John The Ripper-Password Cracking Tool

John-The-Ripper (JTR) is an open source password cracking tool which is used by Penetration testers to crack passwords . John the Ripper can be used to crack Network Passwords, NTLM hashes, /etc/shadow files, Password Protected Zip Files , Password Protected RAR Archives, SSH Keys. We will get into the details later-on in the blog.

How Passwords are Stored:

Before we dive into cracking passwords we should first understand how passwords are stored.Any program which uses password protection stores passwords as Hashes. For example: “Admin’ is stored as Md5 hash as “21232f297a57a5a743894a0e4a801fc3” . John the Ripper(JTR) automatically detects what type of password hash is employed. John the ripper uses a dictionary of passwords in hashed and raw format. John the Ripper matches different hashed passwords against a program to crack it. If it finds a match it will then show the password in raw format as cracked password.

Installing John the Ripper:

It comes preinstalled in the Kali Linux. However we will see how to install it on other linux systems like Ubuntu:

Open the terminal and write:

sudo apt-get install john -y

and recommended method:

snap install john-the-ripper

Use both ways to install JTR for ease of use.

This command will run john the ripper.

ubuntu@mypc:~$ john

It shows the that version 1.8.0 is installed on your machine. Now that it is installed; it is time to get into cracking the passwords.

Cracking the Passwords with JTR:

We will need different commands to exploit different types of targets.

1. Cracking Zip files:

demo.zip is a file which requires password to open.

now use:

$john-the-ripper.zip2john demo.zip > demo.txt
$john demo.txt

you can see the cracked password is Admin. you can used john demo.txt —show to see the password.

2. Cracking RAR Archive Files:

We are going to use “rar2john” tool to convert the rar file into a hash format.

john-the-ripper.rar2john demorar.rar > rarhash.txt

john rarhash.txt

as you can see ‘admin’ is the password.

3. Cracking NTLM Hashes:

Here we have saved ntlm hash ‘329153F560EB329C0E1DEEA55E88A1E9’ for ‘root’ in a file ntlmhash.txt

john --format=nt ntlmhash.txt

we can see for the ‘root’ is cracked.

4. Cracking SSH keys:

Now we will see how to crack ssh keys with the john the ripper.

python3 ssh2john.py demossh.id_rsa > rsa.hash
john --wordlist=path/to/wordlist/ rsa.txt
john rsa.txt --show

you may need to install ssh2john "wget https://raw.githubusercontent.com/magnumripper/JohnTheRipper/bleeding-jumbo/run/ssh2john.py"

Cracked ssh key password is “admin”

5. Cracking /etc/shadow file:

to crack /etc/shadow passwords we need to combine it with /etc/passwd/ file so JTR can understand the data that is being given to it.

$unshadow /etc/passwd /etc/shadow > unshadow.db
john --wordlist=/Downloads/rockyou.txt unshadowed.txt

it will start password cracking.

You may need a strong password file to crack these passwords. One such password file is: https://github.com/praetorian-inc/Hob0Rules/blob/master/wordlists/rockyou.txt.gz download this to you system and use it.

Conclusion:

This demonstration is easy to use and beginner friendly. JTR is one of the most usable password cracking tool with different modes.

Thankyou.