Windows 7 ntlm hash

One of the newer solutions are self-encrypting drives that require a boot into their own firmware for access. In all of this answer, I am considering the problem of recovering the password or an equivalent password from a purloined hash, as stored in a server on which the attacker could gain read access.

This last weakness allows for very efficient cracking regardless of the care taken in choosing the password ; see this answer for a some details. This time, the password is case sensitive, and can be quite long.

There is some dispute as to the real maximum password length which could apparently be up to characters or so. Since MD4 is computed over UTF encoding of the password, the whole range of Unicode could theoretically be used, but since the user needs to type the password regularly and without visual feedback , using characters beyond the printable ASCII set is looking for trouble.

What is weak in NTLM hash is that it is unsalted, and that MD4 is fast MD4 is also cryptographically broken in several ways, but not for raw preimage resistance as is used for password hashing; for that, MD4 is as robust as it ever was. MD4 is actually faster than MD5. This makes it easy for the attacker to explore vast sets of potential passwords what is known as a dictionary attack. The only defense is to choose your passwords from an even vaster set. Let's throw some maths at it: since NTLM is unsalted, a dedicated group of attacker might find it worthwhile to build a big rainbow table.

There are various possible optimizations, but, as a rule, things would go like this:. If the table is split over a hundred mechanical hard disks, then about lookups can be done per second. If the attacker is really motivated, he might wish to spend one hour or so per password, which means a maximum t of for the lookups let's say 2 22 ; the corresponding CPU cost is down to about 2 32 hashes per second, which is feasible with a couple recent GPU.

The hundred disks allow for TB storage I am talking about 3 TB disk, which are off-the-shelf today , which brings the possible N to about 2 That's rather huge, but technologically feasible.

Our group of attackers could buy a hundred GPU and a big air conditioning unit and be done with computing that table within a few months. So, in order to defeat our motivated adversaries, we need to choose passwords at random from a set bigger than their N. If our set of possible passwords has size more than 2 77 and our passwords are chosen randomly and uniformly in that set i. This ought to be sufficient to dissuade him. How do we get 77 bits of entropy? If we restrict ourselves to letters uppercase and lowercase and digits, so that the password can be typed on arbitrary keyboards, then we can have a little less than 6 bits of entropy per character.

Therefore, 13 characters are sufficient. Isn't it swell? Only 13! No need to go to huge passphrases. But mind the small type: that's 13 totally random letters or digits. No question of letting a human choose these characters, or even generating a dozen passwords of 13 characters and letting him choose the one he likes best.

You take the generator, you produce one password, and you learn it. The mental effort is the price of using an unsalted fast password hashing mechanism like NTLM. Of course, the attacker group described above is realistic. You may want to increase complexity a bit, so that your passwords will also be strong with regards to tomorrow's attackers; so make it 14 or 15 characters to be safer.

There are of course rainbow tables for NTLM e. From a brute forcing perspective though, you should be limiting the number of failed login attempts before you are locked out. This can be set using local policy. Physical security trumps all. Block BIOS from booting a cd or usb and put a lock on the box.

Of course, I reiterate the comment above, use full disc encryption, maybe even multifactor. Cold boot and evil maid require someone to really invest time in breaking your machine. However: even after updating and changing the passwords , the SysKey encryption remains in RC4 format. This step-by-step only applies to Windows systems that where installed as a post v version.

The entire process is slightly simplified but remains roughly the same. This means bit or 16byte keys are required together with a 16 byte Initial Vector or IV. I am in no way a real programmer or developer and have created this script just to educate myself and prove my findings. I am fully aware that these scripts can be made a lot more portable, shorter and generally better…. I always try to make them as self contained as possible, requiring little extra libraries.

They only library required is pycrypto which is installed by default on e. Kali Linux. If you're creating a custom policy template that may be used on both Windows and Windows XP or Windows Server , you can create both the key and the value. The value is in the same place as the key, and a value of 1 disables LM hash creation. The key is upgraded when a Windows system is upgraded to Windows Server However, it's okay if both settings are in the registry.

The simplest way is to use a password that's at least 15 characters long. In this case, Windows stores an LM hash value that can't be used to authenticate the user. Skip to main content. This browser is no longer supported. Download Microsoft Edge More info. Contents Exit focus mode.

Please rate your experience Yes No. Any additional feedback? Important This section, method, or task contains steps that tell you how to modify the registry. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base: How to back up and restore the registry in Windows The NoLMHash registry key and its functionality were not tested or documented and should be considered unsafe to use in production environments before Windows SP2.

Note This registry key change must be made on all Windows domain controllers to disable the storage of LM hashes of users' passwords in a Windows Active Directory environment. This registry key prevents new LM hashes from being created on Windows computers.