# man > Crypt::UnixCrypt(3pm)

## NAME
    [Crypt::UnixCrypt](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3AUnixCrypt/markdown) - perl-only implementation of the "crypt" function.

## SYNOPSIS
      use [Crypt::UnixCrypt](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3AUnixCrypt/markdown);
      $hashed = crypt($plaintext,$salt);

      # always use this module's crypt
      BEGIN { $[Crypt::UnixCrpyt::OVERRIDE_BUILTIN](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3AUnixCrpyt%3A%3AOVERRIDEBUILTIN/markdown) = 1 }
      use [Crypt::UnixCrypt](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3AUnixCrypt/markdown);

## DESCRIPTION
    This module is for all those poor souls whose perl port answers to the use of "crypt()" with the
    message `The crypt() function is unimplemented due to excessive paranoia.'.

    This module won't overload a built-in "crypt()" unless forced by a true value of the variable
    $[Crypt::UnixCrypt::OVERRIDE_BUILTIN](https://www.chedong.com/phpMan.php/perldoc/Crypt%3A%3AUnixCrypt%3A%3AOVERRIDEBUILTIN/markdown).

    If you use this module, you probably neither have a built-in "crypt()" function nor a [crypt(3)](https://www.chedong.com/phpMan.php/man/crypt/3/markdown)
    manpage; so I'll supply the appropriate portions of its description (from my Linux system) here:

    crypt is the password encryption function. It is based on the Data Encryption Standard algorithm
    with variations intended (among other things) to discourage use of hardware implementations of a
    key search.

    $plaintext is a user's typed password.

    $salt is a two-character string chosen from the set [a-zA-Z0-9./]. This string is used to
    perturb the algorithm in one of 4096 different ways.

    By taking the lowest 7 bit of each character of $plaintext (filling it up to 8 characters with
    zeros, if needed), a 56-bit key is obtained. This 56-bit key is used to encrypt repeatedly a
    constant string (usually a string consisting of all zeros). The returned value points to the
    encrypted password, a series of 13 printable ASCII characters (the first two characters
    represent the salt itself).

    Warning: The key space consists of 2**56 equal 7.2e16 possible values. Exhaustive searches of
    this key space are possible using massively parallel computers. Software, such as [crack(1)](https://www.chedong.com/phpMan.php/man/crack/1/markdown), is
    available which will search the portion of this key space that is generally used by humans for
    passwords. Hence, password selection should, at minimum, avoid common words and names. The use
    of a [passwd(1)](https://www.chedong.com/phpMan.php/man/passwd/1/markdown) program that checks for crackable passwords during the selection process is
    recommended.

    The DES algorithm itself has a few quirks which make the use of the [crypt(3)](https://www.chedong.com/phpMan.php/man/crypt/3/markdown) interface a very
    poor choice for anything other than password authentication. If you are planning on using the
### crypt
    one of the widely available DES libraries.

## COPYRIGHT
    This module is free software; you may redistribute it and/or modify it under the same terms as
    Perl itself.

## AUTHORS
    Written by Martin Vorlaender, <martin@radiogaga.harz.de>, 11-DEC-1997. Based upon Java source code
    written by <jdumas@zgs.com>, which in turn is based upon C source code written by Eric Young,
    <eay@psych.uq.oz.au>.

## CAVEATS
    In extreme situations, this function doesn't behave like [crypt(3)](https://www.chedong.com/phpMan.php/man/crypt/3/markdown), e.g. when called with a salt
    not in [A-Za-z0-9./]{2}.

## SEE ALSO
### perl