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Pkcrack

May 26, 2018

Utility for breaking pkzip encryption

This package implements an algorithm for breaking the PkZip cipher that was devised by Eli Biham and Paul Kocher.

This program applies a known plaintext attack to an encrypted file. A known-plaintext-attack recovers a password using the encrypted file and part of the unencrypted file.

Please note that cryptographers use the word ‘plaintext’ for any kind of unencrypted data - not necessarily readable ASCII text.

Before you ask why somebody may want to know the password when he already knows the plaintext think of the following situations

  • Usually there’s a large number of files in a ZIP-archive. Usually all these files are encrypted using the same password. So if you know one of the files, you can recover the password and decrypt the other files.
  • You need to know only a part of the plaintext at least 13 bytes. Many files have commonly known headers, like DOS .EXE-files. Knowing a reasonably long header you can recover the password and decrypt the entire file.

WWW http//www.unix-ag.uni-kl.de/~conrad/krypto/pkcrack.html