Internationalized Email Addresses in X.509 certificates
draft-ietf-lamps-eai-addresses-07
The information below is for an old version of the document.
| Document | Type | Active Internet-Draft (lamps WG) | |
|---|---|---|---|
| Authors | Alexey Melnikov , Wei Chuang | ||
| Last updated | 2017-03-08 | ||
| Replaces | draft-melnikov-spasm-eai-addresses | ||
| Stream | Internet Engineering Task Force (IETF) | ||
| Formats | plain text xml htmlized pdfized bibtex | ||
| Reviews |
GENART Last Call review
(of
-05)
Ready with Nits
SECDIR Last Call review
(of
-05)
Has Nits
|
||
| Stream | WG state | Submitted to IESG for Publication | |
| Document shepherd | Russ Housley | ||
| Shepherd write-up | Show Last changed 2016-12-27 | ||
| IESG | IESG state | Waiting for Writeup | |
| Consensus boilerplate | Yes | ||
| Telechat date | (None) | ||
| Responsible AD | Stephen Farrell | ||
| Send notices to | "Russ Housley" <housley@vigilsec.com> | ||
| IANA | IANA review state | Version Changed - Review Needed |
draft-ietf-lamps-eai-addresses-07
LAMPS A. Melnikov, Ed.
Internet-Draft Isode Ltd
Intended status: Standards Track W. Chuang, Ed.
Expires: September 9, 2017 Google, Inc.
March 8, 2017
Internationalized Email Addresses in X.509 certificates
draft-ietf-lamps-eai-addresses-07
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
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
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 9, 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
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Melnikov & Chuang Expires September 9, 2017 [Page 1]
Internet-Draft I18N Mail Addresses in X.509 certificates March 2017
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 . . . . . . . . . . . . . . . . . . 8
8. Security Considerations . . . . . . . . . . . . . . . . . . . 8
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
10.1. Normative References . . . . . . . . . . . . . . . . . . 9
10.2. Informative References . . . . . . . . . . . . . . . . . 10
Appendix A. ASN.1 Module . . . . . . . . . . . . . . . . . . . . 10
Appendix B. Example of SmtpUTF8Name . . . . . . . . . . . . . . 11
Appendix C. Acknowledgements . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
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
document calls for all email address domain in X.509 certificates to
conform to IDNA2008 [RFC5890].
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
The GeneralName structure is defined in [RFC5280], and supports many
different names forms including otherName for extensibility. This
section specifies the SmtpUTF8Name name form of otherName, so that
Internationalized Email addresses can appear in the subjectAltName of
Melnikov & Chuang Expires September 9, 2017 [Page 2]
Internet-Draft I18N Mail Addresses in X.509 certificates March 2017
a certificate, the issuerAltName of a certificate, or anywhere else
that GeneralName is used.
id-on-SmtpUTF8Name OBJECT IDENTIFIER ::= { id-on 9 }
SmtpUTF8Name ::= UTF8String (SIZE (1..MAX))
When the subjectAltName (or issuerAltName) 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 was defined
in Section 3.3 of [RFC6531] which was 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 was
described by Section 3.1 of [RFC6532]. Also, sub-domain was 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 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 <Mailbox> 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.
Melnikov & Chuang Expires September 9, 2017 [Page 3]
Internet-Draft I18N Mail Addresses in X.509 certificates March 2017
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
possibility of conversion errors between alternate forms. This
applies to SmtpUTF8Mailbox and rfc822Name in subjectAltName,
issuerAltName and anywhere else that GeneralName is used.
5. 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 domain to A-label, this document
RECOMMENDS transforming to UTF-8 U-label instead. This reduces the
likelihood of errors by reducing conversions as more implementations
natively support U-label domains.
