John the Ripper's behavior can be customized by editing its configuration file. The configuration file can be named either john.conf (on Unix-like systems) or john.ini (on systems which have a notion of filename "extensions" and limit them to 3 characters).
This file is searched for in private John's "home directory" and, if not found in the private directory and John is installed system-wide, also in John's system-wide shared data files directory.
You can set global options, define wordlist and "single crack" mode rules, define parameters for "incremental" modes, or even define a new external cracking mode.
The configuration file consists of several sections. Each section starts with a line containing its name, in brackets ("[...]"). Sections consist either of "variable = value" assignments (each on its own line) or of some other content specific to the particular section's type (names of such sections start with "List."). Section and variable names are not case sensitive. Comment lines start with a hash character ("#") or a semicolon (";") and are ignored. Also ignored are any empty lines.
Some global options can be defined in the [Options] section. Currently, you can set the following options:
Wordlist = FILENAME
Set this to your wordlist file name, to be used in batch mode (which is activated when you start John with password files, but not specifying a cracking mode). The default is "$JOHN/password.lst", that is, the file named "password.lst" in John's "home directory".
Idle = Y|N
If set to "Y" (yes), John will try to use idle processor cycles only, thereby greatly reducing its impact on other system processes. The impact on performance of John itself is negligible except on otherwise overloaded systems. This setting does not affect John's startup time and non-cracking invocations of John; it only affects the actual cracking. The default is "Y" (yes).
Starting with version 1.7.7, this setting is ignored for OpenMP-enabled hash types when the actual number of threads is greater than 1. Unfortunately, it did not work right at least with GNU libgomp on Linux.
Save = SECONDS
This is the time interval (in seconds) between crash recovery file updates. The default is 600 seconds (10 minutes).
Beep = Y|N
If set to "Y" (yes), John will beep when a password is found. On Unix-like systems, it does this by sending the bell character (ASCII code 7) to the "standard error" file descriptor (which is normally directed to the terminal). The default is "N" (no).
The word mangling rules for wordlist and "single crack" modes are defined in separate sections, [List.Rules:Wordlist] and [List.Rules:Single], respectively. John the Ripper uses an extension of Crack's syntax for the rules. John supports all of the commands of Crack 5.0a plus a few more and, most importantly, it adds a preprocessor, which can generate multiple rules from a single source line.
When defining rules, simply place one rule (which may include preprocessor commands) per line. See RULES for information on the rules syntax and on the preprocessor.
To define the incremental mode parameters you need to create a section called [Incremental:MODE], where MODE is any name that you assign to the mode. There are some pre-defined incremental modes in the default configuration file supplied with John, you can use them as templates.
The following parameters are supported:
File = FILENAME
Set this to your charset file name. See EXAMPLES for an example on how to generate a custom charset file. There's no default.
MinLen = LENGTH
Minimum password length (the number of characters) to try. The default is 0.
MaxLen = LENGTH
Maximum password length to try. The default is 8 (or CHARSET_LENGTH as defined in src/params.h at compile time).
CharCount = COUNT
This allows you to limit the number of different characters (or rather, character indices) used. The effect is that John would favor simple longer candidate passwords over more complicated shorter ones, and would never attempt rare characters and character combinations, not even for really short passwords. Most of the time, this is undesired. Another use for this option is to make John print a warning if the charset only defines less than CharCount characters; this is how the pre-defined "incremental" modes use it. The default is to use as many different characters as are defined.
Extra = CHARACTERS
This can be used to make John try some extra characters that don't appear in the charset file. Just list all those characters here and they will be added, but considered the least probable.
$Owl: Owl/packages/john/john/doc/CONFIG,v 1.5 2011/02/27 07:16:16 solar Exp $