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Network Working Group                                            U. ChoiRequest for Comments: 1557                                       K. ChonCategory: Informational                                            KAIST                                                                 H. Park                                                     Solvit Chosun Media                                                           December 1993Korean Character Encoding for Internet MessagesStatus of this Memo   This memo provides information for the Internet community.  This memo   does not specify an Internet standard of any kind.  Distribution of   this memo is unlimited.Introduction   This document describes the encoding method being used to represent   Korean characters in both header and body part of the Internet mail   messages [RFC822].  This encoding method was specified in 1991, and   has since then been used.  It has now widely being used in Korean IP   networks.   This document also describes the name of the encoding method which is   to be used in order to match the message header and body format of   MIME [MIME1,MIME2].   This document describes only the encoding method for plain text.   Other text subtypes, rich text and similar forms of text, are beyond   the scope of this document.Description   It is assumed that the starting code of the message is ASCII.  ASCII   and Korean characters can be distinguished by use of the shift   function.  For example, the code SO will alert us that the upcoming   bytes will be a Korean character as defined in KSC 5601.  To return   to ASCII the SI code is used.   Therefore, the escape sequence, shift function and character set used   in a message are as follows:           SO           KSC 5601           SI           ASCII           ESC $ ) C    Appears once in the beginning of a line                            before any appearance of SO characters.Choi, Chon & Park                                               [Page 1]

RFC 1557               Korean Character Encoding           December 1993   The KSC 5601 [KSC5601] character set that includes Hangul, Hanja   (Chinese ideographic characters), graphic and foreign characters,   etc., is two bytes long for each character.   For more information about Korean character sets please refer to the   KSC 5601-1987 document.  Also, for more detailed information about   the escape sequence and the shift function you can look for the ISO   2022 [ISO2022] document.Formal Syntax   Where this document in its formal syntax does not agree with the   description part, priority should be given to the formal syntax of   the document.   The notations used in this section of the document are according to   those used in STD 11,RFC 822 [RFC822] with the same meaning.        * (asterisk) has the following meaning :             l*m "anything"   The above means that "anything" has to be used at least l times and   at most m times.  Default values for l and m are 0 and infinitive,   respectively.   body            = *e-line *1( designator *( e-line / h-line ))   designator      = ESC "$" ")" "C"   e-line          = *text CRLF   h-line          = *text 1*( segment *text ) CRLF   segment         = SO 1*(one-of-94 one-of-94 SI                                               ; ( Octal, Decimal.)   ESC             = <ISO 2022 ESC, escape>    ; ( 33, 27.)   SO              = <ASCII SO, shift out>     ; ( 16, 14.)   SI              = <ASCII SI, shift in>      ; ( 17, 15.)   SP              = <ASCII SP, space>         ; ( 40, 32.)Choi, Chon & Park                                               [Page 2]

RFC 1557               Korean Character Encoding           December 1993   one-of-94       = <any char in 94-char set> ; (41-176, 33.-126.)   CHAR            = <any ASCII character>     ; ( 0-177, 0.-127.)   text            = <any CHAR, including bare CR & bare LF, but NOT                      including CRLF, and not including ESC, SI, SO>MIME andRFC 1522 Considerations   The name to be used for the Hangul encoding scheme in the contents is   "ISO-2022-KR".  This name when used in MIME message form would be:                Content-Type: text/plain; charset=iso-2022-kr   Since the Hangul encoding is done with 7 bit format in nature, the   Content-Transfer-Encoding-header does not need to be used. However,   while using the Hangul encoding, current Hangul message softwares   does not support Base64 or Quoted-Printable encoding applied on   already encoded Hangul messages.   The Hangul encoded in the header part of the message is Korean EUC   [EUC-KR].  In the EUC-KR encoding, the bytes with 8th bit set will be   recognized as KSC-5601 characters.  To use Hangul in the header part,   according to the method proposed inRFC 1522, the encoded Hangul are   "B" or "Q" encoded. When doing so, the name to be used will be EUC-   KR.Background Information   The Hangul encoding system is based on the ISO 2022 [ISO2022]   environment according to its 4/4 announcement.  However, the Hangul   encoding does not include the announcement's escape sequence.   The KSC 5601 used in this document is, in definition, identical to   the KSC 5601-1987, KSC 5601-1989 and KSC 5601-1992's 94x94 octet   definition.  Therefore, any revision that refers to KSC-5601 after   1992 is to be considered as having the same meaning.   At present, the Hangul encoding system is based on the experience   acquired from the former widely used "N-Byte Hangul" among UNIX   users.  Actually, the encoding method, "N-Byte Hangul", using SO and   SI was the encoding method used in SDN before KSC 5601 was made a   national standard.   This code is intended to be used for the information interchange of   Hangul messages; any other use of the code is not considered   appropriate.Choi, Chon & Park                                               [Page 3]

RFC 1557               Korean Character Encoding           December 1993References   [ASCII] American National Standards Institute, "Coded character set           -- 7-bit American national standard code for information           interchange", ANSI X3.4-1968   [ISO2022] International Organization for Standardization (ISO),             "Information processing -- ISO 7-bit and 8-bit coded             character sets -- Code extension techniques",             International Standard, 1986, Ref. No. ISO 2022-1986 (E).   [KSC5601] Korea Industrial Standards Association, "Code for             Information Interchange (Hangul and Hanja)," Korean             Industrial Standard, 1987, Ref. No. KS C 5601-1987.   [EUC-KR] Korea Industrial Standards Association, "Hangul Unix            Environment," Korean Industrial Standard, 1992, Ref. No.            KS C 5861-1992.   [RFC822] Crocker, D., "Standard for the Format of ARPA Internet            Text Messages", STD 11,RFC 822, UDEL, August 1982.   [MIME1] Borenstein, N., and N. Freed, "MIME (Multipurpose           Internet Mail Extensions): Part One: Mechanisms for           Specifying and Describing the Format of Internet Message           Bodies",RFC 1521, Bellcore, Innosoft, September 1993.   [MIME2] Moore, K., "MIME (Multipurpose Internet Mail Extensions)           Part Two: Message Header Extensions for Non-ASCII Text",RFC 1522, University of Tennessee, September 1993.Security Considerations   Security issues are not discussed in this memo.Acknowledgments   The authors wants to thank all the people who assisted in writing   this document.  In particular, we thank Erik von der Poel, Felix M.   Villarreal, Ienup Sung, Kyoung Namgoong, and Kyuho Kim.Choi, Chon & Park                                               [Page 4]

RFC 1557               Korean Character Encoding           December 1993Authors' Addresses   Uhhyung Choi   Korea Advanced Institute of Science and Technology   Department of Computer Science   Taejon, 305-701, Republic of Korea   Phone: +82-42-869-8718   Fax: +82-42-869-3510   EMail: uhhyung@kaist.ac.kr   Kilnam Chon   Korea Advanced Institute of Science and Technology   Department of Computer Science   Taejon, 305-701, Republic of Korea   Phone: +82-42-869-3514   Fax: +82-42-869-3510   EMail: chon@cosmos.kaist.ac.kr   Hyunje Park   Solvit Chosun Media, Inc.   748-16 Yeoksam-Dong, Kangnam-Gu   Seoul, 135-080, Republic of Korea   Phone: +82-2-561-0361   Fax: +82-2-569-4847   EMail: hjpark@dino.media.co.krChoi, Chon & Park                                               [Page 5]