NAME
    Crypt::SKey - Perl S/Key calculator

SYNOPSIS
      # In perl script:
      use Crypt::SKey qw(compute);
      $output = compute($sequence_num, $seed, $password);
      @output = compute($sequence_num, $seed, $password, $count);
  
      # Command line:
      perl -MCrypt::SKey -e key 500 fo099804
      perl -MCrypt::SKey -e key 500 fo099804 100
      perl -MCrypt::SKey=key_md4 -e key_md4 500 fo099804
  
      # The following shell alias may be useful:
      alias key 'perl -MCrypt::SKey -e key'
      # This allows you to simply type:
      key 500 fo099804

DESCRIPTION
    This module contains a simple S/Key calculator (as described in RFC
    1760) implemented in Perl. It exports the function `key' by default, and
    may optionally export the function `compute'.

    `compute_md4', `compute_md5', `compute_sha1', `key_md4', `key_md5', and
    `key_sha1' are provided as convenience functions for selecting MD4, MD5,
    or SHA1 hashes. The default is MD4; this may be changed with with the
    `$Crypt::SKey::HASH' variable, assigning it the value of `MD4', `MD5',
    or `SHA1'. You can access any of these functions by exporting them in
    the same manner as `compute' in the above example.

    Most S/Key systems use MD4 hashing, but a few (notably OPIE) use MD5.

INSTALLATION
    Follow the usual steps for installing any Perl module:

      perl Makefile.PL
      make test
      make install

FUNCTIONS
  `compute($sequence_num, $seed, $password [, $count])'

  `compute_md4($sequence_num, $seed, $password [, $count])'

  `compute_md5($sequence_num, $seed, $password [, $count])'

  `compute_sha1($sequence_num, $seed, $password [, $count])'

    Given three arguments, computes the hash value and returns it as a
    string containing six words separated by spaces (or as a string of 16
    hex digits if `$Crypt::SKey::HEX' is set to a true value). If $count is
    specified and greater than one, returns a list of several such strings.
    The meanings of the arguments is as follows:

    * sequence_number
        Which output in the sequence of calculated S/Key responses to
        generate. This is called `N' in RFC 1760. It will usually be the
        first number shown in an S/Key challenge.

    * seed
        This is a random seed. It is usually the second number/string shown
        in an S/Key challenge.

    * password
        This is your secret password.

    * count
        This argument is optional and defaults to `1'. It specifies the
        number of S/Key responses to generate. This may be useful if you
        want to pre-generate a bunch of responses and print them on a piece
        of paper so that you don't need to have an S/Key calculator around
        later.

  `key()'

  `key_md4()'

  `key_md5()'

  `key_sha1()'

    Acts just like the 'key' executable program that comes with the standard
    distribution of s/key. Reads several arguments from the command line
    (`@ARGV'), prompts for the user's password, and prints one or more
    calculated s/key responses to `STDOUT'. The command line arguments are,
    in order:

    * sequence_number
    * seed
    * count (optional)
    Their meanings are exactly the same as with the `compute' function
    above.

NOTES
    If you care about security, you'd probably be better off using SSH than
    S/Key, because SSH encrypts your entire session whereas S/Key only
    encrypts your password. I wrote this module because nobody else seemed
    to have done it yet, and because sometimes I'm on systems with neither
    SSH nor the `key' program, but I want to telnet to a system that offers
    S/Key password transmission.

    The original `key' program takes the `count' parameter using the `-n'
    flag, but this version takes it as an optional final argument. Unless I
    hear from someone that needs the behavior changed, I'm not likely to add
    the `-n' flag.

    I currently have no plans to write any code that checks the validity of
    S/Key responses at login, i.e. the code that the server has to run when
    authenticating users. It shouldn't be hard, though, and if someone wants
    to send me a patch implementing this functionality I'll be happy to add
    it.

AUTHOR
    Ken Williams, kwilliams@cpan.org

    Thanks to Chris Nandor and Allen Chen for testing MD5 functionality.

COPYRIGHT
    Copyright 2000-2009 Ken Williams. All rights reserved.

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

SEE ALSO
    perl(1). RFC 1760. Digest::MD4(1). Digest::MD5(1). Term::ReadKey(1).