Standardization of Internationalized Domain Name at IETF

Standardization of Internationalized Domain Name

at IETF

24 Jan 2002

Yoshiro YONEYA <yone@nic.ad.jp>

JPNIC

24 Jan 2002 APAN2002 Conference 2

What is IDN?

• Internationalized Domain Name.– Current domain name is represented with

ASCII alpha-numeric and hyphen characters.– IDN is a technical challenge to represent

domain name with not only ASCII but also NON-ASCII characters.

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What is Internationalization?

• Framework to extend character repertoire for domain names.

• Need to be a Global Standard not to lose global communication.

• IETF IDN (Internationalized Domain Name) WG is doing the work.

• Some confusion by using the word ‘Multilingualization’.– Character is just one of a component of languages.– Multilingual domain name is a service level’s aspect.

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Internationalized Domain Names

华人 .公司 .cn 華人 .商業 .tw

高島屋 . 会社 .jp

삼성 . 회사 .kr 三星 . 회사 .krم. االهرام

viagénie.qc.caקום.ישראל

ที�เอชนิ�ค.พาณิ�ชย์ .ไทีย์

現代 .com ヤフー .comhttp://www.jdna.jp/activities/event/jdn-tutorial/IDNSDK.pdf

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Why IDN?

• Increases of the Internet users who are not familiar with English.– Easy to memorize, type in, etc.

• Drastic changes of usage of domain name.– Domain name is now used as not only host

name but also signboard.

• Creates new business opportunities.– Many ventures began services.

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Drawback of IDN

• Loses global acceptability at end-user interface.– Hard to type in or display NON-ASCII characte

rs without appropriate I/O devices and / or softwares.

• Cause impact to the operation.– Requires software update and / or additional pr

ocessing.– Deployment issue.

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History of IDN WG

• Established on Jan 2000.– Mainly discussion is done on mailing list.

• Had 1st meeting at 47th IETF at Adelaide.– From then, having meeting every IETF.

• Decided WG’s solution at last (52nd) IETF.– IDNA, NAMEPREP and Punycode (formerly k

nown as AMC-ACE-Z).– Waiting for WG last call.

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Scope and priority of IDN WG

• Provide standard.– Not to divide the global connectivity and communication

of the Internet.

• Backward compatibility.– Compatibility with current DNS and application protocols

to work with current Internet infrastructure.

• No localization.– Independent from certain regions, countries and / or

languages– Refer to existing universal standards– Common framework essential to internationalization

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IDNA(Internationalizing Domain Names In Applications)

draft-ietf-idn-idna-06.txt

• An architecture denotes how to process IDN.– Use Unicode which is upper compatible with ASCII as

a character codeset.– Normalize internal representation of characters which h

as multiple code points such as upper/lower, full-width/half-width and composing characters, into a single representation not to fail matching.

– Represent NON-ASCII characters which inputted or displayed at user interface as an ASCII Compatible Encoding (ACE) string on the Network.

– Those processes be performed in application software.

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Important point of IDNA

• Representation at the user interface layer and the network layer is different.– Though the same for ASCII domain names.

• Application solution.– Least impact to the Internet infrastructure.

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Image of the IDNA

User

InternalRepresentation

UI

API

Application servers

End system

Application

Local

Int’l

Resolver

DNS servers

NAMEPREPTo/From Unicode

To/From ACE

NAMEPREP

To/From ACE

To/From Unicode

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NAMEPREP(Stringprep Profile for Internationalized Host Name

s) draft-ietf-idn-nameprep-07.txt

• Profile for STRINGPREP (Preparation of Internationalized Strings)– draft-hoffman-stringprep-00.txt

• Some scripts such as alphabet have multiple representation for a character.– Domain name is case insensitive.

• Normalization process to unify representation of strings that is the same in meaning or displaying into a single representation.– Case (upper / lower)– Compatible character (full / half width)– Composing character

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Important point of NAMEPREP

• Normalize representation of Internationalized domain name string to match correctly.– ‘a’ vs ‘A’– ‘u’+‘¨’ vs ‘ü’– ‘ ア’ vs ‘ ’ｱ

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Processes in NAMEPREP

1. map• Case folding of upper/lower characters

(UTR#21)

2. normalize• Normalize representation of string (UAX#15

NFKC)

3. prohibit• Check out inappropriate character as domain

name.

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ACE(ASCII Compatible Encoding)

• Represent NON-ASCII characters by ASCII characters.– Easy to apply current DNS.– Least impact to current applications.

• Decreases maximum characters in each label.– Penalty of using only 5bit to represent 8bit data.– Requires some sort of compression algorithm.

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ACE Identifier

• Requires explicit ACE-identifier.– For reverse conversion.– Choice of ACE-ID is political issue.

