PKZIP is an archiving tool originally written by the late Phil Katz, and marketed by his company PKWARE, Inc. PKZIP is an acronym for Phil Katz's ZIP program.
Contents |
History
File archival routines date back to at least the 1970s, when they were distributed as standard utilities with operating systems. They include the Unix utilities ar, shar, and tar. These utilities were designed to gather a number of separate files into a single archive file for easier copying and distribution. During the 1980s, the company System Enhancement Associates (SEA) developed a shareware utility called ARC, based on earlier programs such as tar, that not only grouped files into a single archive file but also compressed them to save disk space, a feature of great importance on early personal computers, where space was very limited and modem transmission speeds were very slow. The archive files produced by ARC had file names ending in ".ARC" and were sometimes called "arc files" as a result. Later, Phil Katz developed his own shareware utilities, PKARC and PKXARC, to create archive files and extract their contents. These files worked with the archive file format used by ARC, but were faster than ARC. Unlike SEA, which combined archive creation and archive file extraction in a single program, Katz divided these functions among two separate utilities, reducing the amount of memory needed to run them. This also allowed the file extractor to be incorporated into the archive file to create self-extracting archives, which could unpack themselves without requiring an external file extraction utility. The competition from Katz did not please SEA, who sued Katz for trademark infringement, as well as copyright infringement as it alleged that Katz had plagiarised sections of the code. Katz lost the lawsuit and was forced to pay $62,500 to SEA to cover their legal fees. It was found during the court case that Katz had used SEA's ARC source code for the majority of the application but had only made code optimizations to increase speed. Primarily he changed the word length used by the algorithm from 12 bits to 13 bits resulting in a higher compression for typical binary files. As a result of the lawsuit, Katz changed the names of his utilities to PKPAK and PKUNPAK, and then developed PKZIP and PKUNZIP, which were based on new and different file compression techniques. The suit by SEA angered many shareware users, perceiving that SEA was a 'large, faceless corporation' and Katz was 'the little guy'. In fact, at the time, both SEA and PKWARE were small home-based companies. However, the community largely sided with Katz, and became persuaded by the superior compression capabilities of PKZIP. SEA's ARC was largely abandoned in favor of PKZIP and PKUNZIP as the predominant data compression software on MS DOS. Other archivers also appeared during the 1980s, including Rahul Dhesi's ZOO, Dean W. Cooper's DWC, and LHarc by Haruhiko Okomura and Haruyasu Yoshizaki. The first version of PKZIP appeared in 1989. It was a DOS command-line tool and was distributed as shareware with a $25 registration fee.
Version history
PKZIP 0.9 supports Reducing algorithm with 4 compression settings and shrinking. PKZIP 1.x used a new compression algorithm, colourfully referred to as "imploding", which was chosen based on the characteristics of the file being compressed. Reducing is supported for expansion only. Although popular at the time, files in PKZIP 1 format are now rare, and many modern unzip tools are unable to handle "shrinking" and "reducing", although "imploding" is usually supported. However, shrinking uses dynamic LZW, which Unisys held patents; patent for Reduce algorithm had also been filed in June 19, 1984, long before PKZIP had been produced. [1] In 1993, PKWARE released PKZIP 2.0. This new version dispensed with the miscellaneous compression methods of PKZIP 1.x and replaced them with a single new compression method which Katz called "deflating" (although several compression levels of deflating were provided by the program). The resulting file format has since become ubiquitous on Microsoft Windows and on the Internet - almost all files with the .ZIP (or .zip) extension