draft-ietf-idn-nameprep-10.txt   rfc3491.txt 
Internet Draft Paul Hoffman
draft-ietf-idn-nameprep-10.txt IMC & VPNC
May 17, 2002 Marc Blanchet
Expires in six months ViaGenie
Nameprep: A Stringprep Profile for Internationalized Domain Names Network Working Group P. Hoffman
Request for Comments: 3491 IMC & VPNC
Category: Standards Track M. Blanchet
Viagenie
March 2003
Status of this memo Nameprep: A Stringprep Profile for
Internationalized Domain Names (IDN)
This document is an Internet-Draft and is in full conformance with all Status of this Memo
provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering Task This document specifies an Internet standards track protocol for the
Force (IETF), its areas, and its working groups. Note that other groups Internet community, and requests discussion and suggestions for
may also distribute working documents as Internet-Drafts. 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.
Internet-Drafts are draft documents valid for a maximum of six months Copyright Notice
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."
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Abstract Abstract
This document describes how to prepare internationalized domain name This document describes how to prepare internationalized domain name
labels in order to increase the likelihood that name input and name (IDN) labels in order to increase the likelihood that name input and
comparison work in ways that make sense for typical users throughout the name comparison work in ways that make sense for typical users
world. This profile of the stringprep protocol is used as part of a throughout the world. This profile of the stringprep protocol is
suite of on-the-wire protocols for internationalizing the DNS. used as part of a suite of on-the-wire protocols for
internationalizing the Domain Name System (DNS).
1. Introduction 1. Introduction
This document specifies processing rules that will allow users to enter This document specifies processing rules that will allow users to
internationalized domain names in applications and have the highest enter internationalized domain names (IDNs) into applications and
chance of getting the content of the strings correct. It is a profile of have the highest chance of getting the content of the strings
stringprep [STRINGPREP]. These processing rules are only intended for correct. It is a profile of stringprep [STRINGPREP]. These
internationalized domain names, not for arbitrary text. processing rules are only intended for internationalized domain
names, not for arbitrary text.
This profile defines the following, as required by [STRINGPREP] This profile defines the following, as required by [STRINGPREP].
- The intended applicability of the profile: internationalized - The intended applicability of the profile: internationalized
domain names processed by IDNA domain names processed by IDNA.
- The character repertoire that is the input and output to stringprep: - The character repertoire that is the input and output to
Unicode 3.1, specified in Section 2 stringprep: Unicode 3.2, specified in section 2.
- The mappings used: specified in Section 3 - The mappings used: specified in section 3.
- The Unicode normalization used: specified in Section 4 - The Unicode normalization used: specified in section 4.
- The characters that are prohibited as output: specified in section 5 - The characters that are prohibited as output: specified in section
5.
- Bidirectional character handling: specified in section 6.
1.1 Interaction of protocol parts 1.1 Interaction of protocol parts
Nameprep is used by the IDNA [IDNA] protocol for preparing domain names; Nameprep is used by the IDNA [IDNA] protocol for preparing domain
it is not designed for any other purpose. It is explicitly not designed names; it is not designed for any other purpose. It is explicitly
for processing arbitrary free text and SHOULD NOT be used for that not designed for processing arbitrary free text and SHOULD NOT be
purpose. Nameprep is a profile of Stringprep [STRINGPREP]. used for that purpose. Nameprep is a profile of Stringprep
Implementations of Nameprep MUST fully implement Stringprep. [STRINGPREP]. Implementations of Nameprep MUST fully implement
Stringprep.
Nameprep is used to process domain name labels, not domain names. IDNA Nameprep is used to process domain name labels, not domain names.
calls nameprep for each label in a domain name, not for the whole domain IDNA calls nameprep for each label in a domain name, not for the
name. whole domain name.
1.2 Terminology 1.2 Terminology
The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY"
"MAY" in this document are to be interpreted as described in RFC 2119 in this document are to be interpreted as described in BCP 14, RFC
[RFC2119]. 2119 [RFC2119].
2. Character Repertoire 2. Character Repertoire
This profile uses Unicode 3.1, as defined in [STRINGPREP] Appendix This profile uses Unicode 3.2, as defined in [STRINGPREP] Appendix A.
A.1.
3. Mapping 3. Mapping
This profile specifies mapping using the following tables from This profile specifies mapping using the following tables from
[STRINGPREP]: [STRINGPREP]:
Table B.1
Table B.2 Table B.1
Table B.2
4. Normalization 4. Normalization
This profile specifies using Unicode normalization form KC, as described This profile specifies using Unicode normalization form KC, as
in [STRINGPREP]. described in [STRINGPREP].
5. Prohibited Output 5. Prohibited Output
This profile specifies prohibiting using the following tables from This profile specifies prohibiting using the following tables from
[STRINGPREP]: [STRINGPREP]:
Table C.1
Table C.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 Table C.1.2
IDNA protocol has additional prohibitions that are checked outside of Table C.2.2
this profile. Table C.3
Table C.4
Table C.5
Table C.6
Table C.7
Table C.8
Table C.9
In addition, this profile adds the prohibitions. Thus, the full set of IMPORTANT NOTE: This profile MUST be used with the IDNA protocol.
prohibited characters are those from the tables above plus those listed The IDNA protocol has additional prohibitions that are checked
individually below. outside of this profile.
