Crypt::UnixCrypt - perl-only implementation of the crypt function.


  use Crypt::UnixCrypt;
  $hashed = crypt($plaintext,$salt);
  # always use this module's crypt
  BEGIN { $Crypt::UnixCrpyt::OVERRIDE_BUILTIN = 1 }
  use Crypt::UnixCrypt;


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.

If you use this module, you probably neither have a built-in crypt() function nor a crypt(3) 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), 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) 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) interface a very poor choice for anything other than password authentication. If you are planning on using the crypt(3) interface for a cryptography project, don't do it: get a good book on encryption and one of the widely available DES libraries.


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


Written by Martin Vorlaender,, 11-DEC-1997. Based upon Java source code written by, which in turn is based upon C source code written by Eric Young,


In extreme situations, this function doesn't behave like crypt(3), e.g. when called with a salt not in [A-Za-z0-9./]{2}.


perl(1), perlfunc(1), crypt(3).