Crypt::SKey - Perl S/Key calculator
# 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
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
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
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.
Follow the usual steps for installing any Perl module:
perl Makefile.PL make test make install
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:
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.
This is a random seed. It is usually the second number/string shown in an S/Key challenge.
This is your secret password.
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.
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:
Their meanings are exactly the same as with the
compute function above.
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.
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
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.
Ken Williams, email@example.com
Thanks to Chris Nandor and Allen Chen for testing MD5 functionality.
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.