Editing ZIP (file format) (section)

== History ==
The {{mono|.ZIP}} file format was designed by [[Phil Katz]] of [[PKWARE, Inc|PKWARE]] and Gary Conway of Infinity Design Concepts. The format was created after Systems Enhancement Associates (SEA) filed a [[ARC (file format)#Lawsuits|lawsuit]] against PKWARE claiming that the latter's archiving products, named PKARC, were derivatives of SEA's [[ARC (file format)|ARC]] archiving system.<ref>{{cite news| url=https://www.wsj.com/articles/SB961363319756539141 |title=The Rise and Fall of a Software Star; Phil Katz Loved Code -- and Liquor |date=1997-08-15 |first1=Matt |last1 = Murray |first2 = Jeffrey A. |last2 = Tannenbaum |work=[[The Wall Street Journal]] |edition=online |archive-url = https://web.archive.org/web/20160304211123/http://www.wsj.com/articles/SB961363319756539141 |archive-date = 2016-03-04 }} [http://www.bbsdocumentary.com/library/CONTROVERSY/LAWSUITS/SEA/pkzip.htm Alt URL]  Updated 2000-06-19.</ref>  The name "zip" (meaning "move at high speed") was suggested by Katz's friend, Robert Mahoney.<ref name="BBS Documentary">{{Cite web|title=The BBS Documentary Library|url=http://www.bbsdocumentary.com/library/CONTROVERSY/LAWSUITS/SEA/|access-date=2020-09-25|website=www.bbsdocumentary.com}}</ref>  They wanted to imply that their product would be faster than [[ARC (file format)|ARC]] and other compression formats of the time.<ref name="BBS Documentary" />  {{citation needed span|date=May 2018|The earliest known version of ''.ZIP File Format Specification'' was first published as part of [[PKZIP]] 0.9 package under the file APPNOTE.TXT in 1989.}}  By distributing the zip file format within APPNOTE.TXT, compatibility with the zip file format proliferated widely on the public Internet during the 1990s.<ref name="zipattack"/>

PKWARE and Infinity Design Concepts made a joint press release on February 14, 1989, releasing the {{mono|.ZIP}} file format into the [[public domain]].<ref>{{citation |url=http://brianlivingston.com/eweek/article2/0,4149,1257562,00.html |title=PKZip Must Open Up |author=Brian Livingston |quote=The ZIP file format is given freely into the public domain and can be claimed neither legally nor morally by any individual, entity or company |date=8 September 2003 |access-date=5 January 2012}}</ref><ref>{{citation |url=http://www.idcnet.us/ziphistory.html |title=Where Did Zip Files Come From Anyway? |publisher=Infinity Design Concepts, Inc. |access-date=2012-01-05 |archive-date=20 November 2012 |archive-url=https://web.archive.org/web/20121120090241/http://www.idcnet.us/ziphistory.html |url-status=dead }}</ref><ref>{{citation |url=http://cd.textfiles.com/pcmedic9310/MAIN/MISC/COMPRESS/ZIP.PRS |title=Press Release |year=1989 |access-date=5 January 2012}}</ref><ref>{{citation |url=http://www.pkware.com/about-us/phil-katz |title=Our Founder - Phil Katz |publisher=PKWARE |access-date=5 January 2012 | archive-url=https://web.archive.org/web/20101001181829/http://www.pkware.com/about-us/phil-katz | archive-date=2010-10-01 | url-status=dead}}</ref><ref>{{citation |url=http://mailman.vse.cz/pipermail/sc34wg1study/2010-November/000082.html |title=sc34-wg1 |author1=Gareth Horton |author2=Rob Weir |author3=Alex Brown |date=2 November 2010 |access-date=5 January 2012}}</ref>

=== Version history ===
The .ZIP File Format Specification has its own version number, which does not necessarily correspond to the version numbers for the PKZIP tool, especially with PKZIP 6 or later. At various times, PKWARE has added preliminary features that allow PKZIP products to extract archives using advanced features, but PKZIP products that create such archives are not made available until the next major release. Other companies or organizations support the PKWARE specifications at their own pace.

