7z

In computing, 7z is an archive format which allows data compression using a number of compression algorithms. The format was initially implemented by the 7-Zip archiver but the file format is public and 7-Zip's implementation of it is publicly available under the GNU LGPL licence.

The main features of the 7z format are:

  • Open, modular architecture (which allows any compression, conversion, or encryption method to be used)
  • High compression ratio (depending on which compression method is used)
  • Strong AES-256 encryption
  • Support for large files (up to approximately 16000 petabytes)
  • Unicode file names
  • Compression of archive headers

The format's open architecture allows additional compression methods to be added to the standard. The following are defined in the current version:
  • LZMA - Improved and optimized version of LZ77 algorithm
  • PPMD - Dmitry Shkarin's PPMdH with small changes
  • BCJ - Converter for 32-bit x86 executables
  • BCJ2 - Converter for 32-bit x86 executables
  • Bzip2 - Standard Burrows-Wheeler algorithm
  • DEFLATE - Standard LZ77-based algorithm

7z also supports encryption with the AES algorithm with a 256-bit key. The key is generated from a user-supplied passphrase using an algorithm based on the SHA-256 hash algorithm (with a large number of iterations, to make a brute-force search for the passphrase more difficult).

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