Internationalized Email Addresses in X.509 certificates
draft-ietf-lamps-eai-addresses-00
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| Document | Type | Active Internet-Draft (lamps WG) | |
|---|---|---|---|
| Authors | Alexey Melnikov , Wei Chuang | ||
| Last updated | 2016-07-24 | ||
| Replaces | draft-melnikov-spasm-eai-addresses | ||
| Stream | Internet Engineering Task Force (IETF) | ||
| Formats | plain text xml htmlized pdfized bibtex | ||
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draft-ietf-lamps-eai-addresses-00
lamps A. Melnikov, Ed.
Internet-Draft Isode Ltd
Intended status: Standards Track W. Chuang, Ed.
Expires: January 25, 2017 Google, Inc.
July 24, 2016
Internationalized Email Addresses in X.509 certificates
draft-ietf-lamps-eai-addresses-00
Abstract
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.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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This Internet-Draft will expire on January 25, 2017.
Copyright Notice
Copyright (c) 2016 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
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described in the Simplified BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions Used in This Document . . . . . . . . . . . . . . 2
3. Name Definitions . . . . . . . . . . . . . . . . . . . . . . 2
4. Matching of Internationalized Email Addresses in X.509
certificates . . . . . . . . . . . . . . . . . . . . . . . . 3
5. Name constraints in path validation . . . . . . . . . . . . . 4
6. Resource Considerations . . . . . . . . . . . . . . . . . . . 5
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
8. Security Considerations . . . . . . . . . . . . . . . . . . . 6
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
9.1. Normative References . . . . . . . . . . . . . . . . . . 6
9.2. Informative References . . . . . . . . . . . . . . . . . 7
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
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 smtputf8Name name as a form of otherName
from the GeneralName structure in SubjectAltName defined in
[RFC5280].
id-on-smtputf8Name OBJECT IDENTIFIER ::= { id-on XXX }
smtputf8Name ::= UTF8String (SIZE (1..MAX))
When the subjectAltName extension contains an Internationalized Email
address, the address MUST be stored in the smtputf8Name name form of
otherName. The format of smtputf8Name is defined as the ABNF rule
smtputf8Mailbox. smtputf8Mailbox is a modified version of the
Internationalized Mailbox which is defined in Section 3.3 of
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[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> was updated to also
support UTF8-non-ascii. UTF8-non-ascii is described by Section 3.1
of [RFC6532]. Also sub-domain is extended to support U-label, as
defined in [RFC5890]
This document further refines Internationalized [RFC6531] Mailbox
ABNF rules and calls this smtputf8Mailbox. In smtputf8Mailbox, sub-
domain that encode non-ascii characters SHALL use U-label Unicode
native character labels and MUST NOT use A-label [RFC5890]. This
restriction prevents having to determine which label encoding A- or
U-label is present in the Domain. As per Section 2.3.2.1 of
[RFC5890], U-label use UTF-8 [RFC3629] with Normalization Form C and
other properties specified there. In smtputf8Mailbox, sub-domain
that encode solely ASCII character labels SHALL use NR-LDH
restrictions as specified by section 2.3.1 of [RFC5890]. Note that a
smtputf8Mailbox 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 5. 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.
4. Matching of Internationalized Email Addresses in X.509 certificates
In equivalence comparison with smtputf8Name, there may be some setup
work to enable the comparison i.e. processing of the smtputf8Name
content or the email address that is being compared against. The
process for setup for comparing with smtputf8Name is split into
domain steps and local-part steps. The comparison form for local-
part always is UTF-8. The comparison form for domain depends on
context. While some contexts such as certificate path validation in
[RFC5280] specify transforming to A-label, this document RECOMMENDS
transforming to UTF-8 U-label even in place of those other
specifications. As more implementations natively support U-label
domain, requiring U-label reduces conversions required, which then
reduces likelihood of errors caused by bugs in implementation.
Comparison of two smtputf8Name can be straightforward. No setup work
is needed and it can be an octet for octet comparison. For other
email address forms such as Internationalized email address or
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rfc822Name, the comparison requires additional setup to convert the
format for comparison. Domain setup is particularly important for
forms that may contain A- or U-label such as International email
address, or A-label only forms such as rfc822Name. This document
specifies the process to transform the domain to U-label. (To
convert the domain to A-label, follow the process process specified
in section 7.5 and 7.2 in [RFC5280]) The first step is to detect
A-label by using section 5.1 of [RFC5891]. Next if necessary,
transform the A-label to U-label Unicode as specified in section 5.2
of [RFC5891]. Finally if necessary convert the Unicode to UTF-8 as
specified in section 3 of [RFC3629]. In setup for smtputf8Mailbox,
the email address local-part MUST be converted to UTF-8 if it is not
already. The <Local-part> part of an Internationalized email address
is already in UTF-8. For the rfc822Name local-part is IA5String
(ASCII), and conversion to UTF-8 is trivial since ASCII octets maps
to UTF-8 without change. Once the setup is completed, comparison is
an octet for octet comparison.
