1) First thing's first
I guess you're a newbie in pass-cracking like I was and you've probably
started John the Ripper full of enthusiasm, and got.... nothing. So the first
thought you have is 'my god this must be hard, and I'm a newbie'. Forget it!!!
You're always a newbie, and we all are... in pass cracking world, pardon, pass
recovering world (or any world else) you always have something to learn.
Sometimes, even if you are experienced in password cracking, you won't be able
to crack the password or even get your own password. This is a pure technical
manual and will give you only the recipe for cracking, but every password needs
different approach...
OK, so a good way to get somewhere is to start getting somewhere...
What
you're about to learn is to crack *nix(Unix/Linux/etc.) password files. It does
not mean that you need to have some Unix distribution on your box, but it means
you'll have to stop clicking your ass off all around the screen... 'What this
fool is trying to say', you'll probably ask... This fool is trying to say that
john is a DOS program (there is also Linux/Unix version, but I guess that most
of the people that read this tutorial have win boxes). I will try to put this
tutorial through the examples so it wouldn't look like a boring script with
incredible amount of switches. After reading this text it wouldn't be a bad idea
to look at the texts you get with John. I learnt it all from there, but that, of
course, was the hard way, and you want the easy way, right? Right.
First, it wouldn't be a bad idea to get yourself John the Ripper, I guess...
if you don't have it you can find it at:
1) packetstorm.securify.com (look at archives, password cracking)
2)
neworder.box.sk (do some searching by yourself)
John can be found practically anywhere. For example: try going to
altavista.com and running a search for 'john the ripper'.
Second thing you'll need is.... a HUUUUGE amount of password dictionaries
(I'll explain what these are in a minute). The best dictionary around is at
www.theargon.com and packetstorm (look at the archives) and is called
theargonlistserver1 and is about 20Mb packed, and over 200Mb
unpacked... get
it!!!! The people at theargon did a terrific job.
You should also get some smaller dictionary files (I'll explain why
later).
2) Do we look like *nix?
So now you have john, loaded with that huuuuge pass dictionary, and you
think that you can crack anything... If you plan to live for 100000 years, that
wouldn't be a problem, but you only have some 80 years left in the best case
scenario (unless, of course, scientists find a way to... oh, nevermind).
Now, the first thing is that you have to make sure your password file really
looks like a Unix password file (were talking about the /etc/passwd file).
Let's see how Unix pass files look like
owner:Ejrt3EJUnh5Ms:510:102:Some free text:/home/subdir/owner:/bin/bash
The important part is the username and the encrypted password, which are the
first and the second parts (each line is divided into seven parts by :
symbols)
owner:Ejrt3EJUnh5Ms
Owner is the username and 'that other thing' is the crypted password
(encrypted in altered DES (Data Encryption Standard) encryption). For the other
part you can put anything that looks like that but the structure must be same so
the john could recognize it as unix pass. In fact the other part
:510:102:Some free text:/home/subdir/owner:/bin/bash
Is just some information about the user, his home directory, etc...
Sometimes you'll have passes that have only the first and second part, such
as password files that you got from a webboard running matt's web board
script.
owner:Ejrt3EJUnh5Ms
You'll have to put the other part so that password would look like unix pass,
and you can do a copy-paste from another pass, you can even use
:510:102:His name:/home/subdir/owner:/bin/bash
What you have now should look like:
owner:Ejrt3EJUnh5Ms:510:102:His name:/home/subdir/owner:/bin/bash
Hell, you can even put
owner:Ejrt3EJUnh5Ms:a:a:a:a:a
It won't matter to john at all.
3) We're getting
somewhere... nowhere
Now you're ready to crack. Type in
john -w:words.lst password.file
Where words.lst is password dictionary and password file where you have your
password or passwords. If you use it on example i gave to you you'll probably
get password because it's really weak pass. You'd be surprised to see that
people usually use really weak passes like their names, pet names, or even their
username (for example: username=zalabuk, password=zalabuk).
Hint: Don't be stupid! Use strong passes
like
p4sswr!@
p@s$w11s
with as many characters you can remember.
Hint is to use special characters and numbers those passes are much harder to
crack (I'll explain why in a minute).
The other hint is to use passes as long
as you can remember, 8 characters are sometimes not enough... it depends what
box that someone who cracks has... on dual alpha is certainly not enough... in
other words... more than 10 characters will do fine, even more wouldn't hurt
(like 16...). By the way, older *nix have fixed pass length of 8 chars... that
is old DES crypted pass that uses a 64-bit key... now there are 128-bit keys,
and some perverts use even more, so there is more fun now :)
john
-w:words.lst password.file
Wait wait wait! What am I doing here?
