NAME¶
john - a tool to find weak passwords of your users
SYNOPSIS¶
john [
options] password-files
DESCRIPTION¶
This manual page documents briefly the
john command. This manual page was
written for the Debian GNU/Linux distribution because the original program
does not have a manual page.
john, better known as John the Ripper, is
a tool to find weak passwords of users in a server. John can use a dictionary
or some search pattern as well as a password file to check for passwords. John
supports different cracking modes and understands many ciphertext formats,
like several DES variants, MD5 and blowfish. It can also be used to extract
AFS and Windows NT passwords.
USAGE¶
To use John, you just need to supply it a password file and the desired options.
If no mode is specified, john will try "single" first, then
"wordlist" and finally "incremental".
Once John finds a password, it will be printed to the terminal and saved into a
file called ~/.john/john.pot. John will read this file when it restarts so it
doesn't try to crack already done passwords.
To see the cracked passwords, use
john -show passwd
Important: do this under the same directory where the password was cracked (when
using the cronjob, /var/lib/john), otherwise it won't work.
While cracking, you can press any key for status, or Ctrl+C to abort the
session, saving point information to a file (
~/.john/john.rec by
default). By the way, if you press Ctrl+C twice John will abort immediately
without saving. The point information is also saved every 10 minutes
(configurable in the configuration file,
~/.john/john.ini or
~/.john/john.conf ) in case of a crash.
To continue an interrupted session, run:
john -restore
Now, you may notice that many accounts have a disabled shell, you can make John
ignore these (assume that shell is called
/etc/expired ):
john -show -shells:-/etc/expired passwd
You might want to mail all the users who got weak passwords, to tell them to
change the passwords. It's not always a good idea though (unfortunately, lots
of people seem to ignore such mail, it can be used as a hint for crackers,
etc), but anyway, I'll assume you know what you're doing. Get a copy of the
'mailer' script supplied with John, so you won't change anything that's under
/usr/sbin ; edit the message it sends, and possibly the mail command
inside it (especially if the password file is from a different box than you
got John running on). Then run:
./mailer passwd
Anyway, you probably should have a look at
/usr/share/doc/john/OPTIONS
for a list of all the command line options, and at
/usr/share/doc/john/EXAMPLES for more John usage examples with other
cracking modes.
OPTIONS¶
All the options recognized by john start with a single dash (`-'). A summary of
options is included below.
- -external:MODE
- Enables an external mode, using external functions defined in ~/john.ini's
[List.External:MODE] section.
- -format:NAME
- Allows you to override the ciphertext format detection. Currently, valid
format names are DES, BSDI, MD5, BF, AFS, LM. You can use this option when
cracking or with '-test'. Note that John can't crack password files with
different ciphertext formats at the same time.
- -groups:[-]GID[,..]
- Tells John to load users of the specified group(s) only.
- -incremental[:MODE]
- Enables the incremental mode, using the specified ~/john.ini definition
(section [Incremental:MODE], or [Incremental:All] by default).
- -makechars:FILE
- Generates a charset file, based on character frequencies from
~/.john/john.pot, for use with the incremental mode. The entire
~/.john/john.pot will be used for the charset file unless you specify some
password files. You can also use an external filter() routine with this
option.
- -restore[:FILE]
- Continues an interrupted cracking session, reading point information from
the specified file (~/.john/john.rec by default).
- -rules
- Enables wordlist rules, that are read from [List.Rules:Wordlist] in
/etc/john/john.conf (or the alternative configuration file you
might specify on the command line).
This option requires the -wordlist option to be passed as
well.
- -salts:[-]COUNT
- This feature sometimes allows you to achieve better performance. For
example you can crack only some salts using '-salts:2' faster, and then
crack the rest using '-salts:-2'. Total cracking time will be about the
same, but you will get some passwords cracked earlier.
- -savemem:LEVEL
- You might need this option if you don't have enough memory, or don't want
John to affect other processes too much. Level 1 tells John not to waste
memory on login names, so you won't see them while cracking. Higher levels
have a performance impact: you should probably avoid using them unless
John doesn't work or gets into swap otherwise.
- -session:FILE
- Allows you to specify another point information file's name to use for
this cracking session. This is useful for running multiple instances of
John in parallel, or just to be able to recover an older session later,
not always continue the latest one.
- -shells:[-]SHELL[,..]
- This option is useful to load accounts with a valid shell only, or not to
load accounts with a bad shell. You can omit the path before a shell name,
so '-shells:csh' will match both '/bin/csh' and '/usr/bin/csh', while
´-shells:/bin/csh' will only match '/bin/csh'.
- -show
- Shows the cracked passwords in a convenient form. You should also specify
the password files. You can use this option while another John is
cracking, to see what it did so far.
- -single
- Enables the "single crack" mode, using rules from
[List.Rules:Single].
- -status[:FILE]
- Prints status of an interrupted or running session. To get an up to date
status information of a detached running session, send that copy of John a
SIGHUP before using this option.
- -stdin
- These are used to enable the wordlist mode (reading from stdin).
- -stdout[:LENGTH]
- When used with a cracking mode, except for "single crack", makes
John print the words it generates to stdout instead of cracking. While
applying wordlist rules, the significant password length is assumed to be
LENGTH, or unlimited by default.
- -test
- Benchmarks all the enabled ciphertext format crackers, and tests them for
correct operation at the same time.
This option does not need any file passed as argument. Its only
function is to benchmark the system john is running on.
- -users:[-]LOGIN|UID[,..]
- Allows you to filter a few accounts for cracking, etc. A dash before the
list can be used to invert the check (that is, load all the users that
aren't listed).
- -wordlist:FILE
- These are used to enable the wordlist mode, reading words from FILE.
MODES¶
John can work in the following modes:
- Wordlist
- John will simply use a file with a list of words that will be checked
against the passwords. See RULES for the format of wordlist files.
- Single crack
- In this mode, john will try to crack the password using the login/GECOS
information as passwords.
- Incremental
- This is the most powerful mode. John will try any character combination to
resolve the password. Details about these modes can be found in the MODES
file in john's documentation, including how to define your own cracking
methods.
FILES¶
- /etc/john/john.conf
- is where you configure how john will behave.
- /etc/john/john-mail.msg
- has the message sent to users when their passwords are successfully
cracked.
- /etc/john/john-mail.conf
- is used to configure how john will send messages to users that had their
passwords cracked.
SEE ALSO¶
mailer(8),
unafs(8),
unique(8),
unshadow(8),
The programs and the configuration files are documented fully by John's
documentation, which should be available in
/usr/share/doc/john or
other location, depending on your system.
AUTHOR¶
This manual page was written by Jordi Mallach <jordi@debian.org> and
Jeronimo Pellegrini <pellegrini@mpcnet.com.br>, for the Debian GNU/Linux
system (but may be used by others).
John the Ripper was written by Solar Designer <solar@openwall.com>. The
complete list of contributors can be found in the CREDITS file in the
documentation directory.