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rfc:rfc8399

Internet Engineering Task Force (IETF) R. Housley Request for Comments: 8399 Vigil Security Updates: 5280 May 2018 Category: Standards Track ISSN: 2070-1721

              Internationalization Updates to RFC 5280

Abstract

 The updates to RFC 5280 described in this document provide alignment
 with the 2008 specification for Internationalized Domain Names (IDNs)
 and add support for internationalized email addresses in X.509
 certificates.

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 7841.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 https://www.rfc-editor.org/info/rfc8399.

Housley Standards Track [Page 1] RFC 8399 I18n Updates to RFC 5280 May 2018

Copyright Notice

 Copyright (c) 2018 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
 (https://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.
 This document may contain material from IETF Documents or IETF
 Contributions published or made publicly available before November
 10, 2008.  The person(s) controlling the copyright in some of this
 material may not have granted the IETF Trust the right to allow
 modifications of such material outside the IETF Standards Process.
 Without obtaining an adequate license from the person(s) controlling
 the copyright in such materials, this document may not be modified
 outside the IETF Standards Process, and derivative works of it may
 not be created outside the IETF Standards Process, except to format
 it for publication as an RFC or to translate it into languages other
 than English.

Table of Contents

 1. Introduction ....................................................3
    1.1. Terminology ................................................3
 2. Updates to RFC 5280 .............................................3
    2.1. Update in the Introduction (Section 1) .....................4
    2.2. Update in Name Constraints (Section 4.2.1.10) ..............4
    2.3. Update in IDNs in GeneralName (Section 7.2) ................5
    2.4. Update in IDNs in Distinguished Names (Section 7.3) ........6
    2.5. Update in Internationalized Electronic Mail
         Addresses (Section 7.5) ....................................6
 3. Security Considerations .........................................7
 4. IANA Considerations .............................................8
 5. References ......................................................8
    5.1. Normative References .......................................8
    5.2. Informative References .....................................9
 Acknowledgements ...................................................9
 Author's Address ...................................................9

Housley Standards Track [Page 2] RFC 8399 I18n Updates to RFC 5280 May 2018

1. Introduction

 This document updates the Introduction in Section 1, the Name
 Constraints certificate extension discussion in Section 4.2.1.10, and
 the Processing Rules for Internationalized Names in Section 7 of RFC
 5280 [RFC5280] to provide alignment with the 2008 specification for
 Internationalized Domain Names (IDNs) and add support for
 internationalized email addresses in X.509 certificates.
 An IDN in Unicode (native character) form contains at least one
 U-label [RFC5890].  With one exception, IDNs are carried in
 certificates in ACE-encoded form.  That is, all U-labels within an
 IDN are converted to A-labels.  Conversion of a U-label to an A-label
 is described in [RFC5891].
 The GeneralName structure supports many different name forms,
 including otherName for extensibility.  RFC 8398 [RFC8398] specifies
 the SmtpUTF8Mailbox for internationalized email addresses, which
 includes IDNs with U-labels.
 Note that Internationalized Domain Names in Applications
 specifications published in 2003 (IDNA2003) [RFC3490] and 2008
 (IDNA2008) [RFC5890] both refer to the Punycode algorithm for
 conversion [RFC3492].

1.1. Terminology

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
 "OPTIONAL" in this document are to be interpreted as described in
 BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
 capitals, as shown here.

2. Updates to RFC 5280

 This section provides updates to several paragraphs of RFC 5280
 [RFC5280].  For clarity, if the entire section is not replaced, then
 the original text and the replacement text are shown.

Housley Standards Track [Page 3] RFC 8399 I18n Updates to RFC 5280 May 2018

2.1. Update in the Introduction (Section 1)

 This update provides references for IDNA2008.
 OLD
  • Enhanced support for internationalized names is specified in

Section 7, with rules for encoding and comparing

      Internationalized Domain Names, Internationalized Resource
      Identifiers (IRIs), and distinguished names.  These rules are
      aligned with comparison rules established in current RFCs,
      including [RFC3490], [RFC3987], and [RFC4518].
 NEW
  • Enhanced support for internationalized names is specified in

Section 7, with rules for encoding and comparing

      Internationalized Domain Names, Internationalized Resource
      Identifiers (IRIs), and distinguished names.  These rules are
      aligned with comparison rules established in current RFCs,
      including [RFC3987], [RFC4518], [RFC5890], and [RFC5891].

2.2. Update in Name Constraints (Section 4.2.1.10)

 This update removes the ability to include constraints for a
 particular mailbox.  This capability was not used, and removing it
 allows name constraints to apply to email addresses in rfc822Name and
 SmtpUTF8Mailbox [RFC8398] within otherName.
 OLD
 A name constraint for Internet mail addresses MAY specify a
 particular mailbox, all addresses at a particular host, or all
 mailboxes in a domain.  To indicate a particular mailbox, the
 constraint is the complete mail address.  For example,
 "root@example.com" indicates the root mailbox on the host
 "example.com".  To indicate all Internet mail addresses on a
 particular host, the constraint is specified as the host name.  For
 example, the constraint "example.com" is satisfied by any mail
 address at the host "example.com".  To specify any address within a
 domain, the constraint is specified with a leading period (as with
 URIs).  For example, ".example.com" indicates all the Internet mail
 addresses in the domain "example.com", but not Internet mail
 addresses on the host "example.com".

