Network Working Group P. Hoffman Request for Comments: 3491 IMC & VPNC Category: Standards Track M. Blanchet Viagenie March 2003 Nameprep: A Stringprep Profile for Internationalized Domain Names (IDN) Status of this Memo This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (2003). All Rights Reserved.
AbstractThis document describes how to prepare internationalized domain name (IDN) labels in order to increase the likelihood that name input and name comparison work in ways that make sense for typical users throughout the world. This profile of the stringprep protocol is used as part of a suite of on-the-wire protocols for internationalizing the Domain Name System (DNS). STRINGPREP]. These processing rules are only intended for internationalized domain names, not for arbitrary text. This profile defines the following, as required by [STRINGPREP]. - The intended applicability of the profile: internationalized domain names processed by IDNA. - The character repertoire that is the input and output to stringprep: Unicode 3.2, specified in section 2.
- The mappings used: specified in section 3. - The Unicode normalization used: specified in section 4. - The characters that are prohibited as output: specified in section 5. - Bidirectional character handling: specified in section 6. IDNA] protocol for preparing domain names; it is not designed for any other purpose. It is explicitly not designed for processing arbitrary free text and SHOULD NOT be used for that purpose. Nameprep is a profile of Stringprep [STRINGPREP]. Implementations of Nameprep MUST fully implement Stringprep. Nameprep is used to process domain name labels, not domain names. IDNA calls nameprep for each label in a domain name, not for the whole domain name. BCP 14, RFC 2119 [RFC2119]. STRINGPREP] Appendix A. STRINGPREP]: Table B.1 Table B.2 STRINGPREP].
STRINGPREP]: Table C.1.2 Table C.2.2 Table C.3 Table C.4 Table C.5 Table C.6 Table C.7 Table C.8 Table C.9 IMPORTANT NOTE: This profile MUST be used with the IDNA protocol. The IDNA protocol has additional prohibitions that are checked outside of this profile. STRINGPREP] section 6. IDNA] specifies that a list of unassigned code points be used, the system uses table A.1 from [STRINGPREP] as its list of unassigned code points. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [STRINGPREP] Hoffman, P. and M. Blanchet, "Preparation of Internationalized Strings ("stringprep")", RFC 3454, December 2002. [IDNA] Faltstrom, P., Hoffman, P. and A. Costello, "Internationalizing Domain Names in Applications (IDNA)", RFC 3490, March 2003.
[STD13] Mockapetris, P., "Domain names - concepts and facilities", STD 13, RFC 1034, and "Domain names - implementation and specification", STD 13, RFC 1035, November 1987. STD13]. This document vastly increases the number of characters available in domain names. Every program that uses "special" characters in conjunction with domain names may be vulnerable to attack based on the new characters allowed by this specification.
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