is identical to the use in subjectAltName as specified in Section 3.

Constraint comparisons specified with eaiName name are only done on the subjectAltName eaiName name, and says nothing more about constaints on other email address forms. Constraint comparison on complete email address with eaiName name uses the matching procedure defined by Section 4. As with rfc822Name name constraints as specified in Section of [RFC5280], eaiName 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.

6. IANA Considerations

[CREF1]Just need a new OID.

7. Security Considerations

8. References

8.1. 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.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, DOI 10.17487/RFC5234, January 2008.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley, R. and W. Polk, "Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008.
[RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321, DOI 10.17487/RFC5321, October 2008.
[RFC6531] Yao, J. and W. Mao, "SMTP Extension for Internationalized Email", RFC 6531, DOI 10.17487/RFC6531, February 2012.

8.2. Informative References

[RFC5322] Resnick, P., "Internet Message Format", RFC 5322, DOI 10.17487/RFC5322, October 2008.
[RFC6532] Yang, A., Steele, S. and N. Freed, "Internationalized Email Headers", RFC 6532, DOI 10.17487/RFC6532, February 2012.

Appendix A. Acknowledgements

Thank you to Magnus Nystrom for motivating this document. Thanks to Nicolas Lidzborski, Laetitia Baudoin, and Ryan Sleevi for their early feedback.

Authors' Addresses

Alexey Melnikov (editor) Isode Ltd 14 Castle Mews Hampton, Middlesex TW12 2NP UK EMail:
Weihaw Chuang (editor) Google, Inc. 1600 Amphitheatre Parkway Mountain View, CA 94043 US EMail: