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rfc:rfc5992

Independent Submission S. Sharikov Request for Comments: 5992 Regtime Ltd Category: Informational D. Miloshevic ISSN: 2070-1721 Afilias

                                                            J. Klensin
                                                          October 2010
   Internationalized Domain Names Registration and Administration
          Guidelines for European Languages Using Cyrillic

Abstract

 This document is a guideline for registries and registrars on
 registering internationalized domain names (IDNs) based on (in
 alphabetical order) Bosnian, Bulgarian, Byelorussian, Kildin Sami,
 Macedonian, Montenegrin, Russian, Serbian, and Ukrainian languages in
 a DNS zone.  It describes appropriate characters for registration and
 variant considerations for characters from Greek and Latin scripts
 with similar appearances and/or derivations.

Status of This Memo

 This document is not an Internet Standards Track specification; it is
 published for informational purposes.
 This is a contribution to the RFC Series, independently of any other
 RFC stream.  The RFC Editor has chosen to publish this document at
 its discretion and makes no statement about its value for
 implementation or deployment.  Documents approved for publication by
 the RFC Editor are not a candidate for any level of Internet
 Standard; see Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc5992.

Copyright Notice

 Copyright (c) 2010 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.

Sharikov, et al. Informational [Page 1] RFC 5992 Cyrillic IDNs October 2010

Table of Contents

 1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
   1.1.  Similar Characters and Variants  . . . . . . . . . . . . .  3
   1.2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  4
 2.  Languages and Characters . . . . . . . . . . . . . . . . . . .  5
   2.1.  Bosnian and Serbian  . . . . . . . . . . . . . . . . . . .  5
   2.2.  Bulgarian  . . . . . . . . . . . . . . . . . . . . . . . .  5
   2.3.  Byelorussian (Belarusian, Belarusan) . . . . . . . . . . .  5
   2.4.  Kildin Sami  . . . . . . . . . . . . . . . . . . . . . . .  6
   2.5.  Macedonian . . . . . . . . . . . . . . . . . . . . . . . .  7
   2.6.  Montenegrin  . . . . . . . . . . . . . . . . . . . . . . .  7
   2.7.  Russian  . . . . . . . . . . . . . . . . . . . . . . . . .  7
   2.8.  Serbian  . . . . . . . . . . . . . . . . . . . . . . . . .  7
   2.9.  Ukrainian  . . . . . . . . . . . . . . . . . . . . . . . .  8
 3.  Language-Based Tables  . . . . . . . . . . . . . . . . . . . .  8
 4.  Table Processing Rules . . . . . . . . . . . . . . . . . . . .  8
 5.  Table Format . . . . . . . . . . . . . . . . . . . . . . . . .  8
 6.  Steps after Registering an Input Label . . . . . . . . . . . .  9
 7.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
 8.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 10
 9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
   9.1.  Normative References . . . . . . . . . . . . . . . . . . . 10
   9.2.  Informative References . . . . . . . . . . . . . . . . . . 10
 Appendix A.  European Cyrillic Character Tables  . . . . . . . . . 13

1. Introduction

 Cyrillic is one of a fairly small number of scripts that are used,
 with different subsets of characters, to write a large number of
 languages, some of which are not closely related to the others.  When
 those languages might be used together in a zone (typical of generic
 TLDs (gTLDs) but likely in other zones both at and below the root),
 special considerations for intermixing characters may apply.
 Cyrillic also has the property that, while it is usually considered a
 separate script from the Latin (Roman) and Greek ones, it shares many
 characters with them, creating opportunities for visual confusion.
 Those difficulties are especially pronounced when "all of Cyrillic"
 is used rather than only the characters associated with a particular
 language.
 This specification provides guidelines for the use of Cyrillic, as
 encoded in Unicode [Unicode52] with internationalized domain name
 (IDN) labels derived from most "European" languages that use the
 script (use of the term "European" is a convenience, since there is
 disagreement about the relevant boundaries for different purposes
 and, of course, much of Russia lies within geological Asia).
 Specifically, it covers (in alphabetic order) Bosnian, Bulgarian,

Sharikov, et al. Informational [Page 2] RFC 5992 Cyrillic IDNs October 2010

 Byelorussian, the Kildin member of the Sami (often written "Saami")
 language family, Macedonian, Montenegrin, Russian, Serbian, and
 Ukrainian.  Supplemental tables, based on information in the Unicode
 Standard and a recently completed Montenegrin government standard
 [MontenegrinChars] are provided for use with Montenegrin.  Moldovan
 is no longer in official use with Cyrillic script: no registrations
 are considered likely in Cyrillic, at least within the relevant
 ccTLD, and it is not further discussed in this document.  Languages
 of Asia that use Cyrillic are not considered here and should be the
 subject of separate specifications.
 While Cyrillic script is the primary one used for many of the
 relevant languages and countries, Latin script is often used instead
 of, or in combination with, it.  Standard keyboards used in most of
 the countries have both Cyrillic and Latin characters.  Therefore,
 some registries could use Latin scripts for domain name registration
 in their zones.  From time to time, some registries and users have
 claimed that there is a requirement for mixing Cyrillic and Latin
 characters in the same label.  We strongly recommend against such
 mixing as user confusion is almost certain to result.  In addition,
 registries that support many scripts will probably encounter the need
 to support labels in Greek or Latin scripts as well as Cyrillic, and
 a large number of character forms are shared among those three
 scripts.
 Because the DNS has no way for the end user to distinguish among the
 languages that might have been used to inspire a particular label, it
 seems useful to treat the characters of a large number of languages
 that use Cyrillic in their writing systems together, rather than
 trying to differentiate them.  The discussion and tables in this
 specification should provide a foundation for developing more
 restrictive rules for zones in which only a single language is likely
 to be used, but it does not specify those language-specific rules.
 Readers of this document should be aware that its recommendations are
 about use in DNS labels.  The orthography for some of the languages
 involved, especially Kildin Sami, is not completely standardized and
 local usage sometimes permits substitution of Latin-based characters
 for their Cyrillic equivalents.  Unless they are required by official
 orthographies, those substitutions should generally be avoided in DNS
 labels because of the risk of additional user confusion with the
 Latin characters that are visually similar.

1.1. Similar Characters and Variants

 For some human languages, there are characters and/or strings that
 have equivalent or near-equivalent meanings.  If someone is allowed
 to register a name with such a character or string, the registry

Sharikov, et al. Informational [Page 3] RFC 5992 Cyrillic IDNs October 2010

 might want to automatically register all the names that have the same
 meaning in that language.  Further, some registries might want to
 restrict the set of characters to be registered for language-based
 reasons.
 So-called "variant techniques", introduced in the JET specification
 for the CJK script [RFC3743] and its generalization [RFC4290],
 describe ways of registering IDNs to decrease the risk of
 misunderstandings, cybersquatting, and other forms of confusion.
 The tables below (Appendix A) identify confusable characters in Latin
 and Greek scripts that might be easily confused with Cyrillic ones.
 As with variant approaches for other scripts (e.g., see RFC 4713
 [RFC4713] for the Chinese language or RFC 5564 [RFC5564] for the
 Arabic language), this document identifies sets of characters that
 need special consideration and provides information about them.  A
 registry that handles names using these characters can then make a
 policy decision about how to actually handle them.  The options for
 those policy decisions would include automatically registering all
 look-alike strings to the same registrant, registering one such
 string and blocking the others, and so on.

1.2. Terminology

 The terminology that follows is derived from the JET specification
 for the CJK script [RFC3743] and its generalization [RFC4290], but
 this specification does not depend on them.  All characters listed
 here have been verified to be "PVALID" under the IDNA2008
 specification [RFC5890] [RFC5892].
 A "string" is a sequence of one or more characters.
 This document discusses characters that have equivalent or near-
 equivalent characters or strings.  The "base character" is the
 character that has one or more equivalents; the "variant(s)" are the
 character(s) and/or string(s) that are equivalent to the base
 character.
 A "registration bundle" is the set of all labels that comes from
 expanding all base characters for a single name into their variants.
 A registry is the administrative authority for a DNS zone.  That is,
 the registry is the body that makes and enforces policies that are
 used in a particular zone in the DNS.  The term "registry" applies to
 all zones in the DNS, not only those that exist at the top level.

Sharikov, et al. Informational [Page 4] RFC 5992 Cyrillic IDNs October 2010

2. Languages and Characters

 In the interest of clarity and balance, this document describes a
 "Base Cyrillic" set of 23 characters for use in comparing the
 character usage for Russian and Central European languages that use
 Cyrillic.  The balance of this section compares the character usage
 of the individual languages in that group.
 "Base Cyrillic" consists of the following Unicode code points (names
 associated with these code points and those below appear in
 Appendix A): U+0430, U+0431, U+0432, U+0433, U+0434, U+0435, U+0436,
 U+0437, U+043A, U+043B, U+043C, U+043D, U+043E, U+043F, U+0440,
 U+0441, U+0442, U+0443, U+0444, U+0445, U+0446, U+0447, U+0448.
 In addition, modern writing systems that use Cyrillic do not have
 digits separate from the "European" ones used with Latin characters.
 For registries that permit digits to appear in domain name labels,
 the "Base Cyrillic" code point listed above should be considered to
 include U+0030, U+0031, U+0032, U+0033, U+0034, U+0035, U+0036,
 U+0037, U+0038, and U+0039 (Digit Zero, and Digit One through Digit
 Nine).  The Hyphen-Minus character (U+002D) may also be used.
 It is worth noting that the EU top-level domain registry allows
 Cyrillic registrations using 32 code points [EU-registry].  That list
 is sufficient for some of the languages listed here but not for
 others.
 The individual languages that are the focus of this specification are
 discussed below (in English alphabetical order).

2.1. Bosnian and Serbian

 Bosnian and Serbian have 30 letters in the alphabet and the
 additional seven characters to the base of 23 shared Cyrillic
 characters: U+0438, U+0458, U+0452, U+0459, U+045A, U+045B, U+045F.

2.2. Bulgarian

 The Bulgarian alphabet has 30 characters, seven in addition to the
 basic 23: U+0438, U+0439, U+0449, U+044A, U+044C, U+044E, U+044F.

2.3. Byelorussian (Belarusian, Belarusan)

 The Byelorussian (now often spelled Belarusian or Belarusan) alphabet
 has 32 characters, i.e., nine characters in addition to the Base
 Cyrillic set of 23 characters: U+0451, U+0456, U+0439, U+044B,
 U+044C, U+045E, U+044D, U+044E, U+044F.

Sharikov, et al. Informational [Page 5] RFC 5992 Cyrillic IDNs October 2010

2.4. Kildin Sami

 The phonetics of the Kildin Sami are quite complex and not easily
 represented in Cyrillic (see, e.g., Kertom's work [Kert]).  The
 orthography is not standardized and the writing system may best be
 thought of as an attempt to transcribe the language phonetically
 (primary in Latin script in the 1930s but in Cyrillic more recently).
 Different scholars have reported different numbers of phonemes,
 further complicating the transcription process.  Kertom identifies 53
 consonants with long-short distinctions and, in many cases, hard-soft
 ones.  He also identifies ascending and descending diphthongs and one
 triphthong as well as more common short and long vowels.
 The primary reference for Kildin Sami, widely circulated for some
 time but only in draft, is apparently used by Sami language(s)
 experts in Scandinavian countries [Riessl07].  It, and the references
 it cites, uses 56 characters, 33 of which do not appear in the basic
 set.  Eight* of these characters have no precomposed forms in Unicode
 and hence must be written as a sequence of two code points with the
 second one being COMBINING MACRON (U+0304).  Using parentheses to
 make the two-code-point sequences more obvious, the additional
 characters are: (U+0430 U+0304)*, (U+0435 U+0304)*, U+0438, U+0439,
 (U+043E U+0304), U+044A, U+044B, (U+044B U+0304), U+044C, U+044D,
 (U+044D U+0304), U+044E, (U+044E U+0304), U+044F, (U+044F U+0304),
 U+0451, (U+0451 U+0304), U+0458, U+048B, U+048D, U+048F, U+04BB,
 U+04C6, U+04C8, U+04CA, U+04CE, U+04D3, U+04E3, U+04E7, U+04ED,
 U+04EF, U+04F1, U+04F9.
  • These characters, CYRILLIC SMALL LETTER A (U+0430) with a

COMBINING MACRON (U+0304) and CYRILLIC SMALL LETTER IE (U+0435)

    with a COMBINING MACRON (U+0304), respectively, have the same
    visual appearance as LATIN SMALL LETTER A WITH MACRON (U+0101) and
    LATIN SMALL LETTER E WITH MACRON (U+0113).  There are no known
    keyboards designed specifically for Kildin Sami.  If an extended
    Latin-based keyboard and associated software are used, these
    characters might appear with the code point based on Latin (e.g.,
    U+0113 for the second case).  By contrast, keyboards and input
    software that are designed to be more Cyrillic-friendly are more
    likely to produce code points for the Cyrillic base characters.
    The use of a Latin character base for that second case occurs in
    some Western European sources including Riessler's work
    [Riessl07].  While we have not found explicit substitutions for A
    with Macron, we believe they might be found in practice.  These
    alternatives are not mapped together by Unicode Normalization Form
    C (NFC) (or Normalization Form KC (NFKC)), so registries, and
    possibly applications software, should exercise some care about

Sharikov, et al. Informational [Page 6] RFC 5992 Cyrillic IDNs October 2010

    these coding variations.  However, U+0101 and U+0113 are Latin
    Script characters so, if either is used, any tests on homogeneity
    of the script within a label need to be made with care.
    Similar issues may apply to other Kildin Sami characters
    constructed with combining sequences.
 The key references in Russian ([Anto90], [Kert86], [Kuru85]) all
 propose slightly different character tables relative to each other
 and to Riessler's list.  Because the latter list appears to be more
 comprehensive and to represent more recent scholarship, we have based
 the tables in this document on it.  We recommend, however, that
 registries review these recommendations and the relevant papers
 should registration requests for Kildin Sami actually appear.
 Additional perspectives on Kildin Sami can be found on the Omniglot
 Sami pages [OmniglotSaami].

2.5. Macedonian

 Macedonian has 31 characters in the alphabet.  This is eight in
 addition to the basic set: U+0438, U+0458, U+0452, U+0459, U+045A,
 U+045C, U+045F, U+0491, U+0455.

2.6. Montenegrin

 According to the most recent, and now final, government specification
 [MontenegrinChars], Montenegrin has 32 characters in its alphabet,
 including two that have no precomposed forms in Unicode.  This is
 nine in addition to the basic set and two in addition to Bosnian and
 Serbian: U+0437 U+0301, U+0438, U+0441 U+0301, U+0452, U+0458,
 U+0459, U+045A, U+045B, U+045F.
 See Bosnian, Section 2.1, above.

2.7. Russian

 The current Russian alphabet has 33 characters, consisting of the
 Base Cyrillic set plus an additional ten characters: U+0451, U+0438,
 U+0439, U+0449, U+044A, U+044B, U+044C, U+044D, U+044E, U+044F.

2.8. Serbian

 See Bosnian, Section 2.1, above.

Sharikov, et al. Informational [Page 7] RFC 5992 Cyrillic IDNs October 2010

2.9. Ukrainian

 The character list for modern Ukrainian has apparently not completely
 stabilized.  Some references claim 31 characters and therefore an
 additional 8 characters to the Base Cyrillic set of 23.  Others claim
 33, adding U+0438 and U+0439 and replacing U+044A (Hard Sign) with
 U+044C (Soft Sign), for a total of an additional 11 characters as
 compared to the Base Cyrillic set.  Unless better information is
 available, the prudent registry should probably assume that all 34
 characters are in use, i.e., the Base Cyrillic set plus U+0438,
 U+0439, U+0454, U+0456, U+0457, U+0491, U+0449, U+044A, U+044C,
 U+044E, U+044F.

3. Language-Based Tables

 The registration strategy described in this document uses a table
 that lists all characters allowed for input and any variants of those
 characters.  Note that the table lists all characters allowed, not
 only the ones that have variants.

4. Table Processing Rules

 The input to the process is called the "input label".  The output of
 the process is either failure (the input label cannot be registered
 at all), or a registration bundle that contains one or more labels in
 A-label form.

5. Table Format

 The table in Appendix A consists of four columns.  The first and
 second identify the Cyrillic character, and the third and fourth
 identify Latin or Greek characters that might be easily confused with
 them visually.  If both a Latin and Greek character are present, the
 Greek one appears in the third and fourth columns on the subsequent
 line (with "..." in the first column to indicate more information
 about the character specified on the previous line).  Variants needed
 only because of case folding are shown with "+++" in the first
 column, as noted in the table.
 Each character in the table is given in the "U+" notation for Unicode
 characters followed, in the next column, by its name as shown in the
 Unicode Standard.  For easy reference, the characters are listed in
 the order in which they appear in the Unicode Standard.
 The table does not, and any future revision MUST NOT, have more than
 one entry for a particular base character.

Sharikov, et al. Informational [Page 8] RFC 5992 Cyrillic IDNs October 2010

6. Steps after Registering an Input Label

 A registry has at least three policy options for handling the cases
 where the registration bundle has more than one label.  These
 options, and their key implications, are:
 o  Allocate all labels to the same registrant, making the zone
    information identical to that of the input label.
    This option will cause end users to be able to find names with
    variants more easily, but will result in larger zone files.  In
    principle, the zone file could become so large that it could
    negatively affect the ability of the registry to perform name
    resolution.
 o  Block all labels so they cannot be registered in the future.
    This option does not increase the size of the zone file, but it
    may cause end users to not be able to find names with variants
    that they would expect.
 o  Allocate some labels and block some other labels.
    This option is likely to cause the most confusion with users
    because including some variants will cause a name to be found, but
    using other variants will cause the name to be not found.
 With any of these three options, the registry MUST keep a database
 that links each label in the registration bundle to the input label.
 This link needs to be maintained so that changes in the non-DNS
 registration information (such as the label's owner name and address)
 are reflected in every member of the registration bundle as well.

7. Security Considerations

 The information provided in this document may assist DNS zone
 administrators and registrants in selecting names that are less
 likely to be confused with others and in adopting policies that help
 avoid confusion.  It may also assist user-interface designers in
 identifying possible areas of confusion so that they can better
 protect users.  The document otherwise has no consequences for the
 security of the Internet.

Sharikov, et al. Informational [Page 9] RFC 5992 Cyrillic IDNs October 2010

8. Acknowledgments

 Support from Afilias for a major portion of this work is appreciated.
 The material on Kildin Sami would not have been possible without the
 efforts of Cary Karp for his help directly and his pointer to
 Riessler's work [Riessl07] and from Vladimir Shadrunov and Sergey
 Nikolaevich Teryoshkin for their own analyses and references
 ([Anto90], [Kert86], and [Kuru85]) and partial translations from
 them.  We are grateful for their efforts that facilitated treating it
 nearly the same way as other actively used European languages that
 use Cyrillic script.
 Careful reading of late drafts of this document by Bill McQuillan,
 Alexey Melnikov, and Peter Saint-Andre, identified a number of
 editorial problems, some of which might not have been caught
 otherwise.

9. References

9.1. Normative References

 [RFC5895]           Resnick, P. and P. Hoffman, "Mapping Characters
                     in Mapping Characters for Internationalized
                     Domain Names in Applications (IDNA) 2008",
                     RFC 5895, September 2010.
 [Unicode52]         The Unicode Consortium.  The Unicode Standard,
                     Version 5.2.0, defined by: "The Unicode Standard,
                     Version 5.2.0", (Mountain View, CA: The Unicode
                     Consortium, 2009. ISBN 978-1-936213-00-9).
                     <http://www.unicode.org/versions/Unicode5.2.0/>.

9.2. Informative References

 [Anto90]            Antonova, A., "Primer for Sami schools first
                     grade: Sami language, 2nd edition", Leningrad:
                     Prosveshchenie, Leningrad department, 1990.
                     Published in Russian, no authoritative
                     translation is known.
 [EU-registry]       European Registry of Internet Domain Names
                     (EURid), ".eu Supported Characters",
                     January 2010, <http://www.eurid.eu/en/
                     eu-domain-names/technical-limitations/
                     supported-characters>.

Sharikov, et al. Informational [Page 10] RFC 5992 Cyrillic IDNs October 2010

 [Kert]              Kertom, G., "Kildin dialect of the Sami
                     language".  Published in Russian, no
                     authoritative translation is known.
 [Kert86]            Kertom, G., "Sami-Russian and Russian-Sami
                     dictionary: textbook for primary school pupils",
                     Leningrad: Prosveshchenie Leningrad Department,
                     1986.  Published in Russian, no authoritative
                     translation is known.
 [Kuru85]            Kuruch, R., "Sami-Russian dictionary: eight
                     thousand words", Moscow: Russkiy yazyk, 1985.
                     Published in Russian, no authoritative
                     translation is known.
 [MontenegrinChars]  Crna Gora Ministarstvo prosvjete i nauke
                     (Ministry of Science and Education, Montenegro),
                     "Pravopis Crnogorskoga Jezika I", 2009,
                     <http://www.gov.me/files/1248442673.pdf>.  In
                     Montenegrin, no known English translation.  See
                     especially the table on page 8.
 [OmniglotSaami]     Ager, S., "Sami (Saami)", 2009,
                     <http://www.omniglot.com/writing/saami.htm>.
 [RFC3743]           Konishi, K., Huang, K., Qian, H., and Y. Ko,
                     "Joint Engineering Team (JET) Guidelines for
                     Internationalized Domain Names (IDN) Registration
                     and Administration for Chinese, Japanese, and
                     Korean", RFC 3743, April 2004.
 [RFC4290]           Klensin, J., "Suggested Practices for
                     Registration of Internationalized Domain Names
                     (IDN)", RFC 4290, December 2005.
 [RFC4713]           Lee, X., Mao, W., Chen, E., Hsu, N., and J.
                     Klensin, "Registration and Administration
                     Recommendations for Chinese Domain Names",
                     RFC 4713, October 2006.
 [RFC5564]           El-Sherbiny, A., Farah, M., Oueichek, I., and A.
                     Al-Zoman, "Linguistic Guidelines for the Use of
                     the Arabic Language in Internet Domains",
                     RFC 5564, February 2010.
 [RFC5890]           Klensin, J., "Internationalized Domain Names for
                     Applications (IDNA): Definitions and Document
                     Framework", RFC 5890, August 2010.

Sharikov, et al. Informational [Page 11] RFC 5992 Cyrillic IDNs October 2010

 [RFC5892]           Faltstrom, P., "The Unicode Code Points and
                     Internationalized Domain Names for Applications
                     (IDNA)", RFC 5892, August 2010.
 [Riessl07]          Riessler, M., "Kola Saami character chart
                     (draft)", November 2007.

Sharikov, et al. Informational [Page 12] RFC 5992 Cyrillic IDNs October 2010

Appendix A. European Cyrillic Character Tables

 These tables are constructed on the basis of the characters that can
 actually occur in the DNS, i.e., those that are valid in U-labels as
 defined in RFC 5890.  If the characters that can be mapped into those
 characters are to be considered instead, then the number of variants
 would increase considerably.  For example, while CYRILLIC SMALL
 LETTER A (U+0430) and GREEK SMALL LETTER ALPHA (U+03B1) are readily
 distinguished visually, their capital letter equivalents are not, so,
 if case mappings such as those discussed in the IDNA2008 Mapping
 document [RFC5895] are considered, the two small letters must be
 considered variants of each other.  Some of the variants have been
 selected on the assumption that unusual fonts may be used and that
 users will see what they expect to see; others, involving subtle
 decorations but considered more far-fetched out of context, have not
 been listed.
 These additional, possibly required, variants are shown below with
 "+++" in the first column of the table.
 "..." in the first column is used to indicate more information about
 the character specified on the previous line.

Sharikov, et al. Informational [Page 13] RFC 5992 Cyrillic IDNs October 2010

 Characters needed for European languages, other than Montenegrin and
 Sami, written in Cyrillic.
 +----------+--------------------------+---------+-------------------+
 | Cyrillic | Unicode Name             | Variant | Unicode Name      |
 | Char     |                          |         |                   |
 +----------+--------------------------+---------+-------------------+
 | U+0430   | CYRILLIC SMALL LETTER A  | U+0061  | LATIN SMALL       |
 |          |                          |         | LETTER A          |
 |          |                          |         |                   |
 | +++      |                          | U+03B1  | GREEK SMALL       |
 |          |                          |         | LETTER ALPHA      |
 |          |                          |         |                   |
 | U+0431   | CYRILLIC SMALL LETTER BE |         |                   |
 |          |                          |         |                   |
 | U+0432   | CYRILLIC SMALL LETTER VE | U+0062  | LATIN SMALL       |
 |          |                          |         | LETTER B          |
 |          |                          |         |                   |
 | +++      |                          | U+03B2  | GREEK SMALL       |
 |          |                          |         | LETTER BETA       |
 |          |                          |         |                   |
 | U+0433   | CYRILLIC SMALL LETTER    | U+0072  | LATIN SMALL       |
 |          | GHE                      |         | LETTER R          |
 |          |                          |         |                   |
 | +++      |                          | U+03B3  | GREEK SMALL       |
 |          |                          |         | LETTER GAMMA      |
 |          |                          |         |                   |
 | U+0434   | CYRILLIC SMALL LETTER DE |         |                   |
 |          |                          |         |                   |
 | +++      |                          | U+03B4  | GREEK SMALL       |
 |          |                          |         | LETTER DELTA      |
 |          |                          |         |                   |
 | U+0435   | CYRILLIC SMALL LETTER IE | U+0065  | LATIN SMALL       |
 |          |                          |         | LETTER E          |
 |          |                          |         |                   |
 | +++      |                          | U+03B5  | GREEK SMALL       |
 |          |                          |         | LETTER EPSILON    |
 |          |                          |         |                   |
 | U+0436   | CYRILLIC SMALL LETTER    |         |                   |
 |          | ZHE                      |         |                   |
 |          |                          |         |                   |
 | U+0437   | CYRILLIC SMALL LETTER ZE |         |                   |
 |          |                          |         |                   |
 | U+0438   | CYRILLIC SMALL LETTER I  | U+0075  | LATIN SMALL       |
 |          |                          |         | LETTER U          |
 |          |                          |         |                   |
 | U+0439   | CYRILLIC SMALL LETTER    |         |                   |
 |          | SHORT I                  |         |                   |

Sharikov, et al. Informational [Page 14] RFC 5992 Cyrillic IDNs October 2010

 |          |                          |         |                   |
 | U+043A   | CYRILLIC SMALL LETTER KA | U+006B  | LATIN SMALL       |
 |          |                          |         | LETTER K          |
 |          |                          |         |                   |
 | ...      |                          | U+03BA  | GREEK SMALL       |
 |          |                          |         | LETTER KAPPA      |
 |          |                          |         |                   |
 | U+043B   | CYRILLIC SMALL LETTER EL |         |                   |
 |          |                          |         |                   |
 | +++      |                          | U+03BB  | GREEK SMALL       |
 |          |                          |         | LETTER LAMBDA     |
 |          |                          |         |                   |
 | U+043C   | CYRILLIC SMALL LETTER EM | U+006D  | LATIN SMALL       |
 |          |                          |         | LETTER M          |
 |          |                          |         |                   |
 | +++      |                          | U+03BC  | GREEK SMALL       |
 |          |                          |         | LETTER MU         |
 |          |                          |         |                   |
 | U+043D   | CYRILLIC SMALL LETTER EN | U+0048  | LATIN CAPITAL     |
 |          |                          |         | LETTER H          |
 |          |                          |         |                   |
 | +++      |                          | U+0068  | LATIN SMALL       |
 |          |                          |         | LETTER H (in some |
 |          |                          |         | fonts)            |
 |          |                          |         |                   |
 | +++      |                          | U+03B7  | GREEK SMALL       |
 |          |                          |         | LETTER ETA        |
 |          |                          |         |                   |
 | U+043E   | CYRILLIC SMALL LETTER O  | U+006F  | LATIN SMALL       |
 |          |                          |         | LETTER O          |
 |          |                          |         |                   |
 | ...      |                          | U+03BF  | GREEK SMALL       |
 |          |                          |         | LETTER OMICRON    |
 |          |                          |         |                   |
 | U+043F   | CYRILLIC SMALL LETTER PE | U+006E  | LATIN SMALL       |
 |          |                          |         | LETTER N          |
 |          |                          |         |                   |
 | ...      |                          | U+03C0  | GREEK SMALL       |
 |          |                          |         | LETTER PI         |
 |          |                          |         |                   |
 | U+0440   | CYRILLIC SMALL LETTER ER | U+0070  | LATIN SMALL       |
 |          |                          |         | LETTER P          |
 |          |                          |         |                   |
 | ...      |                          | U+03C1  | GREEK SMALL       |
 |          |                          |         | LETTER RHO        |
 |          |                          |         |                   |
 | U+0441   | CYRILLIC SMALL LETTER ES | U+0063  | LATIN SMALL       |
 |          |                          |         | LETTER C          |

Sharikov, et al. Informational [Page 15] RFC 5992 Cyrillic IDNs October 2010

 |          |                          |         |                   |
 | U+0442   | CYRILLIC SMALL LETTER TE | U+0074  | LATIN SMALL       |
 |          |                          |         | LETTER T          |
 |          |                          |         |                   |
 | +++      |                          | U+03C4  | GREEK SMALL       |
 |          |                          |         | LETTER TAU        |
 |          |                          |         |                   |
 | U+0443   | CYRILLIC SMALL LETTER U  | U+0079  | LATIN SMALL       |
 |          |                          |         | LETTER Y          |
 |          |                          |         |                   |
 | +++      |                          | U+03C5  | GREEK SMALL       |
 |          |                          |         | LETTER UPSILON    |
 |          |                          |         |                   |
 | U+0444   | CYRILLIC SMALL LETTER EF | U+03D5  | GREEK PHI SYMBOL  |
 |          |                          |         |                   |
 | +++      |                          | U+03C6  | GREEK SMALL       |
 |          |                          |         | LETTER PHI        |
 |          |                          |         |                   |
 | U+0445   | CYRILLIC SMALL LETTER HA | U+0078  | LATIN SMALL       |
 |          |                          |         | LETTER X          |
 |          |                          |         |                   |
 | ...      |                          | U+03C7  | GREEK SMALL       |
 |          |                          |         | LETTER CHI        |
 |          |                          |         |                   |
 | U+0446   | CYRILLIC SMALL LETTER    |         |                   |
 |          | TSE                      |         |                   |
 |          |                          |         |                   |
 | U+0447   | CYRILLIC SMALL LETTER    |         |                   |
 |          | CHE                      |         |                   |
 |          |                          |         |                   |
 | U+0448   | CYRILLIC SMALL LETTER    |         |                   |
 |          | SHA                      |         |                   |
 |          |                          |         |                   |
 | U+0449   | CYRILLIC SMALL LETTER    |         |                   |
 |          | SHCHA                    |         |                   |
 |          |                          |         |                   |
 | U+044A   | CYRILLIC SMALL LETTER    | U+0062  | LATIN SMALL       |
 |          | HARD SIGN                |         | LETTER B          |
 |          |                          |         |                   |
 | U+044B   | CYRILLIC SMALL LETTER    |         |                   |
 |          | YERU                     |         |                   |
 |          |                          |         |                   |
 | U+044C   | CYRILLIC SMALL LETTER    | U+0062  | LATIN SMALL       |
 |          | SOFT SIGN                |         | LETTER B          |
 |          |                          |         |                   |
 | U+044D   | CYRILLIC SMALL LETTER E  |         |                   |
 |          |                          |         |                   |
 | U+044E   | CYRILLIC SMALL LETTER YU |         |                   |

Sharikov, et al. Informational [Page 16] RFC 5992 Cyrillic IDNs October 2010

 |          |                          |         |                   |
 | U+044F   | CYRILLIC SMALL LETTER YA |         |                   |
 |          |                          |         |                   |
 | U+0451   | CYRILLIC SMALL LETTER IO | U+00EB  | LATIN SMALL       |
 |          |                          |         | LETTER E WITH     |
 |          |                          |         | DIAERESIS         |
 |          |                          |         |                   |
 | U+0452   | CYRILLIC SMALL LETTER    |         |                   |
 |          | DJE                      |         |                   |
 |          |                          |         |                   |
 | U+0453   | CYRILLIC SMALL LETTER    |         |                   |
 |          | GJE                      |         |                   |
 |          |                          |         |                   |
 | U+0454   | CYRILLIC SMALL LETTER    | U+03B5  | GREEK SMALL       |
 |          | UKRAINIAN IE             |         | LETTER EPSILON    |
 |          |                          |         |                   |
 | U+0455   | CYRILLIC SMALL LETTER    | U+0073  | LATIN SMALL       |
 |          | DZE                      |         | LETTER S          |
 |          |                          |         |                   |
 | U+0456   | CYRILLIC SMALL LETTER    | U+0069  | LATIN SMALL       |
 |          | BYELORUSSIAN-UKRAINIAN I |         | LETTER I          |
 |          |                          |         |                   |
 | +++      |                          | U+03B9  | GREEK SMALL       |
 |          |                          |         | LETTER IOTA       |
 |          |                          |         |                   |
 | U+0457   | CYRILLIC SMALL LETTER    | U+03CA  | GREEK SMALL       |
 |          | UKRAINIAN YI             |         | LETTER IOTA WITH  |
 |          |                          |         | DIALYTIKA         |
 |          |                          |         |                   |
 | +++      |                          | U+00EF  | LATIN SMALL       |
 |          |                          |         | LETTER I WITH     |
 |          |                          |         | DIAERESIS         |
 |          |                          |         |                   |
 | U+0458   | CYRILLIC SMALL LETTER JE | U+006A  | LATIN SMALL       |
 |          |                          |         | LETTER J          |
 |          |                          |         |                   |
 | ...      |                          | U+03F3  | GREEK LETTER YOT  |
 |          |                          |         |                   |
 | U+0459   | CYRILLIC SMALL LETTER    |         |                   |
 |          | LJE                      |         |                   |
 |          |                          |         |                   |
 | U+045A   | CYRILLIC SMALL LETTER    |         |                   |
 |          | NJE                      |         |                   |
 |          |                          |         |                   |
 | U+045B   | CYRILLIC SMALL LETTER    |         |                   |
 |          | TSHE                     |         |                   |
 |          |                          |         |                   |

Sharikov, et al. Informational [Page 17] RFC 5992 Cyrillic IDNs October 2010

 | U+045C   | CYRILLIC SMALL LETTER    |         |                   |
 |          | KJE                      |         |                   |
 |          |                          |         |                   |
 | U+045D   | CYRILLIC SMALL LETTER I  |         |                   |
 |          | WITH GRAVE               |         |                   |
 |          |                          |         |                   |
 | U+045E   | CYRILLIC SMALL LETTER    |         |                   |
 |          | SHORT U                  |         |                   |
 |          |                          |         |                   |
 | U+045F   | CYRILLIC SMALL LETTER    |         |                   |
 |          | DZHE                     |         |                   |
 |          |                          |         |                   |
 | U+0491   | CYRILLIC SMALL LETTER    | U+0072  | LATIN SMALL       |
 |          | GHE WITH UPTURN          |         | LETTER R          |
 |          |                          |         |                   |
 | U+04C2   | CYRILLIC SMALL LETTER    |         |                   |
 |          | ZHE WITH BREVE           |         |                   |
 +----------+--------------------------+---------+-------------------+
 Additional characters needed for Montenegrin written in Cyrillic.
 +--------------+-----------------------------+---------+------------+
 | Cyrillic     | Unicode Name                | Variant | Unicode    |
 | Char         |                             |         | Name       |
 +--------------+-----------------------------+---------+------------+
 | U+0437 +     | CYRILLIC SMALL LETTER ZE    |         |            |
 | U+0301       | WITH ACUTE                  |         |            |
 |              |                             |         |            |
 | U+0441 +     | CYRILLIC SMALL LETTER ES    |         |            |
 | U+0301       | WITH ACUTE                  |         |            |
 +--------------+-----------------------------+---------+------------+

