#!/usr/bin/perl
##############################################################
# Anastasios Monachos - anastasiosm@gmail.com
#
# Usage: stemext.pl input_password number_of_iterations append_to_start_or_end_of_stem
# 
# Takes three inputs: a word (our stem) eg my_secret_passwordp80,
# a number in the range 1-3, and the words post or pre.  Then 
# it generates all combinations of the charset appended at the
# beginning or the end on the stem.  The second argument 
# defines how many times the script will go through the charset.
# And the third arguments tells where to append the charset.
#
# Useful when you know that a user chooses for password a 
# specific word and each time she changes her password, the
# only thing she modifies is the last (or the first) 1, 2 or 3
# characters.
##############################################################

die "\n Usage: $0 [stem] [number_of_iterations] [append_to_start_or_end_of_stem]\n\n". 
	"\twhere number_of_iterations can take values: 1 or 2 or 3\n".
	"\tand append_to_start_or_end_of_stem takes the values pre and post.\n\n" unless $#ARGV == 2;
	
my $stem = @ARGV[0];
my $iterations = @ARGV[1];
my $order = @ARGV[2];

# define the characters to be used as extension on our stem parameter
$charset=("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789");
$size = length($charset);

# split into individual words and store in array
@array = split (//, $charset);

if ($order eq 'post')
{
if ($iterations==1)
{
	for ($count=0; $count < $size;$count++)
	{
		print $stem . $array[$count]."\n";
	}
}

if ($iterations==2)
{
	for ($count=0; $count < $size;$count++)
	{
		for ($count_inner=0; $count_inner < $size;$count_inner++)
		{
			print $stem . $array[$count_inner] . $array[$count]."\n";
		}
	}
}

if ($iterations==3)
{
	for ($count=0; $count < $size;$count++)
	{
		for ($count_inner=0; $count_inner < $size;$count_inner++)
		{
			for ($count_core=0; $count_core < $size;$count_core++)
			{
				print $stem . $array[$count_core] .$array[$count_inner] . $array[$count]."\n";
			}
		}
	}
}
}#end of post

if ($order eq 'pre')
{
if ($iterations==1)
{
	for ($count=0; $count < $size;$count++)
	{
		print $array[$count] . $stem."\n";
	}
}

if ($iterations==2)
{
	for ($count=0; $count < $size;$count++)
	{
		for ($count_inner=0; $count_inner < $size;$count_inner++)
		{
			print $array[$count_inner] . $array[$count] . $stem."\n";
		}
	}
}

if ($iterations==3)
{
	for ($count=0; $count < $size;$count++)
	{
		for ($count_inner=0; $count_inner < $size;$count_inner++)
		{
			for ($count_core=0; $count_core < $size;$count_core++)
			{
				print $array[$count_core] .$array[$count_inner] . $array[$count].$stem."\n";
			}
		}
	}
}
}#end of pre