John the Ripper/Password Generation

The Basics of Password Generation with John

This page will walk through some basic password cracking with John the Ripper. We'll go from wanting to test certain passwords to being able to generate a stream of them with John the Ripper. This is important to be able to do, so that we don't need to devote gigabytes of disk space to word files. Intelligent use of patterns can save us a whole lot of headaches.

John and Stdout

Note that if you're using Kali 2.0, you'll need to install John jumbo 1.8 from source, instead of using the Kali 2.0 repository version of John, if you want to send John's password guesses to stdout (or pipe them to aircrack).

Rules and Modes

Rules and modes are ways of telling John how to guess passwords. John can be simplistic, only testing passwords that are in the wordfile, or sophisticated, doing letter/number substitutions, etc.

This page is going to cover some basic rules and modes for guessing passwords in John. We'll figure out how to start with low-hanging fruit, in terms of password guesses, and implementing those in John the Ripper.

Rules

Rules are specified in the John configuration file /etc/john/john.conf and are ways of using a wordlist to generate password variations.

Here's an example of a rule:

[List.Rules:KoreLogicRulesAppendYears]
cAz"19[0-9][0-9]"
Az"19[0-9][0-9]"
cAz"20[01][0-9]"
Az"20[01][0-9]"

The rule is named KoreLogicRulesAppendYears.