RE: XP password and encryption

["Nero, Nick" <Nick.Nero () disney com>]

I think this is a common misconception.  This flaw in the password
storage was indeed there but only in the older LAN Manager days.  Since
Windows NT 4 (I can't remember if it was part of the SP2 upgrade to
NTLMv2 or not), MS OS's have used a much more complex password storage
scheme.

> From the MS Press Windows 2000 Security Technical Reference (p.31):

"LAN Manager-
The password is effectively 2 x 7 character strings represented by 2 x 8
byte DES encrypted values.   Each can be attacked indepenently; each is
limited to the original equipment manufacturer character set; and none
are case-sensitive.
        * Possible characters = 36 (numbers and letters)
        * 7-character password = 2 x 36^7 = 2 x 78 Billion combinations

Windows NT -
The password is a single 16-byte digest of a variable-length string
(effectively limited to 14 characters), computed using the RSA MD-4
encryption algorithm. Windows NT passwords are case-sensitive  and can
be a mix of upper/lowercase characters, numbers, and punctuation.
        * Possible characters = 96 (uppers/lowercase characters,
numbers, and 34 punctuation)
        * 14 character password = 96^14 = 5 billion billion billion
combinations"

Oddly enough there is no mention in this technical reference about the
strength of Windows 2000 passwords stored for local authentication (all
domain passwords in a 2k domain use Kerberos which is practically
impossible to attack using man in the middle of brute forcing without
local access to the Domain Controller).  This
(http://www.microsoft.com/technet/treeview/default.asp?url=/technet/secu
rity/prodtech/win2000/win2khg/03osinstl.asp) article describes the hash
a bit.  2k can support a maximum of 127 character password.  The hash is
a one-way (non-reversible encryption) of variable size.  Basically, to
brute force it there are really no shortcuts.  You cannot derive the
length of the password from the hash and there are no shortcuts.  That
is assuming of course you already have administrator access to the
machine since only the Admin (or SYSTEM account) can apply the SYSKEY
(which is on by default in 2k/XP) to actually decrypt the SAM (128bit
RC4) and read the hashes.  If you fire up LC4 you will find that even
with a moderately secure password with any ALT characters or other
symbols (@,#,$,%,&, . .) it can take forever to bruteforce.  It is far
easier to get local access to the machine, boot to an NTFS boot disk and
simply overwrite the SAM with a known one.  As recent as Solaris 8,
there were only 8 characters in the password that were encrypted in any
significant way.  And that is not by default even.

To be thorough, I should mention this article:
http://reviews-zdnet.com.com/4520-7297_16-4208088.html.  Theoretically
you can crack passwords faster but I still doubt anyone could get
through a reasonably complex password without extended access to the
local SAM.  And let's face it, if someone has Admin privileges and
extended physical access to your box you already screwed up somewhere
and it is only a matter of time.

Nick Nero
CISSP, MCSE, MCSA, CCNA

-----Original Message-----
From: David Gillett [mailto:gillettdavid () fhda edu] 
Sent: Monday, January 05, 2004 7:29 PM
To: 'J. Yoon'; security-basics () securityfocus com
Subject: RE: XP password and encryption 

  I believe I've heard that there are conditions under which it only
functions as a single 7-character password.  I may have misunderstood;
the point may have been that this behaviour theoretically allows you to
crack the first half of the password on one box while a second box in
parallel tackles the second half, so that the total crack time is the
same as if a single 7-character password was used.

1)  No.  Any characters you supply beyond 15 will be ignored.  (And see
above -- an attacker with access to two machines might easily have
access to three....)

2)  If you're running XP, you may have the option of turning off NTLM
(depending on the presence of legacy equipment...).  Recommended
wherever possible.  Note that you also have the option of requiring
IPSEC encryption of all local client/server traffic, and this too is a
good thing.

3/a/b)  Check out Kerberos; it might be able to do what you want.

David Gillett


> -----Original Message-----
> From: J. Yoon [mailto:supercool9000 () hotmail com]
> Sent: January 5, 2004 13:01
> To: security-basics () securityfocus com
> Subject: XP password and encryption
>
>
> I have heard that any password less than 15 characters is worthless on

> NTLM because it's in reality just two 7 char passwds.  If cracking a 7

> char passwd only takes a couple of hours (say 10 hours avg on a 
> tip-top PC), then cracking a 14 char passwd (which is just TWO 7 char 
> passwds) will take only twice which is about 20 hours...
>
> 1) Does this mean that even if I use a 21 char password I am still 
> wasting my time since it will only take 3 times the 7-char , which is 
> 30 hours or so? I was always under the impression that each additional

> character increases the encryption in a non-linear way... but maybe I 
> was wrong.
>
> 2) From your expert opinion, how many characters should our passwords 
> on XP box be in order for us to keep our sanity AND still rest at ease

> being secure enough for most everday purposes?
>
> 3) Is there any way to strengthen the encryption so that even when 
> someone gets access to my keyfile they won't be able to crack it any 
> time soon (for a whole entire month or even upto a year on a 4 
> Gigahertz Processor) ?
>
> 3a) Is this possible within the existing Win XP Pro / Win2000 
> architecture?
>
> 3b) do Linux versions such as Mandrake or Suse support such 
> crazy-strength encryption?
>
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