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Network Working Group                                           J. MuraiRequest for Comments: 1468                               Keio University                                                              M. Crispin                                                       Panda Programming                                                         E. van der Poel                                                               June 1993Japanese Character Encoding for Internet MessagesStatus 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 changedMurai, Crispin & van der Poel                                   [Page 1]

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 inRFC 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-charMurai, Crispin & van der Poel                                   [Page 2]

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 announcedMurai, Crispin & van der Poel                                   [Page 3]

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 setsMurai, Crispin & van der Poel                                   [Page 4]

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 <lunde@adobe.com>, "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.Murai, Crispin & van der Poel                                   [Page 5]

RFC 1468   Japanese Character Encoding for Internet Messages   June 1993Authors' Addresses   Jun Murai   Keio University   5322 Endo, Fujisawa   Kanagawa 252 Japan   Fax: +81 466 49 1101   EMail: jun@wide.ad.jp   Mark Crispin   Panda Programming   6158 Lariat Loop NE   Bainbridge Island, WA 98110-2098   USA   Phone: +1 206 842 2385   EMail: MRC@PANDA.COM   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: erik@poel.juice.or.jpMurai, Crispin & van der Poel                                   [Page 6]