Alright, listen up carefully. The
DES encryption that Unix uses CANNOT be reversed. Some encryptions can be
reversed using a sometimes simple or sometimes incredibly complicated algorithm
(in the 3rd century AD, Ceasar used to send encrypted letters which used a
formula of "shift by three", which means that d stands for a, e stands for b
etc'. At that time, such an algorithm was just fine. Today, it isn't).
So
anyway, the altered DES encryption that Unix uses for it's password files cannot
be reversed. Why? Because it's a key-based encryption. The encryption algorithm
uses a bunch of letters (lowercase and uppercase), numbers and symbols within
the algorithm. So, in other words, to run the decryption algorithm you will need
this key, which you simply cannot just have, because the key is the password!
You see, when a user picks a password, the system generates an encrypted
password for him, called a hash (which is what you get when you somehow acquire
a password file), which is created by running this altered DES algorithm using
the user's password as a key. If you try to decrypt the password using standard
reversable DES encryption, you get a null string.
So how do John and other
password crackers do it? Easy. They try to recreate this process by taking
passwords out of these dictionary files (or wordlists) and using them as keys
for this altered DES algorithm process. Then, they compare the result to all the
encrypted passwords within the password file you've given them. If the two
strings match - there you have it! The password is yours!
If the first step doesn't work, the next step would be to do this:
john -w:words.lst -rules password.file
This switch turn on not only browsing through the dictionary, but it uses
some modifications of the words that are word dictionary (like adding a number
at the end of pass - fool -> fool1, etc' etc'). This one will take long with
huge pass dictionary, but it may give better results... For a start you could do
a try with a small pass dictionary, and if it doesn't works you can try it with
a huge pass dictionary.
Sometimes people are not stupid when they choose passwords and basic rules
won't do a job... aaargh. As you've seen it takes more and more time for your
CPU to crack this thing out as we go further. Now you can leave your computer on
and go to sleep....
If you want to get even more possible passwords out of your password file,
try typing
john -i password.file
This -i stands for incremental cracking, not a really good word for it,
but...
Okay, what the hell does it do? It uses the default incremental mode
parameters, which are defined in john.ini.
What does this mean? Do you
remember -rules? Yes, well, of course you do, unless you're either incredibly
senile or you've stopped reading after this part and only came back, like... a
couple of years later. That is very much like rules, but much much more powerful
than -rules, and it takes much, much more time.
4) So where
are we now (dictionary vs. brute-force)?
You can see that in all cases you use so-called dictionary cracking...
but hell, why not just run John on a mode where it tried all possible
combinations of lowercase and uppercase letters, numbers and symbols? I mean,
this would be much more efficient, right? ... WROOOOOOONGG!!!
This method is
called 'brute-force' attack (basically, dictionary attack is also sort of
brute-force attack, but most people use the word brute-force for this specific
attack).
What are the differences? First and most important, with dictionary
you go through the selected words that could be passwords and their
modifications, and with brute force cracking you use ALL possible combinations.
That means you have
comb=nrch^let
where:
comb - number of possible combinations
nrch - number of chars
let -
number of letters used
In case you're dealing with john's default -i 95 character set and, presume,
a 6 letter password you have possible 735091890625 combinations! OUCH!!
Sure,
this is useful for passwords like 2405v7, but still... with the computational
powers of today's modern PC, I'd just give up, unless I had access to some
University's supercomputer, which I'd bet noone would ever give me (well, at
least not for free, and certainly not to run a password cracker on it).
As
you can see it can take a looooong time until you crack a single one pass, do a
little math and try to calculate how many possible combinations there are for
10, 12 and 16 chars.
I don't think you'll like the answer :)
Of course,
sometimes dictionary attacks are not enough, but john has very powerful
'thinking'. In 'incremental' mode john will do all possible combinations from 0
to 8 characters (by zero password length is considered a hashed empty string,
this sometimes happens). So incremental mode is one sort of brute-force attack
in some way...
If you want to fire all weapons at one then you use
john password.file
this will do first basic dictionary attack, then -rules, then -i
5) What if...
Ok, you have to turn off your box from time to time, don't you? If you're
doing that haaard password that will take more than 20 hours of cracking you can
set john with ctrl+c and then resume with
john -restore
If your box crashes or if there's a power failure, you won't be able to
restore your cracking sessions (sometimes)... well that's just too bad. Hell, it
happened
to me once :-(
John is modular, and that is the most powerful thing about john the ripper,
and that is what makes john the most advanced password cracker. John is very,
very modular. John uses modes that are described in john.ini (do you still
remember that incremental cracking i was talking about? Modes for rules and
incremental are described in john.ini).
