SAM Files and NT Password Hashes

§ Introduction

I know that this topic has been covered by others on more than one
occasion, but I figured I'd go over it yet again and throw in an update
or two. Let me start with what this is all about: SAM Files & NT
Password Hashes.

NT Password Hashes - When you type your password into a Windows NT,
2000, or XP login Windows encrypts your password using an encryption
scheme that turns your password into something that looks like this:

7524248b4d2c9a9eadd3b435c51404ee

This is a password Hash. This is what is actually being checked against
when you type your password in. It encrypts what you typed and bounces
it against what is stored in the Registry and/or SAM File.

SAM File - Holds the user names and password hashes for every account on
the local machine, or domain if it is a domain controller. Simple enough
wouldn't you say?

§ Where do I find the SAM/Hashes?

You can find what you're looking for in several locations on a given
machine.

It can be found on the hard drive in the folder
%systemroot%system32config. However this folder is locked to all
accounts including Administrator while the machine is running. The only
account that can access the SAM file during operation is the "System"
account.

You may also be able to find the SAM file stored in %systemroot% epair
if the NT Repair Disk Utility a.k.a. rdisk has been run and the
Administrator has not removed the backed up SAM file.

The final location of the SAM or corresponding hashes can be found in
the registry. It can be found under HKEY_LOCAL_MACHINESAM. This is also
locked to all users, including Administrator, while the machine is in
use.

So the three locations of the SAMHashes are:

- %systemroot%system32config

- %systemroot% epair (but only if rdisk has been run)

- In the registry under HKEY_LOCAL_MACHINESAM

§ Obtaining the SAMPassword Hashes

Wow, how wonderful. Now we know where the goods are, and the problem is
this... "How do I get my hands on those hashes?" The answer is "One of
four ways."

1) Probably the easiest way to do this is to boot your target machine to
an alternate OS like NTFSDOS or Linux and just copy the SAM from the
%systemroot%system32config folder. It's quick, it's easy, and it's
effective. You can get a copy of NTFSDOS from
Sysinternals(http://www.sysinternals.com) The regular version of NTFSDOS
is freeware, which is always nice, but only allows for Read-Only access.
This should be fine for what you want to do, however, if you're the kind
of person that just has to have total control and has some money to
burn. NTFSDOS Pro, which is also by Sysinternals has read/write access
but it'll cost you $299.

2) Once again, you may be able to obtain the SAM from %systemroot% epair
if rdisk has been run and you are lucky enough to have a sloppy admin.

3) You can also get password hashes by using pwdump2. pwdump uses .DLL
injection in order to use the system account to view the password hashes
stored in the registry. It then pulls the hashes from the registry and
stores them in a handy little text file that you can then import into a
password cracking utility like l0phtcrack.

4) The final way to obtain password hashes is to listen directly to the
network traffic as it floats by your computer and grab hashes using the
above mentioned l0phtcrack.

§ Cracking Password Hashes

With the hashes in hand and an eagerness to find out what passwords lie
waiting. Let's get cracking. While there are numerous programs available
for the use of password cracking I will quickly cover two of the most
popular ones.

John the Ripper - John the Ripper is to many, the old standby password
cracker. It is command line which makes it nice if you're doing some
scripting, and best of all it's free. The only real thing that JtR is
lacking is the ability to launch Brute Force attacks against your
password file. But look at it this way, even though it is only a
dictionary cracker, that will probably be all you need. I would say that
in my experience I can find about 85-90% of the passwords in a given
file by using just a dictionary attack. Not bad, not bad at all.

L0phtCrack - Probably the most wildly popular password cracker out
there. L0phtCrack is sold by the folks at @Stake. And with a pricetag of
$249 for a single user license it sure seems like every one owns it.
Boy, @Stake must be making a killing. :) This is probably the nicest
password cracker you will ever see. With the ability to import hashes
directly from the registry ala pwdump and dictionary, hybrid, and
brute-force capabilities. No password should last long. Well, I
shouldn't say "no password". But almost all will fall to L0phtCrack
given enough time.

§ Injecting Password Hashes into the SAM

Probably one of my favorite and easiest ways to gain Administrator
privileges on a machine, is by injecting password hashes into the SAM
file. In order to do this you will need physical access to the machine
and a brain larger than a peanut. Using a utility called "chntpw" by
Petter Nordhal-Hagen you can inject whatever password you wish into the
SAM file of any NT, 2000, or XP machine thereby giving you total
control. I would suggest backing up the SAM file first by using an
alternate OS. Go in, inject the password of your choosing. Login using
your new password. Do what you need to do. Then restore the original SAM
so no one knows you were there.

§ Password Strength

By looking at the methods above, you can see the importance in keeping
strong passwords. Someone may be able to get there hands on your hashes,
but it's whether or not they can crack them that is the real test. Don't
make it easy on them.

When I create a password I like to use the first letter of each word in
a phrase. Like "Password Strength is important so I pick good passwords"
would be "psiisipgp". Now you have a 9 character password that isn't in
any dictionary I know of. Bye Bye John the Ripper.

Now I like to flank passwords in special characters like "@$%?", now
your password is ?psiisipgp?. This will ensure L0phtCrack takes a long
time cracking it, giving you time to change it if you discover a breach,
or just change your passwords regularly.

If you want to get insane, like I do, you can add non-printable ascii
characters to your passwords. Using the Alt key and the numbers on your
number pad, hold Alt and key in 149. you should get a character like
this "ò". Flank your password with this before your question marks and
now you've got a secure password. ?òpsiisipgpò? can't be cracked by
L0phtCrack since it doesn't allow for non-printable ascii characters.
Bye Bye L0phtCrack.

I know this may seem like a lot to do, but let's face it, a weak
password is a cracked password.

-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-

NTFSDOS - (http://www.sysinternals.com)

pwdump2 - (http://www.webspan.net/~tas/pwdump2/)

John the Ripper - (http://www.openwall.com/john/)

L0phtCrack - (http://www.atstake.com/research/lc3/)

chntpw - (http://home.eunet.no/~pnordahl/ntpasswd/)