Comparison of two SmtpUTF8Name is straightforward with no setup work
needed. They are considered equivalent if there is an exact octet-
for-octet match. Comparison with other email address forms such as
Internationalized email address or rfc822Name requires additional
setup steps. 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 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]. For ASCII NR-LDH labels, upper case letters are converted
to lower case letters. In setup for SmtpUTF8Mailbox, the email
address local-part MUST conform to the requirements of [RFC6530] and
[RFC6531], including being a string in UTF-8 form. In particular,
the local-part MUST NOT be transformed in any way, such as by doing
case folding or normalization of any kind. The <Local-part> part of
an Internationalized email address is already in UTF-8. For
rfc822Name the local-part, which is IA5String (ASCII), trivially maps
Melnikov & Chuang Expires September 9, 2017 [Page 4]
Internet-Draft I18N Mail Addresses in X.509 certificates March 2017
to UTF-8 without change. Once setup is complete, they are again
compared octet-for-octet.
To summarize non-normatively, the comparison steps including setup
are:
1. If the domain contains A-labels, transform them to U-label.
2. If the domain contains ASCII NR-LDH labels, lowercase them.
3. Ensure local-part is UTF-8.
4. Compare strings octet-for-octet for equivalence.
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 subjectAltName
names, they are specified in the following profile to prevent
bypassing of name constraints. Host name and domain constraints MUST
use both rfc822Name and SmtpUTF8Name forms in the issuing certificate
with the constraint. Complete email address constraint with UTF-8
local-part MUST only use SmtpUTF8Name form. Complete email address
constraint with ASCII local-part MUST use both rfc822Name and
SmtpUTF8Name forms. When both rfc822Name and SmtpUTF8Name name
Melnikov & Chuang Expires September 9, 2017 [Page 5]
Internet-Draft I18N Mail Addresses in X.509 certificates March 2017
constraints forms are present, they MUST carry the equivalent
constraints as defined by Section 5 and MUST be found in the same
node and in the same permittedSubtrees or excludedSubtrees. This
specification intentionally leaves unchanged rfc822Name name
constraint processing as described in Section 4.2.1.10 of [RFC5280].
This document specifies that SmtpUTF8Name aware path validators check
for SmtpUTF8Name name constraint profiles as an additional path
validation step in Section 6 of [RFC5280]. SmtpUTF8Name aware
validators MUST NOT accept any certificate whose path contains an
issuing certificate whose rfc822Name or SmtpUTF8Name name constraints
do not match the above profile. That is the path validator verifies
that a rfc822Name name constraint has a corresponding SmtpUTF8Name
constraint and that a SmtpUTF8Name name constraint has a
corresponding rfc822Name constraint when the constraint contains host
name, domain or email address with an ASCII local-part. This
correspondence is required to be in the same issuing certificate node
and in the same nameConstraint permittedSubtrees or excludedSubtrees.
The name constraint requirement with SmtpUTF8Name subjectAltName is
illustrated in the following non-normative diagram Figure 1. This
show a SmtpUTF8Name aware issuer that constrained the intermediate CA
with host name and email address name constraints. In particular the
email address constraint with UTF8 local-part only used a single
SmtpUTF8Name name constraint, while the email address constraint with
ASCII local-part used both rfc822Name and SmtpUTF8Name name
constraints. The next non-normative diagram Figure 2 illustrates
legacy name constraints to contrasts the changes this document
specifies. The legacy approach has only a single rfc822Name name
email address name constraint.
