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 vs 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.

First: No Rules

First, let's look at how we run John and generate passwords from a wordfile, with no rules at all specified. This is a kind of "Hello World" for John the Ripper. We'll specify a 92-word list.

$ ./john -wordlist:/root/codes/john/rockyou10.lst -stdout | head -n10
words: 92  time: 0:00:00:00 DONE (Tue Aug 18 23:36:33 2015)  w/s: 1314  current: junior
123456
12345
123456789
password
iloveyou
princess
1234567
12345678
abc123
nicole

So far so good. Now let's look at how the rules will modify each entry in the wordfile.

Rules

The John_the_Ripper/Rules page has a guide for installing the KoreLogic password generation rules from the Defcon 2010 Crack Me If You Can.

What is a rule?

A rule is a way for John to create variations (rule-based generation of variations) on a wordlist, turning a short wordlist into a much more powerful cracking tool.

Here's an example of a rule that appends years to passwords:

[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.

To use the rule, call john with the --rules=KoreLogicRulesAppendYears argument:

$ john --wordlist=rockyou-10.txt --format=wpapsk --rules=KoreLogicRulesAppendYears crackme