The .ZIP file format specification is formally named "APPNOTE - .ZIP File Format Specification" and it is published on the PKWARE.com website since the late 1990s.<ref>{{citation |url=http://www.pkware.com/support/zip-app-note/ |title= .ZIP Application Note |access-date=2012-07-20}}</ref> Several versions of the specification were not published. Specifications of some features such as [[BZIP2]] compression, strong encryption specification and others were published by PKWARE a few years after their creation. The URL of the online specification was changed several times on the PKWARE website.

A summary of key advances in various versions of the PKWARE software and/or specification:
* 2.0: (1993)<ref name=iana/> File entries can be compressed with [[DEFLATE]] and use traditional PKWARE encryption (ZipCrypto).
* 2.1: (1996) Deflate64 compression support (claimed in APPNOTE 6.1.0 published much later).<ref name="zip610" /> APPNOTE may not have been published for 2.1.
* 2.5: PKWARE DCL Implode compression.<ref name="zip610" /> APPNOTE may not have been published for 2.5.
* 2.5: Deflate64 compression support (claimed in later user manuals, e.g. in 2004.)<ref>{{Cite book |title=Users Manual: PKZIP Server; SecureZIP Server |publisher=PKWARE, Inc. |year=2004 |pages=72 |url=https://archive.org/details/manualzilla-id-5778059/page/72/mode/2up}}</ref>
* 4.0: (2000) Deflate64 compression support (according to information provided by Jim Peterson, Chief Scientist, PKWARE, to the Library of Congress; and APPNOTE 4.0).<ref name="loc">{{Cite web |title=ZIP File Format (PKWARE) |url=https://www.loc.gov/preservation/digital/formats/fdd/fdd000354.shtml#notes |website=Sustainability of Digital Formats: Planning for Library of Congress Collections |publisher=[[Library of Congress]] |date=2020-05-28 |access-date=2025-04-16}}</ref><ref name="zip40-2000">{{Citation |title=File: APPNOTE.TXT - .ZIP File Format Specification Version: 4.0 Revised: 11/01/2000 |date=2000-11-01 |url=https://www.loc.gov/preservation/digital/formats/digformatspecs/APPNOTE%2820001101%29_Version_4.0.txt |access-date=2025-04-16}}</ref>
* 4.5: (2001)<ref name="zip45">{{citation |url=http://www.pkware.com/support/appnote.txt |archive-url=https://web.archive.org/web/20011203085830/http://www.pkware.com/support/appnote.txt |archive-date=3 December 2001 |title=File: APPNOTE.TXT - .ZIP File Format Specification Version: 4.5 Revised: 11/01/2001 |date=3 December 2001 |access-date=21 April 2012}}</ref> Documented 64-bit zip format.
* 4.6: (2001) BZIP2 compression (not published online until the publication of APPNOTE 5.2)
* 5.0: (2002) SES: [[Data Encryption Standard|DES]], [[Triple DES]], [[RC2]], [[RC4]] supported for encryption (not published online until the publication of APPNOTE 5.2)
* 5.2: (2003)<ref>{{citation |url=http://www.pkware.com/documents/APPNOTE/APPNOTE-5.2.0.txt |title=APPNOTE.TXT - .ZIP File Format Specification, Version: 5.2 - Notification of Change |date=16 July 2003 |access-date=5 January 2012}}</ref><ref>{{citation |url=http://pkware.com/products/enterprise/white_papers/appnote.html |archive-url=https://web.archive.org/web/20030702014023/http://pkware.com/products/enterprise/white_papers/appnote.html |archive-date=2 July 2003 |title=File: APPNOTE.TXT - .ZIP File Format Specification Version: 5.2 - Notification of Change – Revised: 06/02/2003 |date=2 July 2003 |access-date=21 April 2012}}</ref> AES encryption support for SES (defined in APPNOTE 5.1 that was not published online) and AES from WinZip ("AE-x"); corrected version of RC2-64 supported for SES encryption.
* 6.1: (2004)<ref name="zip610">{{citation |url=http://www.pkware.com/company/standards/appnote/ |archive-url=https://web.archive.org/web/20040819182806/http://www.pkware.com/company/standards/appnote/ |archive-date=19 August 2004 |title=File: APPNOTE - .ZIP File Format Specification Version: 6.1.0 - Notification of Change – Revised: 01/20/2004 |date=19 August 2004 |access-date=21 April 2012}}</ref> Documented certificate storage.
