Network Working Group                                           J. Murai
Request for Comments: 1468                               Keio University
                                                             M. Crispin
                                                      Panda Programming
                                                        E. van der Poel
                                                              June 1993


          Japanese Character Encoding for Internet Messages

Status of this Memo

  This memo provides information for the Internet community.  It does
  not specify an Internet standard.  Distribution of this memo is
  unlimited.

Introduction

  This document describes the encoding used in electronic mail [RFC822]
  and network news [RFC1036] messages in several Japanese networks. It
  was first specified by and used in JUNET [JUNET]. The encoding is now
  also widely used in Japanese IP communities.

  The name given to this encoding is "ISO-2022-JP", which is intended
  to be used in the "charset" parameter field of MIME headers (see
  [MIME1] and [MIME2]).

Description

  The text starts in ASCII [ASCII], and switches to Japanese characters
  through an escape sequence. For example, the escape sequence ESC $ B
  (three bytes, hexadecimal values: 1B 24 42) indicates that the bytes
  following this escape sequence are Japanese characters, which are
  encoded in two bytes each.  To switch back to ASCII, the escape
  sequence ESC ( B is used.

  The following table gives the escape sequences and the character sets
  used in ISO-2022-JP messages. The ISOREG number is the registration
  number in ISO's registry [ISOREG].

      Esc Seq    Character Set                  ISOREG

      ESC ( B    ASCII                             6
      ESC ( J    JIS X 0201-1976 ("Roman" set)    14
      ESC $ @    JIS X 0208-1978                  42
      ESC $ B    JIS X 0208-1983                  87

  Note that JIS X 0208 was called JIS C 6226 until the name was changed



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RFC 1468   Japanese Character Encoding for Internet Messages   June 1993


  on March 1st, 1987. Likewise, JIS C 6220 was renamed JIS X 0201.

  The "Roman" character set of JIS X 0201 [JISX0201] is identical to
  ASCII except for backslash () and tilde (~). The backslash is
  replaced by the Yen sign, and the tilde is replaced by overline. This
  set is Japan's national variant of ISO 646 [ISO646].

  The JIS X 0208 [JISX0208] character sets consist of Kanji, Hiragana,
  Katakana and some other symbols and characters. Each character takes
  up two bytes.

  For further details about the JIS Japanese national character set
  standards, refer to [JISX0201] and [JISX0208].  For further
  information about the escape sequences, see [ISO2022] and [ISOREG].

  If there are JIS X 0208 characters on a line, there must be a switch
  to ASCII or to the "Roman" set of JIS X 0201 before the end of the
  line (i.e., before the CRLF). This means that the next line starts in
  the character set that was switched to before the end of the previous
  line.

  Also, the text must end in ASCII.

  Other restrictions are given in the Formal Syntax below.

Formal Syntax

  The notational conventions used here are identical to those used in
  RFC 822 [RFC822].

  The * (asterisk) convention is as follows:

      l*m something

  meaning at least l and at most m somethings, with l and m taking
  default values of 0 and infinity, respectively.


  message             = headers 1*( CRLF *single-byte-char *segment
                        single-byte-seq *single-byte-char )
                                          ; see also [MIME1] "body-part"
                                          ; note: must end in ASCII

  headers             = <see [RFC822] "fields" and [MIME1] "body-part">

  segment             = single-byte-segment / double-byte-segment

  single-byte-segment = single-byte-seq 1*single-byte-char



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RFC 1468   Japanese Character Encoding for Internet Messages   June 1993


  double-byte-segment = double-byte-seq 1*( one-of-94 one-of-94 )

  single-byte-seq     = ESC "(" ( "B" / "J" )

  double-byte-seq     = ESC "$" ( "@" / "B" )

  CRLF                = CR LF

                                                   ; ( Octal, Decimal.)

  ESC                 = <ISO 2022 ESC, escape>     ; (    33,      27.)

  SI                  = <ISO 2022 SI, shift-in>    ; (    17,      15.)

  SO                  = <ISO 2022 SO, shift-out>   ; (    16,      14.)

  CR                  = <ASCII CR, carriage return>; (    15,      13.)

  LF                  = <ASCII LF, linefeed>       ; (    12,      10.)

  one-of-94           = <any one of 94 values>     ; (41-176, 33.-126.)

  7BIT                = <any 7-bit value>          ; ( 0-177,  0.-127.)

  single-byte-char    = <any 7BIT, including bare CR & bare LF, but NOT
                         including CRLF, and not including ESC, SI, SO>

MIME Considerations

  The name given to the JUNET character encoding is "ISO-2022-JP". This
  name is intended to be used in MIME messages as follows:

      Content-Type: text/plain; charset=iso-2022-jp

  The ISO-2022-JP encoding is already in 7-bit form, so it is not
  necessary to use a Content-Transfer-Encoding header. It should be
  noted that applying the Base64 or Quoted-Printable encoding will
  render the message unreadable in current JUNET software.

  ISO-2022-JP may also be used in MIME Part 2 headers.  The "B"
  encoding should be used with ISO-2022-JP text.