are in PKZIP 2.x format, and utilities to read and write these files are available on all common platforms. PKZIP 2.x also supports spanning archives to multiple disk, which simply splits the files into multiple pieces, and using volume label on each drive to differentiate each other. A new Authenticity Verification (AV) signature format is used. On March 1, 1999, PKWARE released its final MS-DOS version of PKZIP - namely, PKZIP 2.50 for DOS. Future command-line versions of PKZIP would run only under Microsoft Windows and various UNIX platforms, under the name "PKZIP Command Line" (later expanded to "PKZIP Server"). PKZIP 2.5 supports Deflate64 algorithm. PKZIP 4.5 included 64-bit file sizes support. PKZIP 5.0 introduced Strong Encryption Specification (SES), which initially included DES, 3DES, RC2, RC4. It also include the use of certificate-based encryption. PKZIP 6.0 supports BZip2 (based on Burrows-Wheeler transform) compression, with Professional Edition supporting 256 Bit AES. PKZIP 7.0 changed SES to use non-OAEP key wrapping. In 2004, PKWARE renamed its PKZip Professional to SecureZIP 8.0, which consists of PKZIP with the use of X.509 Certificates. PKZIP 9.0 include support of PPMD compression. On April 24, 2007, PKWARE announced the release of SecureZIP Standard Version 11 as freeware, available on www.securezip.com. [2] Version 10 was simply skipped. This version supports LZMA compression. SecureZIP comes with SecureZIP Standard (SecureZIP for Windows Desktop), SecureZIP Enterprise, SecureZIP Command Line Interface, SecureZIP for Server, SecureZIP for Server with Directory Integration Module.
.ZIP file format
To help ensure the interoperability of the ZIP format, Phil Katz published the original .ZIP File Format Specification in the APPNOTE.TXT documentation file. PKWARE continued to maintain this document and periodically published updates. The specification has its own version number, which do not necessarily correspond to the PKZIP version numbers, especially with PKZIP 6 or later.
Strong encryption controversy
When WinZip 9.0 public beta was released in 2003, WinZip introduced its own AES-256 compression, using a different file format, along with the documentation for the new specification. [3] The encryption standards themselves were not proprietary, but PKWare had not updated APPNOTE.TXT to include SES since 2001, which were used by PKZip 5.0 and 6.0. WinZip technical consultant Kevin Kearney and Stuff-It product manager Mathew Covington accused PKWare for withholding SES, PKZip chief technology officer Jim Peterson claimed that Certificate-based encryption was still incomplete. Contemporary products such as StuffIt and PentaZip 'implemented' strong ZIP encryption by encrypting ZIP archives into a different file format. [4] To further the controversy, in July 16, 2003, PKWARE also filed patent for combining .ZIP and strong encryption to create a secure .ZIP file. [5] In the end, PKWARE and WinZip agreed to support each other's products. On 2004-1-21, PKWARE announced the support of WinZip-based AES compression format. [6] In later version of WinZip beta, it is able to support SES-based ZIP files. [7] PKWARE eventually documented SES in version 6 of .ZIP File Format Specification.
Other products
PKWARE also used its PKZIP standards on following products:
- PartnerLink (including SecureZIP/PartnerLink, SecureZIP Partner)
- PKZIP Explorer
See also
References
- ^ http://www.faqs.org/faqs/compression-faq/part1/section-7.html
- ^ http://www.pkware.com/documents/announcements/SecureZIPGiveawayAnnouncement_FINAL.doc
- ^ http://www.winzip.com/aes_info.htm
- ^ http://www.infoworld.com/article/03/06/10/HNzipsplinters_1.html
- ^ http://www.infoworld.com/article/03/07/25/HNpkware_1.html
- ^ http://www.news.com/2100-1012_3-5145491.html?tag=fd_nbs_ent
- ^ http://www.theregister.co.uk/2004/01/21/zip_file_encryption_compromise_thrashed/
External links
- PKWARE Homepage
- PKZIP from PKWARE
- PKZIP 2.50 for DOS
- SecureZIP from PKWARE
- SecureZIP Homepage
- APPNOTE
- Commentary from SEA owner about Phil Katz, the lawsuit, and his death
- CONTROVERSY: LAWSUITS: SEA vs. PKWARE
- How to Use PKZIP From the Command Line