5. 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 4. 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 [RFC5280] is specified
with smtputf8Name name are only done on the subjectAltName
smtputf8Name name, and says nothing more about constaints on other
email address forms such as rfc822Name. Consequently it may be
necessary to include other name constraints such as rfc822Name in
addition to smtputf8Name to constrain all potential email addresses.
For example a domain with both ascii and non-ascii local-part email
addresses may require both rfc822Name and smtputf8Name name
constraints. This can be illustrated in the following Figure 1 which
shows a name constraint set in the intermediate CA certificate, which
then applies to the children entity certificates. Note that a
constraint on rfc822Name does not apply to smtputf8Name and vice
versa.
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+-------------------------------------------------+
| Root CA Cert |
+-------------------------------------------------+
|
v
+-------------------------------------------------+
| Intermediate CA Cert |
| Name Constraint Extension |
| Permitted |
| rfc822Name: allowed.com |
| smtputf8Name: allowed.com |
| Excluded |
| rfc822Name: ignored.com |
+-------------------------------------------------+
| |
v |
+-------------------------------------------------+
| Entity Cert (w/explicitly permitted subjects) |
| SubjectAltName Extension |
| rfc822Name: student@allowed.com |
| smtputf8Name: \u8001\u5E2B@allowed.com |
+-------------------------------------------------+
|
v
+-------------------------------------------------+
| Entity Cert (w/permitted subject- excluded |
| rfc822Name does not exclude smtputf8Name) |
| SubjectAltName Extension |
| smtputf8Name: \u4E0D\u5C0D@ignored.com |
+-------------------------------------------------+
Figure 1
6. Resource Considerations
For email addresses whose local-part is ASCII it may be more
reasonable to continue using rfc822Name instead of smtputf8Name. Use
of smtputf8Name incurs higher byte representation overhead due to
encoding with otherName and the additional OID needed. This document
RECOMMENDS using smtputf8Name when local-part contains non-ASCII
characters, and otherwise rfc822Name.
7. IANA Considerations
[[CREF1: Just need a new OID.]]
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8. Security Considerations
Use for smtputf8Name for certificate subjectAltName will incur many
of the same security considerations of Section 8 in [RFC5280] but
further complicated by permitting non-ASCII characters in the email
address local-part. As mentioned in Section 4.4 of [RFC5890] and in
Section 4 of [RFC6532] Unicode introduces the risk for visually
similar characters which can be exploited to deceive the recipient.
The former document references some means to mitigate against these
attacks.
9. 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,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
2003, <http://www.rfc-editor.org/info/rfc3629>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<http://www.rfc-editor.org/info/rfc5234>.
[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,
<http://www.rfc-editor.org/info/rfc5280>.
[RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
DOI 10.17487/RFC5321, October 2008,
<http://www.rfc-editor.org/info/rfc5321>.
[RFC5890] Klensin, J., "Internationalized Domain Names for
Applications (IDNA): Definitions and Document Framework",
RFC 5890, DOI 10.17487/RFC5890, August 2010,
<http://www.rfc-editor.org/info/rfc5890>.
[RFC5891] Klensin, J., "Internationalized Domain Names in
Applications (IDNA): Protocol", RFC 5891,
DOI 10.17487/RFC5891, August 2010,
<http://www.rfc-editor.org/info/rfc5891>.
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[RFC6531] Yao, J. and W. Mao, "SMTP Extension for Internationalized
Email", RFC 6531, DOI 10.17487/RFC6531, February 2012,
<http://www.rfc-editor.org/info/rfc6531>.
[RFC6532] Yang, A., Steele, S., and N. Freed, "Internationalized
Email Headers", RFC 6532, DOI 10.17487/RFC6532, February
2012, <http://www.rfc-editor.org/info/rfc6532>.
9.2. Informative References
[RFC5322] Resnick, P., Ed., "Internet Message Format", RFC 5322,
DOI 10.17487/RFC5322, October 2008,
<http://www.rfc-editor.org/info/rfc5322>.
Appendix A. Acknowledgements
Thank you to Magnus Nystrom for motivating this document. Thanks to
Nicolas Lidzborski, Laetitia Baudoin, Ryan Sleevi and Sean Leonard
for their early feedback. Also thanks to John Klensin for his
valuable input on internationalization, Unicode and ABNF formatting.
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
Mountain View, CA 94043
US
Email: weihaw@google.com
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