This method is useful for cracking passwords which do not appear in dictionary wordlists, but it takes a long time to run. 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 the Ripper can use is the dictionary attack. Larger the database, more the words covered. Rainbow tables basically store common words and their hashes in a large database. Just go to one of the sites, submit the hash and if the hash is made of a common word, then the site would show the word almost instantly. Now a days hashes are more easily crackable using free rainbow tables available online. So the greater challenge for a hacker is to first get the hash that is to be cracked. Hydra does blind brute-forcing by trying username/password combinations on a service daemon like ftp server or telnet server. John the Ripper is different from tools like Hydra. Cracking password in Kali Linux using John the Ripper is very straight forward. 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 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. 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). John the Ripper is a free password cracking software tool.
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