Top ten password cracking techniques

If you want to ensure your password, and the data it protects, is as secure against hackers as possible then be sure to read The Ultimate Guide to Passwords in the upcoming issue of PC Pro, on sale next week.

In case you think you're safe from the attentions of such criminal types, or think they'd never be able to guess your password, perhaps you might be interested to learn just how wrong you are.

Here are the ten most common password cracking techniques in use:

1. Dictionary attack

This uses a simple file containing words that can, surprise surprise, be found in a dictionary. In other words, if you will excuse the pun, this attack uses exactly the kind of words that many people use as their password.

Cleverly grouping words together such as ‘letmein’ or ‘superadministratorguy’ will not prevent your password from being cracked this way - well, not for more than a few extra seconds.

2. Brute force attack

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This method is similar to the dictionary attack but with the added bonus, for the hacker, of being able to detect non-dictionary words by working through all possible alpha-numeric combinations from aaa1 to zzz10.

It’s not quick, provided your password is over a handful of characters long, but it will uncover your password eventually. Brute force attacks can be shortened by throwing additional computing horsepower, in terms of both processing power - including harnessing the power of your video card GPU - and machine numbers, such as using distributed computing models and zombie botnets.

3. Rainbow table attack

A rainbow table is a list of pre-computed hashes - the numerical value of an encrypted password, used by most systems today - and that’s the hashes of all possible password combinations for any given hashing algorithm mind. The time it takes to crack a password using a rainbow table is reduced to the time it takes to look it up in the list.

However, the table itself will be huge and require some serious computing horse power to run, and it’s useless if the hash it is trying to find has been ‘salted’ by adding random characters to the password before applying the hashing algorithm.

There is talk of salted rainbow tables existing, but these would be so large as to be difficult to use in practice. They would likely only work with a predefined ‘random character’ set and password strings below 12 characters as the size of the table would be prohibitive to even state-level hackers otherwise.

4. Phishing

There's an easy way to hack: ask the user for his or her password. A phishing email leads the unsuspecting reader to a faked online banking, payment or other site in order to login and put right some terrible problem with their security.

Why bother going to the trouble of cracking the password when the user will happily give it you anyway?

5. Social engineering

Social engineering takes the whole ‘ask the user’ concept outside of the inbox that phishing tends to stick with and into the real world.

A favorite of the social engineer is to telephone an office posing as an IT security tech guy and simply ask for the network access password. You’d be amazed how often this works. Some even have the necessary gonads to don a suit and name badge before walking into a business to ask the receptionist the same question face to face.

6. Malware

A key logger or screen scraper can be installed by malware which records everything you type or takes screen shots during a login process, and then forwards a copy of this file to hacker central.

Some malware will look for the existence of a web browser client password file and copy this which, unless properly encrypted, will contain easily accessible saved passwords from the user's browsing history.

7. Offline cracking

It’s easy to imagine that passwords are safe when the systems they protect lock out users after three or four wrong guesses, blocking automated guessing applications. Well, that would be true if it were not for the fact that most password hacking takes place offline, using a set of hashes in a password file that has been ‘obtained’ from a compromised system.

Often the target in question has been compromised via an hack on a third party, which then provides access to the system servers and those all-important user password hash files. The password cracker can then take as long as they need to try and crack the code without alerting the target system or individual user.

8. Shoulder surfing

The most confident of hackers will take the guise of a parcel courier, aircon service technician or anything else that gets them access to an office building.

Once they are in, the service personnel ‘uniform’ provides a kind of free pass to wander around unhindered, and make note of passwords being entered by genuine members of staff. It also provides an excellent opportunity to eyeball all those post-it notes stuck to the front of LCD screens with logins scribbled upon them.

9. Spidering

Savvy hackers have realize that many corporate passwords are made up of words that are connected to the business itself. Studying corporate literature, website sales material and even the websites of competitors and listed customers can provide the ammunition to build a custom word list to use in a brute force attack.

Really savvy hackers have automated the process and let a spidering application, similar to those employed by leading search engines to identify keywords, collect and collate the lists for them.

10. Guess

The password crackers best friend, of course, is the predictability of the user. Unless a truly random password has been created using software dedicated to the task, a user generated ‘random’ password is unlikely to be anything of the sort.

Instead, thanks to our brains' emotional attachment to things we like, the chances are those random passwords are based upon our interests, hobbies, pets, family and so on. In fact, passwords tend to be based on all the things we like to chat about on social networks and even include in our profiles. Password crackers are very likely to look at this information and make a few - often correct - educated guesses when attempting to crack a consumer-level password without resorting to dictionary or brute force attacks.

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