* 6.2.0: (2004)<ref name="zip620">{{citation |url=http://www.pkware.com/documents/APPNOTE/APPNOTE-6.2.0.txt |title=APPNOTE.TXT - .ZIP File Format Specification, Version: 6.2.0 - Notification of Change |date=26 April 2004 |access-date=5 January 2012}}</ref> Documented Central Directory Encryption.
* 6.3.0: (2006)<ref name="zip630">{{citation |url=http://www.pkware.com/documents/APPNOTE/APPNOTE-6.3.0.TXT |title=APPNOTE.TXT - .ZIP File Format Specification, Version: 6.3.0 |date=29 September 2006 |access-date=5 January 2012}}</ref> Documented Unicode ([[UTF-8]]) filename storage. Expanded list of supported compression algorithms ([[LZMA]], [[PPMd|PPMd+]]), encryption algorithms ([[Blowfish (cipher)|Blowfish]], [[Twofish]]), and hashes.
* 6.3.1: (2007)<ref name="zip631">{{citation |url=http://www.pkware.com/documents/APPNOTE/APPNOTE-6.3.1.TXT |title=APPNOTE.TXT - .ZIP File Format Specification, Version: 6.3.1 |date=11 April 2007     |access-date=25 June 2018}}</ref> Corrected standard hash values for SHA-256/384/512.
* 6.3.2: (2007)<ref name="zip632">{{citation |url=http://www.pkware.com/documents/APPNOTE/APPNOTE-6.3.2.TXT |title=APPNOTE.TXT - .ZIP File Format Specification Version: 6.3.2  |date=28 September 2007 |access-date=25 June 2018}}</ref> Documented compression method 97 ([[WavPack]]).
* 6.3.3: (2012)<ref name="zip633">{{citation |url=http://www.pkware.com/documents/APPNOTE/APPNOTE-6.3.3.TXT |title=APPNOTE.TXT - .ZIP File Format Specification Version: 6.3.3  |date=1 September 2012  |access-date=25 June 2018}}</ref> Document formatting changes to facilitate referencing the PKWARE Application Note from other standards using methods such as the JTC 1 Referencing Explanatory Report (RER) as directed by JTC 1/SC 34 N 1621.
* 6.3.4: (2014)<ref name="zip634">{{citation |url=http://www.pkware.com/documents/APPNOTE/APPNOTE-6.3.4.TXT |title=APPNOTE.TXT - .ZIP File Format Specification Version: 6.3.4  |date=1 October 2014    |access-date=25 June 2018 }}</ref> Updates the PKWARE, Inc. office address.
* 6.3.5: (2018)<ref name="zip635">{{citation |url=http://www.pkware.com/documents/APPNOTE/APPNOTE-6.3.5.TXT |title=APPNOTE.TXT - .ZIP File Format Specification Version: 6.3.5  |date=20 December 2018    |access-date=3 January 2019 }}</ref> Documented compression methods 16, 96 and 99, DOS timestamp epoch and precision, added extra fields for keys and decryption, as well as typos and clarifications.
* 6.3.6: (2019)<ref name="zip636">{{citation |url=http://www.pkware.com/documents/APPNOTE/APPNOTE-6.3.6.TXT |title=APPNOTE.TXT - .ZIP File Format Specification Version: 6.3.6  |date=26 April 2019    |access-date=3 January 2019 }}</ref> Corrected typographical error.
* 6.3.7: (2020)<ref name="zip637">{{citation |url=http://www.pkware.com/documents/APPNOTE/APPNOTE-6.3.7.TXT |title=APPNOTE.TXT - .ZIP File Format Specification Version: 6.3.7  |date=1 June 2020    |access-date=6 June 2020 }}</ref> Added [[Zstandard]] compression method ID 20.
* 6.3.8: (2020)<ref name="zip638">{{citation |url=http://www.pkware.com/documents/APPNOTE/APPNOTE-6.3.8.TXT |title=APPNOTE.TXT - .ZIP File Format Specification Version: 6.3.8  |date=15 June 2020    |access-date=7 July 2020 }}</ref> Moved Zstandard compression method ID from 20 to 93, deprecating the former. Documented method IDs 94 and 95 ([[MP3]] and [[XZ Utils|XZ]] respectively).
* 6.3.9: (2020)<ref name="zip639">{{citation |url=http://www.pkware.com/documents/APPNOTE/APPNOTE-6.3.9.TXT |title=APPNOTE.TXT - .ZIP File Format Specification Version: 6.3.9  |date=15 July 2020    |access-date=8 August 2020 }}</ref> Corrected a typo in Data Stream Alignment description.
* 6.3.10: (2022)<ref name="zip6310">{{citation |url=https://pkware.cachefly.net/webdocs/APPNOTE/APPNOTE-6.3.10.TXT |title=APPNOTE.TXT - .ZIP File Format Specification Version: 6.3.10 |date=1 November 2022    |access-date=20 November 2022 }}</ref> Added several z/OS attribute values for APPENDIX B. Added several additional 3rd party Extra Field mappings.

