This document is obsolete. Please
refer to RFC 5891.
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.
Abstract
This 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).
This document specifies processing rules that will allow users to enter internationalized domain names (IDNs) into applications and have the highest chance of getting the content of the strings correct. It is a profile of stringprep [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.
Nameprep is used by the IDNA [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.
IMPORTANT NOTE: This profile MUST be used with the IDNA protocol. The IDNA protocol has additional prohibitions that are checked outside of this profile.
This profile specifies checking bidirectional strings as described in [STRINGPREP] section 6.
7. Unassigned Code Points in Internationalized Domain Names
If the processing in [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.
The Unicode and ISO/IEC 10646 repertoires have many characters that look similar. In many cases, users of security protocols might do visual matching, such as when comparing the names of trusted third parties. Because it is impossible to map similar-looking characters without a great deal of context such as knowing the fonts used, stringprep does nothing to map similar-looking characters together nor to prohibit some characters because they look like others.
Security on the Internet partly relies on the DNS. Thus, any change to the characteristics of the DNS can change the security of much of the Internet.
Domain names are used by users to connect to Internet servers. The security of the Internet would be compromised if a user entering a single internationalized name could be connected to different servers based on different interpretations of the internationalized domain name.
Current applications might assume that the characters allowed in domain names will always be the same as they are in [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.
Copyright (C) The Internet Society (2003). All Rights Reserved.
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Acknowledgement
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