full-disclosure - NEW windows password encryption flaw..

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From: chrisp at ngssoftware.com (Chris Paget)
Subject: NEW windows password encryption flaw..

This is not a Microsoft screwup, or any kind of screwup in fact.  It's a
technique called "Hash Chaining", that the guys at Lasec have improved upon.
It's a way of trading off time for memory usage for effectively generating a
table of precomputed hashes; the only flaw here lies in the fact that the hashes
involved are unsalted.  The technique has been around a long time, and is good
against ANY hash function, assuming it's unsalted.  The Lasec guys have found a
few improvements to the standard technique, and written a demo.

(For those who know about hash chaining but can't follow the maths in the paper,
the main improvement is to salt the mapping function with a predictable dynamic
salt, so as to pretty much eliminate chain merging and greatly speed up lookup
times.  Pretty cunning).

I've forwarded the message from Bugtraq below, for the benefit of those who only
subscribe here.

Chris

---------- Forwarded message ----------
Date: 22 Jul 2003 20:37:19 -0000
From: "bugtraq@...hslin.net" <bugtraq@...hslin.net>
To: "bugtraq@...urityfocus.com" <bugtraq@...urityfocus.com>
Subject: Cracking windows passwords in 5 seconds

As opposed to unix, windows password hashes can be calculated in advance
because no salt or other random information si involved. This makes so
called time-memory trade-off attacks possible. This vulnerability is not
new but we think that we have the first tool to exploit this.

At LASEC (lasecwww.epfl.ch) we have developed an advanced time-memory
trade-off method. It is based on original work which was done in 1980 but
has never been applied to windows passwords. It works by calculating all
possible hashes in advance and storing some of them in an organized
table. The more information you keep in the table, the faster the
cracking will be.

We have implemented an online demo of this method which cracks
alphanumerical passwords in 5 seconds average (see
http://lasecpc13.epfl.ch/ntcrack). With the help of 0.95GB of data we can
find the password after an average of 4 million hash operation. A brute
force cracker would need to calculate an average of 50% of all hashes,
which amounts to about 40 billion hases for alphanumerical passwords
(lanman hash).

More info about the method can be found at in a paper at
http://lasecwww.epfl.ch/php_code/publications/search.php?ref=Oech03.

  Philippe Oechslin

On Wed, 23 Jul 2003, Darren Bennett wrote:

> Is this new? I read about it on slashdot...
>
> http://lasecpc13.epfl.ch/ntcrack/
>
> Basically, it seems that Microsoft has (yet again) screwed up the
> implementation of their encryption scheme. This makes cracking any hash
> a matter of seconds. Oops...
> --
> -----------------------------------------------
> Darren Bennett
> CISSP, Certified Unix Admin., MCSE, MCSA, MCP +I
> Sr. Systems Administrator/Manager
> Science Applications International Corporation
> Advanced Systems Development and Integration
> -----------------------------------------------
>
> _______________________________________________
> Full-Disclosure - We believe in it.
> Charter: http://lists.netsys.com/full-disclosure-charter.html
>
>