[[WinZip]], starting with version 12.1, uses the extension {{mono|.zipx}} for ZIP files that use compression methods newer than DEFLATE; specifically, methods BZip, LZMA, PPMd, Jpeg and Wavpack. The last 2 are applied to appropriate file types when "Best method" compression is selected.<ref>{{cite web | url = http://www.winzip.com/comp_info.htm | title = Additional Compression Methods Specification | work = WinZip | publisher = [[WinZip]] Computing, S.L | location = [[Mansfield, CT]] | date = 19 May 2009 | access-date = 2009-05-24}}</ref><ref>{{cite web |url=http://kb.winzip.com/kb/entry/7/ |title=What is a Zipx File? |work=Winzip: Knowledgebase |publisher=[[WinZip]] Computing, S.L |location=[[Mansfield, CT]] |date=13 August 2010 |access-date=17 August 2010}}</ref>

=== Standardization ===
In April 2010, [[JTC 1|ISO/IEC JTC 1]] initiated a ballot to determine whether a project should be initiated to create an ISO/IEC International Standard format compatible with ZIP.<ref>{{Cite web |url=http://kikaku.itscj.ipsj.or.jp/sc34/open/1414.pdf |title=ISO/IEC JTC 1/SC 34 — Document Description and Processing Languages |date=2010-04-12 |access-date=10 May 2014 |archive-url=https://web.archive.org/web/20140512221201/http://kikaku.itscj.ipsj.or.jp/sc34/open/1414.pdf |archive-date=12 May 2014 |url-status=dead |df=dmy-all }}</ref> The proposed project, entitled ''Document Packaging'', envisaged a ZIP-compatible 'minimal compressed archive format' suitable for use with a number of existing standards including [[OpenDocument]], [[Office Open XML]] and [[EPUB]]. It would solve problems such as the need for a formal standard, the variety of extensions of ZIP, the undesirability of a technology used for [[Open Standard]]s potentially having proprietary extensions or "submarine" patents (i.e. which could surface unexpectedly), the need for better internationalization, and a desire not to actually fragment the technology further by purporting to provide an alternative specification to the PKWARE APPNOTE document. 

In 2015, ISO/IEC 21320-1 "Document Container File — Part 1: Core" was published which states that "Document container files are conforming Zip files", normatively referencing the PKWARE APPNOTE document. It requires the following main restrictions of the ZIP file format:<ref>{{cite web |publisher=ITTF |title=ISO/IEC 21320-1:2015 Document Container File — Part 1: Core |url=http://www.iso.org/iso/catalogue_detail.htm?csnumber=60101 |date=2015}}</ref>
* Files in ZIP archives may only be stored uncompressed, or using the "deflate" compression (i.e. compression method may contain the value "0" - stored or "8" - deflated). The patent on the core "deflate" compression method expired in late 2010.<ref>{{cite web |last1=Katz |first1=Phillip W. |title=String searcher, and compressor using same |url=https://patents.google.com/patent/US5051745 |date=24 September 1991}}</ref> 
* The encryption features are prohibited.
* The digital signature features (from SES) are prohibited.
* The "patched data" features (from PKPatchMaker) are prohibited.
* Archives may not span multiple volumes or be segmented.