Housley Standards Track [Page 4] RFC 8399 I18n Updates to RFC 5280 May 2018

 NEW
 A name constraint for Internet mail addresses MAY specify all
 addresses at a particular host or all mailboxes in a domain.  To
 indicate all Internet mail addresses on a particular host, the
 constraint is specified as the host name.  For example, the
 constraint "example.com" is satisfied by any mail address at the
 host "example.com".  To specify any address within a domain, the
 constraint is specified with a leading period (as with URIs).  For
 example, ".example.com" indicates all the Internet mail addresses
 in the domain "example.com" but not Internet mail addresses on
 the host "example.com".

2.3. Update in IDNs in GeneralName (Section 7.2)

 This update aligns with IDNA2008.  Since all of Section 7.2 is
 replaced, the OLD text is not provided.
 NEW
 Internationalized Domain Names (IDNs) may be included in certificates
 and CRLs in the subjectAltName and issuerAltName extensions, name
 constraints extension, authority information access extension,
 subject information access extension, CRL distribution points
 extension, and issuing distribution point extension.  Each of these
 extensions uses the GeneralName type; one choice in GeneralName is
 the dNSName field, which is defined as type IA5String.
 IA5String is limited to the set of ASCII characters.  To accommodate
 IDNs, U-labels are converted to A-labels.  The A-label is the
 encoding of the U-label according to the Punycode algorithm [RFC3492]
 with the ACE prefix "xn--" added at the beginning of the string.
 When comparing DNS names for equality, conforming implementations
 MUST perform a case-insensitive exact match on the entire DNS name.
 When evaluating name constraints, conforming implementations MUST
 perform a case-insensitive exact match on a label-by-label basis.  As
 noted in Section 4.2.1.10, any DNS name that may be constructed by
 adding labels to the left-hand side of the domain name given as the
 constraint is considered to fall within the indicated subtree.
 Implementations SHOULD convert IDNs to Unicode before display.
 Specifically, conforming implementations convert A-labels to U-labels
 for display.

Housley Standards Track [Page 5] RFC 8399 I18n Updates to RFC 5280 May 2018

 Implementation consideration: There are increased memory requirements
 for IDNs.  An IDN ACE label will begin with the four additional
 characters "xn--", and an IDN can require as many as five ASCII
 characters to specify a single international character.

2.4. Update in IDNs in Distinguished Names (Section 7.3)

 This update aligns with IDNA2008.
 OLD
 Domain Names may also be represented as distinguished names using
 domain components in the subject field, the issuer field, the
 subjectAltName extension, or the issuerAltName extension.  As with
 the dNSName in the GeneralName type, the value of this attribute is
 defined as an IA5String.  Each domainComponent attribute represents a
 single label.  To represent a label from an IDN in the distinguished
 name, the implementation MUST perform the "ToASCII" label conversion
 specified in Section 4.1 of RFC 3490.  The label SHALL be considered
 a "stored string".  That is, the AllowUnassigned flag SHALL NOT be
 set.
 NEW
 Domain names may also be represented as distinguished names using
 domain components in the subject field, the issuer field, the
 subjectAltName extension, or the issuerAltName extension.  As with
 the dNSName in the GeneralName type, the value of this attribute is
 defined as an IA5String.  Each domainComponent attribute represents a
 single label.  To represent a label from an IDN in the distinguished
 name, the implementation MUST convert all U-labels to A-labels.

2.5. Update in Internationalized Electronic Mail Addresses

    (Section 7.5)
 This update aligns with IDNA2008 and RFC 8398 [RFC8398].  Since all
 of Section 7.5 is replaced, the OLD text is not provided.
 NEW
 Electronic Mail addresses may be included in certificates and CRLs in
 the subjectAltName and issuerAltName extensions, name constraints
 extension, authority information access extension, subject
 information access extension, issuing distribution point extension,
 or CRL distribution points extension.  Each of these extensions uses
 the GeneralName construct.  If the email address includes an IDN but
 the local-part of the email address can be represented in ASCII, then
 the email address is placed in the rfc822Name choice of GeneralName,

