John the Ripper is a free password cracking software tool. Initially developed for the Unix operating system, it now runs on fifteen different platforms (eleven of which are architecture-specific versions of Unix, DOS, Win32, BeOS, and OpenVMS). It is one of the most popular password testing and breaking programs as it combines a number of password crackers into one package, autodetects password hash types, and includes a customizable cracker. It can be run against various encrypted password formats including several crypt password hash types most commonly found on various Unix versions (based on DES, MD5, or Blowfish), Kerberos AFS, and Windows NT/2000/XP/2003 LM hash. Additional modules have extended its ability to include MD4-based password hashes and passwords stored in LDAP, MySQL, and others. Cracking password in Kali Linux using John the Ripper is very straight forward. In this post, I will demonstrate that.
In Linux, password hash is stored in /etc/shadow file. For the sake of this exercise, I will create a new user names john and assign a simple password ‘password’ to him.
I will also add john to sudo group, assign /bin/bash as his shell. There’s a nice article I posted last year which explains user creating in Linux in great details. It’s a good read if you are interested to know and understand the flags and this same structure can be used to almost any Linux/Unix/Solaris operating system. Also, when you create a user, you need their home directories created, so yes, go through creating user in Linux post if you have any doubts. Now, that’s enough mambo jumbo, let’s get to business.
Disclaimer – Our tutorials are designed to aid aspiring pen testers/security enthusiasts in learning new skills, we only recommend that you test this tutorial on a system that belongs to YOU. We do not accept responsibility for anyone who thinks it’s a good idea to try to use this to attempt to hack systems that do not belong to you
First let’s create a user named john and assign password as his password.
[email protected]:~# useradd -m john -G sudo -s /bin/bash
[email protected]:~# passwd john
The unshadow command will combine the extries of /etc/passwd and /etc/shadow to create 1 file with username and password details. When you just type in unshadow, it shows you the usage anyway.
I’ve redirected the output to /root/johns_passwd file because I got the ticks for organizing things. Do what you feel like here.
Cracking process with John the Ripper
At this point we just need a dictionary file and get on with cracking. John comes with it’s own small password file and it can be located in /usr/share/john/password.lst. I’ve showed the size of that file using the following command.
You can use your own password lists too or download a large one from Internet (there’s lots of dictionary file in terabyte size).
Looks like it worked. So we can now use john –show option to list cracked passwords. Note that it’s a simple password that existed in the dictionary so it worked. If it wasn’t a simple password, then you would need a much bigger dictionary and lot longer to to crack it.