Crypt-SKey - README

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

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).