Melnikov & Chuang Expires September 9, 2017 [Page 6]
Internet-Draft I18N Mail Addresses in X.509 certificates March 2017
+--------------------------------------------------------------+
| Root CA Cert |
+--------------------------------------------------------------+
|
v
+--------------------------------------------------------------+
| Intermediate CA Cert |
| Name Constraint Extension |
| Permitted |
| rfc822Name: allowed_host.example.com |
| SmtpUTF8Name: allowed_host.example.com |
| |
| SmtpUTF8Name: u+8001u+5E2B@allowed_email.example.com |
| |
| rfc822Name: student@allowed_email.example.com |
| SmtpUTF8Name: student@allowed_email.example.com |
+--------------------------------------------------------------+
|
v
+--------------------------------------------------------------+
| Entity Cert (w/explicitly permitted subjects) |
| SubjectAltName Extension |
| SmtpUTF8Name: u+533Bu+751F@allowed_host.example.com |
| |
| SmtpUTF8Name: u+8001u+5E2B@allowed_email.example.com |
| |
| rfc822Name: student@allowed_email.example.com |
+--------------------------------------------------------------+
Name constraints with SmtpUTF8Name
Figure 1
Melnikov & Chuang Expires September 9, 2017 [Page 7]
Internet-Draft I18N Mail Addresses in X.509 certificates March 2017
+--------------------------------------------------------------+
| Root CA Cert |
+--------------------------------------------------------------+
|
v
+--------------------------------------------------------------+
| Intermediate CA Cert |
| Name Constraint Extension |
| Permitted |
| rfc822Name: allowed_host.example.com |
+--------------------------------------------------------------+
|
v
+--------------------------------------------------------------+
| Entity Cert (w/explicitly permitted subjects) |
| SubjectAltName Extension |
| rfc822Name: student@allowed_host.example.com |
+--------------------------------------------------------------+
Legacy name constraints with rfc822Name
Figure 2
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 smptUtf8Name 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
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.
Melnikov & Chuang Expires September 9, 2017 [Page 8]
Internet-Draft I18N Mail Addresses in X.509 certificates March 2017
9. 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
10.1. 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>.
Melnikov & Chuang Expires September 9, 2017 [Page 9]
Internet-Draft I18N Mail Addresses in X.509 certificates March 2017
[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>.
[RFC6530] Klensin, J. and Y. Ko, "Overview and Framework for
Internationalized Email", RFC 6530, DOI 10.17487/RFC6530,
February 2012, <http://www.rfc-editor.org/info/rfc6530>.
[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>.
10.2. 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,
<http://www.rfc-editor.org/info/rfc5912>.
Appendix A. ASN.1 Module
The following ASN.1 module normatively specifies the SmtpUTF8Name
structure. This specification uses the ASN.1 definitions from
[RFC5912] with the 2002 ASN.1 notation used in that document.
[RFC5912] updates normative documents using older ASN.1 notation.
Melnikov & Chuang Expires September 9, 2017 [Page 10]
Internet-Draft I18N Mail Addresses in X.509 certificates March 2017
LAMPS-EaiAddresses-2016
{ iso(1) identified-organization(3) dod(6)
internet(1) security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-lamps-eai-addresses-2016(TBD) }
DEFINITIONS IMPLICIT TAGS ::=
BEGIN
IMPORTS
OTHER-NAME
FROM PKIX1Implicit-2009
{ iso(1) identified-organization(3) dod(6) internet(1) security(5)
mechanisms(5) pkix(7) id-mod(0) id-mod-pkix1-implicit-02(59) }
id-pkix
FROM PKIX1Explicit-2009
{ iso(1) identified-organization(3) dod(6) internet(1) security(5)
mechanisms(5) pkix(7) id-mod(0) id-mod-pkix1-explicit-02(51) } ;
--
-- otherName carries additional name types for subjectAltName,
-- issuerAltName, and other uses of GeneralNames.
--
id-on OBJECT IDENTIFIER ::= { id-pkix 8 }
SmtpUtf8OtherNames OTHER-NAME ::= { on-SmtpUTF8Name, ... }
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 3
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".
Melnikov & Chuang Expires September 9, 2017 [Page 11]
Internet-Draft I18N Mail Addresses in X.509 certificates March 2017
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 4
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, Viktor Dukhovni and Patrik
Falstrom for their feedback. Also special thanks to John Klensin for
his valuable input on internationalization, Unicode and ABNF
formatting, and to Jim Schaad for his help with the ASN.1 example and
his helpful feedback.
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
Melnikov & Chuang Expires September 9, 2017 [Page 12]