In-depth

The top ten password-cracking techniques used by hackers

Think your passwords are secure? Think again

list of poor passwords on notepad

Understanding the password-cracking techniques hackers use to blow your online accounts wide open is a great way to ensure it never happens to you.

You will certainly always need to change your password, and sometimes more urgently than you think, but mitigating against theft is a great way to stay on top of your account security. You can always head to www.haveibeenpwned.com to check if you're at risk, but simply thinking your password is secure enough to not be hacked is a risky position to take.

So, to help you understand just how hackers get your passwords, secure or otherwise, we've put together a list of the top ten password-cracking techniques used by hackers. Some of the below methods are certainly old-fashioned, but that doesn't mean they aren't still being used.

The top ten password-cracking techniques used by hackers:

1. Dictionary attack

The dictionary attack uses a simple file containing words that can be found in a dictionary, hence its rather straightforward name. In other words, this attack uses exactly the kind of words that many people use as their password.

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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

Similar to the dictionary attack, the brute force attack comes with an added bonus for the hacker. Instead of simply using words, a brute force attack lets them 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 like online bitcoin miners.

3. Rainbow table attack

Rainbow tables aren't as colourful as their name may imply but, for a hacker, your password could well be at the end of it. In the most straightforward way possible, you can boil a rainbow table down into a list of pre-computed hashes the numerical value used when encrypting a password. This table contains hashes of all possible password combinations for any given hashing algorithm. Rainbow tables are attractive as it reduces the time needed to crack a password hash to simply just looking something up in a list.

However, rainbow tables are huge, unwieldy things. They require serious computing power to run and a table becomes useless if the hash it's trying to find has been "salted" by the addition of random characters to its password ahead of hashing the 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 log in page associated with whatever service it is the hacker wants to access, requesting the user to put right some terrible problem with their security. That page then skims their password and the hacker can go use it for their own purpose.

Why bother going to the trouble of cracking the password when the user will happily give it to 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 favourite of the social engineer is to call an office posing as an IT security tech guy and simply ask for the network access password. You'd be amazed at how often this works. Some even have the gall 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 keylogger, or screen scraper, can be installed by malware which records everything you type or takes screenshots during a login process, and then forwards a copy of this file to hacker central.

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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 a 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, giving them the opportunity to snoop literally over the shoulders of genuine members of staff to glimpse passwords being entered, or spot passwords that less security-conscious workers have written down on post-it notes or in notepads. 

9. Spidering

Savvy hackers have realised 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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