Network Working Group M. Duerst Internet-Draft W3C/Keio University Expires: December 23, 2002 June 24, 2002 Internationalized Domain Names in URIs draft-duerst-idn-uri-00 Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. 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." The list of current Internet-Drafts can be accessed at http:// www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on December 23, 2002. Copyright Notice Copyright (C) The Internet Society (2002). All Rights Reserved. Abstract This document proposes to upgrade the definition of URIs (RFC 2396) [RFC2396] to work consistently with internationalized domain names. Duerst Expires December 23, 2002 [Page 1] Internet-Draft IDNs in URIs June 2002 Table of Contents 1. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1 Changes from draft-ietf-idn-uri--01 to draft-duerst-idn-uri-00 3 1.2 Changes from draft-ietf-idn-uri--00 to draft-ietf-idn-uri-01 . 3 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. URI syntax changes . . . . . . . . . . . . . . . . . . . . . . 4 4. Security considerations . . . . . . . . . . . . . . . . . . . 5 References . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Author's Address . . . . . . . . . . . . . . . . . . . . . . . 6 Full Copyright Statement . . . . . . . . . . . . . . . . . . . 7 Duerst Expires December 23, 2002 [Page 2] Internet-Draft IDNs in URIs June 2002 1. Change Log 1.1 Changes from draft-ietf-idn-uri--01 to draft-duerst-idn-uri-00 Changed to only change URIs; IRI syntax updated directly in IRI draft. Removed syntax restriction on %hh in the US-ASCII part, but made clear that restrictions to domain names apply. Made clear that escaped domain names in URIs should only be an intermediate representation. 1.2 Changes from draft-ietf-idn-uri--00 to draft-ietf-idn-uri-01 Changed requirement for URI/IRI resolvers from MUST to SHOULD Changed IRI syntax slightly (ichar -> idchar, based on changes in [IRI]) Various wording changes 2. Introduction Internet domain names serve to identify hosts and services on the Internet in a convenient way. The IETF IDN working group [IDNWG] has been working on extending the character repertoire usable in domain names beyond a subset of US-ASCII. One of the most important places where domain names appear are Uniform Resource Identifiers (URIs, [RFC2396], as modified by [RFC2732]). However, in the current definition of the generic URI syntax, the restrictions on domain names are 'hard-coded'. In Section 2, this document relaxes these restrictions by updating the syntax, and defines how internationalized domain names are encoded in URIs. The syntax in this document is defined for consistency. Uniformity of syntax is a very important principle of URIs. In practice, escaped domanin names should be used as rarely as possible. Wherever possible, the actual characters in Internationalized Domain Names should be preserved as long as possible by using IRIs [IRI] rather than URIs, and only converting to URIs and then to ACE-encoded domain names (or directly to ACE-encoding without even using URIs) when resolving the IRI. Also, this document does in no way exclude the use of ACE encoding directly in an URI domain name part. ACE encoding may be used directly in an URI domain name part if it is considered necessary for interoperability. Duerst Expires December 23, 2002 [Page 3] Internet-Draft IDNs in URIs June 2002 3. URI syntax changes The syntax of URIs [RFC2396] currently contains the following rules relevant to domain names: hostname = *( domainlabel "." ) toplabel [ "." ] domainlabel = alphanum | alphanum *( alphanum | "-" ) alphanum toplabel = alpha | alpha *( alphanum | "-" ) alphanum The later two rules are changed as follows: domainlabel = anchar | anchar *( anchar | "-" ) anchar toplabel = achar | achar *( anchar | "-" ) anchar and the following rules are added: anchar = alphanum | escaped achar = alpha | escaped Characters outside the repertoire are encoded by first encoding the characters in UTF-8 [RFC 2279], resulting in a sequence of octets, and then escaping these octets according to the rules defined in [RFC2396]. Using UTF-8 assures that this encoding interoperates with IRIs [IRI]. It is also aligned with the recommendations in [RFC2277] and [RFC2718], and