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Internet Engineering Task Force (IETF)                        R. HousleyRequest for Comments: 8399                                Vigil SecurityUpdates:5280                                                   May 2018Category: Standards TrackISSN: 2070-1721Internationalization Updates toRFC 5280Abstract   The updates toRFC 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 inSection 2 of RFC 7841.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttps://www.rfc-editor.org/info/rfc8399.Housley                      Standards Track                    [Page 1]

RFC 8399 I18n Updates toRFC 5280 May 2018Copyright Notice Copyright (c) 2018 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject toBCP 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 Contents1. Introduction ....................................................31.1. Terminology ................................................32. Updates toRFC 5280 .............................................32.1. Update in the Introduction (Section 1) .....................42.2. Update in Name Constraints (Section 4.2.1.10) ..............42.3. Update in IDNs in GeneralName (Section 7.2) ................52.4. Update in IDNs in Distinguished Names (Section 7.3) ........6 2.5. Update in Internationalized Electronic Mail Addresses (Section 7.5) ....................................63. Security Considerations .........................................74. IANA Considerations .............................................85. References ......................................................85.1. Normative References .......................................85.2. Informative References .....................................9 Acknowledgements ...................................................9 Author's Address ...................................................9Housley Standards Track [Page 2]

RFC 8399                I18n Updates toRFC 5280                May 20181.  Introduction   This document updates the Introduction inSection 1, the Name   Constraints certificate extension discussion inSection 4.2.1.10, and   the Processing Rules for Internationalized Names in Section 7 ofRFC5280 [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 inBCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all   capitals, as shown here.2.  Updates toRFC 5280   This section provides updates to several paragraphs ofRFC 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 toRFC 5280 May 20182.1. Update in the Introduction (Section 1) This update provides references for IDNA2008. OLD * Enhanced support for internationalized names is specified inSection 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 inSection 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 toRFC 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 ofSection 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 inSection 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 toRFC 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 inSection 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 andRFC 8398 [RFC8398]. Since all ofSection 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 toRFC 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 inRFC 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 inSection 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 inSection 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 toRFC 5280                May 20184.  IANA Considerations   This document has no IANA actions.5.  References5.1.  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 toRFC 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 inRFC2119 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.comHousley                      Standards Track                    [Page 9]

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