How to use John the Ripper in Kali Linux

John the Ripper, which in general we all know as John is a very popular and free password-cracking tool that is included by default in the Kali Linux Operating System. John tool was first introduced in 1996 and nowadays it has become an important tool for security researchers and professionals for analyzing passwords and also for cracking passwords. John the Ripper is an optimized tool to recover lost passwords and assess the strength of password protection systems through its dictionary and brute-force attacks for hashed passwords. It can work across many different types of hashing, such as MD5 and SHA1, SHA2, NTLM, and many other hash-type passwords. John the Ripper can also automatically detect the lengths and sets of characters in passwords. There are many features that make it so powerful for example we can say it have the ability to perform quick, parallelized cracking on different cores of the CPU. Using John the Ripper password cracking tool help we can recover a forgotten password and also we can check the strength of our own passwords, and conduct full-scale security audits in our password-protected systems and services.

John the Ripper provides us various cracking modes, which we can apply as per our different needs and situations. Following are the three main modes which are mostly being used nowadays.

1. Dictionary Attack Mode: In this type of mode, John the Ripper uses a predefined list of possible passwords, which we call a dictionary or wordlist, for cracking passwords. It simply tries, word by word against the hashed password. This is a very effective way, as the password may be a usual word, or it may be a slight variation of one so we can find it in very less time. Dictionary attacks are usually the first attacks to crack a password, as they are fast and sometimes able to give quick results for weak passwords.

2. Brute Force Attack Mode: If a dictionary attack fails, John the Ripper can switch to brute force mode to find the password. In this mode, the tool tries all possible combinations of characters until finding the correct password. Brute force attacks can be time-consuming, attack especially in the situation where we are trying to find longer and more complex passwords. Brute force attack mode can be profitable when we have a high computing system and then it can break passwords in very little time.

3. Incremental Mode: The incremental mode in John the Ripper is used to generate and test passwords based on our specified rules and character sets. It starts with simple passwords and it increases their complexity step by step. it is more efficient than pure brute force attacks in certain cases where we have our original password near to our testing password.

To understand in a better way how to use John the Ripper in Kali Linux let’s see the below demo which shows how we can crack passwords using John the Ripper in Kali Linux.

Step 1: In Kali Linux John the ripper tool is pre-installed but if you are facing any issues then you install again it using the following command.

$ sudo apt install john

Step 2: Now using following command we can check the john the ripper version and other related information.

$ john

Step 3: For our testing and demo purpose we have hash file which consists hash password in diffirent diffirent format and also we have custom wordlist for dictionary attack using john the ripper. For listing everything and seeing we can use following command.

$ ls

Step 4: Now for findig password using dictionary attack we can use following command where rockyou.txt file is wordlist which exists by default in kali linux and alpha.txt is our hash stored file which contains our real password in MD5 hash format. Using following command we can see we cracked the password which is abcd.

$ john --wordlist=/usr/share/wordlists/rockyou.txt  alpha.txt  --format=raw-md5

Step 5: In another file num.txt we have MD5 hash format . We can also use incremental mode for cracking this password file where our john the ripper tool increment its value one by one and tries to match password one by one and when it matches it give us result that password has been found out.

$ john --format=raw-md5 num.txt --incremental

Step 6: Now in this step we will use our custom dictionary file instead of pre saved file in kali linux. This method can be very useful when we have list of passwords in which one is correct.

Following is our hash1.txt file data in md5 format which we will crack using john the ripper.

Following is command for cracking password hash using custom dictionary file.

$ john --wordlist=customwc.txt hash1.txt --format=raw-md5

Step 7: In john the ripper we can use multiple type of hash format for cracking the passwords. Following is example for cracking the password of SHA1 type hash using john the ripper in kali linux.

$ john --wordlist=customwc.txt hashsha.txt --format=raw-sha1

John the Ripper is a popular and free password-cracking tool that comes by default with the Kali Linux Operating System. This tool is designed to recover lost passwords and check password-protected systems’ security using dictionary attacks and brute-force attacks. John the ripper consists many variety of hashing passwords cracking algorithms such as MD5, SHA1, SHA2, NTLM, and many more. This makes John the Ripper capable of automatically detecting the length of a password and the character set. It can be also used for cracking passwords on multiple CPU cores simultaneously which makes it much effective in order to crack passwords. Use of John the Ripper also helps us when we forget our password and we have only its hash type. This tool in kali linux can be also used to test the strength of password, and to conduct deeper security auditing on password protected systems. Further its totally depends on us how we are using this tool. As legal consideration we must not use this tool on the any kind of system without the proper permissions to the respective authority.

Is John the Ripper pre-installed on Kali Linux, and if not, how do I install it

Yes, John the Ripper is pre-installed on Kali Linux as it’s a popular penetration testing tool. You don’t need to download it separately. However, if you’re unsure or using a custom Kali installation, you can verify its presence using the john –version command in your terminal. If not installed, use the sudo apt update and sudo apt install john commands to get it.

I have a password hash file. How do I crack it using John the Ripper?

John the Ripper requires the hash format to be specified for efficient cracking. First, identify the hash type using tools like hashcat or online resources. Then, use the following structure in your terminal:

john --format=<hash_format> <hash_file> [wordlist]

Is John the Ripper safe to use? What are the ethical considerations?

John the Ripper is a powerful tool, but it can be misused. It’s intended for ethical penetration testing on authorized systems to identify weak passwords and improve security. Never use it to crack passwords on systems you don’t have permission to access. Ensure you have proper authorization before using John the Ripper for any penetration testing activity.