User:Rod J Smith/sandbox

izOnly is a computer project whose goal is to embody privacy properties of US Data Compression patents 6,414,610 and 5,748,955 in software and hardware.

The patents
The patented algorithms and structures differ from typical dictionary-based data compression algorithms and structures in that the dictionary is external to the output of the compressor and usually is not transmitted with it. Thus a same or relevantly same dictionary must pre-exist at each end of a transmission, and the compressor algorithm need not be adaptive.

Basic claims
The system's inventor, Rod Smith, claims that methods and structures of the patents yield uncrackable transmissions, and the original cannot be recovered from an intercept, no matter how powerful the computer or how much time is allowed.

He says this is because the system separates the codec dictionary from the transmission, and what is transmitted is only an address stream (a stream of pointers) to locations inside the dictionary. The transmission is thus insufficient for recovery of the original. The correct dictionary is also needed.

This system could be regarded as an approximate electronic equivalent of the traditional book cipher in which the page number, line number and word-on-line number, or word number from the start of the book, are transmitted for each word in the original, and a copy of the book at issue pre-exists at each end of the transmission. This is regarded as an uncrackable traditional method REF.

History
Patent US 5,748,955 was filed 20 December, 1993 (PCT application filed 20 December, 1994, published as WO95/17783). US 6,414,610 was filed 24 February, 1997 (PCT application filed 24 February, 1998, published as WO98/39723). Both are patents in the Computer Science research field of Data Compression.

Privacy Properties
A transmission consists of a sequence of addresses of locations inside the dictionary used by the compressor. Hence an address in the stream is an address of a location outside of the stream. This means that, unlike with encryption, the original cannot be recovered from an intercept of the stream.

Compared to Encryption
A fundamental weakness of encryption is that the inforamtion (email text, for exmaple), though not in human-readable form, is contained in the transmission. The orignal can always be recovered from an intercept by at least a brute force attack. Wheras in the izOnly case, the inforamtion is not contained in the transmission, which transmission rather contains addresses of locations outside of the transmission, which, when accessed in the right order allow identification and assembly of the informtion.

open source file archiver, or an application used to compress files. 7-Zip operates with the 7z archive format, but can read and write several other archive formats. The program can be used from a command line interface, graphical user interface, or with a window-based shell integration. 7-Zip began in 1999 and is developed by Igor Pavlov. The cross-platform version of the command line utility, p7zip, is also available.

7-Zip is open source software. Most of the source code is under the GNU LGPL license. The unRAR code is under a mixed license: GNU LGPL + unRAR restrictions.

7z
By default, 7-Zip creates 7z format archives with a  file extension. Each archive can contain multiple directories and files. As a container format, security or size reduction are achieved using a stacked combination of filters. These can consist of pre-processors, compression algorithms, and encryption filters.

The core .7z compression uses a variety of algorithms, the most common of which are bzip2, LZMA2, and LZMA. Developed by Pavlov, LZMA is a relatively new system, making its debut as part of the 7z format. LZMA consists of a large LZ-based sliding dictionary up to 4 GB in size, backed by a range coder.

The native 7z file format is open and modular. All filenames are stored as Unicode.

TopTenReviews found that the 7z compression is at least 17% better than ZIP, and 7-Zip's own site reports that while compression ratio results are very dependent upon the data used for the tests, "usually, 7-Zip compresses to 7z format 30–70% better than to zip format, and 7-Zip compresses to zip format 2–10% better than most other zip compatible programs."

The official 7z file format specification is distributed with the program's source code, in the 'doc' subdirectory.