Expires on 14-September-2001 H. Nussbacher
Request for Comments: XXXX Israeli Inter-University
Category: Informational Computer Center
Obsoletes: RFC 1555 Y. Bourvine
The Hebrew University of Jerusalem
March 2000
Hebrew Character Encoding for Internet Messages
draft-nussbacher-bourvine-hebrew-email-00.txt
Status of this Memo
This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC2026.
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.
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Abstract
This document describes the encoding used in electronic mail [RFC822]
for transferring Hebrew. The standard devised makes use of MIME
[RFC2045] and ISO-8859-8.
This memo is based on the Israeli standard IS-1904 and is compatible
with it.
Revision note: The change over RFC1555 is that the default
directionality in a composed Hebrew message was changed to Implicit
from Visual, and a receiving entity needs to understand both visual
and implicit messages. Explicit directionality has been removed, as
it was never used.
Description
All Hebrew text when transferred via e-mail must first be translated
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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 (DOS) 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 logical (implicit). This
means that the Hebrew text is encoded according to the directionality
of the involved characters, and is trasmitted in the same order as a
person would type the stated text. The methods to control
directionality are supported and are covered in the complementary RFC
1556, "Handling of Bi-directional Texts in MIME". The algorithm used
to convert from logical directionality to visual is the Unicode one.
This algorithm is used to reformat the text for displaying on a
non-Hebrew aware terminal.
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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
Character set
Due to the lack of directionality field in MIME headers it was decided
to superimpose the directionality over the character set. Thus, the
following character sets are available:
iso-8859-8 for visual directionality
iso-8858-8-i for implicit (logical) directionality.
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-i
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 STD0010 and RFC 1652 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 2047. 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.
Conformance
A conforming sender MUST use Logical order (charset=iso-8858-8-i). A
conforming receiver MUST be able to properly decode logical order
(charset=iso-8859-8-i) encoding and SHOULD be able to properly decode
visual order encoding (charset=iso-8859-8). The latter is for support
older software which implemented RFC-1555 visual mode.
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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-i
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.
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[RFC822] Crocker, D., "Standard for the Format of ARPA Internet
Text Messages", STD 11, RFC 822, UDEL, August 1982.
[STD0010] Klensin, J., Freed N., Rose M., Stefferud E., and
D. Crocker, "SMTP Service Extensions", RFC 1869,
United Nations University, Innosoft International, Inc.,
Dover Beach Consulting, Inc., Network Management
Associates, Inc., The Branch Office, February 1993.
[RFC1652] Klensin, J., Freed N., Rose M., Stefferud E., and
D. Crocker, "SMTP Service Extension for 8bit-MIME
Transport", RFC 1652, United Nations University,
Innosoft
International, Inc., Dover Beach Consulting, Inc.,
Network
Management Associates, Inc., The Branch Office, February
1993.
[RFC2045] 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.
[RFC2047] 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' Address
Hank Nussbacher
Computer Center
Tel Aviv University
Ramat Aviv
Israel
Fax: +972 3 6409118
Phone: +972 3 6408309
EMail: hank@interall.co.il
Yehavi Bourvine
Computer Center
Hebrew University
Jerusalem
Israel
Phone: +972 2 6585684
Fax: +972 2 6527349
EMail: yehavi@vms.huji.ac.il
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