Thursday, January 17, 2008

Perl Random Password Generator For Linux and Unix

As we noted in yesterday's post, we took a look at how it's possible to use Perl on Linux and Unix to try and find whether or not any given password exists within a system's /etc/shadow file.

In today's post, we're going to look at another part of the password puzzle: Password generation. This is slightly different than sequential password generation (which we'll look at tomorrow), in that the passwords that are generated are intended to annoy ;) In other words, the probability that any of these passwords could be found in a shadow password file is highly unlikely. And, if you did find one, I don't know if it would be grounds for penalty. That user would have an unbelievable secure password under any other circumstance!

This code has been tested on Solaris Unix and RedHat Linux and works almost every time (I can't speak to the infinite, but it hasn't failed me yet ;)

This script makes use of Perl's built-in rand function, which works in much the same way as the standard Unix or Linux random function does. The rand function is fed some slightly random data (certainly not good enough to seed any viable encryption) and generates random ASCII characters.

I wrote this up so that it can be invoked simply by its name, like so:


and requires no argument. This script will pump out 8 character garbage passwords, like this:


and it will go on forever until you either kill it or it finds that it has created a duplicate. Check it out, enjoy it and feel free to improve upon it. A simple change can make it so it only spits out a certain number of random passwords.

If you use it creatively, you can incorporate it with other Linux and Unix shell scripts to provide input for password cracking programs. Although, as I mentioned above, if I found any of these passwords among my users' passwords, I certainly wouldn't complain ;) Tomorrow we'll look at a way to generate real passwords (kind of like JTR does) that can be fed to the script we looked at yesterday to do some in-house brute-force password cracking against your shadow database file. Again; this sort of shell scripting is only recommended for security enhancement!

Best Wishes,


# pwdgen - Create insane 8 character passwords to
# encourage users to beef up their password strength
# 2008 - Mike Golvach -
# Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License

for ( $i = 1; $i > 0 ; $i++ ) {
$random = rand('netstat -a'*10000);
$newpassword = "";
while ( $count < 8 ) {
$tester = rand('netstat -a')*100;
if ( $tester < 33 ) {
$tester += 33;
} elsif ( $tester > 93 ) {
$tester -= 7;
$newpassletter = sprintf("%c", $tester);
$newpassword .= $newpassletter;
$newpassword =~ s/ ?//g;
if ( exists $passwords{$newpassword} ) {
print "Found a pattern on step $i with password $newpassword\n";
} else {
$passwords{$newpassword} = $i;
print "$newpassword\n";

, Mike