John uses character frequency tables to try plaintexts containing more frequently used characters first. In this type of attack, the program goes through all the possible plaintexts, hashing each one and then comparing it to the input hash. Many of these alterations are also used in John's single attack mode, which modifies an associated plaintext (such as a username with an encrypted password) and checks the variations against the hashes.

It can also perform a variety of alterations to the dictionary words and try these. It takes text string samples (usually from a file, called a wordlist, containing words found in a dictionary or real passwords cracked before), encrypting it in the same format as the password being examined (including both the encryption algorithm and key), and comparing the output to the encrypted string. One of the modes John can use is the dictionary attack. We also see that the attempt required one guess at a time of 0 with a 100% guess rate. Loaded 1 password hash - the one we saw with the ' cat' command - and the type of hash John thinks it is (Traditional DES). ' password.lst' is the name of a text file full of words the program will use against the hash, pass.txt makes another appearance as the file we want John to work on. The third line is the command for running John the Ripper utilizing the ' -w' flag. the user ( AZl) and the hash associated with that user ( zWwxIh15Q). The next line is the contents of the file, i.e. The first line is a command to expand the data stored in the file ' pass.txt'. Loaded 1 password hash (Traditional DES ) example (user) guesses: 1 time: 0:00:00:00 100% c/s: 752 trying: 12345 - pookie

User:AZl.zWwxIh15Q $ john -w:password.lst pass.txt Here is a sample output in a Debian environment. Additional modules have extended its ability to include MD4-based password hashes and passwords stored in LDAP, MySQL, and others.

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. It is among the most frequently used 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. Originally developed for the Unix operating system, it can run on fifteen different platforms (eleven of which are architecture-specific versions of Unix, DOS, Win32, BeOS, and OpenVMS). John the Ripper is a free password cracking software tool.

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