• ACE-ID itself is ASCII string, so that if any proposal for ACE-ID is raised, it will be registered as ASCII domain name.

• Actually happened at gTLD.

• IANA will assign the ACE-ID.

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Criteria of ACE selection

• Simple algorithm.– For ease implementation.– Interoperability.

• Effective compression results for practical IDNs.– To accommodate characters as much as possible.

• bilateral corresponding between encoding and decoding.– To avoid existence of alternative encoded representatio

n for one IDN.– Security consideration.

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Comparison of ACE proposals

RACE BQ--3BS6KZZMRKPDBSJQ4EYKIMHTKQGYUZU2CM.JP

Punycode ZQ--ECKWD4C7C777U7MWO4BOV4JIOAU09J.JP

Encoding sample of ‘ 日本語ドメイン名試験 .JP’

Evaluation resultfrom existingJapanese JPdomain names

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Punycode draft-ietf-idn-punycode-00.txt

• Selected ACE of IDN WG.• Compression algorithm.

– Extract characters by ascending order of codepoint.– Encode difference of codepoint from previously proces

sed character’s and the position into an integer.– Extract Letters, Digits and Hyphen as bootstring.

• ASCII conversion algorithm.– Introduced new concept named ‘Generalized variable-l

ength integers’.– BASE36 (A-Z, 0-9).

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Compression process of Punycode(simplified for understanding)

• “ 文字列例”• Compression.

1. 1:U+6587 2:U+5B57 3:U+5217 4:U+4F8B

2. 4:0x4F8B 3:0x28C 2:0x440 1:0xA30

3. 0x13E30 0xA33 0x1102 0x28C1

sort, diff

To integer(diff*chars+position)

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Generalized variable-length integers of Punycode

• 12345 in decimal is represented as 1*10^4+2*10^3+3*10^2+4*10^1+5*10^0

• Digits in all place are 0-9, so components in sequential 12345 cannot distinguish 123 and 45 or 1234 and 5.

• Furthermore, 012345 and 12345 are the same value with different representation.

• GVLI (Generalized variable-length integers) is an idea to solve this problem.

• Defines threshold for each place, and recognize a number below the threshold is delimiter.

• Threshold is an appropriate number smaller than base number.

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Encoding process of Punycode (simplified for understanding)

• Assign A-Z0-9 to GVLI.– Assume 36 for base, 10, 18, 25, 25 for thresholds.1. 0x13E30 0xA33 0x1102 0x28C1

2. OIUD3. BS44. CN85. XML

• “ 文字列例” =>“OUIDBS4CN8XML” .– Real Punycode generates “FSQW5D78MBSK”.

24*1+18*26(=1*(36-10))+30*468(=26*(36-18))+13*5148(=468*(36-25))

11*1+28*26+4*46812*1+23*26+8*468

33*1+22*26+21*468

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Standardization of IDN is just the start point of utilization

• End users uses IDN with application softwares.– Web, Mail, etc.

• IDNA requires application’s correspondence.• Must define how to deal IDNs in application proto

cols.

Standardization of IDN does not mean ready to use. Just a start point for applications incorporating

new features.

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HTTP Request(DNS resolve only)

Web

User

http:// ジェーピーニック .JP/

ZQ--HCKQZ9BZB1CYRB.JP

Web server’s

IP adress

GET http:// ジェーピーニック .JP/ HTTP/1.1Host: ジェーピーニック .JPReferer: http:// ジェーピーニック .JP/

Error!

DNS

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HTTP Request(ACE in HTTP header)

Web

User

http:// ジェーピーニック .JP/

ZQ--HCKQZ9BZB1CYRB.JP

Web server’s IP address

GET http://ZQ--HCKQZ9BZB1CYRB.JP/ HTTP/1.1Host: ZQ--HCKQZ9BZB1CYRB.JPReferer: http://ZQ--HCKQZ9BZB1CYRB.JP/

Contents

DNS

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References

• IETF IDN WG Web page– http://www.i-d-n.net/

• Unicode Consortium– http://www.unicode.org/

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Acknowledgement

• Telecommunications Advancement Organization of Japan (TAO).– JPNIC’s research activity of security investigati

on of IDN is a part of TAO’s research.– http://www.shiba.tao.go.jp/

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IDN Compliant clients & implementations

• Mozillahttp://playground.i-dns.net/mozilla/index.html– Plug-in to Mozilla, resolution using RACE

• Operahttp://www.opera.com/– Native, Resolution using RACE

• Internet Explorer 5 or higherhttp://www.microsoft.com/windows/ie/default.asp– Uses keyword search engine as RACE converter

• mDNkithttp://www.nic.ad.jp/jp/research/idn/mdnkit/download/– Opensource toolkit for developing IDN compliant softwares