5.1 Inappropriate characters from common input mechanisms 6. Bidirectional characters
U+3002 is used as if it were U+002E in many domain name input mechanisms This profile specifies checking bidirectional strings as described in
used by applications, particularly in Asia. Thus, U+3002 is prohibited [STRINGPREP] section 6.
in domain names by this specification.
3002; IDEOGRAPHIC FULL STOP 7. Unassigned Code Points in Internationalized Domain Names
6. 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.
If the processing in [IDNA] specifies that a list of unassigned code 8. References
points be used, the system uses table A.1 from [STRINGPREP] as its list
of unassigned code points.
7. References 8.1 Normative References
7.1 Normative references [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[IDNA] Patrik Faltstrom, Paul Hoffman, and Adam M. Costello, [STRINGPREP] Hoffman, P. and M. Blanchet, "Preparation of
"Internationalizing Domain Names in Applications (IDNA)", Internationalized Strings ("stringprep")", RFC 3454,
draft-ietf-idn-idna, work-in-progress. December 2002.
[STRINGPREP] Paul Hoffman and Marc Blanchet, "Preparation of [IDNA] Faltstrom, P., Hoffman, P. and A. Costello,
Internationalized Strings ("stringprep")", draft-hoffman-stringprep, "Internationalizing Domain Names in Applications
work in progress. (IDNA)", RFC 3490, March 2003.
7.2 Informative references 8.2 Informative references
[RFC2119] Scott Bradner, "Key words for use in RFCs to Indicate [STD13] Mockapetris, P., "Domain names - concepts and
Requirement Levels", March 1997, RFC 2119. facilities", STD 13, RFC 1034, and "Domain names -
implementation and specification", STD 13, RFC 1035,
November 1987.
[STD13] Paul Mockapetris, "Domain names - concepts and facilities" (RFC 9. Security Considerations
1034) and "Domain names - implementation and specification" (RFC 1035,
STD 13, November 1987.
8. Security Considerations 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.
The Unicode and ISO/IEC 10646 repertoires have many characters that look Security on the Internet partly relies on the DNS. Thus, any change
similar. In many cases, users of security protocols might do visual to the characteristics of the DNS can change the security of much of
matching, such as when comparing the names of trusted third parties. the Internet.
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 Domain names are used by users to connect to Internet servers. The
to the characteristics of the DNS can change the security of much of the security of the Internet would be compromised if a user entering a
Internet. single internationalized name could be connected to different servers
based on different interpretations of the internationalized domain
name.
Domain names are used by users to connect to Internet servers. The Current applications might assume that the characters allowed in
security of the Internet would be compromised if a user entering a domain names will always be the same as they are in [STD13]. This
single internationalized name could be connected to different servers document vastly increases the number of characters available in
based on different interpretations of the internationalized domain name. 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.
Current applications might assume that the characters allowed in domain 10. IANA Considerations
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.
9. IANA Considerations This is a profile of stringprep. It has been registered by the IANA
in the stringprep profile registry
(www.iana.org/assignments/stringprep-profiles).
This is a profile of stringprep. When it becomes an RFC, it should be Name of this profile:
registered in the stringprep profile registry. Nameprep
10. Acknowledgements RFC in which the profile is defined:
This document.
Many people from the IETF IDN Working Group and the Unicode Technical Indicator whether or not this is the newest version of the
Committee contributed ideas that went into the first draft of this profile:
document. This is the first version of Nameprep.
The IDN namprep design team made many useful changes to the first 11. Acknowledgements
draft. That team and its advisors include:
Asmus Freytag Many people from the IETF IDN Working Group and the Unicode Technical
Cathy Wissink Committee contributed ideas that went into this document.
Francois Yergeau
James Seng
Marc Blanchet
Mark Davis
Martin Duerst
Patrik Faltstrom
Paul Hoffman
Additional significant improvements were proposed by: The IDN Nameprep design team made many useful changes to the
document. That team and its advisors include:
Jonathan Rosenne Asmus Freytag
Kent Karlsson Cathy Wissink
Scott Hollenbeck Francois Yergeau
Dave Crocker James Seng
Erik Nordmark Marc Blanchet
Mark Davis
Martin Duerst
Patrik Faltstrom
Paul Hoffman
11. Author Contact Information Additional significant improvements were proposed by:
Paul Hoffman Jonathan Rosenne
Internet Mail Consortium and VPN Consortium Kent Karlsson
127 Segre Place Scott Hollenbeck
Santa Cruz, CA 95060 USA Dave Crocker
paul.hoffman@imc.org and paul.hoffman@vpnc.org Erik Nordmark
Matitiahu Allouche
Marc Blanchet 12. Authors' Addresses
Viagenie inc.
2875 boul. Laurier, bur. 300 Paul Hoffman
Ste-Foy, Quebec, Canada, G1V 2M2 Internet Mail Consortium and VPN Consortium
Marc.Blanchet@viagenie.qc.ca 127 Segre Place
Santa Cruz, CA 95060 USA
EMail: paul.hoffman@imc.org and paul.hoffman@vpnc.org
Marc Blanchet
Viagenie inc.
2875 boul. Laurier, bur. 300
Ste-Foy, Quebec, Canada, G1V 2M2
EMail: Marc.Blanchet@viagenie.qc.ca
13. Full Copyright Statement
Copyright (C) The Internet Society (2003). All Rights Reserved.
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included on all such copies and derivative works. However, this
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the copyright notice or references to the Internet Society or other
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The limited permissions granted above are perpetual and will not be
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Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
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