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

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])"

    Given three arguments, computes the hash value and returns it as a string
    containing six words separated by spaces. 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()"

    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, ken@forum.swarthmore.edu

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

COPYRIGHT
    Copyright 2000-2002 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).