John The Ripper - Password Cracking Tool

John the Ripper is a free password cracker, free designed for Unix systems but now Windows and macOS versions are released. It works via dictionary attacks and can also brute force encrypted password incremental methods or word mangling for those who prefer a graphical user interface JTR has one called johnny.

John the Ripper tool provides three different options - Single Crack, Wordlist Crack, or Incremental Crack.

A single crack is done by using information available to it like login fields, users' directories names, or GECOS fields by applying word mangling and that's the fastest way. 

john [single] [passwd file]

A dictionary attack is done by testing passwords provided in a given file until the correct one by testing every single phrase in the application.

john [passwd file] [wordlist]

Word mangling is similar to a dictionary attack but has a feature that modifies the word in many ways like john, john?, john2, johnjohn, 7john.

john rules [passwd file] [wordlist wordlist]

A brute force attack is done by checking every possible combination out there until one finds the correct one, but if there are too many combinations, it may take a long time to guess or it may lag or crash, or to be more precise it works with an incremental method which doesn't use a wordlist but try every possible combination

john -I --format [passwd file]

HOW AND WHEN IT CAN BE USED

• It can be used to crack zip/rar-protected files with the password. First, we need to convert the file into a hash which is accepted by the tool using 2john scripts. Example,

zip2john [filename.zip] > [filename.txt]

• Cracking Hashes Password - It can be used to crack a hashed password by identifying the type of hash through the format option. Then use the command, 

john -format=[format] [filename] -wordlist=[wordlist]

JohnTheRipper supports more than 400 formats, you can check that using the command john --list-formats.

• Cracking the Linux Password - It simply can crack a user account password with this command: john /etc/shadow but it also depends on the strength of the password.

We hope this helps. If any suggestions or doubts you can add a comment and we will reply as soon as possible.