Re: Password hashes

From: Steven L Umbach (
Date: 10/30/05

Date: Sun, 30 Oct 2005 11:11:11 -0600

The terminology is all confusing. Take a look at "value using the 16-byte
NTLM hash as the key. This results in a 16-byte value
 - the NTLMv2 hash." What NTLMV2 [an authentication protocol] does is to
use the NTLM [or known as NT hash or Unicode hash] hash stored in the
operating system as the key to use in the challenge/response for
authentication over the network to encrypt the nonce for the challenge.
There is however no locally stored NTLMV2 hash of passwords. The link below
explains a little bit more.;EN-US;q299656&

"The NTLM, NTLMv2, and Kerberos all use the NT hash, also known as the
Unicode hash. The LM authentication protocol uses the LM hash"

I do believe in enforcing the use of very strong passwords as part of and
the core step of defense in depth. Auditing and reviewing the security logs
is a good way to get a feel of what is going on by looking for unusual
pattern of failed logons or use of administrators account when it should not
be used as in questionable times or from questionable computers. The free
tool from Microsoft called Event Comb makes it easy to scan multiple
computer logs looking for specific event ID's and text strings such as a
user or computer name. With Windows 2003 and XP Pro, particularly the latest
service packs Microsoft gives the admin a lot of built in technologies to
secure their network and data and the documentation to do such at TechNet
Security homepage. While it may appear that larger networks may have better
security that could be an illusion. Yes they may have a big budget for
hardware and software but they also have a lot more employees in their
support staff for IT and all it takes is one admin or support staff that is
not trained correctly, is lazy, and/or malicious to open a huge security
hole as you are only as secure as your weakest link. This is sometimes
referred to as "layer 8" issues that include social engineering attacks
which is too often overlooked as a serious vulnerability to address.

 If you have not been there yet be sure to check out the TechNet security
page and read the free guides such as the Windows 2003 Server Security
Guide, Windows XP Security Guide, Threats and Countermeasures, Antivirus in
Depth Guide, etc. The last link is to a great white paper on ipsec and you
would want to read at least appendix A. Also if you are considering ipsec be
sure to test any ipsec policies first and beware that domain controllers
MUST be exempt from trying to use ipsec for communicational between domain
computers and domain controllers. --- Steve --- TechNet
Security homepage
 --- Server and Domain Isolation Using IPSec and Group Policy

"Lawson Poling, MCSA" <> wrote in
> Steve, thank you for your informative response. You've certainly given me
> some things to think about, and to research. While doing more research I
> came
> across the following web page that contradicts your first sentence which
> states there is no such thing as an NTLMv2 hash. A portion of the text
> contained on the web page states:
> "The Unicode uppercase username is concatenated with the Unicode uppercase
> authentication target (domain or server name). The HMAC-MD5 message
> authentication code algorithm (described in RFC 2104) is applied to this
> value using the 16-byte NTLM hash as the key. This results in a 16-byte
> value
> - the NTLMv2 hash."
> The URL for this info is:
> I'm continuing to look in to your other recommendations, like using IPSec
> for network communications, encrypting data, etc.
> Converstationally, we are fortunate to have pretty decent physical
> security
> in place i.e. Cisco firewall and router.
> With regards to super-complex passwords, I'm trying to address the fact
> that
> these systems are not bullet proof. This is evident by large corporation's
> networks that get compromised that have better physical security than we
> do.
> I'm considering outsourcing to Verisign the task of monitoring our network
> for unscrupulous activity. I hear they do this 24/7 and will notify
> network
> admins any time day or night if something pops up on their radar. This
> would
> negate the need for 'super-complex' passwords since we would be able to
> respond to threats in a timely manner.
> I'm going to test turning off NT and NTLM responses and utilize only the
> NTMLv2 and Kerberos authentication protocols.
> I find this all very exciting stuff and again I thank you for your input.
> Lawson...
> "Steven L Umbach" wrote:
>> There is no such thing as an NTLMV2 hash. There are only LM and NT
>> hashes.
>> LM is very weak by today's standards. The reason it is turned on by
>> default
>> is for backward compatibility for W9X computers but it certainly is easy
>> enough to disable via a security option. LM passwords can not be longer
>> that
>> 14 characters though both NTLM and NTLMV2 can be up to 128 characters.
>> While I am a believer of enforcing complex passwords the bigger issue is
>> if
>> you are concerned about someone trying to crack passwords on your domain
>> computers you need to review the physical security of your computers.
>> Domain
>> controllers [the grand prize] and any other sensitive computers need to
>> be
>> physically secured. Enforcing complex passwords of at least eight
>> characters
>> in length will make it extremely difficult for a user to try and break
>> the
>> password of other users over the network. Sensitive user accounts can use
>> multi factor authentication of smart cards and the accounts can be
>> configured to required to use a smart card to logon.
>> If I can get access to a computer then I don't even care what the
>> password
>> is because I can access any data on it that is not encrypted via proper
>> procedures. Passwords are an important part of network security but don't
>> think that forcing users to use super complex passwords alone is going to
>> secure your network and data. Many users will gladly tell someone else
>> their
>> password when that person talks a good game [social engineering] and too
>> many domain administrators will logon to domain computers [other than
>> domain
>> controllers] with their domain administrator account which can compromise
>> the most complex password. Data that absolutely needs to remain
>> confidential needs to be encrypted on the computer and network [using
>> something like ipsec] and accessed and managed by well trained, aware,
>> and
>> trustworthy employees. --- Steve
>> "Lawson Poling, MCSA" <> wrote
>> in
>> message
>> > After reading some security articles about making passwords and
>> > authentications more secure on a Windows Server 2003 domain, I was
>> > surprised
>> > to learn that storing LM hashes is turned on by default, and that it is
>> > broken up into two 7 character units. That would explain why, when
>> > using
>> > L0ftcrack to audit user passwords with 8 characters, that the last
>> > character
>> > was always found so easily. It places only one character in the second
>> > hash.
>> > So much for the idealistic minimum 8 character passwords.
>> > I also learned that the NTLM hash was a single 14 character hash, but
>> > it's
>> > still as vulnerable at the LM hash. It would just take longer to crack
>> > a
>> > solid 14 character password.
>> > I thought I'd get clever and I made my password 15 characters long.
>> > L0ftCrack was no longer able to recognize it. It marked my user account
>> > under
>> > the LM column as *empty* and won't even try to crack it. I got all warm
>> > and
>> > fuzzy and was feeling good about myself until I learned about Rainbow
>> > Crack.
>> > My understanding about it is that it's hash tables only go to 14
>> > characters
>> > because the storage space required to store hashes up to 15 characters
>> > take
>> > too much storage space. If that's true, then it would have to resort to
>> > brute
>> > force which I imagine would take a very long time to crack a 15
>> > character
>> > password. I should say pass-phrase at this point. I don't know too many
>> > 15
>> > character words. I'm not that smart...
>> > So this leads me to my penultimate question(s): Does a 15 character
>> > pass-phrase automatically get stored in an NTMLv2 hash? It certainly
>> > won't
>> > fit into a LM or NTLM hash.
>> > Isn't an NTLMv2 hash good for up to 128 characters? If this is true,
>> > then
>> > how come when I try to set the minimum password length in the default
>> > domain
>> > policy that I can only toggle it up to 14 characters?
>> > If my company adopts 15 character pass-phrases as policy I don't want
>> > to
>> > count on trusting the end users for the last character.
>> > If you've read this far I'll bet you have some comments and guidance.
>> > I'd
>> > love to hear from you.
>> >
>> > Thanks,
>> > Lawson...