Sharikov, et al. Informational [Page 18] RFC 5992 Cyrillic IDNs October 2010

 Additional characters needed for Kildin Sami written in Cyrillic.
 +----------+---------------------+----------+-----------------------+
 | Cyrillic | Unicode Name        | Variant  | Unicode Name          |
 | Char     |                     |          |                       |
 +----------+---------------------+----------+-----------------------+
 | U+0430 + | CYRILLIC SMALL      | U+0101   | LATIN SMALL LETTER A  |
 | U+0304   | LETTER A WITH       |          | WITH MACRON           |
 |          | MACRON              |          |                       |
 |          |                     |          |                       |
 | ...      |                     | U+03B1 + | GREEK SMALL LETTER    |
 |          |                     | U+0304   | ALPHA WITH MACRON     |
 |          |                     |          |                       |
 | U+0435 + | CYRILLIC SMALL      | U+0113   | LATIN SMALL LETTER E  |
 | U+0304   | LETTER IE WITH      |          | WITH MACRON           |
 |          | MACRON              |          |                       |
 |          |                     |          |                       |
 | U+043E + | CYRILLIC SMALL      | U+014D   | LATIN SMALL LETTER O  |
 | U+0304   | LETTER O WITH       |          | WITH MACRON           |
 |          | MACRON              |          |                       |
 |          |                     |          |                       |
 | ...      |                     | U+03BF + | GREEK SMALL LETTER    |
 |          |                     | U+0304   | OMICRON WITH MACRON   |
 |          |                     |          |                       |
 | U+044B + | CYRILLIC SMALL      |          |                       |
 | U+0304   | LETTER YERU WITH    |          |                       |
 |          | MACRON              |          |                       |
 |          |                     |          |                       |
 | U+044D + | CYRILLIC SMALL      |          |                       |
 | U+0304   | LETTER E WITH       |          |                       |
 |          | MACRON              |          |                       |
 |          |                     |          |                       |
 | U+044E + | CYRILLIC SMALL      |          |                       |
 | U+0304   | LETTER YU WITH      |          |                       |
 |          | MACRON              |          |                       |
 |          |                     |          |                       |
 | U+044F + | CYRILLIC SMALL      |          |                       |
 | U+0304   | LETTER YA WITH      |          |                       |
 |          | MACRON              |          |                       |
 |          |                     |          |                       |
 | U+0451 + | CYRILLIC SMALL      | U+00EB + | LATIN SMALL LETTER E  |
 | U+0304   | LETTER IO WITH      | U0304    | WITH DIAERESIS AND    |
 |          | MACRON              |          | MACRON                |
 |          |                     |          |                       |
 | U+048B   | CYRILLIC SMALL      |          |                       |
 |          | LETTER SHORT I WITH |          |                       |
 |          | TAIL                |          |                       |
 |          |                     |          |                       |

Sharikov, et al. Informational [Page 19] RFC 5992 Cyrillic IDNs October 2010

 | U+048D   | CYRILLIC SMALL      |          |                       |
 |          | LETTER SEMISOFT     |          |                       |
 |          | SIGN                |          |                       |
 |          |                     |          |                       |
 | U+048F   | CYRILLIC SMALL      |          |                       |
 |          | LETTER ER WITH TICK |          |                       |
 |          |                     |          |                       |
 | U+04BB   | CYRILLIC SMALL      | U+0068   | LATIN SMALL LETTER H  |
 |          | LETTER SHHA         |          |                       |
 |          |                     |          |                       |
 | U+04C6   | CYRILLIC SMALL      |          |                       |
 |          | LETTER EL WITH TAIL |          |                       |
 |          |                     |          |                       |
 | U+04C8   | CYRILLIC SMALL      |          |                       |
 |          | LETTER EN WITH HOOK |          |                       |
 |          |                     |          |                       |
 | U+04CA   | CYRILLIC SMALL      |          |                       |
 |          | LETTER EN WITH TAIL |          |                       |
 |          |                     |          |                       |
 | U+04CE   | CYRILLIC SMALL      |          |                       |
 |          | LETTER EM WITH TAIL |          |                       |
 |          |                     |          |                       |
 | U+04D3   | CYRILLIC SMALL      | U+00E4   | LATIN SMALL LETTER A  |
 |          | LETTER A WITH       |          | WITH DIAERESIS        |
 |          | DIAERESIS           |          |                       |
 |          |                     |          |                       |
 | U+04E3   | CYRILLIC SMALL      | U+016B   | LATIN SMALL LETTER U  |
 |          | LETTER I WITH       |          | WITH MACRON           |
 |          | MACRON              |          |                       |
 |          |                     |          |                       |
 | U+04E7   | CYRILLIC SMALL      | U+00F6   | LATIN SMALL LETTER O  |
 |          | LETTER O WITH       |          | WITH DIAERESIS        |
 |          | DIAERESIS           |          |                       |
 |          |                     |          |                       |
 | U+04ED   | CYRILLIC SMALL      |          |                       |
 |          | LETTER E WITH       |          |                       |
 |          | DIAERESIS           |          |                       |
 |          |                     |          |                       |
 | U+04EF   | CYRILLIC SMALL      |          |                       |
 |          | LETTER U WITH       |          |                       |
 |          | MACRON              |          |                       |
 |          |                     |          |                       |
 | U+04F1   | CYRILLIC SMALL      |          |                       |
 |          | LETTER U WITH       |          |                       |
 |          | DIAERESIS           |          |                       |
 |          |                     |          |                       |

Sharikov, et al. Informational [Page 20] RFC 5992 Cyrillic IDNs October 2010

 | U+04F9   | CYRILLIC SMALL      |          |                       |
 |          | LETTER YERU WITH    |          |                       |
 |          | DIAERESIS           |          |                       |
 +----------+---------------------+----------+-----------------------+

Authors' Addresses

 Sergey Sharikov
 Regtime Ltd
 Kalinina str.,14
 Samara  443008
 Russia
 Phone: +7(846) 979-9039
 Fax:   +7(846)979-9038
 EMail: s.shar@regtime.net
 Desiree Miloshevic
 Afilias
 Oxford Internet Institute, 1 St. Giles
 Oxford  OX1 3JS
 United Kingdom
 Phone: +44 7973 987 147
 EMail: dmiloshevic@afilias.info
 John C Klensin
 1770 Massachusetts Ave, #322
 Cambridge, MA  02140
 USA
 Phone: +1 617 491 5735
 EMail: john-ietf@jck.com

Sharikov, et al. Informational [Page 21]

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