Background Information

  The JUNET encoding was described in the JUNET User's Guide [JUNET]
  (JUNET Riyou No Tebiki Dai Ippan).

  The encoding is based on the particular usage of ISO 2022 announced



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RFC 1468   Japanese Character Encoding for Internet Messages   June 1993


  by 4/1 (see [ISO2022] for details). However, the escape sequence
  normally used for this announcement is not included in ISO-2022-JP
  messages.

  The Kana set of JIS X 0201 is not used in ISO-2022-JP messages.

  In the past, some systems erroneously used the escape sequence ESC (
  H in JUNET messages. This escape sequence is officially registered
  for a Swedish character set [ISOREG], and should not be used in ISO-
  2022-JP messages.

  Some systems do not distinguish between ESC ( B and ESC ( J or
  between ESC $ @ and ESC $ B for display. However, when relaying a
  message to another system, the escape sequences must not be altered
  in any way.

  The human user (not implementor) should try to keep lines within 80
  display columns, or, preferably, within 75 (or so) columns, to allow
  insertion of ">" at the beginning of each line in excerpts. Each JIS
  X 0208 character takes up two columns, and the escape sequences do
  not take up any columns. The implementor is reminded that JIS X 0208
  characters take up two bytes and should not be split in the middle to
  break lines for displaying, etc.

  The JIS X 0208 standard was revised in 1990, to add two characters at
  the end of the table. Although ISO 2022 specifies special additional
  escape sequences to indicate the use of revised character sets, it is
  suggested here not to make use of this special escape sequence in
  ISO-2022-JP text, even if the two characters added to JIS X 0208 in
  1990 are used.

  For further information about Japanese character encodings such as PC
  codes, FTP locations of implementations, etc, see "Electronic
  Handling of Japanese Text" [JPN.INF].

References

  [ASCII] American National Standards Institute, "Coded character set
  -- 7-bit American national standard code for information
  interchange", ANSI X3.4-1986.

  [ISO646] International Organization for Standardization (ISO),
  "Information technology -- ISO 7-bit coded character set for
  information interchange", International Standard, Ref. No. ISO/IEC
  646:1991.

  [ISO2022] International Organization for Standardization (ISO),
  "Information processing -- ISO 7-bit and 8-bit coded character sets



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RFC 1468   Japanese Character Encoding for Internet Messages   June 1993


  -- Code extension techniques", International Standard, Ref. No. ISO
  2022-1986 (E).

  [ISOREG] International Organization for Standardization (ISO),
  "International Register of Coded Character Sets To Be Used With
  Escape Sequences".

  [JISX0201] Japanese Standards Association, "Code for Information
  Interchange", JIS X 0201-1976.

  [JISX0208] Japanese Standards Association, "Code of the Japanese
  graphic character set for information interchange", JIS X 0208-1978,
  -1983 and -1990.

  [JPN.INF] Ken R. Lunde <[email protected]>, "Electronic Handling of
  Japanese Text", March 1992,
  msi.umn.edu(128.101.24.1):pub/lunde/japan[123].inf

  [JUNET] JUNET Riyou No Tebiki Sakusei Iin Kai (JUNET User's Guide
  Drafting Committee), "JUNET Riyou No Tebiki (Dai Ippan)" ("JUNET
  User's Guide (First Edition)"), February 1988.

  [MIME1] Borenstein N., and N. Freed, "MIME (Multipurpose
  Internet Mail Extensions): Mechanisms for Specifying and
  Describing the Format of Internet Message Bodies", RFC 1341,
  Bellcore, Innosoft, June 1992.

  [MIME2] Moore, K., "Representation of Non-ASCII Text in Internet
  Message Headers", RFC 1342, University of Tennessee, June 1992.

  [RFC822] Crocker, D., "Standard for the Format of ARPA Internet
  Text Messages", STD 11, RFC 822, UDEL, August 1982.

  [RFC1036] Horton M., and R. Adams, "Standard for Interchange of USENET
  Messages", RFC 1036, AT&T Bell Laboratories, Center for Seismic
  Studies, December 1987.

Acknowledgements

  Many people assisted in drafting this document. The authors wish to
  thank in particular Akira Kato, Masahiro Sekiguchi and Ken'ichi
  Handa.

Security Considerations

  Security issues are not discussed in this memo.





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RFC 1468   Japanese Character Encoding for Internet Messages   June 1993


Authors' Addresses

  Jun Murai
  Keio University
  5322 Endo, Fujisawa
  Kanagawa 252 Japan

  Fax: +81 466 49 1101
  EMail: [email protected]


  Mark Crispin
  Panda Programming
  6158 Lariat Loop NE
  Bainbridge Island, WA 98110-2098
  USA

  Phone: +1 206 842 2385
  EMail: [email protected]


  Erik M. van der Poel
  A-105 Park Avenue
  4-4-10 Ohta, Kisarazu
  Chiba 292 Japan

  Phone: +81 438 22 5836
  Fax:   +81 438 22 5837
  EMail: [email protected]






















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