is consistent with the URN syntax [RFC2141] as well as recent URL scheme definitions that define encodings of non-ASCII characters based on UTF-8 (e.g., IMAP URLs [RFC2192] and POP URLs [RFC2384]). The above syntax rules permit for domain names that are neither permitted as US-ASCII only domain names nor as internationalized domain names. However, such syntax should never be used, and must always be rejected by resolvers. For US-ASCII only domain names, the syntax rules in [RFC2396] are relevant. For example, http:// www.w%33.org is legal, because the corresponding 'w3' is a legal 'domainlabel' according to [RFC2396]. However, http:// %2a.example.org is illegal because the corresponding '*' is not a legal 'domainlabel' according to [RFC2396]. For domain names containing non-ASCII characters, the legal domain names are those for which the ToASCII operation ([IDNA], [Nameprep]; using the unescaped UTF-8 values as input) is successful. For consistency in comparison operations and for interoperability with older software, the following should be noted: 1) US-ASCII characters in domain names should never be escaped. 2) Because of the principle of syntax uniformity for URIs, it is always more Duerst Expires December 23, 2002 [Page 4] Internet-Draft IDNs in URIs June 2002 prudent to take into account the possibility that US-ASCII characters are escaped. The work of the IDN WG includes some procedures for name preparation [Nameprep]. Before encoding an internationalized domain name in an URI, this preparation step SHOULD be applied. However, the URI resolver MUST also apply any steps required by [IDNA] as part of domain name resolution. 4. Security considerations The security considerations of [RFC2396] and those applying to internationalized domain names apply. There may be an increased potential to smuggle escaped US-ASCII-based domain names across firewalls, although because of the uniform syntax principle for URIs, such a potential is already existing. References [IDNWG] "IETF Internationalized Domain Name (idn) Working Group". [IRI] Duerst, M. and M. Suignard, "Internationalized Resource Identifiers (IRI)", draft-duerst-iri-00 (work in progress), April 2002. [ISO10646] International Organization for Standardization, "Information Technology - Universal Multiple-Octet Coded Character Set (UCS) - Part 1: Architecture and Basic Multilingual Plane", ISO Standard 10646-1, October 2000. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2141] Moats, R., "URN Syntax", RFC 2141, May 1997. [RFC2192] Newman, C., "IMAP URL Scheme", RFC 2192, September 1997. [RFC2277] Alvestrand, H., "IETF Policy on Character Sets and Languages", BCP 18, RFC 2277, January 1998. [RFC2279] Yergeau, F., "UTF-8, a transformation format of ISO 10646", RFC 2279, January 1998. [RFC2384] Gellens, R., "POP URL Scheme", RFC 2384, August 1998. [RFC2396] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform Resource Identifiers (URI): Generic Syntax", RFC 2396, August 1998. Duerst Expires December 23, 2002 [Page 5] Internet-Draft IDNs in URIs June 2002 [RFC2640] Curtin, B., "Internationalization of the File Transfer Protocol", RFC 2640, July 1999. [RFC2718] Masinter, L., Alvestrand, H., Zigmond, D. and R. Petke, "Guidelines for new URL Schemes", RFC 2718, November 1999. [RFC2732] Hinden, R., Carpenter, B. and L. Masinter, "Format for Literal IPv6 Addresses in URL's", RFC 2732, December 1999. [IDNA] Faltstrom, P., Hoffman, P. and A. Costello, "Internationalizing Domain Names in Applications (IDNA)", draft-ietf-idn-idna-09.txt (work in progress), May 2002, . [Nameprep] Hoffman, P. and M. Blanchet, "Nameprep: A Stringprep Profile for Internationalized Domain Names", draft-ietf- idn-nameprep-10.txt (work in progress), May 2002, . Author's Address Martin Duerst W3C/Keio University 5322 Endo Fujisawa 252-8520 Japan Phone: +81 466 49 1170 Fax: +81 466 49 1171 EMail: duerst@w3.org URI: http://www.w3.org/People/D%C3%BCrst/ Duerst Expires December 23, 2002 [Page 6] Internet-Draft IDNs in URIs June 2002 Full Copyright Statement Copyright (C) The Internet Society (2002). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Acknowledgement Funding for the RFC Editor function is currently provided by the Internet Society. Duerst Expires December 23, 2002 [Page 7]