View source for HZ (character encoding)

{{Short description|Format for sending GB 2312 text over a 7-bit ASCII channel}}
{{Infobox character encoding
| name = HZ encoding
| image = 
| mime = HZ-GB-2312
| alias = 
| standard = {{IETF RFC|1843}}
| lang = [[Simplified Chinese]], [[English language|English]], [[Russian language|Russian]]
<!-- Not | extends = [[US-ASCII]] as even plain ASCII text can be reinterpreted. -->
| encodes = [[GB 2312]]
| status = 
| prev = zW
| next = [[Quoted-printable]], [[UTF-7]], [[8BITMIME]]
| classification = [[CJK characters|CJK encoding]], [[ASCII armor]], [[variable-width encoding]], [[state (computer science)|stateful encoding]]
| by = Fung Fung Lee
}}
The '''HZ character encoding'''<ref name="hz">{{cite web|url=http://umunhum.stanford.edu/~lee/chicomp/HZ_spec.html|title=HZ &mdash; A Data Format for Exchanging Files of Arbitrarily Mixed Chinese and ASCII Characters|archive-url=https://web.archive.org/web/20051027040810/http://umunhum.stanford.edu/~lee/chicomp/HZ_spec.html|archive-date=2005-10-27}}</ref> is an [[Character encoding|encoding]] of [[GB 2312]] that was formerly commonly used in email and [[USENET]] postings. It was designed in 1989 by Fung Fung Lee ({{zh|李楓峰}}) of [[Stanford University]], and subsequently codified in 1995 into RFC 1843.<ref name="rfc">{{IETF RFC|1843}}</ref>

The HZ, short for ''[[Hanzi]]'' ({{zh|t=漢字|s=汉字|l=Chinese Characters}}), encoding was invented to facilitate the use of Chinese characters through e-mail, which at that time only allowed 7-bit characters. Therefore, in lieu of standard ISO 2022 escape sequences (as in the case of [[ISO-2022-JP]]) or 8-bit characters (as in the case of [[Extended Unix Code|EUC]]), the HZ code uses only printable, 7-bit characters to represent Chinese characters.

It was also popular in USENET networks, which in the late 1980s and early 1990s, generally did not allow transmission of 8-bit characters or escape characters.

==History==
HZ superseded the earlier "zW" encoding, which marked entire lines as being GB 2312 text by beginning them with the characters <code>zW</code>.<ref>{{cite web|url=https://ccjktype.fonts.adobe.com/wp-content/uploads/2013/09/cjk_inf.txt|last=Lunde|first=Ken|author-link=Ken Lunde|title=CJK.INF Version 1.9|date=1995-12-18}}</ref>

==Structure and use==
In the HZ encoding system, the character sequences "~{" and "~}" act as escape sequences; anything between them is interpreted as Chinese encoded in GB 2312 (the most significant bits are ignored). Outside the escape sequences, characters are assumed to be [[ASCII]].

An example will help illustrate the relationship between [[GB 2312]], [[Extended Unix Code#EUC-CN|EUC-CN]], and the HZ code:

{| border=1 cellpadding=4 style="border-collapse: collapse;"
|+ Various forms of the GB 2312 code (0xD2BB) for the character "一" (one)
|---
! Form || Code || With escape sequences || Remarks
|---
| [[Kuten]] / Qūwèi / {{lang|zh-hans|区位}} form || 5027 || — || Zone/ward/row (ku/qū/{{lang|zh-hans|区}}) 50, point (ten/wèi/{{lang|zh-hans|位}}) 27 
|---
| ISO 2022 form || 52<sub>16</sub> 3B<sub>16</sub> || 0E<sub>16</sub> 52<sub>16</sub> 3B<sub>16</sub> 0F<sub>16</sub> || 50 + 32 = 82 = 52<sub>16</sub>
|---
| EUC-CN form || D2<sub>16</sub> BB<sub>16</sub> || D2<sub>16</sub> BB<sub>16</sub> || 52<sub>16</sub> ∨ 80<sub>16</sub> = D2<sub>16</sub>
|---
| HZ form (standard) || 52<sub>16</sub> 3B<sub>16</sub> || 7E<sub>16</sub> 7B<sub>16</sub> 52<sub>16</sub> 3B<sub>16</sub> 7E<sub>16</sub> 7D<sub>16</sub> || Appears as {{mono|<nowiki>~{R;~}</nowiki>}} without HZ decoder
|---
| HZ form (alternate) || D2<sub>16</sub> BB<sub>16</sub> || 7E<sub>16</sub> 7B<sub>16</sub> D2<sub>16</sub> BB<sub>16</sub> 7E<sub>16</sub> 7D<sub>16</sub> || EUC form acceptable to at least some decoders
|}

HZ was originally designed to be used purely as a 7-bit code. However, when situations allow, the escape sequences "~{" and "~}" sometimes surround characters represented in EUC-CN; this alternative use allows Chinese to be readable either with the help of HZ decoder software, or with a system that understands EUC-CN.

Additionally, the specification defines that:

* the sequence "~~" is to be treated as encoding a single ASCII "~" and,
* the character "~" followed by a newline is to be discarded.

However, not all HZ decoders follow these two rules.

==HZ encoders and decoders==
The first HZ encoder and decoder were written in 1989 by the code's inventor for the [[Unix]] operating system.<ref name="hz-package">{{cite web|url=http://ftp.cuhk.hk/pub/chinese/ifcss/software/unix/convert/HZ-2.0.tar.gz|title=HZ package 2.0 &mdash; HZ spec, reference encoder and decoder source code}}</ref>

The {{mono|hztty}} program, also for the [[Unix]] operating system, was also among the first and one of the most popular HZ decoders. It deviates from the specification in that it will display the escape sequences (i.e., "~{" and "~}"), and it does not treat "~~" and "~" followed by a newline specially. This was probably to allow software which assumes one character to occupy one screen position (on a text screen) to function correctly without modification.

Support on [[Microsoft Windows]] came later, and a number of third-party "Chinese systems" support HZ. These systems may provide an option to hide the escape sequences.

==Disadvantages==
Because of its escape sequences, and furthermore because its escape delimiters are printable characters in ASCII, it is fairly easy to construct attack byte sequences that round-trip from HZ to Unicode and back. Use of HZ encoding is thus treated as suspicious by malware protection suites.<ref>{{Cite web|url=https://bugzilla.mozilla.org/show_bug.cgi?id=935453|title=935453 - Gather telemetry about HZ and other encodings we might try to remove|access-date=2018-06-18|archive-date=2017-05-19|archive-url=https://web.archive.org/web/20170519153033/https://bugzilla.mozilla.org/show_bug.cgi?id=935453|url-status=live}}</ref>{{better source needed|date=September 2020}}

==References==
<references />

{{character encoding}}

[[Category:Chinese character encodings]]