John the Ripper Password Cracker

John the Ripper is free and Open Source software, distributed in source code form. John the Ripper is a fast password cracker, currently available for many flavors of Unix, Windows, DOS, BeOS, and OpenVMS. Its primary purpose is to detect weak Unix passwords

John the Ripper Pro  is distributed   in the form of “native” packages for the target operating systems and   easy to install along with delivering optimal performance.
John is available for several different platforms which enables you to use the same cracker everywhere (you can even continue a cracking session which you started on another platform).

John supports and autodetects the following Unix crypt(3) hash types:
•    traditional and double-length DES-based,
•    BSDI extended DES-based,
•    FreeBSD MD5-based
•    and OpenBSD Blowfish-based
•    Kerberos/AFS
•    Windows LM (DES-based) hashes.

It is one of the most popular password testing/breaking programs as it combines a number of password crackers into one package, auto detects password hash types, and includes a customizable cracker.

Attack types:

•    Dictionary attack mode:

It takes text string samples (usually from a file, called a wordlist, containing words found in a dictionary), 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.

•    Brute force mode:

In this type of attack the program goes through all the possible plaintexts, hashing each one and comparing it to the input hash. It uses character frequency tables to try plaintexts containing more frequently-used characters first. This method is useful for cracking passwords that does not appear in dictionary wordlists, but it does take a long time to run.

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