Category: Password Cracking

Hello aspiring Ethical hackers. In this article, you will learn what is password cracking and various types of password cracking. In Ethical hacking, password cracking is recovering passwords from data that has been stored in or transmitted by a computer system. Hackers use password cracking to grab credentials which can be helpful in further exploiting of the system. There are various password cracking techniques. They are,

1. Shoulder Surfing
2. Password Guessing
3. Dictionary Attack
4. Brute Force Attack
5. Rainbow Table Attack  
6. Phishing
7. Sniffing
8. Malware

Let’s learn in detail of each attack.

1. Shoulder Surfing

Shoulder Surfing is one of the easiest password cracking techniques that doesn’t require use of any technology. In shoulder surfing, the hacker stands behind (or sits behind, position is not really important) the victim when he is entering his credentials and captures the credentials by simple observation. As you can see, this is the easiest way to capture credentials of the target.

2. Password Guessing

Another password cracking technique that doesn’t require any technology. In this technique, hacker tries to guess the password of the victim using his own mind. You may be surprised but this technique yielded me results at least 20% of the total attempts made.

3. Dictionary Attack

In a dictionary attack, a hacker uses a dictionary to crack passwords. A dictionary or wordlist has a huge list of words (possible passwords), each one of which is tried as a password. In Kali Linux, the dictionary or wordlists are present in /usr/share/dirb/wordlists directory.

4. Brute Force Attack

In a brute force attack, hackers use every possible criteria or password to crack the credentials. A brute force attack may be slow but it will eventually crack the password. A brute force attack works by calculating the hash function of every password string it has and compares it with one on the target system or victim.

5. Rainbow Table Attack

To understand Rainbow Table Attack, you need to first understand what is a Rainbow Table. A Rainbow Table is a database that contains huge list of plaintext passwords and their precompiled hashes. Unlike a Brute Force attack, Rainbow table attack bypasses calculation of a hash for every password string as it already has a pre compiled list of hashes.

6. Phishing

Phishing is one of the easiest methods to crack passwords. You have already learnt about phishing in our previous blogposts.

7. Sniffing

Sniffing or Man In The Middle (MITM) attack can also be used to crack passwords while they are on transit in a network.  Learn more about sniffing here.

8. Malware

Malware is another way hackers capture credentials of their victims. Once hackers gain initial access to a system, they install malware which allows hackers to not only perform further malicious actions but also capture user credentials from the target system.

Password cracking plays a very important role in hacking. We are not always lucky to get credentials during enumeration. There are two types of password cracking.

Online password cracking
Offline password cracking

In this tutorial we will learn about online password cracking. There are many techniques used in online password cracking. Some of them are,

Dictionary Attack: Dictionary password attack is a password cracking attack where each word in a dictionary (or a file having a lot of words) is tried as password until access is gained. This method will be successful when simple passwords are set. By simple, I mean common passwords which can be found in a dictionary like “password”, “iloveyou” etc. This type of attack consumes less time but is not bound to be successful always especially if the password is not present in the dictionary.

Brute force Attack: Brute Force attack is a password cracking attack similar to dictionary attack. The only difference is in this attack, each and every possible combination is tried until the password is successfully cracked. For example, if there are two words say “abc” and “123” in a wordlist, other combinations like “abc1”, “abc2” and “abc3” a re also tried. Brute force attack will definitely succeed even if it means it will take years to do that.

Hybrid Attack: As the name suggests, it uses a combination of both dictionary and brute force password attacks to crack the password.

Rainbow Table Attack: Rainbow Table password cracking technique uses pre -computed hashes to crack the encrypted hashes.

Kali Linux has various tools in its arsenal for both online and offline password cracking. Some of the online password cracking tools are Acccheck, John The Ripper, Hydra and Medusa etc.

We have already seen the working of the tool Accheck during SMB enumeration. In this tutorial, we will see how to crack passwords with a tool called Hydra. THC-Hydra is a password cracker which uses brute forcing to crack the passwords of remote authentication services. It can perform rapid dictionary attacks against more than 50 protocols, including telnet, FTP, HTTP, HTTPS, SMB, several databases and much more.

On our target Metasploitable2, we have many services which allow remote authentication like telnet, ftp and SSH. We also have rlogin available. We will use Hydra on one of these services. Hydra can be accessed from the applications menu of Kali Linux. It is available both in GUI and command line utility. For this tutorial, I’m using the graphical one.

Once opened, Hydra will look like shown below.

Change the target IP to that of Metasploitable’ s IP. There are many protocols to choose from Here I am choosing ftp. Change the port to 21 as ftp is running on port 21. I selected options “Be Verbose” and “show attempts” to see the cracking process.

Click on “passwords” tab. We can give a single username and password or a file containing a number of usernames and passwords. Here I am giving the same dictionary or wordlist for both username and password. This dictionary is big.txt. I selected the options “Try Login as password” , “Try empty password” and “Try reverse login”. These options are self explanatory.

The tuning tab is used to configure proxy and number of simultaneous tries. I left it as default.

I left even “specific” tab to default. When all the settings are set, go to “Start” tab. To start the attack, click on “Start” button.

The attack is displayed as shown below.

The time of the attack depends on the number of words present in the dictionary or the wordlist we specified. The password is cracked if the phrase is present in the dictionary. If the password is not there in the wordlist, we need to use another dictionary. The big.txt dictionary I used failed to crack the password. So I used another wordlist we made during enumeration “pass.txt”. After some time, Hydra found three valid passwords.

Scroll up to see what are those passwords.

Apart from Hydra, Kali Linux also has command line tools to use for password cracking. One such tool is Medusa. Open a terminal and type medusa to see the options of that tool. Below is the command in medusa to crack ftp using a wordlist.

Once medusa cracks a password, it will be shown as below. Once again we got three credentials we found also with Hydra.

We have used the same dictionary in both methods, but where do we find this dictionary or wordlist. Most wordlists of Kali Linux are present in /usr/share directory. Given below are different dictionaries in the “wordlists” folder.

These wordlists are named accordingly. For example, “common.txt” contains most common passwords used by users. But what if none of the dictionaries are helpless in cracking the password. Kali Linux also has tools to create our own dictionary or wordlist. Crunch is one such tool. The syntax is given below.

Here’s an example of how to create a wordlist with crunch.

We can also save the wordlist to a  file as shown below.