Housley Standards Track [Page 6] RFC 8399 I18n Updates to RFC 5280 May 2018

 which is defined as type IA5String.  If the local-part of the
 internationalized email address cannot be represented in ASCII, then
 the internationalized email address is placed in the otherName choice
 of GeneralName using the conventions in RFC 8398 [RFC8398].
 7.5.1.  Local-Part Contains Only ASCII Characters
 Where the host-part contains an IDN, conforming implementations MUST
 convert all U-labels to A-labels.
 Two email addresses are considered to match if:
    1) the local-part of each name is an exact match, AND
    2) the host-part of each name matches using a case-insensitive
       ASCII comparison.
 Implementations SHOULD convert the host-part of internationalized
 email addresses specified in these extensions to Unicode before
 display.  Specifically, conforming implementations convert A-labels
 to U-labels for display.
 7.5.2.  Local-Part Contains Non-ASCII Characters
 When the local-part contains non-ASCII characters, conforming
 implementations MUST place the internationalized email address in the
 SmtpUTF8Mailbox within the otherName choice of GeneralName as
 specified in Section 3 of RFC 8398 [RFC8398].  Note that the UTF8
 encoding of the internationalized email address MUST NOT contain a
 Byte-Order-Mark (BOM) [RFC3629] to aid comparison.
 The comparison of two internationalized email addresses is specified
 in Section 5 of RFC 8398 [RFC8398].
 Implementations SHOULD convert the host-part of internationalized
 email addresses specified in these extensions to Unicode before
 display.  Specifically, conforming implementations convert A-labels
 to U-labels for display.

3. Security Considerations

 Conforming CAs SHOULD ensure that IDNs are valid.  This can be done
 by validating all code points according to IDNA2008 [RFC5892].
 Failure to use valid A-labels and valid U-labels may yield a domain
 name that cannot be correctly represented in the Domain Name System
 (DNS).  In addition, the CA/Browser Forum offers some guidance
 regarding internal server names in certificates [CABF].

Housley Standards Track [Page 7] RFC 8399 I18n Updates to RFC 5280 May 2018

4. IANA Considerations

 This document has no IANA actions.

5. References

5.1. 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,
            <https://www.rfc-editor.org/info/rfc2119>.
 [RFC3492]  Costello, A., "Punycode: A Bootstring encoding of Unicode
            for Internationalized Domain Names in Applications
            (IDNA)", RFC 3492, DOI 10.17487/RFC3492, March 2003,
            <https://www.rfc-editor.org/info/rfc3492>.
 [RFC3629]  Yergeau, F., "UTF-8, a transformation format of ISO
            10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
            2003, <https://www.rfc-editor.org/info/rfc3629>.
 [RFC3987]  Duerst, M. and M. Suignard, "Internationalized Resource
            Identifiers (IRIs)", RFC 3987, DOI 10.17487/RFC3987,
            January 2005, <https://www.rfc-editor.org/info/rfc3987>.
 [RFC4518]  Zeilenga, K., "Lightweight Directory Access Protocol
            (LDAP): Internationalized String Preparation", RFC 4518,
            DOI 10.17487/RFC4518, June 2006,
            <https://www.rfc-editor.org/info/rfc4518>.
 [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,
            <https://www.rfc-editor.org/info/rfc5280>.
 [RFC5890]  Klensin, J., "Internationalized Domain Names for
            Applications (IDNA): Definitions and Document Framework",
            RFC 5890, DOI 10.17487/RFC5890, August 2010,
            <https://www.rfc-editor.org/info/rfc5890>.
 [RFC5891]  Klensin, J., "Internationalized Domain Names in
            Applications (IDNA): Protocol", RFC 5891,
            DOI 10.17487/RFC5891, August 2010,
            <https://www.rfc-editor.org/info/rfc5891>.

Housley Standards Track [Page 8] RFC 8399 I18n Updates to RFC 5280 May 2018

 [RFC5892]  Faltstrom, P., Ed., "The Unicode Code Points and
            Internationalized Domain Names for Applications (IDNA)",
            RFC 5892, DOI 10.17487/RFC5892, August 2010,
            <https://www.rfc-editor.org/info/rfc5892>.
 [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
            2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
            May 2017, <https://www.rfc-editor.org/info/rfc8174>.
 [RFC8398]  Melnikov, A., Ed. and W.  Chuang, Ed., "Internationalized
            Email Addresses in X.509 Certificates",
            DOI 10.17487/RFC8398, May 2016,
            <http://www.rfc-editor.org/info/rfc8398>.

5.2. Informative References

 [CABF]     CA/Browser Forum, "Internal Server Names and IP Address
            Requirements for SSL: Guidance on the Deprecation of
            Internal Server Names and Reserved IP Addresses provided
            by the CA/Browser Forum", Version 1.0, June 2012,
            <https://cabforum.org/internal-names/>.
 [RFC3490]  Faltstrom, P., Hoffman, P., and A. Costello,
            "Internationalizing Domain Names in Applications (IDNA)",
            RFC 3490, DOI 10.17487/RFC3490, March 2003,
            <https://www.rfc-editor.org/info/rfc3490>.

Acknowledgements

 Thanks to Alexey Melnikov for the encouragement to write this update.
 Thanks to John Klensin and Patrik Falstrom for confirming many of the
 details in this update.  Thanks to Ben Campbell, Wei Chuang, Spencer
 Dawkins, Phillip Hallam-Baker, Warren Kumari, Alexey Melnikov, Adam
 Roach, Tim Ruehsen, and Sean Turner for their careful review and
 comments.

Author's Address

 Russ Housley
 Vigil Security, LLC
 918 Spring Knoll Drive
 Herndon, VA 20170
 United States of America
 Email: housley@vigilsec.com

Housley Standards Track [Page 9]

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