Hebrew Character Encoding for Internet Messages

Status 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.

Abstract

This document describes the encoding used in electronic mail [RFC822] for transferring Hebrew. The standard devised makes use of MIME [RFC1521] and ISO-8859-8.

Description

All Hebrew text when transferred via e-mail must first be translated into ISO-8859-8, and then encoded using either Quoted-Printable (preferable) or Base64, as defined in MIME.

The following table provides the four most common Hebrew encodings:

                       PC    IBM     PC     ISO
           Hebrew                           8859-8
           letter     8-bit         7-bit   8-bit
                      Ascii  EBCDIC Ascii   Ascii
           ---------- -----  ------ -----   ------
           alef        128     41    96     224
           bet         129     42    97     225
           gimel       130     43    98     226
           dalet       131     44    99     227
           he          132     45   100     228
           vav         133     46   101     229
           zayin       134     47   102     230
           het         135     48   103     231
           tet         136     49   104     232
           yod         137     51   105     233
           kaf sofit   138     52   106     234
           kaf         139     53   107     235
           lamed       140     54   108     236
           
           mem sofit   141     55   109     237
           mem         142     56   110     238
           nun sofit   143     57   111     239
           nun         144     58   112     240
           samekh      145     59   113     241
           ayin        146     62   114     242
           pe sofit    147     63   115     243
           pe          148     64   116     244
           tsadi sofit 149     65   117     245
           tsadi       150     66   118     246
           qof         151     67   119     247
           resh        152     68   120     248
           shin        153     69   121     249
           tav         154     71   122     250

Note: All values are in decimal ASCII except for the EBCDIC column which is in hexadecimal.

ISO 8859-8 8-bit ASCII is also known as IBM Codepage 862.

The default directionality of the text is visual. This means that the Hebrew text is encoded from left to right (even though Hebrew text is entered right to left) and is transmitted from left to right via the standard MIME mechanisms. Other methods to control directionality are supported and are covered in the complementary RFC 1556, "Handling of Bi-directional Texts in MIME".

All discussion regarding Hebrew in email, as well as discussions of Hebrew in other TCP/IP protocols, is discussed in the ilan- h@vm.tau.ac.il list. To subscribe send mail to listserv@vm.tau.ac.il with one line of text as follows:

subscribe ilan-h firstname lastname

MIME Considerations

Mail that is sent that contains Hebrew must contain the following minimum amount of MIME headers:

         MIME-Version: 1.0
         Content-type: text/plain; charset=ISO-8859-8
         Content-transfer-encoding: BASE64 | Quoted-Printable

Users should keep their text to within 72 columns so as to allow email quoting via the prefixing of each line with a ">". Users should also realize that not all MIME implementations handle email quoting properly, so quoting email that contains Hebrew text may lead to problems.

   In the future, when all email systems implement fully transparent 8-
   bit email as defined in RFC 1425 and RFC 1426 this standard will
   become partially obsolete.  The "Content-type:" field will still be
   necessary, as well as directionality (which might be implicit for
   8BIT, but is something for future discussion),  but the "Content-
   transfer-encoding" will be altered to use 8BIT rather than Base64 or
   Quoted-Printable.

Optional

It is recommended, although not required, to support Hebrew encoding in mail headers as specified in RFC 1522. Specifically, the Q- encoding format is to be the default method used for encoding Hebrew in Internet mail headers and not the B-encoding method.

Caveats

Within Israel there are in excess of 40 Listserv lists which will now start using Hebrew for part of their conversations. Normally, Listserv will deliver mail from a distribution list with a "shortened" header, one that does not include the extra MIME headers. This will cause the MIME encoding to be left intact and the user agent decoding software will not be able to interpret the mail. Each user is able to customize how Listserv delivers mail. For lists that contain Hebrew, users should send mail to Listserv with the following command:

set listname full

where listname is the name of the list which the user wants full, unabridged headers to appear. This will update their private entry and all subsequent mail from that list will be with full RFC822 headers, including MIME headers.

In addition, Listserv usually maintains automatic archives of all postings to a list. These archives, contained in the file "listname LOGyymm", do not contain the MIME headers, so all encoding information will be lost. This is a limitation of the Listserv software.

Example

Below is a short example of Quoted-Printable encoded Hebrew email:

   Date:         Sun, 06 Jun 93 15:25:35 IDT
   From:         Hank Nussbacher <HANK@VM.BIU.AC.IL>
   Subject:      Sample Hebrew mail
   To:           Hank Nussbacher <Hank@BARILVM>,
                 Yehavi Bourvine <yehavi@hujivms>
   MIME-Version: 1.0
   Content-Type: Text/plain; charset=ISO-8859-8
   Content-Transfer-Encoding: QUOTED-PRINTABLE
   
   The end of this line contains Hebrew            .=EC=E0=F8=F9=E9 =F5=
   =F8=E0=EE =ED=E5=EC=F9
   
   Hank Nussbacher                                  =F8=EB=E1=F1=E5=
   =F0 =F7=F0=E4

Acknowledgements

Many thanks to Rafi Sadowsky and Nathaniel Borenstein for all their help.

References

   [ISO-8859] Information Processing -- 8-bit Single-Byte Coded
              Graphic Character Sets, Part 8: Latin/Hebrew alphabet,
              ISO 8859-8, 1988.
   
   [RFC822]   Crocker, D., "Standard for the Format of ARPA Internet
              Text Messages", STD 11, RFC 822, UDEL, August 1982.
   
   [RFC1425]  Klensin, J., Freed N., Rose M., Stefferud E., and
              D. Crocker, "SMTP Service Extensions", RFC 1425,
              United Nations University, Innosoft International, Inc.,
              Dover Beach Consulting, Inc., Network Management
              Associates, Inc., The Branch Office, February 1993.
   
   [RFC1426]  Klensin, J., Freed N., Rose M., Stefferud E., and
              D. Crocker, "SMTP Service Extension for 8bit-MIME
              Transport", RFC 1426, United Nations University, Innosoft
              International, Inc., Dover Beach Consulting, Inc., Network
              Management Associates, Inc., The Branch Office, February
              1993.
   
   [RFC1521]  Borenstein N., and N. Freed, "MIME (Multipurpose
              Internet Mail Extensions) Part One: Mechanisms for
              Specifying and Describing the Format of Internet Message
              Bodies", Bellcore, Innosoft, September 1993.
   
   [RFC1522]  Moore K., "MIME Part Two: Message Header Extensions for
              Non-ASCII Text", University of Tennessee, September 1993.

Security Considerations

Security issues are not discussed in this memo.

Authors' Addresses

Hank Nussbacher
Computer Center
Tel Aviv University
Ramat Aviv
Israel

   Fax: +972 3 6409118
   Phone: +972 3 6408309
   EMail: hank@vm.tau.ac.il

Yehavi Bourvine
Computer Center
Hebrew University
Jerusalem
Israel

   Phone: +972 2 585684
   Fax:   +972 2 527349
   EMail: yehavi@vms.huji.ac.il