If you're some inventive guy then you
may change the parameters in john.ini.
Here is example how some default parameters for -i look like:
# Incremental modes
[Incremental:All]
File = ~/all.chr
MinLen =
0
MaxLen = 8
CharCount = 95
Ok... what do we have here?
[Incremental:All] - this stands for the beginning of the definition for the
-i:all switch
File - filename of file that has characters used in mode -i:all
(whole character
set)
MinLen - logically, minimum length of password that
john -i:all would try
MaxLen - even more logical, maximum length of password
that will john -i:all try
CharCount - number of chars used by john when you
'turn on' this switch
So, there are some more switches... heh
Yes there are and down there are
all default modes pasted from john the ripper's documents:
John the Ripper's Command Line Options
You can list any number of password files on John's command line, and
also
specify some of the following options (all of them are case sensitive,
but
can be abbreviated; you can also use the GNU-style long options
syntax):
- single "single crack" mode Enables the "single crack" mode, using rules from
[List.Rules:Single].
- wordfile:FILE wordlist mode, read words from FILE,
- stdin or from stdin These are used to enable the wordlist mode.
- rules enable rules for wordlist mode Enables wordlist rules, that are read
from [List.Rules:Wordlist].
- incremental[:MODE] incremental mode [using section MODE] Enables the
incremental mode, using the specified ~/john.ini definition (section
[Incremental:MODE], or [Incremental:All] by default).
- external:MODE external mode or word filter Enables an external mode, using
external functions defined in ~/john.ini's [List.External:MODE] section.
- stdout[:LENGTH] no cracking, write words to stdout 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.
- restore[:FILE] restore an interrupted session Continues an interrupted
cracking session, reading point information from the specified file (~/restore
by default).
- session:FILE set session file name to 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.
- status[:FILE] print status of a session [from 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.
- makechars:FILE make a charset, overwriting FILE Generates a charset file,
based on character frequencies from ~/john.pot, for use with the incremental
mode. The entire ~/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.
- show show cracked passwords 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.
- test perform a benchmark Benchmarks all the enabled ciphertext format
crackers, and tests them for
correct operation at the same time.
- users:[-]LOGIN|UID[,..] load this (these) user(s) only 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).
- groups:[-]GID[,..] load this (these) group(s) only Tells John to load users
of the specified group(s) only.
- shells:[-]SHELL[,..] load this (these) shell(s) only 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'.
- salts:[-]COUNT set a passwords per salt limit This feature sometimes allows
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.
- format:NAME force ciphertext 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.
- savemem:LEVEL enable memory saving, at LEVEL 1..3
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.
6) Tips
I) A good schedule to do your cracking job is
john -w:words.lst password.file
john -w:words.lst -rules
password.file
john -w:words.lst password.file
john -i:digits
password.file
john -i:all password.file
II) If you have a file that has only passes that look like
owner:*:510:102:His name:/home/subdir/owner:/bin/bash
you have a
shadowed passwords file.
Go to the Byte-Me page at blacksun.box.sk and try to
find out more about
password files (I'll leave it up to you to do this. It's
important that you'll
learn how to find things by yourself).
III) You have some little tools that you get with john, they are
all
listed below (from john's docs)
unshadow PASSWORD-FILE SHADOW-FILE
Combines the passwd and shadow
files (when you already have access to
both) for use with John. You might
need this since if you only used your
shadow file, the GECOS information
wouldn't be used by the "single crack"
mode, and also you wouldn't be able to
use the '-shells' option. You'll
usually want to redirect the output of
'unshadow' to a file.
unafs DATABASE-FILE CELL-NAME
Gets password hashes out of the binary AFS
database, and produces a file
usable by John (again, you should redirect the
output yourself).
unique OUTPUT-FILE
Removes duplicates from a wordlist (read from stdin),
without changing
the order. You might want to use this with John's '-stdout'
option, if
you got a lot of disk space to trade for the reduced cracking
time.
mailer PASSWORD-FILE
A shell script to send mail to all the users who got
weak passwords. You
should edit the message inside before using.
So, that was about it... hope you've got something from this
text.
Further readings: try reading ALL the documentation you get with john
in the docs
directory. Maybe it's a little bit chaotic, but.... man those are
the docs :)
Ohh, wait, wait!!
Remember, not all password files can be cracked!
Smart admins alter the
encryption that they are using, especially when it
comes to root passwords.
But there are always other ways to get passwords.
These are covered in other
BSRF tutorials. Collect them all (lol) at
http://blacksun.box.sk.
