Aspell is an interactive, command-line spell checking tool. It’s really easy to use, reliable, and flexible. You can even use aspell to generate word lists for tools like password cracking tools (and we’d only use those types of tools when we have lost our own passwords right!). In this article I will show you how install and use the command line tool aspell.

Installation

In most cases, aspell should be installed on your machine as it is used by a number of applications. In the event it is not, the installation is simple. Naturally, since aspell is a command-line tool, let’s install it via the command line. This installation can be done with a single command like so:

sudo apt-get install aspell

The above is for Ubuntu and/or Debian-based distributions. If you are using a Fedora-like distribution (think rpm-based), you could install with the command:

yum install aspell

There may, or may not, be dependencies to install along with aspell which your installer should pick up.

That’s it. You should now have a working copy of aspell installed.

Usage

The basic usage of aspell is as such:

aspell [options] <command> file

Figure 1

The above may seem a bit confusing, but remember, since aspell is used by numerous applications, it is a very powerful tool. That power can be simplified very easily. Let’s first take a look at how aspell can be used to spell check a file. Say you have a file, my_file.txt, that you need checked. From the command line you could issue:

aspell -c my_file.txt

For example’s sake I copied text from a recent article I wrote and named it my_file.txt. When I run aspell against that file it looks like what you see in Figure 1. As you can see, what aspell will do is step through the file, word by word, and check the spelling. When aspell comes across a word it thinks is incorrect you get a list of possible solutions that you can choose from. Choose your solution and aspell will move on to the next word. It’s really quite simple.

Use the aspell dictionary

Aspell can be used in many ways. One very interesting way is to take advantage of the included dictionary. Let’s say you need to generate an alphabetized word list (I had to do this recently to try to crack a forgotten password for a client – it was completely legit). To do this I took advantage of aspell’s dictionary like so:

Download the specific aspell dictionary I needed from here.

Unpack the dictionary with the commands bunzip2 aspell-XXX.tar.bz2 and tar xvf aspell-XXX.tar (Where XXX is the release number).

1. Change into the aspell-XXX directory.
2. Expand the .wl files with the command preunzip *wl
3. Merge the dictionary files into one file with the command sort –unique –ignore-case *wl > wordlist.txt.
4. Convert the list to UTF-8 with the command iconv -f ISO8859-1 -t UTF-8 list.txt >utf_wordlist.txt.

Now you will have a word list, containing a single word per line, thanks to the aspell dictionaries. Pretty cool.

Final thoughts

Aspell is a very powerful tool. But don’t think that its only use is for external applications. Because this is Linux, you can also take advantage of the tools that other tools take advantage of. If you need more information on aspell (and all of it’s options and commands – there are a LOT of them), issue the command man aspell to find out more.

To explain the brute force concept in a few words. It basically is a method to try every possible combination until the right password has been discovered. Passwords that use lots of characters and make use of the complete char set including upper case, lower case, numbers and special chars are harder to brute force.

The Brute Force Calculator lets you enter the amount of chars of the password divided into upper case, lower case, numbers and special characters.

According to the script a single computer can brute force a password consisting of seven lower case chars and one number in 29 minutes while a password consisting of 7 upper case, 7 lower case, 1 number and 1 special char would take 3,129,145,610.89 days to crack on a single machine.

All based on a computer that is able to try 137,438,953,472 combinations per hour. The script is basically interesting for users who are still using short passwords who do not make use of the complete character set possible. It shows them that someone could crack their password in a short amount of time not even taking into consideration using distributed computing to brute force the password.

The common password approach is the one that could give him instant success if the user is really using one of those common passwords for his accounts. His next approach would be to brute force his way in by brute forcing the password on a website that has weak security. Those sites would not react if large amounts of password requests would come in in short time. Most sites however ban IPs at least temporary after several failed attempts, still no problem if you know how to use proxies to attack with different IPs.

But the brute force programs that he suggests are way outdated. Brutus ? wwwHack ? That’s last millennium. Current state of the art bruteforcers for basic authorization and form protected sites are C-Force or Sentry. The brute force approach has one disadvantage. If you do not know the username you have to try username and password combinations and there is no guarantee that you will discover the combination for the user that you want to hack. You could get login details for other users which are absolutely worthless to you. This means, bruteforcing is only an option if you know the username of the user.

There are actually two ways to bruteforce an account. The first would be to use pregenerated lists of usernames and passwords or try combinations to get into an account. The second to try every char combination possible. It should be noted that the second option could very well last several years or even centuries depending on the size of the selected password.

So, bruteforcing is not really an option and he is not explaining how he would get the username of the user in question except mentioning cookies. Cookies are stored on the targets machine which would mean that he needs either access to that machine or an exploit to get them while the user is online. Not very practicable.

So, what can users learn from his analysis ?

• Don’t overuse passwords, it’s more secure to use different passwords. If you only use one password someone who finds this one out gets access to everything else that is protected by that single password
• Don’t use passwords that are easy to guess or common. No names, no sport teams, relatives, pets, work related, hobbies , and so on
• Use numbers and special chars if possible to increase the security of the password. Remember that size matters.
• Write them down locally and put them in a safe or use a software that encrypts them. You could for instance use a True Crypt partition to store a textfile with your passwords in them
• Every password could be important to gain additional information about a user, never choose weak ones